Etiology of Parsley Damping-off and Influence of Temperature on Disease Development

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Abstract
Damping-off of seedlings resulted in extensive stand reductions of parsley in southern New Jersey [USA] during the 1981-1982 growing seasons. The fungi most frequently isolated from field-grown seedlings with symptoms of postemergence damping-off were Fusarium oxysporum, F. solani, Pythium irregulare, P. ultimum, and Rhizoctonia solani (AG-4, AG-1, and AG-2, type 2). In pathogenicity tests, most isolates of P. irregulare and P. ultimum were highly pathogenic and caused extensive preemergence and postemergence damping-off. Similarly, most isolates of R. solani AG-4 and AG-2, type 2, were highly pathogenic. Isolates of AG-2, however, varied considerably in pathogenicity. No other fungi tested for pathogenicity incited disease in parsley. In sand bed studies, a combination of P. irregulare and P. ultimum isolates was highly pathogenic at 15, 23, and 30 C. R. solani, however, was much less pathogenic at 15 C than at either 23 or 30 C. A similar response was obtained in experiments in environmental chambers.