Host resistance breeding against the virus diseases of soybean in Nepal

A wonderful crop soybean (Glycine max L. Merril, 2n = 40) belongs to Leguminosae family is the third most important grain legume of Nepal in terms of acreage and production after lentil and blackgram. It is widely distributed in the mid hills and to a less extent in the terai& inner terai. In mid hills and valleys it occupies about 80% in terms of total soybean area and production. Soybean can be grown successfully at altitude ranging from 500 to 1500 m amsl (Neupane and Bharati 1990), showing diverse adaptability to varied agro-ecological zones. In mid hill, it is mainly grown as intercrop or mix crop with maize and on paddy bund. It is also relayed with maize in the valleys. It is grown mainly as mixed cropping with minimum inputs which have very much affected its intensification of production especially in mid hills. In recent years, soybean cultivation as mono or relay with maize is slowly gaining popularity in terai and inner terai due to its extensive use as poultry feed. There is a great potential to increase the area and production due to its stable nature of the production and grown in diverse climate from terai to high hills. The demand of soybean is increasing day by day with increase in poultry business in the country as it is important and basic ingredients of poultry feed. Mostly, soybean for feed industries is imported from India. At the same time, Nepal imports huge amount of raw materials of soybean for oil and feed purposes. Since soybean contains cholesterol free oil, which is additional useful to the heart patients (safer). In the year 2014 alone, soybean crude oil of Nepalese Rupees 12483.2 million (around $120.030 million) was imported from India, Argentina, Brazil and Paraguay (MoAD, 2015). Thus there is high potential of soybean cultivation as a commercial scale in the terai, innerterai and mid hills regions of Nepal. Soybean has high nutritional value for human being as it contains high amount of protein (40-50%), oil (20%), and rich in multi-vitamins and essential minerals. It is reported that locally available black and brown coated soybean landraces are rich in protein while creamy white, yellow coated soybean are rich in oil content. There is possibility of rich oil and protein content imported exotic lines from IITA and IVRDC. It can be used as a good supplemental food with cereal especially in the underdeveloped country where people suffer from mal-nutrition. As a human food soybean seeds are utilized in many ways green pods as vegetables and dry seeds eaten roasted or fried. Soybean oil is used for manufacturing vegetable ghee. Soybean is used to prepare baby food and food for diabetic patients. Soybean cake and meal are utilized for preparing various livestock and poultry feeds. Soybean crop can be used as green manure and as a fodder crop. Particularly for developing country like Nepal where chemical fertilizers are extremely expensive & inclusion of soybean in existing cropping pattern has a substantial benefit both in terms of human health for producing protein rich food and also in improving the soil health. Figure indicated soybean‘s area, production and productivity has been increased trends by 36%, 189% and 115 % respectively in between 1983/84 and 2012/13. The increasing trend of soybean production and productivity was due to the available of technologies, HY varieties, soybean mission and international strong support for genetic materials. However, the national yield of soybean is very low in international level and evener has been slightly increased from 546 (1984/85) to 1180 kg/ha (MOAD, 2015). Contributing low yield of the Nepalese soybean might be due to the disease severity like Yellow Mosaic Virus (YMV), anthracnose/ pod blight (Colletotrichumtruncatum), charcoal rot (Macrophominaphaseolina) and bacterial pustule (Xanthomonasphaseolivarsojensis) in the terai and inner terai while CLS (Cercosporakikuchii), anthracnose/ pod blight and BP in the mid hills and frog eye leaf spot (Cercosporasojina) in the high hills are important (NGLRP, 2010).

 • Figure indicated soybean ‘s area, production and productivity has been increased trends by 36%, 189% and 115 % respectively in between 1983/84 and 2012/13 

• Imported huge amount of soybean raw materials and oil products (About $ 163.26 million) 

• Starts soybean mission in Nepal since 2012 

Vector white fly (Bemisiatabaci Genn.) is responsible for transmitting Mungbean Yellow Mosaic Virus disease has been escalated a serious threat to blackgram, soybean, mungbean and cowpea production in terai/ inner terai and foot hills of Nepal. Yield losses recorded up to 100%, 52.6% and 21% have been reported due to MYMV in blackgram, mungbean and soybean, respectively. Soybean is susceptible to several viruses transmitted by the vectors aphids, beetles and whiteflies prevailing in Nepal. Most of the virus infection results in foliar symptoms such as mosaic and mottling, thickening/brattling of older leaves, puckering, leaf distortion, severe reduction in leaf size, and stunting of plants. Mixed infection with more than one virus is common under field conditions. Mungbean yellow mosaic virus transmitted by whitefly (Bemisiatabaci Gennidius) is the most prevalent virus associated with soybean mosaic disease in Nepal. Depending on genotype and age of infection symptoms range from mosaic and mottling, leaf curling, green vein banding, and stunting. Most severe symptoms are observed in plants infected at early stages of growth (pre-flowering) and significant reduction in pods. Soybean yellow mosaic virus was found to be the most prevalent virus associated with this disease. Soybean mottle mosaic virus, which also causes similar symptoms, was found to be less frequent in the fields. Virus-infected plants produce bright yellow mosaic or specks, and develop into large blotches on the leaf lamina, but this infection does not result in leaf distortion or reduction in lamina size. This is the most convenient, economical, and effective approach for controlling soybean virus diseases. Even though, the maximum yield potential obtained in sole cropping at research station was recorded as high as 3.5 t/ha. Till date Hardee, Cobb, Puja are released for inner terai/terai, while Ransom, Seti, Lumle 1 and Tarkari Bhatmas 1 for Kathmandu valley and similar environments. Released varieties have more or less smaller seed size, susceptible to different foliar diseases like YMV, pod blight, Bacterial pustule, frog eye leaf spot and longer maturity period (135-145 days), which farmers usually don't prefer. The performances of varietal differences have been observed due to its severity. Chemical control measures may have the option but they are not environmentally friendly and healthier. Under such situation use of resistant varieties and manipulations in cultivation practices are important choices for the proper management of grain legume diseases. This approach is accessible to marginal and disadvantaged farmers too. High population of white fly (Bemisiatabaci) was observed at the station and on farm level during the crop season in the fiscal year 2012-2014 which was the challenges and opportunity to select the best YMV resistant lines. G x E interaction is the directly associated with the diseases intensifying and depends on the favorable climate to multiply the whitefly. Considering these all facts, the main objective of the study was carried out to identify and select the high yielding and host resistant diseases to yellow mosaic virus of soybean suited in the existing cropping system. MYMV severity is gradually building up year after year and challenges to the breeders at Rampur, Chitwan.