Journal of Plant Physiology & Pathology ISSN: 2329-955X

All submissions of the EM system will be redirected to Online Manuscript Submission System. Authors are requested to submit articles directly to Online Manuscript Submission System of respective journal.

Research Article, J Plant Physiol Pathol Vol: 1 Issue: 3

Effect of Castor Bean Oil on Post Harvest Fungal Pathogen of Coconut: Lasiodiplodia theobromae

Maria das Graças Machado Freire1, Cláudio Luiz Melo de Souza1, Thayana Paranhos Portal1, Roberta Manhães Alves Machado1, Pedro Henrique Dias dos Santos2 and Vicente Mussi-Dias2*
1Laboratório de Química e Biomoléculas – Centro de Pesquisas, Institutos Superiores de Ensino do CENSA – ISECENSA; Rua Salvador Correa, 139, Centro, Campos dos Goytacazes, RJ, CEP: 28035-310, Brazil
2Laboratório de Entomologia e Fitopatologia – CCTA, Universidade Estadual do Norte Fluminense Darcy Ribeiro – UENF; Av. Alberto Lamego, 2000, Parq. Califórnia, Campos dos Goytacazes, RJ, CEP 28013-602, Brazil
Corresponding author : Vicente Mussi-Dias
Laboratório de Entomologia e Fitopatologia – CCTA, Universidade Estadual do Norte Fluminense Darcy Ribeiro – UENF; Av. Alberto Lamego, 2000, Parq. Califórnia, Campos dos Goytacazes, RJ, CEP 28013-602, Brazil
Tel: 55-22-27262721
E-mail: [email protected]
Received: April 15, 2013 Accepted: June 25, 2013 Published: July 02, 2013
Citation: Freire MGM, Souza CLM, Portal TP, Machado RMA, Santos PHD, et al. (2013) Effect of Castor Bean Oil on Post Harvest Fungal Pathogen of Coconut: Lasiodiplodia theobromae. J Plant Physiol Pathol 1:3. doi:10.4172/2329-955X.1000108

Abstract

Effect of Castor Bean Oil on Post Harvest Fungal Pathogen of Coconut: Lasiodiplodia theobromae

Lasiodiplodia theobromae is a cosmopolitan soil-borne fungus that causes both field and storage diseases in plant species leading to economic losses. The fungicides used to control these diseases are harmful as they leave residues, which may be regarded as problem for the marketing and export of Brazilian fruits. This study evaluated the in vitro effect of castor bean oil (Ricinus communis), and its constituents, on the mycelial growth and spore germination of this pathogen, suggesting an alternative to chemical control during the post-harvest.

Keywords: Post-harvest decay; Fatty acids; Biological control

Keywords

Post-harvest decay; Fatty acids; Biological control

Introduction

Lasiodiplodia theobromae (Pat.) Griffon & Maubl. (syn). Botryodiplodia theobromae Pat.) was reported, over a century ago attacking Theobromae L. fruits in Santo Domingo de los Colorados (Equador) [1]. Varied reports of the consequences of L. theobromae have been published, including human pneumonia [2] until the production of Taxol, a highly effective and broad-spectrum natural anti-cancer drug [3] and more than 30 other chemical compositions used by humans [4,5].
L. theobromae is a cosmopolitan fungus that is a polyphagous and widespread unspecialized virulent rot pathogen. This fungus is generally regarded as a weak pathogen that invades stressed or wounded plants after drought, hail, wind, frost or insect damage and also following human damage as a consequence of cultural practices [6]. The fungus is distributed in the tropics and subtropics [7], provoking diseases in more than 500 vegetable species. It is associated with different symptoms such as shoot blights, stem rot, cankers, fruit rots, die-back, gummosis, collar and root rot, lesions in cuttings, leaves and seeds, death of seedlings and fruit rot in coconut, cucurbit, cupuassu, soursop, cassava, mango, sugar apple trees, rubber trees and annatto [8,9].
L. theobromae is considered a serious problem for agriculture, as it is associated with several diseases of tropical fruits including the cocoa tree, the passion fruit, avocado, orange, the barbados cherry, and ciriguela [10,11]. L. theobromae is an efficient pathogen, which causes a fast spread of the disease due to its wide range of unspecialized hosts [12]; L. theobromae has also been frequently isolated as endophytic in the leaves of many plants in the states of Ceara and Pernambuco, Brazil [13]. Post-harvest storage rots in fruits and vegetables cause serious economic losses worldwide [14].
The methods for conservation and storage of the fruits, although well structured, have not been well studied and consist of the manipulation of the atmosphere, the application of chemical fungicides with fungistatic or fungitoxic actions, associated or not with wax emulsions and plastic films, among other techniques [15-19]. The efficiency of some fungicides in vitro indicates the possibility of the chemical control of L. theobromae [20]. Currently, the chemical products registered by the Ministry for Agriculture (Brazil) for the control of fruit rotting caused by this fungus during the post-harvest, are chemicals with Triazol and Benzimidazol groups, with systemic actions and classified as extremely toxic and of intermediate toxicity, respectively [21].
The intensive and continuous use of systemic fungicide has resulted in the development of resistant strains of pathogens, leading agricultural scientists to pursue alternative controls that are more environmentally friendly. Biological control is a potential alternative to the use of fungicides and other pesticides [22]. In addition, although there are specific periods of deprivation for each toxic fungicide residue, which are not controlled in the marketed fruits, the safety interval for these products is not determined.
In consequence of the demands of international agencies, which impose protective measures against plant diseases, the Brazilian fruits present a low quality, due to inadequate synthetic fungicide use and inefficient post-harvest technology management [23]. Therefore, studies to find suitable alternative products, such as oils and vegetable extracts, are necessary for fungal disease control, particularly during the post-harvest [24,25].
Research indicates that use of biopesticides in the post-harvest environment may have a greater chance for success than biological control in the field [26]. Thus, biological control appears to be a promising strategy for managing post-harvest fruit diseases. Researchers have found that a large number of fatty acids have antimicrobial activities and hold potential as medicines in nutritional therapy [27]. Palmitic acid has shown a stronger antifungal activity than the unsaturated fatty acids, i.e. oleic acid. Caproic acid, caprylic acid, capric acid, and palmitic acid almost completely inhibit the spore germination of fungi tested (Alternaria solani Sorauer, Colletotrichum orbiculare (Berk.) Arx and Fusarium oxysporum Schltdl) at higher concentrations, indicating their relative broad antifungal activities [27]. In this study, we present data regarding the antifungal properties of fatty acids from castor bean oil (Ricinus comunnis L.).

Materials and Methods

Culture of the fungus
The fungus, L. theobromae, was grown on potato dextrose agar (Himedia®) and the culture stocks were stored at room temperature, in Petri dishes (90 mm in diameter). L. theobromae were cultured under the same conditions for 7 days, to allow the germination of spores of the fungi. Plugs of mycelium and agar (1 cm diameter) were collected from the peripheral growth zone of the Potato Dextrose Agar (PDA) and these plugs were then placed reversely on the center of each Petri dish, which was filled with 25 mL PDA medium and incubated at 25 ± 2°C, so that the fresh culture could be prepared for later use.
Chemicals and solvents tested
Purified castor bean oil used in this study was obtained from Talgo (São Paulo, Brazil) and its major constituents, e.g., Ricinoleic Acid (87.5%); Oleic Acid (4.5%); Stearic Acid (1.75%) and Palmitic Acid (1.2%) were obtained from Merk® [28]. The initial emulsion was prepared using 7.5 mg.100 mL-1 Tween® 80 (0.1%, (v/v), Merk®) [27]. Starting from this emulsion, serial dilutions were made using a suspension of Tween® 80 at 0.1% to obtain the concentrations of 0, 5, 10, 15 and 20% (v/v) for the first experiment and 0, 25, 50, 75% (v/v) castor bean oil for the second experiment. The concentrated oil (100%) was also tested, as well as the fatty acids, in similar concentrations to that of its composition. Stearic and palmitic acids were diluted in 0.3 mL of ethanol p.a. (0.6%, v/v, Merk®) and the volume was made up to 3 mL with sterile water. Thiabendazole (Tecto® SC from Syngenta®) was used as standard at 200 ppm, in accordance with its indication for the post-harvest treatment of papaya, mango and melon.
Mycelial growth of pathogens
Different oil concentrations were mixed into each of three replicated plates of PDA, providing a total volume of 15 mL/plate, just before solidification. The plates were then centrally inoculated with a single 1 cm diameter mycelia plug of L. theobromae from the PDA plate and incubated at room temperature. PDA, with Tween® 80 (0.1%, v/v) and ethanol (0.6%, v/v), but no oil was used as a positive growth control. The diameter of mycelial growth was measured when the fungus occupied the entire plate surface (48 h). It was measured in two directions and the average was obtained [29].
Residual effect on spore germination
A residual effect was considered when the spores used in the experiment were produced starting from the mycelium that was assessed on PDA medium containing castor bean oil or its constituents. A total of 100 μl of spore suspension (2 x 105 spores mL-1) was transferred to each petridish containing agar-water medium distributed in three randomly selected fields. The plates were then incubated in the dark at 25 ± 2°C for 10 hours. The percentage of germinating spores was determined by observing and counting a total of 100 spores in each field of three randomly-selected fields by means of a microscope. Spores for which the germ tube was at least the same length as the spore were considered to be germinated. The average of three counts was used for each of three Petri dishes per treatment [30].
Castor bean oil biocontrol ability on fruit
Coconut fruits, collected to obtain coconut water, were used in all the tests. The fruits were collected from São João da Barra, Rio de Janeiro, Brazil. Fruits were surface-disinfested with sodium hypochlorite (0.1% for 5 minutes) and wounded by removing blocks of tissue of 3 mm x 4 mm from the basal portion of the stem (the bracts were not removed; only the floral stalk was used). Groups of three fruits were then treated with concentrations of castor bean oil, Ricinoleic Acid, Palmitic Acid and the fungicide, Tecto® SC. After air-drying, a 20-μL spore suspension of L. theobromae was pipetted into each wound. The inoculum levels of the pathogen were 2 x 105 spore mL-1. Control fruits were treated only with water and fungus controls were inoculated with L. theobromae. All the fruits were maintained for 11 days at 28°C. After completion of the incubation period, each fruit was sectioned and the disease severity was evaluated by observing the fruit mesocarp degradation. Each half of the coconut fruits was photographed with Canon® PowerShot digital camera and the lesion area was evaluated with the help of the Quant® program.
Statistical analyses
The experiments were conducted according to a completely randomized design with three replicates per treatment. Each experiment was repeated three times. The data were subjected to analysis of variance (ANOVA) and means were compared by the Tukey’s Test (P<0.05) and by standard deviation. When necessary, the data were transformed by square root of the number (x+0.5) and the means were presented without transformations. The data of mycelial growth as a function of the concentrations or of the incubation times were subjected to analysis of variance to the effect of polynomial regression to find the “best equations” (P<0.05) [31]. Statistical analyses were calculated using the Statistical Analysis System program [32].

Results and Discussion

Regression analysis of the mycelial growth as a function of concentration of castor bean oil showed that the mycelial growth for 12 hours of incubation was estimated at 0.58 cm, and after 48 hours reached 6.38 cm. Rate inhibition of mycelial growth by oil was estimated at -0.22 cm for 12 hours of incubation, and -0.11 cm after 48 hours (linear equations, Table 1).
Table 1: Diameter mycelial growth (cm) of Lasiodiplodia theobromae incubated (12-48 h) in culture medium containing different concentrations (0-20 %, volum/volum) of castor bean oil (Ricinus communis L.).
After 48 hours of incubation, the mycelia growth in the presence of castor bean oil at 5% (6.30 cm) did not differ significantly (P<0.05) compared to the PDA – control (6.50 ± 0.01 cm). However, the 10% (5.40 ± 0.20 cm), 15% (5.80 ± 0.02 cm) and 20% (4.65 ± 0.15 cm) concentrations of the oil were able to significantly decrease mycelial growth compared to the control (Table 1). The retardation of growth was observed after 24 hours of incubation, remained static until 36 hours and was evident at 48 hours of assessment. These data indicate that castor bean oil only has a fungistatic effect against L. theobromae. This effect was also confirmed at a concentration of 100% (4.71 ± 0.53 cm) and in this case, the mycelial growth was reduced by 36.36%, when compared to control (7.4 ± 0.62 cm) (Figure 1). Similar results were also observed by Packer and Luz [33], who studied the effects of the natural oils of copaiba, rosemary, melaleuca, garlic and andiroba against Staphylococcus aureus Rosenbach, Escherichia coli Migula, Pseudomonas aeruginosa (Schroeter) Migula and Candida albicans (C.P. Robin) Berkhout. The best results were achieved with melaleuca and rosemary oils, which showed bacteriostatic and fungistatic activity against the four microorganisms.
Figure 1: Effect of different concentrations (0-100%) of castor bean oil (Ricinus communis L.) on the mycelial growth of Lasiodiplodia theobromae, at 48 hours of incubation. (Means and standard deviation, N=9). *Significant effect for the analysis of variance of the linear regression beetween the mycelial growth and the concentrations of castor bean oil (Fisher F-test, P<0.05).
Vegetable oils present two main characteristics as antifungal agents; the first is their natural origin which means increased safety for humans and the environment. Secondly, they are considered as low risk for resistance development by pathogenic microorganisms. It is believed that it is difficult for the pathogens to develop resistance to such a mixture of oil components with, apparently, different mechanisms of antimicrobial activity [34].
In this experiment, Tween® 80 and ethanol were classified as control treatments. Therefore, the effects of these solvents were also evaluated on the mycelial growth of L. theobromae. Tween® 80 (2.05 cm) and ethanol (2.42 cm) had no significant effects (P<0.05) on mycelial growth, but significant effects were observed in relation to the PDA medium (control, 2.90 cm) and the solvents. Thus, when statistical analyzes were processed, the effects of solvents were subtracted from the results (Table 2).
Table 2: Diameter mycelial growth (cm) of Lasiodiplodia theobromae incubated in culture medium containing castor bean oil (Ricinus communis L.) and their fatty acids constituents.
Tween® 80 may interact with organisms and drugs, affecting their antimicrobial activity in vitro. Nascimento et al. [35] evaluated the effect of long-pepper essential oil (Piper hispidinervum C. DC.) and of a Tween® 80 emulsifier on the mycelial growth of Alternaria alternata (Fr.) Keissl. A 100% inhibition with a 1000 mgL-1 concentration was observed, where the percentage of emulsifier (Tween® 80) influenced the fungitoxic activity at the concentrations of 250mgL-1 and 500mgL-1 of the essential oil, confirming the data Gomez-Lopez et al. [36]. High concentrations of Tween® may reduce the fungitoxic activities that affect micelle formation, since this surfactant can prevent the contact of essential oil constituents with the microorganism [37] or induce alterations in cellular membrane permeability, antagonizing the actions of the essential oil components [38].
Daferera et al. [34] studied the effectiveness of plant essential oils including oregano (Origanum vulgare L.), thyme (Thymus capitatus (L.) Hoffmanns. & Link), dictamnus (Origanum dictamnus L.), marjoram (Origanum majorana L.), lavender (Lavandula angustifolia Mill.), rosemary (Rosmarinus officinalis L.), sage (Salvia fruticosa Mill.), and pennyroyal (Mentha pulegium L.) on the growth of Botrytis cinerea Pers., Fusarium Link and Clavibacter michiganensis subsp. michiganensis (Smith, 1910) and observed that oil solubility was enhanced by using ethanol as an emulsifier (0-0.5%).
After 48 hours, the experiments demonstrated that the ricinoleic acid (4.62 cm) induced similar effects to those observed to castor bean oil at 100% (4.72 cm), reducing mycelial growth significantly (P<0.05) compared to that of the controls (Table 2). Regression analysis of mycelial growth confirmed the fungistatic effects of ricinoleic acid and castor bean oil at 100%, as indicated by linear equations (Table 2). Fatty acids widely occur in natural fats and dietary oils and they play an important role as nutritious substances and metabolites in living organisms [39]. Many fatty acids are known to have antibacterial and antifungal properties [40]. Lauric, palmitic, linolenic, linoleic, oleic, stearic and myristic acids are all known to have potential as antibacterial and antifungal agents. Siqueira Júnior et al. [41] analyzed the constituents of essential oils from castor bean seeds for their ability to prevent the papaya diseases caused by Glomerella cingulata (Stoneman) Spauld. & H. Schrenk (syn. Colletotrichum gloeosporioides (Penz.) Penz. & Sacc.) and Pseudomonas caricapapayae Robbs, and showed that the major inhibitory activity of castor bean oil was due to ricinoleic acid.
Lipidic compounds are considered to provide good coatings on fruit due to their hydrophobic characteristics; they present a low permeability to water vapor [42] and act as a barrier to external elements, such as oil and organic vapor, protecting the products and extending their shelf life [43,44]. The use of carnauba wax and individual films for the wrapping of fresh fruits and vegetables greatly reduce weight loss by reducing the transpiration rate, and maintaining fruit firmness and shine, increasing their commercial value [45]. As carnauba wax is not toxic it can be consumed on fruits with peel and may be easily removed with water [46].
The association of carnauba wax emulsion immersion and plastic film wrapping can increase the post-harvest life of the yellow passion fruit, resulting in a smaller percentage of fresh matter loss and larger water relative tenor [47]. Immersion of the persimmon fruits, cv. Fuyu in 27.8% wax solutions efficiently reduced loss of pulp firmness, extending their storage period [46]. Chiumarelli and Ferreira [48] evaluated the effect of edible coatings on tomato cv. Debora postharvest quality and observed that the Megh Wax ECF 124® wax treatment resulted in a higher percentage of tomatoes appropriate for human consume.
On the other hand, post-harvest management may be unsatisfactory when environmental or external factors, such as relative humidity of the air, atmospheric composition, light and appropriate temperatures are not monitored [16]. However, the maintenance of firmness by shrink wrapping and/or the wax treatment of fruits and vegetables may result in the formation of a favorable atmosphere for fungi development and the deterioration of the products which will be marketed. Viana et al. [18] tested several processing methods in order to avoid coconut (Cocos nucifera L.) deterioration and observed that the association of basal section cutting, carnauba wax emulsion and fungicide was the best alternative for controlling L. theobromae infection.
Results showed that the biological efficiency gradually increased as plant extract separation is executed [49,50]. Siqueira Júnior et al. [41] studied papaya fruits treated with castor bean oil and its fatty acid constituents in aqueous emulsions and observed an effective inhibition of C. gloeosporioides mycelial growth. These authors showed that the major inhibitory activity in castor bean oil was due to ricinoleic acid (85-95%), but an interesting effect was observed when C. gloeosporioides were treated with oleic acid (2-6%). However, in the present study, our results showed that the treatments with palmitic acid and ricinoleic acid reduced the mycelial growth of L. theobromae in a manner similar to that of castor been oil.
Palmitic acid possessed fungistatic activity against L. theobromae at 1.2% (weight/volum (w/v)), which is a much lower concentration than that reported by Grimaldi et al. [51] who studying Brazilian commercial fats observed an average value of greater than 15% for palmitic acid for most of the samples of palm and/or cotton seed oils.
In addition, palmitic acid is used in the production of Brazilian fats, whose ingestion is distributed extensively due to its use in a great variety of products [52]. Moreover, the Brazil nut (Bertholletia excelsa Bonpl.) is noteworthy for its high content of lipids and proteins of elevated biological value. Brazil nut oil contains 85% unsaturated fatty acids, where palmitic acid represents 13% of the oil [53]. In consequence, it is safe to suggest the use of carnauba wax emulsions including palmitic acid for the post-harvest conservation of fruits against L. theobromae.
The Figure 2 showed a decline in the spore germination of L. theobromae in the presence of the castor bean oil at 100% (57.00 ± 8.23%). Results suggest that germination occurred under a residual effect of the oil, since the spores were placed to germinate in agarwater media.
Figure 2: Residual effect of different concentrations (0-100%) of castor bean oil (Ricinus communis L.) on germination of spores of Lasiodiplodia theobromae. (Means and standard deviation, N=9). *Significant effect for the analysis of variance for polymonial regression beetween the mycelial growth and the concentrations of castor bean oil (Fisher F-test, P<0.05).
Ferreira et al. [54] evaluated the topical action of several systemic fungicides (benzimidazol, pyridine, strobyrulin and pyridine) for the control of Calonectria scoparia Ribeiro & Matsuoka ex Peerally (syn. Cylindrocladium candelabrum Viégas); these authors observed that the inhibition of germination varied in function of the active ingredient of each tested product. Essential oils of Lippia sidoides Cham., Ocimum gratissimum L., Lippia citrodora Kunth (name illegitimate), Cymbopogon citratus (DC.) Stapf and Psidium guajava L. “var. porifera” were tested topically for their impact on the spore germination of C. gloeosporioides. These oils completely inhibited (100%) fungal colony development at 1.0 uL-1 [55].
In this study, the topical action of castor bean oil was not tested but its residual action was observed, suggesting that the spores were influenced by a systemic action and indicating that the castor bean oil probably interfered in the physiology of mitosporic production of L. theobromae. This residual effect is different that obtained from conventional protocols in germination tests for topical actions on the spores [41,55,56].
Although the present study provides some information regarding the systemic effects of the castor bean oil and its components on fungi, it is necessary to conduct further research on the mechanism by which the fatty acids control the pathogenic fungi. Few similarities to those mechanisms that cause partial genetic resistance in plants were observed. This resistance, also called quantitative or incomplete resistance, may provide low rates of disease development, starting from the association of several components, such as the infection frequency, pustule size, amount of spores produced by pustule and latent period [57] and, in our specific case, the considerable decrease in the production of L. theobromae viable spores. At an epidemic level this may represent a reduction in the inoculum production in the polycyclic process, constituting an important strategy for disease control, and suggesting environmentally and economically desirable results.
Results indicated that palmitc acid substantially inhibited spore germination (53.33%), as previously observed by Liu et al. [27] (Figure 3). The effects of palmitc acid were compared with those of castor bean oil (57.00%), and no differences were found between them; these effects differed significantly to those of ricinoleic acid (91.67%) and for the controls (P<0.05).
Figure 3: Effect of castor bean oil (Ricinus communis L.) and its fatty acid constituents on the spore germination of Lasiodiplodia theobromae. Control treatments: Potato Dextrose Agar medium (PDA), PDA containing Tween® 80 and PDA containing ethanol (0.6% volum/volum). *Means followed by same letters not differ according to Least Significant Difference (LSD= 4.84) of Tukey’s test (P<0.05, N=12).
Fatty acids are thought to play a role in plant defense mechanisms against phytopathogenic microorganisms. However, the in vivo efficacy and practical activity of only a few of the fatty acids have been studied. One general mechanism that has been proposed for antifungal fatty acids is that the activity is due to detergent-like properties of the compounds, affecting the structure of cell membranes of the target organisms. This increases membrane permeability and the release of intracellular electrolytes and proteins, eventually, leading to cytoplasmic disintegration of fungal cells [58]. On the other hand, it has been assumed that the fatty acids penetrate the lipid membrane and dissociate in the more alkaline interior, causing metabolic uncoupling [59].
In vivo studies showed that the application of castor bean oil (47.70%) and ricinoleic acid (54.60%) on fruits had inhibitory effects against the post-harvest basal rot of coconuts (p ≤ 0.05), when compared to the controls. Palmitic acid and Tecto® SC proved to be less effective (Figure 4).
Figure 4: Effect of castor bean oil (Ricinus communis L.) and its fatty acid constituents on the lesioned area (disease severity) in post-harvest of coconuts inoculated with Lasiodiplodia theobromae. *Means followed by same letters not differ according to Least Significant Difference (LSD=4.30) of Tukey’s test (P<0.05, N=36).
The fungus control presented a similar severity to that of the control, confirming the characteristics of latent fungus infection in the fruits used in the experiment and association of the experimental inoculum. Similarly to infections in mango, L. theobromae may remain quiescent in the stem-end region, manifesting during the post-harvest period [60,61].
The use of castor bean oil and ricinoleic acid presented a significant reduction (p ≤ 0.05) in the severity of disease in fruits (Figure 1). The effects of castor bean oil (in vitro) on both mycelial growth inhibition (Figure 1) and germination inhibition (Figures 2 and 3) were confirmed by the protection of the fruit in vivo (Figure 4), as the castor bean oil inhibited spore germination on the fruit and controlled mycelial growth systemically.
When the fruits were treated with ricinoleic acid, a similar protection occurred, but there was no inhibition of spore germination in vitro (Figure 3). These results indicate that ricinoleic acid acts systemically on coconut fruits, inhibiting the development of the mycelium within the fruit and, consequently, reducing the severity of post-harvest disease.
During the post-harvest period, the control of spore germination is limited to environmental contamination and spread to other susceptible fruit. During coconut storage, this spreading is not important, since sporulation only occurs when the coconut is in an advanced stage of degradation and internal colonization, and unsafe for consumption [9]. Palmitic acid, which proved effective in inhibiting spore germination, in vitro (Figure 3), when applied to coconuts, did not prevent the development of quiescent mycelium.
Castor bean oil and ricinoleic acid showed significantly higher results (p ≤ 0.05) than Tecto® SC (29.6%), a systemic fungicide belonging to the Benzimidazol chemical group, and recommended for the post-harvest protection of different fruits (Figure 4), where it acts on the cell division of fungi, disrupting the mitotic cycle [62].

Conclusion

In conclusion, we may say that castor bean oil, at a concentration of 7.5 mgmL-1, reduces the mycelial growth of L. theobromae by 36.36%. This effect is fungistatic, as only a delay in mycelial growth is observed. Castor bean oil reduces spore germination by 40% due to a residual effect, e.g., when the spores are obtained from mycelia grown in culture media containing this oil. Mycelial growth of L. theobromae is reduced by palmitic acid (1.2%, w/v) and ricinoleic acid (87.5%, w/v) added into the culture media. Finally, results suggest that the effect of castor bean oil on spore germination inhibition and mycelial growth, both in vivo and in vitro, may be attributed to palmitic and ricinoleic acid, respectively.

Acknowledgement

We thank Dr. Francisco Marto P. Viana (Embrapa Agroindústria Tropical – Fortaleza/CE-Brasil) for providing tested fungus; Syngenta® for suppling the fungicide Tecto® SC and Talgo (São Paulo, Brazil) for delivering the castor bean oil. We are grateful to Nicola Conran for the language review of this manuscript.

References































































Track Your Manuscript