Differential zygotic abortion in an interspecific Lycopersicon cross

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Abstract
Monogenic segregations of seven isozyme markers were analyzed in F2 and reciprocal backcross progenies of an interspecific hybrid between Lycopersicon esculentum and L. pennellii (LA 716). In the F2 population, four markers, which map to three different chromosomes, deviated significantly from the expected Mendelian ratios and in all cases an excess of the L. pennellii alleles was observed. In the backcrosses all the genes segregated normally. These results and the lack of effect of different gametophytic selection conditions on the deviations indicated that the elimination of L. esculentum alleles in the F2 did not occur at prezygotic stages. Three of the isozymes were assayed in mature F2 seed and revealed similar deviations to those observed in F2 plants. These findings, as well as the lower numbers of seed per fruit observed in the F2 than in the backcross (where the hybrid functioned as female parent), indicate that differential zygotic abortion is the main cause of the unequal segregations. In addition, analysis of two linkage groups in the reciprocal backcrosses revealed higher recombination frequencies on the female side. Key words: Lycopersicon esculentum, L. pennellii, unequal segregations, differential zygotic abortion, recombination.