Inhibitors of Ethylene Biosynthesis and Action Do Not Prevent Injury to Wheat Seedlings Infested with Schizaphis graminum (Homoptera: Aphididae)

Abstract

Experiments were conducted to determine whether inhibitors of ethylene biosynthesis and action can prevent symptoms of aphid damage to wheat seedlings. ‘TAM 107’ wheat, Triticum aestivum L., seedlings infested with biotype G greenbugs, Schizaphis graminum (Rondani), for 6 h developed chlorosis and necrotic spots within 4 d after the aphids were removed. AVG (1 mM 2-aminoethoxyvinylglycine), an ethylene biosynthesis inhibitor, reduced ethylene production but not development of lesions or loss of chlorophyll from infested seedlings. STS [silver thiosulfate complex (0.5 mM AgN03, 2.0 mM Na thiosulfate)], an inhibitor of ethylene action, did not prevent a reduction in chlorophyll concentration or the development of lesions. A secondary objective was to determine how the ethylene biosynthetic pathway was differentially affected by aphid biotypes previously shown to stimulate high or low levels of ethylene. ‘Largo’ and TAM 107 wheat seedlings were infested with biotype E or G greenbugs, then harvested after 1, 6, or 48 h. Both wheat genotypes are susceptible to biotype G. TAM 107 is susceptible to biotype E and Largo is resistant. Increased ethylene production 6 h after seedlings were exposed to biotype G was associated with an increase in ACC (1-aminocyclopropane-l-carboxylic acid, the immediate precursor of ethylene) and EFE (ethylene-forming-enzyme) activity in both wheat genotypes. Ethylene production, ACC content, and EFE activity declined by 48 h, concomitant with an increase in MACC (N-malonyl-ACC, an inactive conjugate of ACC). Biotype E triggered a smaller increase in ethylene production than biotype G. ACC levels were not affected by biotype E, but EFE activity increased by 33% in Largo and 151% in TAM 107 after 6 h. Ethylene production from greenbug-infested wheat seedlings was controlled primarily by ACC content. Ethylene appeared to be a symptom, not a mediator of green bug-induced injury.