BIOEFFICACY OF PLANT EXTRACTS TO CONTROL CERCOSPORA LEAF SPOT OF MUNGBEAN ( Vigna radiata )

The experiment was conducted at Bangladesh Agricultural Research Institute farm, Joydebpur, Gazipur during March to July 2007 to evaluate the bioefficacy of some plant extracts in controlling Cercospora leaf spot of mungbean. Six indigenous plant species i.e. Neem leaves extract (1:4 w/v), Garlic cloves extract (1:5 w/v), Biskatali leaves extract (1:4 w/v), Alamanda leaves extract (1:6 w/v), Arjun leaves extract (1:4 w/v) and Debdaru leaves extract (1:5 w/v) were used in this experiment. The experiment was laid out in RCBD with seven treatments and four replications. Data on disease incidence, severity, yield contributing characters and yield of mungbean were recorded. Naturally, infection of the disease was considered in this experiment. The lowest disease incidence (7.33%) at 60 DAS was found in T1. Lowest and similar disease severity (PDI= 4.55) was found in T2 and T3 at the same DAS. Neem extract treated plots gave better response in yield (1.26 t ha-1) and all the yield contributing parameters like inflorescences plant-1 (13.45), tallest plant (51.44 cm), the maximum number of pods plant-1 (26.81), length of pod (8.56 cm), number of seeds pod-1 (12.64) and 1000 seeds weight (27.33 g) followed by T2 and T3. The highest disease incidence (26.50%) and disease index (13.65%) were recorded in treatment T7 at 60 DAS. Yield and all yield contributing factors were lowest in same treatment. The results of the experiment suggested that the use of neem leaves extracts are effective for minimizing Cercospora leaf spot incidence, severity and increasing yield of mungbean.


Introduction
Mungbean (Vigna radiata), belongs to the family leguminosae and sub family papilionaceae, is one of the most important pulse crops having global economic importance as a dietary ingredient of the staple food in tropical and subtropical region.It is grown three times in a year covering 21862 ha with an average yield of 0.82 t ha -1 (BBS, 2009).It can fix atmosphere nitrogen through symbiotic relationship with soil bacteria and improve the soil fertility (Yadav et al., 1994).Mungbean has been considered as a "poor men's protein" (Mian, 1976).Apart from 26% protein, it also contains 51% carbohydrate, 10% moisture, 4% minerals and 3% vitamins (Khan, 1981).In Bangladesh, total sixteen diseases of mungbean have been recorded (Fakir, 1983 andBakr, 1993) which are responsible for lower yield of mungbean.Among the diseases, Cercospora leaf spot is a serious disease of mungbean (Verma and Sandhu, 1992) and causes yield losses of up to 58% (Lal et al., 2001).It is widely distributed all over the country where mungbean is cultivated.The causal organisms of this disease are Cercospora cruenta, C. conescens, C. kikuchii and C. caracallae.Among these, Cercospora cruenta is the most prevalent species (Talukder, 1974).The initial symptoms of the disease appear as water soaked spot on leaves.As spots become older may coalesce together, causing enlarged dead area on the infected leaves.Heavy infections of Cercospora can cause premature defoliation of the mungbean plant.Sometimes the leaves may become malformed and wrinkled.Maturity is delayed in the diseased plants resulting poor pod formation.Seeds that developed on severely infected plants are small and immature (Poehlman, 1991).Different approaches such as spray of chemical fungicides (Singh and Singh, 1978), spray of different plant extracts and use of resistant variety are tried to control Cercospora leaf spot of mungbean.Though the released varieties of mungbean in Bangladesh are described as resistant variety but most of them show susceptible reaction towards this disease and the susceptibility varied due to variation of weather situation during trail before release and commercial cultivation.Indiscriminate and frequently use of chemicals affects the soil health.Harmful chemical substances enter into the food chain that ultimately causes serious health hazards.Ecofriendly management like use of plant extract against plant diseases control is however, a recent approach to plant diseases management and it has drawn the special attention of the plant pathologist all over the world.Most of the plant extracts are cost effective and do not have harmful effects on beneficial soil microorganisms.In Bangladesh, only a few attempts have been made to evaluate plant extracts against plant diseases (Ashrafuzzaman and Hossain, 1992;Hossain et al., 1993;Ashrafuzzaman and Khan, 1992;Suratuzzaman et al., 1994).Many researchers reported that plant extracts have antifungal properties and potentially used against many plant diseases (Singh and Dwivedi, 1987;Tariq and Magee, 1990;Lakshmanan et al., 1990).It can help to avoid environmental pollution caused by chemicals and thus become most rewarding one to our existing socio-economic conditions and environmental threats.In the light of above background, the present piece of research work has been undertaken to estimate the effects of different botanicals on the incidence and severity of the Cercospora leaf spot of mungbean, yield and yield contributing characters of Cercospora leaf spot infected mungbean.

Materials and Methods
The experiment was conducted in the farm of Bangladesh Agricultural Research Institute (BARI), Joydebpur, Gazipur, Bangladesh during the period from March to July 2007.In this research work, BARI moog-3 was used as test crop where as BARI moog-3 is resistant to Cercospora leaf spot and Yellow mosaic virus of mungbean.Seeds were collected from pulse crop research division of BARI, Joydebpur, Gazipur.Seven different treatments including untreated control were explored in the experiment.Treatments were T1 = Neem (Azadirachta indica) leaves extract (1:4 w/v), T2 = Garlic (Allium sativum) cloves extract (1:5 w/v), T3 = Biskatali (Polygonum hydropiper) leaves extract (1:4 w/v), T4 = Alamanda (Allamanda cathertica) leaves extract (1:6 w/v), T5 = Arjun (Terminalia aurjuna) leaves extract (1:4 w/v), T6 = Debdaru (Polyalthia longifolia) leaves extract (1:5 w/v), T7 = Untreated (control).The experiment was laid out in Randomized Complete Block Design (RCBD) with four replications.The unit plot size was 4.0 m × 3.0 m.The distance between two blocks and two plots were 1.0 m and 0.5 m, respectively.The beds were prepared manually after ploughing and laddering.Then the seeds were sown in the bed in line sowing with 30 cm line-to-line distance.Fertilizers and manures were applied as per recommendation of BARI.Watering and intercultural operations were done when necessary.Plant extracts were collected from Bangladesh Agricultural Research Institute, Joydebpur, Gazipur.The extracts were prepared by using the method of Ashrafuzzaman and Hossain (1992).After washing weighted leaf, the big leaves were cut into small pieces.For getting extract, weighted plant parts were blended and then distilled water was added into the jug of the blender.The pulverized mass was squeezed through 3 folds of fine cotton cloth.For getting 1:4 (w/v) ratio 400 ml of distilled water was added with 100 g of plant parts, 1:5 (w/v) ratio 500 ml of distilled water was added with 100 g of plant parts, 1:6 (w/v) ratio 600 ml of distilled water was added with 100 g of plant parts.Plant extracts were applied in the field as foliar spray.Spraying was done 3 times at 7 days interval starting from vegetative growth.The plants were naturally infected.The disease incidence and severity was recorded at 30, 40, 50 and 60 DAS (Days after Sowing).For disease incidence, the infected plants were identified by comparing it symptoms critically with those already published by Ahmed (1985).The incidence of Cercospora leaf spot was calculated as follows: Percentage Infected plants Number of infected plant in each plot = ×100 Total number of plants in each plot Disease severity were calculate by using (0-9) disease severity score of Metha and Mondal (1978) and determined as PDI (Percent Disease Incidence) by using following formula (Krisna Prasad et al., 1979).

Percent Disease Index (PDI)
Sum of total ratting = × 100 Total number of observation × Highest grade in the scale The severity of Cercospora leaf spot disease was recorded according to the grade of Metha and Mondal (1978)  71% and above leaf area infection Data on plant height (cm), number of primary branches plant -1 , number of inflorescences plant -1 , number of pods plant -1 were collected from standing crops and data on pod length (cm), number of seeds pod -1 , 1000 seed weight (g), yield plot -1 (kg), yield (ton) hectare -1 were recorded after harvesting.The data obtained for different characters were analyzed to find out the significant differences among the treatments.The analysis of variance was performed by using MSTAT program.The significance of the difference among the treatment means was estimated by DMRT (Duncan's Multiple Range Test) at 5% level of probability (Gomez and Gomez, 1984).

Results and Discussion
A gradual increasing trend for both disease incidence and severity was found with the increasing of DAS.There were no significant variations in Cercospora disease incidence and disease severity (0-9 scale) for different treatments at 30 DAS (Table 1).Ahmed (1985) reported that neem extract had potential for controlling Cercospora leaf spot in mungbean.It has been observed that neem leaves extract resulted significant reduction of Cercospora leaf spot of mungbean over untreated (control) (BARI, 2007;Khan, 1981;Mehta and Mondal, 1978).
Table 1.A little variation were recorded for plant height due to application of different plant extracts used in this experiment for controlling Cercospora leaf spot of mungbean ( inflorescences plant -1 (13.45) was recorded from treatment T1 which was identical with T3 (13.05)(Table 2).Alternatively, the lowest number of inflorescences plant -1 (10.02) was recorded from the treatment T7. Williams et al. (1968); Poehlman (1991); Roy and Malathi (2001) reported the similar effect on number of inflorescences per plant and plant height of mungbean.The highest number of primary branches per plant (5.38) was recorded from treatment T1 which was more or less statistically similar with treatment T2-T6 (Table 2).Conversely, the lowest number of primary branches per plant (3.62) was recorded from the treatment T7.The maximum number of pods per plant (26.81) was recorded from the treatment T1 (Table 2).On the other hand, the minimum number of pods per plant (21.07) was recorded in treatment T7.The maximum pod length (8.56 cm) was recorded from the treatment T1 which was statistically similar with treatment T3 (8.51 cm) (Table 2).On the contrary, the minimum pod length (6.08 cm) was recorded from the treatment T7 followed by T6 treatment (6.85 cm) which was identical T4.The maximum number of seeds pod -1 (12.64) was recorded for treatment T1, which was statistically similar with treatment T2, and T3 (12.04 and 12.00 respectively) (Table 3).On the other, hand the minimum number of seeds per pod (10.26) was recorded from the treatment T7 which was statistically similar with treatments T6, T5 and T4 (10.82, 10.96 and 11.00 respectively).Increase of number of seeds per pod -1 over control showed variation for different treatments in the present experiment (Table 3).
The maximum increased number of seeds pod -1 (23.20%) was recorded from the treatment T1 and the minimum was recorded in treatment T6 (5.46%).The maximum 1000 seeds weight (27.33 g) was recorded in treatment T1 which was statistically similar with treatments T2, T3, T4, T5, and T6 (26.15 g, 27.26 g, 26.02 g, 26 g and 26.46 g, respectively) (Table 3).Oppositely, the minimum 1000 seeds weight (23.73 g) was recorded from the treatment T7.Increases of 1000 seeds weight over control in percentages showed variation for different treatments under the present experiment.The maximum increase 1000 seeds weight (15.17%) was recorded from the treatment T1 and the minimum was recorded from treatment T6 (9.57%) (Table 3).
Table 2. Effects of different treatments on yield contributing characters of Cercospora leaf spot infected mungbean (cv.BARI moog-3) Different letter (s) in the same column showed the significant different at 0.05 level of probability The maximum yield plot -1 (1.51 kg) was recorded from the treatment T1 i.e. by applying neem extract which was statistically similar with treatment T3 (1.45 kg) i. e. biskatali leaf extracts (Table 3).In contrast, the minimum yield plot -1 (1.21 kg) was recorded from the treatment T7 where no extract was applied.Increase of yield per plot over control showed differences for different treatments in this experiment.The data of yield plot -1 was computed to yield hectare -1 .The maximum yield (1.26 ton) was recorded for treatment T1 which was statistically similar with treatments T3 and T2 (1.21 and 1.20 ton) (Table 3).
On the other hand, the minimum yield per hectare (1.01 ton) was recorded from the treatment T7.The maximum increased yield hectare -1 (24.75%) over control was recorded from treatment T1 and the minimum was recorded from treatment T6 (12.87%).Among the different plant extracts, neem leaves extracts was more effective and bishkathali also had similar effects (Table 3).Islam et al. (2006)

Conclusion
The overall results suggested that the use of neem leaves extracts are effective for minimizing Cercospora leaf spot incidence, severity and increasing yield of mungbean than other treatments.The enthusiastic researchers can be motivated to explore other plant extracts and spell out the extract concentration for control Cercospora leaf spot of mungbean.
describe in the following table:

Table 3 .
Number of pods plant -1 , pod length, seed yield and increase of seed yield as influenced by different treatments used for the management of leaf spot of mungbean (cv.BARI moog-3)In a column figures having dissimilar letter(s) differ significantly at 0.05 level of probability.