Induction of Ethylene Biosynthesis in Compatible and Incompatible Interactions of Soybean Roots with Phytophthora megasperma f. sp. glycinea and its Relation to Phytoalexin Accumulation

Abstract

Summary Seedling roots of different varieties of soybean have been infected with various strains of the soybean pathogen Phytophthora megasperma f. sp. glycinea (Pmg), resulting in compatible and incompatible interactions. Infected roots displayed an increase in ethylene biosynthesis in all cases. Upon infection of the soybean cultivar Harosoy with Pmg race 1 or 3 or of cultivar Harosoy 63 with Pmg race 3, resulting in compatible interactions, the rate of ethylene biosynthesis started to increase ca. 6 h after infection and reached ca. 10–15-fold induction 11–12 h after inoculation. In the incompatible interaction of the soybean cultivars Maple Arrow or Harosoy 63 with Pmg race 1, however, ethylene production was stimulated 5–10-fold as early as 3 h after infection and reached its maximum, a ca. 50-fold induction, already 6 h after inoculation. Soybean roots treated with elicitor preparations from Phytophthora megasperma cell walls showed no increase in ethylene biosynthesis although they accumulated glyceollin, the main phytoalexin of soybean, to a similar degree as infected roots. Addition of 1-aminocyclopropane-1-carboxylic acid to soybean roots increased ethylene production without affecting glyceollin accumulation. We conclude that in soybean roots, an early burst of ethylene biosynthesis is a characteristic symptom of the incompatible reaction that cannot be mimicked by treatment with fungal elicitors.