Haploids of the wild tetraploid potato Solanum acaule ssp. acaule: generation, meiotic behavior, and electrophoretic pattern for the aspartate aminotransferase system

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Abstract
Solanum acaule Bitt. (acl) is a wild tetraploid potato, with bivalent pairing in meiosis. This species has been regarded as a segmental allotetraploid by cytological genome analysis, and one of its subspecies, acaule, as a fixed heterozygote for one of the two loci that codify the dimeric enzyme aspartate aminotransferase (AAT). Since haploid plants of acl could constitute unique tools to prove these previous views, controlled crosses between acl and a haploid inducer were carried out to try to obtain gynogenetic haploids. Two haploid plants (2n = 2x = 24) were identified among the progenies derived from 100 pollinations. Meiotic and electrophoretic analyses were performed in both of these plants. The mean frequency of univalents and bivalents per cell were 10.64 and 6.72, respectively. At the tetrad stage, monads (1.1%), dyads (15.0%), and triads (36.0%) were observed in addition to tetrads. Male fertility, however, was very low. It is conjectured that chromosome distribution in anaphase I was irregular and that dyads originated by a second division restitution mechanism. For the AAT system, two zones of activity, with one gene each, were detected in haploids and control tetraploids. In the slow zone, the same three-banded phenotype was observed in all individuals, although the bands stained with less intensity in the haploids. These observations confirmed that 4x acl is a segmental allotetraploid and that alleles in homoeologous loci, conforming to a fixed heterozygous genotype, do not segregate in meiosis.Key words: haploid, Solanum acaule, fixed heterozygosity, segmental allotetraploid.

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