Rice varietal difference in sheath blight development and its association with yield loss at different levels of N fertilization

Abstract

Variety and nitrogen (N) fertilizer input are the two main factors that influence the development of sheath blight (ShB) caused by Rhizoctonia solani in intensive and high-input rice ( Oryza sativa L.) production systems. This study was conducted to determine the varietal difference in ShB development and its association with yield loss across N rates. Two indica inbred and two indica/indica F 1 hybrid varieties were grown under 0 and 90 kg N ha −1 in 2003 wet season (WS) and under 0, 75, 145, and 215 kg N ha −1 in 2004 dry season (DS). Inoculation was done in 3.2 m 2 in each experiment unit to achieve uniform disease development. Disease intensity was quantified by measuring relative lesion height (RLH) and ShB index (ShBI) of inoculated 10 hills at flowering and 14 days after flowering. Plant traits, grain yield, temperature, and relative humidity inside the canopy were also measured. Consistent and significant varietal differences in ShB intensity were observed across N rates in both WS and DS. Among the four varieties, IR72 and IR75217H had higher RLH and ShBI than PSBRc52 and IR68284H at all N rates. Sheath blight index at 14 days after flowering had the closest correlation with yield loss from ShB. Varieties with taller stature, fewer tillers, and lower leaf N concentration such as IR68284H generally had lower RLH and ShBI, and consequently lower yield loss from the disease. Disease intensity and yield loss from ShB increased with increasing N rates, but the magnitude of yield loss varied among varieties. This suggests that fertilizer N should be managed more precisely and differently for varieties with different plant type in order to reduce the disease development and maximize grain yield in the irrigated rice systems.