Ageratum conyzoides and its Role in Begomoviral Epidemics; Ageratum enation Virus: An Emerging Threat in India

Diseases caused by begomoviruses (family Geminiviridae, genus Begomovirus) constitute a serious constraint to tropical and sub-tropical agro-ecosystems worldwide. Begomoviral diseases can reduce yields to zero in extreme cases, leading to catastrophic losses in agriculture. These diseases continue to evolve and pose a serious threat to sustainable agriculture throughout the world, particularly in the tropics and sub-tropics. The rapid emergence of begomoviral epidemics might be occurring in connection with some factors like evolution of new virus variants, the appearance of efficient vectors, changes in cropping systems, introduction of susceptible plant varieties, and changes in climatic conditions. Another concern is the emergence of a begomovirus complex and satellite DNA molecules. Weeds are the major reservoir of begomoviruses for crops as they provide shelter to the virus and their insect-vectors during cropping and off-season. Weeds, as host of many begomoviruses, are known across the world, but a limited number of studies have been conducted on the role of weed hosts in causing wide-spread epidemics of begomoviral diseases in crop plants. Ageratum conyzoides is a global weed, found widely and frequently occurring in south Asia, and is very difficult to control. It has been reported to be the reservoir of many economic diseases caused by begomoviruses in tropical and subtropical parts of the world. Recently, Ageratum enation virus has quickly spread to many economically important crops and is posing a serious threat to agriculture in India. The variants/ strains of the virus are evolving very fast and are becoming the major limiting factor to agro-eco systems particularly in the northern part of the country. So far, 33 isolates originating from different plant species (including ornamentals, vegetables, legumes, and weeds) have been reported from India and the neighboring countries of Pakistan and Nepal.