CHARACTERIZATION OF SOMATIC HYBRIDS OF POTATO BY USE OF RAPD MARKERS AND ISOZYME ANALYSIS

Electrofusion of mesophyll protoplasts from two male sterile dihaploid Solanum tuberosum genotypes, DHAK-11 and DHAK-33, was performed. Sele ction of putative fusion products was based on vigorous callus growth. Regeneration of rooted putative hybrid plants was scored 14 weeks aft er fusion. Characterization of hybrids was performed by use of morphol ogical assessment, random amplified polymorphic DNA (RAPD), and cytolo gical and isozyme analysis. The rate of regenerated hybrids from callu s was ca 6%. Of the putative hybrids, 45% were confirmed as true hybri ds. Morphological assessment of the putative hybrids revealed that tet raploid and near-tetraploid hybrids were vigorous plants with intermed iate characteristics between the two parental phenotypes in respect to internode length, leaf size and shape, and purple pigmentation on the abaxial side of the leaves. Near-hexaploid hybrids were slender plant s with small leaves and short petioles. Selected RAPD primers showed u nique marker bands for the two parental genotypes. Hybrid plants revea led the unique marker bands from both parents. A total of 53 randomly chosen decamer primers were tested and 26 primers (49%) detected polym orphism between the two dihaploid parentals. Two primers revealed that one parental marker band was missing in two aneuploid hybrids. Howeve r, of 51 putative hybrids, a double test with two independently chosen primers showed unequivocally the hybrid character of 23 plants. The p loidy level of the hybrids was analysed by chromosome numbers in root tip cells and by number of guard cell chloroplasts. A strong correlati on between the chromosome number and the number of chloroplasts was ob tained. The hybrid nature of all RAPD-verified hybrids was confirmed b y isozyme analysis with malate dehydrogenase.