Effect of Betel leaf extract on the control of stem-end rot disease and overall quality retention of Papaya (Carica papaya L.) during cold storage

Postharvest losses of papaya due to fungal diseases is one of the major problem in fruit industry in Malaysia and worldwide. Stem-end rot an important postharvest fungal disease in papaya fruit is caused by Lasiodiplodia theobromae (synonym Botryodiplodia theobromae) This pathogen is a causative agent for the stem-end rot diseases in many other fruits such as Mango, Rambutan, Avocado, Annona and Citrus fruits. No specific control measures have been developed for this disease however, field sprays with systemic and contact fungicides could reduce field inoculum levels and reduce disease incidence. Moreover, due to developed resistance in pathogen and health concerns, there is a great demand to find alternatives to synthetic fungicides. Betel leaves, Piper betle L., widely available in Malaysia and Asian region, has been known for its antifungal and antimicrobial activities due to its bioactive chemical constituents, such as hydoxychavicol, fatty acids (stearic acid and palmitic acid) and hydroxy fatty acid esters. However, for Piper betel L., most of the studies were carried out to find the antibacterial property of the plant, especially with human pathogens. The aim of this study was to evaluate the in vitro and in vivo efficacy of Betel Leaf Extract against L. theobromae, stem-end rot pathogen of Papaya and many other fruits. Two crude extracts were used for this research, one was Betel leaf extract in propylene glycol (BLPG) and Betel leaf ethanol extract (BLET). 6%, 8%, 10%, and 12% concentrations of each type of Betel Leaf extracts, were tested for their antagonistic potential against L. theobromae. Maximum inhibition in radial mycelia growth 98.48% and 93.67% of L. theobromae was observed in 12% Betel leaf ethanol extract(BLET) and 12% Betel leaf propylene glycol(BLPG) extract respectively, as compared to the control. Maximum spore germination inhibition 93.2% was observed in 12% Betel leaf ethanol extract. Scanning Electron Microscopy (SEM) images revealed that morphological changes in fungal hyphae and fungal conidial spores and complete cell lysis, with 10% and 12% of Betel leaf extract. In vivo studies show that, percentages of disease Incidence and disease severity of coated papaya during 28 days of cold storage (10+2oC,80%RH), is significantly low in coated fruits with Betel leaf extract as compared to the control. Assessment of weight loss, colour development, firmness, soluble solids content (SSC), titratable acidity (TA) and antioxidant level (Ascorbic acid and Lycopene content) of the fruits during the cold storage at 10+2oC (RH 80%) period was initially conducted at regular intervals for 28 days. Significant increase (p < 0.05) in the SSC, TA and Antioxidant amount of papaya was observed in response to the treatment with edible coating BLET and BLPG, along with delayed firmness loss. This provided physiological evidence of a relationship between treatment of Betel leaf extract edible coating and enhanced quality attributes in papaya ‘Sekaki’. In the present study, fruit treated with BLET and BLPG did not show the greatest changes in colour development and weight loss, despite better disease control provided by Betel leaf extracts, suggesting that fruit treated with BLET and BLPG delayed physiological changes in papaya fruit hence resulting in firmer fruit. Preliminary sensory results also confirmed the efficacy of using composite coatings based on Betel leaf extract. Delay ripening of fruit was obtained with the low ethylene production and low respiration rate in BLET coated papaya fruits. The present results are the first to show that extracts from Betel leaf extract can act as antifungal agents against stem-end rot disease in papaya. It can be concluded from this study that 60% control of stem-end rot disease on papaya in the 28 days cold storage at 10+20C (RH 80%) achieved with 12% BLET extract combined with 1% Tween80. This could be considered as an effective and potential edible coating as an alternative to synthetic fungicides. This extract might be particularly suitable for the papaya growers and exporters as a postharvest biopesticide. In conclusion, Betel leaf ethanolic extract can be fruitfully utilized as an eco-friendly “green fungicide” to reduce stem-end rot disease at 12% concentration and extend quality and shelf-life of papaya in cold storage, thus minimize the postharvest economic loss