Genetic recombination in a diploid synaptic mutant and a Solanum tuberosum × S. chacoense diploid hybrid

Abstract

A diploid synaptic mutant, M6 with the genotype sy3/sy3,ps/ps, was identified as heterozygous for four enzyme-coding loci, and for the tuber flesh colour locus (Y). Through 4x-2x crosses, half-tetrad analysis was applied to determine the ability of the M6 clone to transmit its heterozygosity to tetraploid offspring. On the average, an 89-03 per cent reduction in recombination was found within the chromosome segments sampled, resulting in 98 per cent transmission of heterozygosity. Cytological observations of microsporogenesis revealed frequent pachytene associations and a high proportion of univalents at diakinesis. These findings show that chromosome pairing in M6 is mostly desynaptic. Diploid and 4x-2x testcrosses were made to study recombination in a 2 ai-pollen producing diploid hybrid T704 (ps/ps); S. tuberosum L. xS. chacoense Bitt. For the loci compared, recombination was reduced 34·56 per cent on the average. This hybrid transmitted on the average 89·2 per cent of its heterozygosity which was significantly higher than the value previously observed in non-hybrid individuals. Unlike M6, T704 produced both viable n and 2n pollen. In addition, cytological examination of PMCs indicate normal bivalent associations. It is suggested that genomic differentiation between S. tuberosum and S. chacoense could account for the reduced recombination levels.