Plant Virus Diseases: Research Approach and Current Activities at Plant Pathology Division S. Joshi, RD. Timila and BN. Mahto Plant Pathology Division Nepal Agricultural Research Council (NARC), Khumaltar, Nepal

Contents Introduction Survey Detection and diagnosis of seed- borne viruses Host resistance Seed Cleaning for virus free lot Current research activities

Introduction Virus diseases are one of the major constraints for higher production of crop plants Heavy losses in yield of crop plants due to viruses especially in vegetables Combined infestation of more than two viruses at time in a particular crop The incidence and severity of different virus diseases on different crops are in increasing trend.

Introduction (contd.) Economic yield losses in various crops are not known Sometimes 100% yield loss was observed in Zucchini crop Farmers experiences more than 90% yield losses in cucumber, other cucurbits and tomato crops Virus disease management particularly in vegetables and leguminous crops are most essential

Survey of Virus Diseases

Tomato yellow leaf curl virus in tomato and pepper TYLCV is a serious problem in tomato and chilli especially in terai and foothills (Joshi et. al. 1996). The incidence ranged from 5 to 70% in tomato and 20-80% in pepper. (c-DNA hybridization test at AVRDC, Taiwan and University of Wisconsin, USA) showed 42% of tomato samples positive to Indian probe of TYLCV TYLC

Virus Diseases in Pepper Cucumber mosaic virus (CMV) and Chilli veinal mottle virus (CVMV) are widely spread disease in pepper cultivated areas. CVMV mostly recorded in the mid hills CMV and CVMV were identified by Double Antibody Sandwich ELISA (Antiserum and IgG were provided by AVRDC). Tomato yellow leaf curl virus (TYLCV) reported in chilli growing areas (diagnosed with c-DNA hybridization) 57% of pepper samples showed positive reaction to Indian probe of TYLCV and 17% to Thai probe.

Cucurbits virus complex: Complex infection of CMV, ZYMV, WMV 1 and 2, SqMV, CGMMV found in Zucchini squash and cucumber Wide spread in the mid hills of Nepal CMV reported in most of the cucumber growing areas

Virus Diseases of Zucchini The tested zucchuni plants were found to be infested by ZYMV and WMV1

Mungbean Yellow mosaic virus (MYMV) MYMV observed as a severe threat in Mungbean, blackgram and soybean in terai and inner terai of Nepal MYMV also detected in horsegram and pigeon pea

Detection and diagnosis of seed-borne viruses in some legumes

Pea seed-borne mosaic virus (PSbMV) in Lentil Lentil seed samples tested at different time intervals were observed to be infested with PSbMV (Joshi et. al. 1993 and 2004). Detection Method: Growing-on test followed by DAC ELISA Indicator plant assay: Infection ranged from 0.5 to 12.7%

Pea seed-borne mosaic virus (PSbMV) Broad bean seed samples were also found to be infested with PSbMV Infection ranged from 3.8 to 7.8%. (Joshi et.al.,1993)

Bean common mosaic virus Bean common mosaic virus was detected in seed samples of blackgram Infection ranged from 0.6 to 2.5%

Host Resistance

Screening tomato genotypes against TLCV: Out of 19 genotypes , Thirteen were found resistant under artificial inoculation condition through viruliferous whiteflies (Bemicia tabaci) under screen house On field condition at Sarlahi, ATY2, ATY4, ATY6 , Fiona, TY Gold lines of tomato were found resistant while at Nepalgunj, all the above lines were found susceptible. .

Screening Pepper against CMV and CVMV Under screen house condition: Pepper genotypes, P- 3, Perennial HDV, PSP 11, Tiwari 2, and LV 2722 were observed resistant to local isolate of CMV Local cultivars of pepper from Bhaktapur, HAD 832, Huareu (Hybrid) and Toom were resistant to local isolate of CVMV.

Screening Mungbean genotypes against Mungbean yellow mosaic virus Out of 15 genotypes, three lines, VC 6370, VC 6369, VC 6370 (21-16) were found resistant at Rampur Almost all the lines were resistant at Sarlahi conditions a tarai district of Nepal Two resistant genotypes have been released for cultivation as a varieties in the name of Pratikchya and Kalyan.

Cucumber Seed Cleaning for CMV free state

Seed samples collected from hilly districts (during 2004 and 2005) Growing on test followed by ELISA for detection CMV was detected in 40% of seed samples tested

Cucumber seed Cleaning for CMV free state The extent of infection ranged from 2 to 80 %. No infection was found in the seed samples tested during 2005, Seed samples were produced from seed lot sorted free of infection during 2004 test.

Current Research Activities

Current research activities focuses on Survey of plant virus diseases Identification and preservation of identified virus (long term preservation on host plant and dry preservation) Testing of different antiviral products and botanicals for management of cucurbits virus diseases

Management of Virus Diseases Use of antiviral products and botanicals Spraying of antiviral products like Anti-VS (Korean), Victovirus, Privintal, Viricon Other natural products like cow milk, Bougainvillea leaf extract Insecticide Oshin before inoculation of virus was found effective to minimize virus diseases Reduced incidence and severity up to 5 weeks from the date of first spray (PPD 2013)

Management of Virus Diseases Significantly higher yield of fruits were produced by Victovirus, Anti V-S and fresh Bougainvillea leaf extract in zucchini squash

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