Pollen irradiation in tomato: minor effects on enzymic gene transfer

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Abstract
Pollen irradiation was tested as a possible means of expediting gene transfer in tomato breeding. The experiment was also designed to examine the possibility that irradiation effects which have been previously reported for Nicotiana were due to gametophytic selection against mutated male and female gametes. Pollen from the wild tomato species Solanum pennellii was irradiated with γ-rays and used in crosses with Lycopersicon esculentum. Pollen from five M1 hybrid plants and five control hybrids was used in backcrosses to an esculentum variety and the same plant also functioned as female parents in crosses with normal S. pennellii pollen. Seven enzymic gene markers which differ between the species were assayed in the backcross populations in the two directions. Allele frequencies did not differ between the populations that were derived from the M1 or F1 hybrids except for one marker, Pgm-2. Elimination of male and female gametes containing the irradiated parent allele of Pgm-2 was observed in a single population. This gene is located on chromosome 4 close to the gamete eliminator (Ge) locus. A review of some of the main characteristics of Ge raises the possibility of the existence of a controlling element activity.