S-24. Improved diagnostics and genomics of citrus tristeza virus and citrus yellow mosaic virus and their management

Out of sixteen pathogens recorded to infect citrus in India, citrus tristeza clostero virus (CTV) and citrus yellow mosaic badna virus (CYMV) are associated with serious citrus decline particularly in central part of India. Conventional biological indexing using indicator plants though highly useful to diagnose majority of the graft transmissible citrus pathogens but it has its own limitations. During last two decades tremendous development has taken place to standardize various biotechnological tools for diagnosis purposes. Developing virus specific polyclonal antibodies and large-scale sample analysis by ELISA has proven to be very useful particularly during periods of optimal virus concentration in citrus plant. Today a multitude of PCR based techniques viz. PCR, RT-PCR, IC-PCR, multiplex PCR etc. have standardized and are being used routinely for detection of these pathogens in single or in mixed infected citrus plant samples. In field-infected plants during periods of non-optimal virus concentration PCR based detection technique has proved to be very useful to diagnose CTV. RT-PCR technique has been standardized to detect CTV successfully even from a single brown citrus aphid (Toxoptera citricida) the most efficient insect vector of CTV. This will be highly useful for epidemiological and virus-vector relationship studies. Using combination of polyclonal and monoclonal antibodies efforts have been made to identify suitable mild strains for cross protection. Similarly molecular diagnostics based on sequence divergence between recognized taxa is now well established as a generic approach in Plant Pathology. Genomes of CTV and CYMV infecting citrus have been cloned, sequenced and their phylogenetic relationships is established.