Application of a hydrothermal-calcium chloride treatment to inhibit postharvest anthracnose development in papaya

• HT-Ca delayed anthracnose appearance on papaya.
• Mycelial growth was inhibited by HT-Ca.
• HT-Ca melted the cuticular wax and covered fruit stomata.

Anthracnose is considered an important postharvest disease in papaya. The hydrothermal treatment (HT) and calcium chloride (Ca) have been shown to be effective to inhibit anthracnose. The objective of this study was to investigate the effect of the combination HT-Ca on the development of anthracnose in papaya. Fruit were inoculated with Colletotrichum gloeosporioides by immersion in a spore suspension and then were divided into two groups: one received a HT treatment (48 °C, 20 min) combined with Ca (1% w/v, 20 min) and the other was used as control. Afterwards, fruit were stored during 20 days at 12 °C to allow the development of the fungal infection. Anthracnose incidence and severity were estimated visually while the development of the disease was analyzed by light and electron microscopy. HT-Ca reduced anthracnose incidence and severity compared with the control. Microscopy analysis showed that HT-Ca melted the epicuticular wax, which covered most of the stomata; this resulted in a lower mycelial growth in HT-Ca fruit with respect to the control samples. HT-Ca also induced the formation of round shaped vesicles, which corresponded with the greater accumulation of total phenolics observed in treated fruit. HT-Ca was effective to delay the symptoms of anthracnose up to 10 days during storage of papaya at 12 °C.