Evidence for systemic, cross-resistance in white clover (Trifolium repens) and annual medic (Medicago truncatula var truncatula) induced by biological and chemical agents

Abstract

Soil-based growth cabinet and greenhouse experiments were designed to determine whether a resistance response previously noted in Trifolium repens to the clover cyst nematode Heterodera trifolii was systemic and also effective against a pest from a different taxon. Root applications of benzo(1,2,3)thiadiazole-7-carbothioic acid-S-methyl ester (BTH) or a Pseudomonas-like bacterial strain P29 to white clover seedlings induced resistance to the blue-green aphid, Acyrthosiphon kondoi. A similar response was observed in the annual medic, Medicago truncatula var truncatula. Estimation of lignin and callose content of whole plants at the termination of the bioassay showed no differences between treated and control plants. The significance of these findings is discussed.