Submitted to: Journal of Chemical Ecology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/24/2007
Publication Date: 4/1/2007
Citation: Ranger, C.M., Singh, A.P., Johnson-Cicalese, J., Polavarapu, S., Vorsa, N. 2007. Intraspecific Variation in Aphid Resistance and Constitutive Phenolics Exhibited by the Wild Blueberry Vaccinium darrowi. Journal of Chemical Ecology. 33:711-729. Interpretive Summary: Viruses pose a considerable threat to the commercial production of highbush blueberries, Vaccinium corymbosum. Aphids infesting cultivated blueberry fields are one of the primary modes of virus transmission from infected to healthy plants. Managing aphid-transmitted viruses mainly occurs through insecticide applications and rouging infected plants. Aphid-resistant cultivars could provide a multifaceted approach to aphid and virus management. Since uncultivated blueberry species represent valuable sources of insect and disease resistance traits, wild accessions of V. darrowi were evaluated for resistance to the blueberry aphid, Illinoia pepperi. Phenolics, which are documented to confer resistance to aphids, were also measured in leaves and stems of V. darrowi to determine if such compounds predicted resistance levels. Several wild accessions of V. darrowi with resistance against I. pepperi were identified and are being used in a traditional breeding program to improve the resistance levels of existing cultivars. A correlation was not detected between phenolics and aphid resistance, which means other plant factors need to be considered as indicators of resistance.
Technical Abstract: Illinoia pepperi (MacGillivray) infests cultivated highbush blueberries, Vaccinium corymbosum L., in the Northeastern United States. Allopatric resistance to I. pepperi was examined using Vaccinium darrowi Camp, which evolved in the absence of I. pepperi in the Southeastern United States. Vaccinium corymbosum cv. ‘Elliott’ was used as a susceptible control. Between population variability in I. pepperi resistance was assessed by measuring length of the prereproductive period, fecundity, and survivorship on 14 V. darrowi accessions representing 11 discrete wild populations. Length of I. pepperi’s prereproductive period and survivorship were not significantly affected. However, significant differences were detected in fecundity and the intrinsic rate of increase (rm). Within population variability in resistance was measured by confining 1st instars to 24 accessions from a single wild population of V. darrowi (NJ88-06). Significant differences in the mean total number of aphids occurring after 20 d were only detected between 2 of the 24 V. darrowi accessions. A greater degree of diversity in I. pepperi resistance exists between populations of V. darrowi compared to within a population. Constitutive leaf and stem polyphenolics were also identified by HPLC-MS and quantified from 14 of the V. darrowi accessions. The accessions varied considerably in concentrations of five phenolic acids and seven flavonol glycosides, but a correlation was not found between individual or total phenolics and aphid performance. Overall, screening within and between populations of V. darrowi identified promising sources of aphid resistance, but phenolic acid and flavonol glycoside profiles did not predict resistance levels. The mechanism of resistance remains to be identified.