Analysis of genes controlling f(1) sterility in rice by the use of isogenic lines.

In order to look into the genetic basis of intervarietal F(1) sterility in rice (Oryza sativa L.), a series of backcrosses (up to B(13)) was carried out using Taichung 65 (Japonica type) as the recurrent parent and several Indica varieties as donor parents. A number of "isogenic F(1)-sterile lines" were isolated by test-crossing fertile F(2) plants obtained from the selfing of partly pollensterile backcross segregants. Crossing experiments with the isogenic lines confirmed the author's previous hypothesis that there are sets of duplicate gametic lethals (s genes) and that gametes carrying a double recessive combination (s(1)s(2)) of these deteriorate during development, though in the present hypothesis the genes are considered to affect the development of microspores only. Assuming that Taichung 65 has the genotype s(1)/s(1) + (2)/+(2) and a donor parent (like an isogenic F(1)-sterile line derived from it) has +(1)/+(1)s(2)/s(2), pollen grains with +(1)s(2) have shown a higher fertilizing capacity in the genetic background of Taichung 65 than those with s(1) +(2), while those with +(1) +(2) have a lower fertilizing capacity. This certational advantage of alien genes was considered to be an internal mechanism that helped the development of F(1) sterility relationships among rice varieties. The isogenic F(1)-sterile lines derived from different donor parents each had a set of s genes at different loci. Linkage relations were detected between the s loci and three gene markers.