Genealogy and gene flow among annual domesticated species of Cucurbita

Abstract

Over the years, workers have gathered data from various sources in the attempt to understand the evolutionary histories and relationships of the domesticated members of Cucurbita. We used allozyme data to address questions of genealogy, interspecific gene flow, and allelic diversity for 23 commercial cultivars and 17 indigenous landraces of C. maxima, C. mixta, C. moschata, and C. pepo. Allelic diversity was greatest in C. pepo (especially ssp. ovifera) and C. moschata, reflecting complex histories for these taxa. Cucurbita maxima and C. mixta were relatively homogeneous despite morphological heterogeneity. Infraspecific classifications based on morphological characters were not supported by the allozyme data for C. maxima, C. mixta, and C. moschata. The allozymes supported morphological evidence of introgression from C. mixta in Oriental cultivars and southwestern United States and northwestern Mexico landraces of C. moschata. Phylogenetic analyses indicated that C. moschata and C. mixta are probably sister species and that C. pepo shares a common ancestor with these species that is not shared with C. maxima.

Morphological and allozyme variation in a collection of Cucumeropsis mannii Naudin (Cucurbitaceae) from Côte d'Ivoire

“…argyrosperma and C. moschata Duch. Estimates obtained by Decker-Walters et al (1990) in Cucurbita pepo L. were 19%, 2.24 and 0.068, respectively for P, A, and H e . Akimoto et al (1999) estimated the mean value of H e to 0.225 for an androdioecious cucurbit (Schizopepon bryoniaefolius Maxim.).…”

Cucurbits (Cucurbitaceae; Cucumis spp., Cucurbita spp., Citrullus spp.)

“…More extensive surveys of isozyme variation among Cucurbita species (Puchalski and Robinson 1990) and, more specifically, in wild, weedy, domesticated Mexican Cucurbita presented more complex views of genetic differentiation and gene flow among taxa (Wilson 1989). Isozyme analyses by Decker-Walters et al (1990) did not support traditional infraspecific classifications for C. maxima, C. argyosperma, or C. moschata. The most thorough isozyme analyses, however, have been devoted to C. pepo in its wild, weedy, and domesticated forms (Ignart and Weeden 1984;Decker and Wilson 1987;Decker-Walters et al 1993) and have been instrumental in clarifying patterns of variation and domestication within this species.…”

“…Spontaneous crosses between the cultivated Cucurbita species are uncommon, but hybrids interspecific natural can occasionally be detected in landraces mostly from Mexico (Decker-Walters et al 1990;Merrick 1990Merrick , 1991. In addition, Kfistkova (1991) reported a spontaneous hybrid of C. maxima by C. pepo under central European field conditions.…”

“…Studies of isozyme variation in Cucurbita by Andres (1990), Decker (1988), Decker-Walters et al (1990, and Merrick (1991) revealed moderate amounts of genetic differentiation within C. pepo and C. moschata while, in marked contrast, little genetic differentiation has occurred within C. argyrosperma and C. ficifolia (and perhaps in C. maxima as well, although the survey of the latter species has been less comprehensive than those of the others; Merrick 1995). Similar analyses to survey the variation present in DNA markers have been conducted, but on a somewhat more limited scale, with the most comprehensive work accomplished within C. pepo Decker-Walters et al 2002b;Ferrio!, Pico, and Nuez 2003a;.…”

Comparative Ontogeny of a Wild Cucurbit and Its Derived Cultivar

“…The family is highly variable morphologically and it includes several pairs of wild and cultivated taxa in which the wild taxa are considered progenitors ofthe cultivars. There are at least three such pairs within the genus Cucurbita (the pumpkins and squashes) (Decker-Walters et al, 1990), one pair being the two subspecies of Cucurbita argyrosperma (Merrick and Bates, 1989;Merrick, 1990). Subspecies argyrosperma var.…”