The Matanuska-Susitna Valley is one of the most fertile regions in Alaska for growing cool-season vegetables. Barley (Hordeum vulgare) and oat (Avena sativa) crops are also sown for animal feed and green manure. The most damaging and widely distributed viral disease of small grains worldwide is barley yellow dwarf (BYD), caused by several species from two genera in the family Luteoviridae: luteovirus (Barley yellow dwarf virus [BYDV-MAV and BYDV-PAV]) and polerovirus (Cereal yellow dwarf virus [CYDV-RPV, formerly BYDV-RPV]) and three unassigned species (BYDV-RMV, BYDV-SGV, and BYDV-GPV) (2,4). Even though barley and oat have been grown in Alaska for more than 50 years, BYD has not been documented in small grains in this region. During September 2001, barley plants with bright yellow leaves were collected from five barley fields near Palmer. Three plants from each field were assayed using a reverse transcription-polymerase chain reaction (RT-PCR) protocol targeting members of the luteoviridae (3). The resulting ≈530-bp PCR product and its restriction fragment length polymorphism (RFLP) produced by digestion with NdeII implied that plants were infected with BYDV-PAV. In September 2002, three of the five sites were surveyed again for BYDV. Two of the fields (BF-1 and BF-2) had been replanted with barley and the other (OF-3) was planted with oats. Leaf samples from 36 symptomatic barley plants from each field and 60 symptomatic oat plants were randomly collected and stored at -80°C. In 2002, in addition to RT-PCR and RFLP analyses, enzyme-linked immunosorbent assays (ELISA) using Agdia kits (Agdia, Elkhart, IN) for BYDV-PAV, CYDV-RPV, and BYDV-SGV were also performed (1). First, RT-PCR and RFLP were completed on all samples using 0.5 g of tissue. Of samples from BF-1, BF-2, and OF-3, 61, 100, and 70%, respectively, generated luteoviridae-specific fragments. The RFLP profiles from barley were all PAV-like, whereas 71% of oat samples were PAV-like, and 29% were of an unknown pattern. No bands were observed from apparently healthy field plants. ELISA (0.2 g of tissue) was performed on all PCR-positive samples, resulting in 22, 97, and 33% detection for BYDV-PAV from BF-1, BF-2, and OF-3, respectively. An additional 29% of oat samples (OF-3) tested positive for CYDV-RPV, whereas none of the barley plants tested positive. One oat plant had a mixed infection with both PAV and RPV profiles, and all oat plants with the unidentified RFLP pattern were serologically positive for RPV. No BYDV-SGV was detected in either barley or oats. The PCR assay was clearly more sensitive than ELISA, especially for plants that had mature and necrotic tissue, which were predominately found in BF-1 and OF-3. Based on these direct tests on the coat protein's nucleic acid (PCR) and serology (ELISA), it is concluded that two distinct viruses, BYDV-PAV and CYDV-RPV, were found in oats, whereas only the former was found in barley. To my knowledge, this is the first report of luteovirus and polerovirus infection in small grains in Alaska. References: (1) M. F. Clark and A. N. Adams. J. Gen. Virol. 34, 475, 1977. (2) C. J. D'Arcy and P. A. Burnett. Barley Yellow Dwarf: 40 Years of Progress. The American Phytopathological Society, St. Paul, MN, 1995. (3) N. L. Robertson and R. French. J. Gen. Virol. 72,1473, 1991. (4) M. H. V. van Regenamortel et al. Virus Taxonomy. Seventh Report of the International Committee on Taxonomy of Viruses. Academic Press, NY, 2000.
Genetic Diversity of Potyviruses Associated with Tulip Breaking Syndrome
