Calcium deficiency and gibberellic acid enhance susceptibility of pumpkin and sunflower seedlings toSclerotinia sclerotioruminfection

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Abstract
Pumpkin (Cucurbita pepo L.) and sunflower (Helianthus annuus L.) seedlings were grown in culture deficient in calcium and inoculated with Sclerotinia sclerotiorum (Lib.) de Bary. Three days after inoculation the seedlings showed a susceptibility to the pathogen that was inversely proportional to the calcium content of the nutrient solution. Plants treated with gibberellic acid (GA3) became more susceptible to infection by S. sclerotiorum. Increased addition of GA3 resulted in increases in infection both in rate and severity. Sunflower was more susceptible to the pathogen than was pumpkin. GA3 treatment consistently decreased the calcium content in both species. The effect of calcium deficiency on infection by S. sclerotiorum was greatly amplified by GA3 addition.