Germinability of Teliospores of Tilletia indica after Hot Water and Sodium Hypochlorite Treatments

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Abstract
Hot water and sodium hypochlorite (NaOCl) were evaluated to eradicate teliospores of the Karnal bunt fungus, Tilletia indica, for the purpose of decontaminating grain storage and handling equipment. The germinability of free teliospores and teliospores within the sori of infected wheat was assessed. Temperatures of 25, 60, and 80°C, NaOCl concentrations (wt/vol, pH 11.5) of 0, 0.53, and 1.60%, and immersion periods of 1, 5, 15, and 30 min were evaluated. In other tests, the influence of pH on NaOCl potency and of a delay between treatment and water rinsing were evaluated. Immersion at 80°C in water alone or with NaOCl killed both free teliospores and those within the sori of infected seeds within 1 min. NaOCl at 1.60% at 25°C killed teliospores suspended in water within 15 min, but some teliospores inside sori survived 30 min of this treatment. NaOCl adjusted to pH 8 before use was superior to NaOCl at pH 11.5. An application of 1.60% NaOCl at 25°C for 5 min followed by a 10-min delay before the seeds were rinsed in fresh water killed free teliospores but not all teliospores within sori. This treatment was more effective than the 5-min treatment alone but inferior to the 15-min treatment with NaOCl at a concentration of 1.60%. Because teliospores within the sori of infected seeds are partially protected and much more resistant to NaOCl, we recommend the removal and disposal of seeds from equipment before the treatments are applied. NaOCl radically altered the appearance of the teliospores, leaving a persistent visual indication that they had been treated, while hot water treatment alone did not. Therefore, it is beneficial to add NaOCl to hot water, although the improvement in the sporicidal efficacy was often small.