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Resistance

Induction of Systemic Resistance of Cucumber to Colletotrichum orbiculare by Select Strains of Plant Growth-Promoting Rhizobacteria. Gang Wei, Department of Plant Pathology and Alabama Agricultural Experiment Station, Auburn University 36849; Joseph W. Kloepper, and Sadik Tuzun. Department of Plant Pathology and Alabama Agricultural Experiment Station, Auburn University 36849. Phytopathology 81:1508-1512. Accepted for publication 26 July 1991. Copyright 1991 The American Phytopathological Society. DOI: 10.1094/Phyto-81-1508.

Ninety-four strains of plant growth-promoting rhizobacteria (PGPR) were screened for induction of systemic resistance using a model system of cucumber and anthracnose, caused by Colletotrichum orbiculare. Compared with a nonbacterized, challenged control, treatment of cucumber seeds with six PGPR strains resulted in a significant reduction in lesion size after challenge-inoculation with C. orbiculare. Four of the six PGPR strains that induced resistance in cucumber produced HCN in vitro. Antagonism in vitro toward Pythium ultimum, Rhizoctonia solani, and C. orbiculare on three media generally was absent with five PGPR strains and weak with one strain. Rifampicin-resistant mutants of the PGPR strains colonized roots at mean population densities of log 6.5 to 8.3 cfu g1 of root at 7 days after planting and log 4.1 to 6.1 cfu g1 at 21 days after planting. None of the strains was recovered from surface-disinfested petioles on the day of challenge with C. orbiculare. Roots from plants bacterized with PGPR strains showed less necrosis than the nonbacterized, challenged control. The results support the conclusion that some PGPR strains applied to seed can induce systemic resistance to C. orbiculare.

Additional keywords: Colletotrichum lagenarium.