Effect of rice blast and sheath blight on physical properties of selected rice cultivars

Observations in 1997 indicated a significant reduction in kernel bulk densi ty and head rice yield of rice cultivar LaGrue due to blast (Pyricularia gr isea). A more detailed study on rice cultivar M202 in 1998 confirmed such o bservations but it also showed negative effects of blast on other physical properties of rice. Rough rice from blast-infected panicles was drier by 7- 10 percentage points and 10% thinner than rough rice from blast-free panicl es. Blast also caused incidences of chalky, unfilled, and fissured kernels that were 21, 30, and 7 percentage points higher, respectively. The effects of sheath blight (Rhizoctonia solani) on kernel thickness and moisture con tent of rice cultivars Cocodrie, Cypress, Drew, and LaGrue were similar to the effect of blast on M202. Sheath blight generally reduced kernel bulk de nsity but did not significantly affect head rice yield of the cultivars in 1997 and 1998 (except in one sample of Drew). There was a general trend tow ard higher incidences of unfilled, chalky, and fissured kernels in sheath-b light-infected samples. The data indicated that blast could be a significan t preharvest factor in causing high variability in physical properties as w ell as in reducing the milling quality of rice. Sheath blight is also a pot entially significant preharvest factor in affecting these properties in sit uations where sheath blight pressure is high.