Allozyme Variation in the Cucurbita pepo Complex: C. pepo var. Ovifera vs. C. texana

Abstract

Starch gel electrophoresis was employed to examine allozyme variation within and between the domesticated gourds (Cucurbita pepo var. ovifera) and the closely related, wild C. texana. Data on 12 loci representing six enzyme systems (GOT, IDH, MDH, PER, PGI, and PGM) were analyzed for 17 C. texana populations from Texas, six spontaneous populations from beyond Texas, 12 gourd cultivars, and four edible C. pepo cultivars. Populations of C. texana were relatively homogeneous with low levels of polymorphism and mean heterozygosity, while diversity within and among gourds was much higher. Relative genetic affinity among gourds and edible cultivars suggests that circumscription of var. ovifera (s. lat.) based on ornamental fruits does not reflect biological relationships. The pumpkin cultivar and associated gourds formed a distinct group in both cluster and principal component analyses. Cucurbita texana populations were also distinct, having a mean genetic identity value with C. pepo of I = 0.731. Position of the unclassified spontaneous populations was intermediate with respect to the two species. Relatively high frequencies of C. texana alleles in these populations suggest an ancient link between spontaneous populations in Texas and those northeast of Texas. The presence of typical C. pepo alleles in spontaneous populations is probably the result of gene flow between wild and cultivated populations.