Abstract
The efficiency of Streptomyces melanosporofaciens strain EF-76, a geldanamycin producer, and of chitosan, a
polymer derived from chitin that elicits plant defense mechanisms, to protect potato tubers against common scab
was evaluated under both controlled and field conditions (years 2000 and 2001). S. melanosporofaciens EF-76
reduced disease incidence in the greenhouse assay and in the 2001 field assay. EF-76 also reduced symptom
severity on potato tubers grown under field conditions. Chitosan provided a protective effect against S. scabies, the
causal agent of potato common scab during the 2000 field assay by reducing both disease incidence and symptom
severity. Combination of S. melanosporofaciens EF-76 and chitosan ensures a level of protection that was at least
equivalent to the protection conferred by one of the two products used alone. In some instances, an additive effect
of protection was observed when both products were used in combination. Combination of S. melanosporofaciens
EF-76 and of chitosan thus represents a promising method of biocontrol against common scab.