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Title: INCIDENCE, SPACIAL PATTERNS AND ASSOCIATION AMONG VIRUSES IN SNAP BEANS AND ALFALFA IN NEW YORK

Author
item SHAH, DENIS - CORNELL
item DILLARD, HELENE - CORNELL
item MAZUMDAR-LEIGHTON, SUDESHNA - CORNELL
item Gonsalves, Dennis
item NAULT, BRIAN - CORNELL

Submitted to: Plant Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/20/2005
Publication Date: 2/20/2006
Citation: Shah, D.A., Dillard, H.R., Mazumdar-Leighton, S., Gonsalves, D., Nault, B.A. 2006. Incidence, spacial patterns and association among viruses in snap beans and alfalfa in New York. Plant Disease 90:203-210.

Interpretive Summary: In recent years, symptoms induced by viruses have been associated with yield losses on a wide scale in processing snap bean in the Midwest and Northeast US. Epidemics caused by viruses have coincided with the recent introduction of the soybean aphid, raising the question of how important aphid-transmitted viruses may be in causing the disease and yield reduction in snap bean. We surveyed commercial snap bean fields in New York for the aphis-transmitted viruses Alfalfa mosaic virus (AMV), Cucumber mosaic virus (CYVV) and the Bean yellow mosaic virus (BYMV)/Clover yellow vein virus (CYVV) complex in 2002 and 2003, using ELISA. Since alfalfa is a possible source of these viruses, we included snap bean fields that were either adjacent to or remote from alfalfa. Viruses were common in both snap bean and alfalfa, but incidences of virus-infected plants were higher in 2002 (72.4% in alfalfa, 52.9% in snap bean) than in 2003 (39.2% in alfalfa, 15.2% in snap bean). We found it impossible to relate visual symptoms in fields to infection by any one of the viruses. In fact, most snap bean fields surveyed at the bloom stage did not have any symptoms of virus infection. Although 25.9% of snap bean plants were infected by more than one virus in 2002, <1% had more that one virus in 2003. The presence of alfalfa next to snap beans did not increase the risk of virus infection in the latter. Late-planted snap beans appeared to be more at risk to virus infection in 2002 for all viruses, but only to BYMV/CYVV in 2003. In 2002, AMV and CMV tended to occur together in the name snap bean plants. A potential approach for reducing the risk of yield loss by these viruses in snap bean fields is discussed.

Technical Abstract: Recent epidemics in snap bean (Phaseolus vulgaris L.) characterized by virus-like symptoms prompted a survey of commercial fields for Alfalfa mosaic virus (AMV), Cucumber mosaic virus (CMV) and the Bean yellow mosaic virus (BYMV)/Clover yellow vein virus (ClYVV) complex in 2002 and 2003. Snap bean fields were either remote from or adjacent to alfalfa (Medicago sativa L.), a putative source of these viruses. Bean fields were sampled at the bloom stage in both years. Model-adjusted mean incidences of infection by AMV, BYMV/ClYVV and CMV were 41.96, 6.56 and 6.69% respectively, in alfalfa, and 6.66, 6.38 and 17.20% in snap bean. In 2002, 25.9% of snap bean plants were infected by more than one virus; <1% had more than one virus in 2003. Virus incidences did not differ between snap bean adjacent to or remote from alfalfa, but incidence of infection by AMV and BYMV/ClYVV was significantly higher in snap bean planted later in the season rather than earlier. In 2002, there was a positive association between AMV and CMV in the tendency to find both viruses in the same snap bean plant. In some years infection by aphid-transmitted viruses can become widespread in snap bean in New York.