Isolation,Identification,Biological Characterization of Diaporthe longicolla and Screening of Antifungal Drugs

YIN Kun; HUANG Yubo; LIANG Lu; ZHUANG Qiuli; TIAN Kaiyue; XU Bohan; ZHANG Weijie; ZHANG Donghui

doi:10.15933/j.cnki.1004-3268.2026.03.010

Abstract：To clarify the pathogenic characteristics and potential for chemical control of soybean Phomopsis seed decay in Zhoukou City,Henan Province,typical diseased soybean stems were collected for pathogen isolation and identification.The effects of temperature and humidity on mycelial growth and spore germination were determined,and the in vitro fungicidal activity of ten fungicides against the isolate was assessed using the mycelial growth inhibition method,and seed-coating trials were conducted to evaluate the protective efficacy of each treatment in terms of seed germination and suppression of pathogen infection.The results showed that one fungal strain,designated ZK-2024,was obtained.Based on morphological characteristics and phylogenetic analysis of multi-locus DNA sequences(rDNA ITS and TEF1-α),the isolate was conclusively identified as Diaporthe longicolla,the causal agent of soybean Phomopsis seed decay.The optimal temperature for mycelial growth was 30℃,while the optimum for conidial germination was 25℃.High humidity significantly promoted both mycelial growth and conidial germination,with a statistically significant interaction between temperature and humidity.Fungicide screening revealed that 90%carbendazim water-dispersible granules and 430 g/L tebuconazole suspension concentrate exhibited the strongest inhibitory activity against the isolate ZK-2024,with median effective concentrations(EC50)of 0.366 0 mg/L and 0.444 4 mg/L,respectively.In seed-coating trials,seeds treated with pyraclostrobin plus infested soil achieved a germination rate of 93.33%and showed no mycelial coverage,significantly outperforming all other fungicide treatments.This performance was statistically comparable to the untreated control(non-coated seeds+sterile soil).In summary,this study reported the first successful field isolation and molecular identification of Diaporthe longicolla in Zhoukou.It elucidated key biological traits of the pathogen and identifies carbendazim and tebuconazole as highly effective fungicides for in vitro suppression.Moreover,pyraclostrobin demonstrated excellent protective efficacy in seed-coating assays under controlled conditions,highlighting its potential as a candidate seed treatment agent for managing Phomopsis seed decay in soybean.