Studies on the Control of Postharvest Fungal Diseases in Some Fruits and Vegetables

Abstract

Postharvest losses of fruits and vegetables reached very high value representing more than 25% of the total production in developed countries and more than 50% in developing countries. Postharvest losses have not received the consideration that the degree of the problem requires. Economical losses due to postharvest decays are very significant globally. Fungicides are the chief source of controlling postharvest losses caused by diseases. Public fear in food safety and the increase of pathogen resistant population has boosted the interest in developing alternatives to fungicides to control postharvest fungal diseases. The research in biological control using antagonistic microorganisms has been developed as an important food safety alternative. In the present study epiphytic fluorescent Pseudomonas and epiphytic yeasts from healthy fruits of tomato, melon, mango, orange, green chili, lemon and grape fruit were isolated. Selected isolates were applied on three main commodities of Pakistan, mango, citrus (Kinnow) and tomato at postharvest stage during storage at room temperature to evaluate their potential to control postharvest losses. Beside the use of biocontrol in this study attempts were also made to evaluate plant extract and essential oils for their potential in the control of postharvest losses caused by fungal disease. Pathogenic fungi were isolated from diseased tomato, kinnow, lemon, green chili, melon and mango. These fungi were identified as Penicllium digitatum, Alternaria alternata, Fusarium oxysporum, Fusarium solani, Aspergillus niger and Botryodiplodia theobromae. Epiphytic fluorescent Pseudomonas and epiphytic yeast were isolated from healthy fruits of melon, lemon, mango, green chili, grape fruit and mango. Thirty isolates of Epiphytic fluorescent Pseudomonas and twenty five isolates of epiphytic yeast were tested for their in-vitro antifungal activity against isolated pathogenic fungi from diseased fruit: Penicllium digitatum, Alternaria alternata, Fusarium oxysporum, Fusarium solani, Aspergillus niger and Botryodiplodia theobromae. Majority of isolates from fluorescent Pseudomonas successfully inhibited the mycelial growth of all fungal pathogens except HAB-23 and HAB-27 which showed either no or least activity against P. digitatum. Isolates from yeast: HAB-43, HAB-46 and HAB-49 failed to inhibit the growth of P. digitatum in-vitro. In our study, eight isolates of epiphytic yeast (HAB-45, HAB-48, HAB-31, HAB-35, HAB-47, HAB-51, HAB-53 and HAB-44) and three isolates of epiphytic fluorescent Pseudomonas (HAB-10, HAB-25 and HAB-15) were tested individually and in combination for their biocontrol activity against postharvest losses of orange (kinnow), mango and tomato fruits. Individual as well as combined treatments have shown significant results in terms of quality retention and control of postharvest fungal losses compared to the control set. Epiphytic yeast and fluorescent Pseudomonas used individually or in combination successfully minimized the undesirable changes in the physiochemical properties of all three types of fruits during storage as compared to control. However, their biocontrol pattern varies from produce to produce. In case of yeast individual treatment with HAB-31 and HAB-53 has been more promising showing least percent decay than other yeast isolates treatments given to mangoes. HAB-31, HAB-47 and HAB-53 showed complete control of postharvest decay in oranges showing their maximum potential against postharvest losses in kinnow. HAB-31, HAB-53 and HAB-44 demonstrated strong potential to control the decay of tomato fruits during 15 days of storage. Epiphytic fluorescent Pseudomonas isolates namely HAB-10 and HAB-25 controlled the postharvest decay of mangoes with minimum quality loss up to ten days showing decay percent less than the positive control, while HAB-15 has shown its potential equivalent to positive control (1 % K-sorbate). Results of three isolates of fluorescent Pseudomonas HAB-10, HAB-15 and HAB-25 showed good control of postharvest decay than positive control. However the results of HAB-25 were more promising in case of oranges and demonstrated maximum control of decay and maintaining quality. In tomato fruits HAB-10 and HAB-15 have shown maximum control of postharvest losses with zero percent decay compared to HAB-25. Combined action of epiphytic yeast with fluorescent Pseudomonas (HAB-41+HAB-10, HAB-31+HAB-1, HAB-53+HAB-25) showed very good control of postharvest decay in tomato compared to positive control and control. In case of oranges combined treatment of HAB-41+HAB-10 and HAB-31+HAB-1 were more effective, however HAB-41+HAB-10 showed minimum decay and retained quality maximum. Treatment with HAB-53+HAB-25 have shown control of anthracnose infection on mangoes in comparison of control set, however decay control was not very significant till the end of storage period of ten days. In the current study oranges were sprayed with Penicillium digitatum to produce infection and were treated with epiphytic yeast. The results showed that yeast has the potential to control decay caused by Penicillium digitatum in oranges compared to control and positive (K-sorbate) control during sixteen days of storages period at room temperature. The effect of refrigerated temperature was also studied on postharvest losses in mango treated with biocontrol yeast. Mango fruits showed positive impact of refrigerated temperature in the control of postharvest losses and showed zero percent decay. However isolates of epiphytic yeast HAB-31 and HAB-40 demonstrated better control of postharvest decay (41.62 %) of mango in comparison with control (91.65 %) at room temperature. Identification and genetic variation between selected fluorescent Pseudomonas isolates including HAB-1, HAB-2, HAB-5, HAB-8, HAB-9, HAB-12, HAB-14, HAB-15, HAB-21, HAB-24, HAB-29 and HAB-30 were confirmed by using PCR amplification of 16SrDNA and RFLP analysis of 16S rDNA gene PCR products obtained by the restriction enzyme Hae-III. Yeast isolates viz; HAB-31, HAB-35, HAB-44, HAB-45, HAB-47, HAB-48, HAB-51, HAB-53 and HAB-54 were identified on molecular basis by PCR amplification of internal transcribed spacer sequences (ITS DNA) as a molecular marker of yeast identification and RFLP analysis of ITS gene was obtained by the restriction enzyme Hae-III. Traditionally, berberine species are known for their medicinal properties. The antimicrobial activity and control of postharvest fungal diseases of horticulture commodities of Berberis pseudumbellata has not been reported so far. This is the first report on antimicrobial activity of ethanol extract of B. pseudumbellata fruits and its use in the control of fungal diseases of fruits and vegetables. Ethanol extract of B. pseudumbellata fruits was used for the study of its in-vitro antimicrobial activity against bacteria (Bacillus subtilis, E. coli, S. aureus, P. syringae) and mycotoxin producing fungi (Fusarium oxysporum & Aspergillus niger).. Fruit extract of B. pseudumbellata successfully inhibit the growth of bacteria and fungi by forming zone of inhibition. Ethanolic fruit extract of B. psedumbellata was further used to control postharvest decay of tomato, citrus (kinnow) and mango fruits on the basis of its effective in-vitro antimicrobial activity. Ethanol extract of fruits of B. pseudoumbellata was used to control postharvest decay of tomato, citrus (kinnow) and mango. Results of ethanolic extract of B. pseudoumbellata demonstrated the successful control of postharvest losses of tomato and kinnow at the concentration of 800 mg/L up to fifteen days, while in mangoes, 800 mg/ L of fruit extract showed slight decay (16.66 %) after nine days of storage. In this study essential oils from cinnamon, coriander, and yellow mustard were also evaluated for their ability to control postharvest fungal losses in same commodities i.e. tomato, Kinnow and mango. Cinnamon oil showed 100 % control of fungal deterioration in citrus up to fifteen days of storage period while in mango and tomato the control of postharvest fungal losses was comparatively less. In the study very good biocontrol of postharvest diseases by epiphytic yeast and epiphytic fluorescent Pseudomonas was observed. The study revealed epiphytic fluorescent Pseudomonas as a new biocontrol that could be utilized for the control of postharvest disease of fruits and vegetables in future.