Epidemiology of Phytophthora capsici on bell pepper

Abstract

SUMMARY: The number of pepper seedlings (Capsicum annuum L.) surviving transplanting in a glasshouse decreased from 100% in the control to 84 ± 6,55 ± 8, and 18 ± 6% in field soil containing 1, 5 and 25 propagules of Phytophthora capsici Leonian per gram soil, respectively. When detached leaves were inoculated with a sporangial suspension at 15 and 31 °C, an incubation period of 24 h was required before an infection level of 50% was reached. Incubation at 27 °C for 4 h resulted in 60% of the leaves infected. Neither sporangia nor mycelia survived a week in leaf tissue if the relative humidity was 47% or less or if the temperature was -12 or 40 °C. Recovery of sporangia from inoculated stem pieces (2 cm long) stored for 1 week at 25 °C was reduced from 1455 to 30 sporangia per stem piece when the relative humidity was reduced from 100 to 87%. P. capsici could not be isolated from inoculated leaf tissue 2 days after being placed on the soil surface in a field, but was easily isolated after 14 days if buried. The distribution of disease within a test field followed the field's drainage pattern. Splashing rain and run-off water appear to be the main means of spread. Combined rainfall for days 3, 4, 5 and 6 prior to symptom development correlated with disease incidence (r = 0·53, P < 0·01).