Control of Invasive Ruellia Simplex By Herbicide Treatments in Natural Areas and Breeding Sterile Cultivars

Ruellia simplex (Mexican petunia) is native to Mexico and Western South America. It has profuse flowering and low maintenance requirements, and is a popular landscape plant in Southern U.S. However, this introduced plant has escaped cultivation and become invasive in natural areas in seven Southern states, Hawaii, Puerto Rico, and the U.S. Virgin Islands. For many years, ‘Purple Showers’ (origin unknown) with tall habit and purple flowers was the only sterile cultivar. One objective was to control invasive Ruellia simplex in natural areas. Twelve 3 m x 3m plots were used in a floodplain forest wetland natural area in central Florida. Herbicide treatments included four levels of glyphosate application frequency (0, 1, 2 or 3 applications) and two application seasons (spring and fall).  Results showed that glyphosate treatments reduced R. simplex by 60-70% when sprayed once, either in the spring or the fall. Additionally, the plant composition of the seedbank and the potential for recolonization of the native plant community were assessed. Results indicate that the recovery of native species may be a multi-year process with several revegetation efforts, and that additional chemical control incorporating a growth regulator herbicide that targets Ruellia rhizome growth may be necessary. Additionally, we are developing sterile Ruellia cultivars with different flower colors and growth habits. Breeding techniques utilize ploidy manipulations and interspecific hybridizations. Tetraploid R. simplex plants in three different flower colors have been obtained by treating diploid plants with oryzalin. Hybridizations are performed between tetraploids and diploids, as well as between different morphotypes and species of Ruellia. Seeds are sown every year and progenies are grown in a greenhouse at Gainesville, Florida.  Plants are selected for female sterility and lack of fruit formation, and their ploidy levels are determined by flow cytometry. Selected breeding lines and commercial cultivars as controls are evaluated in replicated field trials located in northwestern, north central and southwestern Florida.  Breeding lines are evaluated monthly from May to September for landscape performance, flowering and fruiting.  Selected lines with demonstrated female and male fertility need to be approved by the UF IFAS Invasive Plants Task Force and the UF IFAS Cultivar Release Committee. So far, we have released Ruellia ‘Mayan Purple’, ‘Mayan White’, and ‘Mayan Pink’, and all are commercially available.  The first two cultivars are patented while ‘Mayan Pink’ is pending. Release of a fourth cultivar is in process, and breeding efforts are ongoing.