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Nitrogen Fertilization of the Host Plant Influences Production and Pathogenicity of Botrytis cinerea Secondary Inoculum

First, third, and fourth authors: INRA, UR407 Pathologie végétale, Domaine Saint Maurice, CS 60094, F-84143 Montfavet cedex, France; and second author: INRA, UR 1115 Plantes et systèmes de cultures horticoles, Domaine Saint Paul, CS 40509, F-84914, Avignon cedex, France.

The influence of nitrogen (N) nutrition on a plant's susceptibility to Botrytis spp. and other pathogens is well documented. However, little is known of possible effects on sporulation of the pathogen on diseased tissue and on the pathogenicity of resulting secondary inoculum. To address this question, sporulation by two strains of Botrytis cinerea was quantified on tomato plants produced under different N irrigation regimes with inputs of NO₃– at 0.5 to 45 mmol liter^–1 (mM). Sporulation decreased significantly (P < 0.05) with increasing N fertilization up to NO₃– at 15 to 30 mM. The secondary inoculum was collected and used to inoculate pruning wounds on tomato plants produced under a standard fertilization regime. Pathogenicity of the spores was significantly influenced by the nutritional status of their production substrate. Disease severity was highest with spores produced on plants with very low or very high N fertilization (NO₃– at 0.5 or 30 mM). It was lowest for inoculum from plants with moderate levels of N fertilization. These results suggest that it may be possible to find an optimum level of N fertilization to reduce the production of secondary inoculum and its pathogenicity to tomato.

Additional keywords: gray mold, Solanum lycopersicum.