Plant Extracts in Post-Harvest Disease Management of Fruits and Vegetables-A Review

Findings: Plant products are an important source of agrochemicals used for the control various post harvest loses which include diseases as well as insect pests. The widely studied plants in this context are the neem tree (Azadirachta indica), chinaberry (Melia azadrach) and marigold (Tagetes spp). They are being used to manufacture natural or bio insecticides, which are environmental friendly and do not have any toxic effects on plants and soil. More ever they possess fungicidal and insecticidal properties. Various extracts such as neem leaf extract, castor oil and neem oil on citrus fruits and reported that, among these extracts neem was best in retaining most of biochemical characteristics such as TSS (16.01°B), acidity (0.38%), pectin (0.98%) and ascorbic acid content (20.56 mg/100 ml juice).


Introduction
Although satisfactory control of the disease by using various chemicals have been documented in the literature [1][2][3] during recent years, global concern for protection of the environment has led researchers to investigate the use of natural flora as one of the sources for crop protection [4].
Antimicrobial activity of water and ethanolic extracts from five medicinal plants against bacteria isolated from disease fairy shrimps. The antimicrobial efficacy of Andrographis paniculata, Garcinia mangostana, Psidium guajava, Punica granatum and Terninalia catappa was evaluated against four gram negative bacteria including Aeromonas sobria, Klebsiella pneumonia, Enterobacter sp. and Chryseobacterium sp. using agar well diffusion method at three concentration levels (100, 10 and 1 mg/ml). Among the tested plants, Punica granatum extract showed the highest level of antimicrobial activity against all four bacterial strains at 10 mg/ml. The ethanolic extract of Punica granatum was very active against Aeromonas sobria at a concentration of 3.125 mg/ml. A considerable amount of work has been carried out all over the world on the effect of plant extracts on the quality and shelf life in various fruit and vegetable crops. Fungal infections are one of the major causes of post harvest rots of fresh fruits and vegetables whether in transit or storage. They cause significant economic losses in the commercialization phase,and are rendered unfit for human consumption. Neem (Azadirachta indica A. Juss) and chinaberry (Melia azadrach) are two trees belonging to the mahogany family (Meliaceae). Neem is an evergreen tree [5], whereas chinaberry is a deciduous tree native to South Asia Australia. Fishwick [6] and Eeswara [7] studied the reputed value for its antifungal properties. Siddiqui et al. [8] evaluated the efficacy of leaf extract of neem (Azadirachta indica) and Chinaberry (Melia azadrach) against two tomato pathogenic fungi Alternaria solani and Fusarium oxysporium, the causal agents of early blight and wilt disease of tomato plants respectively were studied. Leaf extracts of different concentration (5%, 10%, 15% and 20%) of aqueous, ethanol and ethyl acetate of neem and chinaberry were added to growth media prior to inoculation. Inhibition values recorded characteristic variation between neem and chinaberry. In case of neem inhibition percentages were 17.88%, 23.66%, 52.77% and 70.50%against Alternaria solani. While for F. oxysporum were 14.77%, 23.88%, 31.22% and 100% for all four concentrations used. Whereas for chinaberry inhibition values for Alt. solani is3.11%, 5.22%, 5.53%, and 5.77% and 5.44%, 6.11%, 6.35% and 6.55% for F. oxysporum [9]. The efficacy of the two plant extracts against the tomato fruit rot fungi was tested in vitro. The results showed that, the extracts significantly (P < 0.05) inhibited the mycelial growth of the fungal pathogens at the different concentrations tested and the rate of inhibition differed from one extract to the other. Ilondu et al. [10] reported that some plants contain phenolic substances and essential oils, which are inhibitory to micro-organisms. The presence of these compounds in these extracts has been reported to be responsible for their antifungal properties [11]. These antifungal properties control various pests including fungi while the extract of ginger rhizomes is specially valued for their effectiveness against fungi [11].
properties. Biopesticides are a good alternative to the synthetic pesticide. Both leaves and fruit of neem plant are known to have bitter taste having fungicidal, insecticidal and nematicidal properties. Azadirachtin, chemically a tetranorterpenoid component of neem acts on the mitotic cells and blocks the microtubule polymerization. Certain activities of genes and proteins are also altered by azadirachtin. As a botanical insecticide azadirachtin is effective against many biological processes. It may cause a reduction in feeding habit, suspend the molting process, larvae and pupae death and also cause sterility in the emerging adults, this all depend on the given dose. Apart from azadirachtin, many other components of neem also have insecticidal properties. Among them are saponins that are found to have antimicrobial activity that inhibits moulds and protecting plant from attack of insects [12]. Many biologically active compounds have been isolatedfrom neem, Azadirachta indica A. Juss, including triterpenoids, azadirachtin [13] and melantriol [14]. This reduced the feeding of insects. Azadirachtin is a mixture of seven isomeric compounds as Azadirachtin-A to Azadirachtin-G of which Azadirachtin-E is the most effective insect growth regulator [15]. Azadirachtin possess insecticidal, ovicidal, antifeedant and growth inhibiting effects against many insect pests [16][17][18]. Azadirachtin has minimal impact on nontarget organisms and is compatible with other eco-friendly bio control agents [19]. Effects of a botanical pesticide, azadirachtin, were evaluated on non-target aquatic macroinvertebrates found in SW Montana. A neem product formulated for commercial use and its petroleum-based, inert carrier alone were used to test the hypothesis that a commercial, U.S. Environmental Protection Agency-approved formulation of the pesticide, azadirachtin-A, derived from extracts of neem tree seeds, Azadirachta indica A. Juss. (Family: Meliaceae), is toxic to nontarget aquatic macroinvertebrates in Montana river systems. LC50 s (24 h) for 5 insect species, Drunella grandis (McDunnough), Drunella doddsi (Needham), Skwala parallela (Frison), Brachycentrus occidentalis Banks, and Brachycentrus americanus (Banks), and 1 isopod species, Caecidotea inter-media (Forbes) varied from 1.8 ppm to 9.2 ppm of the full formulation. The full formulation consisted of: azadirachtin (3% wt:wt); other neem-extracted material (32% wt/wt); petroleum solvents (65% wt:wt). LT50 s for 4 ppm of this formulation was 9.4 to 748 hours for these peld-collected macro-invertebrates. Without azadirachtin, but with the petroleum-based carrier, LT50 s was 13.6 h to 46.7 h. These bioassays conducted late in winter and early spring of 1994 and 1995 and late summer and early fall of 1994 indicated mortality from the neem formulation was similar to herbicides 2,4-D and picloram, but mortality could be accounted for by action of petroleum solvents in the inert materials. This suggests the registration process of new pesticides should also include documented potential toxicity of inert components in the formulation to non-target aquatic insects [20]. Marigold belongs to the genus Tagetes (Asteraceae) with 56 species and includes the popular ornamental budding plants known as marigolds. Deshmukh et al. [21] have reported the beneficial effect of Tagetes erecta flower on various horticultural and agricultural crops, which are attributed primarily to the presence of an organic compound 'camacin' exhibiting antifungal and insecticidal effect. Chauhan et al. [22] treated apple cv. Starking delicious with plant leaves/flower based formulation of neem leaf extract (10%, 20%), spearmint (Mentha spicata) leaf extract (10%, 20%), marigold (Tagetes erecta) flower extract (10%, 20%) and semper fresh (control 1.5%). Freshly harvested fruits were treated with above treatments and were kept under refrigerated storage (1 ± 1°C) for analysis at a month interval up to 180 days. Among treatments, 20% spearmint leaf extract proved to be highly effective in reducing fruit spoilage followed by 20% neem leaf extract. Fruit treated with 20% drake leaf extract proved to be most effective treatment in reducing weight loss and also 20% drake and 20% neem leaf extract were capable to retain maximum total soluble solids.
Pandey et al. [23] applied leaf extracts of Mentha and Melia to guava fruits and observed that these treatments were effective in retaining physical quality characteristics of fruits as they reduced moisture loss and storage rot symptoms. Rameshwar et al. [24] also observed that a combination of neem leaf extract at 20% + UV radiation exposure for 10 minutes + rice starch 6% proved to be the most appropriate treatment in minimizing the reduction of juice contents and fruit rotting and fluctuation in physiological loss in weight was also minimum as compared to control.
Hasabnis and D' souza [25] reported beneficial effects of natural plant products for the control of storage rots in Alphonso mango. They further reported that these treatments also checked the incidence of disease development in banana. Neem is the most promising and widely used against a number of insect pests due to its versatile mode of action. It has a broad spectrum action on insects and is very useful. However, the problems of quality, shelf life, presence of aflatoxins and phytotoxicity limit its efficacy and eco-safet. Rameshwar et al. [26] observed that a combination of neem leaf extract at 20% + UV radiation exposure for 10 minutes + rice starch 6% proved to be the most appropriate treatment in minimizing the reduction of juice contents and fruit rotting and fluctuation in physiological loss in weight was also minimum as compared to control. Wijewardane and Guleria [19] studied about the concentration (1.5-2%) of neem oil as a surface coating along with pre-cooling at 10°C was the most effective in providing a better physico-chemical umbrella, significantly lowering the fruit spoilage. The neem oil surface coating along with shrink-wrapped tray packing at 2°C (85% to 90% RH) resulted in the longest storage life up to 150 days. Among the rates tested, the highest retention of fruit firmness, and pectin content, anthocyanin pigments, and polygalacturonase enzyme activity in fruits was recorded by 20%marigold extract, surface coated with shrink-wrapped tray packing along with pre-cooling. Arya [26] reported that higher concentration (75%) leaf extract of neem was effective in reducing spores (82.3%) of two fruit rot pathogens, Phomopsis psidii and Phomopsis viticola. From Table 1 the pre and post inoculation rot could not be checked completely by any plant extract but, the disease severity was reduced with all the plant extracts in comparison to control [27].
Chauhan and Joshi [22] reported the efficacy of phytoextracts on the storage quality of mango cv. Ratna and found them significantly better in retaining total soluble solids and sugar contents and in reducing reduction in the possible incidence of anthracnose pathogen in comparison to untreated fruits where lower soluble solid and sugar content and higher incidence of anthracnose pathogen was reported. The increase in TSS and sugar content may be due to the hydrolysis of insoluble polysaccharides into simple sugars. Such changes are expected to be slower and more gradual when the metabolism of  Srivastava and Lal [34] reported that leaf extract of Azadirachta indica was effective in the control of fruit rot of pear and pomegranate. Sindhan et al. [35] reported the beneficial effects of neem, eucalyptus, tulsi, datura, bougainvillea and ginger on the bio-chemical and physical quality characteristics of citrus and mango fruits, as these extracts significantly reduced moisture loss and retained higher soluble solid content over the uncoated fruits. Rameshwar et al. [24] observed that a combination of neem leaf extract at 20% + UV radiation exposure for 10 minutes + rice starch 6% proved to be the most appropriate treatment in minimizing the reduction of juice contents and fruit rotting and fluctuation in physiological loss in weight was also minimum as compared to control ( Table 2). Bhardwaj and Sen [36] observed that PLW, rotting, loss in juice content and reduction in diameter of fruits of sweet orange cv. Nagpur Santra under zero energy cool chamber + 20% neem leaf extract were significantly less, whereas high under ambient condition + 10% neem leaf extract after 42 days of storage. Borthakar et al. [37] conducted experiments on the effects of neem leaf (5%), melia leaf (5%) garlic (5%) and neem oil (2%) on physicochemical characteristics of Baramasi lemon fruit and concluded that among various treatments neem leaf extract and melia leaf extract was better in retaining most of the physico-chemical characteristics of fruits.
Chauhan et al. [38] treated apple cv. Starking Delicious with plant leaves/flower based formulation of neem leaf extract (10%, 20%), spearmint (Mentha spicata) leaf extract (10% and 20%), marigold (Tagetes erecta) flower extract (10%, 20%) and semper fresh (control 1.5%). Freshly harvested fruits were treated with above treatments and were kept under refrigerated storage (1 ± 1°C) for analysis at a month interval up to 180 days. Among treatments, 20% spearmint leaf extract proved to be highly effective in reducing fruit spoilage followed by 20% neem leaf extract. Fruit treated with 20% drake leaf extract proved to be most effective treatment in reducing weight loss and also 20% drake and 20% neem leaf extract were capable to retain maximum total soluble solids. Similar findings have been reported by Ali et al. [39], Abid and Maqbool [40] on tomato fruits. Bhardwaj and Sen [37] studied the effect of different concentrations of neem leaf extracts on the storage quality of mandarin (Citrus reticulata) cv. Nagpur Santra and reported that among various treatments used neem leaf extract (20%) was significantly better in retaining higher ascorbic acid content (27.17 mg/100 ml. of juice) as compared to control fruits where it was only after storage. Chaudhary [41] reported that aqueous extracts from different plants can be a viable alternative to chemicals in controlling post-harvest pathogens as they are environmentally safe strategies for controlling the post-harvest storage pathogens in different crops. Singh et al. [42] also reported the effect of various extracts such as neem leaf extract, castor oil and neem oil on citrus fruits and reported that, among these extracts neem was best in retaining most of biochemical characteristics such as TSS (16.01° B), acidity (0.38%), pectin (0.98%) and ascorbic acid content the commodity is slowed down by the application of various coating treatments, pre-cooling and under low temperature storage.
Tiwari [28] Rao and Singh [29] have reported beneficial effect of various botanical extracts such as neem leaf extract, Melia leaf extract, onion extract, garlic extract, mahua extract and eucalyptus extract on the post-harvest quality of fruits and vegetables. They are also reported to act as antifeedent and antirepellent agents against various storage pathogens. Rameshwar et al. [24] observed that a combination of neem leaf extract at 20% + UV radiation exposure for 10 minutes + rice starch 6% proved to be the most appropriate treatment in minimizing the reduction of juice contents and fruit rotting and fluctuation in physiological loss in weight was also minimum as compared to control.
Deshmukh et al. [21] have reported beneficial effects of Melia (Melia Azadirachta) and bavistin in controlling the storage fungi and insect-pests. They have also advocated commercial use of Melia extract as a substitute for fungicides and insecticides. Melia azedarach L. extracts were studied in comparison with selected biorational insecticides against the citrus leaf miner Phyllocnistis citrella Stainton under field conditions. Citrus limon (L.) Burm. F. trees were exposed to: Melia extracts of green and mature fruits, Neem oil (30% a.i.), abamectin (1.8% a.i.) and control. Two sprays of each treatment (except for Melia mature fruit extract) were executed at 10-day intervals. The live number of the 1 st and later (2 nd & 3 rd ) larval instars per leaf were recorded at initial sampling date and at 10-day intervals after each spray application. Results indicated that there were significant differences in the number of live larval instars among treatments. Melia extracts and the two biorationals, neem oil and abamectin, decreased the larvae population significantly to lower numbers than that of the control at 10 days after each spray application. However, the decrease caused by neem oil and abamectin was significantly higher than that of Melia extracts. Thus, these extracts might be considered as potential alternative with other biorational control methods in management of the leaf miner. Further research including bioassays is needed to determine the factors responsible for reducing larvae population and whether these Melia extracts can be utilized in future citrus IPM programs as a tool for citrus leaf miner management [30].
Lehmann and Ibenthal [31], Bottenburg and Singh [32] reported beneficial effects of treatments with neem leaf and mentha leaf extract on the marketing quality characteristics of cow pea and sugar beet and concluded that these treatments were effective in retaining the physicochemical characteristics of these crops. The TSS, acidity, phenols and ascorbic acid showed less decrease as compare to the control. In control the degradation of quality is more as compare to that of treated with neem leaf and menthe leaf extract. Sarvamangla [33] studied the effect of leaf extracts from Azadirachta indica, Calotropis gigantean, Calthranthus sp. Eucalyptus sp., Parthenium chysterophorus and Pongamia pinnata on fruit quality of mulberry and reported that among these extracts Azadirachta indica was the most effective in retaining higher sugar content, maintaining fruit size and shape, and resistance to fungal pathogens. Azadirachta indica control the fungal pathogen more effectively and retaining the maximum sugar content  (20.56 mg/100 ml juice) as compared to control fruits in which the values for these parameters were 12.03° B, 0.23%, 0.55% and 15.68 mg/100 ml juice, respectively after 12 days of storage.
Singh et al. [43] observed that the quality of untreated mango cv. Langra fruit started deteriorating after about two weeks of storage and the fruits became unacceptable after five weeks. However, the fruits were reported to be acceptable even after five weeks of storage when they were given post-harvest dip of GA 3 (500 ppm) and 20% neem leaf extract and retained high pectin content (0.98%) over the control (0.55%) fruits. Singh et al. [42] tested the efficacy of aqueous leaf extracts of 20 plant species and 3 essential oils against management of Penicillium expansum rot of apple cv. Red Delicious. Among various treatments leaf extract of Azadirachta indica significantly reduced P. expansum rot when used as post-infection dip treatment. Chauhan et al. [38] treated apple cv. Starking Delicious with plant leaves/ flower based formulation of neem leaf extract (10%, 20%), spearmint (Mentha spicata) leaf extract (10%, 20%), marigold (Tagetes erecta) flower extract (10%, 20%) and semper fresh (control 1.5%). Freshly harvested fruits were treated with above treatments and were kept under refrigerated storage (1 ± 1°C) for analysis at a month interval up to 180 days. Among treatments, 20% spearmint leaf extract proved to be highly effective in reducing fruit spoilage followed by 20% neem leaf extract. Fruit treated with 20% drake leaf extract proved to be most effective treatment in reducing weight loss and also 20% drake and 20% neem leaf extract were capable to retain maximum total soluble solids. Hassanein et al. [44] studied the effectiveness of leaf extracts of neem and china berry against two tomato pathogenic fungi Alternaria solani and Fusasuim oxysporum, the causal agent of early blight and wilt disease of tomato plants respectively and reported promising results. Jakhar et al. [45] reported that the physiological loss in weight, colour, texture, shriveling and rotting of Chakaiya cultivar of aonla fruit was significantly affected by packaging materials, neem leaf extracts and diphenyl fumigation and their combination throughout the storage period up to 21 days.
Patel et al. [46] reported that the extract from Allium sativum was significantly better followed by extract of Jatropha curcas, Aloe barbadensis and Azadirachta indica in controlling Aspergillus niger of aonla fruit rot. Okigbo et al. [47] used ethanolic and water extractions of Azadirachta indica leaves and Aframomum melegueta seeds as antifungal agents against pathogenic fungi Aspergillus niger, Botryodiplodia theobromae, Fusarium solani and Penicillium oxalicum of cassava and reported that A. indica was more active on the organisms than A. melegueta in preventing post-harvest deterioration of cassava. Bhardwaj et al. [48] reported that Azadiracta indica and Chromoleana odorata were able to suppress rot-causing fungi of yam. Therefore, serve as a good natural plant fungicide (protectant) against yam tubers in storage.

Conclusion
Plant extracts are being used to manufacture natural or bio insecticides, which are environmental friendly and do not have any toxic effects on plants and soil. More ever they possess fungicidal and insecticidal properties. So these can be used as compare to synthetic/ chemical products. Various extracts such as neem leaf extract castor oil and neem oil on citrus fruits and reported that, among these extracts neem was best in retaining most of biochemical characteristics such as TSS, acidity, pectin and ascorbic acid content. Moreover the extract of neem, marigold and other plant extracts increase the shelf life of the fruits and vegetables by reducing the fungal and bacterial spoilage during storage. Neem extracts was best in retaining most of biochemical characteristics such as TSS, acidity, pectin and ascorbic acid content. Plant extracts are important in order to reduce the environmental pollution by synthetic chemicals. In day to day life the world is facing the threat of global warming and pollution, in order to contribute in keeping the environment clean to some extent and reduce the residual effect of synthetic insecticide and pesticides.