Direct inhibitory effect and enhanced antifungal activity of postharvest soluble silica treatment against anthracnose and crown rot pathogens in banana

Abstract

Soluble silica (Si) treatment has been reported to control postharvest fungal diseases and extend shelf life of bananas. In this study, the effects of soluble silica treatment on antifungal activity of fruit peel and direct inhibitory effect against anthracnose and crown rot (CR) pathogens in banana were investigated. Mature banana cv. ‘Embul’ fruits, treated with potassium silicate (1500 μg mL-1 K2SiO3 solution for 20 min) or with water (control) were artificially inoculated with anthracnose pathogen (Colletotrichum sp.) and CR pathogen (Lasiodiplodia sp.), and assessed for anthracnose lesion diameters and CR Index. Bioassays with Cladosporium and Colletotrichum sp. were performed to assess antifungal activity in ethyl acetate extracts of Si treated (Si+) and control (Si-) fruit peel tissues. Total phenolic (TP) contents of Si+ and Si- peel extracts were determined by Folin Ciocalteu assay. To test direct inhibitory effect of Si on growth, the two pathogens were grown in Potato Dextrose Broth (PDB) media amended with silica (0, 500, 1000, 1500 and 2000 μg mL-1) and harvested for mycelial dry weights and spore counts. A significant delay in symptom development and reduction of severity of both diseases was observed in Si+ fruits. In bioassay plates, three antifungal zones (Rf = 0.14, 0.48, 0.79) appeared in both Si+ and Si- extracts, indicating them to be pre-formed antifungal compounds (phytoanticipins). Si+ extracts showed higher antifungal activity and TP levels. Reduction of mycelial growth and spore production was observed with increased Si levels in PDB. Si-enhanced resistance to fungal rots in bananas can be partly attributed to enhanced phytoanticipin levels, including phenolics, and direct inhibitory effect on pathogens.

Keywords

• anthracnose, banana, crown rot, soluble silica