Induction of resistance to Penicillium digitatum in tangerine fruit cv. Sai Num Phung flavedo by hot water treatment

Abstract

The effects of hot water treatment (HWT) were investigated for enhancing host resistance to green mold rot caused by Penicillium digitatum. Tangerine fruits cv. Sai Num Phung were dipped in hot water at 50±2°C for 3 minutes and 55±2°C for 2 and 3 minutes after inoculation with P. digitatum and then stored at 4±2C with 90±5% relative humidity for 30 days. The results showed that the HWT remarkably delayed the onset of disease infection, reduced the number of infected fruits and lowered the severity of infection (lesion diameter). The chitinase and β-1,3-glucanase activities in flavedo tissues of treated fruits increased after storage for 15 days, but activity of peroxidase increased after storage for 25 days, compared with untreated and uninoculated fruits. The protein patterns of tangerine fruit peels treated with HWT appeared to have 112.20 and 100.00 kDa proteins only on the fifth day of storage which indicated that HWT led to heat stress circumstances in the fruit peel tissue and induced biochemical changes. The protein patterns of HWT treated fruit at 22.39 kDa exhibited thicker band compared to untreated and uninoculated fruit peels. The findings indicated that HWT reduced disease incidence partly by inducing defence mechanism in the fruit peel tissue.