Abstract
Correlations between the susceptibility levels of 23 onion cultivars to infestation of the onion maggot and various biochemical characteristics of onion seedlings were investigated following Boelen's scheme of the metabolic pathway of S-propenylcysteine sulfoxide by both chemical analysis and bioassay of the metabolites. The onion seedlings of susceptible cultivars gave a larger quantity of propylthio compounds, the oviposition- and maggot-attractants, than those of resistant cultivars, because the alliinase activity was higher in them than in the resistant cultivars. However, the contents of S-propenylcysteine sulfoxide, precursor of the attractants, was rather inversely proportional to the maggot-infestation rates, possibly due to its higher decomposition rate in the susceptible cultivar samples during transportation and storage. The hybrid FX1 cultivars were more resistant to maggot infestation due to less emanation of the attractants and lower activity of alliinase than their parent cultivars were.
