Assessment of genetic and phenotypic variation among intraspecific somatichybrids of potato, Solanum tuberosum L.

Intraspecific somatic hybrids have been produced by protoplast fusion in ei ght combinations involving 10 dihaploids (2n = 2x = 24) in an attempt to pr ovide new material for potato breeding. Cytological analysis revealed exten sive variation in chromosome number, such as aneuploid, aneusomatic and mix oploid hybrids. Most of the hybrids represented the expected chromosome num ber of 48; however, the frequency of aneuploids reached 50% in some combina tions. Some hybrids carried structurally rearranged chromosomes and exhibit ed a high frequency of aberrant anaphases. Isozyme and random amplified pol ymorphic DNA (RAPD) patterns of the hybrids from the same fusion combinatio n were uniform. In the field, somatic hybrids showed wide phenotypic variat ion in 20 morphological characters. There was a significant correlation bet ween certain leaf characters and the ploidy level, which may be used to dis tinguish the tetraploid hybrids from hexaploids and octoploids. Tuber yield and flowering intensity were highest in tetraploid hybrids (2n = 4x = 48). Eighteen of the 73 hybrids reached higher yields than the standard variety 'Adretta'. Floral development and fertility were restored in hybrids deriv ed from fusions between non-flowering or sterile dihaploids.