Multivalent frequency and seed fertility in raw and evolved tetraploids of Brassica campestris var. toria

Abstract

1. The types of chromosome associations found during diakinesis and metaphase I of meiosis in microsporocytes was studied in plants belonging to the C1, C2, C17, C18 and C19 generations of induced tetraploids of strain 22 ofBrassica campestris var.toria. It was found that there was a considerable decrease in the frequency of multivalents and increase in the frequency of bivalents in tetraploid plants belonging to the later generations in comparison with those belonging to the earlier generations. 2. The mean number of seeds per siliqua in the C1 and C2 tetraploids was 1.5 and 3.0 respectively, while this number increased to 14.5, 14.9 and 16.8 in C17, C18 and C19 generations respectively. The increase in seed fertility had been brought about by adopting the mass pedigree system of selection. 3. From the observation that coincident with an increase in seed fertility there is a tendency towards a decrease in multivalent frequency in autotetraploidToria, it is suggested that the relationship between these two processes may not be wholly casual.