An Asynaptic Mutation in Soybean (Glycine max (L.) Merrill) Associated with Total Absence of Sister Chromatid Cohesiveness

A mutation affecting microsporogenesis and causing complete male sterility has been detected in line BR97-13777H from Embrapa National Soybean Research Center breeding program. In prophase I, the meiotic behavior of this mutant was similar to the synaptic mutants previously reported in soybeans. Many univalents and few bivalents were found in diakinesis. The main and distinctive characteristic of this mutant was the complete inability of univalents to congregate in the metaphase plate. Scattered in the cytoplasm, univalents underwent premature sister chromatid separation, so that 80 chromatids could be easily counted. Telophases II with a varied number of different-sized nuclei were observed. Pollen sterility was estimated at 93.12%. The inability of univalents to congregate at the equator made us classify it as asynaptic mutant. Its special characteristic related to precocious sister chromatids separation suggests that it is probably defective in proteins that promote sister chromatid cohesion. Segregation ratio for male sterility was 3:1 and shows that mutation, similar to other synaptic mutations previously reported in soybean, is associated with the homozygous condition of a single recessive gene. Allele tests with the st series of synaptic mutants are in progress.