Genetics and population improvement of resistance to bacterial soft rot inChinese cabbage

Resistance to bacterial soft rot caused by Erwinia carotovora subsp. caroto vora is a quantitative trait. The narrow-sense heritability was from 42% to 60% in the studied populations. Griffing's diallel analysis and generation mean analysis indicated that additive genetic effects were most significan t, and the resistant sources involved in this study appeared to have differ ent genes or alleles. Recurrent phenotypic selection was used for improving the resistance level by combining different resistance genes from the sele cted genotypes of Chinese cabbage. After 3 cycles of recurrent selection, t he level of resistance increased markedly. When the cycle 3 population was compared with the cycle 0 population, the mean disease severity rating was reduced 38% from 6.3 to 3.9, and the percentage of plant survival increased from 65% to 97% based on the mean of two years experiments using mist-cham ber seedling inoculation methods. The improvement of resistance was also de monstrated in field assays.