RESISTANCE TO PERONOSPORA-VICIAE EXPRESSED AS DIFFERENTIAL COLONY GROWTH IN 2 CULTIVARS OF PISUM-SATIVUM

Peronospora viciae sporulated frequently following localized inoculati on of leaflets of Pisum sativum cv. Krupp Pelushka but rarely on cv. E arly Onward (60 and < 1% of plants respectively). Similar results were obtained following inoculation of seedling shoot apices. The proporti ons of sporangia that germinated, formed appressoria, invaded via stom ata or cuticle, and established colonies, were similar on leaflets of both cultivars. After 2 days, total hyphal lengths of most colonies we re greater than 100 mu m (94% in Krupp Pelushka, 64% in Early Onward), but in Krupp Pelushka there were five times as many haustoria per uni t length of hypha. Subsequently, only occasional colonies in Early Onw ard grew to the same extent as in Krupp Pelushka, with 8% and 88% resp ectively attaining lengths > 800 mu m after 4 days. Reduced growth of hyphae in Early Onward was associated with increased frequency of host cells stained by trypan blue.