RESEARCH ARTICLE Induction of systemic resistance through antiviral agents of plant origin against papaya ring spot disease (Carica papaya L.) Shyam Singh a , L.P. Awasthi c and R.K. Singh a,c * a Division of Plant Pathology, Central Coffee Research Institute, Chikmagalur District, Karanataka-577117; b Department of Plant Pathology, N.D. University of Agriculture and Technology, Kumarganj, Faizabad-224229 (U.P.), India; c Department of Mycology and Plant Pathology Institute of Agricultural Sciences, Banaras Hindu University Varanasi (U.P.), India (Received 5 March 2010; final version received 12 March 2010) The antiviral agents namely Boerhaavia diffusa root extract and Clerodendron aculeatum leaf extract were found to be significantly effective in inducing systematic resistance against papaya ring spot virus in papaya. However, B. diffusa root extract showed more efficient properties as compared to C. aculeatum leaf extract. Maximum reduction in disease incidence (72.25% and 74.00%), maximum plant height (119.05 and 126.61 cm), number of fruit (20.04 and 24.05 plant 71 ) and fruit yield (22.86 and 25.93 kg plant 71 ) were observed with the application of B. diffusa root extract as seed treatment þ nursery treatment þ field treatment during 2005–2006 and 2006–2007 respectively. However, maximum disease incidence (78.79% and 70.56%) minimum plant height (87.46 and 92.40 cm), number of fruit (11.36 and 13.50 plant 71 ) and fruit yield (9.85 and 11.03 kg plant 71 ) were recorded with the application of B. diffusa root extract as seed treatment þ nursery treatment þ field treatment during both the years. Keywords: papaya; Carica papaya; papaya ringspot virus; Boerhaavia diffusa; Clerodendron aculeatum; antiviral agents; botanicals Introduction Papaya (Carica papaya L.) is a herbaceous tree belonging to family Caricaceae, is a native of Tropical Central America, and is being cultivated throughout the tropical and subtropical countries of the World. India is the second largest producer of papaya fruits in the world after Brazil. It is known as a wholesome fruit which ranks first in respect to nutritional, medicinal and nourishment properties. The unripe fruits are used for extraction of papain, which has proteolytic enzymatic activity (Joshi et al. 1976). The total area under cultivation of papaya has recorded a regular increase in the recent past but its production has not shown corresponding increase. This might be due to the losses caused by various diseases incited by fungi, bacteria, phytoplasma and viruses. Among these, viral diseases are the limiting factors of papaya cultivation in northern India. Large numbers of viruses belonging to cucumo, *Corresponding author. Email: rakesh_bhuin@hotmail.com Archives of Phytopathology and Plant Protection Vol. 44, No. 17, October 2011, 1676–1682 ISSN 0323-5408 print/ISSN 1477-2906 online Ó 2011 Taylor & Francis DOI: 10.1080/03235408.2010.482742 http://www.informaworld.com