Effectiveness of systemic resistance in bean against foliar and soilborne pathogens as induced by biological and chemical means

Abstract

Unifoliate leaves of 9‐day‐old green bean, Phaseolus vulgaris cv. Redlands Pioneer, were inoculated with 104 conidia/ml Colletotrichum lindemuthianum, causing local lesions, or sprayed with 20 μg 2, 6‐dichloro‐isonicotinic acid/ml formulated by Ciba‐Geigy Ltd as CGA 41396. At various times afterwards (7–16 days), first, second or third trifoliate leaves of these plants were challenge‐inoculated with 105 conidia/ml C. lindemuthianum or with the rust pathogen, Uromyces appendiculatus. The numbers of anthracnose lesions or rust uredinia resulting from challenge‐inoculation were reduced to similar extents by both pre‐treatments compared with control plants. Halo blight, caused by Pseudomonas syringae pv. phaseolicola, was reduced in first trifoliates following treatment of unifoliate leaves 6 days earlier with CGA 41396. Induced resistance to root‐infecting pathogens was not observed when stems of either 14‐ or 16‐day‐old plants were inoculated with mycelial plugs of Fusarium solani f. sp. phaseoli, or when 11‐ and 15‐day‐old plants were inoculated with Rhizoctonia sp., Treatment with CGA 41396 did not protect seedlings when they were transplanted into a mix containing the Fusarium sp. 1 day later.