Initiation of resistant responses in bean by mycelial wall fractions from three races of the bean pathogen Colletotrichum lindemuthianum

Abstract

Phytoalexin production and browning were elicited in Dark Red Kidney bean cotyledons by application of mycelial walls isolated from three races of Colletotrichum lindemuthianum. Two races, α and δ, were avirulent on this bean cultivar and a third, β, was virulent. Heat treatment of aqueous suspensions of the α, (β, and δ mycelial walls released soluble polysaccharides that elicited browning and phytoalexin production on bean cotyledons. These polysaccharides were not adsorbed by anion or cation exchange resins and ranged in size up to at least a molecular weight of 106. The highest molecular weight fractions were predominantly glucans and showed elicitor activity on cotyledons with application of less than 10−6 g glucose equivalents. The soluble polysaccharide extracts also possessed minor amounts of sugars which differed among the α, β, and δ races.