Genetic and cytogenetic analysis of spikelet sterility in Indica x Japonica crosses in Oryza sativa L.

Expression of variable degree of spikelet sterility in indica x japonica inter-subspecific crosses is one of the barriers in the exploitation of higher degree of heterosis manifested in such crosses. Twenty six inter-subspecific crosses derived from four japonicas and seven indicas (including two wide compatible varieties) and 12 F₂ progenies were evaluated for spikelet fertility and sterility expression. Structural heterozygosity in highly sterile cross was not detected at various stages of meiosis. Therefore, chromosomal differentiation has not been attributed to spikelet sterility in the present indica x japonica cross. Based on erratic mode of segregation for fertility and sterility, expression of wide compatible gene has been suggested to be highly cross specific, which may be due to the presence of different set(s) of modifier genes and epistasis. Trigenic complementary ratio with one basic gene for wide compatible trait obtained during the present study in four crosses may partly account for complex genetics of spikelet sterility in inter-subspecific crosses.