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

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.