Heterothallism and Pathogenic Specialization inUncinula necator

A collection of 35 isolates of Uncinula necator was established. Each isolate originated from a single chain of conidia. The collection included isolates from 10 species of Vitis and isolates from Vitis interspecific hybrids. Isolates were paired in all possible combinations on tissue culture plants of the Vitis interspecific hybrid cultivar Chancellor and were incubated for 60 days at 20 C. Initially, U. necator appeared to be composed of two mating types that comprised a bipolar heterothallic system. Ascocarps were produced abundantly within 14 days in approximately one-half of the pairings (...)