Stem and Root Resistance to Tobacco Black Shank.

Stem lesion development in the absence of root decay in tobacco black shank caused by Phytophthora parasitica var. nicotianae has become common in the Coastal Plain tobacco growing area in Georgia. All aboveground symptoms of wilting, blackening of lower stem, and destruction of the pith can occur on tobacco without or with minor root decay. This type of black shank disease development occurred in 14 of 15 locations evaluated and accounted for about 30% of diseased plants. Cultivars with Florida 301-derived resistance had very low stem resistance to race 0 of the pathogen. However, root inoculations of these cultivars resulted in disease reactions typical of those expected in vivo in Georgia. Cultivars Coker 371-Gold and NC 71 and the breeding line 1071 demonstrated high resistance to inoculation with race 0 of P. parasitica var. nicotianae in both the stem and the roots, but they were susceptible when stem-inoculated with race 1 of the pathogen. Severity of root decay was isolate dependent.