CYTOGENETIC STUDIES ON BRASSICA-CAMPESTRIS PRIMARY TRISOMICS

Meiosis, trisomic transmission, and inheritance of erucic acid content were studied in a nucleolar trisomic (No. 2891) and a non-nucleolar t risomic (No. 2881) of Brassica campestris. The two trisomics originate d from a B. campestris-alboglabra monosomic addition line whose alien chromosome carried the gene for erucic acid content. Meiotic analyses revealed that the trivalent frequencies in the pollen mother cells (PM Cs) at diakinesis/metaphase I were 33.3 % and 20 % in No. 2891 and No. 288 1, respectively. The transmission rates of the extra chromosome t hrough the ovule in No. 2891 and No. 2881 were about 30.6 % and 32.4 % , respectively. The inheritance of erucic acid content was investigate d in the two crosses, No. 2891 x B. campestris landrace ''Wu Chang Bei You Cai'' and No. 2881 x B. campestris landrace ''Xi Shui You Cai Bei ''. The segregation of erucic acid content in the F2 progenies of the selfed trisomic F1 plants from the two crosses showed a disomic inheri tance pattern, thus indicating that the trisomy in No. 2891 and No. 28 81 did not involve the chromosome carrying the erucic acid gene. The g enetic divergence of homoeologous chromosomes between B. campestris an d B. alboglabra is discussed.