PRODUCTION OF SOMATIC HYBRIDS BETWEEN SOLANUM-TUBEROSUM L. AND LATE BLIGHT-RESISTANT MEXICAN WILD POTATO SPECIES

Interspecific somatic hybrids between dihaploid breeding clones of pot ato, S. tuberosum and two accessions of wild Mexican species S. pinnat isectum and the hybrid line S. pinnatisectum x S. bulbocastanum were r egenerated following electrofusion of mesophyll protoplasts to combine important agricultural traits of S. tuberosum and a high level of lat e blight resistance from selected wild accessions. In two fusion combi nations 239 calli were regenerated; 162 from 195 calli analysed were i dentified as hybrids by means of isozyme analysis of peroxidases and, for some hybrid clones, by RAPD analysis. Depending on the fusion comb ination, 47-89 percent of the somatic hybrids had the expected ploidy level and 7-16 percent were mixoploids. Somatic hybrids were phenotypi cally intermediate as compared to their parents and some of them were able to be backcrossed sexually with potato. Fertility and crossabilit y depended on combination and ploidy level of the somatic hybrids. In tests with detached leaves the wild partner clones had a high late bli ght resistance score of 8,6 and 8,9; the susceptible tuberosum-partner s of 2,8 and 3,5, respectively. Nearly 25 percent of somatic hybrids h ad a resistance level of 6 or higher in the first year of assessment. The average resistance value of most somatic hybrids was lower than th e average parental level. The reasons for variation in resistance valu es are discussed in connection with the practical application of fusio n hybrids.