Evaluation of seed treatments against Colletotrichum kahawae subsp. cigarro on Eucalyptus spp.

Abstract

Anthracnose leaf spot is a common disease caused by Colletotrichum species. Non-chemical seed treatments that included Bacillus, Trichoderma, hot water, microwave radiation, and hydrogen peroxide were evaluated at disinfecting Eucalyptus seeds infected with Colletotrichum kahawae subsp. cigarro. The seed treatments were assessed on Eucalyptus grandis and E. nitens seed lots. When both reduction in the incidence of Colletotrichum and increased seed germination are considered, hot water seed treatments at 55 °C for 15 min and 60 °C for 1 min were optimum treatment/time parameters for Eucalyptus. Seed germination improved when Eucalyptus seeds were soaked in 10% H2O2 for 10 min to the equivalent of that of the chemical seed treatment (Celest® XL). Exposure of moist Eucalyptus seeds to microwave radiation of 1400 W for 30 s was the only microwave power-time combination that significantly improved seed germination similar to that of the Celest® XL treatment. In -vitro assays showed no diseases on seedlings raised from seeds soaked in hot water baths set at 55 and 60 °C for 15 min and above, and seeds soaked in 10 and 15% H2O2 for 5 min and above. Moreover, no disease symptoms were observed on seedlings raised from moist seeds exposed to microwave radiation at 1400 W for 90 s and above or dry seeds exposed to microwave radiation at 1400 W for 120 s and above. Bacillus, however, was the only non-chemical seed treatment that demonstrated effectiveness against anthracnose leaf spot under greenhouse conditions.