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Hybrids between various species of Hibiscus in the Muenchhusia section are popular in commercial markets due to their colorful, floriferous blooms. However, many commercial cultivars are too vigorous for use in smaller garden spaces and often have only a few flowers in bloom. Stable, heritable mutants exhibiting dwarf stature and better branching architecture will be valuable to the commercial production of hardy Hibiscus. The goal of this project was to induce stable, heritable mutations using ethyl methanesulfonate that result in increased branching and a dwarf compact phenotype and introgress the compact phenotypes into lines of hardy Hibiscus to generate a series of diverse compact cultivars for use in commercial markets. Multiple mutations associated with dwarf, compact phenotypes were successfully induced. Hybridizations were made between M2 plants displaying a dwarf phenotype and hybrids developed through conventional breeding that do not possess the dwarf mutation in their background to develop diverse selections of dwarf plants. Inheritance patterns of the dwarf genes were determined through the segregation ratios of the dwarf phenotype in the F1 and F2 generations of these hybrids. Compared with wild-type progeny, dwarf progeny had shorter internode lengths and a greater number of primary branches. [ABSTRACT FROM AUTHOR]

The promising possibilities of mutation breeding in ornamental plants have led to a great interest in effective mutagenic treatment protocols for various species. This review discusses mutagenic treatments of a large number of ornamental genera, the advantages and disadvantages of various techniques, and the possibilities of improving the associated protocols. A number of nontargeted mutagenesis methods are available, ranging from chemical treatment with alkylating agents to irradiation with X-rays, gamma rays, and neutron or heavy ion beams at various doses. These are all relatively inexpensive and have been proven to be effective mutagens in a large number of diverse species. Genetic engineering, however, remains mostly impractical for many ornamental breeding operations because of the high cost and lack of knowledge necessary to successfully transform and regenerate ornamental crops. Of the available nontargeted mutagens, irradiation with gamma rays is still the most popular. It provides high consistency compared with chemical mutagens, albeit at a seemingly lower mutagenic efficiency. Changes in the radiation dose rate may increase the efficiency, although chronic irradiation over a longer period causes fewer deleterious mutations than the commonly used acute irradiation protocols. Heavy ion beam irradiation may also provide highly consistent mutation induction at higher efficiencies because of the high particle energy associated with these treatments. There are also opportunities to improve chemical mutagenesis. Although the required knowledge of specific gene functions in many ornamentals is still lacking, combination mutagenesis with ethyl methanesulfontate with genetic screening in a process known as TILLING (Targeting Induced Local Lesions IN Genomes) may lead to a powerful mutation breeding tool in the future. Mutation breeding is still very useful, and many opportunities are available to improve the existing methods.