Abstract
Walnut ( Juglans regia L.) is a widely grown nut plant worldwide, including in Guizhou Province, located in southwest China. The high quality and special taste make Guizhou walnuts, particularly those produced in Hezhang County, a “Chinese National Geographical Indication Product” that substantially contributes to the local economy and grower’s income. In July 2022, a serious occurrence of leaf spot disease was observed in a walnut plantation area, Shuitang Town, Hezhang County, Guizhou Province, China (27°07′67″N, 104°64′61″E). The causal agent was identified as Didymella segeticola through morphological characterization and amplification and sequencing of the internal transcribed spacer (ITS) region, beta-tubulin ( TUB ) gene, and glyceraldehyde-3-phosphate dehydrogenase ( G3PD ) gene. Koch’s postulates, including re-isolation and identification, were performed to confirm its pathogenicity on healthy leaves. To our knowledge, this is the first report of D. segeticola causing leaf spot on walnuts worldwide. Further, to determine its biological characteristics, which could be utilized for future disease management, the effects of temperature, light, and carbon and nitrogen resources on mycelial growth, conidia production, and conidia germination and the effects of humidity on conidia germination were studied. The optimum temperature for mycelial growth of representative strain D. segeticola C27 was 20°C. Increasing the light period significantly decreased conidia production and conidia germination. Maltose and beef extract were the best carbon and nitrogen sources, respectively, for the pathogen. Conidia germination was enhanced at 90% humidity. In vitro screening of effective fungicides was conducted. Among the 20 screened fungicides, difenoconazole showed the best inhibition rate, with an EC 50 (concentration for 50% of the maximal effect) of 0.0007 μg/mL. Tetramycin also showed sufficient inhibitory effects against D. segeticola , with an EC 50 value of 0.0009 μg/mL. Our study provides new insights into the causal agent of walnut leaf spot in Guizhou, China, as well as the first pathogen characteristics and promising candidate fungicides for its management.
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Claims 10
Claim · model-written summary
Walnut leaf spot was observed in a plantation in Shuitang Town, Guizhou, in July 2022.
Verbatim
e0“In July 2022, a serious occurrence of leaf spot disease was observed in a walnut plantation area, Shuitang Town, Hezhang County, Guizhou Province, China (27°07′67″N, 104°64′61″E).”
Claim · model-written summary
Didymella segeticola was identified and confirmed as the pathogen causing walnut leaf spot.
- Taxon
- walnutt0
- Organ / stage
- healthy leavese0
- Interactor
- Didymella segeticolaDidymella segeticolae0pathogen
- Outcome
- causal agente0
Verbatim
e0“The causal agent was identified as Didymella segeticola through morphological characterization and amplification and sequencing of the internal transcribed spacer (ITS) region, beta-tubulin ( TUB ) gene, and glyceraldehyde-3-phosphate dehydrogenase ( G3PD ) gene. Koch’s postulates, including re-isolation and identification, were performed to confirm its pathogenicity on healthy leaves.”
t0“walnut leaf spot”
Claim · model-written summary
This is reported as the first worldwide occurrence of D. segeticola causing walnut leaf spot.
- Interactor
- D. segeticolaDidymella segeticolae0pathogen
- Outcome
- first reporte0
JuglansOrganisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“To our knowledge, this is the first report of D. segeticola causing leaf spot on walnuts worldwide.”
Claim · model-written summary
The optimum temperature for growth of D. segeticola C27 mycelia was 20°C.
- Taxon
- walnutt0
- Interactor
- D. segeticola C27Didymella segeticolae0pathogen
- Outcome
- mycelial growthe0
- Value
- 20°Ce0
Verbatim
e0“The optimum temperature for mycelial growth of representative strain D. segeticola C27 was 20°C.”
t0“walnut”
Claim · model-written summary
Longer light periods significantly decreased D. segeticola conidia production and germination.
Verbatim
e0“Increasing the light period significantly decreased conidia production and conidia germination.”
t0“walnut”
Claim · model-written summary
Maltose was the best carbon source for D. segeticola.
Not reportedInteractor
Verbatim
e0“Maltose and beef extract were the best carbon and nitrogen sources, respectively, for the pathogen.”
t0“walnut”
Claim · model-written summary
Beef extract was the best nitrogen source for D. segeticola.
Verbatim
e0“Maltose and beef extract were the best carbon and nitrogen sources, respectively, for the pathogen.”
t0“walnut”
Claim · model-written summary
Humidity of 90% enhanced D. segeticola conidia germination.
Verbatim
e0“Conidia germination was enhanced at 90% humidity.”
t0“walnut”
Claim · model-written summary
Difenoconazole had the strongest in vitro inhibition among 20 fungicides, with EC50 of 0.0007 μg/mL.
Verbatim
e0“Among the 20 screened fungicides, difenoconazole showed the best inhibition rate, with an EC 50 (concentration for 50% of the maximal effect) of 0.0007 μg/mL.”
t0“walnut”
Claim · model-written summary
Tetramycin inhibited D. segeticola in vitro, with EC50 of 0.0009 μg/mL.
- Taxon
- walnutt0
- Treatment
- Tetramycine0
- Interactor
- D. segeticolaDidymella segeticolae0pathogen
- Outcome
- inhibitory effectse0
- Direction
- inhibitorye0
- Value
- 0.0009 μg/mLe0
Not reportedComparator
Verbatim
e0“Tetramycin also showed sufficient inhibitory effects against D. segeticola , with an EC 50 value of 0.0009 μg/mL.”
t0“walnut”