Diagnostics of Seed Borne Plant Pathogens for Safe Introduction and Healthy Conservation of Plant Genetic Resources
Most of the crop diseases are either seed or soil borne or both. Hence, seeds alone or along with soil clods, plant debris and fruiting structures of the pathogens are primary source of inoculum for long distance dispersal. Some of the examples of dangerous pathogens/diseases disseminated during transboundary movement of seeds and other planting materials in international trade and exchange caused havoc and leading to profound political, economic and social consequences such as late blight of potato (Phytophthora infestans) from Central America (Peru) to Ireland in 1845, powdery and downy mildews of grapes (Uncinula necator and Plasmopara viticola) from Central America to France in 1847, flag smut of wheat (Urocystis agropyri) from Australia to Mexico, chestnut blight (Cryphonectria parasitica) from orient countries including Japan and Korea to USA, coffee rust (Hemileia vastatrix) from Sri Lanka to India in 1875, Karnal bunt of wheat (Neovossia indica) from India to USA in 1996 and bunt of wheat (Tilletia caries) from India to Mexico in 1970 and pine wood nematode (Bursaphelenchus xylophilus) introduced from North America to Japan in the early 1900s and then to have distributed in China, Korea, and Taiwan, etc. Therefore, seed health testing (SHT) involving conventional and molecular techniques has major applications in quarantine processing of plant genetic resources (PGR) under exchange as well as conservation of PGR for long term storage in Gene Bank after making them free from associated pathogens, seed certification and decision making for seed treatment. Thus, critical laboratory examinations with specialized tests, involving conventional and molecular approaches, are conducted in seed health testing for quarantine as well as conservation of PGR to ensure the interception/detection and identification of associated pathogens with seeds and other planting materials.