Comparison of noninfected pepper (left) with one infected with CMV.
Over the past couple of decades the cultivation of sweet peppers has become a profitable business for some farmers in the southern Illinois floodplains of the Ohio and Mississippi rivers. In 1992 several growers in this area noticed dark brown lesions on their peppers in August. In 1993 the same lesions, accompanied by additional symptoms, led plant epidemiologists at the University of Illinois to conclude that a viral disease caused by the cucumber mosaic virus (CMV) was responsible. In 1993 some pepper fields were plowed under, and in 1994 at least one long-time grower of peppers stopped growing the crop because of the potential for crop loss by this virus. In 1995 evidence of CMV infection was seen at an increasing number of farms, including the largest pepper grower in the Midwest with over 800 acres of peppers. Significant crop losses occurred that season, and the long-term result has been that pepper cultivation has been reduced in the region with significant loss of revenue.
CMV is transmitted by aphids in a simple manner. When an aphid lands on a plant it usually probes the plant with its mouthparts and by so doing can determine if the plant is an acceptable host. If the plant is not acceptable, the aphid will withdraw its mouthparts and fly to another plant where it also probes to test (taste) the plant. These probes are all that is necessary for the aphid vector to pick up CMV from an infected plant and transmit it to an uninfected one. Infestations of 100% and virtual total crop loss can occur in peppers if the infection of the plants occurs early enough in the season.
Comparison of noninfected pepper (left) with one infected with
CMV.
Epidemiologists from the University of Illinois have determined that the virus is present in at least two weeds common in the area, a Physalis sp. and Solanum sp., both in the Solanaceae or nightshade family. To move the virus into the pepper fields from these reservoir hosts, an appropriate aphid species would have to land on them, probe, pick up the virus, then move into the field, land on a pepper, and probe. In situations like this it is important to determine the identity of the aphid vectors as well as the reservoir host of the virus. Aphids were trapped in pepper fields during the 1996 and 1997 growing seasons and identified by a Survey entomologist. More than 80 species were present in these collections, of which 17 are known to be capable of transmitting CMV to peppers. To determine which species of aphids were vectors of CMV, over 4,000 individual aphids were collected as they flew over the pepper field. Each was placed on a separate virus-free pepper seedling and left for several hours to probe. Aphids were then removed and saved for identification. The seedlings were kept under aphid-free growing conditions long enough for symptoms to develop. Two of the plants developed symptoms; however, this is insufficient evidence to implicate any particular species as the primary vector.
Research into this problem is expected to continue for the next several years. The focus will be on determining the aphid species responsible for the transmission of CMV and the seasonal biology of the species. The potential for limiting the spread of the virus by weed control will also be explored. This ongoing research is a collaborative effort between scientists at the Crop Sciences Department at the University of Illinois and the Illinois Natural History Survey.
David J. Voegtlin, Center for Biodiversity
Next Article
Index
to This Issue
Index
to
Survey Reports
INHS Home Page
Please report any problems with or suggestions about this page to:
in hspubs@mail.inhs.uiuc.edu
Subject: INHSPUB-00458