FACTORS AFFECTING THE VERTICAL DISTRIBUTION OF RHIZOCTONIA SOLANI WITH SPECIAL REFERENCE TO CO 2 CONCENTRATION

D urbin , R ichard D. (U. Minnesota, St. Paul.) Factors affecting the vertical distribution of Rhizoctonia solani, with special reference to CO 2 concentration. Amer. Jour. Bot. 46(1) : 22‐25. Illus. 1959.—Thirty‐three heterogeneous clones of 3 ecological types of Rhizoctonia solani (aerial, surface, and subterranean, based on their vertical distribution on the host plant) were grown in flowing atmospheres containing various levels of CO 2 . The linear growth rates were compared with those obtained when the clones were grown in normal air. Significant differences were found among the clones with respect to their tolerance of CO 2 . Those found normally in the soil were more tolerant of CO 2 than were clones occurring in either surface or aerial environments. Additional experiments with other plant pathogenic soil fungi, plus data obtained from the literature, indicate that tolerance of CO 2 is a common attribute of fungi normally found in the soil and in rotting organic matter, environments where high CO 2 concentrations are to be expected. Significant differences were also found in the linear growth rates of 86 clones from the 3 types. The ratio of the mean growth rates for aerial, surface, and subterranean clones was about 4:3:2, respectively. The 2 characteristics, linear growth rate and CO 2 tolerance, were negatively correlated (r = +.773). The percentage of the aerial, surface, and subterranean types producing sclerotia was 82, 48, and 21, respectively. In 9 clones tested linear growth rate was not found to be correlated with endogenous O 2 uptake rate. Carbon dioxide tolerance, linear growth rate, and sclerotial formation are characteristics which seem to play a part in determining the habitat of clones of this fungus.