Grain Quality of Panicle Portions in Chalky and Low-Chalky Rice Cultivars.

Carbohydrate stress reduces grain size and head rice percentage and increases the chalkiness in rice. This study aims to compare low and high-quality cultivars for their milled rice and chalky grain percentages, as well as grain size, in the top, middle, and bottom panicle portions. Low-chalky and chalky long-grain rice cultivars were grown at Beaumont in 2019 and 2022. Panicles were harvested, partitioned into top, middle, and bottom portions, and phenotyped for grain size, head rice percentage, and chalkiness. Grain area reduction percentage from top to middle panicle portions is higher in the low-chalky cultivars, Presidio and Kaybonnet. This could relieve the carbohydrate stress that leads to chalkiness. The rice cultivars were also genotyped for Chalk5 and OsPPDK. The low-chalky cultivars had the same allele as the low-chalk Lemont for Chalk5. Presidio had a different allele for OsPPDK compared with the cultivars tested. Consistent with the genotyping result for Chalk5, Presidio and Kaybonnet had lower chalkiness than LaGrue and Leah. There was a positive correlation between the number of primary panicle branches and head rice percentage. The improvement in breeding efficiency for high grain quality requires phenotypic screening for a high number of primary panicle branches and for low chalky and partially chalky grain percentages.