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. Redl ands Pioneer, were inoculated with 10(4) conidia/ml Colletotrichum lin demuthianum, causing local lesions, or sprayed with 20 mu g 2,6-dichlo ro-isonicotinic acid/ml formulated by Ciba-Geigy Ltd as CGA 41396. At various times afterwards (7-16 days), first, second or third trifoliat e leaves of these plants were challenge-inoculated with 10(5) conidia/ ml C. lindemuthianum or with the rust pathogen, Uromyces appendiculatu s. The numbers of anthracnose lesions or rust uredinia resulting from challenge-inoculation were reduced to similar extents by both pre-trea tments compared with control plants. Halo blight, caused by Pseudomona s syringae pv. phaseolicola, was reduced in first trifoliates followin g treatment of unifoliate leaves 6 days earlier with CGA 41396. Induce d resistance to root-infecting pathogens was not observed when stems o f 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 t he Fusarium sp. 1 day later.