A number of instances of underperformance and strawberry plant collapse in Santa Maria and Salinas along with the identification of the viruses responsible have brought around attention to this aspect of plant pathology in strawberry:
//ucanr.edu/blogs/blogcore/postdetail.cfm?postnum=10773
To add to this fine article, three weeks ago I had the good fortune to attend with my colleague Steve Koike a seminar given by University of Arkansas virologist Dr. Ioannis Tzanetakis. The theme was viruses in blackberries, but we learned a few important principles associated with viruses in berries in general.
Three topics of interest:
Titer of virus in contrast to its identification: A key point brought up was that the type of each virus is less important to the plant response than its very presence and titer (concentration). In other words, the response of the plant is correlated stronger to the total amount of virus present rather than to their taxonomy. Importantly, virus infections which are expressed like this additively would be seen in the field as plants having heavy exposure expressing more severe decline than those which have less. Therefore, symptoms would be manifested over a range, rather than simply just dead plants or live plants.
Viral transmissibility by vectors varies. We discussed the 2003 virus decline in Watsonville and Salinas strawberries resulting from an association of strawberry pallidosis and beet pseudo yellows virus along with twelve other viruses.
USDA- ARS virologist Dr. Bill Wintermantel, who pointed out that at a success rate around 80%, strawberry pallidosis is very transmissible by whiteflies, but since the background levels are usually low it doesn’t get moved around very much even though it transmits so easily. However, when an area like the fields along the coast in Watsonville in 2003 and then again in certain areas of Guadalupe last fall are swamped with the huge inflows of whiteflies as they did, even a low percentage of pathogen in the background doesn't matter because the low probability of transmission is overwhelmed by the number of attempts and the odds of success rise greatly.
Beet pseudoyellows virus, which was part of the problem in 2003, but not in 2013 apparently, has a far lower rate of transmissibility by whiteflies. However, since the background levels are so high in many local weed and crop plant species, it again has fair odds of getting moved around when the numbers of whiteflies are high.
Virus infection of strawberries the Eastern United States: Dr. Tzanetakis expanded on the topic of viruses in strawberry by talking about the virus infection this past season in Florida and several other states of the Eastern USA. The infection was traced back to a single nursery in Nova Scotia which was situated next an untreated commercial field and virtually 100% of the plants were later found to be infected with strawberry mild yellow edge virus (SMYEV) and strawberry mottle virus (SMoV), both of which are aphid transmitted.
More from Growing Produce online:
http://www.growingproduce.com/article/34043/strawberry-virus-alert