Document Type : Research Article
Introduction: Strawberry (fragaria×ananassa Duch.) fruit characterized by short storage life, often estimated last less than one week even under optimum conditions at 8°C. The loss of fruit quality is often caused by gray mold (Botrytis cinerea) that is the most frequent reported postharvest disease in strawberry during storage (6). In recent years, considerable attention has given to elimination of synthetic chemical and fungicides application and development of various alternative strategies for controlling fruit and vegetables diseases (2). One strategy is replacement of natural products with plant origin such as essential oil and methyl salicylate (MeSA). Essential oils are volatile, natural and complex compounds characterized by a strong odor formed by aromatic plants in form of secondary metabolites. In nature, essential similar oils that extract from lavender (Lavandula angustifolia) play an important role in protection of the plants against pathogen incidence that can be replaced by synthetic fungicides (1, 4 and 14). MeSA is also a volatile natural compound synthesized from salicylic acid which has an important role in the plant defense-mechanism, as well as plant growth and development (5, 19 and 20). Therefore, the main objective of this research was to study the effects of MeSA and lavender essential oil (LEO) on decay control caused by Botrytis cinerea as well as post-harvest quality indices of strawberry fruits during cold storage.
Material and Methods: First, antifungal activity was studied by using a contact assay (in vitro), which produces hyphal growth inhibition. Briefly, potato dextrose agar (PDA) plates were prepared using 8 cm diameter glass petri dishes and inhibitory percentage was determined. For in-vivo assessment of LEO and MeSA effects on Botrytis-caused fungal disease control, the experiment was conducted as factorial in completely randomized design (CRD) with 3 replicates. The treatments were 3 concentration of LEO including 0, 500 and 1000 µl L-1 and 3 level of MeSA including 0, 0.1 and 0.2 mM. After treatment, the fruits were inoculated by Botrytis suspension and transferred to storage and quality parameters were evaluated after 7, 14 and 21 days. At each sampling time, disease incidence, weight loss, titratable acidity, pH, soluble solids content, vitamin C and antioxidant activity were measured.
Results and Discussion: The results showed that both LEO and MeSA treatments had significant effects on inhibition of mycelium growth within in-vitro condition (p < 0.05). Inhibition rate of mycelium growth significantly improved by LEO and MeSA concentration increase of, (Table 1). At in-vivo assessment, diseases incidence of treated fruits with 500 µl L-1 LEO and 0.1 mM MeSA were 32% and 64% lower than untreated fruits, respectively (Fig. 1 and 2). During storage period, the percentage of infected fruits increased. In addition, LEO and MeSA treatments affected quality parameters of strawberry fruits including titratable acidity, soluble solids content, vitamin C and antioxidant activity. Treated fruits had a high content of soluble solids, vitamin C and antioxidant activity in comparison to untreated fruits (Table 3 and 4). Probably ascorbic acid decreased through fungal infection duo to cell wall break down during storage. Any factors such as essential oil and salicylate that inhibit fungal growth can help preserving vitamin C in stored products. High level of vitamin C and antioxidant activity was observed in treated fruits with 0.1 mM MeSA and 500 µl L-1 LEO. In controlling weight loss of fruits, 0.2 mM of MeSA and 500 µl L-1 of LEO had significant effects, although MeSA was more effective than LEO treatments, possibly due to elimination of respiration rates and fungi infection (Table 4). Therefore, LEO and MeSA with fungicide effects could be replaced with synthetic fungicides in controlling fungal diseases of strawberry and maintain fruits quality during storage.
Conclusion: In conclusion, our results showed that LEO and MeSA treatments could be safe and used to prevent infection of strawberry during storage, although LEO was more effective than MeSA treatments. Concentration of 500 μl L-1 of LEO and 0.1 mM MeSA could control fungal infection of fruits during storage. Also, LEO and MeSA treatments can extend shelf life for over the minimum period required to transit strawberries to foreign markets and without affecting quality, adversely. However, future studies are necessary to fully understand the mechanisms by which LEO and MeSA treatments may act as a fungicide and increase their postharvest life.