Abstract
Five rice sclerotial disease fungi, Rhizoctonia oryzae, R. solani AG-1 IA, R. fumigata, R. oryzae-sativae, and Sclerotium hydrophilum, were surveyed for the influence of different concentrations of CO2 and O2 on mycelial growth, and sclerotial formation and germination. The ratio (%) of mycelial growth (mm) at two CO2 ∕ O2 concentrations, i.e., 0.1 ∕ 20% and 5 ∕ 5%, compared to mycelial growth at 0.03/20% (control) was similar among the five isolates of each fungus, resulting in a lower coefficient of variation (%) that ranged from 1.4 to 3.6%, except for R. solani AG-1 IA, showing 8.2%. A growth decrease of 22–53% and 23–47% occurred at 15% and 1% among four CO2 concentrations ranging from 0.03 to 15%, and four O2 concentrations from 1 to 20%, respectively. R. solani AG-1 IA proved to be most sensitive to relatively higher concentrations of CO2 and lower concentrations of O2. On the other hand, S. hydrophilum and R. oryzae-sativae, especially S. hydrophilum, was tolerant. In R. solani AG-1 IA and R.oryzae-sativae, sclerotial formation showed a 42–95% decrease at CO2: 5% and also a 57–100% decrease (non-formation for sclerotia) at CO2: 15%. Moreover, sclerotia kept under a low growth CO2 /O2 concentration of 5/5% for 60 days showed 86–99% of germination for R. solani AG-1 IA and R. oryzae-sativae. These results are possible to contribute better understanding of the fungal development of Rhizoctonia and Sclerotium spp. in soil, and consequently, the respective spread of disease in paddy fields.
