Heritability of resistance to foliar late blight in a diploid hybrid potato population of Solanum phureja x Solanum stenotomum

The emergence of new races of Phytophthora infestans has necessitated the search for additional sources of potato germplasm with resistance to late blight. This study examined 281 clones, derived from 72 families of a diploid random-mated hybrid population of Solanum phureja x Solanum stenotomum. The clones were evaluated in a replicated field trial for 2 years with the control cultivar 'Atlantic' in Pennsylvania, USA. The P. infestans US-8 A2 mating type culture was used to inoculate spreader rows of susceptible S. tuberosum cv. 'Russet Burbank'. Percent defoliation caused by the late blight fungus was estimated visually in each plot three times near the end of the growing season. Area under the disease progress curve (AUDPC) was estimated and showed that late blight was more severe in 1997 than in 1996. Genetic differences among clones and significant, but small, clone-environment interaction were detected for AUDPC. Broad-sense and narrow-sense heritability estimates, over years, were 0.79 ± 0.05 (P = 0.05) and 0.78 ± 0.29, respectively. Seventy-five percent of the diploid clones had a significantly lower mean AUDPC than Atlantic. These results support the idea that this diploid population is worthy of use in breeding for late blight resistance in tetraploid potato cultivars.