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Wayne A. Mackay

Micropropagation studies of several desirable species native to west Texas were initiated to develop clonal propagation systems for ornamental production. Actively growing shoots were collected from mature Texas Madrone and Mexican Redbud trees and successfully cultured on basal medium consisting of WPM salts, MS vitamins, 30g·l-1 sucrose, 0.8% Phytagar supplemented with 2.5 mg·l-1 BA. Shoots were subcultured every 4 weeks on the same medium to obtain sufficient culture material for experiments. Experiments were performed examining inorganic salt formulations, growth regulator materials, and gelling agents to optimize shoot proliferation and rooting.

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John Sloan* and Wayne Mackay

Soils exhibit a degree of hydrophobicity and can repel water rather than absorb it. Surfactants lower the surface tension of water which may increase its infiltration into the soil and adsorption to soil solids. The objective of this study was to determine if water treated with a surfactant would increase conserve soil moisture and decrease the amount of water needed to sustain healthy plant growth. Clay and sandy loam soils were placed in 15-cm greenhouse pots. Impatiens seedlings were transplanted into each pot. All pots were fertilized equally and the Impatiens flowers were allowed to grow for 8 weeks. Then the pots were treated with tap water or tap water mixed with a commercial surfactant at one times (1×) or two times (2×) the recommended rate. After applying the water treatments, pots received no additional water. Each pot was weighed twice per day and the plants were observed for signs of wilting. Upon initial signs of wilting, each plant was rated on a scale of 1 to 3 with 1 = no wilting, 2 = leaves starting to droop, and 3 = wilting leaves and stems. Addition of the surfactant at the 1× and 2× rates slowed the loss of water from both the sandy loam and the clay soils. The effects of the surfactant were apparent within 3 to 5 days in the sandy loam soil and 6 to 10 days in the clay soil. The benefits of reduced water loss from soil were manifested by reduced wilting in Impatiens plants in soils treated with 1× and 2× the recommended rate of surfactant. In the clay soil, use of the surfactant increased the amount of time before Impatiens plants began to wilt. It appears that adding a surfactant to irrigation water can conserve soil moisture and extend the time between water applications.

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Wayne A. Mackay

Mature flowering Arbutus texana trees were successfully micropropagated from shoot tips. Optimum shoot proliferation was achieved on a basal medium consisting of WPM salts, MS vitamins, and sucrose supplemented with 11.1 or 22.2 μm BA and no auxin. Microcuttings rooted readily when pulsed with 6.1 μm IBA for 1 week and transferred to auxin-free medium. The addition of charcoal to the rooting medium improved root branching and elongation but suppressed root formation. Chemical names used: N-(phenylmethyl)-1H-purin-6-amine (BA); indole-3-butyric acid (IBA).

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Wayne A. Mackay

Seeds of Lupinus havardii Wats. and L. texensis Hook. were subjected to scarification, storage temperature (4 or 22 °C), and relative humidity (RH) treatments (11%, 23%, 52%, 75%, or 97% RH) for 12 months. Seed moisture increased as relative humidity increased with scarified seed having the greatest increase in seed moisture content regardless of storage temperature. For both species, the combination of seed scarification before storage, 75% RH, and 22 °C storage temperature resulted in a significant and rapid decline in germinability beginning at 4 months. Scarified L. texensis seed stored at 52% RH and 22 °C also exhibited a significant decline in germinability following 6 months storage. Seed of both species stored under all other conditions germinated similar to or higher than the initial germination rate after 12 months. These results clearly show that scarification can be performed before seed packaging as long as the seed packets are stored at ≤23% RH under 4 or 22 °C with no loss in germinability for at least 1 year.

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Wayne A. Mackay and Narendra Sankhla

Phlox paniculata `John Fanick' produces long lasting, dense terminal flower heads and has potential as a specialty cut flower. Quality and postharvest display life of cut flower heads depends primarily on ethylene-induced flower abscission, flower bud opening, and maintenance and development of flower color during vase life. Late events, such as flower and leaf senescence may also be detrimental to flower quality. In the control treatment, the initial red-pink and purple flower color changes to violet blue in 3 to 4 days, and may lose >50% of initial anthocyanins. Incorporating sucrose (SUC) in the vase solution not only maintained >75% of the initial floral pigments, but also promoted opening of additional flowers and anthocyanin development. Although both ethylene biosynthesis (AOA, ReTain, a.i. AVG) and action inhibitors (STS, 1-MCP) delayed flower abscission, STS and 1-MCP were relatively more effective than AOA and AVG. As in the control, newly opened flowers remained very small when treated with ethylene inhibitors, did not develop red-pink color, and exhibited only shades of violet blue color. Sucrose antagonized the effect of ethylene inhibitors. As such, the flowers in SUC+ethylene inhibitors treatments enlarged in size and developed a reddish-pink blue color. However, the flower quality in SUC alone was much superior than those in SUC+ethylene inhibitors. These results indicate that ethylene inhibitors, alone and in combination with SUC, were not of any additional value in improving postharvest performance and display life of cut phlox flower heads.

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Narendra Sankhla, Wayne Mackay* and Tim Davis

Low concentration fumigation with nitric oxide (NO*) has been shown to extend the postharvest life of a range of flowers, fruits and vegetables by down-regulating ethylene production. Since ethylene is involved in flower abscission and leaf senescence of `John Fanick' phlox cut flower heads, a superior selection of perennial phlox (Phlox paniculata L.) bearing attractive long-lasting flowers, we have evaluated the effect of NO* delivered in vivo using sodium nitroprusside (SNP) as the source of NO* donor, on postharvest performance of `John Fanick' phlox flower heads. Although the presence of SNP (10-200 μmol·L-1) in the vase solution promoted the abscission of the open flowers, the young flower buds continued to open even in the presence of high SNP concentrations. On the other hand, at high SNP concentrations, the leaves became either yellow, or more frequently turned progressively black and senesced. Inclusion of sucrose in the vase solution, or pretreatment of flower heads with either 1-MCP or STS, significantly delayed the abscission of flowers and blackening of leaves. The pretreatment of flower heads with either 1-MCP or STS, or the presence of sucrose in the vase, together with SNP, greatly reduced the toxicity of the latter chemical resulting in improved postharvest display life. These results indicate that in `John Fanick' the leaves are relatively more susceptible to NO*-induced toxicity than the flowers. However, both sucrose and ethylene perception inhibitors are able to minimize the toxicity of high concentrations of NO* delivered in vivo via SNP.

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Wayne Mackay*, Narendra Sankhla and Tim Davis

Over the years, by recurrent phenotypic selection, breeding and evaluation, we have developed blue, white, and pink flowered lines of Big Bend bluebonnet (L. havardii Wats.). The racemes, which differ in their sensitivity to ethylene, hold promise as a new specialty cut flower crop. The key determinants of postharvest longevity and performance of cut racemes are flower abscission and senescence. Our studies indicated that the addition of sucrose in the holding solution greatly enhanced the vase life, although the optimum sucrose concentration varied considerably in different lines. In blue flowered lines (e.g., `Texas Sapphire', Blue Select) sucrose concentration greater than 2% induced `osmotic wilting' followed by senescence of the standard petal (banner spot petal), while the petals in white flowered lines (e.g., `Texas Ice', White Select) did not show any wilting even in 4% to 6% sucrose. Ethylene perception inhibitors such as 1-MCP or STS completely suppressed the induction of flower abscission in racemes of all the bluebonnet lines. Ethylene biosynthesis inhibitors (e.g., ReTain, CO++), on the other hand, were relatively less effective than 1-MCP/STS. Both ethylene perception as well as biosynthesis inhibitors, in combination with sucrose, acted additively and further enhanced the postharvest performance by delaying flower abscission/senescence.

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Wayne A. Mackay and Tim D. Davis

Seeds of four lupine species (L. microcarpus var. aureus, L. havardii, L. succulentis, and L. texensis) were subjected to 0, –2, –4, –6, or –8 bars osmotic potential using PEG 8000 solutions. Seeds of all species were acid scarified prior to placement in petri dishes containing the osmotic solutions. Petri dishes were placed in a seed germination chamber at 25°C with germination data collected daily for 15 days. Seeds of L. havardii, a desert species native to west Texas exhibited the greatest germination as osmotic potential declined while L. succulentis, a species adapted to moist sites, exhibited the greatest decline in germination as osmotic potential decreased. The other species exhibited intermediate germinability under the lower osmotic potentials.

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Katherine L. Vasquez and Wayne A. Mackay

Lupinus havardii and L. texensis are two commercially important species of lupines (bluebonnets) in Texas. There is no current information for the storage requirements of these two bluebonnet species seeds. A study was undertaken to examine the effects of relative humidity, temperature, and scarification on seed germinability. Seeds of the two bluebonnet species were stored under five relative humidity treatments (11%, 23%, 52%, 75%, and 95%) and two temperature treatments (3°C or 22°C) either scarified or nonscarified in factorial combination. Seed samples were removed monthly. Nonscarified seed were scarified and all seed were placed in a seed germination chamber and germinated in petri dishes containing moistened filter paper. All samples of seed stored under 95% relative humidity were lost to seed-borne contamination. Germinability of scarified seed of both species decreased within 5 months in the 22°C/75% RH treatment. Other treatments had no effect on germinability during 7 months of seed storage.

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Genhua Niu, Denise S. Rodriguez and Wayne Mackay

Oleander (Nerium oleander L.), native to southern Asia and the Mediterranean region, is a fast-growing evergreen shrub planted widely in the southern United States. A greenhouse study was conducted to quantify the growth and physiological responses of two cultivars, Hardy Pink and Hardy Red, and two breeding lines, EP1 and EP2, of oleander to a 12-week cyclic drought stress. Drought stress was imposed by irrigating the plants to near container capacity and then withholding irrigation until predetermined container weights were reached. Compared with the control where plants were well-irrigated throughout the experiment, shoot dry weight (DW) was reduced by 52%, 41%, 34%, and 11% in EP1, EP2, ‘Hardy Red’, and ‘Hardy Pink’, respectively. Root-to-shoot DW ratio was higher for the drought-treated plants than the control, regardless of cultivar or breeding line (hereafter, clone). The increase in root-to-shoot DW ratio from the drought treatment was highest in EP1, followed by EP2, ‘Hardy Pink’, and ‘Hardy Red.’ New shoot growth was greatest in ‘Hardy Pink’, followed by ‘Hardy Red’, EP1, and EP2. The number of newly developed shoots during the drought treatment period was 6.8, 3.0, 0.7, and 0.0 in ‘Hardy Pink’, ‘Hardy Red’, EP1, and EP2, respectively. As substrate volumetric moisture content decreased from 30%, leaf net photosynthetic rate (Pn), evapotranspiration rate (E), and stomatal conductance (gs) decreased in all clones. A curvilinear relationship between Pn and gs was found in all clones. EP1 had a lower maximum Pn (Pm) than those of ‘Hardy Pink’ and EP2 but was not different from that of ‘Hardy Red’. Predawn leaf water potential began to decrease rapidly when substrate moisture content dropped below 15% in all clones. During the dry-down, compared with the control, increases in minimal fluorescence (F0) or decreases in maximal fluorescence (Fm) and Fv/Fm (Fv = Fm – F0) in drought-stressed plants were observed in all clones, indicating some damage in photosystem II from the drought treatment. However, compared with growth parameters, the differences in physiological responses to drought stress among the clones were much smaller. ‘Hardy Pink’ was more tolerant to drought stress than ‘Hardy Red’ and the other two clones in terms of productivity because it maintained greatest growth during the drought-stress period. However, EP2 and EP1 may be more tolerant if survival is concerned because they had a higher root-to-shoot DW ratio with minimal new growth.