Plant Pathology Department
Herbarium, Florida Museum of Natural History, University of Florida, Gainesville 32611
Since 1995, severe epidemics of cucumber mosaic virus (CMV) have occurred in select fields of tobacco (Nicotiana tabacum) and pepper (Capsicum annuum) in three counties in northern Florida. Yield losses greater than 50% have occurred in both crops. Baker and Zettler (1) identified the presence of CMV in one plant of tropical spiderwort (Commelina benghalensis) in an organic garden on the campus of the University of Florida 10 years ago. In addition, they infected tropical spiderwort and Asiatic dayflower (Commelina communis) with isolates of CMV. Since 1995, in one area of northern Alachua County, Asiatic dayflower has been found in abundance in and around some fields and found to be infected with CMV. Prior to this time, CMV had not been known to be epidemic in any crop in northern Florida. Also, commelinaceous weeds did not occur in such abundance in northern Florida. In Hamilton County, an epidemic of CMV occurred in one field of tobacco in 1997. Tropical spiderwort with viral-like symptoms was growing abundantly in that field. The symptoms in this weed included chlorotic ringspots and chevron-like line patterns. Light microscopy, with Azure A stain, revealed the presence of typical inclusions of CMV in pepper, tobacco, tropical spiderwort, and Asiatic dayflower. Symptomatic samples of the tobacco and the tropical spiderwort reacted in an immunodiffusion test with antiserum to a winged bean isolate of CMV (2). Extracts from tropical spiderwort (isolate 3603) were rubbed on squash. This isolate was thereafter maintained in squash (Cucurbita pepo cvs. Prelude II or Early Prolific Straightneck). Infected plants of both of these cultivars developed strong mosaic symptoms and were stunted. After passage through squash, the 3603 isolate induced mosaic in tobacco (cv. Burley 21). Some plants of the squash cultivars Destiny III and Liberator III, which have transgenic, coat protein-mediated resistance to CMV, developed restricted symptoms after inoculation with this isolate. CMV was recovered by back inoculation from symptomatic plants of these cultivars. Symptomless plants of tropical spiderwort transplanted from the field developed chlorotic ringspots and chevron-like line patterns following inoculation in the greenhouse with isolate 3603. Back inoculations to squash followed by immunodiffusion assays confirmed the presence of CMV in the inoculated tropical spiderwort plants but CMV was not detected in noninoculated control plants. This is the first report of tropical spiderwort being infected with CMV in a commercial situation in the United States. Because commelinaceous plants are well known to be excellent hosts of CMV (1), we believe that the increased presence of perennial, commelinaceous weeds is a factor contributing to the epidemics of CMV in northern Florida.
References: (1) C. A. Baker and F. W. Zettler. Plant Dis. 72:513, 1988. (2) C. A. Ku-wite and D. E. Purcifull. Plant Dis. 66:1071, 1982.