INHERITANCE OF RESISTANCE TO BLACK SHANK IN NICOTIANA TABACUM L.

Abstract

Resistance to race 0 of black shank (Phytophthora parasitica var. Nicotianae) derived from Nicotians longiflora Cav. and transferred to the burley tobacco breeding line L8 appears to be conditioned by a single dominant gene. However, on the basis of expected ratios for a single dominant gene, a deficiency of resistant progeny was observed in the F2 and backcross generations. Haploid plants extracted from F1 individuals heterozygous for black shank resistance substantiated the deficiency in the resistance class. The haploid segregation with reduced recovery of the resistant genotype rules out preferential pollination as the cause for the altered ratios. The mechanism responsible for impaired function of the gamete carrying the allele for resistance is not known.