Basidiospore Dispersal and Survival

Abstract

Rhizoctonia solani Kühn is well known as a root-infecting fungus. Under certain conditions such as high relative humidity, it attacks aerial parts of a wide variety of plants. These aerial diseases occur in countries having tropical, temperate and subpolar climates. The common names given to these diseases are based on the particular symptoms occurring on various hosts and include: sheath blight, web blight, aerial blight, foliage or leaf blight, target spot, leaf spot, brown spot, and others (Baker, 1970; Sneh et al., 1991). Symptoms of these diseases can occur on plants from ground level to more than 100 cm above ground in tall plants. Under natural field conditions, hymenia of the teleomorph state of R. solani [Thanatephorus cucumeris (Frank) Donk] are formed by isolates of certain anastomosis groups (AGs). Hymenia are formed on a wide variety of plant hosts, either on the stem bases, or on other plant and soil surfaces, which are protected under the plants’ canopies. Airborne basidiospores can be disseminated rapidly over long distances, reaching the upper plant parts, and eventually, causing severe aerial epidemics under suitable moist conditions. Basidiospore infections have been reported in several host plants. citrus (Stahel, 1940), sugar beet (Kotila, 1947; Naito, 1984, 1990), soybean (Naito et al., 1995), bean (Echandi, 1965; Galindo et al., 1983), jute (Tu et al., 1977), ground nut (Dubey and Dwivedi, 1992a), Peruvian barbasco (Crandall, 1950), rubber tree (Carpenter, 1951); cotton (Luke et al., 1974), tobacco (Vargas, 1973; Shew and Main, 1985; 1990), sesame (Matsuura and Takahashi, 1953), rice (Fukazu et al., 1960), Eupatorium cannabinum (Dwivedi and Dubey, 1985), tomato (Kodama et al., 1982), sugarcane (Duvey and Dwivedi, 1992b), cabbage (Hoshi et al., 1995), night shade (Shew and Main, 1985), Sida rhombifolia (Galindo et al., 1983), Amaranthus lividus and Chenopodium album (Naito et al., 1995). When infections are caused by hyphae or sclerotia originating from soil, the disease spreads considerably slower than when epidemics originate from airborne propagules. The rapid spread of aerial epidemics occurs primarily due to the presence of basidiospores as primary and secondary inocula. Nevertheless, the severity of field epidemics is decisively influenced by micro- and macro environmental as well as cultural conditions.