Evaluation of commercial chitosan and aqueous extracts of coconut shell (Cocos nucifera L.) for the control of Rhizopus stolonifer isolated from soursop (Annona muricata L.): In vitro tests

Abstract

The antifungal effectiveness of aqueous extracts of coconut mesocarp (Cocos nucifera L.) (AEC) and commercial chitosan (CQ) applied individually and in combination was evaluated against Rhizopus stolonifer in terms of mycelial growth, sporulation, spore germination, as well the primary growth models at two storage temperatures (15-25 ^oC) was obtained. The use of AEC applied individually, significantly reduced the mycelial growth of R. stolonifer (> 45 %); on the other hand, CQ (1.5 %) showed up to 87 % of control, however, the combination of AEC (10 %) with CQ (1.5 %) was more effective in reducing mycelial growth (> 93 %). All treatments were effective in inhibiting spore production (> 94 %) compared to control (agar). CQ combined with AEC was more effective by inhibiting the germ tube elongation (> 98 %) compared to the individual treatments (< 48 %). The modified Gompertz model showed an adequate fit for both temperature ranges (> 98-99 %), observing significant differences (p ≤ 0.05) between the variables maximum speed (V_max) and latency period (ƛ), however all treatments showed a fungistatic effect on the mycelial development of R. stolonifer. The combination of AEC and CQ can be an eco-friendly alternative against soft rot in soursop fruits.