Autonomous cell death, temperature sensitivity and the genetic control associated with resistance to cucumber mosaic virus (CMV) in diploid potatoes (Solanum spp.)

Cucumber mosaic virus (CMV) is a commonly occurring plant virus that causes severe damage in many crops, including the diploid crop species tomato and pepper (Lycopersicon spp. and Capsicum spp., respectively) of the family Solanaceae, but it is neither common nor economically important in cultivated potatoes (Solanum tuberosum: Solanaceae). Resistance to CMV was examined in two diploid (2n=2x=24). highly heterozygous potato populations (Solanum spp.; Solanaceae) consisting of 76 and 126 progeny. Resistance to long-distance transport of CMV controlled by one locus with a major effect and functional at a low temperature (18 degrees C) but overcome at a high temperature (28 degrees C) was identified in one population. In the other population, resistance was controlled by two loci with major effects. In both populations, additional genes with minor effects were probably also involved. Induced resistance to CMV, associated with autonomously developing cell death lesions (Anl) previously not known in potato, was expressed in one parental line. The mechanisms of resistance to CMV may be associated with an inherent or developmental lack of host factors required for compatible CMV-host interactions in viral long distance transport and/or inability of CMV to efficiently suppress the host gene silencing mechanism in potatoes. Polyploidy (gene dose) and high heterozygosity (multiple homologous genes) of potato cultivars may be significant in conferring the durable resistance to CMV. These data provide explanations why CMV is not common and economically important in cultivated potatoes, even though CMV commonly occurs in other crops, weeds and wild plants in potato production areas.