Lettuce resistant to nasonovia ribisnigri biotype 0 and 1

Abstract

The present invention relates to a QTL providing resistance to Nasonovia ribisnigri biotypes Nr:0 and Nr:1 when present on chromosome 2 in a Lactuca sativa plant, wherein the QTL on chromosome 2 is located between marker LS10601 having SEQ ID NO:1 or SEQ ID NO:2 and 5 marker LS10403 having SEQ ID NO:35 or SEQ ID NO:36. The present invention further relates to a plant or plant material comprising the QTL of the invention. Additionally, the invention relates to markers for the identification of the presence of a QTL of the invention. The invention further relates to amethods for selecting and producing a Lactuca sativa plant resistant to Nasonovia ribisnigri biotypes 0 and 1.

Description

[0001] LETTUCE RESISTANT TO NASONOVIA RIBISNIGRI BIOTYPE 0 AND 1

[0002] The present invention relates to a QTL that confers resistance to Nasonovia Ribisnigri biotypes Nr:0 and Nr:l. The invention further relates to Lactuca sativa plant comprising the resistance conferring QTL. The invention also relates to progeny, cells and seed of the plant comprising the resistance conferring QTL, and to propagation material suitable for producing the L. sativa plant comprising the resistance conferring QTL. The invention also relates markers for the identification of the resistance conferring QTL and the use thereof. The invention further relates to methods for identifying, producing and growing a L. sativa plant comprising the resistance conferring QTL.

[0003] The lettuce aphid, Nasonovia ribisnigri (Mosley), is a major pest occurring in lettuce (Lactuca sativa L.) worldwide. The problem started to be severe for lettuce production in the 1970s in Northwestern Europe and spread rapidly all across Europe. In the 1980s, the aphid was detected in Canada. Later on, the problem was reported in the USA (California and Arizona). More recently, the lettuce aphid was found in New Zealand and Australia. Lettuce aphids can colonize lettuce plants at any plant stage and feed preferably from younger leaves. Large amounts of aphids on the plant are able to reduce plant growth and deform the shape of the head so that the lettuce heads are not marketable anymore. The presence of high amounts of aphids in lettuce heads is a reason for retailers to refuse to buy lettuce from growers. At the young plant stage, it is possible to control the lettuce aphid using insecticide. Several products were reported to be efficient to control aphid population. However, resistance to chemicals was reported in some aphid population. Moreover, at maturity, it is not possible to control aphid using insecticide, because the chemical product cannot enter the lettuce head. There are systemic insecticides, which are absorbed and spread throughout the plants, which are effective against aphids, also in the heading stage. However, this type of insecticides is banned (neonicotenoids) or being banned (spirotetramat) in the EU at this moment. Lettuce consumers perceive pesticide residue on and in lettuce leaves as undesirable and prefer residue-free lettuce. Growers spend valuable time and money on insecticide applications. So, there is a strong desire among producers and consumers to reduce or stop insecticide use.

[0004] Therefore, one of the most valuable strategies to control lettuce aphids is a resistance based on genetics. An extensive gene bank screening was performed on L. sativa and its wild relatives such as Lactuca serriola and Lactuca virosa. It was found that some L. virosa accessions were found completely resistant to N. ribisnigri. However, interspecific crosses between L. sativa and L. virosa produce sterile offspring. Therefore, L. serriola was required to form a bridge species in order to bring the resistance into L. sativa. Genetic analyses showed that this resistance to N. ribisnigri was controlled by a single dominant gene (Nr gene) in a L. sativa background. Using this single dominant gene in breeding was not straightforward, because the Nr-resistance gene was tightly linked to recessive genes conferring strong pleiotropic effect, such as a reduced growth, a pale green color and a lack of fertility in seed set. Nevertheless, the inventors of W097 / 46080 managed to find recombinant lettuce plants that still had the single dominant Nr gene but lost the negative pleiotropic effects that were linked to it.

[0005] In 2007, populations of lettuce aphids able to infect varieties resistant to N. ribisnigri carrying the Nr gene were found in 4 distinct areas in Europe (France, Germany, Belgium and Austria). Four isolates (2 from France and 2 from Germany) were analysed further by Naktuinbouw (Netherlands Inspection Service for Horticulture) and they concluded the existence of a new N. ribisnigri biotype. This biotype is officially named Nr: 1 and is able to overcome the Nr resistance gene. The old Nr:0 biotype can still be efficiently controlled by the Nr gene. Naktuinbouw also reported that IVT 280, the original source of the Nr:0 resistance, was susceptible in their tests. After the breakthrough of the Nr gene by the Nr:l biotype, there was a need to find a resistance to the Nr:l biotype.

[0006] Although there are reports of resistances developed against Nr: 1 , none of these resistances seem to be present in varieties currently on the market. Probably this is due to the fact that these resistances are only partial and / or polygenic in nature. Therefore, there is still a need to find a genetic resistance to N. ribisnigri biotype 1 (Nr:l).

[0007] In the research that led to the present invention a resistance conferring QTE against both biotypes of N. ribisnigri was identified in an accession of Lactuca aculeata. This species is a wild relative of lettuce having a distribution area that ranges from the eastern Mediterranean to western Iran. The QTE that was identified in L. aculeata was introgressed to L. sativa (cultivated lettuce) and it was further found that the resistance to Nr:0 and Nr:l is located on chromosome 2 of L. sativa and inherits in a dominant fashion.

[0008] Thus, the present invention provides a QTE that confers resistance to N. ribisnigri biotypes 0 (Nr:0) and 1 (Nr:l ) when present in a L. sativa plant on chromosome 2. This QTL is herein interchangeably referred to as ‘resistance conferring QTL’, ‘resistance conferring QTL of the invention’, or ‘QTL of the invention’.

[0009] In one embodiment the QTL of the invention when present in a L. sativa plant is located on chromosome 2 between marker LS 10601 having SEQ ID NO:1 or SEQ ID NO:2 and marker LS10403 having SEQ ID NO:35 or SEQ ID NO:36.

[0010] In another embodiment the QTL of the invention when present in a L. sativa plant is located on chromosome 2 between marker LSI 1096 having SEQ ID NO:7 or SEQ ID NO:8 and marker LSI 1685 having SEQ ID NO:27 or SEQ ID NO:28. In yet another embodiment the QTL of the invention when present in a L. sativa plant is located on chromosome 2 between marker LS17344 having SEQ ID NO:9 or SEQ ID NO: 10 and marker LS17360 having SEQ ID NO:23 or SEQ ID NO:24.

[0011] In one embodiment the QTL of the invention when present in a L. sativa plant is located on chromosome 2 between marker LS10601 having SEQ ID NO:1 or SEQ ID NO:2 and marker LS10403 having SEQ ID NO:35 or SEQ ID NO:36, and comprises at least one marker selected from: marker LS10600 comprising an A at position 51 of SEQ ID NO: 4, or an A at position 51 of a sequence comprising at least 95% sequence identity to SEQ ID NO: 4; marker LS10399 comprising a C at position 51 of SEQ ID NO: 6, or a C at position 51 of a sequence comprising at least 95% sequence identity to SEQ ID NO: 6; marker LS17348 comprising a T at position 51 of SEQ ID NO: 13, or a T at position 51 of a sequence comprising at least 95% sequence identity to SEQ ID NO: 13; marker LS17349 comprising a G at position 51 of SEQ ID NO: 14, or a G at position 51 of a sequence comprising at least 95% sequence identity to SEQ ID NO: 14; marker LS17355 comprising a T at position 51 of SEQ ID NO: 15, or a T at position 51 of a sequence comprising at least 95% sequence identity to SEQ ID NO: 15; marker LS17356 comprising a G at position 51 of SEQ ID NO: 16, or a G at position 51 of a sequence comprising at least 95% sequence identity to SEQ ID NO: 16; marker LS17350 comprising a T at position 51 of SEQ ID NO: 17, or a T at position 51 of a sequence comprising at least 95% sequence identity to SEQ ID NO: 17; marker LS17357 comprising an A at position 51 of SEQ ID NO: 18, or an A at position 51 of a sequence comprising at least 95% sequence identity to SEQ ID NO: 18; marker LS17358 comprising a G at position 51 of SEQ ID NO: 19, or a G at position 51 of a sequence comprising at least 95% sequence identity to SEQ ID NO: 19; marker LS17351 comprising a T at position 51 of SEQ ID NO: 20, or a T at position 51 of a sequence comprising at least 95% sequence identity to SEQ ID NO: 20; marker LS10401 comprising an A at position 51 of SEQ ID NO: 26, or an A at position 51 of a sequence comprising at least 95% sequence identity to SEQ ID NO: 26; marker LS14064 comprising a C at position 51 of SEQ ID NO: 30, or a C at position 51 of a sequence comprising at least 95% sequence identity to SEQ ID NO: 30; marker LS14066 comprising a T at position 51 of SEQ ID NO: 32, or a T at position 51 of a sequence comprising at least 95% sequence identity to SEQ ID NO: 32; and marker LS14067 comprising a T at position 51 of SEQ ID NO: 34, or a T at position 51 of a sequence comprising at least 95% sequence identity to SEQ ID NO: 34. Marker LS17348 having SEQ ID NO: 13, marker LS17349 having SEQ ID NO: 14, marker LS17355 having SEQ ID NO: 15, marker LS17356 having SEQ ID NO: 16, marker LS17350 having SEQ ID NO: 17, marker LS17357 having SEQ ID NO: 18, marker LS17358 having SEQ ID NO: 19 and marker LS 17351 having SEQ ID NO: 20 are marker sequences that are unique for the resistance conferring QTL introgressed from L. aculeata. In a wild-type L. sativa plant, i.e. a susceptible L. sativa plant, these markers are absent and will not give a score at all. Therefore, in a L. sativa plant the absence of the marker correlates with absence of the resistance conferring QTL and thus with susceptibility. The presence of the marker in L. sativa correlates with the presence of the resistance conferring QTL of the invention.

[0012] In a preferred embodiment the QTL of the invention when present in a L. sativa plant is located on chromosome 2 between marker LS10601 having SEQ ID NO:1 or SEQ ID NO:2 and marker LS10403 having SEQ ID NO:35 or SEQ ID NO:36, and comprises at least one marker selected from: marker LS17348 comprising a T at position 51 of SEQ ID NO: 13, or a T at position 51 of a sequence comprising at least 95% sequence identity to SEQ ID NO: 13; marker LS17349 comprising a G at position 51 of SEQ ID NO: 14, or a G at position 51 of a sequence comprising at least 95% sequence identity to SEQ ID NO: 14; marker LS17355 comprising a T at position 51 of SEQ ID NO: 15, or a T at position 51 of a sequence comprising at least 95% sequence identity to SEQ ID NO: 15; marker LS17356 comprising a G at position 51 of SEQ ID NO: 16, or a G at position 51 of a sequence comprising at least 95% sequence identity to SEQ ID NO: 16; marker LS17350 comprising a T at position 51 of SEQ ID NO: 17, or a T at position 51 of a sequence comprising at least 95% sequence identity to SEQ ID NO: 17; marker LS17357 comprising an A at position 51 of SEQ ID NO: 18, or an A at position 51 of a sequence comprising at least 95% sequence identity to SEQ ID NO: 18; marker LS17358 comprising a G at position 51 of SEQ ID NO: 19, or a G at position 51 of a sequence comprising at least 95% sequence identity to SEQ ID NO: 19; and marker LS17351 comprising a T at position 51 of SEQ ID NO: 20, or a T at position 51 of a sequence comprising at least 95% sequence identity to SEQ ID NO: 20;

[0013] In an even more preferred embodiment, the QTL of the invention when present in a L. sativa plant is located on chromosome 2 between marker LS10601 having SEQ ID NO:1 or SEQ ID NO:2 and marker LS10403 having SEQ ID NO:35 or SEQ ID NO:36, and comprises marker LS17348 comprising a T at position 51 of SEQ ID NO: 13, or a T at position 51 of a sequence comprising at least 95% sequence identity to SEQ ID NO: 13, and / or marker LS17349 comprising a G at position 51 of SEQ ID NO: 14, or a G at position 51 of a sequence comprising at least 95% sequence identity to SEQ ID NO: 14. In one embodiment the QTL of the invention when present in a L. sativa plant is located on chromosome 2 between marker LSI 1096 having SEQ ID NO:7 or SEQ ID NO:8 and marker LSI 1685 having SEQ ID NO:27 or SEQ ID NO:28, and comprises at least one marker selected from: marker LS17348 comprising a T at position 51 of SEQ ID NO: 13, or a T at position 51 of a sequence comprising at least 95% sequence identity to SEQ ID NO: 13; marker LS17349 comprising a G at position 51 of SEQ ID NO: 14, or a G at position 51 of a sequence comprising at least 95% sequence identity to SEQ ID NO: 14; marker LS17355 comprising a T at position 51 of SEQ ID NO: 15, or a T at position 51 of a sequence comprising at least 95% sequence identity to SEQ ID NO: 15; marker LS17356 comprising a G at position 51 of SEQ ID NO: 16, or a G at position 51 of a sequence comprising at least 95% sequence identity to SEQ ID NO: 16; marker LS17350 comprising a T at position 51 of SEQ ID NO: 17, or a T at position 51 of a sequence comprising at least 95% sequence identity to SEQ ID NO: 17; marker LS17357 comprising an A at position 51 of SEQ ID NO: 18, or an A at position 51 of a sequence comprising at least 95% sequence identity to SEQ ID NO: 18; marker LS17358 comprising a G at position 51 of SEQ ID NO: 19, or a G at position 51 of a sequence comprising at least 95% sequence identity to SEQ ID NO: 19; and marker LS17351 comprising a T at position 51 of SEQ ID NO: 20, or a T at position 51 of a sequence comprising at least 95% sequence identity to SEQ ID NO: 20; and marker LS10401 comprising an A at position 51 of SEQ ID NO: 26, or an A at position 51 of a sequence comprising at least 95% sequence identity to SEQ ID NO: 26.

[0014] In a preferred embodiment the QTL of the invention when present in a L. sativa plant is located on chromosome 2 between marker LSI 1096 having SEQ ID NO:7 or SEQ ID NO:8 and marker LSI 1685 having SEQ ID NO:27 or SEQ ID NO:28, and comprises at least one marker selected from: marker LS17348 comprising a T at position 51 of SEQ ID NO: 13, or a T at position 51 of a sequence comprising at least 95% sequence identity to SEQ ID NO: 13; marker LS17349 comprising a G at position 51 of SEQ ID NO: 14, or a G at position 51 of a sequence comprising at least 95% sequence identity to SEQ ID NO: 14; marker LS17355 comprising a T at position 51 of SEQ ID NO: 15, or a T at position 51 of a sequence comprising at least 95% sequence identity to SEQ ID NO: 15; marker LS17356 comprising a G at position 51 of SEQ ID NO: 16, or a G at position 51 of a sequence comprising at least 95% sequence identity to SEQ ID NO: 16; marker LS17350 comprising a T at position 51 of SEQ ID NO: 17, or a T at position 51 of a sequence comprising at least 95% sequence identity to SEQ ID NO: 17; marker LS17357 comprising an A at position 51 of SEQ ID NO: 18, or an A at position 51 of a sequence comprising at least 95% sequence identity to SEQ ID NO: 18; marker LS17358 comprising a G at position 51 of SEQ ID NO: 19, or a G at position 51 of a sequence comprising at least 95% sequence identity to SEQ ID NO: 19; and marker LS17351 comprising a T at position 51 of SEQ ID NO: 20, or a T at position 51 of a sequence comprising at least 95% sequence identity to SEQ ID NO: 20.

[0015] In an even more preferred embodiment, the QTL of the invention when present in a L. sativa plant is located on chromosome 2 between marker LSI 1096 having SEQ ID NO:7 or SEQ ID NO:8 and marker LSI 1685 having SEQ ID NO:27 or SEQ ID NO:28, and comprises marker LS17348 comprising a T at position 51 of SEQ ID NO: 13, or a T at position 51 of a sequence comprising at least 95% sequence identity to SEQ ID NO: 13, and / or marker LS17349 comprising a G at position 51 of SEQ ID NO: 14, or a G at position 51 of a sequence comprising at least 95% sequence identity to SEQ ID NO: 14.

[0016] In one embodiment the QTL of the invention when present in a L. sativa plant is located on chromosome 2 between marker LS17344 having SEQ ID NO:9 or SEQ ID NO: 10 and marker LS17360 having SEQ ID NO:23 or SEQ ID NO:24, and comprises at least one marker selected from: marker LS17348 comprising a T at position 51 of SEQ ID NO: 13, or a T at position 51 of a sequence comprising at least 95% sequence identity to SEQ ID NO: 13; marker LS17349 comprising a G at position 51 of SEQ ID NO: 14, or a G at position 51 of a sequence comprising at least 95% sequence identity to SEQ ID NO: 14; marker LS17355 comprising a T at position 51 of SEQ ID NO: 15, or a T at position 51 of a sequence comprising at least 95% sequence identity to SEQ ID NO: 15; marker LS17356 comprising a G at position 51 of SEQ ID NO: 16, or a G at position 51 of a sequence comprising at least 95% sequence identity to SEQ ID NO: 16; marker LS17350 comprising a T at position 51 of SEQ ID NO: 17, or a T at position 51 of a sequence comprising at least 95% sequence identity to SEQ ID NO: 17; marker LS17357 comprising an A at position 51 of SEQ ID NO: 18, or an A at position 51 of a sequence comprising at least 95% sequence identity to SEQ ID NO: 18; marker LS17358 comprising a G at position 51 of SEQ ID NO: 19, or a G at position 51 of a sequence comprising at least 95% sequence identity to SEQ ID NO: 19; and marker LS17351 comprising a T at position 51 of SEQ ID NO: 20, or a T at position 51 of a sequence comprising at least 95% sequence identity to SEQ ID NO: 20.

[0017] In a preferred embodiment, the QTL of the invention when present in a L. sativa plant is located on chromosome 2 between marker LS17344 having SEQ ID NO:9 or SEQ ID NO: 10 and marker LS17360 having SEQ ID NO:23 or SEQ ID NO:24, and comprises marker LS17348 comprising a T at position 51 of SEQ ID NO: 13, or a T at position 51 of a sequence comprising at least 95% sequence identity to SEQ ID NO: 13, and / or marker LS17349 comprising a G at position 51 of SEQ ID NO: 14, or a G at position 51 of a sequence comprising at least 95% sequence identity to SEQ ID NO: 14.

[0018] In one embodiment, the QTL of the invention when present in a L. sativa plant is located on chromosome 2 between marker LS10601 having SEQ ID NO:1 or SEQ ID NO:2 and marker LS10403 having SEQ ID NO:35 or SEQ ID NO:36 or located between marker LSI 1096 having SEQ ID NO:7 or SEQ ID NO: 8 and marker LSI 1685 having SEQ ID NO:27 or SEQ ID NO:28, and comprises marker LS10400 comprising a G on position 51 of SEQ ID NO: 12, or a G at position 511 of a sequence comprising at least 95% sequence identity to SEQ ID NO: 12, and marker LS17344 comprising a G on position 51 of SEQ ID NO: 10, or a G at position 51 of a sequence comprising at least 95% sequence identity to SEQ ID NO: 10, and / or marker LSI 6311 comprising a G on position 51 of SEQ ID NO: 22, or a G at position 51 of a sequence comprising at least 95% sequence identity to SEQ ID NO: 22, and / or marker LS17360 comprising a G on position 51 of SEQ ID NO: 24, or a G at position 51 of a sequence comprising at least 95% sequence identity to SEQ ID NO: 24. The QTL thus comprises marker LS10400 comprising a G on position 51 of SEQ ID NO: 12, or a G at position 511 of a sequence comprising at least 95% sequence identity to SEQ ID NO: 12 in combination with at least one of the following markers: marker LS 17344 comprising a G on position 51 of SEQ ID NO: 10, or a G at position 51 of a sequence comprising at least 95% sequence identity to SEQ ID NO: 10, marker LSI 6311 comprising a G on position 51 of SEQ ID NO: 22, or a G at position 51 of a sequence comprising at least 95% sequence identity to SEQ ID NO: 22, and marker LS 17360 comprising a G on position 51 of SEQ ID NO: 24, or a G at position 51 of a sequence comprising at least 95% sequence identity to SEQ ID NO: 24.

[0019] In one embodiment, the QTL of the invention when present in a L. sativa plant is located on chromosome 2 between marker LSI 0601 having SEQ ID NO:1 or SEQ ID NO: 2 and marker LS10403 having SEQ ID NO:35 or SEQ ID NO:36, and comprises marker LS14067 comprising a T on position 51 of SEQ ID NO: 34, or a T at position 51 of a sequence comprising at least 95% sequence identity to SEQ ID NO: 34, and marker LSI 1096 comprising an A on position 51 of SEQ ID NO: 8, or an A at position 51 of a sequence comprising at least 95% sequence identity to SEQ ID NO: 8, and / or marker LSI 1685 comprising a T on position 51 of SEQ ID NO: 28, or a T at position 51 of a sequence comprising at least 95% sequence identity to SEQ ID NO: 28. Thus the QTL comprises marker LS 14067 comprising a T on position 51 of SEQ ID NO: 34, or a T at position 51 of a sequence comprising at least 95% sequence identity to SEQ ID NO: 34 in combination with at least one of the following markers: marker LSI 1096 comprising an A on position 51 of SEQ ID NO: 8, or an A at position 51 of a sequence comprising at least 95%sequence identity to SEQ ID NO: 8, and marker LSI 1685 comprising a T on position 51 of SEQ ID NO: 28, or a T at position 51 of a sequence comprising at least 95% sequence identity to SEQ ID NO: 28.

[0020] In one embodiment, the QTL of the invention when present in a L. sativa plant is located on chromosome 2 between marker LS10601 having SEQ ID NO:1 or SEQ ID NO:2 and marker LS10403 having SEQ ID NO:35 or SEQ ID NO:36, and comprises marker LSI 1096 comprising an A on position 51 of SEQ ID NO: 8, or an A at position 51 of a sequence comprising at least 95% sequence identity to SEQ ID NO: 8, and marker LS06285 comprising a C on position 51 of SEQ ID NO: 38, or a C at position 51 of a sequence comprising at least 95% sequence identity to SEQ ID NO: 38, and marker LS 17936 comprising an A on position 51 of SEQ ID NO: 40, or an A at position 51 of a sequence comprising at least 95% sequence identity to SEQ ID NO: 40.

[0021] As used herein, a QTL comprising a marker means that the marker is genetically linked to said QTL.

[0022] In one aspect of the invention, the QTL of the invention is a nucleic acid molecule, in particular an isolated nucleic acid molecule.

[0023] In yet one aspect of the invention, the QTL of the invention is a genomic DNA region. In one aspect of the invention, the QTL of the invention is as comprised in the genome of a L. sativa plant representative seed of which was deposited with the NCIMB under deposit number NCIMB 44421.

[0024] The invention further relates to a L. sativa plant, wherein the plant comprises the QTL of the invention as described in the present application in its genome. A L. sativa plant comprising the QTL of invention is herein referred to as a plant of the invention.

[0025] The invention also relates to L. sativa plants grown from seed deposited under NCIMB accession numbers NCIMB 44421.

[0026] The invention further relates to L. sativa plants comprising the QTL of the invention, wherein the QTL is introgressed from a plant, which is grown from seed deposited with the NCIMB under deposit number NCIMB 44421 or a progeny plant of seed of NCIMB accession 44421 that has retained the QTL of the invention.

[0027] In a particular embodiment, the plant of the invention is an agronomically elite L. sativa plant.

[0028] In the context of this invention, an agronomically elite plant is a plant having a genotype that, as a result of human intervention, comprises an accumulation of distinguishable and desirable agronomic traits which allow a producer to harvest a product of commercial significance, preferably the agronomically elite plant of the invention is a plant of an inbred line or a hybrid. As used herein, a plant of an inbred line is a plant of a population of plants that is the result of three or more rounds of selfing, or backcrossing; or which plant is a double haploid. An inbred line may e.g. be a parent line used for the production of a commercial hybrid.

[0029] As used herein, a hybrid plant is a plant which is the result of a cross between two different plants having different genotypes. More in particular, a hybrid plant is the result of a cross between plants of two different inbred lines, such a hybrid plant may e.g. be a plant of an Fi hybrid variety.

[0030] As used herein, resistance to or susceptibility to N. ribisnigri biotypes Nr:0 and Nr:l is determined in a bioassay. For this bioassay seeds of genotypes that are to be tested are sown in peat blocks and after 18 days transplanted to the soil, covered by a polytunnel. Nine plants per genotype are evaluated, per repetition. Young plants are infested 3.5 weeks after transplanting by distributing high amounts of aphids of the relevant N. ribisnigri biotype on the top of the plants. At 15 days and 22 days after infestation the test is scored. In case of a slow developing infection a third assessment is done at 29 days.

[0031] The resistance level of the plants is rated using a relative visual scale ranging from 0 to 4 to assess aphid population growth on the plants. For each bioassay a positive control in the same genetic background is included to assist in the scoring. The different classes of this scale are described in Table 2 below. For each genotype the above described bioassay will be performed in triplicate. The average of the final assessment moment (at 22 or 29 days) of the three bioassays determines the resistance level of a genotype.

[0032] As used herein a genotype is considered to exhibit resistance to Nr:0 and / or Nr:l when the average of the three bioassays together is 2.5 or lower according to the scale described in Table 2.

[0033] As used herein a genotype is considered to be susceptible to Nr:0 and / or Nr:l when the average of the three bioassays together is higher than 2.5 according to the scale described in Table 2.

[0034] A plant comprising the resistance conferring QTL of the invention, i.e. a plant of the invention will show an average score over the three bioassays of 2.5 or lower for both N. ribisnigri biotypes, and therefore is considered to be resistant Nr:0 and Nr:l.

[0035] Another aspect of the invention relates to a seed capable of growing into a plant of the invention wherein said plant comprises the QTL of the invention. The invention also relates to use of said seed for the production of a plant of the invention, by growing said seed into a plant.

[0036] Another aspect of the invention relates to a harvest product of a L. sativa plant of the invention wherein the harvest product is a leaf or head of lettuce and wherein the harvested product can be either in natural or processed form.

[0037] The invention also relates to propagation material suitable for producing a plant of the invention, wherein the propagation material is suitable for sexual reproduction, and is in particular selected from a microspore, a pollen, an ovary, an ovule, an embryo sac and an egg cell, or is suitable for vegetative reproduction, and is in particular selected from a cutting, a root, a stem a cell, and a protoplast, or is suitable for tissue culture of regenerable cells or protoplasts, and is in particular selected from a leaf, a pollen, an embryo, a cotyledon, a hypocotyl, a meristematic cell, a root, a root tip, an anther, a flower, a seed and a stem, wherein the plant produced from the propagation material comprises the QTL of the invention.

[0038] The invention further relates to a cell of a plant of the invention. Such a cell may either be in isolated form, or a part of the complete plant or parts thereof and still forms a cell of the invention because such a cell comprises the QTL of the invention. Each cell of a plant of the invention carries the QTL of the invention. A cell of the invention may also be a regenerable cell that can regenerate into a new plant of the invention.

[0039] The invention further relates to plant tissue of a plant of the invention, which comprises the QTL of the invention. The tissue can be undifferentiated tissue or already differentiated tissue. Undifferentiated tissue is for example a stem tip, an anther, a petal, or pollen, and can be used in micropropagation to obtain new plantlets that are grown into new plants of the invention. The tissue can also be grown from a cell of the invention.

[0040] The invention further relates to a method for the production of a plant comprising the QTL of the invention, which plant is resistant to N. ribisnigri biotypes Nr:0 and Nr:l, by using tissue culture or by using vegetative propagation.

[0041] The invention moreover relates to progeny of a plant, a cell, a tissue, or a seed of the invention, which progeny comprises the QTL of the invention. Such progeny can in itself be a plant, a cell, a tissue, or a seed. The progeny can in particular be progeny of a plant of the invention, representative seeds of which were deposited under NCIMB number 44421. As used herein, progeny comprises the first and all further descendants from a cross with a plant of the invention, wherein a cross comprises a cross with itself or a cross with another plant, and wherein a descendant that is determined to be progeny comprises the QTL of the invention. Descendants can be obtained through selfing and / or further crossing of the deposit. Progeny also encompasses material that is obtained by vegetative propagation or another form of multiplication.

[0042] The invention further relates to the germplasm of plants of the invention. The germplasm is constituted by all inherited characteristics of an organism and according to the invention encompasses at least the resistance trait of the invention. The germplasm can be used in a breeding program for the development of plants that show resistance to N. ribisnigri. The use of germplasm that comprises the QTL of the invention in breeding is also part of the present invention.

[0043] The invention also relates to the use of the QTL of the invention for producing a L. sativa that is resistant to N. ribisnigri. The current invention also relates to the use of a plant of the invention as a crop, as a source of seed or as a source of propagation material.

[0044] The invention also relates to a marker and / or the use thereof for the identification of the presence of the QTL of the invention in a L. sativa plant, wherein the marker is selected from any of the markers presented in Table 1.

[0045] In a preferred embodiment the invention relates to a marker and / or the use thereof for the identification of the presence of the QTL of the invention in a L. sativa plant, wherein the marker is selected from the group consisting of: marker LS10600 comprising an A at position 51 of SEQ ID NO: 4, or an A at position 51 of a sequence comprising at least 95% sequence identity to SEQ ID NO: 4; marker LS10399 comprising a C at position 51 of SEQ ID NO: 6, or a C at position 51 of a sequence comprising at least 95% sequence identity to SEQ ID NO: 6; marker LSI 1096 comprising an A on position 51 of SEQ ID NO: 8, or an A at position 51 of a sequence comprising at least 95% sequence identity to SEQ ID NO: 8 marker LS17344 comprising a G on position 51 of SEQ ID NO: 10, or a G at position 51 of a sequence comprising at least 95% sequence identity to SEQ ID NO: 10 marker LS10400 comprising a G on position 51 of SEQ ID NO: 12, or a G at position 511 of a sequence comprising at least 95% sequence identity to SEQ ID NO: 12 marker LS17348 comprising a T at position 51 of SEQ ID NO: 13, or a T at position 51 of a sequence comprising at least 95% sequence identity to SEQ ID NO: 13; marker LS17349 comprising a G at position 51 of SEQ ID NO: 14, or a G at position 51 of a sequence comprising at least 95% sequence identity to SEQ ID NO: 14; marker LS17355 comprising a T at position 51 of SEQ ID NO: 15, or a T at position 51 of a sequence comprising at least 95% sequence identity to SEQ ID NO: 15; marker LS17356 comprising a G at position 51 of SEQ ID NO: 16, or a G at position 51 of a sequence comprising at least 95% sequence identity to SEQ ID NO: 16; marker LS17350 comprising a T at position 51 of SEQ ID NO: 17, or a T at position 51 of a sequence comprising at least 95% sequence identity to SEQ ID NO: 17; marker LS17357 comprising an A at position 51 of SEQ ID NO: 18, or an A at position 51 of a sequence comprising at least 95% sequence identity to SEQ ID NO: 18; marker LS17358 comprising a G at position 51 of SEQ ID NO: 19, or a G at position 51 of a sequence comprising at least 95% sequence identity to SEQ ID NO: 19; marker LS17351 comprising a T at position 51 of SEQ ID NO: 20, or a T at position 51 of a sequence comprising at least 95% sequence identity to SEQ ID NO: 20; marker LSI 6311 comprising a G on position 51 of SEQ ID NO: 22, or a G at position 51 of a sequence comprising at least 95% sequence identity to SEQ ID NO: 22; marker LS17360 comprising a G on position 51 of SEQ ID NO: 24, or a G at position 51 of a sequence comprising at least 95% sequence identity to SEQ ID NO: 24. marker LS10401 comprising an A at position 51 of SEQ ID NO: 26, or an A at position 51 of a sequence comprising at least 95% sequence identity to SEQ ID NO: 26; marker LSI 1685 comprising a T on position 51 of SEQ ID NO: 28, or a T at position 51 of a sequence comprising at least 95% sequence identity to SEQ ID NO: 28 marker LS14064 comprising a C at position 51 of SEQ ID NO: 30, or a C at position 51 of a sequence comprising at least 95% sequence identity to SEQ ID NO: 30; marker LS14066 comprising a T at position 51 of SEQ ID NO: 32, or a T at position 51 of a sequence comprising at least 95% sequence identity to SEQ ID NO: 32; and marker LS14067 comprising a T at position 51 of SEQ ID NO: 34, or a T at position 51 of a sequence comprising at least 95% sequence identity to SEQ ID NO: 34; and marker LS02685 comprising a C at position 51 of SEQ ID NO: 38, or a C at position 51 of a sequence comprising at least 95% sequence identity to SEQ ID NO: 38; and marker L17936 comprising an A at position 51 of SEQ ID NO: 40, or an A at position 51 of a sequence comprising at least 95% sequence identity to SEQ ID NO: 40.

[0046] In an even more preferred embodiment relates to a marker and / or the use thereof for the identification of the presence of the QTL of the invention in a L. sativa plant, wherein the marker is selected from the group consisting of: marker LS17348 comprising a T at position 51 of SEQ ID NO: 13, or a T at position 51 of a sequence comprising at least 95% sequence identity to SEQ ID NO: 13; marker LS17349 comprising a G at position 51 of SEQ ID NO: 14, or a G at position 51 of a sequence comprising at least 95% sequence identity to SEQ ID NO: 14; marker LS17355 comprising a T at position 51 of SEQ ID NO: 15, or a T at position 51 of a sequence comprising at least 95% sequence identity to SEQ ID NO: 15; marker LS17356 comprising a G at position 51 of SEQ ID NO: 16, or a G at position 51 of a sequence comprising at least 95% sequence identity to SEQ ID NO: 16; marker LS17350 comprising a T at position 51 of SEQ ID NO: 17, or a T at position 51 of a sequence comprising at least 95% sequence identity to SEQ ID NO: 17; marker LS17357 comprising an A at position 51 of SEQ ID NO: 18, or an A at position 51 of a sequence comprising at least 95% sequence identity to SEQ ID NO: 18; marker LS17358 comprising a G at position 51 of SEQ ID NO: 19, or a G at position 51 of a sequence comprising at least 95% sequence identity to SEQ ID NO: 19; and marker LS17351 comprising a T at position 51 of SEQ ID NO: 20, or a T at position 51 of a sequence comprising at least 95% sequence identity to SEQ ID NO: 20. In a particular embodiment the invention relates to a set of markers and / or the use thereof for the identification of the presence of the QTL of the invention in a L. sativa plant, wherein the set of markers comprises marker LS10400 comprising a G on position 51 of SEQ ID NO: 12, or a G at position 511 of a sequence comprising at least 95% sequence identity to SEQ ID NO: 12, in combination with at least one of the following markers: marker LSI 7344 comprising a G on position 51 of SEQ ID NO: 10, or a G at position 51 of a sequence comprising at least 95% sequence identity to SEQ ID NO: 10, marker LS16311 comprising a G on position 51 of SEQ ID NO: 22, or a G at position 51 of a sequence comprising at least 95% sequence identity to SEQ ID NO: 22, and marker LS17360 comprising a G on position 51 of SEQ ID NO: 24, or a G at position 51 of a sequence comprising at least 95% sequence identity to SEQ ID NO: 24.

[0047] In another embodiment the invention relates to a set of markers and / or the use thereof for the identification of the presence of the QTL of the invention in a L. sativa plant, wherein the set of markers comprises marker LS14067 comprising a T on position 51 of SEQ ID NO: 34, or a T at position 51 of a sequence comprising at least 95% sequence identity to SEQ ID NO: 34 in combination with at least one of the following markers: marker LSI 1096 comprising an A on position 51 of SEQ ID NO: 8, or an A at position 51 of a sequence comprising at least 95% sequence identity to SEQ ID NO: 8, and marker LSI 1685 comprising a T on position 51 of SEQ ID NO: 28, or a T at position 51 of a sequence comprising at least 95% sequence identity to SEQ ID NO: 28.

[0048] In yet another embodiment the invention relates to a set of markers and / or the use thereof for the identification of the presence of the QTL of the invention in a L. sativa plant, wherein the set of markers comprises marker LSI 1096 comprising an A on position 51 of SEQ ID NO: 8, or an A at position 51 of a sequence comprising at least 95% sequence identity to SEQ ID NO: 8, marker LS02685 comprising a C on position 51 of SEQ ID NO: 38, or a C at position 51 of a sequence comprising at least 95% sequence identity to SEQ ID NO: 38, and marker LS17936 comprising an A on position 51 of SEQ ID NO: 40, or an A at position 51 of a sequence comprising at least 95% sequence identity to SEQ ID NO: 40.

[0049] The invention also relates to the use of markers as described herein for the identification of a L. sativa plant resistant to N. ribisnigri biotypes 0 and 1.

[0050] This invention also relates to a method for selecting a L. sativa plant of the invention, comprising identifying the presence of the QTL of the invention, and selecting a plant that comprises said QTL. Suitably, identifying the presence of the QTL of the invention is done by using any one of the markers in Table 1 as described herein. The identification or selection of a L. sativa plant of the invention can be done by performing a bioassay or by using markers or a combination these methods. A marker can be defined as a reference sequence that comprises the modification(s) that can be detected using any suitable method known. The term “marker”, “molecular marker”, "genetic marker" or “DNA marker” refers to a feature of an organism’s genome (e.g. a nucleotide or a polynucleotide sequence that is present in an organism’s genome) that is associated with one or more loci of interest. In some embodiments, a genetic marker is polymorphic in a population of interest. Genetic markers include, for example, single nucleotide polymorphisms (SNPs), indels (i.e. insertions / deletions), simple sequence repeats (SSRs), restriction fragment length polymorphisms (RFLPs), random amplified polymorphic DNAs (RAPDs), cleaved amplified polymorphic sequence (CAPS) markers, Diversity Arrays Technology (DArT) markers, and amplified fragment length polymorphisms (AFLPs), among many other examples. Genetic markers can, for example, be used to locate genetic loci containing alleles on a chromosome that contribute to variability of phenotypic traits. The term “marker” or “genetic marker” can also refer to a polynucleotide sequence complementary to a genomic sequence, such as a sequence of a nucleic acid used as a probe. The term “marker” then refers to a physical entity that can be used in molecular biological techniques for detecting the mutation.

[0051] In the context of the present invention, a marker of Table 1 as described herein allows for the detection of the QTL of the invention that is responsible for the resistance against N. ribisnigri, and the selection of L. sativa plants that harbor in their genome the QTL of the invention at any stage of their life cycle, even when the plants are only in the seedling stage. Marker-assisted breeding and selection greatly increases the speed with which a trait can be introduced into different genetic backgrounds, and with which it can be commercialized.

[0052] The markers of Table 1 as described herein can also be used to develop other markers that are genetically linked to the QTL of the invention.

[0053] Therefore the invention also relates to any marker genetically linked to the QTL of the invention wherein the marker in order of increased preference is located between marker LSI 0601 having SEQ ID NO:1 or SEQ ID NO:2 and marker LS10403 having SEQ ID NO:35 or SEQ ID NO:36, or between marker LSI 1096 having SEQ ID NO:7 or SEQ ID NO:8 and marker LSI 1685 having SEQ ID NO:27 or SEQ ID NO:28, or between marker LS17344 having SEQ ID NO:9 or SEQ ID NO: 10 and marker LS 17360 having SEQ ID NO:23 or SEQ ID NO:24.

[0054] Methods for detecting markers and specific alleles are abundantly known in the field. In general, these methods allow to distinguish between two different alleles of a marker, or the presence or absence of a marker on a specific chromosome. Detection of a polymorphism can be achieved by electrophoretic techniques, but the widespread availability of DNA sequencing often makes it easier to simply sequence amplified products directly. Once the polymorphic sequence difference is known, rapid assays for the detection of a polymorphism can be designed for progeny testing, generally involving some version of PCR amplification of specific alleles. The invention further relates to a method for producing a L. sativa plant resistant to N. ribisnigri biotypes Nr:0 and Nr:l, said method comprising: a) crossing a plant of the invention with another plant to obtain a first generation population; b) performing one or more rounds of selfing and / or crossing of the plant resulting from the cross to obtain a further generation population; c) selecting from among the plants resulting from the further generation population of step b) a plant that comprises the QTL of the invention, which plant is resistant Nasonovia ribisnigri biotypes 0 and 1.

[0055] In one embodiment, selecting a plant comprising the QTL of the invention is done by using a molecular marker genetically linked to the QTL, preferably a marker of Table 1 as described herein.

[0056] In another embodiment, a plant comprising the QTL of the invention is phenotypically selected, in particular by determining resistance to N. ribisinigri biotype Nr:0 and / or Nr:l as described in Example 1.

[0057] In a specific embodiment the plant of the invention in step a) for producing a L. sativa plant resistant to N. ribisnigri biotypes Nr:0 and Nr:l is a plant grown from seed deposited under NCIMB accession number NCIMB 44421, or a progeny plant thereof that has retained the QTL of the invention.

[0058] In another embodiment the source plant of the invention for producing a L. sativa plant resistant to N. ribisnigri biotypes Nr:0 and Nr:l is a plant of the species L. aculeata.

[0059] The invention further relates to a hybrid L. sativa seed and to a method for the production of a hybrid L. sativa seed comprising crossing a first parent plant with a second parent plant and harvesting the resultant hybrid seed, wherein the first parent plant and / or the second parent plant is a plant comprising the QTL of the invention.

[0060] In a particular embodiment the first and / or second parent plant is a plant grown from seed deposited under NCIMB accession number NCIMB 44421, or a progeny plant thereof that has retained the QTL of the invention.

[0061] The invention also relates to a method for growing a L. sativa plant resistant to Nasonovia ribisnigri biotypes 0 and 1 , which method comprises the step of germinating a seed comprising the QTL of the invention in its genome. In a particular embodiment the L. sativa plant is grown from a seed deposited under NCIMB accession number NCIMB 44421, or a seed of a progeny plant thereof that has retained the QTL of the invention. DEPOSIT

[0062] Seeds of Lactuca sativa L. comprising the aphid resistance conferring QTL of the invention were deposited with NCIMB Ltd, Wellheads Place, Dyce, Aberdeen AB21 7GB, UK, on 29 August, 2024, under deposit accession numbers NCIMB 44421. The deposit was made pursuant to the terms of the Budapest Treaty. Upon issuance of a patent, all restrictions upon the deposit will be removed, and the deposit is intended to meet the requirements of 37 CFR § 1.801-1.809. The deposit will be irrevocably and without restriction or condition released to the public upon the issuance of a patent. The deposit will be maintained in the depository for a period of 30 years, or 5 years after the last request, or for the effective life of the patent, whichever is longer, and will be replaced if necessary during that period.

[0063] SEQUENCE INFORMATION

[0064] The markers indicates with are markers unique for the resistance conferring QTL introgressed from L. aculeata. In a wildtype L. sativa plant, i.e. a susceptible L. sativa plant, these markers are absent and will not give a score at all. Therefore, in a L. sativa plant the absence of the marker correlates with absence of the resistance conferring QTL and thus with susceptibility. The presence of the marker in L. sativa correlates with the presence of the resistance conferring QTL of the invention.

[0065] The markers indicates with are only indicative of the presence of the resistance conferring QTL in combination with certain other markers, so-called haplotypes, as described in this application.

[0066] The present invention is further illustrated in the Examples that follow and that are not intended to limit the invention in any way.

[0067] EXAMPLES

[0068] EXAMPLE 1

[0069] Nasonovia ribisnigri Bioassay

[0070] In the process of identifying a new source of N. ribisnigri resistance, lettuce accessions and accessions of wild relatives of lettuce were subjected to N. ribisnigri bioassay. For this bioassay, seeds of many different genotypes were sown in peat blocks and after 18 days transplanted to the soil, covered by a polytunnel. Nine plants per genotype were evaluated, per repetition. Young plants are infested 3.5 weeks after transplanting by distributing high amounts of aphids of the relevant N. ribisnigri biotype on the top of the plants. At 15 days and 22 days after infestation the test was scored. In case of a slow developing infection a third assessment is done at 29 days.

[0071] The resistance level of the plants was rated using a relative visual scale ranging from 0 to 4 to assess aphid population growth on the plants. For each bioassay a positive control with a similar genetic background was included to assist in the scoring. The different classes of the scale are described in Table 2 below. For each genotype the above described bioassay was performed in triplicate. The average of the final assessment moment (at 22 or 29 days) of the three bioassays determines the resistance level of a genotype. A plant is considered to exhibit resistance to Nr:0 and / or Nr: 1 when the average of the three tests together is 2.5 or lower according to the scale described in Table 2. The Nr:0 isolate used in this example was sampled in The Netherlands and maintained on the variety Reskia. The Nr:l isolate used in this example was sampled in 2007 from Kongen (Germany) on a Nr:0 resistant variety Estelle (Nunhems): sample 279. The aphid isolate is maintained on the variety Kitare (Nr:0 resistant variety, Rijk Zwaan). Table 2.

[0072] In Table 3 the results of the above described bioassay are summarized for the source accession L. aculeata 13-68, a plant of the deposit (NCIMB 44421) and an isogenic susceptible control of the deposit performed in the above described bioassay.

[0073] Table 3. Bioassay results

[0074] In the assay columns of the table the number of plants for each class (0 to 4 from left to right) is noted. The score is the average class value across all plants.

[0075] EXAMPLE 2

[0076] QTL mapping and marker development

[0077] In order to map the Nr:l resistance conferring QTLs from the identified sources, 186 F3 families derived from the cross between the Nr:l resistant L. aculeata 13-68 and a Nr:l susceptible L. sativa plant (cv. Kitare) were phenotyped for Nr:l resistance; parents were also included for reference; DNA samples were taken of each family for genotyping. Phenotypic scores 0 to 4 according to Table 2 were present in all F3 population.

[0078] A genetic map was constructed for the segregating population; non-polymorphic markers and markers with a strong segregation distortion were removed. Around 150 markers were mapped and were well-distributed over the genome, with an average spacing of 7 cM. The marker order was determined; the public genome assembly was used to determine numbering and orientation of the linkage groups.

[0079] Phenotypic scores, genotypic data, and the genetic map containing marker positions were used as input data for the QTL mapping. QTL analysis was performed, and mapping of the data resulted in the identification of a major QTL on chromosome 2.

[0080] Through further observations on several populations that segregated for resistance to the Nr:l and Nr:0 biotypes, and subsequent fine-mapping of the QTL, the region on chromosome 2 could be further narrowed down to an interval of approximately 5 cM, conferring resistance to both Nr:0 and Nr:l biotypes. The markers that were identified in this analysis and can be used to detect these QTLs are presented in Table 1. These markers can be used to identify the presence of the QTL in plants grown from the deposits. These markers can further be used to identify the presence of the resistance conferring QTL of the invention on chromosome 2 in any other L. sativa population that comprises said QTL.

Claims

CLAIMS1. A QTL providing resistance to Nasonovia ribisnigri biotypes Nr:0 and Nr:l when present in a Lactuca sativa plant, wherein the QTL is located on chromosome 2 between marker LS10601 having SEQ ID NO:1 or SEQ ID NO:2 and marker LS10403 having SEQ ID NO:35 or SEQ ID NO:36.

2. The QTL of claim 1 , wherein the QTL comprises at least one marker selected from: marker LS10600 comprising an A at position 51 of SEQ ID NO: 4, or an A at position 51 of a sequence comprising at least 95% sequence identity to SEQ ID NO: 4; marker LS10399 comprising a C at position 51 of SEQ ID NO: 6, or a C at position 51 of a sequence comprising at least 95% sequence identity to SEQ ID NO: 6; marker LS17348 comprising a T at position 51 of SEQ ID NO: 13, or a T at position 51 of a sequence comprising at least 95% sequence identity to SEQ ID NO: 13; marker LS17349 comprising a G at position 51 of SEQ ID NO: 14, or a G at position 51 of a sequence comprising at least 95% sequence identity to SEQ ID NO: 14; marker LS17355 comprising a T at position 51 of SEQ ID NO: 15, or a T at position 51 of a sequence comprising at least 95% sequence identity to SEQ ID NO: 15; marker LS17356 comprising a G at position 51 of SEQ ID NO: 16, or a G at position 51 of a sequence comprising at least 95% sequence identity to SEQ ID NO: 16; marker LS17350 comprising a T at position 51 of SEQ ID NO: 17, or a T at position 51 of a sequence comprising at least 95% sequence identity to SEQ ID NO: 17; marker LS17357 comprising an A at position 51 of SEQ ID NO: 18, or an A at position 51 of a sequence comprising at least 95% sequence identity to SEQ ID NO: 18; marker LS17358 comprising a G at position 51 of SEQ ID NO: 19, or a G at position 51 of a sequence comprising at least 95% sequence identity to SEQ ID NO: 19; marker LS17351 comprising a T at position 51 of SEQ ID NO: 20, or a T at position 51 of a sequence comprising at least 95% sequence identity to SEQ ID NO: 20; marker LS10401 comprising an A at position 51 of SEQ ID NO: 26, or an A at position 51 of a sequence comprising at least 95% sequence identity to SEQ ID NO: 26; marker LS14064 comprising a C at position 51 of SEQ ID NO: 30, or a C at position 51 of a sequence comprising at least 95% sequence identity to SEQ ID NO: 30; marker LS14066 comprising a T at position 51 of SEQ ID NO: 32, or a T at position 51 of a sequence comprising at least 95% sequence identity to SEQ ID NO: 32; marker LS14067 comprising a T at position 51 of SEQ ID NO: 34, or a T at position 51 of asequence comprising at least 95% sequence identity to SEQ ID NO: 34.

3. The QTL of claim 1 wherein the QTL comprises marker LSI 0400 comprising a G on position 51 of SEQ ID NO: 12, or a G at position 511 of a sequence comprising at least 95% sequence identity to SEQ ID NO: 12, and marker LS17344 comprising a G on position 51 of SEQ ID NO: 10, or a G at position 51 of a sequence comprising at least 95% sequence identity to SEQ ID NO: 10, and / or marker LSI 6311 comprising a G on position 51 of SEQ ID NO: 22, or a G at position 51 of a sequence comprising at least 95% sequence identity to SEQ ID NO: 22, and / or marker LS17360 comprising a G on position 51 of SEQ ID NO: 24, or a G at position 51 of a sequence comprising at least 95% sequence identity to SEQ ID NO: 24.

4. The QTL as claimed in any of the claims 1 to 3 wherein the QTL is as comprised in the genome of a Lactuca sativa plant representative seed of which was deposited with the NCIMB under deposit number NCIMB 44421.

5. A Lactuca sativa plant comprising the QTL as claimed in any of the claims 1 to 4.

6. The plant of claim 5, wherein the QTL is introgressed from a plant, which is grown from seed deposited with the NCIMB under deposit number NCIMB 44421 or a progeny plant of seed of NCIMB accession 44421 that has retained the QTL as defined in any of the claims 1 to 4.

7. The plant of claim 5 or 6, wherein the plant is an agronomically elite plant.

8. A cell of a Lactuca sativa plant according to any of the claims 5 to 7, which cell comprises a QTL as claimed in any of the claims 1 to 4 in its genome.

9. A Lactuca sativa seed comprising the QTL as claimed in any of the claims 1 to 4 in its genome, wherein a plant grown from the seed is a plant as claimed in any one of the claims 5 to 7.

10. Propagation material capable of developing into and / or being derived from a Lactuca sativa plant according to claims 5 to 7, wherein the propagation material is suitable for sexual reproduction, and is in particular selected from the group comprising a microspore, pollen, an ovary, an ovule, an embryo sac, and an egg cell; or is suitable for vegetative reproduction, and is in particular selected from the group comprising a cutting, a root, a stem, a cell, and a protoplast; or is suitable for tissue culture of regenerable cells, and is in particular selected from the groupcomprising a leaf, pollen, an embryo, a cotyledon, a hypocotyl, a meristematic cell, a root, a root tip, an anther, a flower, a seed, and a stem; wherein the plant developed from the propagation material comprises the QTL as claimed in any of the claims 1 to 4.

11. Marker for the identification of the presence of a QTL as claimed in any of the claims 1 to 4 in a Lactuca sativa plant, which marker is selected from the group comprising: marker LS10600 comprising an A at position 51 of SEQ ID NO: 4, or an A at position 51 of a sequence comprising at least 95% sequence identity to SEQ ID NO: 4; marker LS10399 comprising a C at position 51 of SEQ ID NO: 6, or a C at position 51 of a sequence comprising at least 95% sequence identity to SEQ ID NO: 6; marker LSI 1096 comprising an A on position 51 of SEQ ID NO: 8, or an A at position 51 of a sequence comprising at least 95% sequence identity to SEQ ID NO: 8 marker LS17344 comprising a G on position 51 of SEQ ID NO: 10, or a G at position 51 of a sequence comprising at least 95% sequence identity to SEQ ID NO: 10 marker LS10400 comprising a G on position 51 of SEQ ID NO: 12, or a G at position 511 of a sequence comprising at least 95% sequence identity to SEQ ID NO: 12 marker LS17348 comprising a T at position 51 of SEQ ID NO: 13, or a T at position 51 of a sequence comprising at least 95% sequence identity to SEQ ID NO: 13; marker LS17349 comprising a G at position 51 of SEQ ID NO: 14, or a G at position 51 of a sequence comprising at least 95% sequence identity to SEQ ID NO: 14; marker LS17355 comprising a T at position 51 of SEQ ID NO: 15, or a T at position 51 of a sequence comprising at least 95% sequence identity to SEQ ID NO: 15; marker LS17356 comprising a G at position 51 of SEQ ID NO: 16, or a G at position 51 of a sequence comprising at least 95% sequence identity to SEQ ID NO: 16; marker LS17350 comprising a T at position 51 of SEQ ID NO: 17, or a T at position 51 of a sequence comprising at least 95% sequence identity to SEQ ID NO: 17; marker LS17357 comprising an A at position 51 of SEQ ID NO: 18, or an A at position 51 of a sequence comprising at least 95% sequence identity to SEQ ID NO: 18; marker LS17358 comprising a G at position 51 of SEQ ID NO: 19, or a G at position 51 of a sequence comprising at least 95% sequence identity to SEQ ID NO: 19; marker LS17351 comprising a T at position 51 of SEQ ID NO: 20, or a T at position 51 of a sequence comprising at least 95% sequence identity to SEQ ID NO: 20; marker LSI 6311 comprising a G on position 51 of SEQ ID NO: 22, or a G at position 51 of a sequence comprising at least 95% sequence identity to SEQ ID NO: 22; marker LS17360 comprising a G on position 51 of SEQ ID NO: 24, or a G at position 51 of a sequence comprising at least 95% sequence identity to SEQ ID NO: 24.marker LS10401 comprising an A at position 51 of SEQ ID NO: 26, or an A at position 51 of a sequence comprising at least 95% sequence identity to SEQ ID NO: 26; marker LSI 1685 comprising a T on position 51 of SEQ ID NO: 28, or a T at position 51 of a sequence comprising at least 95% sequence identity to SEQ ID NO: 28 marker LS14064 comprising a C at position 51 of SEQ ID NO: 30, or a C at position 51 of a sequence comprising at least 95% sequence identity to SEQ ID NO: 30; marker LS14066 comprising a T at position 51 of SEQ ID NO: 32, or a T at position 51 of a sequence comprising at least 95% sequence identity to SEQ ID NO: 32; and marker LS14067 comprising a T at position 51 of SEQ ID NO: 34, or a T at position 51 of a sequence comprising at least 95% sequence identity to SEQ ID NO: 34.

12. Use of a marker as claimed in claim 11 for identification of a Lactuca sativa plant comprising the QTL as claimed in any one of the claims 1 to 4.

13. Use of a marker as claimed in claim 11 for identification of a Lactuca sativa plant resistant to Nasonovia ribisnigri biotypes Nr:0 and Nr:l.

14. Method for selecting a Lactuca sativa plant resistant to Nasonovia ribisnigri biotypes 0 and 1 , comprising detecting the presence of a QTL as claimed in any one of the claims 1 to 4 and selecting a plant that comprises said QTL.

15. Method as claimed in claim 14, wherein the presence of the QTL is detected by using a marker as claimed in claim 11.

16. Method for producing a Lactuca sativa plant resistant to Nasonovia ribisnigri biotypes 0 and 1, said method comprising: a) crossing a plant according to any one of the claims 5 to 7 with another plant to obtain a first generation population; b) performing one or more rounds of selfing and / or crossing of the plant resulting from the cross to obtain a further generation population; c) selecting from among the plants resulting from the further generation population of step b) a plant that comprises a QTL as claimed in any one of the claims 1 to 4, which plant is resistant Nasonovia ribisnigri biotypes Nr:0 and Nr:l.

17. Method as claimed in claim 16, wherein the plant comprising the QTL as claimed in any one of the claims 1 to 4 is selected by using a molecular marker genetically linked to the QTL, preferably a marker as claimed in claim 11.

18. Method as claimed in claim 16, wherein the plant as defined in any one of the claims 5 to 7 is phenotypically selected, in particular by determining resistance against Nasonovia ribisnigri biotypes Nr:0 and / or Nr:l.

19. Method as claimed in any one of the claims 16 to 18, wherein the plant according to any one of the claims 5 to 7 is a plant grown from seed deposited under NCIMB accession number NCIMB 44421, or a progeny plant thereof that has retained the QTL as claimed in any of the claims 1 to 4.

20. A method for growing a Lactuca sativa plant resistant to Nasonovia ribisnigri biotypes Nr:0 and Nr:l, which method comprises the step of germinating a seed comprising the QTL as claimed in any of the claims 1 to 4 in its genome.

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