Effect of Wetness Duration and Temperature on Infection of Geranium byBotrytis cinerea

Abstract

Duration and temperature of postinoculation wetness periods were investigated in relation to infection of flowers and leaves of geranium by Botrytis cinerea. Infection was assessed indirectly by estimating sporulation incidence of the pathogen in inoculated tissues. Sporulation incidence in whole flowers inoculated with conidia increased sharply when wetness duration at 15, 21, 25, and 30 degrees C was increased from 8 to 24 h, 4 to 12 h, 4 to 12 h, and 4 to 6 h, respectively. The pathogen did not sporulate after shorter wetness periods at these temperatures or after 24 h wetness at 5 and 10 degrees C. No sporulation was observed in sepals, petals, and stamens when the wet period at 25 degrees C was less than or equal to 4 h, or in pistils and pedicels when wetness lasted less than or equal to 6 h, but sporulation increased to 100, 100, 100, 73, and 60% in the respective organs as the wet period was increased to 24, 12, 12, 24, and 24 h. Following conidial inoculations of the foliage, B. cinerea sporulated in 1-week-old leaves only when the postinoculation wetness period at 15, 21, 25, and 30 degrees C was greater than or equal to 6, greater than or equal to 4, greater than or equal to 6, and greater than or equal to 6 h, respectively, and in 10-week-old leaves when wetness at the respective temperatures lasted greater than or equal to 6, greater than or equal to 6, greater than or equal to 8, and greater than or equal to 28 h. Sporulation was observed in 4-week-old leaves after greater than or equal to 12, grater than or equal to 8, and greater than or equal to 6 h wetness at 15, 21, and 25 degrees C, respectively. The pathogen did not sporulate in leaves of any age group when postinoculation wet periods were 0 to 24 h at 5 or 10 degrees C, or in 4-week-old leaves at 30 degrees C. Botrytis cinerea sporulated more frequently in 1- and 10-week-old leaves than in 4-week-old leaves when wetness lasted for 8 to 24 h at 25 degrees C. The pathogen infected leaves more efficiently when conidia were applied to geranium petals that after 24 h were positioned on the leaves, than when conidia were applied directly to the leaves. Logistic regression models were developed that adequately described effects of postinoculation wetness duration and temperature on sporulation incidence and, by inference. infection incidence, in flowers and leaves.