Tomato (Lycopersicon esculentum Mill.) is the second most important remunerable solanaceous vegetable crop after potato. It is native to South America and is widely cultivated in 140 countries of the world with an annual production of 150 million tons (FAO, 2009). Tomato ranks next to the potato crop and ranks first among the processing crops in the world acreage. Tomato is commonly consumed in our daily life and it is a good source of antioxidants [1]. Tomato contains 95.3% of water, 0.07% calcium and niacin, all of which have great importance in metabolic activities of humans. With high nutritional value, it provides a balance source of Vitamin A, C and E needed to maintain good human health [2,3]. Varied climatic adaptability and high nutritive value made the tomato cultivation more popular in the recent years. At present, in Pakistan average production of tomato is 10.51 tons per hectare which is quite low as compared to other tomato growing countries such as USA (89.33 t/ha), China (52.98 t/ha), Egypt (43.53 t/ha), Turkey (36.44 t/ha) and India (21.30 t/ha) (FAO, 2009). Tomato crop is vulnerable to infect by bacterial, viral, nematode and fungal diseases. Among the fungal diseases, Alternaria leaf blight of tomato caused by Alternaria solani is the worst damaging one [4,5] that cause reduction in quantity and quality of the potato crop. Alternaria solani (Ellis and Martin) is a soil inhabiting air-borne pathogen responsible for leaf blight, collar and fruit rot of tomato disseminated by fungal spores [6]. It is an important disease of tropical and sub-tropical areas. Distinctive bulls-eye pattern of leaf spots with concentric rings of spores surrounded by a halo of chlorotic leaf area are the common. Leaves turn yellow and dry up when only a few spots are present [7]. The pathogen causes infection on leaves, stem, petiole, twig and fruits as well as leads to the defoliation, drying of twigs and premature fruit drop which ultimately reduce the yield. The disease, if favored by high temperature and humidity (crowded plantation, high rainfall and extended period of leaf wetness from dew) and plants are more susceptible to the blight infection during fruiting period [8]. Primary methods of controlling Alternaria leaf blight include preventing long periods of wetness on the leaf surface, cultural scouting, sanitation, and development of the host plant resistance with the application of fungicides [9,10]. Cultivation of resistant varieties is the ultimate control of this disease. However, farmers in pursuance of high yield are inclined to cultivate some varieties which may be less resistant to disease. Fungicide application can increase the genetic potential and yield reduction due to disease can be minimized. Preventive fungicides inhibit the spore germination and penetration but pathogen can derive resistance against fungicide application so repeated application of fungicides at proper dose and interval of time is mandatory [9,11]. Application of mancozeb (a subclass of carbamate pesticides called dithiocarbamates) against late blight has been reported in Pakistan [12-14]. Unplanned and wide use of fungicides often leads to serious environmental problems besides affecting the health of users and consumers. So, it is necessary to minimize the use of chemicals for controlling disease. Present study was aimed to determine the efficacies of different doses of fungicide (Mancozeb) against Alternaria leaf blight of tomato.

A field experiment for the evaluation of different doses of mancozeb (4 g/L, 8 g/L, 12 g/L and 16 g/L) was conducted at the research area of Barani Agricultural Research Institute, Chakwal. Well sprouted tomato seedlings of five varieties (Litah545, Litah514, Eurica, Ti-166 and Astra) were transplanted in the tunnel with 35 cm between row spacing and 30 cm within row spacing. The experiment was laid out in randomized complete block design with five replications using variety modern. Fungicide application treatments were done by hand sprayer consisting of a boom with two XR11003VS flat fan nozzles at regular intervals of seven, fourteen, twenty one and twenty eight days. Data on the disease severity was recorded after every ten days intervals from flowering stage to onwards using 0-5 disease rating scale as shown in the Table 1.

Table 1: Disease rating scale for the assessment of Alternaria blight of tomato.

Data analysis

Recorded data were subjected to statistical analysis using ANOVA of SAS statistical data analysis software. Duncan’s multiple range tests was used to determine the most significant treatment [15].

All fungicide applications significantly reduced the disease severity. Data regarding percent disease severity in different varieties 7 days after the application of fungicide (Mancozeb) demonstrated that minimum disease (29%) was recorded in Litah514 followed by (30%) in Litah545 by the application mancozeb 12 g/L of water. Disease severity recorded by the application of 16 g/L was almost same as that of 12 g/L of water. The response of all other cultivars fungicide treatment 4 g/L and 8 g/L of water was also satisfactory as compared to control but less than 12 g/L of water as shown in Figure 1.

Figure 1: Disease severity of five potato cultivars - 7days after the application of fungicide (Mancozeb).

Disease data recorded 14 days after the application of fungicide demonstrated that all fungicide treatments significantly reduced the disease percentage. Minimum disease severity (26%) was recorded in Litah545 followed by (27%) in Litah514 by the application of mancozeb 12 g/L of water. Same results were obtained by the application of mancozeb at 16 g/L of water. All other fungicide treatments were less effective as shown in Figure 2.

Figure 2: Disease severity of five potato cultivars 14 days after the application of fungicide (Mancozeb).

Data regarding disease severity percentage recorded 21 days after the application of fungicide treatment as shown in Figure 3 revealed that all fungicide treatments caused significant reduction in Alternaria leaf blight infection as compared to untreated check. Minimum disease severity (26%) was recorded in Litah545 followed by (27%) in Litah514 by the application of mancozeb 12 g/L of water. All other fungicide treatments were less effective as compared to 12 g/L of water. Disease severity percentage 28 days after the application of fungicide treatments revealed that mancozeb 12 g/L of water show maximum yield reduction (19%) in variety Litah545 followed by (20%) in Litah514. All other fungicide treatments were less effective. Among all five varieties, Litah545 and Litah514 remained best as compared to Eurica, Ti-166 and Astra as shown in the Figure 3.

Figure 3: Disease severity of five potato cultivars 28 days after the application of fungicide (Mancozeb).

After ten pickings, yield of each variety was calculated which demonstrated that variety Litah545 gave maximum yield (3000g) per plant under the fungicide application 12g/L of water followed by Litah514 (2675g), Astra (2208g), Eurica (1350g) and Ti-166 (1325g) as shown in the Figure 4. All other fungicide treatments had significant effect on the average yield of ten pickings but yield was less for the plant treated with mancozeb 12 g/L of water.

Figure 4: Average yield of each variety after ten picking.

Results of the present study showed that all fungicide treatments significantly controlled the early blight infection on tomato as compared to untreated control. There was a significant difference in all the treatments. Application of mancozeb 12 g/L and 16 g/L of water showed best results as spraying of mancozeb has been recommended for the control of early blight of tomato by several workers [16-20]. Among the five cultivars tested, Litah-545 showed best results followed by Litah514. This variation in different response to the Alternaria blight infection might be due to their genetic makeup.