Rice grain discoloration effect on physical properties and head rice yield in three rice cultivars

Rice grain discoloration is a complex disease which develops by a range of micro-organisms. Effects of fungal agents such as Alternaria sp., Curvularia sp., Cladosporium spp., Bipolaris spp. on the physical properties and head rice yield (HRY) were examined during the cropping season 2013-2014. The experiment was conducted in factorial design with two factors; three rice cultivars of Hashemi, Gohar and Khazar, and two grain disease severity levels (high and low) based on a randomised complete design with four replications. In order to attain high disease severity level, water was sprayed at the heading stage of the crop. The grains axial dimensions, geometric and arithmetic mean diameters, sphericity, surface area, volume, slenderness ratio, 1000-grain weight, as well as HRY were measured at a moisture content of 9% (wet basis). The average of length, width, thickness, surface area, volume and 1000-grain weight at the high disease severity were found to be 7.64, 2.04, 1.67 mm, 20.375 mm(2), 13.796 mm(3) and 24.6 g, respectively, and at the low disease severity 7.78, 2.04, 1.69 mm, 20.944 mm(2), 14.341 mm(3) and 26.32 g, respectively. There were significant differences between the tested cultivars for all physical properties and HRY. The average HRY with high disease severity was 54.18% and 58.18% with low disease severity.