Incidence and epidemiology of rice (<i>Oryza sativa</i>) false smut caused by <i>Ustilaginoidea virens</i> in northern India

Abstract

False smut of rice (Oryza sativa L.) caused by Ustilaginoidea virens (Cooke) Takah., 1896 is an important emerging disease of rice. An experiment was conducted during 2018–19 and 2019–20 at Institute of Agricultural Sciences, Banaras Hindu University, Varanasi, Uttar Pradesh to study the U. virens prevalence and morphological variability in northern India with the effect of weather variables on the percentage disease incidence (PDI) of false smut of rice. The study revealed that the false smut incidence was higher in Varanasi district of Uttar Pradesh (53.64%). The lowest percentage (20.68–27.55%) of infected tillers was found in Kangra district of Himachal Pradesh, and Tehri Garhwal district of Uttarakhand. The grain replacement percentage was highest in the Moti cultivar (51.17%), while the highest yield loss percentage was in the Pusa Basmati (57.11 %) variety. The majority of the isolates in our investigation had fluffy, raised, and irregular colony morphology. The correlation between the false smut disease incidence and weather has been evaluated in the Varanasi district, and found that the temperature of 20.36°C with an RH of 85.13% and low rainfall of 8.92 mm was conducive to disease initiation and positively correlated with the PDI. Other epiphytotic factors like sunshine hours, and wind speed were all found to be negatively linked with PDI. In this investigation, for the first time, the viability of spores was also checked. It was found that 2-year-old spores were not viable because they did not retain any Brilliant Cresyl blue colour dye, which stains the stored food material in spores, while 1-month-old spores were found to be 100% viable. All the isolates were further confirmed with the specific ITS marker.