Coupling Phase R-Gene Stacking in Lettuce Breeding
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Solution Overview
Problem
Current breeding techniques for lettuce plants are limited in stacking Bremia resistance genes due to their clustering, making it difficult to achieve effective resistance against multiple Bremia lactucae races, and the production of hybrid varieties is costly and complex, limiting the use of heterozygous plants.
Innovation Solution
Development of lettuce plants with Bremia resistance genes Dm3, Dm6, and R18 in coupling phase, which are previously found in repulsion phase, allowing for enhanced resistance against multiple Bremia lactucae races and simplifying breeding by behaving as a single dominant gene, linked to specific markers for identification.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If different Bremia resistance genes are stacked to slow down pathogen virulence, then resistance effectiveness is improved, but the complexity of breeding increases due to gene clustering and repulsion phase inheritance
Solution Approach 1:
The patent combines three resistance genes (Dm3, Dm6, and R18) that were previously found in repulsion phase into a single coupling phase configuration on chromosome 2. This merging allows the genes to be inherited together as a single unit, effectively stacking multiple resistance genes without the complexity of managing separate heterozygous loci. The combined resistance profile covers Bremia lactucae races Bl:1, Bl:4, Bl:5, Bl:6, Bl:7, Bl:10, Bl:12, Bl:13, Bl:14, Bl:15, Bl:16, Bl:17, Bl:18, Bl:21, Bl:22, Bl:23, Bl:24, Bl:25, and Bl:28.
Solution Approach 2:
The patent performs preliminary action by developing and depositing seed material (accession number NCIMB 41761) that already contains the coupled resistance genes Dm3, Dm6, and R18. This preliminary development eliminates the need for breeders to perform complex crossing and selection procedures to achieve gene stacking, as the coupled genes are readily available in a standardized seed source that can be directly introduced into breeding programs.
2Reliability
If heterozygous plants with multiple R-genes are used to achieve maximum resistance stacking, then resistance coverage is improved, but production costs and complexity increase
Solution Approach 1:
The patent inverts the conventional approach by creating homozygous inbred lines with coupled resistance genes instead of relying on heterozygous hybrids. Traditionally, maximum resistance stacking required heterozygous plants with one copy of each gene, but this invention achieves equivalent or superior resistance through homozygous lines containing multiple coupled genes. This inversion eliminates the need for expensive and complex hybrid seed production while maintaining broad resistance coverage against multiple Bremia lactucae races.
Solution Approach 2:
The patent utilizes inexpensive inbred line breeding instead of expensive hybrid seed production. By developing standardized inbred lines with coupled resistance genes that can be propagated through simple selfing, the system replaces costly hybrid seed manufacturing with a more economical approach using disposable inbred line material that can be regenerated annually at low cost.
3Ease of manufacture
If inbred lines are used instead of hybrid varieties, then production cost is reduced, but the number of stackable R-genes per cluster is limited to one
Solution Approach 1:
The patent merges multiple resistance genes (Dm3, Dm6, and R18) into a single coupled configuration on chromosome 2, allowing them to be inherited together in inbred lines. This merging overcomes the traditional limitation where genes in repulsion phase could only be stacked as single heterozygous loci. The coupled genes behave as a single inheritance unit, enabling inbred lines to carry multiple resistance genes simultaneously, thus achieving both cost-effectiveness and multi-gene stacking.
Solution Approach 2:
The patent changes the dimensional arrangement of resistance genes from a repulsion phase configuration (where genes are on opposite homologous chromosomes) to a coupling phase configuration (where genes are on the same homologous chromosome). This dimensional change in gene arrangement allows multiple resistance genes to be co-inherited in inbred lines, transforming the inheritance pattern from single-gene per cluster to multi-gene per cluster while maintaining inbred line simplicity.
Data Source
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AI summary
The present invention relates to A lettuce plant resistant to Bremia lactucae races B1:1, B1:4, B1:5, B1:6, B1:7, B1:10, B1:12, B1:13, B1:14, B1:15, B1:16, B1:17, B1:18, B1:21, B1:22, B1:23, B1:24, B1 : 25 and B1:28, which plant comprises a genetic determinant which causes the resistance and which genetic determinant is obtainable by introgression from a plant grown from seeds of which a representative sample was deposited under accession number NCIMB 41761, and wherein the said genetic determinant in the seeds of seed deposit number NCIMB 41761 is at least linked to marker SCM05 with SEQ ID NO: 4, marker LR0029 with SEQ ID NO:5, and marker LK0036 with SEQ ID NO:6, and optionally also to one or more of the markers selected from the group consisting of marker SCW09 with SEQ ID NO : 1, marker CL922 with SEQ ID N0:2, marker SCV12 with SEQ ID N0:3, marker LR0096 with SEQ ID NO : 7, and marker SCI11 with SEQ ID NO:8. Preferably, the genetic determinant comprises genes Dm3, Dm6 and R18 in coupling phase.