Grain quality consideration in hybrid rice

Grain size, shape, and weight are determined by maternal genotype. However, the ultimate economic product of hybrid rice is basically a bulk of segragating endosperms of the F2 generation. This makes hybrid rice breeding complicated. In most cases, hybrid rice grain size and shape are intermediate between those of the parents. But some long slender-grained varieties, like IR58025 A, maintain their shape in most F1 combinations. Heterosis in grain weight differs according to cross combination. Endosperm appearance is primarily decided by the amylose content. It varies from waxy to dull to translucent as amylose content increases. If one parent has waxy or dull endosperm and the other has translucent, the grains on the hybrid plant show a segregation of 3 translucent and 1 waxy or dull endosperm. Waxy, dull, and translucent are controlled by different alleles and genes of different loci. Therefore, segregations of 1:2:1 or even 1:1:1:1 may be observed. Parents with the same genotype for endosperm opacity should be selected because consumers do not like the segregation in endosperm appearance. Amylose content is also highly related to cooking and eating quality. Hybrid rice grains have different cooking and eating qualities from the parents because of the segregation in amylose content. Generally, cooking and eating qualities are intermediate. However, in some cases, the influence of the high-amylose parent remains strong. Gelatinization temperature may also be related to cooking quality but does not affect it severely and, therefore, may not influence the acceptability of hybrid rice. Gel consistency (GC) in rice determines softness/hardiness of cooked rice on cooling. In single-grain analysis of F2 grains, segregation could be observed and hard or immediate 6C was found to be dominant over intermediate or low. Aromatic rices are preferred in many parts of the world. The aroma of Basmati rices was observed to be recessive in F1 seed tests. A ratio of 13 nonaromatic: 3 aromatic seeds was observed in the F2 grains from a cross of aromatic and nonaromatic varieties. When cooked, such samples emitted a mild aroma compared with the aromatic variety. If aromatic rice is preferred, it is suggested that both parents of hybrid should be aromatic