Comparison of Infection by W‐type and R‐type Isolates of the Eyespot Pathogen, Pseudocercosporella herpotrichoides, in Relation to Host Species and Cultivar, Temperature and Watering Regime in Controlled Environments

Abstract

Abstract The incidence and severity of infection by W‐type and R‐type isolates of the eyespot pathogen, Pseudocercosporella herpotrichoides, were compared on artificially inoculated wheat (cvs Armada and Avalon) and barley (cv. Opera) grown in pots atdifferent temperatures (8–13°C and 16–21°C), and on wheat (cv. Avalon) with different watering regimes. On leaf sheaths of seedlings and on stems of older plants, infection was usually more prevalent after inoculation with the W‐type, although infection by the R‐type equalled that by the W‐type as the plants neared maturity. Infection by the W‐type, but not by the R‐type, was usually more prevalent on the more susceptible host species (wheat) or wheat cultivar (Armada). The warmer conditions duringseedling growth favoured seedling infection, but the cooler conditions during seedling infection favoured subsequent infection of the stems. Infection was greater with more frequent watering. Relative amounts of infection by the W‐type and R‐type were not influenced by temperature or watering regimes. It is suggested that epidemiological differences between the W‐type and R‐type, suspected from previous field observations, are more likely to result from inherent differences in virulence, from differences in the ways they interact with the host and with the microflora of the shoot base and from mutual interactions, rather than directly from interactions with the environment.