Effect of cultivar susceptibility and planting date on narrow brown leaf spot progression in rice

Narrow brown leaf spot (NBLS) of rice (Oryza sativa L.) is caused by Cercospora janseana (Racib). O. Const. (Synonyms: Cercospora oryzae Miyake, Passalora janseana Racib. U.). Experimental studies were conducted in Louisiana to study NBLS progression in resistant to very susceptible cultivars at different planting dates. The very susceptible cultivars CL131 and Cheniere, susceptible CL111, moderately susceptible CL151, and resistant cultivars, Della and Presidio were planted in mid-April and mid-May plantings. Weekly disease assessments began at 45 days after sowing (DAS) and the final disease assessments were done at 109 DAS. Results revealed that AUDPC and final NBLS severity were greater in very susceptible and susceptible cultivars as compared to resistant cultivars. The AUDPC for mid-May plantings were greater for all cultivars. AUDPC increased with increasing susceptibility rating in the mid-April planting. Early onset of NBLS was observed in very susceptible and susceptible cultivars regardless of planting date. Significant interactions were detected between cultivar and planting date for AUDPC and final disease but were non-significant for apparent infection rate. Apparent NBLS infection rate was greatest in the highly susceptible Cheniere and CL131 in the mid-May planting. Apparent infection rates were less in the susceptible and moderately susceptible cultivars and least for the resistant cultivars in both plantings.