ARS | Publication request: GENETIC RELATIONSHIPS WITHIN THE CUCURBITACEAE AS ASSESSED BY CCSSR MARKER AND SEQUENCE ANALYSIS

Submitted to: Canadian Journal of Botany
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: April 17, 2003
Publication Date: August 10, 2003
Citation: Chung, S., Decker-Walters, D.S., Staub, J.E. 2003. Genetic relationships within the cucurbitaceae as assessed by ccssr marker and sequence analysis. Canadian Journal of Botany.

Interpretive Summary: Taxonomy is the science of plant classification and genetic relationship analysis (i.e., determining similarities of between individuals). It is important to determine the relationships between economically important species because new biotechnologies can be used to allow for combining genes from species that normally do not intermate (are not interfertile). These interspecies matings can allow for the transfer of disease resistance genes from a disease resistant species to a susceptible species. The Cucurbitaceae is a family composed of many cross incompatible species (can not intermate) but which have may genes (entities that control trait expressioin) for disease resistance. The Cucurbitaceae is broken down into tribes based on their cross compatibility (ability to intermate). Molecular markers, a relatively new biotechnology, were used to investigate the genetic relationships among representative individuals of these tribes. Data indicate that genetic relationships exist between and among individual representatives of these tribes, and that some of these relationships are closer than others. This analysis suggests that those with relatively close genetic relationships (i.e., most similar) could be used for transferring genes between tribes, and thus increase the opportunity and possibility for introducing disease resistance genes into economically important species (e.g., genes for resistance to green mottle mosaic virus into cucumber which is susceptible to this disease) that are currently susceptible to disease (susceptibility lowers yield). This is important to plant breeders because it will increase their ability to produce highly disease resistant varieties. Disease resistant varieties will increase the competitiveness of the U.S. grower and lower the cost of the final product to the consumer.

Technical Abstract: Consensus chloroplast simple sequence repeats primer pairs (ccSSR) obtained from tobacco chloroplast DNA were used to investigate genetic relationships in Benincaseae (19 accessions) and other tribes (8 accessions) of the family Cucurbitaceae. Variation in the length and putative sequence substitution events of PCR products were analyzed. Sequencing of four fragments (ccSSR-1, -7, -8, and -19) revealed that convergence in fragment length occurs in more distant species comparisons. In ccSSR-1 and ccSSR-8, the same fragment lengths occurred as the result of different insertion/deletion events. Nevertheless, the examination of a large number of ccSSR fragments suggested that this apparent homoplasy could be overshadowed by taxonomic interrelationships among taxa. This hypothesis is supported by the relative degree of positive congruence of taxa groupings after cluster and PCA analyses based on bp-length and sequence substitution data. Moreover, these analyses support previous biochemical and morphological data indicating that distinct lineages exist within the Benincaseae. Likewise, data support the hypothesis that Benincasa genus is descended from an ancient African ancestor, and that the progenitor of the New World Sicyeae tribe shares a common ancestor with the genus Luffa of the Old World Benincaseae.