The effect of hot water on viability of pathogenic fungi under laboratory conditions, in addition to evaluate its effect as soil treatment on cucumber root rot disease in pot experiments was studied. The purified isolates, of Rhizoctonia solani, Fusarium solani, Sclerotium rolfsii and Pythium ultimum were tested for pathogenic ability on cucumber plants in pot experiments. Results indicate that the most aggressive fungi are S. rolfsii and P. ultimum, they caused disease incidence as 59.4 & 50.0% at pre-emergence and 80.7 & 75.0% at post- emergence stages, respectively. Meanwhile, R. solani and F. solani showed moderate effect against cucumber plants. Agar disks with mycelia and growth suspension of R. solani, F. solani, S. rolfsii and P. ultimum were exposed to different hot water temperatures and exposure times under laboratory conditions. Results indicate that growth suspension more sensitive than agar disks with mycelia to temperature and exposure times. The lethal temperatures to R. solani, F. solani, S. rolfsii and P. ultimum are 54.0, 58.0, 56 or 58.0oC and 52.0, 56.0, 54.0 or 56.0 oC when exposed to hot water temperatures for one minutes as agar disks with mycelia or growth suspension respectively. Complete reduction in total count of all tested fungi was obtained with boiling water as soil treatments at 0.4 & 0.5 L/kg soil and hot water at 90.0 & 100°C at rate 0.5 L/kg soil. As for the disease incidence the highest reduction in root rot disease was obtained with boiling water at rate 0.4 & 0.5 L/kg soil and hot water at 90.0 & 100 °C (0.5 L/ kg soil) which reduced the disease incidence more than 88.4 and 92.9% for pre and post emergence respectively. It could be suggested that hot water as soil treatments might be safely used commercially as a new approach for controlling root rot disease of cucumber plants under greenhouse conditions. |
