Isolation and characterization of potato-tomato somatic hybrids using an amylose-free potato mutant as parental genotype.

Using different genotypes of tomato and diploid potato, possessing alien selectable markers as well as endogenous markers, very high frequencies of protoplast fusion hybrids were obtained. One endogenous genetic marker, the amylose-free (amf) mutant of potato, was helpful not only for the confirmation of fusion products but also for the study of genetic complementation and the segregation of amylose-free starch in microspores. Cytological analysis of the fusion hybrids indicated that except for one which was hexaploid, all of them had a perfectly balanced chromosome number of allotetraploid constitution (2n = 4x = 48). Despite normal chromosome pairing and a diploid behaviour, the microspores in some of the fusion hybrids segregated for the recessive amf-locus. This anomalous segregation of a recessive character in these hybrids was shown not to be due to chromosome elimination or to the absence of the wild-type tomato Amf gene. Although all fusion hybrids were totally sterile, the hexaploid produced stainable pollen and berries with badly developed seeds. Embryo rescue has so far failed to produce backcross progeny.