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Genetic Characterization by RAPD Analysis of Isolates of Fusarium oxysporum f. sp. erythroxyli Associated with an Emerging Epidemic in Peru

First and fifth authors: Biocontrol of Plant Diseases Laboratory, ARS, USDA, Beltsville, MD 20705; second author: Systematic Botany and Mycology Laboratory, ARS, USDA, Beltsville, MD 20705; third author: Universidad Nacional Agraria de la Selva, Tingo María, Peru; and fourth author: Weed Science Laboratory, ARS, USDA, Beltsville, MD 20705

An epidemic of vascular wilt caused by Fusarium oxysporum f. sp. erythroxyli is currently occurring on Erythroxylum coca var. coca in the coca-growing regions of the Huallaga Valley in Peru. Random amplified polymorphic DNA (RAPD) analysis of isolates of the pathogen was undertaken to elucidate its genetic complexity, as well as to identify a specific DNA fingerprint for the pathogen. Two hundred isolates of Fusarium were collected from 10 coca-growing regions in Peru. Of these, 187 were confirmed to be F. oxysporum, and 143 of the F. oxysporum were shown to be pathogens of coca by a root-dip pathogenicity test. The pathogens could be grouped into two subpopulations based on RAPD analysis, and no polymorphism in RAPD pattern was observed among isolates of either subpopulation. Both subpopulations were present in the central Huallaga Valley, where earliest reports of the epidemic occurred. RAPD analysis could easily distinguish the isolates of F. oxysporum f. sp. erythroxyli from the nonpathogenic isolates of F. oxysporum from E. coca var. coca, indicating its utility in DNA fingerprinting.