Interspecific hybridization between Brassica napus L . (2n = 38, alaicici) and B. oleracea var. capitata L . (2x-and 4x-cabbage ; 2n = 2x =18, cc and 2n = 4x = 36, cccc) was carried out for the purpose of transferring clubroot disease resistance from the amphidiploid species to cabbage . Nineteen hybrids with three different chromosome levels (2n = 28, a,cic ; 2n = 37, aiclcc and 2n = 55, aicicccc) were obtained . The F, plants were mostly intermediate between the two parents but as

T w o clubroot-susceptible cabbage cultivars, Red Acre and Golden Acre, were crossed with the resistant line, 8-41. I;, data showed that susceptibility was dominant over resistance and data from I;? and backcross progenies supported a duplicate gene I~ypothcsis. Genes Pb, and Pb, were proposed t o designate susceptible loci. All genotypes of these n v o genes were susceptible cxccpt the homozygous recessive pb,, pb,, pb,, ph, which was resistant.

Keller et al. (1975). Cultures were exposed to three elevated temperature treatment regimes -35'C for I day; 30"C for 3 days; 35"C for 1 day then 30'C for 6 days (Keller and Armstrong 1979) before being incubated at 25'C in the dark. Embryogenesis was expi'essed in terms of auther productivity (the number of embryos produced by responding anthers) and embryo yield per 1000 anthers (Keller et al. 1982).

No abstract

The inheritance of head splitting was probed by studying two moderate inbred lines of early-splitting and late-splitting cabbages, their F1, F, and backcross progenies under field condition. It was concluded that there were at least 3 gene pairs for controlling head splitting. Gene action was mostly additive but partial dominance for early splitting was detected. Narrow sense heritability was estimated as 47 %.