The 2012 ASHS Annual Conference

Most modern cultivars of berry crops are often tolerant, asymptomatic, to single virus infection. It was thus a surprise, when fresh market blackberries in the southeast United States showed severe virus-like symptoms often associated with declining plants. The disease was named blackberry yellow vein disease (BYVD) since the most common symptom is vein banding whereas chlorosis, mottling, and in severe cases, decline and plant death have also been observed. Originally and because of the geographic distribution of the disease, it was assumed that Tobacco ringspot viruswas a major component of the problem. Test for this and other common Rubus viruses like Raspberry bushy dwarf and Strawberry necrotic shock failed to reveal any association with the disease, and thus, research was initiated to identify the causal agents of the disorder and study their epidemiology.  In the last few years and as part of the SCRI project ‘Management of Rubus complexes in Rubus’ we have identified more than 15 viruses associated with BYVD. Most of them are new to science whereas others are known viruses that have been identified in blackberry for the first time.  None of the new viruses cause BYVD in single infections; the disease develops when two or more viruses infect plants. Symptoms are independent of the virus species infecting plants, whereas severity appears to be directly correlated to the number of viruses infecting the plants. Vectors of the new viruses include aphids, hoppers, whiteflies and mites, whereas some are seed and pollen-transmitted. Mite-transmitted viruses are of major concern as they are being discovered at an accelerated rate, and it is very difficult to identify the vectors in the field as they require microscopic examination. A group of pathologists, entomologists and breeders are working closely to understand the disease and implement measures that will its impact.  Our approach, given the great number of new viruses and vectors, is to eliminate the vectors that are easier to control. This may not eliminate viruses but may eliminate BYVD if plants are infected with a defined number of viruses that do not cause severe symptoms. In areas where there are several viruses and vectors present this approach will prolong plant life to over the 5-year rotation, common now in severely affected areas, and sustain profitable yields for the growers.