Patent Application
20080028491
These and other features of the invention will become more apparent from the following description in which reference is made to the appended drawings wherein:
=production of many primary interspecific hybrids (>50)
=production of some primary interspecific hybrids (10 to 50)
=production of few primary interspecific hybrids (<10)
and inefficient plants are indicated by multiple thin open circles
.
The present invention relates to plants of the genus Exacum. More specifically, the present invention provides interspecific hybrid populations of Exacum derived from several Sri Lankan Exacum taxa having desirable traits for commercial floriculture.
The following description is of a preferred embodiment.
As described in more detail below, Exacum hybrids were derived from an interspecific crosses with Exacum taxa E. pedunculatum, E. macranthum, E. pallidum, E. trinervium and E. trinervium ssp. ritigalensis native to Sri Lanka (see
The hybrid Exacum plants of the present invention are more easily produced, and characterized as having increased hardiness, are of a reduced plant height, and that are more easily cultivated than the parental lines (identified in
Plant habit or growth habit refers to the form of the plant, for example a plant can be erect (upright), where at least 80% of one or more than one main stem is within about ±10° from perpendicular; leaning, where at least 80% of the one or more than one main stem is about ±20° to about 45° from perpendicular; or sprawling, where about 80% of the one or more than one main stem is procumbent.
Plant height is a measure taken from the pot edge to the top of the plant canopy and is measured in centimeters. Plant height is variable and age dependant. Further, plant height may be dependant upon a range of criteria including growth conditions, for example, light intensity, temperature, humidity, fertilization regime, addition of growth regulators, and zinc supplementation. Therefore plant height may be manipulated by varying one or more of these variables. Plant height may reach up to about 60 cm, however, a plant height of about 10 cm to about 30 cm, or any amount therebetween is typically a desired range in plant height.
Flowering of the Exacum hybrids of the present invention may also be varied. The onset of flowering may be delayed under conditions of low light, by growing a taller plant, by adding exogenous compounds, for example, ethreyl (an ethyl-ethyl dimmer), or a combination thereof.
Hardiness. Hardiness refers to the US National Arboretum (USDA) Plant Hardiness Zone Map, USDA Miscellaneous Publication No. 1475 Issued January 1990, available from U.S. National Arboretum, Agricultural Research Service, U.S. Department of Agriculture, Washington, D.C. 20002. Zone 11 represents any area where the average annual minimum temperature is above 40 F (4.4 C).
Stem branching or branching density is a measure of the number of branches emerging from, or nodes associated with a branch within a defined length of one or more than one main stem when measured over the length of the stem, or in the top 50% of plant height. For example, a branching density of 3 per 5 cm over the length of the main stem, indicates that along the length of the stem, on average there will be 3 branches per 5 cm. Alternatively, within any 5 cm length of stem in the upper half of the plant, approx. 3 branches will emerge from the one or more than one main stem.
“RHS” refers to the Royal Horticultural Society of England official botanical color chart quantitatively identifying colors according to a defined numbering system. The chart is available from Royal Hort Society Enterprise Ltd RHS Garden; Wisley, Woking; Surrey GU236QB, UK.
By increased hardiness, it is meant that the plants are tolerant to a range of environmental factors when compared to the parental plant lines, including but not limited to increased tolerance to Fusarium infection, zinc, and pot culture. Parental plant lines exhibit poor growth when potted and grown under greenhouse conditions. However, the plants of the present invention are readily produced under greenhouse growth conditions.
Resistance to a disease is when about 80% to about 100% of the plants in a given population do not show any symptoms of the disease through a production cycle. Preferably, 90% to about 100% of the plants do not show any symptoms of the disease through a production cycle. By tolerance to a disease it is meant that the disease may still grow on the plant, but that the plant does not display any negative effects, for example which is not to be considered limiting, plant biomass may not reduced, disease progression may be inhibited, or both.
Zinc efficiency is the ability of a genotype to grow normally under low zinc availability conditions. In the case of the parental Sri Lanka Exacum species (
By symptoms of zinc deficiency it is meant the appearance of any one or more than one of the following deficiency symptoms: chlorosis, rosette formation, longitudinal leaf curl, and necrosis. A zinc inefficient Exacum plant exhibits an uptake of Zn of less than about 6.5 μmol Zn/cm root surface, for example from about 1.0 to about 6.4 μmol Zn/cm root surface or any amount therebetween. A zinc efficient Exacum plant exhibits an uptake of Zn of greater than or equal to about 6.5 μmol Zn/cm root surface, for example from about 6.5 to about 20 μmol Zn/cm root surface or any amount therebetween, or about 6.7 to about 12.5 μmol Zn/cm root surface, or any amount therebetween. Other parameters may also be used to determine zinc efficiency/inefficiency including zinc uptake/cm root length, or μmol Zn/mg root as disclosed in Riseman and Craig (2000, Plant and Soil 219:41-47). Zinc efficiency may also be defined in terms of frequency within a population, for example, a Zn inefficient plant cultivar may comprise from about 80 to about 100% of a population of plants, or any amount therebetween, and require zinc supplementation as described above.
An example of conditions for the growth of the Exacum plants of the present invention include:
The Exacum plants of the present invention were produced through repeated cycles of selection, the selected genotypes include all the distinguishing traits identified in the original Sri Lankan Exacum population shown in Table 1. However, as a result of initial interspecific hybridizations and subsequent breeding, these traits are expressed in novel combinations and as intermediate forms not displayed in the original taxa. The selected genotypes display full sexual compatibility.
More particularly the selected genotypes of the present invention are characterized as having the following traits:
Plants are procumbent to erect having stems that are cylindrical to quadrangular, with wings present or lacking;
Leaves are glossy green, lanceolate to ovate or narrowly elliptic;
Leaf tips are acute to acuminate and leaf bases cuneate to rounded; and
Flowers are blue to violet with pale to dark hues. The flowers are flattened to cup-shaped or rarely with petals reflexed with the corolla base short and tubular. The petals are rhomboidial to broadly obovate, and overlapping along their entire length to overlapping only at their broadest point or not overlapping. The anthers are bright yellow and 8 to 18 mm long.
Seeds from examples of plants obtained as described herein include but are not limited to genotypes 01-09-01, 01-37-08, 01-37-61, 01-42-03, 01-47-21, 01-47-47, 01-48-10, 01-50-46, 01-69-17, 02-174-09 as described in Tables 2a-2d, below. Representative seed of this grex to be deposited in the ATCC.
E. macranthum
E. pallidum
E.
pedunculatum
E. trinervium
E. trinervium
Examples of characteristics of genotypes 01-09-01, 01-37-08 and 01-37-61, obtained as shown in
Table 2b shows the traits for selected genotype 01-42-03, 01-47-21, and 01-47-21 obtained as shown in
Table 2c shows the traits for selected genotype 01-48-10 (obtained as shown in
Genotype 02-174-09 (see
Each of genotypes 01-09-01, 01-37-08, 01-37-61, 01-42-03, 01-47-21, 01-47-47, 01-48-10, 01-50-46, 01-69-17, or 02-174-09 is suitable for horticultural production.
All plant genotypes can be asexually propagated by stem cuttings. However, higher rooting percentages are typically observed when cuttings are harvested from non-flowering stock plants. For stem cuttings of Exacum, cuttings 2-3 nodes in length are typically basally treated with 1% IBA (Hormodin #1, MSD-AGVET, Division of Merck and Co., NJ) in talc, or 10 mM NAA solution for 20 seconds. The cuttings can then be inserted into cell packs filled with a well-drained substrate (for example a peat-based potting mix) and placed under intermittent mist until rooted. Rooted cuttings are generally obtained within 2-4 weeks and rooting percentages typically range from 50% to 100% depending on genotype and reproductive status of the stock plant. Rooted cuttings are generally transplanted into 10-12 cm pots with a well-drained peat based media (pH 4.5-5.5).
Hybrid Exacum plants may also be propagated by tissue culture using regenerable cells and methods that are well known to one of skill in the art (for example Riesman and Chennareddy, 2004, J. Ameri. Soc. Hort. Sci. 129:698-703, which is incorporated herein by reference). Regenerable cells include embryos, protoplasts, seeds, callus, pollen, leaves, anthers, roots, and meristematic cells.
The present invention includes a cell culture comprising regenerable cells obtained from the Exacum hybrid as defined herein, and Exacum plants regenerated from these tissue cultures. This invention also provides a method of producing an Exacum hybrid involving, providing regenerable cells, and growing the Exacum hybrid from the regenerable cells.
An acidifying fertilizer high in nitrogen, such as Plant-Prod 21-7-7, is suitable used at a rate of 150-200 ppm total nitrogen. The medium pH may be managed through the use of fertilizer; a higher ammonium:nitrate ratio helped to maintain a low medium pH. The optimal media pH range is typically 4.0 to 6.0, or any amount therebetween, for example, pH 5.0-6.0, and the optimal medium electrical conductivity (EC) between 1 to 2.25 dS·cm−1. Plants were treated with zinc sulfate at 10 ppm every two weeks to prevent the development of zinc stress during seed production.
Plants generally perform best when grown on the ‘dry side’ but without undo wilting. In general, plants seemed more tolerant of drought than overly wet conditions. Typically, excessive water or a severe drought followed by excessive water leads to increased susceptibility to root pathogens. Also, plant growth is generally enhanced by periodically wetting the foliage with either water or a dilute fertilizer solution.
Greenhouse whitefly (Trialeurodes vaporariorum) may be controlled through application of several commercial pesticides. However, Malathion® is shown to have phytotoxic effects on mature buds and open flowers. Fungus gnats (Bradysia ssp. Winnertz) may be controlled through introduction of parasitic nematodes or by application of a Bti (Bacillus thuringiensis Berliner spp. israelensis) based product. In addition, the root pathogens Pythium Pringsh., Phytophthora deBary., and Fusarium Link ex Fr. may be controlled though a combination of cultural modification (e.g., less frequent irrigations) and media drenches with commercial fungicides.
Aerial temperature is ideally maintained between 18-26° C. day and 16-20° C. night and relative humidity maintained between 70-85% throughout the production cycle. Photoperiod control is generally not required for flowering.
Flowering time varies based on genotype. The earliest genotypes typically flower 6-8 weeks after transplanting into a finishing container while the latest genotypes flower between 16-20 weeks following transplanting. Flowering time generally decreases with increasing light intensities, however, during naturally low light months, supplemental irradiance may promote earlier and more robust flowering for all genotypes.
The present invention will be further illustrated in the following examples.
Five taxa of Exacum were collected from their native habitats in Sri Lanka, namely E. pedunculatum L., E. macranthum Arn., E. pallidum Trimen., E. trinervium (L.) Druce and E. trinervium ssp. ritigalensis (Willis) Cramer. The distinguishing characteristics for each of these five taxa are provided in gtabl1 (above) and briefly as follows:
Stems 29-55 cm long, cylindrical in cross-section; basal internodes medium to long. Leaves mainly ovate to oval-suborbicular, seldom elliptical, 4.5-9.7×1.8-4.3 cm; apices broadly acute to broadly acuminate. Flowers dark violet, sometimes with red tinge, 5-merous. Calyx lobes 8-19×1-3 mm. Corolla lobes broadly ovate, obtuse, 14-32×8-25 mm. Anthers 6-13 mm long.
Key characters: Stems terete with no wings or ridges; leaves oval-orbicular with undulating blades.
Stems 17-48 cm long, cylindrical with 2 opposite grooves; internodes at base compact to medium. Leaves ovate 3.0-7.5×1.6-2.3 cm; apices broadly acute. Flowers pale blue-violet, 5-merous. Calyx lobes 9-10×1-1.5 mm. Corolla lobes elliptic, 10-11×6-8 mm. Anthers 2-4 mm long, often triangular to oblong.
Key characters: Stems cylindrical with furrows whose alignment alternates with internodes; flowers small, pale blue with short anthers; branching profuse; leaves pale green.
Stems 39-73 cm long; basal internodes medium to long. Leaves 3-nerved, elliptical-linear to elliptical-lanceolate, 5.6-11.8×1.8-4.7 cm. Flowers medium to light violet, 5-merous. Calyx lobes 7-17 mm long. Corolla lobes elliptical-ovate, obtuse 6-16×3-15 mm.
Key characters: Slender stems with upright branching.
Stems 20-63 cm long; internodes always quadrangular. Leaves elliptical-ovate to lanceolate-elliptic, 6.5-14.8×1.4-4.3 cm, mostly narrowly acuminate. Flowers medium to dark violet, 5-merous. Calyx lobes 10-24 mm long. Corolla lobes broadly ovate to ovate, 6-25×6-20 mm, always obtuse. Anthers 6-13 mm long.
Key characters: Stems robust, diffusely branching; leaves long, sometime 5-nerved.
The distinguishing traits among the original taxa of Sri Lankan Exacum used in the breeding program are summarized in Table 1.
Primary interspecific hybrids were produced from the crosses as detailed in
Through all generations, selection was for fertility, greenhouse production traits (e.g., domestication), and combinations of horticulture traits that are indicative of hybrid status. These selection criteria were continued through 12 generations beyond the primary hybrids.
Each plant in the breeding program was assigned a unique genotype identification (ID) consisting of three numbers. The first number is the year the seed was sown; the second number is the family code (i.e., specific parents in a specific combination) by convention, seed parent (female) is listed first followed by pollen parent (male); and the third number is the individual sibling from that family. When multiple individuals from a family were selected their IDs are separated by a ‘/’. Since they are siblings, they have the same pedigree.
Seed were produced on asexually propagated plants. All families were produced through controlled pollinations under greenhouse conditions. Each pollinated flower was labeled with the seed parent, the pollen parent and the date. Emasculation was not necessary because Exacum pollen is dehisced through apical pores in the anthers which need to be mechanically manipulated for pollen release. In addition, no fruit were ever observed on unpollinated control plants. Fruit were collected at maturity and stored in individual glassine packets until sowing.
Seed were produced on asexually propagated plants. Pollination procedures were as described above. A minimum of 200 pollinations was made for each genotype to ensure adequate seed production.
Both hybrid and inbred seed and resulting seedlings were treated identically. Seeds were surface sown onto a well drained peat moss based media in individual seed trays with identification labels. Trays were sub-irrigated, allowed to drain, and then enclosed in clear plastic bags. The bagged trays were placed under cool-white fluorescent lamps (GTE, Lighting Division, Salem, Mass.) and maintained at 20 C until germination. Once germination occurred, plastic bags were opened for one day, and then removed. Four weeks after germination, seedlings were transplanted into individual slots in 50 unit plug trays filled with MetroMix 500™ and moved to the greenhouse. All seedlings were maintained in a single greenhouse section in order to minimize environmental variation. Seedlings were sub-irrigated for an additional three weeks until they were large enough to sustain overhead irrigation. Starting at the time of transplanting, and continuing throughout the experiment, seedlings were fertigated with 100 ppm total nitrogen fertilizer supplied by 20-10-20 peat-lite™ (Scotts-Sierra Horticultural Products Co. Marysville, Ohio). Greenhouse conditions were maintained at 20 C night temperature and 25 C day temperature. Plants remained in the plug trays for an additional six weeks and then were transplanted into 10 cm pots filled with the same media. Cultural and environmental conditions were uniform for all plants.
All citations are hereby incorporated by reference.
The present invention has been described with regard to one or more embodiments. However, it will be apparent to persons skilled in the art that a number of variations and modifications can be made without departing from the scope of the invention as defined in the claims.
