Plant Virus Diseases in Nepal: Current Status and Future Strategies Dr. RD. Timila , S. Joshi and Dr. BN. Mahto Plant Pathology Division, Nepal Agriculture Research Institute, Nepal Agricultural Research Council Khumaltar Contents • Background Information • Economic Significance • Prevalent plant virus diseases in Nepal and their distribution • Current status of major virus diseases in vegetable crops • Seed-borne virus diseases of vegetable crops • Diagnostic Methodologies • Constraints • Future Strategies and Needs Introduction • Cultivation of various vegetables is one of the most potential income generating sources for the livelihood of the majority of the farmers • High value crops • Vegetable cultivation: Area under = 245037 h Production = 3298816 mt Productivity= 13.46 mt/h (Source: Vegetable Development Directorate, Annual Report, 2011/12) • Diseases are one of the major constraints of successful cultivation • Epidemic of some of the diseases are causing havoc with negative impact on the economy of the farmers • In recent years, viral disease problem appearing as the most important diseases for some of the major vegetable crops. • It induces broad range of symptoms affecting growth, yield and quality of the produce • Its incidence and severity is increasing • New virus emerging like diseases are also • Research and studies on plant viruses are limited in Nepal Economic Significance . Crop loss estimated 15-20% due to disease alone (Rajbhandary and Shrestha, 1992) • In recent years, ‘virus diseases‘ caused significant Yield losses • Posed a threat for production and productivity of important crop plants especially vegetables • Deteriorate both quality and quantity of produce and ultimately reduces market price • Its economic importance has been realized since past many years. • Crop or yield losses incurred due to specific virus in specific crop in Nepal is not yet studied. • However, some seed borne viruses could cause yield loss (Shrestha and Albrechtsen,1992) depending on type of virus and the crop. – PSbMV in pea: up to 36% – SBMV in cowpea: up to 59% – CAMV in cowpea: up to 87% Prevalent plant virus diseases in Nepal and their distribution Cereals and Legumes: Crop Virus disease Distribution/inc. Rice Rice Tungro Virus, Rice dwarf Virus Eastern & Central terai, Kath Maize Maize Leaf Fleck Mosaic Virus Rampur Wheat Barley Yellow Dwarf Virus Bhairahawa (Terai) Soybean Soybean Mosaic Virus, Tobacco Ring Spot Virus, Mungbean Yellow Mosaic Virus Terai and mid-hills Cowpea Cowpea Aphid-borne Mosaic Virus, Cowpea Mosaic Virus Chitwan, Pea and Broad bean Pea Seed- borne Mosaic Virus (in seed samples) Prevalent plant virus diseases in Nepal ………(contd.) Cereals and Legumes (contd.): Crop Lentil Virus disease Pea Seed- borne Mosaic Virus Distribution Mid-hills (In seed) Pigeon pea Sterility Mosaic Virus, Yellow Mosaic Terai and inner Virus terai, (15-50% inc.) Blackgram Bean Common Mosaic Virus (in seed) Mungbean Mungbean Yellow Mosaic Virus Terai Groundnut Tomato Spotted Wilt Virus (Bud necrosis) Terai Prevalent plant virus diseases in Nepal …….(Contd) Vegetables crops: Crop Virus disease Distribution Tomato Tomato Mosaic Virus, Tomato Terai, inner terai Leaf Curl Virus, Cucumber Mosaic and mid-hills Virus Pepper (Chili and capsicum) Tomato Leaf Curl Virus, Chili Veinal Mottle Virus, Cucumber Mosaic Virus Terai, inner terai and mid-hills Cucumber and Zucchini squash Cucumber Mosaic Virus, Zucchini Yellow Mosaic Virus, Watermelon Mosaic Virus 1 and 2, Squash Mosaic virus, Cucumber Green Mottle Mosaic Virus Mid-hills, terai Prevalent plant virus diseases in Nepal …….(Contd) Vegetables crops: Crop Virus disease Distribution Broad leaf mustard, Turnip, Radish Turnip Mosaic Virus Mid-hills Okra Yellow Vein Mosaic Virus Terai, inner terai and mid-hills Bean Bean Common Mosaic Virus, Mid-hills, Y. Long bean Southern Bean Mosaic Virus Mid-hill and Terai Prevalent Plant virus diseases in Nepal…. (contd.) Fruits and cash crops: Crop Virus disease Distribution Potato Potato Leaf Roll Virus*, Potato Virus X, Potato Virus Y*, Potato Virus A, Potato Virus S, Potato Virus M *Terai, Mid-hills and high hills Large cardamom Large Cardamom Chirkey Virus Ilam, Panchthar, Chirkey), Cardamom Bushy Dwarf Taplejung, Virus (Foorkey) Citrus Citrus Tristeza Virus Mid-hills: Kaski, Dhankuta and Dailekh Papaya Papaya Ring Spot Virus Terai, Inner terai and foot-hills Tobacco Tobacco Mosaic Virus, Tobacco Leaf Curl, Cucumber Mosaic Virus (Strain) Terai and inner terai Current status of major virus diseases in vegetable crops: Tomato TLCV – First reported in 1994 (Timila and Joshi, 1994) after diagnosis using cDNA hybridization in collaboration with Dr. Maxwell (Univ. of Wisconsin) and AVRDC. – The virus is distributed in terai, inner terai, valleys and foothills. • Incidence ranged from 40-70% (Joshi et al.1997) . • Yield loss estimation in tomato was 50% (Joshi and Shrestha, 1999), 40% in Western hills (Ghimire et al., 2000). • In recent years also, the disease is severe in western terai. Tomato mosaic virus (ToMV): Prevalent in tomato growing areas causing poor plant growth and also appeared in combination with other viruses. Cucumber mosaic virus (CMV): Widely distributed in tomato growing areas of the mid-hills. Observed to be major. Severely affected in some of the fields. CMV in Tomato CMV with other virus comlex Virus ? Pepper: Virus complex varied from 3090%. (joshi and Shrestha, 2001, AVRDC) TLCV: Distributed in terai, inner terai, valleys and foothills. Incidence ranged from 20-80% (Chilli) (Joshi et al.1997) . Chilli veinal mottle virus (CVMV): Higher Incidence and severity in pepper has been observed at Kathmandu valley (mid hills). Virus infected plants were more than 80% recorded (Shrestha and Albrechtsen, 1992). In recent years also, the disease status remaining the same. Cucumber mosaic Virus (CMV): Widely distributed in terai, inner terai and midhills. The incidence ranged from 50-80% (SAVERNET II, midterm report. 1999). Presently also the disease is problematic. Cucurbit: CMV in cucumber , distributed throughout cucumber cultivated areas of mid-hills in severe form as revealed by sample received at PPD, Khumaltar and as observed in the farmers’ fields, causing considerable losses (PPD, 2003-2013). Complex infection of CMV, ZYMV, SqMV, WMV 1 and 2, and CGMMV in zucchini squash. Infection in some of the fields, up to 100% incidence at Kath. valley causing total crop failure (PPD, 2006). Various virus (Complex) disease symptoms in Zucchini squash Bottle gourd Broad leaf mustard: Turnip mosaic virus (TuMV): Observed mainly in broad leaf mustard but radish and turnip also affected. Widely distributed in the mid hills. Incidence up to 100%, causing total crop failure in some of the fields. Beans: Bean common mosaic virus (BCMV) has been observed in Bean fields in low incidence. Its distribution mainly in the mid-hills (as observed in the field visits) Bean common mosaic necrosis virus (BCMNV) recently reported from Kaski and Chitwan in Sweet bean with incidence ranging from 60-70% (Pudasaini et al., 2013). Okra: Mainly distributed in terai, inner terai and valleys of the mid hills. up to 70% incidence observed (Dahal, 1990). At present this disease is under high priority also. Potato: reported six viruses Potato leaf roll virus and potato virus y: distribution high in terai and moderate in midhills. They could cause yield loss 12-50% and 80% respectively. PVX, PVA, PVS and PVM, their distribution ranged from 24-27% higher in the Terai (24, 25, 27, 25%) but lesser than PLRV and PVY), Comparatively, PVX and PVS higher in high hills also. (Source, Dhital et al., 2010) Cardamom: Prevalence of Large cardamom chhirke virus (LCCV) and Cardamom bushy dwarf virus (CBDV) have been reported in the eastern hills with incidence ranging from 15-20% and 10% repectively (Srivastav, 2012). Low incidence of CBDV observed in our survey. (These viruses used to be the issues for cardamom crop, & losses not estimated yet) Some important identified seed-borne viruses in vegetable crops in Nepal • Tomato mosaic virus (Tomato) • Cucumber mosaic virus (Tomato, Pepper, Cucumber) • Cucumber green mottle mosaic virus (Zucchini squash, Cucumber) • Bean common mosaic virus (Common beans) • Cowpea aphid borne mosaic virus (Cowpea) • Southern bean mosaic virus (Yard- long bean) • Pea seed-borne mosaic virus (Pea) Field tolerance limit of infected plants for BCMV has been fixed for seed production of bean crop Foundation seed: 0.1% and for certified seed: 0.2% Diagnostic Methodology adopted • Growing on test • Indicator host plant test • Serological test (ELISA): based on the availability of antiserum • cDNA hybridization test for TLCV: only during SAVERNET project period at AVRDC and Univ. of Wisconsin Previous Collaboration with International Intitutions Training, Technical back-up, Small Lab equipments and little supplies • Danish Seed Health Center for Developing Countries ( Previous DGISP) • World Vegetable Center (AVRDC) • ICRISAT Constraints • Lack of adequate laboratory facilities for virological Research • Lack of controlled condition Green house facility • Lack of trained and adequate manpower • Lack of logistic facilities (Vehicle) for survey and monitoring • Inadequate availability of other lab supplies • Lack of continuous power supply • Lack of incentive Future Strategy • Regular survey and surveillance of virus diseases in different crop plants through out Nepal. • Detection and diagnosis of viruses in major vegetable crops • Epidemiological and yield loss studies on important virus diseases of crop plants • Seed transmission studies on seed-borne virus diseases of vegetable crops in particular • Host resistance screening • Alternative management Integrated management tools for Felt Needs For smooth running of Plant virus Research: • Establishment of molecular laboratory at plant Pathology Division, NARC • Establishment of controlled condition green house. • Collaboration with International Intitutions • Strengthening existing green and screen houses • Adequate Human resource for virus work • Capacity enhancement :Training for personnel in detection, diagnosis, vector virus relationship and etc • Exposure visits for scientists/technicians • Continuous power supply. Conclusion • Past and the present virus disease scenario indicated that the occurrence of several viruses on cucurbits, legumes and solanaceous vegetables and other crops in epidemic form in the country. • Virus suspected diseases observed, yet to be confirmed • Emphasis should be given in conducting research and studies on different aspects of virus diseases to develop management tools.