Microscopic Examination of Race-specific Resistance to Pecan Scab From the 2001 Southeastern Pecan Growers Association Meeting

Many important high quality cultivars are becoming increasingly susceptible to the scab pathogen. Two such cultivars, 'Stuart' and 'Desirable', comprise over one half of Georgia's total pecan acreage. This increasing susceptibility has often been attributed to the increased prevalence of once rare races of scab that are able to infect these cultivars. Demaree and Cole (1929) were the first to demonstrate pathogenic races of scab. They demonstrated that when inoculum was taken from one cultivar and used to inoculate young leaves of the same cultivar and a different cultivar that a heavy infection was found on the original host and a light or no infection on the other. Converse (1960) found evidence for the presence of at least 4 races in Oklahoma using single-spore isolates and greenhouse inoculations.