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Title: ALFALFA, A NON-HOST OF PEA ENATION MOSAIC VIRUS IN WASHINGTON STATE

Author
item Larsen, Richard
item KAISER WALTER J - 5348-15-00
item KLEIN ROBERT E - WSU-PROSSER

Submitted to: Canadian Journal of Plant Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/12/1996
Publication Date: N/A
Citation: N/A

Interpretive Summary: Pea enation mosaic virus (PEMV) can cause significant yield losses in peas, chickpeas, lentils, and faba beans. The virus has been reported to occur worldwide; however, it is of significant importance in the Pacific Northwest because of the large acreages of legumes grown here. PEMV is transmitted to susceptible plants through feeding by infectious pea aphids. The virus can reach epidemic proportions during years of high aphid populations and abundant virus inoculum sources. Alfalfa has been reported and considered the primary perennial virus source plant for PEMV since the late 1950's. However, many scientists have not been able to transmit PEMV into or out of alfalfa, thus hindering progress in controlling this important virus. In our research, alfalfa was collected from eight counties in Washington State during 1988-1994 and evaluated by ELISA, a common and very sensitive detection assay. Many of these samples were also assayed using cDNA analysis, which is a test at least 10 times more sensitive than ELISA. Peas, chickpeas, lentils, faba beans, as well as native legume plants near growing areas, were also collected and tested by ELISA. PEMV was not detected by ELISA in any of 3230 alfalfa samples collected over a five-year period, nor was it detected in any of the 597 samples by cDNA analysis in 1994. In addition, the virus was not detected in any of the native legumes collected. In contrast, PEMV was detected or observed in peas or chickpeas during each growing season. It was concluded that alfalfa should not be considered a host for the virus. The significant source plant for PEMV in the Pacific Northwest, therefore, still remains unknown.

Technical Abstract: Extensive surveys were conducted in Washington State between 1988 to 1994, in an attempt to locate reservoirs of pea enation mosaic virus (PEMV). Symptomatic plants of peas (Pisum sativum L.), chickpeas (Cicer arietinum L.), lentils (Lens culinaris Medik.), or faba beans (Vicia faba L.) tested positive for PEMV each year of the survey when assayed by double antibody sandwich enzyme-linked immunosorbent assay (ELISA). PEMV could not be detected by ELISA in any of 3230 alfalfa samples collected from eight counties in Washington State, even when samples were taken from fields adjacent to where infected peas, lentils, or chickpeas were growing. Dot blot hybridizations using a 4556 nucleotide cDNA fragment of PEMV RNA 1 containing the coat protein region, did not detect the virus in 597 alfalfa samples tested in 1994. Fifty-six attempts to transmit PEMV into or out of alfalfa by aphid or mechanical transmissions were unsuccessful, while transmissions to and from peas, chickpeas, and faba beans, were made routinely. PEMV was not detected in any of the following native leguminous plant species collected: Lathyrus spp., Lupinus spp., Melilotus alba Medik., Trifollium repens L., or Vicia villosa Roth. Our inability to detect PEMV in, or transmit the virus to alfalfa suggests that alfalfa should not be considered a host. The overwintering epidemiologically significant reservoir host(s) of PEMV in the Pacific Northwest remain unknown.