A Virus Associated with Blueberry Fruit Drop Disease

During the past few years a fruit drop symptom has been observed in several blueberry fields in Oregon, Washington and B.C. The plants flower normally, though the young leaves and flowers have a transient red coloration that is absent in healthy plants. The fruit develops to 3-5 mm in diameter and then aborts so that affected bushes mature virtually no fruit. The incidence within fields increases year to year suggesting that a pathogen is involved. Virus purification and mechanical transmissions to herbaceous hosts has been unsuccessful. Only one of more than 40 attempts at dsRNA purification was successful. Thus far, approximately 1700 nucleotides of the dsRNA template have been sequenced and two sets of primers for detection were developed. In RT-PCR assays, amplicons were obtained from symptomatic bushes with both sets of primers but not from asymptomatic bushes. The sequence obtained shows homology with fungal and vertebrate rather than plant viruses. The most closely related virus in a BLAST search was a Totivirus from Zygosaccharomyces. The possibility of a systemic virus-infected fungal pathogen can not be ruled out at this time. INTRODUCTION Growers, consultants and field representatives have noticed a problem with fruit drop in several blueberry fields in the Pacific Northwest over the past ten plus years (Fig. 1). In symptomatic plants the fruit sets but only attains a size of 3-5 mm and often drops several weeks prior to harvest (Fig. I B). Initially, emphasis was based on management problems such as herbicide damage, improper nutrition or poor pollination and frost damage. Symptoms have only been observed in the cultivar 'Bluecrop' and were observed in B.C. and northern Washington, and growers reported that the number of symptomatic plants in a field did not appear to increase over time. However, over the past few years the number of symptomatic plants in these fields has increased with 50 to 60 additional symptomatic plants appearing in one field in the spring of 2003 compared with 2002 and spread occurring in several other fields as well. With the obvious increase in incidence, attempts were made to determine if there was a virus associated with the symptoms. Fields visited during the spring of 2003 showed a reddening of new leaves and the corollas was observed on infected plants (Fig. 1A). As the season progressed the red coloration of the leaves disappeared and by harvest time the plants looked healthy except for the lack of fruit. These plants were more vigorous and could be identified from the edge of the field since they did not have a fruit load and were more upright than the