Challenges in breeding D. Dissotis species are crossed in the greenhouse unless the nursery facility is in a tropical climate. Pollination is done by hand, using a tuning fork to cause pollen to dehisce and collecting the pollen in a vessel for use in pollinations. The crosses are evaluated for abortion rate and seed germination rate, with crossing strategies adjusted for crosses with high abortion rates. Once viable seed is obtained, it is sown on top of slightly acidic potting media and maintained under mist until germination.
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Challenges in breeding D. Dissotis species are crossed in the greenhouse unless the nursery facility is in a tropical climate. Pollination is done by hand, using a tuning fork to cause pollen to dehisce and collecting the pollen in a vessel for use in pollinations.
The crosses are evaluated for abortion rate and seed germination rate, with crossing strategies adjusted for crosses with high abortion rates. Once viable seed is obtained, it is sown on top of slightly acidic potting media and maintained under mist until germination.
The resulting progeny are phenotyped and evaluated for ploidy using flow cytometry. The main traits of importance in phenotyping the hybrids are size of flowers, length of flowering period, and vigor of growth.
Once the progeny is phenotyped, the best of the progeny for ornamental use are used in further crosses, or propagated vegetatively to increase the numbers of the new hybrid. Introduction Dissotis rotundifolia, commonly called Spanish Shawl or Pink Lady, is not well known as an ornamental outside tropical and subtropical regions of the United States; however, it has the potential to be more widely used in the landscape Ruter, personal communication, The trailing habit of this species lends itself well to use in a hanging basket Ruter, personal communication, The species is resistant to drought and very easy to propagate vegetatively Ruter, personal communication, ; personal observation.
Figure 1 Dissotis rotundifolia flower and immature fruits. Figure 2 Dissotis rotundifolia foliage. Figure 3 Dissotis rotundifolia on the greenhouse bench showing creeping growth habit. This population had been potted up from cuttings approximately six months previous to the time this picture was taken. Each plant had already been trimmed back to the edge of the pot once during that time period.
Dissotis rotundifolia also has the potential to be used as a specialty crop for medicinal purposes. In its native range in Africa, D.
An extract of D. Phytochemical screening of D. More pharmacological studies of the species are needed to determine its full potential. Dissotis rotundifolia is a member of the Melastomaceae family, which is comprised of tropical and subtropical plants.
There are to genera and approximately 5, species in the Melastomaceae to date Almeda and Chuang, The genus Dissotis contains species, all native to Africa; D.
According to Porembski et al. Solt and Wurdack report that D. Floral Morphology and Breeding Ecology According to Renner , Dissotis rotundifolia, like all the Melastomaceae, is buzz-pollinated by bees in its native range. Species in the Melastomaceae have poricidal anthers and pollen dehisces from the anthers through one or two pores; the number of the pores depends on the species.
Pollen does not dehisce in species with poricidal anthers unless the anthers are manipulated in some way, usually by an insect. Pollen has also been observed to be dispersed when the plant is shaken by rain or high winds; this occurrence is rare. The vibration imparted to the anthers by bees is at least Hz, making it unlikely that pollen will dehisce accidently from the anthers.
Therefore, pollination in breeding must be performed in a similar fashion to what is done in solanaceous crops in the greenhouse such as tomatoes and peppers. Melastomaceae flowers are perfect, having both pistils and stamens. Luo et al. The feeding anthers are shorter than the pollination anthers and are yellow, a color which attracts bees. When the bees alight on the flower to gather pollen, they concentrate on the feeding anthers.
While the bee sonificates the feeding anthers, it also sonificates the pollination anthers, causing pollen to dehisce from both sets of anthers. The pollen that dehisces from the pollination anthers is deposited on the body of the bee in places that the bee cannot reach while grooming. When the bee lights on the next flower, this pollen is deposited on the stigma of the flower and pollination occurs. Renner reported that Melastomaceae flowers are herkogamous, which means that their stamens and pistils are of different lengths.
In the Melastomaceae the style is often longer than the stamen. The herkogamy of the flower combined with their poricidal anthers promotes outcrossing. Before anthesis, anthers are folded up, with the ends tucked away from the stigma, an arrangement which makes accidental self-pollination very unlikely.
However, if the end of the anthers touch the stigma as the anthers unfold and the flower is shaken or moved in some way that causes pollen to dehisce, it is possible to get self-pollination. Melastomaceae are often self-compatible.
For example, Dissotis rotundifolia will set seed in a greenhouse without being pollinated, indicating that it is probably self-compatible Ruter, personal communication, However, it is possible that Dissotis rotundifolia could set seed by agamospermy, as this has been observed in other species within Dissotis Renner, Breeding Techniques and Strategies Different pollination techniques have been used with crops with poricidal anthers, such as solanaceous crops.
One technique is to use insect pollinators, such as honey bees or bumble bees; another is to use a mechanical pollinating wand. Both techniques have been used with success in solanaceous crops, although fruit set and quality has been shown to be significantly better in insect-pollinated crops Ahmad Al-abbadi, Much labor is saved by using insect pollination, since each flower does not need to be manipulated directly to collect pollen.
However, in breeding D. Melastomaceae flowers typically only offer pollen, and not nectar, which makes them unattractive to honeybees Renner, Also, their herkogamy causes them to be difficult to negotiate for honey bees and other small bees Almeda, personal communication, Even if larger bees, such as bumble-bees, are used, there is no way to tell which flowers have been pollinated or from which plants the pollen came.
Use of a pollination wand is common in greenhouse crops requiring buzz pollination, such as tomatoes. The standard technique is to touch the pollination wand to the pedicel of the flower late in the morning; it is a very effective way of causing pollen to dehisce from the anthers of the flower Hogendoorn et al. The wands are readily available from greenhouse supply companies and require only a supply of batteries to keep them operational. However, due to the herkogamy of the D.
The pollen would still have to be captured in a container and applied to the stigma of the flower to be pollinated. Dissotis pollen may also be gathered by using a tuning fork in the key of E to mimic the sonification of the flowers by bees Ruter, personal communication, The tuning fork is struck upon a hard surface and held to the stamens; a container is needed to catch the pollen as it exits the anthers.
Renner, Figure 4. Renner reported that a copious amount of pollen could be collected using this technique; since the pollen is binucleate, it can be stored by freezing for use at a later time, if necessary.
Figure 4 Pollen collection from Dissotis rotundifolia using a tuning fork. Breeding Objectives and Strategies The main objective in breeding Dissotis rotundifolia is to make interspecific crosses with other Dissotis species, such as D. The goal of the crosses is to bring the best features of the Dissotis species being crossed into the hybrid and to induce polyploidy Ruter, personal communication, Polyploidy can cause plants to produce larger flowers and a more vigorous growth habit and can cause the plants to evince heterosis.
Although diploid plants also exhibit heterosis, the effect may be more pronounced in polyploids, as was shown by a study of diploid and triploid hybrids of maize Auger et al. Homozygous recessives can be masked, increasing the instance of heterozygosity in polyploids Stadler, Heterozygosity is an advantage if the crop is being bred to improve a quantitative trait, such as number of flowers, rate of growth, size of flowers, and some types of disease resistance Stillwell et al.
In a study of red foliage color in flowering dogwood Cornus florida , plants with alleles inherited from both parents showed a marked increase in red foliage Wadl et al. Heterozygosity in Alstroemeria influenced both leaf length and width Han et al. Plants exhibiting polyploidy, especially interspecific hybrids, may be sterile.
Evidence of difficulty in completing normal meiosis was found in a study of allohexaploid wheat by Sears However, inducing polyploidy may restore fertility to sterile diploid hybrids.
Treatment of diploid and triploid roses with oryzalin, an herbicide that acts as a mitotic spindle inhibiter, was shown to induce polyploidy, and led to an increase in pollen viability, increasing the fertility of the species Kermani et al.
If the progeny of an interspecific cross of Dissotis rotundifolia with another Dissotis species is found to be sterile, oryzalin treatment is applied to attempt to restore fertility.
Treatment with oryzalin is done by applying a single drop of 50 umol L-1 in a solution made with 5. The number of applications will vary from one to three, depending on the interspecific cross; each application must be separated by three days Jones et al.
At least twenty seedlings of the progeny of each cross should be used for each treatment, as the treatment will not induce polyploidy in each seedling, and the greater number of seedlings that are used, the better the chances of inducing polyploidy are.
Seedlings should then be grown in the greenhouse for three months, after which time their probable status as polyploid should be determined by examining the morphology of the plants, including leaf thickness and stomatal size.
However, since ploidy may not be definitively determined by the examination of plant morphology, flow cytometry should be used to verify the ploidy of the probable polyploids Contreras et al. The optimum dosage of oryzalin will likely be different for each interspecific cross. Once the optimum dosage of oryzalin to induce polyploidy in the progeny of each cross is determined, this dosage may be applied to all future progeny.
Hybridization Since Dissotis rotundifolia is native to a tropical area, all hybridization must occur in the greenhouse if breeding is done in a temperate area. Even in sub-tropical or tropical areas, it is advisable to make crosses in the greenhouse if possible in order to better control pollination.
Control of the growth and spreading of the plants is much easier in a greenhouse, also. This is essential with D. In the field, this growth habit could cause one population to very easily grow out of its plot and intermingle with another population.
Figure 5 Roots at node of Dissotis rotundifolia. Picture taken approximately four months after plant was potted up from a cutting. Reciprocal crosses should be made between plants in each population if possible Fehr et al. Flowers to be used as the female parent should be emasculated before the anthers unfold completely to prevent accidental self-pollination Figure 6.
Once the pollen is collected from the flowers of the male plant, it is applied to the stigma by paintbrush or other implement Figure 7.
If pollinations are made in the greenhouse, it is not necessary to bag the pollinated flowers. However, if pollinations are made in the field, bagging should be done as a precaution against accidental pollination by insects. The pollinated flowers are then tagged with the name of the parents in the cross and the date of the cross noted on the tag. Figure 6 Emasculation of Dissotis rotundifolia flower to be used as male.
It has been a very rewarding patio plant and increased in size at least five-fold since I got it. The foliage cascades down very luxuriantly and looks great even with no flowers. The botanists keep changing the name. When I bought the plant it was called Heterocentron elegans. There are at least five other names for it.
蔓性野牡丹 Dissotis rotundifolia（Smith）Triana