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Robert Martin
Professor (Courtesy), Botany and Plant Pathology
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RESEARCH:
Plant viruses cause significant losses in most agricultural crops. In the small fruit crops; strawberry, raspberry and blueberry, there are several uncharacterized viruses that cause economic impact wherever these crops are grown. There is a complex of four aphid-borne viruses that lead to rapid decline of strawberry plantings. With the exception of a few tolerant varieties aphid control is required to maintain plantings through two harvest seasons. In order to be able to produce virus-free plants that can be produced for the small fruit growers it is necessary to have reliable diagnostic reagents for the viruses of these crops. We have developed monoclonal and polyclonal antibodies for the detection of Raspberry bushy dwarf, Tomato ringspot, Tobacco streak, Blueberry shock, Strawberry mild yellow edge and Fragaria chiloensis latent viruses. These antibodies are currently being used to assist the breeding programs in the Pacific Northwest and B.C. to ensure that parent material is free of pollen-borne viruses. They are also used in the small fruit certification and virus elimination programs in the Pacific Northwest and B.C. More recently, we have sequenced or partially sequenced viruses from strawberry, Rubus spp. and blueberry and we are using this information along with published information to develop primers for RT-PCR detection of viruses.
Strawberry viruses. In the last 5 years the greenhouse whitefly (Trialeuroides vapororarium) has become naturalized in the southern USA. This has resulted in the rapid increase in the importance of the whitefly transmitted viruses and we have identified two new viruses in strawberry during the last two years; Strawberry pallidosis (SPaV) and Beet pseudoyellows (BPYV) both of which are criniviruses. We have sequenced these two viruses completely. We have also partially sequenced Strawberry necrotic shock, Fragaria chiloensis latent (FCLV) and Strawberry latent ringspot virus (SLRSV). Using this sequence information together with information from GenBank database we have developed primers for the detection of 14 different viruses from strawberry. Using these primers in field tests we have found 4-5 viruses in declining strawberry fields in CA, WA and B.C. The virus complex in CA included SPaV, BPYV, FCLV, SLRSV, Strawberry mild yellow edge virus (SMYEV) and strawberry crinkle virus (SCV) declining plants had a subset of these six viruses. In the Northwest the virus complex included SMYEV, SCV, SMoV, SLRSV and FCIV. We are now trying to determine where in the plant production scheme each of these viruses is getting into the system and the impact of each virus on the plant decline with the objective of optimizing control strategies.
Rubus Working with colleagues in Arkansas (Rose Gergerich and John Clark) and North Carolina (Zvezdana Pesci-van Eesbroeck and Gina Fernandez) we have identified a crinivirus associated with a yellow vein symptom in blackberry, this is another whitefly transmitted virus. In some cultivars the presence of this virus resulted in a serious decline and complete loss of yield while in other cultivars there was little if any effect. In black raspberry we have identified a virus associated with a serious decline in this crop in the Northwest and Ohio. The virus, Black raspberry necrosis virus, is most closely related to SMoV. The virus is aphid transmitted and results in a rapid decline of black raspberry plants resulting in fields being replanted on a 3-4 year rotation. We have partial sequence for both of these viruses. With the BRNV we are looking at timing of vector dispersal to determine if a few well timed pesticide applications will significantly reduce the rate of spread of the virus in the field. With Raspberry bushy dwarf virus (RBDV) we are genetically engineering resistance into ‘Meeker’ raspberry (this cultivar comprises about 75% of the industry in the Northwest). We have developed approximately 200 transgenic lines that have been field tested for four years. There are five lines that appear to be field resistant (0% infection over 4 years when 202 of 202 wild type plants became infected). These lines are currently being evaluated for fruit quality, machine harvestability and horticultural traits.
Blueberry Blueberry scorch virus (BlScV) has become an important issue in the Northwest since 2000 with an outbreak of a severe strain in B.C. After an extensive we have not identified the severe strain in OR or WA nor have we found any new blueberry fields infected with the virus. We did find BlScV in cranberry in B.C., WA and OR which may explain the situation in B.C. where the cranberries and blueberries are grown in close proximity to each other. In WA and OR cranberries are grown along the coast with the blueberries grown more inland, this separation may partially explain the differences in the spread of BlScV. We also identified a virus associated with a fruit drop disease of blueberry. The disease results in a complete drop of fruit shortly after bloom. We obtained the first sequence of this virus in the last few months and have only been able to do field testing with material in the freezer so a very limited number of samples (three fields) have been assayed. Samples from the three fields all tested positive for the Blueberry Fruit Drop Virus and asymptomatic plants tested negative,
We also run the virus clean up program for the Pacific Northwest small fruit crops for production of virus-free plants that can be made available to the industry. We are using chemotherapy combined with tissue culture and meristem tip culture to develop virus-free plants. We are developing the technology to develop virus-free plants in an efficient and simple manner. In this way advanced selections being developed by the three breeding programs in the Pacific Northwest can be moved into replicated trials more quickly.