Comparative Studies of Single-Basidiospore Isolates of Pellicularia Filamentosa and Pellicularia Praticola

SUMMARY

Attempts were made with 69 clones of Rhizoctonia from 15 U. S. soils to develop the perfect state by transferring the clones from nutritionally rich growth media to nutritionally poor sporulation media. Eight growth media and 5 sporulation media were tested. Vitamins, growth-promoting substances, plant extracts, and several other natural and synthetic compounds added to a synthetic sporulation medium did not induce formation of the perfect state. Only soil extract agar proved to be a successful fruiting medium and that only for 8 clones. The 8 clones were indistinguishable on several media on the basis of cultural characters. On the basis of sexual morphological characters 2 clones were tentatively identified as Pellicalaria filamentosa (Rhizoctonia solani) and 3 as P. praticola (R. praticola). The remaining 3 fruiting clones did not belong to either species. Length of sterigmata and number of sterigmata per basidium in the majority of basidia were the only apparent distinguishing characters between wild clones of R. solani and R. praticola. However, numbers of sterigmata per basidium in a number of basidia of the 2 species overlapped.

Single-basidiospore isolates from both species differed from one another in rate of growth, cultural characters, and development of thick-walled moniliform cells. The asexual characteristics of single-spore isolates of the 2 species completely overlapped. None of the 120 singlespore isolates of P. filamentosa fruited on agar and soil surfaces. Of 60 single-spore isolates of P. praticola examined only 5 produced the perfect state and only on soil extract agar. The majority of basidia of the 5 single-spore isolates developed 3 sterigmata, but these were variable in size and occasionally curved and two-celled. All sterigmata of the single-spore isolates in culture were shorter than those of the wild clones. It is suggested that separation of R. praticola from R. solani be reconsidered.