The aim of the present study was to evaluate the effect of temperature (15, 20, 25 and 30ºC), leaf wetness period (0, 6, 12 and 24 h), and planting time (September, October, November and December) and method (direct sowing and transplanting) on the intensity of stem blight (Botrytis cinerea) in Hibiscus sabdariffa. Environmental variables were evaluated under controlled conditions with artificial inoculation, while planting times and methods were assessed under natural infection conditions in the field with natural inoculation. Infection frequency data, analyzed as area under the progress curve of infection frequency (AUPCF), and lesion length related to the environmental variables were subjected to analysis of variance and regression; then, response surfaces were plotted. Incidence data (AUPCI) related to planting times and methods were subjected to analysis of variance using the statistical program Sisvarâ/UFLA. The interaction of temperature and leaf wetness period influenced the infection frequency and the length of stem blight lesions, which increased with the increase in leaf wetness period and with the decrease in temperature. Lesions were larger at 15ºC and 24 hours of leaf wetness. In the absence of leaf wetness, symptoms manifested only at 15ºC. At 30ºC, longer leaf wetness periods were required for symptoms to manifest. There was a significant interaction of planting times and methods on the disease incidence. Stem blight incidence was lower in seedling transplanting compared to direct sowing at all planting times. There was an increase in incidence due to the delay in planting time with both methods. Thus, there was a direct relationship between decrease in temperature and increase in stem blight incidence.
Roselle; incidence; severity
