Isolation, characterization and biomanagement of Villosiclava virens, a unique flower-infecting fungus causing rice false smut disease in India.

Abstract

Villosiclava virens (Ustilaginoidea virens) an ascomycete fungal pathogen that causing false smut disease in rice and has become a serious production constraint in various rice-growing regions of India due to its detrimental effects on grain yield and quality. A roving survey was conducted during Rabi 2020 in Tamil Nadu, Uttar Pradesh and Karnataka state and the false smut disease severity was ranged between 9.2‒ 27.9 %. During survey heavy incidence was noticed in a variety BPT 5204. Totally 97 fungi were isolated and characterized from rice smut balls. Among them nine Uttar Pradesh, thirteen Tamil Nadu and two Karnataka isolates were identified as V. virens and remaining were as associated seed pathogens viz., Microdochium sp., Fusarium sp., Curvularia sp., Nigrospora sp., Aspergillus sp., Penicillium sp., Trichoderma sp., Epicocum sp. and Trichothecium sp. based on cultural and spore morphology. The identity of the pathogen was further confirmed through PCR analysis using ITS 1 and 4 primers and sequencing (NCBI) and the identified cultures were deposited at internationally recognised culture collection NAIMCC, Mau. Different isolates of V. virens showed variation in the cultural morphology, size, colour and shape of the conidia. A total of 16 Trichoderma, 10 Bacillus, 8 Pseudomonas strains were screened against V. virens among them, T. longibrachiatum, T. afroharzianum, T. harzianum, Bacillus subtillis, P. fluorescens and P. aeruginosa were showed highest percent inhibition. Further these strains were evaluated under pot condition along with combination of T. harzianum + B. subtillis + P. fluorescens (Biogrow) in three set of experiments through seed priming, soil application and foliar application. Rather than soil application seed priming and foliar application find more effective to control disease. The survivability of V. virens in the soil was also studied by applying giant cultures produced on rice seeds and grains. The complete experiments were conducted in ICAR-NBAIM, Mau with a time period of study.