Published on International Journal of Food & Nutrition
Publication Date: July 12, 2019
Ngaufe, B. & Kugedera, A. T.
Department of Curriculum Studies, Robert Mugabe School of Education and Culture
Department of Livestock, Wildlife and Fisheries, Gary Magadzire School of Agriculture and Natural Sciences, P. O. Box 1235 Masvingo
Great Zimbabwe University, Zimbabwe
Fungal blights are major threat in tomato production. A trial to assess the efficacy of extracts from garlic (Allium sativum) and chilli (Capsicum annum) as natural pesticides in the control of fungal blights (Alternaria solani and Phytophthora infestans) in tomatoes was conducted at Tabudirira Training Center in Mutoko District, Zimbabwe between 2018 and 2019. The experiment was laid out in a Complete Randomized Block Design with three replicates and two major treatments as follows; Chilli, Garlic, Control (no treatment) and Dithane M45. The treatments were applied two weeks after fungal infestation and fortnightly until harvesting. There was Significant differences based on interaction, concentration and extract type (P<0.001) were observed with respect to plant health and fungal blight infestation, and total yield of tomato fruits. Dithane M45 had the average yield of 29 fruits per plant, chilli with 49 fruits per plant, garlic with 31 fruits per plant and water with 27 fruits per plant. Least yield was recorded in the control treatment. The experiment showed that extracts of chilli and garlic have potential to control fungal blights in tomato production. Chilli treatments best performed at 15% concentration level. The experiment was based on garlic extracts and chilli extracts thus a 2 factor experiment. The use of garlic and chilli can be an option to suppress pest in vegetables. Smallholder farmers are recommended to use garlic and chilli as these are readily available options at cheaper levels to control pests and they do not causes harm to the environment
Keyword: Assessin, concentration, garlic, chilli & blights.
Tomato plants are vulnerable to infection by early blight disease caused by Alternaria solani (Abada et al., 2008), which causes reduction in the quantity and quality of fruit yield. Tomato (Lycopersicon esculentum) is a subtropical plant in the Solanaceae family and is one of the most grown vegetable in the world (Jackson, 2014). It is the most important vegetable crop after rape and cabbage in Zimbabwe (Jackson, 2018). It is a source of nutrients such as vitamins A, C and E and constitutes a part of household diet and national economy (Kaur, 2014). Pests and diseases especially fungal blights are among the major constraints in tomato production (Sigei et al., 2014). The blight pathogens have become one of the most severe cool season diseases of Solanaceae in Africa with predictable, crop losses of up to 90% in Southern Africa (Sibanda et al., 2010).
The Alternaria fungus can cause disease on all parts of the plant and result in severe damage during all stages of plant development (Abada, 2008). This disease is controlled with agro chemicals. However, environmentally-safe methods of plant disease control in sustainable agriculture calls for reducing the use of these synthetic chemical fungicides (Reddy et al., 2013). Some alternative methods of control have been adopted. Efforts are being made to focus on developing environmentally safe, long lasting and effective bio control methods for the administration of plant diseases. Natural plant products are important sources of new agrochemicals for the control of plant diseases (Kagale et al., 2004).
Biocides of plant origin are non-phytotoxic, systemic and generally biodegradable (Qasem, 2013). Various natural plant products can reduce populations of foliar pathogens and control disease development and then these plant extracts have potential as environmentally safe alternatives and as components in integrated pest management programs (Bowers, 2004). A number of plant species have been reported to possess natural substances that are toxic to several plant pathogenic fungi (Goussous et al., 2010).
Curtis et al. (2004) studied the effects of 11 different plant extracts on mycelial growth of Alternaria solani and found that leaf extracts of some plants, like Athel pine, Tamarix aphylla and Saltwort, Salsola baryosma totally inhibit the growth of the pathogen. Wszelaki, (2005) reported that garlic extracts significantly reduced the early blight disease on tomato. Additionally, several plant extracts have shown antimicrobial activity against fungal pathogens under in vitro and in vivo conditions (Kagale et al., 2004). Therefore, our present study investigated the efficacy of Garlic cloves and Chilli capsules extracts for control of blights on tomato under field conditions. The treatments were compared with a commonly used fungicide (Dithane M45).
There are 20,000 species of fungal plant pathogens and about 85% of plant diseases are caused by them (Nyirenda et al., 2011). Tomato (Lycopersicon esculentum) is one of the most important vegetable crops in the world. The fungus has many unwanted symptoms in tomato plants. The appearance of these symptoms depends on plant part, various stages of plant and fruit development. The symptoms of early blight appear on fruit, stem and foliage of tomatoes. These symptoms include early blight of leaves, stem blight and leaf spot on leaves, foot rot and collar rot on young plant stem, black rot and hard rot on fruit, fruit drop, petioles and blossom blight on the calyx (Bowers, 2004). In fruit rot foliar decay is very destructive phase, which damages the fruits completely (Gomez, 2018).
People in developing countries like Zimbabwe have insufficient food supply and at least 10% – 15% of agriculture products are lost due to plant diseases (Seif et al., 2003). Several synthetic chemicals among them being Dithane M45 and copper oxy-chloride have been promoted over the years however Alternaria solani has developed resistance due to prophylactic usage resulting in loss of yield, (Mehraj et al., 2014). Plant extracts are nonphytotoxic and are eco-friendly. The losses incurred due to pests and diseases are a major constraint faced by horticultural farmers in Zimbabwe. Ldah (2004) revealed that chemical control of these pathogens and insect pests is possible, but resource poor farmers who own small farms cannot afford. Tabudirira Training Center is in Mutoko District and Mutoko is only the major supplier of tomatoes at Mbare Musika throughout the year among other districts, therefore it is not an exception to this disease causing organism – Alternaria solani. It is against this background that there is need to use garlic and chilli extracts as an alternative in controlling blights in tomatoes.
2.1 Experimental site
This research was carried at Tabudirira Training Centre in Mutoko District, located in Natural Farming Region 4 of Zimbabwe with the following location17° 32ʹ2΄ʹ S Latitude and 32° 1ʹ13΄ʹ E Longitude. Annual rainfall of this area ranges from 450mm to 600 mm and is characterized by mid-season with severe dry spells during the rainy season with summer temperatures ranging between 27o C and 39oC and winter temperatures between 6oC and 28oC (Moran, 2010). The soil type is red clay soils. Tabudirira Training Centre is on a 17km peg from Mutoko Center and 2km off main road.
2.2 Experimental design and treatments
The experiment was laid out as a randomized complete block design with 2 factors. The first factor was extract type with two levels chilli extracts and garlic extracts. The second factor was concentration of extract with three levels; 5%, 10% and 15%. The experiment had three replicates. There were two Controls (negative) and Dithane M45 – positive control.
2.3 General management of the crop
According to Toroitich et al., (2014) reveals that tomato varieties are resistant to certain races of the late blight fungus are grown where the disease occurs regularly. Remove any nearby volunteer solanaceous crops among others tomato and potato plants and nightshades. Check transplants to ensure they are free of late blight before planting. Nyamapfeni (2010) avails to avoid sprinkler irrigation, if possible, because it favours the development of late blight. Fungicides are generally needed only if the disease appears during a time of year when rain is likely or overhead irrigation is practiced. Mefenoxam-resistant strains of the pathogen are widespread in California and this fungicide is no longer effective. Disc tomato fields in fall to eliminate a winter reservoir for the fungus (Nvajas, 2013).
2.4 Preparation of extracts
A preparation of 500g fresh red chilli were ground and mixed with 5 liters of warm water and 5ml of vegetable oil for 24 hours. The oil was added to enhance the solubility of capsaicin (Rusch, 2010). Water was then added to make a total volume of 5ml. This mixture was filtered and 30ml of dish washing liquid was added as a wetting agent. The mixture was strained using a fine cloth. 500g of concentrated cloves of garlic was crushed and soaked for 24 hours in 5 litres of water. The mixture was then filtered and 30ml of dish washing liquid and 5ml of vegetable oil were added to the garlic mixture. The mixture was strained using a fine cloth. Garlic and red chilli extracts were mixed in the ratio 1:1 during preparation for the red chilli plus garlic treatment. Application of insecticides started two weeks after red spider mite infestation and every 2 weeks thereafter until harvesting (Gomez et al., 2018).
2.5 Data recording procedure timing
According to Kagale et al. (2004) postulate that counting of infected plants was through and through done every fortnight signs of infection :exhibit brown to black spots with concentric rings on leaves, girdling of the stems and brown spots with concentric rings on the underneath of tomato fruits out of 3 lines per bed, only tomato plants from the middle line of the bed are randomly selected for analysis.
2.6 Scoring procedure
The intensity of disease was recorded in each treatment following the shoes of the score chart by Latha et al. (2009). Counting of infected plants is done every fortnight Signs of infection : exhibit brown to black spots with concentric rings on leaves , girdling of the stems and brown spots with concentric rings on the underneath of tomato fruits. Out of 3 lines per bed, only tomato plants from the middle line of the bed are randomly selected for analysis. Reason: overcome border row effects (Tselia et al., 2013).
3. Results and discussion
The results show that prediction is high with high concentration of garlic being used. Low prediction was indicated on low concentration of garlic as shown on Table 1 and presented on Fig 1 below.
Table 1 and figure 1 reflect that Garlic extract concentration had a significant effect on tomato size, weight and quality thus Garlic extract concentration managed to increase the level of tomato on quality. The significant difference is signified by a statistical analysis which shows Probability value at p<0.001. The 15% Chilli concentration level being the most effective treatment to give highest yield of 70 fruits per plant. Organic pesticides were effective in controlling Alternaria Solani. Garlic however recorded a highest yield of 55 fruits. The low concentration of garlic spray used in this experiment could have failed to control the Alternaria Solani (Voorrips et al., 2011). Table 2 and figure 2 above reflected that the concentrations of Garlic (5%, 10%, and 15%) had a statistical difference on controlling Alternaria Solani as compared to control. The results proved that at 10% Garlic concentration levels there was highest reduction in Alternaria solani infection. Garlic as a treatment on its own was not as effective as of red chilli pepper and garlic in terms of consistent on extract concentration level and output. These results suggest that although garlic contains insecticidal properties (Sigei et al., 2014) it alone might not be able to completely suppress the persistent effects of the Alternaria Solani on the tomato plants especially in the conducive environmental conditions (Kazem, 2010). The results exposed that lack of insecticidal treatment results in reduced yield. This is because Alternaria solani indirectly damage tomato foliage, reducing the rate of photosynthesis and causing stunted growth (Voorrips et al., 2011). Chilli was effective in controlling Alternaria solani. Chilli contains an active ingredient capsaicin (8-methyl-N-vanillyl-6-nonemide) which acts as an Alternaria solani feeding depressant and repellent (Moran, 2010). The treatment containing chilli also proved to be effective in maintaining growth rate in terms of plant height. Reddy et al., (2013) also noted that the combination garlic is more effective in controlling pests than garlic on its own. Dithane M45 among synthetic chemicals was able to maintain growth rate although its repeated use results in development of pesticide resistance (WHO, 2015). Abad et al. (2008) showed that the essential oil in garlic diallyl disulphide has insecticidal properties that are effective against many pests including the Alternaria Solani. The results on Table 3 and figure 3 above, show significant treatment effects on the total yield of tomatoes at 5% significant level in all factors. Yields were; chilli (49 per plant); garlic (31 per plant) and control (27 per plant). Kagale et al. (2004) said that the low yields resulted from Alternaria Solani infestation because the fungus reduced photosynthesis, flowering and fruiting. Natural pesticides were effective in controlling blights. Dithane M45 however recorded low yields compared to the other treatments apart from the control. The low concentration of garlic spray used in this experiment could have failed to control the fungus. India, (2014) evidenced the efficacy of garlic (Allium sativum) and Chilli (Capsicum annum) extracts in the Control of fungus in Tomatoes (Lycopersicon esculentum). The concentrations of Chilli (5%, 10%, and 15%) had a statistical difference on controlling Alternaria solani as compared to control. The results proved that at 15% Chilli concentration levels there was highest reduction in Alternaria Solani infection.
Chilli treatments have an average of 49 fruits per plant and least yield of 18 fruits per plant was recorded in the control experiment. The experiment showed that extracts of chilli and garlic controlled Alternaria Solani in tomato production. Water control showed a much decline in yield per plant, showing the impact of the fungus on tomato yield. There was emergency of red spider mite, aphids and boll worms which devastated the tomato plants under control experiment. However under chilli and garlic treatments at levels above 10% there were no red spider mites. Chilli and the combination of garlic and red chilli were as effective as Dithane M45 in suppressing infestation. Efficacy of the natural treatments was due to their insecticidal properties. The results on fruits showed that lack of insecticidal treatment results in reduced growth. This is because Alternaria Solani damages stems, leaves, fruits of tomatoes by reducing the rate of photosynthesis and causing stunted growth. Red chilli contains an active ingredient capsaicin (8-methyl-N-vanillyl-6-nonemide) which acts as a mite feeding depressant and repellent. Garlic and chilli also proved to be effective in maintaining growth rate in terms of plant height. The results also indicated that garlic and chilli can be effective in suppressing pests.