Screening, Identification, Improvement, and Genetics of Resistance to Bacteria Soft Rot (Erwinia carotovora) Disease of Brassica Vegetables

Abstract

More than 700 accessions of Brassica vegetables were screened for resistance to bacterial (Erwinia) soft rot disease using a newly developed testing procedure. Dipping a needle in 2-day-old bacterial culture and pricking petioles of plants gave the most-consistent and distinguishable results in both seedling greenhouse and mature plant field tests. High humidity (100%) and warm temperature (higher than 23°C) are the two essential conditions for this test to be successful. So far, immune material has not been found. In B. rapa, less than 7% of the accessions showed some degree of resistance. High correlation was found between seedling greenhouse tests and mature plant field tests. Genetic study showed that soft rot resistance in B. rapa is a quantitative trait. The broad-sense heritability was 60% and narrow-sense heritability was 42% in the tested population. Following three cycles of recurrent selection, the resistance level in cycle three population was improved by 2.4 disease score points (1–9 scale) compared to the original parental population and the disease score of the best line in cycle 3 was 2.7 compared to a susceptible check on which the disease score was 8 under greenhouse conditions. Under field conditions, the best cycle three line scored 2.0 in comparison to the susceptible check, which scored 7. From our study, the recurrent selection works well for improving the resistance level to the soft rot disease in B. rapa.