STUDY ON THE VIRULENCE DISSOCIATION OF SWEET POTATO BACTERIAL WILT IN FUJIAN AND ITS APPLICATION

During 1984-86, 113 strains of sweet potato bacterial wilt (Pseudomo-nas solanacearum) , which were collected in 26 counties of Fujian, were tested for their pathogenicity. According to the intensity of. virulence, they were divided into five groups (I-V). With the order of I-V, the intensity of virulence gradually increased. The second group (II), which made up 44.3% of the total strains tested,was most widely distributed. The fifth group (V) was the strongest strains in virulence, made up 9.7% of the total strains tested.All the strains tested showed quantitative difference in the intensity of virulence. No distinct specificity was found. The distribution of the strains was that the stronger strains tended to be in old disease areas where the resistant variety was cultivated, and the weaker strains in new disease areas where the susceptible variety was cultivated.The varieties of sweet potato in Fujian and elsewhere in south China for district and probationary comparisons were tested for resistance by using 3 major strains of Groups II-IV. Two highly resistant varieties were obtained. By using the 113 strains of Groups I-V to test the resistance, the results were obtained that Xin Zhong Hua the main variety in Fujian was a highly susceptible variety. 330 and Min Kang 329 were resistant varieties. Min Kang 329 owned the features of strong resistance to disease,high yield,early maturity and good quality. From 1984 to 1986, Ming Kang 329 covered more than 800 thousand mu, over 90% of the area for sweet potato cultivation. 330 was better than Min Kang 329 in the resistance to disease,adaptability,germination and storage. The cultivated area for 330 increased to more than 50 thousand mu this year.