Genetic Analysis of Resistance to Meloidogyne chitwoodi Introgressed from Solanum hougasii into Cultivated Potato.

An accession of Solanum hougasii, a wild tuber-bearing potato species native to Mexico, was found to be resistant to races 1 and 2 of Meloidogyne chitwoodi. A resistant selection was selfed and its progeny possessed the same combined resistance uniformly. A selected resistant seedling from the selfed progeny was crossed to cultivated tetraploid potato (S. tuberosum) to form an F hybrid, and was backcrossed to cultivated tetraploid potato to form a BC population in which resistance to the two races segregated. Progeny of the BC were tested in inoculation experiments with four replicates for each progeny genotype for each race of nematode. Resistance was evaluated on the basis of extracted egg counts from the entire root system of pot-grown plants. Considering resistance to each race separately, for race 1, non-host (Rf </= 0.1) status was exhibited by approximately half of the BC. About one-third of the progeny showed non-host status to race 2. Egg production among progeny that showed non-host status for both races was higher with race 2 than with race 1. Analysis of co-segregation established that genetic control for the two races appears to be independently segregating. Although genes for resistance to race 1 derived from S. bulbocastanum and S. fendleri were previously described, this report is the first analysis showing independent genetic control in Solanum spp. for resistance to race 2 of M. chitwoodi only.