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Effect of Some Host and Microclimate Factors on Infection of Tomato Stems by Botrytis cinerea

The susceptibility of tomato stems to infection by Botrytis cinerea and the influence of temperature and humidity on disease development were investigated with stem pieces and whole plants. Stem rotting resulted after inoculation of wounded stems with a conidial suspension in water or with dry conidia; no symptoms developed following inoculation of unwounded stems. The proportion of inoculated stems developing Botrytis rot increased as the inoculum concentration was increased from 10 to 10,000 conidia per stem. Stem susceptibility to infection declined from 60 to 8% as wound age increased from 0 to 24 h before inoculation. Wounded stem pieces maintained in a low vapor pressure deficit (VPD) environment (<0.2 kPa) remained susceptible for a longer period than those maintained at a high VPD. Infection and stem rotting occurred at temperatures of 5 to 26°C, with disease development most rapid at 15°C. Sporulation was optimal at 15°C and did not occur within 20 days of incubation at 5 or 26°C. Incubation at high humidity following inoculation of fresh wounds (VPD <0.2 kPa) did not increase infection incidence or tissue rotting, compared with incubation at a VPD >1.3 kPa; however, incubation at the lower VPD did increase the intensity of sporulation.