Filamentous fungus involved in reduction of sweet potato foot rot

Abstract

To provide biological control means against the sweet potato foot rot caused by Diaporthe destruens.SOLUTION: Provided is a control agent against the sweet potato foot rot comprising a filamentous fungus as an active ingredient. The filamentous fungus belongs to the genus Humicola or Acrophialophora, exhibiting an effect in inhibiting the growth of the sweet potato foot rot pathogen.SELECTED DRAWING: None

Description

[Technical field]

[0001] The present invention relates to a control agent for sweet potato base rot, a control method for sweet potato base rot using the same, and a strain used in the control agent and control method. [Background technology]

[0002] Sweet potato root rot is a soil-borne disease caused by the filamentous fungus Diaporthe destruens. Infected sweet potatoes first show brownish black spots at the base of the stem, then the symptoms progress to the above-ground and underground parts, adversely affecting growth and causing poor growth. In severe cases, the plant dies and the sweet potato cannot be harvested. The disease was first reported in Okinawa and Kagoshima prefectures in 2018, and has now been confirmed in almost all sweet potato producing areas in Japan, including major sweet potato producing areas, with particularly serious damage in southern Kyushu and Okinawa. Proposed measures to control this disease include the use of resistant varieties, drainage measures for fields, and the use of pesticides (four stem and leaf sprays registered as pesticides as of March 2023). However, soil-borne disease continues for a long time, making control difficult, so it is necessary to establish a method to control soil-borne disease.

[0003] Conventional methods for controlling soil diseases using soil fumigants have concerns about the impact on workers' health and the surrounding environment, and it is necessary to reduce their use. Furthermore, with the recent decline in agricultural workers and their aging, there is a need to promote labor-saving and cost-saving disease control, but the conventional control methods are problematic in that they require a large burden of labor and cost. For this reason, it is necessary to develop methods other than chemical control methods using soil fumigants, etc.

[0004] Biological control techniques using microorganisms and the like that exhibit disease suppression effects are expected to be an alternative to chemical control methods. Many biological control techniques have been known for some time, and for example, it has been reported that the Humicola sp. JS-0112 strain suppresses plant pathogenic fungi such as rice blast, rice sheath blight, and wheat leaf rust by using monordene that has antifungal activity (Non-Patent Document 1), and that the Acrophialophora jodhpurensis Msh5 strain suppresses the tomato early blight fungus (Alternaria alternata) (Non-Patent Document 2). [Prior art documents] [Non-patent literature]

[0005] [Non-Patent Document 1] Nguyen HTT et al. (2020) The Hsp90 inhibitor, Monorden, is a promising lead compound for the development of novel fungicides. Front. Plant Sci. 11, 371. doi: 10.3389 / fpls.2020.00371 [Non-Patent Document 2] Daroodi Z et al (2014) Endophytic fungus Acrophialophora jodhpurensis induced resistance against tomato early blight via interplay of reactive oxygen species, iron and antioxidants. Physiolog Mol Plant Patholog. 115, 101681. doi:10.1016 / j.pmpp.2021.101681 Summary of the Invention [Problem to be solved by the invention]

[0006] As described above, methods for controlling plant diseases using microorganisms have been known for some time, but no microorganisms capable of biological control of sweet potato base rot were known. The present invention has been made under such a background, and aims to provide a biological control method for sweet potato base rot. [Means for solving the problem]

[0007] The present inventors isolated strains belonging to the genus Humicola or Acrophialophora from soil in which the incidence of sweet potato base rot had decreased, and found that these strains suppress the growth of the sweet potato base rot fungus, thereby completing the present invention.

[0008] As described above, Non-Patent Document 1 describes that strains belonging to the genus Humicola suppress rice blast fungus and the like, and Non-Patent Document 2 describes that strains belonging to the genus Acrophialophora suppress tomato early blight fungus. However, sweet potato base rot fungus is an ascomycete fungus, while rice blast fungus and tomato early blight fungus are imperfect fungi, and the two are taxonomically significantly different microorganisms. In addition, sweet potato base rot is a disease of plants of the Convolvulaceae family, while rice blast is a disease of plants of the Poaceae family and tomato early blight is a disease of plants of the Solanaceae family, and the target crops are also significantly different. For these reasons, a person skilled in the art could not predict that strains belonging to the genus Humicola or Acrophialophora could suppress the growth of sweet potato base rot fungus.

[0009] The present invention has been completed based on the above findings. That is, the present invention provides the following (1) to (6).

[0010] (1) A control agent for sweet potato base rot containing a filamentous fungus as an active ingredient, the filamentous fungus being a filamentous fungus belonging to the genus Humicola or Acrophialophora and having an effect of inhibiting the growth of sweet potato base rot fungus.

[0011] (2) The control agent for sweet potato root rot according to (1), characterized in that the filamentous fungus is Humicola sp. strain 1-2 (received number: NITE AP-03947), Humicola sp. strain 3-18 (received number: NITE AP-03949), or Acrophialophora sp. strain 1-4 (received number: NITE AP-03948).

[0012] (3) A method for controlling sweet potato base rot, comprising the step of applying the control agent for sweet potato base rot according to (1) or (2) to a plant or the soil in which the plant is grown.

[0013] (4) The method for controlling sweet potato root rot according to (3), wherein the plant is a plant of the Convolvulaceae family.

[0014] (5) The method for controlling sweet potato root rot according to (3), wherein the plant is sweet potato.

[0015] (6) Humicola sp. strain 1-2 (received number: NITE AP-03947), Humicola sp. strain 3-18 (received number: NITE AP-03949), or Acrophialophora sp. strain 1-4 (received number: NITE AP-03948). Effect of the Invention

[0016] The present invention provides a novel control agent for sweet potato base rot. The control agent of the present invention biologically controls sweet potato base rot, and therefore solves the problems of safety, labor, cost, etc., associated with conventional chemical control agents. [Brief description of the drawings]

[0017] [Figure 1] Graph showing the change over time in the rate of sweet potato root rot disease during the cultivation period. [Diagram 2]A diagram showing the band pattern from the analysis of filamentous fungal community structure by PCR-DGGE (at planting in June 2022, 3 treatments, DNA extraction: triplicate). [Diagram 3] Figure showing the results of amplicon analysis by next-generation sequencing (FY2021). [Figure 4] Phylogenetic tree based on rRNA gene (ITS) sequencing results of the Chaetomiaceae family isolated from the soil disinfection + compost plot. [Diagram 5] A diagram showing the band pattern by PCR-DGGE for the soil disinfection + 5t compost group and the band positions of the isolated strains. [Figure 6] A diagram showing the band intensity and number of diseased strains at the Humicola sp. 3-18 strain position (2022). [Figure 7] FIG. 1 shows the growth inhibitory effect of isolated strains on root rot fungi. [Figure 8] FIG. 1 shows the results of evaluating the ability of isolated strains to inhibit sweet potato root rot in a pot test using soil artificially contaminated with root rot fungus. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0018] The present invention will be described in detail below. The control agent for sweet potato base rot of the present invention is characterized by containing as an active ingredient a filamentous fungus belonging to the genus Humicola or Acrophialophora and having an effect of inhibiting the growth of sweet potato base rot fungus.

[0019] Examples of filamentous fungi to be used include Humicola sp. 1-2 strain, Humicola sp. 3-18 strain, and Acrophialophora sp. 1-4 strain. These strains have been deposited at the National Institute of Technology and Evaluation, Japan Patent Microorganisms Depositary Center. Detailed information on the deposit is as follows.

[0020] (1) Humicola sp. strain 1-2 (1-1) Name and address of the depository institution Name: National Institute of Technology and Evaluation, Patent Microorganism Deposit Center Address: 2-5-8 Kazusa Kamatari, Kisarazu City, Chiba Prefecture, Japan Postal code: 292-0818 (1-2) Date of receipt: July 19, 2023 (1-3) Receipt number: NITE AP-03947 (1-4) Identification display: 1-2

[0021] (2) Humicola sp. strain 3-18 (2-1) Name and address of the depository institution Name: National Institute of Technology and Evaluation, Patent Microorganism Deposit Center Address: 2-5-8 Kazusa Kamatari, Kisarazu City, Chiba Prefecture, Japan Postal code: 292-0818 (2-2) Date of receipt: July 19, 2023 (2-3) Receipt number: NITE AP-03949 (2-4) Identification display: 3-18

[0022] (3) Acrophialophora sp. strain 1-4 (3-1) Name and address of the depository institution Name: National Institute of Technology and Evaluation, Patent Microorganism Deposit Center Address: 2-5-8 Kazusa Kamatari, Kisarazu City, Chiba Prefecture, Japan Postal code: 292-0818 (3-2) Date of receipt: July 19, 2023 (2-3) Receipt number: NITE AP-03948 (3-4) Identification: 1-4

[0023] The filamentous fungus may be any fungus other than the above strains, as long as it belongs to the genus Humicola or Acrophialophora and has the effect of inhibiting the growth of sweet potato base rot fungus. As described in the examples below, such filamentous fungus can be isolated from soil in which the occurrence of sweet potato base rot has been reduced by soil disinfection and compost application. For example, 1) preparing soil in which the occurrence of sweet potato base rot has been reduced by soil disinfection and compost application, 2) isolating microorganisms from the soil, 3) selecting a filamentous fungus belonging to the genus Humicola or Acrophialophora from among the microorganisms using rRNA genes as an indicator, and 4) culturing the selected filamentous fungus against sweet potato base rot fungus to select a filamentous fungus having the effect of inhibiting the growth of sweet potato base rot fungus, thereby obtaining a filamentous fungus that can be used in the present invention.

[0024] The method for culturing the filamentous fungus used in the present invention is not particularly limited, and the filamentous fungus can be cultured by a method generally applied to the filamentous fungus of the genus Humicola or Acrophialophora. For example, PDA medium can be used as the medium. The culture temperature can be about 25°C (for example, 20 to 30°C).

[0025] The content of the filamentous fungus in the control agent of the present invention is not particularly limited as long as it is within a range that allows control of sweet potato root rot. For example, 4 ~10 9 cfu / g soil, preferably 10 6 ~10 7 It can be expressed as cfu / g soil.

[0026] The control agent of the present invention may contain only the culture solution or dried product of the above-mentioned filamentous fungus, but may also be formulated in the same form as a normal pesticide formulation (for example, in the form of a dust, wettable powder, emulsion, liquid, flowable, coating agent, etc.) in combination with other optional components. Examples of optional components used in combination include solid carriers and adjuvants. Examples of solid carriers include organic powders such as bentonite, diatomaceous earth, talc, perlite, vermiculite, sodium carboxymethylcellulose (CMC), beer lees, sugarcane pomace (bacas), soybean lees, bran, chitin, rice bran, and wheat flour, and examples of adjuvants include adhesives and thickeners such as gelatin, gum arabic, sugars, and gellan gum. These additives can be added to the control agent of the present invention in amounts conventionally known in the field of microbial pesticide formulations. In addition, the above additives may be used alone or in combination of two or more.

[0027] Furthermore, in addition to the filamentous fungus as an active ingredient, the control agent of the present invention may contain, as necessary, other commonly used active ingredients, such as insecticides, nematicides, acaricides, herbicides, fungicides, filamentous fungicides, antiviral agents, fertilizers, soil conditioners (peat, etc.), and it is also possible to apply these ingredients other than the filamentous fungus in admixture, or to apply them alternately or simultaneously without mixing.

[0028] The disease to be controlled is sweet potato base rot, which is caused by the sweet potato base rot fungus (Diaporthe destruens) and occurs mainly in sweet potatoes.

[0029] The target plant of the control agent is not particularly limited as long as it is a plant that can be infected with the sweet potato root rot fungus. Since the sweet potato root rot fungus infects plants of the Convolvulaceae family, particularly sweet potato (Ipomoea batatas), the preferred target plant is a plant of the Convolvulaceae family, and the more preferred target plant is sweet potato.

[0030] The method for controlling sweet potato base rot of the present invention is characterized by comprising a step of applying the control agent for sweet potato base rot of the present invention to a plant or the soil in which the plant is grown.

[0031] The application method of the control agent is not particularly limited, and examples thereof include spraying or coating the target plant, and inoculation into the soil in which the target plant is cultivated. The control method of the present invention is mainly intended to prevent soil infection, and therefore inoculation into the soil in which the target plant is cultivated is preferred among the above application methods. The inoculation of the control agent into the soil may be performed directly into the soil in which the target plant is cultivated, but the control agent may also be inoculated into soil to which a nutrient material such as bran has been added, the filamentous fungus in the soil is allowed to grow, and the soil may then be mixed into the soil in which the target plant is cultivated.

[0032] The application amount of the control agent of the present invention is not particularly limited as long as it is within a range in which sweet potato base rot can be controlled, and may be, for example, 1 to 7 t / 10a, and preferably 3 to 5 t / 10a. EXAMPLES

[0033] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples.

[0034] [Experimental Method] Sweet potato cultivation and investigation into sweet potato root rot A test to test the effectiveness of combining soil disinfection and compost application in controlling sweet potato base rot was conducted in sweet potato fields in Kanoya City, Kagoshima Prefecture in 2021 and 2022. In 2021, four treatment areas were set up: a soil disinfection area where Dazomet was sprayed as a soil disinfectant, a compost area where 2t / 10a of fully matured cow manure compost was applied, a soil disinfection + 2t compost area where 2t / 10a or 7t / 10a of cow manure compost was applied after Dazomet spraying, and a soil disinfection + 7t compost area, with each treatment area replicated three times within the field. Dazomet (30kg / 10a) was sprayed on each soil treatment area on April 19, 2021, and after spraying, the area was watered with a sprinkler and covered with plastic, and the covering plastic was removed 10 days later. Compost was applied on May 10, 2021, with fully matured cow manure compost applied to the compost area and the soil disinfection + 2t and 7t compost areas. Sweet potato (variety: Koganesengan) seedlings were planted on June 18, 2021, with 72 plants planted per treatment area and harvested on November 8, 2021.

[0035] In 2022, five treatment areas were set up: a soil disinfection area sprayed with dazomet, a compost area where 2t / 10a of fully matured cow manure compost was applied, a soil disinfection + 2t compost area where 2t / 10a or 5t / 10a of cow manure compost was applied after spraying with dazomet, a soil disinfection + 5t compost area, and an untreated area. Dazomet was sprayed on April 18, 2022, as in 2021. Fully matured cow manure compost was applied to the compost area and the soil disinfection + 2t and 7t compost areas on May 18, 2022. Sweet potato seedlings (variety: Koganesengan) were planted on June 18, 2022, as in 2021, and harvested on November 7, 2022.

[0036] The survey of the occurrence of sweet potato base rot after planting involved observing the base of each sweet potato plant at 7-day intervals after the first occurrence of sweet potato base rot was confirmed, and counting the number of diseased plants with sweet potato base rot. The above survey was conducted until harvest in 2021, and until October 11, 2022, when more than 100 days had passed since planting and the disease incidence rate in the untreated area exceeded 50% in 2022.

[0037] DNA extraction and fungal community structure analysis (PCR-DGGE, next-generation sequencing) The soil samples were collected from each treatment area at the time of planting in 2021 and 2022 using a five-point method. The collected soil was stored in a refrigerator, sieved through a 2 mm sieve, and extracted in triplicate from 0.4 g of soil using the Fast DNA SPIN Kit for Soil (MP Biomedicals, CA, USA) according to Morimoto and Hoshino (2008). When adding the sodium phosphate buffer included in the kit, 80 ml of 20% (w / v) skim milk solution was added, and then the soil was crushed using a crushing device (Q-BioGene FP series) at a rotation speed of 5.5 for 30 seconds. After crushing, DNA extraction was performed according to the product manual. The extracted DNA was purified using DNA Clean & Concentrator-25 (Zymo Research, CA, USA) and eluted with 50 μl.

[0038] Community structure analysis by PCR-DGGE was performed according to Morimoto and Hoshino (2008). PCR was performed using a primer set (NS1: 5'-GTA GTC ATA TGC TTG TCT C-3' (sequence number 1), GCFung: 5'-CGC CCG CCG CGC CCC GCG CCC GGC CCG CCG CCC CCG CCC CAT TCC CCG TTA CCC GTT G-3' (sequence number 2)) targeting the V1-2 variable region of the fungal 18S rRNA gene (18S rDNA). The final concentrations of the 50 ml reaction solution were 1 × PCR buffer, 0.2 mM dNTPs, 1 mM MgSO4, 0.3 μM each primer, 0.4 μg / μl BSA, and 1.0 U / 50 μl enzyme (KOD-Plus-, TOYOBO), and 1 ml of template DNA was used for the PCR reaction. The reaction conditions were 94°C for 2 minutes, followed by 30 cycles of [94°C for 15 seconds, 50°C for 30 seconds, 68°C for 30 seconds]. The PCR products were purified with a QIAquick PCR Purification Kit (Qiagen), and the DNA concentration was measured using a NanoDrop One spectrophotometer (Thermo Fisher Scientific). 100ng of the product was applied to DGGE. DGGE was performed using the DCode system (Bio-Rad) at 60°C, 50 V, and 20 hours on a 7% acrylamide gel with a denaturing gradient of 20 to 45%. As markers, DGGE Marker IV (Nippon Gene) and the sweet potato root rot fungus (D. destruens MAFF 246953) were applied together with the samples. The sweet potato root rot fungus used as a marker was cultured and collected on sweet potato leaf disc medium (Sekiguchi et al., Patent Application No. 2022-160007), and then extracted and purified in the same manner as the soil DNA above. The purified DNA was used as template DNA, and the PCR product (equivalent to 5 ng of DNA) obtained by the same PCR reaction as above was used as a marker.

[0039] After DGGE electrophoresis, the DGGE gel was stained with SYBR Green I (Takara Bio) for 30 minutes, and the band pattern was photographed using a FUSION Chemiluminescence Imaging System FX7. EDGE (Vilber Bio Imaging). The intensity of each DGGE band was quantified using the image analysis software GelCompar II v.5.1 (Fingerprint and Gel Analysis Software, Applied Maths). In addition, the band patterns and band positions of multiple gels were compared.

[0040] Amplicon analysis using next-generation sequencing targeted the ITS2 region (gITS7-ITS4) in soil only in fiscal year 2021, and analyzed the fungal species composition (Seibitsu Giken Co., Ltd., Kanagawa Prefecture).

[0041] Isolation and selection of filamentous fungi from soil 127 strains of filamentous fungi were isolated from soil from the soil disinfection + 7t compost area collected in 2021 using Rose Bengal agar medium (KH2PO4: 1g, MgSO4·7H2O: 0.5g, peptone: 5g, glucose: 10g, Rose Bengal: 0.033g, agar: 20g per L), Czapek-dox agar medium (sucrose: 30g, NaNO3: 3g, MgSO4·7H2O: 0.5g, Fe2(SO4)3: 0.01g, K2HPO4: 1g, agar: 18g per L) or malt extract agar medium (Difco). Of the 127 strains obtained, DNA was extracted from strains that were estimated to belong to the Chaetomiaceae family based on morphological characteristics using a method previously reported (Saito et al. 2006. J.Gen.PlantPathol. 72:348-550). The base sequences of the amplified products of PCR targeting the ITS region (test primers: ITS1: 5'-TCC GTA GGT GAA CCT GCG G-3' (sequence number 3), ITS4: 5'-TCC TCC GCT TAT TGA TAT GC-3' (sequence number 4)) were analyzed using a DNA sequencer, and a homology search was performed using BLAST. Finally, 12 strains belonging to the Chaetomiaceae family were obtained.

[0042] Evaluation of the effect of isolated strains in inhibiting the growth of sweet potato root rot fungus Among the 12 strains of Chaetomiaceae isolated from soil by the above method, three strains (Humicola sp. 1-2, 3-18, and Acrophialophora sp. 1-4) were used as representative strains and cultured against the pathogenic fungus to examine its effect on the growth of the pathogenic fungus. PDA medium (200g / 1L shredded potato was boiled in broth, 20g glucose, 20g agar) was used, and the control groups were inoculated with each isolate at the edge of the plate, the pathogenic fungus group inoculated with only the isolate at the edge of the plate, and the control group was inoculated with each isolate at the edge of the plate and the pathogenic fungus at the opposite edge. They were cultured at 25°C for 7 days. After the culture, the growth of the fungus in each treatment group was confirmed. In particular, in the control area, the growth range of the sweet potato base rot fungus was compared with that of the sweet potato base rot fungus area, and the effects of the isolated strains on the growth of the sweet potato base rot fungus, such as whether or not they inhibited it, were confirmed.

[0043] Evaluation of the effect of isolated strains in suppressing sweet potato root rot disease Each of the three representative strains (Humicola sp. 1-2, 3-18, and Acrophialophora sp. 1-4) was inoculated into a soil bran medium prepared by mixing soil and bran at a ratio of 4:1 (w / w) and cultured at 25°C for one month to obtain bran cultures. The control was an uncultured soil bran medium. The bran cultures of each strain and the control were mixed with commercially available horticultural soil at 10% (w / w), and a spore suspension of the sweet potato root rot fungus F3-MZ strain was then added at 10% (w / w) per 1 g of soil. 5 The mixture was inoculated and mixed to produce individual spores, and filled into 9 cm pots. Seven one-node seedlings of sweet potato (variety Beniazuma) were inserted into each pot. After cultivating each pot seedling in a greenhouse (27-29°C) for 25 days, the incidence of seedlings infected with sweet potato base rot was investigated to evaluate the disease suppression effect of treatment with each strain. The test was performed in triplicate.

[0044] [Experimental Results] Changes in the incidence of sweet potato root rot over time The change over time in the rate of sweet potato base rot disease during the sweet potato cultivation period is shown in Figure 1. As shown in Figure 1, the incidence of sweet potato base rot disease was lower in the soil disinfection + compost area than in the other areas (compost area, soil disinfection area).

[0045] Analysis of fungal community structure by PCR-DGGE Figure 2 shows the band patterns from the analysis of filamentous fungal community structure by PCR-DGGE. PCR-DGGE is a method in which DNA extracted from the environment (soil, water, plants, etc.) is PCR amplified and electrophoresed on an acrylamide gel, etc., and each DNA is separated based on the difference in base sequence. In theory, one band represents one species, the same band position indicates the same species, differences in band patterns indicate differences in the biota between samples, and the shade of the band indicates differences in DNA amount. As shown in Figure 2, the filamentous fungal community structure differed for each soil management. A dominant and characteristic band (arrow in Figure 2) was confirmed in the soil disinfection + compost area. This suggests the possibility that a characteristic and dominant filamentous fungus may be present in the soil disinfection + compost area.

[0046] Amplicon analysis by next-generation sequencing Amplicon analysis by next-generation sequencing was performed on soil collected in 2021 (Figure 3). In addition, based on the rRNA gene (ITS) sequencing results, a phylogenetic tree of the Chaetomiaceae family filamentous fungi isolated from the soil disinfection + compost area was created (Figure 4). As shown in Figure 3, the genus Ascobolus, the family Chaetomiaceae, and the order Mortierellales were dominant in the soil disinfection + compost area. Three strains of the Chaetomiaceae family (Humicola sp. strains 1-2, 3-18, and Acrophialophora sp. strains 1-4) were isolated from the soil.

[0047] Comparison of band patterns in the soil disinfection + compost plot with bands of isolated strains Figure 5 shows the band patterns and band positions of the isolated strains (strains 1-2, 3-18, and 1-4) from the soil disinfection + 5 t compost plot by PCR-DGGE. The bands indicated by the arrows are characteristic of the soil disinfection + compost plot. As shown in Figure 5, of the three strains isolated from the soil of the soil disinfection + compost plot, the bands of Humicola sp. strains 1-2 and 3-18 were in the same position as the bands characteristic of the soil disinfection + compost plot. From this, it is thought that these two strains are filamentous fungi characteristic of the soil disinfection + compost plot.

[0048] The relationship between the band intensity (theoretical DNA amount) at the Humicola sp. 3-18 strain position and the number of diseased strains (2022) is shown in Figure 6. In addition, the correlation coefficients between the band intensity at the Humicola sp. 1-2 strain and 3-18 strain positions and the number of diseased strains are shown in Table 1. [Table 1]

[0049] As shown in Figure 6 and Table 1, there was a negative correlation between the number of damaged plants in 2021 and the band intensity of Humicola 1-2 strain, and between the number of damaged plants in 2022 and the band intensity of 3-18 strain. This suggests that the presence of a large number of Humicola sp. 1-2 strains or 3-18 strains may suppress the development of sweet potato base rot.

[0050] Effect of isolated strains on sweet potato root rot fungus The isolated strains were cultured in parallel with the sweet potato base rot fungus to examine the effect of the isolated strains in inhibiting the growth of the fungus (Figure 7). In addition, a pot test was conducted using soil artificially contaminated with the sweet potato base rot fungus to evaluate the ability of the isolated strains to inhibit the development of sweet potato base rot disease (Figure 8). As shown in Figure 7, all three isolated strains inhibited the growth of the sweet potato base rot fungus, and as shown in Figure 8, all three isolated strains inhibited the development of sweet potato base rot disease. These results suggest that the isolated strains may be able to inhibit the growth of the sweet potato base rot fungus and the damage caused by it. [Industrial Applicability]

[0051] The present invention can be used in the agricultural field and the like.

Claims

1. A control agent for sweet potato base rot disease, comprising a filamentous fungus as an active ingredient, the filamentous fungus being a filamentous fungus belonging to the genus Humicola or Acrophialophora and having an effect of inhibiting the growth of sweet potato base rot fungus.

2. 2. The agent for controlling sweet potato root rot according to claim 1, characterized in that the filamentous fungus is Humicola sp. 1-2 strain (received number: NITE AP-03947), Humicola sp. 3-18 strain (received number: NITE AP-03949), or Acrophialophora sp. 1-4 strain (received number: NITE AP-03948).

3. A method for controlling sweet potato base rot, comprising the step of applying the control agent for sweet potato base rot according to claim 1 or 2 to a plant or the soil in which the plant is grown.

4. 4. The method for controlling sweet potato root rot according to claim 3, wherein the plant is a plant of the Convolvulaceae family.

5. 4. The method for controlling sweet potato root rot according to claim 3, wherein the plant is sweet potato.

6. Humicola sp. strain 1-2 (received number: NITE AP-03947), Humicola sp. strain 3-18 (received number: NITE AP-03949), or Acrophialophora sp. strain 1-4 (received number: NITE AP-03948).

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