Andrea Sierra Mejia and Ioannis E. Tzanetakis, Dept. of Entomology and Plant Pathology and the Arkansas Clean Plant Center, Division of Agriculture University of Arkansas System

Blackberry production in the Southeastern United States has experienced a significant increase in recent years. Production is threatened by many pathogens, amongst them viruses. Blackberry yellow vein disease (BYVD) is the most important virus disease affecting production in the southern United States. The most dramatic effect of BYVD is yield loss; blackberry fields become unproductive in 5 to 7 years, compared to the past normal of 20 years or more.

BYVD is unique as it is not caused by a single but rather a combination of viruses. Symptoms usually appear when two or more viruses from the complex infect blackberry, and consist of vein yellowing, mottling, oak-leaf or line patterns, and ringspots (Fig. 1). Since the disease was first observed, more than a dozen viruses have been identified in the complex.  Viruses associated with the disease can be transmitted by pollen, nematodes, eriophyid mites, whiteflies, thrips and mealybugs, amongst others.  Successful management of BYVD requires knowledge of the viruses involved, such as their host range and vector. Blackberry leaf mottle-associated virus (BLMaV) was discovered in 2014 and is one of the most prevalent viruses in the complex.  The virus has expanded its range and is now widespread in all major production areas including the West Coast. Previous studies demonstrated that a yet unidentified eriophyid species transmitted BLMaV. Eriophyids are microscopic mites, invisible to the naked eye that can be pests and/or virus vectors.

The purpose of this study was to fully characterize and study the vectoring potential of  eriophyid species that feed on BLMaV-infected material. This information will assist in the development of better control strategies that could reduce BYVD incidence.

To identify the eriophyid species involved in transmission, mites were recovered from BLMaV-infected blackberries. Morphological, molecular, and phylogenetic analysis were conducted to properly identify and characterize the species, Phyllocoptes parviflori. Consequently, transmission experiments were undertaken to evaluate the mite’s vectoring capability. To conduct these studies, we used virus and mite-free black raspberry (Rubus occidentalis‘ Munger’), and blackberry (Rubus fruticosus ‘Ouachita’).  Five mites were moved from the infected plant to each of 20 black raspberry plants. In the second experiment, one or five mites were moved to blackberry plants, 20 plants per combination.  We monitored the plants for symptoms and tested for the virus a month post-transfer. P. parviflora can transmit to both raspberry and blackberry. In blackberry, transmission was accomplished using a single mite (35%), and efficiencies doubled when using five mites instead (70%). Transmission efficiency in raspberry was low, only 1 out of 20 tested positive but those results indicate that P. parviflora can move BLMaV between Rubus species.  Additionally, infected ‘Ouachita’ developed symptoms typically associated with BYVD, Figure 2. This is the first time that BYVD symptoms, typically associated with multiple virus infections, have been observed in BYVD plants infected with a single virus.

We successfully identified and characterized an eriophyid species that serves as a vector for BLMaV. For the first time in blackberry, it was demonstrated that the virus can by itself cause BYVD symptoms on ‘Ouachita’ and for this reason the name was changed to blackberry leaf mottle virus (BLMV). P. parviflora may be a key factor involved in the spread of BYVD, due to its presence in wild and cultivated blackberries and its ability to move between Rubus species.  The information collected in this study is a first step towards the development of proper control schemes aiming to minimize the spread of the virus at a farm level and reduce the development of BYVD.

Figure 1. Symptoms associated with blackberry yellow vein disease

Symptoms associated with blackberry yellow vein disease
Symptoms associated with blackberry yellow vein disease
Symptoms associated with blackberry yellow vein disease

Figure 2. Blackberry leaf mottle virus symptoms that are typical of blackberry yellow vein disease. A) Ringspot symptoms B) Vein yellowing and chlorotic feathering pattern (Druciarek et al., 2024).

Ringspot symptoms in blackberry plants
A. Ringspot symptoms
Vein yellowing and chlorotic feathering pattern in blackberry plants
B. Vein yellowing and chlorotic feathering pattern


Druciarek, T., Sierra-Mejia, A., Zagrodzki, S.K., Singh, S., Ho, T., Lewandowski, M. and Tzanetakis, I.E., 2024. Phyllocoptes parviflori is a distinct species and a vector of the pervasive blackberry leaf mottle associated virus. Infection, Genetics and Evolution117, p.105538.

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