MULTIPLE PATERNITY IN COMMON BEAN (PHASEOLUS-VULGARIS L, FABACEAE)

We report on two field experiments that were conducted in 1991 and 199 2 at the South Coast Extension and Research Center, Irvine, CA, to stu dy the incidence of multiple paternity in the common bean (Phaseolus v ulgaris L.). Hypocotyl color and shikimate dehydrogenase (Skdh) isozym es were used as genetic markers. The white-seeded cultivar 'Ferry Mors e 53' (FM 53) was used as the female parent. This cultivar is homozygo us recessive (pp) for hypocotyl color. The pollen source parents were three homozygous dominant (PP) purple-hypocotyled, black-seeded cultiv ars. Three cultivars, 'ICA Pijao,' G4459, and the maternal parent FM 5 3, are of Mesoamerican origin and homozygous for the fast (F) allele a l the Skdh locus. The other cultivar, Black Valentine, is of Andean or igin and is homozygous for the slow (S) allele at the Skdh locus. Over all, 6125 pods were obtained from 57 and 111 plants harvested individu ally in 1991 and 1992 respectively. All progeny, 28 938 seeds, were sc ored for hypocotyl color at the seedling stage. The purple-hypocotyled seedlings were genotyped for the Skdh locus to identify their pollen parents. Multiple paternity was identified in all the pods with hybrid seeds (i.e., those of intercultivar crosses) at 5.8% and 8.1% in 1991 and 1992, respectively. All multiply sired pods produced both nonhybr id and hybrid seeds. As many as three successful fathers per pod were identified, but the number of markers limited measuring higher levels of multiple paternity. Most multiply sired pods (approximate to 70%) w ere filled by nonhybrid seeds plus a single hybrid seed. Ovule positio n effect within multiply sired pods was inferred from the nonrandom di stribution of hybrid seeds within a pod. On average, hybrid seeds occu rred more frequently in ovules in position 7 (most basal) and in posit ion 1 (most stylar) than in ovules in the middle positions of the pod.