WERA_OLD020: Virus and Virus-Like Diseases of Fruit Trees, Small Fruits, and Grapevines.
Statement of Issues and JustificationDiseases caused by viruses and virus-like organisms continue to be important to tree fruit and berry industries in the United States and Canada. The impact of these pathogens can be significant and often limit the economic and biological viability of fruit production. WERA-0020 facilitates a reduction in the impact of disease on this sector of agriculture by providing a forum for information exchange at annual meetings and by establishing contacts that encourage communication throughout the year. The discovery of Plum pox virus (PPV) in North America in 1999, and in Canada in 2000, had an immediate impact on the tree fruit and nursery industries. Globally, this aphid-transmitted virus is the most economically important virus of stone fruits. Subsequently, $80 million US and $65 million CDN have been spent in attempts to detect, eradicate and or manage the virus. The diagnosis of PPV was hastened because WERA-0020 provided a network of researchers and specialists that were able to make the preliminary diagnosis and insure that the necessary testing was conducted to confirm this diagnosis. WERA-0020 continues to foster experts that provided leadership and advice in developing testing and management strategies. Several members of WERA-0020 serve on the science panel which has been overseeing the work on PPV in the US and members have made significant contributions to the work on PPV in Canada. Pollen-borne ilarviruses and nematode-transmitted nepoviruses cause significant decreases in orchard, raspberry, blueberry and vineyard production throughout the United States. Citrus tristeza virus (CTV) is a major limitation to citrus production worldwide and efforts to control this disease in California and Arizona have been critical to maintaining the viability of this fruit tree industry in the western United States. Grapevine leafroll virus, corky bark, rugose wood, Rupestris stem-pitting associated virus and other graft-transmissible pathogens contribute to the decline of grapevines, decrease vegetative growth and fruit yields. Raspberry bushy dwarf virus causes serious yield and quality losses in Rubus spp. and Blueberry scorch carlavirus is becoming a major disease problem in blueberry in the Pacific Northwest and in the Northeast. WERA-0020 also promotes the exchange of information on diseases caused by isolates of the bacteria Xylella on citrus (variegated chlorosis), coffee (leaf scorch), peach (phony), almond (leaf scorch), and grape (Pierce's disease). Phytoplasmas that cause diseases such as Western X disease, pear decline, and peach yellow leafroll seriously reduce the production of stone and pome fruits in the western region of the United States. Phytoplasmas that cause the diseases typically associated with the eastern peach industry (Yellows, rosette, and red suture) are closely related to Western X and, although devastating when present, occur erratically. Although bacterial in nature, phytoplasmas and Xylella spp. have many features in common with viruses such as systemic infection, vector transmission, and graft transmission. WERA-0020 is a unique network that encourages interaction among regulatory, research, and extension personnel. Through this group, WERA-0020 has been effective in providing information and solutions to disease problems and transferring technologies between states and across provincial lines. The cause of a disease affecting significant acreages of blackberry in the southern and southeastern US (Blackberry yellow vein associated virus) was determined through collaboration among members of WERA-0020 in the southeast and on the West Coast. Many of our members are the sole person involved with diseases of fruit trees, small fruits or grapevines in their state. WERA-0020 has fostered the exchange of new and recent information on research findings and regulatory concerns and helps researchers keep current with rapid developments in detection technology. Cooperative projects involving K. Eastwell (Washington State University (WSU)), R.R. Martin (USDA Corvallis, OR), and others have defined the viruses that affect grapevines in Oregon and Washington states. The expertise of R.R. Martin has been used nationally to elucidate the cause of, and establish a molecular test for, pallidosis disease of strawberry. This test has eliminated some of the restrictions on detecting the disease imposed by the use of bioassays and allows better certification of propagative material to control a disease that is widespread in the mid-atlantic states.
Advances in detection and virus treatment technologies during the late 1980's and the 1990's have been impressive and extremely useful. Immunological assays (i.e. ELISA), nucleic acid hybridization assays and amplification of virus, viroid and phytoplasma nucleic acids using polymerase chain reaction (PCR) have been developed for disease detection and to understand relationships between organisms. The dependence of quarantine and certification programs and research programs on these techniques has increased dramatically. Together, these technologies have been critical to developing our knowledge of fruit diseases and their epidemiology. Detection tools are at the heart of clean nursery stock programs that have been implemented by several states and British Columbia. These programs have greatly improved the quality of orchards that use certified pathogen-tested nursery stock and contribute to the reduction in new diseases entering regions. The advice and information generated from group meetings has been important to programs that provide foundation grade material for clean stock programs (i.e. NRSP-5 at WSU, FPMS at UC Davis and the Canadian Food Inspection Agency (CFIA) at the Centre for Plant Health, B.C.) in designing rapid and accurate diagnostic techniques. New insights into the etiology of several diseases of fruit trees and grapevines have been essential in formulating quarantine regulations based on the most recent research findings.
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