VIGOROUS GROWTH OF FUSION PRODUCTS ALLOWS HIGHLY EFFICIENT SELECTION OF INTERSPECIFIC POTATO SOMATIC HYBRIDS - MOLECULAR PROOFS

An early identification of fusion products was based on the presumed v igorous growth of hybrid calluses after fusion between Solanum brevide ns and S. tuberosum leaf protoplasts. The S. brevidens protoplasts wer e unable to form multicellular colonies under the applied culture cond itions. Three size groups of calluses were separated and analyzed at t wo different early phases of culture period. ''Squash blot'' hybridiza tion with a S. brevidens specific repetitive DNA probe showed that the group of the largest calluses consisted of putative somatic hybrids w ith a frequency of 80-100% in three independent experiments. Furthermo re, approximately 80-95% of the middle sized calluses and 33-90% of th e smallest ones were shown to be hybrid. The unexpectedly high percent age of fusion products, even in the case of the smallest calluses, may result from the suppression of the development of parental potato col onies in cultures with mixed cell population. Till this time 120 indep endent colonies selected as putative hybrids have been regenerated int o plants. All of them exhibited hybrid phenotype, and their hybrid ori gin was proved by cytological and restriction fragment length polymorp hism analyses.