S-Propenylcysteine Sulfoxide in Exudates of Onion Roots and Its Possible Decompartmentalization in Root Cells by Bacteria into Attractant of the Onion Maggot, Hylemya antiqua (Diptera : Anthomyiidae)

Abstract

The contents of S-propenylcysteine sulfoxide (PCSO) in roots and exudates of aseptic onion seedlings, and the total root bacteria counts in septic seedlings were all higher in cultivars that are susceptible to the onion maggot, Hylemya antiqua MEIGEN, than in the resistant ones. In addition, more propylthio oviposition attractants were generated in the susceptible cultivars. In aseptic soil where bacterial metabolism was impossible, PCSO accumulated.In vitro metabolism of the PCSO extract of onion by bacteria produced more methylthio compounds than propylthio compounds, which was in contrast to allinase metabolism in chopped onions. Since intact septic onion seedlings generated these compounds in intermediate proportions, it is suggested that both bacterial metabolism of exudates in soil and activation of alliinase by bacterial decompartmentalization are simultaneously taking place in the onion rhizosphere.