Incidence, Distribution, and Symptom Description of Viruses in Cultivated Blackberry (Rubus subgenus Eubatus) in the Southestern United States

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Title: Incidence, Distribution, and Symptom Description of Viruses in Cultivated Blackberry (Rubus subgenus Eubatus) in the Southestern United States
Author: Guzman-Baeny, Tania Lina
Advisors: John R. Clark, Committee Member
James R. Ballington, Committee Member
Zvezdana Pesic-VanEsbroeck, Committee Co-Chair
Gina E. Fernandez, Committee Co-Chair
Steven A. Lommel, Committee Member
Abstract: During the summer of 2000, an alarming number of blackberry plants with virus-like symptoms were found in commercial plantings and research plots in North Carolina. To determine the nature of these symptoms, a survey and related studies were initiated in 2001 to document the virus situation in North Carolina as well as South Carolina and Virginia. The survey revealed that Tobacco ringspot virus (TRSV), Tomato ringspot virus (ToRSV) and Impatiens necrotic spot virus (INSV) were the predominant viruses present in blackberry plantings we tested. In North Carolina, South Carolina and Virginia, the combined incidence of TRSV, ToRSV and INSV in the locations surveyed were 49, 45.2 and 33.1% respectively. In most instances, TRSV, ToRSV and INSV were present as multiple infections in one plant. Detection of viruses varied by plant part tested. Roots generally possessed a higher virus titer and therefore the presence of a virus was more easily detected. Impatiens necrotic spot virus, a virus that had not been previously known to occur in blackberry, had been detected for the first time (completion of Koch's postulates is pending). We also determined that TRSV was present in the embryo of blackberry seeds. Visual symptoms varied among viruses and cultivars. Symptoms observed were: chlorotic line patterns, ringspots, vein chlorosis, vein necrosis, necrotic spots, crumbly fruit, yellow blotches, distorted leaves and oak leaf pattern. In many instances, the appearance of virus-like symptoms was concomitant with a decline in plant health. The relatively sudden appearance of symptomatic plants suggests that viral load reached a critical point not seen before in the region. Plants either came into the fields with infections and/or became infected shortly after they were planted. Many of the plantings we tested were relatively young and therefore, it was likely that infected plants were from commercial nurseries. In addition, these infected plants may have been planted into fields that had viruliferous nematodes and insects. These pests may have been vectors for the introduction of additional viruses. It is likely that other unknown viruses, may be infecting blackberry plantings in the southeastern United States, further complicating the situation. Many questions remain to be answered. For example, systematic studies are needed to determine effects and symptoms of single and multiple infections in each of the cultivars. Unknown viruses and the vectors that introduce them need to be identified. Chemical or biological mechanisms of control for vectors need to be determined. And finally, plant breeders need to identify and utilize germplasm with resistance to vectors in traditional breeding programs or incorporate resistance via molecular techniques. However, it is clear from our studies that some immediate steps can be taken. First, breeding programs need to virus index new releases to ensure that they are not the initial source of infection and second, state nursery certification programs need to be implemented and enforced to insure that the burgeoning blackberry industry remains viable.
Date: 2004-09-08
Degree: MS
Discipline: Horticultural Science

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