The potential role of high photosynthetic capacity in pest resistance mechanisms in Fragaria chiloensis

by 1957- Vega, Alexis

by Alexis R. Vega, Ph. D. Washington State University May 2005 Chair: John K. Fellman Fragaria chiloensis (L.) Duch., a strawberry native from the Pacific coast of North and South America was one of the parent species, along with F. virginiana from North America, of the cultivated strawberry (F. x ananassa), which came from a single cross between both parents. This created a rather narrow genetic variation on the descendants of the original cross, allowing to some researcher to propose an expansion of the genetic base of F. x ananassa with native germplasm, which show several useful agronomic traits, among others, pest resistance and high photosynthetic capacity. A research was carried out to test the hypothesis that pest resistance mechanisms in the Fragaria genus are more likely to be present in genotypes with high photosynthetic capacity, as their require extra energy to be operative. It was confirmed previous findings communicated in the literature that the Fragaria genus has a high phenotypic variability in both traits under study if a wide range of genotypes are tested. Such variability follows a continuous distribution along the observed response ranges, suggesting polygene systems. No strong association between photosynthetic capacity and pest resistance variables was found, however, genotypes placed at the extreme of the observed response ranges, did show consistency vi with the hypothesis. Also, it was determined that the photosynthetic capacity did not segregate under the experimental conditions, however, it was demonstrated that most of the variability observed in photosynthetic capacity in Fragaria can be linked to the leaf residual conductivity to the CO2 (gr). Some pest resistance variables do segregate in the F1 generation from a single cross (total leaf phenolics concentration, total leaf protein and trichome density). Some pest resistance mechanisms appear to be elicited by the feeding upon plants by the arthropod Otiorhynchus sulcatus (L.) (Black vine weevil), some of them in a systemic fashion (phenolics). More studies are required to determine where the pest resistance mechanisms reside in the Fragaria genus. vii