PATHOGENIC INTERACTIONS OF ALTERNARIA-CRASSA AND PHENOLIC METABOLISM IN JIMSONWEED (DATURA-STRAMONIUM L) VARIETIES

Alternaria crassa, a mycoherbicide for jimsonweed control, was tested for differential effects on growth, infectivity, and phenolic metaboli sm of two field-collected jimsonweed varieties. Seeds from field-grown red- and green-stemmed jimsonweed varieties were grown in the greenho use and spores were applied in aqueous solutions. Infection studies sh owed no significant differences between the two weed varieties when te sted at various growth stages from cotyledonary to 8-leaf stage at 2.5 x 10(4) spores ml-1. Spore dose response tests with A. crassa spores (6.25 to 100 x 10(3) spores ml-1) showed no significant varietal diffe rences in disease ratings. Extractable phenylalanine ammonia-lyase act ivity increased nearly equally (2- to 3-fold above control) in both va rieties (8- to 9-leaf stage) 48 to 72 h after treatment with 5 x 10(4) spores ml-1. The only significant differences between treated varieti es occurred 72 h after treatment. Exposure to A. crassa lowered total ethanol-soluble phenolic levels in both varieties 72 h after treatment . Spectro-photometric scans (400 to 700 nm) of ethanol extracts (72 h after treatment) indicated that infection caused some absorbance incre ases, especially in red-stemmed jimsonweed. Anthocyanin content was ab out 11-fold higher in red-stemmed than green-stemmed jimsonweed, and A . crassa treatment slightly increased the anthocyanin absorption peak of the red-stemmed variety.