Evaluation of Wild Potato Species for Resistance to Late Blight

Abstract

Late blight, caused by Phytophthora infestans, is a major disease of potato. This study assessed 51 tuber-bearing Solanum species for resistance to late blight in a series of greenhouse experiments. A total of 80 out of 133 acces-sions presented quantitative resistance patterns. Eighteen species from Central and South America presented both qualitative and quantitative resis-tance responses, whereas accessions of four Mexican and two South American species presented only qualitative resistance to the isolate used. Between one and 90 genotypes in 39 different species have been selected for verification of resistance under field conditions following evaluation of true-seed–grown and tuber-grown plants. The aim of this broad survey is to identify and secure sources of complementary components of stable resis-tance to late blight for use in breeding programs. The results confirm the value of conserving rare populations of potato genetic resources and provide the first evidence of resistance to late blight in at least seven species endemic to the South American center of origin of potatoes. Implications of the vari-ability detected among species and accessions are discussed in terms of conservation and breeding objectives. During the past three years, CIP has intensified efforts to evaluate the in-trust germplasm collection of potato for impor-tant traits such as resistance to late blight, bacterial wilt, and important viruses. Late blight (LB), caused by Phytophthora infestans, is the most devastating disease of potato worldwide. Wild tuber-bearing Solanum species from Mexico, especially S. demissum, have previously been used in the majority of breeding programs as sources of resistance to late blight. Ross (1986) estimated that S. demissum germplasm has been incorporated into more than 50 % of the world’s potato varieties. However, since it has become evident that new races of P. infestans can