Management of Cercospora Leaf Spot of Mungbean [Vigna radiata (L.) Wilczek] using Fungicides and Host Resistance in Bundelkhand Region of Uttar Pradesh, India

Mungbean [Vigna radiata (L.) Wilczek] is an important short duration summer legume in the tropical and subtropical countries of the world. In India, this crop is cultivated in three different seasons viz., Kharif (July- Oct), Rabi (Sept- Dec) and Zaid or summer (March- June). In India, mungbean is one of the thirteen food legumes and is also considered 3rd important pulse crop after chickpea and pigeonpea. Despite its multifaceted importance, the mungbean production could not be stabilized in the country. Mungbean is attacked by several pathogens, especially cercospora leaf spot (C. canescens, C. cruenta), powdery mildew (Erysiphe polygoni), anthracnose (Colletotrichum capsici), charcoal rot (Macrophomina phaseoli), web blight (Rhizoctonia solani), Alternaria leaf spot (Alternaria alternata), Aschochyta blight (Ascochyta phaseolorum), root disease complex (Pythium spp., Rhizoctonia solani, Fusarium spp.), reniform nematode (Rotylenchulus reniformis), root knot (Meloidogyne spp.) nematodes and yellow mosaic virus. Among all these diseases, cercospora leaf spot and yellow mosaic virus have been found to be most destructive in causing qualitative and quantitative losses worldwide (Nair et al., 2019).
               
CLS occurs regularly in the most of the mungbean growing areas. It is very wide spread and has been reported from many countries. The leaf spot caused by Cercospora canescens was declared as a threat to mungbean cultivation in several countries for its devastating appearance in crop stands. CLS causing yield loss ranging from 50-70% has been observed in mungbean (Chand et al., 2012). The yield losses vary depending upon how early the crop is infected in the season, crop variety and prevailing weather. Although scientific recommendations for management of a particular disease are more or less similar in different parts of the world, the management strategies in a particular region prove better when devised out of local scientific studies and according to socio-economic conditions because nature of the host and pathogen may vary according to local climate and weather conditions. Actual determinant of amount and spread of any disease may be variable according to local ecology and environment. Therefore, the biotic stresses experienced by this crop in Bundelkhand region need to be addressed. Until now very few varieties of mungbean have been found resistant or moderately resistant to C. canescens, although several improved varieties have been developed through selection, hybridization and mutation (Hasan et al., 2017). Use of chemicals in disease management programmes is inevitable at some point of time for the management of plant diseases especially those involving polycyclic pathogens. It was an established fact that although ecofriendly and economical strategies are available, but these were not as effective as chemical management. Keeping the importance of mungbean as well as the associated disease in view, the present study was, therefore, intended to find host resistance and chemical molecules for management of CLS understanding crop conditions.

Evaluation of fungicides against CLS under natural epiphytotic conditions
 
Field experiments were carried out during the two successive crop seasons viz, Kharif 2019 and 2020 to study the efficacy of different fungicides on CLS. The crop was sown in mid July and harvested in the last week of September in both years. The NPK fertilizers were applied @ 30:50:30 kg ha^-1, respectively at the time of last harrowing besides ensuring recommended agronomy package of the crop. Sowing was done manually in 10 rows plots. The mean of maximum and minimum temperature, relative humidity and rainfall from July to September, 2019 was 30.58^oC, 24.89^oC, 79.15% and 99.64 mm, respectively, and it was 35.78^oC, 27.07^oC, 83.75% and 47.85 mm during the months from July to September during the year 2020. In the experiment 9 fungicides viz., Propiconazole 25% EC @ 0.10%, Carbendazim 50% WP @ 0.15%, Copper Oxychloride 50% WP @ 0.25%, Captan 70% + Hexaconazole 5% WP @0.20%, Hexaconazole 5% EC @0.25%, Mancozeb 75% WP @ 0.25%, Tebuconazole 25.9% EC @ 0.10%, Carbendazim 12% WP + Mancozeb 63% WP @ 0.20% and Azoxystrobin 23% SC @ 0.10% were assessed against Cercospora leaf spot using IPM 2-3 as a test variety during both the seasons. All treatments were replicated thrice under randomized block design. The fungicide treatments were applied as foliar sprays and a total of two sprays were given at the time of initial disease symptoms appearance and later at fifteen days after first spray. The spray operation was done during the evening with the help of Knap sack sprayer. The crop was sprayed till run off and in check plot only plain water was sprayed.
        
Data was collected regarding per cent incidence of CLS at 60 days of sowing. The severity of CLS was recorded with the help of randomly selected five plants in a plot having 4m × 3 m. size. CLS severity was recorded with the help of standard scale of All India Coordinated Research Project on MULLaRP (Alice and Nadarajan, 2007) and PDI was calculated. Observations of yield attributes viz., number of primary branches/ plant, number of pod/ plant, seed yield/ plant (g) were recorded with the help of randomly selected five plants in a plot. Number of seed/ pod was counted on the basis of five pods randomly selected from each plot just prior to harvesting of crop. Pod yield/ plot (kg) was recorded prior to threshing of harvested pods. One hundred seed weight (g) and yield (q/ha) were recorded after threshing and cleaning of seeds. The data of each observation/ experiment recorded in above investigations were statistically analyzed and calculations were made after applying the test of significance for the treatment means. Analysis of data is carried out using angular transformation at 5% level of significance with the help of OPSTAT software.
        
The observations recorded for CLS and yield parameters were calculated by using appropriate formula as given under:
 
Per cent disease incidence:
          
Per cent disease severity (Wheeler, 1969):
   
Per cent disease control:    
          
Per cent yield increase:
   
Reaction of mungbean genotypes against cercospora leaf spot
 
The experiments were laid out in augmented design with 8 blocks and 5 checks during both seasons i.e. Kharif 2019 and 2020 to evaluate 200 germplasm of mungbean for identification of resistance against CLS under natural epiphytotic conditions. Each genotype was sown in 3m × 0.6m plots (2 rows) with inter-row and inter-plant spacing of 30 cm and 10cm, respectively. One local susceptible cultivar i.e. IPM 2-3 was included in the screening programme which was sown around the experimental blocks to ensure presence of abundant and uniform inoculum in the field. Land preparation, fertilizer application and sowing was done as described in earlier experiment. The genotypes were categorized on the basis of an established scale and observation for disease severity was recorded at 60 days of sowing using 1-9 scale for which a random sample of 5 plants was taken in each plot (Singh et al., 1995). The calculations for disease incidence/ severity and yield attributes were done with the help of above formulae.

Effect of fungicides on CLS and yield parameters
 
The findings of both crop seasons (Kharif 2019 and 2020) indicated that among all treatments of fungicidal sprays given twice at 15 days interval after symptom appearance, carbendazim gave the maximum reduction (45.57%) in CLS incidence over the unprotected crop and it was followed by 35.44% and 30.74% reduction in incidence with treatments Carbendazim + Mancozeb and  Azoxystrobin, respectively. Similar trend of results were found with CLS severity, where both treatment with Carbendazim and combination of Carbendazim + Mancozeb, were found equally effective which were statistically at par  to each other with disease severities of i.e. 58.45% and 52.65%, respectively followed by Azoxystrobin which resulted in 41.11% reduction in severity. In the investigation, it was observed that impact of fungicides on number of primary branches per plant or number of seed per pod was non-significant (Table 2). However, twice application of fungicides enhanced the other yield parameters like number of pod/ plant, pod yield/ plot, seed yield/ plant, hundred seed weight and seed yield/ hectare over the unprotected control (Table 2 and 3). Maximum enhancement in seed yield (53.39%) as well as in yield parameters were recorded due to application of Carbendazim followed by 44.88% and 38.82% enhancement in seed yield due to Carbendazim + Mancozeb and Azoxystrobin, respectively. Among all nine treatments of fungicides, treatment with Captan + Hexaconazole was found to be least effective in reducing disease incidence (7.59%) and severity (6.12%) as well as to increase the yield and its components in comparison to  unprotected crop. There was a noticeable point that the yield components like pod yield per plot (kg/12m²), seed yield per plant (g) and 100 seed weight (g) obtained in treatments with Carbendazim or combination of Carbendazim + Mancozeb were statistically at par with each other. But with respect to overall seed yield (q/ha), carbendazim gave the highest yield (10.63 quintal/ha) as compared to treatment with Carbendazim + Mancozeb. The maximum seed yield was recorded with Carbendazim because of highest number of pods per plant recorded which were significantly higher compared to carbendazim + Mancozeb (Table 1, 2 and 3).
 

 

 

        
The findings of present investigation are quite in conformity with the reports of earlier workers. Bhat et al., (2015) reported that foliar spray of Carbendazim (0.1%) was effective in reducing the disease severity of CLS of mungbean. Palakshappa et al., (2012) evaluated different fungicides against Cercospora leaf spot of sesame and found carbendazim (0.1%) as most effective in controlling the disease. Muhammad and Garba (2015) evaluated the efficacy of three fungicides against cercospora leaf spot and found that least disease incidence, disease severity, highest number of pods per stand, pod weight and 100 seed weight were recorded with Carbendazim 12% + Mancozeb 63%. Yadav et al., (2014) reported that combination of Carbendazim + Mancozeb was found superior against Cercospora leaf spot of greengram. Shrawan et al., (2015) evaluated 13 fungicides against cercospora leaf spot of okra and found that Tebuconazole (0.1%), Propiconazole (0.1%) and Bavistin (0.1%) gave minimum disease incidence and maximum fruit yield. Khunti et al., (2005) recorded minimum intensity of CLS and highest yield with the application of triazoles fungicides. Hence, the findings of earlier workers are quite supportive to the results of present investigation.
 
Screening of mungbean genotypes for resistance against CLS
 
Several workers have made efforts to identify resistant sources; however, most of the lines identified did not maintain the same level of resistance over time. Therefore, continuous efforts are needed to find out the sources of resistance. In this connection a set of 200 mungbean genotypes were evaluated for resistance against Cercospora leaf spot during Kharif 2019 and 2020 crop seasons under natural epiphytotic conditions.
               
Out of 200 mungbean genotypes, only four genotypes viz., PDM 04-123, PDM 54, EC520034-1 and EC 520022 were found to be resistant against CLS during both the Kharif seasons, however, none of the genotype were found with immune reaction to Cercospora canescens. There is a need for intensive screening of available genotypes against the disease so as to indentify the genotypes with high degree of resistance which can be used as resistant donor. Raje and Rao (2002) were also identified 35 genotypes of mungbean possessing resistance against Cercospora leaf spot.