FACTORS AFFECTING THE VERTICAL DISTRIBUTION OF RHIZOCTONIA SOLANI WITH SPECIAL REFERENCE TO CO₂ CONCENTRATION

Abstract

Durbin, Richard D. (U. Minnesota, St. Paul.) Factors affecting the vertical distribution of Rhizoctonia solani, with special reference to CO2 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 CO2. 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 CO2. Those found normally in the soil were more tolerant of CO2 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 CO2 is a common attribute of fungi normally found in the soil and in rotting organic matter, environments where high CO2 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 CO2 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 O2 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.

Biochemical Ecology of Soil Microorganisms

“…Burges (2) suggested that CO2 might be of greater consequence in determining population modifications in poorly aerated cir cumstances than 02, a slight increase in pC02 frequently having a more marked influence upon fungi than the corresponding decrease in pOt. This suggestion is supported by the observation that subterranean strains of Rhizocfonia solani are more tol erant of CO2 than strains whose chief si te of activity is near the soil surface, whereas isolates of this pathogen that attack aerial portions of susceptible plants exhibit the greatest sensitivity (61), the particular habitat seemingly selecting for the predominating R. solani types. Pathogenicity of the fungus is diminished by CO2, moreover, a factor of possible rel evance to investigations of the biological control of soil-borne pathogens (62).…”

“…For example, organic acids commonly liberated during the growth of bacteria and fungi have been detected in soil, and cer tain of the acids were found to inhibit the growth of fungi, especially in acid conditions (71,97) . Carbon dioxide, the concentration of which may become quite high particularly within the microenvironment, is also concerned in amensalistic interactions, altering not only the biochemical activity of indi vidual s pecies but also the composition of the microbial co mmunity at the site of CO2 accumulation (61,62) . Ammonia formed in nitrogen mineraliza tion is a potent inhibitor for Nitrobacter in alkaline habitats, the toxicity being governed by both the pH and the ammonia concentration (98) , and the nitrite that remains by virtue of the repression of nitrite-oxidizing auto trophs may, in turn, affect the survival or biochemical activities of sensitive fungi.…”

Interaction of Meloidogyne hapla and Rhizoctonia solani in alfalfa

“…The pathogenic phase was even-more sensitive to carbon dioxide than the active saprophytic stage. Durbin (1959) found that clones of Rhizoctonia foimd in the soil were more tolerant to carbon dioxide than those found in aerial environments. Certain Fusariian and Trichoderma spp.…”