Growth of Verticillium lecanii in Pustules of Stripe rus t(Puccinia striiformis)

A number of different fungal hyperparasites have been observed to grow in pustules of rust fungi. Examples of these are Verticillium (HASSEBRAUK 1936, KOTTHoFF 1937, GAMS 1971), Darluca fi/um (KRANz 1973), Monocillium nordinii (TSUNEDA and HIRATSUKA 1980), Alternaria and Cladosporium species (OMAR and HEATHER 1979). Verticillium lecanii may be the most interesting fungus for biological control of rust diseases since this fungus not only has a very broad host range in fungi (GAMS 1971 )" but also attacks different insects (BARSON 1976, HALL 1980). This fungus is part of the natural mycoflora of wheat stern rust (Puccinia graminis Pers. f. sp. titici) and stripe rust (Puccinia striiformis) infected leaves (McKENZIE and HUDSON 1976, Dr. EVA FUCHs, pers. communication). V. lecanii may be appropriate for the biological control of carnation rust, Uromyces dianthi (SPENCER 1980). There are only few studies on the mode of action of the parasitism of V. lecanii. Lysis of urediospore germ tubes (GARCIA ACHA et al. 1965), bursting of urediospores of coffee rust, H emileia vastatrix (SILVEIRA and RODRIGUES 1971) and penetration into urediospores of stripe rust, Puccinia striiformis (SCHROEDER and HASSEBRAUK 1957) by V. lecanii has been described. After infection of pustules of bean rust (Uromyces phaseoli), the hyperparasite remained restricted to the pustule area and did not penetrate into the bean leaf tissue (MENDGEN and CASPER 1980). There have been no studies on the optimal conditions for growth of V. lecanii in the rust pustule. This paper reports the interactions of the germ tubes and the urediospores of Puccinia striiformis with Verticillium lecanii and the influence of temperature, light and air humidity on the development of the hyperparasite in the rust pustule.