S-64. Potential threat to tomato and potato crops by the emergence of seed-borneCitrus exocortis viroid found in ornamental plant species, Impatiens and Verbena

Almost 40 years ago viroids were discovered as new plant pathogen in potato, citrus and coconut exhibiting severe disease symptoms. In contrast, viroids in ornamental plants are symptomless. Ornamental plant nurseries play a significant role in the aesthetic landscape of urban and rural centres throughout the world. Numerous plant species, lack of isolation between plant species, rapid vegetative multiplication, and an absence of disease-symptoms in propagating material, make nurseries an ideal environment for viroid evolution. Natural transfer of viroids from ornamental plants to crops, have exhibited potential to cause severe economic losses. For large-scale systematic studies of viroids in ornamental plants, a genus Pospiviroid-specific primer pair and simplified protocols to extract nucleic acid are available. Use of rapid isolation procedures and determination of the nucleotide sequences of cloned viroid provide definitive identification of viroids. Surveys of Impatiens and Verbena species obtained (from the USA) in local nurseries in Fredericton, Canada and Verbena species in New Delhi, India, have indicated widespread infection by Citrus exocortis viroid in both seed-grown and vegetatively propagated plants. Experimental transfer of citrus exocortis viroid isolates, from ornamental plants to potato and tomato have resulted in severe plant and tuber symptoms. Tuber yield can be severely reduced, and potatoes may exhibit anti-quality characteristics such as severe cracks, odd shapes, and darkened skin.