Discordant Patterns of Allozyme and Morphological Variation in Mexican Cucurbita

Abstract

The systematic relevance of contrasting morphological and molecular data sets was examined by comparative analysis of 76 Cucurbita samples. The samples, mostly domesticated and free-living populations from Mexico, included material that is reasonably well defined with regard to diagnostic morphological characters or geographical position, and a subset of ambiguous, un- known samples. Principal component analysis of seed interval areas provided a gross morphological perspective in that free-living populations are phenetically distinguished from domesticates. The approach fails, however, to discriminate among entities within the two groups, although some trends are evident. The pattern of allozyme variation reflected a pattern of genetic differentiation that both supports and contradicts traditional taxonomic treatments. There is a high level of con- gruence to variation in fruit/seed/peduncle characters that define domesticated taxa. All three (Cucurbita pepo, C. mixta, C. moschata) are well differentiated and internally homogeneous. This level of resolution extends to infraspecific differentiation (subspp. pepo and ovifera) of C. pepo. Molecular data, however, do not reflect the more extreme morphological distinction between free-living and domesticated populations. Genetic identities of free-living populations range from autonomy (C. galeottii), through partial association to a domesticate (C. fraternalC. pepo), to full identity with a domesticate (C. sororia/C. mixta). The presence of a single sample that appears to be the result of crop-weed hybridization, in addition to prior comparative analyses of morphometric and molecular data in Cucurbita, indicates that the pattern of molecular variation provides a relatively accurate perspective on biological relationships. Thus, high levels of crop-weed genetic affinity expressed by comparative analyses of molecular variation in other genera are also present in Cucurbita. In addition, the high level of resolution provided by allozyme variation could provide a foundation for characterization of Cucurbita germplasm accessions.