A plant virus as a bioherbicide for tropical soda apple, Solanum viarum.

© 2007. Research Information Ltd. All rights reserved DOI: 10.1564/18aug07 Tropical soda apple (Solanum viarum, Figure 1; abbreviated: TSA) is an exotic, thorny, perennial shrub that has become a highly invasive weed in the southern USA. TSA is native to Brazil, but has spread to several countries of South and Central America, the Caribbean, Africa, and the Indian subcontinent. In Florida, improved pastures, cattle feedlots, citrus groves, ditches, sod farms, and natural areas are seriously affected by this weed (Ferrell & Mullahey 2007, Mullahey et al. 1993). TSA has been reported to occur also in Alabama, Georgia, Mississippi, Louisiana, Texas, North Carolina, South Carolina, Tennessee, and Pennsylvania (NAPIS, 2003). While some of these infestations have been eradicated, the threat of continued influx has not diminished because cattle, deer, wild hogs, birds, and contaminated hay help to disseminate the seed. TSA has the potential to spread throughout the continental USA (Patterson 1996). The realization of the threat posed by TSA has led to its designation as a “noxious weed” under the Federal and Florida noxious weed statutes. In efforts to stop the weed at its source, namely, the infestations in Florida, all potentially effective methods of control, including biological control, are being examined (DOACS-Florida 2007). TSA infestations in pastures cause the cattle stocking rates to be lowered due to the reduced access and available area for grazing. The livestock production costs go up, and out-of-state cattle shipments face a regulatory dilemma since the cattle are partly implicated in spreading the weed to their destinations. Although TSA foliage is inedible due to the presence of sharp thorns on all parts of the shoot, livestock, feral hogs, deer, raccoons, and birds eat the fruits and disperse the seeds (Coile 1993). Contaminated equipment, hay, grass seed, composted manure, and sod from TSA-infested areas also disperse the seeds. TSA seed is highly viable even after passage through animals’ digestive tracts and is the principal means of initial establishment as well as secondary increases in TSA populations. Mature plants can also sucker and re-establish following mowing and chemical treatment. Besides its weediness, TSA is a potential reservoir of several cropdamaging insects and pathogens (McGovern et al. 1994). A PLANT VIRUS AS A BIOHERBICIDE FOR TROPICAL SODA APPLE, SOLANUM VIARUM