Studies on Identification of Resistance to Black Shank Disease of Tobacco Germplasm Resources in Seedling Stage

Resistance of 50 tobacco varieties to black shank in seedling stage was evaluated in this study.Among these varieties,13 were resistant,25 were moderate resistant,10 were medium susceptible and 10 were susceptible.There were 24 varieties(48% of the total screened varieties) with less than 10 differences in value of three times resistance index.Among them,13 were resistant,8 were moderate resistant,2 were moderately susceptible,and 1 was susceptible.There were 9 varieties with over 10 differences in value of three times resistance index which accounted for 18% of the total screened varieties.All of them had moderate resistance(6 varieties) or moderate susceptible(3 varieties) to black shank.These results showed that the resistant or susceptible varieties were sensitive and could be identified within 5d of inoculation,and the disease occurred on seedlings of moderate resistance and moderate sensitive varieties could progress very quickly after 5d to 10d of inoculation.