Submitted to: Journal of Insect Science
Publication Type: Peer reviewed journal
Publication Acceptance Date: 10/20/2010
Publication Date: N/A
Citation: Interpretive Summary: As important as temperate grass accessions in the USDA, ARS gene bank at Pullman, Washington are for breeding new cultivars, so are fungal inhabitants (called Neotyphodium grass endophytes) of Pullman grass accessions for endowing grass cultivars with improved insect resistance and drought tolerance. Continued development of new cultivars with insect resistance traits linked to Neotyphodium infection is contingent upon more information on the effect of endophyte-infected accessions on survival of important grass pests. This research paper by ARS scientists and colleagues in New Zealand and China identifies an endophyte-infected wild timothy grass accession from Argentina storedd in the Pullman gene bank. This paper also presents results from experiments showing that endophyte infection of this wild grass does not provide protection against attack by all insect pests. While endophyte-infected plants were resistant to an aphid pest called the bird cherry oat aphid, these experimental plants and endophyte-free conspecific plants were equally susceptible to attack by the cereal leaf beetle. This research is important because it provides additional evidence of diverse grass-endophyte associations in the Pullman seed bank, while highlighting the variable effects of endophyte-infected grasses on important insect pests.
Technical Abstract: The presence of seed-borne Epichloë/Neotyphodium (Ascomycota: Clavicipitaceae) fungal endophytes in temperate grasses can influence the outcome of grass–insect interactions. For example, the expression of endophyte-mediated resistance to insects depends on the insect species involved. The behavior and performance of Rhopalosiphum padi (L.) (Hemiptera: Aphididae) and Oulema melanopus (L.) (Coleoptera: Chrysomelidae), two important pests of forage and cereal grasses, were quantified on Neotyphodium-infected (E+) and uninfected (E-) test plants of the wild Argentine grass Phleum alpinum L. in growth chamber and greenhouse experiments. R. padi preferred E- over E+ test plants in choice experiments and E+ undamaged test plants constitutively expressed antibiosis resistance to this aphid by suppressing population growth. Prior damage of E+ test plants did not induce higher levels of resistance to R. padi. By contrast, the beetle O. melanopus showed no preference for E+ or E- test plants and endophyte infection did not adversely affect the survival and development of larvae. These results extend the phenomenon of variable effects of E+ wild grasses on the behavior and performance of phytophagous insects. As well, the heretofore undocumented wild grass–Neotyphodium symbiotum in this study broadens the number of wild E+ grasses available for expanded explorations into the effects of endophyte metabolites on insect herbivory.