Unveiling of Refined Isolation, Growth Conditions and Inoculation Assay for Ephelis japonica Inciting Udbatta Disease in Rice

Abstract

Udbatta incited by Ephelis oryzae Syd is a minor significant seed borne, sporadic and systemic disease in rice. Isolation of this pathogen is challenging due to its weak growth and the prevalence of other rapidly proliferating fungi like Curvularia, Aspergillus etc. In this study, a streamlined spore-drop technique was standardized for rapid isolation of Ephelis japonica from infected rice panicles. This method achieved pure cultures with minimal contamination (7.50%) in the shortest time (25 days) with a growth rate of 1.7 mm/day, compared to the spore dilution method (32.50%) in 65 days with 0.83 mm/day and standard tissue isolation method (50.25%) in 70 days with 0.45 mm/day. Optimal conditions for fungal growth in axenic culture were also standardized. E. japonica recorded the fastest growth on potato dextrose agar (PDA) medium at an incubation temperature of 27°C under dark conditions, which were more conducive to growth than light incubation. The fungus recorded a maximum radial growth of 35.60 mm in 25 days with growth rate of 1.42 mm/day on PDA supplemented with 4% dextrose as compared to 30.27 mm and 1.21 mm/day in 2% dextrose. Furthermore, an inoculation method was standardized for inducing Udbatta disease by treating rice seeds with a fungal suspension for 1–2 hours, followed by overnight drying and sowing resulted in disease incidence of 6.25 % and no disease was observed in stem inoculation and rice head inoculation. Plants grown from seeds treated with fungal suspension exhibited characteristic symptoms like black, erect, cylindrical spike-like structured panicles with grains matted with fungal mat. This refined isolation technique, with optimized culture conditions, provides a robust framework for advancing research on E. japonica and Udbatta disease in India.