Limiting Invasive Ruellia Populations via Breeding Sterile Cultivars and Developing Efficient Control in Natural Areas

Ruellia simplex (also known as R. brittoniana, or Mexican petunia) 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 Florida and other Southern states. Currently ‘Purple Showers’ with tall habit and purple flowers is the only sterile cultivar.  Our objective was to develop sterile cultivars in other flower colors such as pink, white, white with a purple corolla tube; and potentially different growth habits such as tall, semi-dwarf, and dwarf.  Breeding techniques utilized ploidy manipulations, irradiation, and interspecific hybridizations. This approach was coupled with efforts to control invasive populations in natural areas. Tetraploid R. simplex plants in four flower colors were obtained by treating diploid plants with oryzalin, and mutant plants were obtained by irradiation treatments. Hybridizations were performed between tetraploid and diploid individuals in both directions, as well as between other interploidy combinations, morphotypes and different species of Ruellia. Seeds from selfing tetraploid individuals and mutants were also collected.  All seeds were sown in 2010, resulting in 495 seedlings.  Initially progenies were grown in a greenhouse at Gainesville, Florida.  Plants were selected for female sterility and lack of fruit formation, and their ploidy levels were determined by flow cytometry.  A total of 15 selected breeding lines and five commercial cultivars as controls were evaluated in replicated field trials located in northwestern, north central and southeastern Florida.  Breeding lines were evaluated monthly from May to October 2011 for landscape performance, flowering and fruiting.  Three breeding lines have potential as new cultivars for the plant industry and have been evaluated for female and male fertility. Plants will be maintained for over one year to also evaluate winter hardiness and vegetative spread. In addition to controlling Mexican petunia indirectly by developing non-invasive alternatives, direct control methods in natural areas were also evaluated.  Using twelve 3 m x 3 m plots, treatments included four levels of aquatic-labeled glyphosate herbicide application frequency (0, 1, 2, or 3 herbicide applications) and two application seasons (spring and fall).  Results showed that glyphosate treatments reduced Mexican petunia cover in this floodplain forest wetland, but that season of spray treatments and application frequency had no effect.