LOW AROMATIC AMINO-ACID-CONCENTRATIONS IN LEAF PROTEINS DETERMINE RESISTANCE TO FRANKLINIELLA-OCCIDENTALIS IN 4 VEGETABLE CROPS

Analysis of total aromatic amino acid (free and bound) in some cucumbe r accessions selected previously for resistance to western flower thri ps, Frankliniella occidentalis (Pergande) [Thysanoptera: Thripidae], i ndicated that low concentrations of these essential nutrients, relativ e to total leaf protein, were correlated with a reduction in damage by the insect. Further analysis of samples of four important horticultur al crops (lettuce, tomato, pepper and cucumber) with unknown levels of resistance to thrips showed a significant genotypic variation in the concentrations of total aromatic amino acids relative to the total lea f protein. Accessions from each crop with low or high concentrations o f aromatic amino acids in proteins were exposed to thrips larvae. Regr ession analysis showed a highly significant positive correlation betwe en aromatic amino acid concentration in leaf protein and thrips damage , regardless of crop species. It is concluded that higher concentratio ns of aromatic amino acids in plant proteins are important for success ful thrips development. These results provide plant breeders with a pr omising tool for indirect selection without using undesirable insect b ioassays.