Sheath rot in rice: Morphological, molecular characterization - Sarocladium oryzae (Sawada) and genotypic response

Rice is one of the vital staple food crops worldwide and it is affected by many fungal diseases. Among these, sheath rot disease caused by Sarocladium oryzae is emerging as a severe threat, leading to yield losses ranging from 10–85 %. Sheath rot disease of rice affects all the stages of the crop, but the disease is utmost critical in booting stage. It damages the boot leaf sheath that protects developing panicles, which delays or prevents panicle emergence. Grain production and quality are severely reduced. Discoloured, chaffy and sterile grains produced in the infected panicles. Survey was conducted in Thoothukudi district of Tamil Nadu during the period 2022 – 23. Ten isolates of S. oryzae were isolated using the infected samples collected. The isolate (So 5) obtained from Peikulam village of Sathankulam block (Lat. 8.51o N, Long. 77.85o E) was found to be the most virulent isolate. Morphological studies showed that the isolate So 5 recorded the maximum mycelial growth of 7.70 cm diameter after 20 days of inoculation in PDA medium. The pathogen produced white cottony aerial mycelial growth and cylindrical shape of conidia. The pathogen was molecularly confirmed as S. oryzae by comparing the similarities with the NCBI database (Accession No. OR298274). Screening of genotypes is essential to identify the resistant sources. One hundred rice genotypes were screened under natural and artificial conditions. The genotypes viz., Aryan 1102, Aryan 1203, Dhalaheera, Kattanoor, Navara black, Purpleputtu, Salem senna, Swarna and Varaprabha showed resistance in both conditions.