Efficacy of hot water, hypochlorite, organic acids and natamycin in the control of post-harvest fungal infection of chestnuts

A study was undertaken on the efficacy of hot water treatment (70degrees, 80degrees and 90degreesC for 5 and 10 min), chlorination (100 and 150 mg 1(-1) available (free) chlorine for 15,30 and 45 min), organic acids (sorbic and propionic acid solutions at 1, 2 and 3% (w/v) for 1 min) and natamycin (50,100,150 and 200 mg 1-1 for 1 min) in suppressing fungal growth on harvested chestnuts. After treatment, the nuts were enclosed in plastic bags and incubated at 25degrees +/- 1degreesC for 20 d. Results were expressed as the proportion (%) of infected chestnuts (infection incidence). Hot water at 70degrees and 80degreesC did not control fungal growth. However, treatment at 90degreesC for 10 min reduced the infection level by 95%. Chlorination with sodium hypochlorite solution reduced the incidence of infection. The best treatments were 150 mg 1(-1) for 30 and 45 min, which reduced infection by 65% and 68%, respectively. Sorbic and propionic acids were very effective in suppressing fungal growth, even at the lowest concentration applied (1% (w/v) for 1 min), with sorbic acid having greater efficacy that propionic acid. Natamycin was the best treatment, completely controlling fungal infection even at the lowest concentration of 50 mg 1(-1).