INHERITANCE OF RESISTANCE TO RACE-0 OF PHYTOPHTHORA-PARASITICA VAR. NICOTIANAE FROM THE FLUE-CURED TOBACCO CULTIVAR COKER 371-GOLD

Black shank, caused by Phytophthora parasitica var. nicotianae, is a w idespread and severe disease of tobacco throughout the southeastern Un ited States. Partial resistance derived from the cigar tobacco cultiva r Florida 301 has been the primary means of reducing losses to the dis ease for many years. The recently released tobacco cultivar, Coker 371 -Gold (C 371-G), was found to provide an additional source of resistan ce to P. parasitica var. nicotianae. Although the resistance in C 371- G is being used widely by breeders, the origin and inheritance of this resistance mechanism was unknown. Two populations of doubled haploid lines derived from C 371-G were used to determine that C 371-G possess es a single, dominant gene designated Ph, which confers a very high le vel of resistance to race 0 of P. parasitica var. nicotianae. A greenh ouse inoculation procedure was developed that provided an efficient me ans of screening for the presence of this resistance gene prior to sel ection in the field, and confirmed that Ph provides complete resistanc e to race 0 but no resistance to race 1 of P. parasitica var. nicotian ae. Because Florida 301 resistance is effective against both races of the pathogen that occur in the major tobacco growing areas of the Unit ed States, combination of these two sources of resistance should provi de enhanced protection of new tobacco cultivars to P. parasitica var. nicotianae.