Effect of humidity and light periods on infection and sporulation of Peronospora viciae on Pisum sativum

Abstract

Plants grown in high relative humidity (RH > 90%) before inoculation supported more sporulation than those kept in drier (RH < 30%) conditions. Sporulation of Peronospora viciae (Berk.) Casp. on Pisum sativum (Berk.) Casp. cv. Superb was lower on plants kept under continuous light for 2 weeks before inoculation than on those maintained in a 12 h light: 12 h dark photoperiod. Treatments involving longer photoperiods after inoculation resulted in greater sporulation (intensity) than those where inoculation was followed by an extended dark period. A minimum of 6 h of high humidity (RH > 90%) in the dark was required to initiate sporulation. However, this period was reduced to 3 h if replaced by lower humidity conditions (RH 65%).