GRAIN FISSURING AND MILLING YIELDS OF RICE CULTIVARS AS INFLUENCED BYENVIRONMENTAL-CONDITIONS

Milling quality of rice (Oryza sativa L.) is a primary factor determin ing its economic value in the U.S. market. It is largely influenced by genotype and environmental conditions prior to harvest. To determine the effect of environment on milling quality of rice genotypes, seven cultivars were evaluated for gain fissuring and milling yield at decre asing grain moisture during 1991 to 1993. Environmental factors, inclu ding air temperature, relative humidity, and rainfall, were monitored during grain maturity and drying period. Harvesting was carried out at 2- to 4-d intervals as grain moisture decreased from 270 to 130 g kg( -1). High daily minimum relative humidity of 58% and mild temperatures during 1992 caused no significant fissuring until average harvest moi sture decreased to 169 g kg(-1). Warmer and drier weather during 1993 test period, with 43% daily minimum relative humidity caused fissuring to be initiated earlier at a higher grain moisture of 184 g kg(-1). W ith decreasing harvest moistures, head rice yield among all cultivars continued to increase until grain moisture was low enough for fissurin g to occur. The optimum harvest moisture with respect to maximum head rice yield among long-grain cultivars, except for 'Lemont', ranged bet ween 179 and 151 g kg(-1) during 1991-1993. Within this range, the opt imum harvest moisture was highly dependent upon cultivars and environm ental conditions. Cultivars with susceptibility to fissuring require h igher harvest moistures for maximum milling performance. Optimum harve st moisture among years in grams per kilogram ranged between 200 to 17 6 for Lemont and 238 to 179 for medium-grain 'Bengal'. Despite the str ong influence of weather conditions on rice milling yield, certain cul tivars, such as 'Cypress' and 'L-202', have shown significant resistan ce to severe environmental fluctuations. Slow drying and fissuring res istance characteristics of Cypress grains provide flexibility in harve sting, transporting, and processing and preserve milling quality.