Research Article
Postharvest Application of Some Essential Oils for Controlling Gray and Blue Moulds of Apple Fruits
Department of Plant Pathology, Faculty of Agriculture, Benha University, Egypt
Worldwide gray mould caused by Botrytis cinerea Pers, Fr. and blue mould caused by Penicillium spp. are the most important diseases attacking apple fruit during storage (Sholberg et al., 2003; Pianzzola et al., 2004; Janisiewicz and Peterson, 2004; Janisiewicz et al., 2005).
Using of chemical fungicides gave satisfactory control against mould infection but have residual harmful effect to human and environment (Eckert and Ogawa, 1988). Moreover, successive use of fungicides could lead to developing to some significant fungal isolates resistant to use fungicides. Therefore, alternative fungicide treatments are needed for the management of postharvest diseases of fruits (Abd-El-Latif and Abd-El-Kareem, 2009; El-Shahawy et al., 2015).
The potential of using essential oils by spraying or dipping fruits for controlling postharvest diseases has been reported by several investigators (Kanherkar et al., 2007). Essential oils are naturally including several fractions which have insecticidal and fungicidal activities against some important plant pathogens (Kanherkar et al., 2007).
Allelopathic effect of eucalyptus (Eucalyptus globulus) against plant pathogens was reported by several investigators (Suryawanshi et al., 2007; Kanherkar et al., 2007).
The essential oil of thyme (Thymus vulgaris L.) and its major component, thymol had antifungal activity against plant pathogenic fungi (Plaza et al., 2004; Angelini et al., 2006) as well as plant diseases of several fruits and vegetables (El Sherbieny et al., 2002; Klaric et al., 2007).
Essential oil extracted from lemon grass (Cymbopogon citratus Stapf.) has antifungal activity against several plant pathogens (Nguefack et al., 2007). The purpose of the present study is evaluating the effects of Eucalyptus, limon grass and thyme essential oils on linear growth and spore germination of pathogenic fungi. Moreover, their efficacy on gray and blue moulds incidence of apple fruits.
Source of pathogenic fungi and apple fruits: Pathogenic isolates of Botrytis cinerea and Penicillium sp. the causal agent of gray and blue mould diseases were kindly obtained from Department of Plant Pathology, National Research Centre, Giza, Egypt. Meanwhile, apple fruits cv. Anna were obtained from commercial markets Egypt.
In vitro inhibition of linear growth of pathogenic fungi by different concentrations of some essential oils: Essential oils of eucalyptus, lemon grass and thyme obtained from Delta Aromatic Company, Egypt at different concentrations i.e., 0.0, 0.2, 0.4, 0.6 and 0.8% (v/v) were prepared. Oil solutions were added to conical flasks containing sterilized PDA medium to obtain the proposed concentrations, then mixed gently and dispensed in sterilized petri plates (9 cm diameter). Plates were individually inoculated at the center with equal disks (5 mm diameter) of 10 day old culture of Botrytis cinerea and Penicillium sp. (obtained from Plant Pathology, Department NRC Egypt). Five plates were used as replicates for each particular treatment. Inoculated plates were incubated at 20±2°C. The average linear growth of fungi tested was calculated after 10 days.
In vitro inhibition of spore germination of pathogenic fungi by different concentrations of some essential oils: Preparation of spore suspension: Spores suspension were prepared by inoculated sterilized PDA medium with disk (6 mm diameter) taken from 10 days old cultures of B. cinerea and Penicillium sp. Plates were incubated at 20±2°C for 10 days. Spores of B. cinerea and Penicillium sp. were harvested and transferred in sterilized water (containing 0.01% Tween 80) to obtain spore suspension which was adjusted to 106 spores/mL using hemocytometers slide (Palou et al., 2001). Essential oils of eucalyptus, lemon grass and thyme at different concentrations i.e., 0.0, 0.2, 0.4, 0.6 and 0.8% (v/v) were prepared as mention before. One milliliter of each prepared spore suspension was placed in test tubes containing different concentrations of tested oils then were incubated at 20°C for 24 h. Germinated spores were counted microscopically and percentage of spore germination was calculated.
In vivo, testing of different concentrations of some essential oils on gray and blue moulds incidence of apple fruits: Sterilized water containing essential oils of Eucalyptus, lemon grass and Thyme at different concentrations i.e., 0.0, 0.6 and 0.8% (v/v) were tested to study their effect against gray and blue moulds incidence on apple fruits. Fresh apple fruits apparently free from physical damage and diseases were artificially wounded using sterilized scalpel. Fruits were dipped in sterilized water containing eucalyptus, lemon grass and thyme at different concentrations i.e., 0.0, 0.6 and 0.8% (v/v) containing 0.01% Tween 80 for 3 min, then air dried. Inoculation of treated fruits was carried out by spraying fruits with spore suspension (106 spores/mL) of B. cinerea and Penicillium sp. then air dried. All treated or un-treated fruits were placed into carton boxes at the rate of 10 fruits/box. Each particular concentration as well as control treatment was represented by three carton box. All boxes were stored at 20±2°C for 20 days. Percentage of infected fruits (disease incidence) and rotted parts of fruits (disease severity) were recorded after 20 days.
Statistical analysis: Tukey test for multiple comparison among means was utilized (Neler et al., 1985).
In vitro inhibition of linear growth of pathogenic fungi by different concentrations of some essential oils: Essential oils of eucalyptus, lemon grass and thyme at different concentrations i.e., 0.0, 0.2, 0.4, 0.6 and 0.8% (v/v) were tested to study their inhibitory effect on linear growth and spore germination of B. cinerea and Penicillium sp. results in Table 1 and 2 indicate that all treatments significantly reduced the linear growth and spore germination of both tested fungi. Essential oils of eucalyptus, lemon grass and thyme at concentration of 0.6 and 0.8% completely inhibit the linear growth and spore germination of B. cinerea and Penicillium sp. except that lemon grass at 0.6%. The highest reduction was obtained with essential oils of Thyme at concentration of 0.4% which reduced the linear growth and spore germination by 67.7 and 80.6 and 74.4 and 79.1% for B. cinerea and Penicillium sp., respectively. Meanwhile, concentration of 0.2% was less effective.
In vivo effect of different concentrations of some essential oils on gray and blue moulds incidence of apple fruits: Sterilized water containing essential oils of eucalyptus, lemon grass and thyme at different concentrations i.e., 0.0, 0.6 and 0.8% (v/v) were tested to study their effect against gray and blue moulds incidence of apple fruits.
Table 1: | Linear growth of B. cinerea and Penicillium sp. as affected with different concentrations of some essential oils |
Values with the same letter are not significantly different (p = 0.05) |
Results in Table 3 and 4 indicate that all treatments significantly reduced the diseases incidence and rotted part tissue (Disease severity).
The most effective treatment was eucalyptus and thyme at 0.8% which reduced the disease incidence more than 83.8 and 82.7% and rotted part tissue by 85.9 and 88.5% for gray and blue moulds, respectively. The highest reduction was obtained with eucalyptus and thyme at concentrations of 0.6% and lemon grass at 0.8% which reduced both diseases incidence and rotted part tissue more than 74.0 and 75.8%, respectively. Meanwhile, other treatments showed moderate effect.
Table 2: | Average percentage of spore germination of pathogenic fungi as affected with different concentrations of some essential oils |
Values with the same letter are not significantly different (p = 0.05) |
Table 3: | Percentage of gray and blue moulds incidence on apple fruits affected with different concentrations of some essential oils |
Values with the same letter are not significantly different (p = 0.05) |
Table 4: | Percentage of rotted part tissue caused by gray and blue moulds on apple fruits as affected with different concentrations of some essential oils |
Values with the same letter are not significantly different (p = 0.05) |
DISCUSSION
Worldwide gray mould caused by Botrytis cinerea Pers, Fr. and blue mould caused by Penicillium sp. are the most important diseases attacking apple fruit during storage (Sholberg et al., 2003; Pianzzola et al., 2004; Janisiewicz and Peterson, 2004; Janisiewicz et al., 2005).
Using of chemical fungicides gave satisfactory control against mould infection but have a residual harmful effect to human and environment (Eckert and Ogawa, 1988). Moreover, some fungal isolates could be resistant to used fungicides. Therefore, alternative fungicide treatments are needed for the management of postharvest diseases of fruits (Abd-El-Latif and Abd-El-Kareem, 2009; El-Shahawy et al., 2015).
Essential oils are naturally including several fractions which have insecticidal and fungicidal activities against some important plant pathogens (Kanherkar et al., 2007; Nguefack et al., 2007). In the present study results indicated that in vitro trails essential oils of eucalyptus, lemon grass and thyme at concentration of 0.6 and 0.8% completely inhibit the linear growth and spore germination of B. cinerea and Penicillium sp. except that lemon grass at 0.6%. Moreover, in vivo, trails, sterilized water containing essential oils of eucalyptus, lemon grass and thyme at different concentrations i.e., 0.0, 0.6 and 0.8% (v/v) were tested to study their effect against gray and blue moulds incidence of apple fruits. Results indicated that all treatments significantly reduced the diseases incidence and rotted part tissue (Disease severity). The most effective treatment was eucalyptus and thyme at 0.8% which reduced the disease incidence more than 83.8 and 82.7% and rotted part tissue by 85.9 and 88.5% for gray and blue moulds, respectively. The highest reduction was obtained with eucalyptus and thyme at concentrations of 0.6% and lemon grass at 0.8% which reduced both diseases incidence and rotted part tissue.
The inhibitory effect of eucalyptus against plant pathogens was reported by Harborne and Tomas-Barberan (1991) and Byron and Hall (2002). In the present study, eucalyptus essential oil completely inhibited the linear growth spore germination of P. digitatum and P. italicum. Moreover, it reduced blue and green moulds of navel orange fruits. In this respect, Singh et al. (1992) reported that essential oils from Eucalyptus has antifungal effect against plant pathogenic fungi that inhibited the growth of Fusarium sp., Colletotrichum sp., Aspergillus sp. and Alternaria alternata. The effect of volatile oil from the leaves of eucalyptus against Macrophomina phaseolina, Celletotrichum lindemuthianum, Fusarium oxysporum f. sp. lycopersici, Helminthosporium oryzae, Alternaria triticina, Rhizoctonia solani and A. solani were evaluated. They found that the volatile oil strongly inhabited the radial growth of all tested fungi and the volatile oil was more effective than the synthetic fungicide, mancozeb (Ramezani et al., 2002). Moreover, aqueous extracts from fresh and dry leaves of eucalyptus and basil significantly inhibited radial growth of P. aphanidermatium and the extract from eucalyptus were more effective as fungitoxic against P. phanidermatum (Oluma and Garba, 2002). Furthermore, Patni and Kolte (2006) reported that eucalyptus leaf extract significant reduce the radial growth, sporulation and spore gemination of A. brassicae. They also revealed that under glass house condition eucalyptus spray gave significantly lesser number of spot/leaf, minimum sporulation intensity and minimum disease index. On the other hand, the effect of leaf extracts from eucalyptus for controlling soil-borne fungi was reported by Kanherkar et al. (2007). Similar results was obtained when soil amendment with leaves, stem, bark and fruit of eucalyptus, at 5% w/w showed significant increase in germination, shoot length, shoot weight, root length and root weight of chick-pea and mung bean plants. They added that the infection by Fusarium sp., M. phaseolina and R. solani was also reduced (Dawar et al., 2007).
The essential oil of thyme and its major component, thymol had antifungal activity against plant pathogenic fungi (Plaza et al., 2004; Angelini et al., 2006). Thymol is an essential oil component from thyme (Thymus capitates L.) and has been used as medicinal drug, food preventative and beverage ingredient as well as plant diseases of several fruits and vegetables (El Sherbieny et al., 2002; Klaric et al., 2007).
In the present study, thyme essential oils in vitro trails at concentration of 0.6 and 0.8% completely inhibit the linear growth and spore germination of both fungi. In this respect, Soliman and Badeaa (2002) reported that thyme was tested for its inhibitory effect against Aspergillus flavus, A. parasiticus, A. ochraceus and F. moniliform. Results indicated that thyme at concentrations 500 ppm completely inhibited all tested fungi. Similar results was obtained by Bouchra et al. (2003), they reported that thyme, clove and cinnamon essential oils completely inhibited P. digitatum and P. italicum growth either when added into the medium or by their volatiles. Moreover, Omidbaigi et al. (2007) reported that the fungistatic and fungicidal activities of the essential oils of thyme, myrtle, clove and lime against A. flavus and showed that the most effective essential oils were found from those of thyme and clove. Thyme and clove oils completely inhibited growth of A. flavus. Furthermore, thyme essential oil possesses a wide range spectrum of fungicidal activity against plant pathogenic fungi Aspergillus, Penicillium, Alternaria, Cladosporium pythium sp., F. oxysporam f. sp. lycopersici, Fusarium oxysporum f. sp. pisi, Verticilium albo-atrum, Rhizoctonia sp. and Clavibacter michiganensis sub sp. michiganesis (Tanovic et al., 2007).
Essential oil extracted from lemon grass (Cymbopogon citratus Stap f.) has antifungal activity against several plant pathogens (Nguefack et al., 2007).
In the present study, results indicate that lemon grass reduced gray and blue moulds of apple fruits. In this respect, Abd El-Khair and Haggag (2007) reported that extract of lemon grass leaves was the best one in controlling both late and early blights. Moreover, Tzortzakis and Economakis (2007) recorded that lemon grass oil has antifungal activity against Colletotrichum coccodes, B. cinerea, Cladosporium herbarium Link; Fr., Rhizopus stolonifer (Ehreb. Fr.) Vuill and A. niger in vitro. Fungal spore production inhibition up to 70% at 25 ppm of lemon grass oil concentration. In the highest oil concentration (500 ppm) employed, fungal sporulation was completely inhibited. Lemon grass oil reduce spore germination and germ tube length of C. coccodes, B. cinerea, C. herbarium and R. stolonifer. It could be suggested that essential oils could be make them an excellent treatment for controlling post harvest diseases of apple fruits.