An ms2 male-sterile, female-fertile soybean sharing phenotypic expression with other ms mutants

Genetic and cytological studies of microsporogenesis and microgametogenesis were conducted with a natural male-sterile, female-fertile soybean mutant (BR97-17971) found in an F-4 breeding line of the Brazilian soybean breeding programme. Allele tests with ms Type Collection from USDA/ARS showed that the gene was allelic to ms2 . Conventional analysis of microsporogenesis revealed a differential meiotic behaviour from the normal one reported in ms2 male-sterile plants. Sterile plants have different levels of meiotic abnormalities related to chromosome segregation. Despite segregational abnormalities in the first and second divisions leading to micronuclei formation, the main meiotic cause of pollen sterility was absent or the defective cytokinesis following telophase II. Absent or defective cytokinesis has never been reported in ms2 mutants, but it was reported in the ms1 and ms4 mutants. After telophase II, one to four nucleate microspores underwent degeneration. Cross-sections of sterile plant anthers showed that, at telophase II, the tapetal cells with large vacuoles degenerated. Despite callose deposition around meiocytes, sterile plants did not form tetrads. They degenerated and collapsed after callose dissolution, forming an amorphous mass. Anthers from male-sterile plants were shrivelled.