Hot Water Treatment to Management Onion White Rot in Infested Soil with Stromatinia cepivora Fungus

Abstract

Impact of hot water temperatures on Stromatinia cepivora fungus in vitro and white rot of onion plants in vivo was investigated. Agar disks containing Stromatinia cepivora mycelia were examined at various temperatures (25, 50, 52, 54, and 56 °C) and exposure times (5, 10, 15, and 20 minutes) using a digital water path. The results showed that the lethal temperatures for S. cepivora were 54.0 and 56.0 0C for 15 and 5.0 minutes, respectively. As for sclerotia, results indicated the lethal temperatures to Sclerotia of S. cepivora were 60.0 and 65.0 oC for 15 and 5.0 min. respectively. Moreover, several volumes of boiling water (100 °C) and varying degrees of hot water at 0.5 L/kg soil were investigated in pot tests to see how they affected soil temperatures, Sclerotia viability, and white rot disease of onion plants. The results showed that the greatest rise in soil temperatures was achieved with hot water at rates of 0.4 and 0.5 L/kg soil, resulted in increasing soil temperature to 80.5 and 85.0 oC, respectively, and increased soil temperatures with degrees of 90.0 and 100.0 °C at rates of 0.5 L/kg soil, to 73.0 and 84.0 °C, respectively. AS for the effect of hot water on Sclerotia germination of S. cepivorum studies revealed that boiling water at 0.4 and 0.5 L/kg soil and degrees of hot water at 90 and 100.0 °C completely inhibited sclerotia germination. The results of the onion white rot revealed that all tested volumes of boiling water or degrees of hot water considerably suppressed the percentage of white rot disease. White rot disease was completely suppressed by boiling water at 0.5 L/kg soil and hot water at 100.0 °C. The greatest reduction was achieved with hot water at 90 °C and boiling water at 0.4 L/kg soil, which
inhibited white rot incidence and severity by 85.0 & 62.5 and 70.0 & 62.5%, respectively. Other treatments proved less effective. All tested volumes of boiling water or degrees of hot water significantly increased all tested vegetative characters of onion plants. Boiling water at 0.4 and 0.5 L/kg soil and hot water at 90 and 100.0 °C recorded the highest increase in all tested of vegetative characters.