Interspecific and Intergeneric Hybridization in Dissotis And
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HORTSCIENCE 51(4):325–329. 2016. The two genera from the Melastomata- ceae family that were chosen for this project are Dissotis and Tibouchina. Dissotis is Interspecific and Intergeneric native to Africa and Tibouchina to Mexico as well as Central and South America Hybridization in Dissotis (Almeda and Chuang, 1992; Renner and Meyer, 2001; Todzia, 1999). Tibouchina and Tibouchina contains species of importance in the orna- mental horticulture trade, such as Tibouchina Susan M. Hawkins ‘Athens Blue’, whereas Dissotis sp. have not Department of Horticulture, University of Georgia, 1109 Experiment Street, been widely used as ornamentals. However, Georgia Station, Griffin, GA 30223-1797 some Dissotis sp., such as D. rotundifolia, have excellent ornamental qualities, such as John M. Ruter1 soft, fuzzy leaves, or attractive pink or purple Department of Horticulture, University of Georgia, 327 Hoke Smith flowers, as well as being easy to cultivate and propagate. Hybridizing Dissotis and Tibou- Building, 1225 Lumpkin Street, Athens, GA 30602 china could create unique combinations of Carol D. Robacker growth form and flower color and produce novel cultivars for the ornamental horticul- Department of Horticulture, University of Georgia, 1109 Experiment Street, ture trade. The overall goal of this project was Georgia Station, Griffin, GA 30223-1797 to investigate the feasibility of hybridization Additional index words. Melastomataceae, Dissotis rotundifolia, Dissotis princeps, Dissotis within and between various species of Dis- sotis and Tibouchina to create interspecific canescens, Tibouchina lepidota, Tibouchina fothergillae 3 pilosa, germination, floral and intergeneric hybrids of these genera. morphology, buzz pollination Abstract. Four species of Dissotis and three species of Tibouchina, two genera of the Materials and Methods Melastomataceae family, were crossed in an attempt to create interspecific and in- tergeneric hybrids. Intergeneric crosses set seed at a rate of 18.1% and interspecific Several species of Dissotis and Tibou- crosses had a 32.3% rate of seed set. Germination was extremely poor, with only four china were placed in a greenhouse in Athens, crosses having germinated seed. Crosses produced 31 seedlings. Three of the seedlings GA in Feb. 2012 (Table 1). Stock plants were were from intergeneric crosses between Dissotis canescens and Tibouchina lepidota. each clones of one genotype of each species. Interspecific crosses produced 25 seedlings from crosses between Dissotis princeps and Cuttings of each species were taken, treated Dissotis rotundifolia and three seedlings from crosses between D. canescens and D. with a 5-s dip of potassium salt of indole-3- princeps. The prognosis for conventional breeding for species in Dissotis and Tibouchina butyric acid (K-IBA) at 1000 mg·L–1, and is poor due to low seed set, poor germination, and slow growth of progeny. stuck in Fafard Germination Mix containing processed pine bark (40%), Canadian sphag- num peat, perlite, and vermiculite (Sun Grow The Melastomataceae family comprises variously reported by Solt and Wurdack Horticulture, Agawam, MA), and placed un- between 185 and 190 genera containing 5000 as having a chromosome count of n =15 der intermittent mist at 8 s every 10 min and species (Almeda and Chuang, 1992). Mela- and by Almeda as having a chromosome 50% shade. After 6 weeks, cuttings were stomataceae species are found in Asia, count of n = 10 (Almeda, 1997; Solt and potted up in Fafard 3B Mix consisting of Africa, North and South America, and Aus- Wurdack, 1980). Dissotis rotundifolia is re- Canadian sphagnum peat, processed pine tralia; South America contains the majority ported to be a diploid with n =15(Soltand bark, perlite, and vermiculite in 2.8-L (15.2 cm of species (Michelangeli et al., 2013; Renner Wurdack, 1980). Dissotis canescens, for- diameter) trade containers. and Meyer, 2001). Some species, such as merly treated as Heterotis canescens,has Dissotis sp. started blooming in July 2012. D. rotundifolia (Sm.) Triana, have natural- been reported to be n = 17 and is possibly Tibouchina sp. started blooming in Aug. ized in places with tropical climates such as polyploid (Almeda, 1997). 2012. Interspecific and intergeneric crosses Indonesia, Brazil, Puerto Rico, and Hawaii Most Melastomataceae species have por- were made as species came into bloom (Liogier and Martorell, 1982; Renner and icidal anthers and exhibit herkogamy (Renner, beginning in July 2012 and ending in Mar. Meyer, 2001). 1989). Herkogamy and poricidal anthers pro- 2013. Flowers were emasculated to prevent Species in the Melastomataceae vary mote outcrossing in Melastomataceae. The self-pollination. Emasculations were carried out widely in ploidy and chromosome count. poricidal anthers require manipulation for the before anthers had completely unfolded when Tibouchina chromosome numbers are based pollen to disperse. Pollen disperses when possible. Pollen was extracted from flowers of on x =9,rangingfromn =9ton =63 the pollinator vibrates the anthers with its male parents by vibrating anthers with a tuning (Almeda, 1997; Almeda and Chuang, 1992). flight muscles, a process called buzz pollina- fork (key of E). Pollen was captured in glass Many species of Tibouchina are polyploid. tion (Luo et al., 2008; Renner, 1989). To containers and applied to the stigmas of flowers Although tetraploidy is the most common obtain pollen for use in hybridization, plant of the female parents using either a Q-tip or polyploid level, ploidy level varies (Almeda, breeders mimic buzz pollination by using a small paintbrush. A total of 1036 crosses were 1997). Tibouchina granulosa has a chromo- a tuning fork in the key of E to get pollen to made, 588 crosses were interspecific and 448 some count of n = 18 and is tetraploid (Solt dehisce (Renner, 1989). crosses were intergeneric. and Wurdack, 1980). Tibouchina lepidota is n = 62 or 2n = 122 and is thought to be 14-ploid (Almeda, 1997). Dissotis has been Table 1. Melastomataceae species used as parents in breeding program. Species Chromosome count Ploidy Dissotis canescens n = 17 Undetermined Received for publication 10 Nov. 2015. Accepted Dissotis debilis Unknown Unknown for publication 23 Feb. 2016. Dissotis princeps Unknown Unknown Dissotis rotundifolia n =15 2x This paper is part of a thesis submitted by Susan M. · Hawkins as part of the fulfillment of a Master’s Tibouchina fothergillae pilosa Unknown Unknown Tibouchina granulosa ‘Gibraltar’ n =18 4x Degree. 1Corresponding author. E-mail: [email protected]. Tibouchina lepidota 2n = 122 or n = 62 Possibly 14-ploid HORTSCIENCE VOL. 51(4) APRIL 2016 325 Fruits were harvested when ripe. Since all Waltham, MA). Pictures were taken with examination of the seedlings from all crosses species produced capsular fruit, fruits were an Olympus D70 microscope camera and showed that seedlings resembled female determined to be ripe when they were light to Olympus DP Controller software. parents in growth habit, leaf shape, and leaf medium brown and hard. Seed was extracted Pollen tube data were taken on the number size. Although several of the D. princeps · from the ripe fruits and examined under of pollinated styles in which pollen tubes D. rotundifolia putative hybrids eventu- a dissecting microscope to assess probable reached the end of the style. Data were taken ally bloomed, all plants except one had viability. Seed that was shriveled and flat- on number of crosses producing fruit with seed tened was deemed to be nonviable. Seed of probable viability and number of crosses determined to be of probable viability was germinating. Percentages of seed-producing sown in 0.56-L (10.2 cm diameter) pots on crosses and germinating crosses were calcu- top of Fafard Germination Mix under fluo- lated from this data. Number of seedlings rescent lighting at a set temperature of 21 °C. resulting from these crosses was counted. Two different methods of germination were used. The first method, used from Sept. Results to Nov. 2012, was a humidity tent. Seeds were sown on top of moist substrate. The pots Pollen tubes were able to grow to the end were covered with clear plastic and substrate of the style in every cross tested (Table 2; was misted periodically to maintain a high Figs. 1 and 2). Intergeneric crosses and level of humidity. Beginning in Jan. 2013, interspecific crosses showed the same pat- harvested seeds were sown on top of substrate tern, indicating that prezygotic barriers to and placed under mist in a greenhouse using fertilization due to pollen and pistil incom- natural lighting only. patibility did not exist in these crosses. Seedlings that germinated were trans- Seed set from both interspecific and in- planted into separate 0.56-L (10.2 cm di- tergeneric crosses was low and showed great ameter) pots containing Fafard Germination variability among parents. For interspecific Mix and placed in a greenhouse under 50% crosses, D. princeps and D. rotundifolia had shade. Once seedlings had grown to at least the highest rate of seed set at 42.7% and 5.08 to 7.62 cm tall, they were transplanted 42.9%, respectively (Table 3). Species with into 2.8-L (15.2 cm diameter) trade con- the lowest rate of seed set were Tibouchina tainers filled with a pine bark substrate with fothergillae ·pilosa at 0.0%, and T. lepidota micronutrients and removed from shade. at 4.3% (Table 3). Seed set among parents in Seed set from initial crosses was low, so intergeneric crosses was also highly variable. pollen germination and pollen tube growth Dissotis canescens had the highest rate of through the styles were evaluated to deter- seed set at 31.5% (Table 4). Tibouchina mine whether barriers to fertilization existed fothergillae ·pilosa and T. lepidota again between the species used as parents in the had the lowest rate of seed set at 3.5% and study. Interspecific and intergeneric crosses 4.0%, respectively (Table 4). Fig. 1. (A) Pollen germinating on end of stigma and (Table 2) were performed during Jan.