Submitted to: Journal of Economic Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/1/2007
Publication Date: 10/1/2007
Citation: Myers, C.T., Leskey, T.C., Forsline, P.L. 2007. Susceptibility of fruit from diverse apple and crabapple germplasm to attack from plum curculio, Conotrachelus nenuphar (Herbst) (Coleoptera: Curculionidae). Journal of Economic Entomology. 100(5):1663-1671. Interpretive Summary: Plum curculio (PC) is a very destructive pest problem on apples and other tree fruits in the eastern United States. Historically, PC has proven to be very difficult to manage without the use of conventional insecticides, and thus, PC control is a significant obstacle to sustainable production of apples. Prior research has lead to questions regarding the potential for host-plant resistance to plum curculio among various domestic and exotic Malus accessions housed in USDA’s germplasm collections. These studies sought to investigate the potential among these collections for PC resistance which may one day be used for development of pest resistant apple cultivars. After a number of field assessments as well as follow up laboratory assays, we conclude that there is little to no potential for genetic host plant resistance to plum curculio among USDA’s ‘core’ Malus germplasm collection. Despite some prior published reports of resistance among some Malus hybrid selections from the Purdue-Rutgers-Illinois (PRI) breeding program, our data indicates that these notations are erroneous. Clarification of the true status of these and other accessions is important as it will help to prevent costly breeding efforts aimed at developing resistant cultivars that would otherwise be based on erroneous information. Instead, elucidation of the true resistance mechanisms among Malus germplasm will allow breeders to better prioritize their efforts, using germplasm that has been rigorously and appropriately evaluated and described.
Technical Abstract: Plum curculio, Conotrachelus nenuphar (Herbst) (Coleoptera: Curculionidae) is an important apple pest that significantly hinders sustainable apple production in eastern North America. The potential for host plant resistance to plum curculio among apple (Malus) germplasm has never been rigorously evaluated. Thus, studies were conducted to assess the susceptibility of a number of exotic and domestic Malus accessions housed at the USDA Plant Genetic Resources Unit (PRGU) ‘core’ collection. Contrary to earlier published reports and promising data from a field assessment in 2005, these results suggest that there is probably little potential for genetic resistance to plum curculio among the Malus germplasm collection evaluated. More specifically, four Malus hybrid selections that have previously been released with claims of plum curculio resistance were shown to be susceptible to plum curculio attack. Because there are additional accessions housed at PGRU outside of the core collection that are currently classified as resistant, further studies are necessary to evaluate the true resistance qualities of these releases. It is also important to clarify such discrepancies in both the USDA online Germplasm Resources Information Network (GRIN) and in the horticultural literature. While other Malus species exhibited some variability in fruit susceptibility, none could be classified as being truly resistant to plum curculio attack by any definition that would have relevance to commercial production and sale of apples.