Submitted to: Entomologia Experimentalis et Applicata
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/25/2004
Publication Date: 1/1/2005
Citation: Clement, S.L., Elberson, L.R., Bosque-Perez, N.A., Schotzko, D.J., 2005. Detrimental and neutral effects of wild barley--neotyphodium fungal endophyte associations on insect survival. Entomologia Experimentalis et Applicata. V. 114. P. 119-125. Interpretive Summary: There are several major insect pests of wheat and barley crops in the United States, including the Hessian fly, Russian wheat aphid, bird cherry-oat aphid, and rose grass aphid. Farmers in some parts of the United States use resistant varieties developed by plant breeders and entomologists to protect their wheat crops from Hessian fly and Russian wheat aphid attack. When insect-resistant varieties are unavailable, farmers often use insecticides to control insect pests. This paper reports the result of USDA-ARS research to locate new sources of insect pest resistance in plant and microbial genetic resources stored in seed banks of the U.S. National Plant Germplasm System, thereby determining the potential for giving growers new and environmentally acceptable insect management options. This papers shows that naturally occurring fungi (called Neotyphodium endophytes) in wild barley accessions protect the host plants from Hessian fly and, to a lesser extent, rose grass aphid damage. Earlier research showed that wild barley endophytes confer plant resistance to Russian wheat aphid. Looking ahead, it may be possible to exploit this knowledge to endow cereal crops with a new form of natural resistance to major pests.
Technical Abstract: Neotyphodium fungal (tribe Balansieae, family Clavicipitaceae) endophyte infection does not always confer temperate grass resistance to insect herbivores, although reports indicate that over 40 species are adversely affected by infection. Laboratory and glasshouse experiments were conducted to expand our knowledge of the anti-insect properties of Neotyphodium-infected (E+) noncommercial grasses, and E+ wild barley (Hordeum) specifically. Neotyphodium infection of four plant inventory (PI) lines of wild barley conferred resistance to Mayetiola destructor (Say) (Diptera: Cecidomyiidae), whereas none of the E+ wild barley accessions reduced the survival of Rhopalosiphum padi (L.) (Hemiptera: Aphididae). Metopolophium dirhodum (Walker) (Hemiptera: Aphididae) densities were significantly lower on E+ clones of H. brevisubulatum subsp. violaceum (Boissier & Hohenacker) (PI 440420), compared with densities on endophyte-free (E-) plants of this species in population growth experiments. Neotyphodium infection of three H. bogdanii (Wilensky) PI lines did not confer resistance to M. dirhodum; however, one of these E+ lines (PI 314696) was resistant to this aphid in a second population growth experiment. Our results provide additional evidence that the outcome of a grass'endophyte'insect interaction is influenced by the host grass species or genotype, Neotyphodium species or genotype, and the insect species involved. They also reinforce this phenomenon for noncommercial grass'endophyte'insect interactions and underscore the potential role of endophytes in mediating wild barley-insect interactions and their potential to act as defensive mutualists.