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N.K. Lownds and W.A. Mackay

Water loss of Nerium oleander growing in two soil types was determined from mid-June through mid-October. Plants (1 year old, 3.8 liter) were obtained from a local nursery and transplanted in May into 18.9-liter Iysimeter pots containing either clay loam or bluepoint sand. Controls were lysimeter pots containing each soil type but without plants. Irrigation was applied at two rates, approximately field (pot) capacity and 50% of that amount. Irrigation frequency was determined by visual inspection of the plants and was held constant for both irrigation rates in a given soil type. Frequency ranged from 2 to 3 days for the sand and 2 to 5 days for the clay loam. Water loss was determined every 24 h. Plant water loss was higher at the higher irrigation rate. Decreasing irrigation rate by 50% resulted in a 20% to 40% reduction in plant water use in clay loam and a 15% to 30% reduction in sand without affecting plant quality. Plant water loss in the sandy soil was ≈50% greater than in clay loam 48 h after irrigation. Implications of these findings in developing an optimum irrigation model for landscape plants will be considered.

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W.A. Mackay, T.J Ng and F.A. Hammerschlag

Genetics of the host-pathogen interaction between Cucumis melo L. (muskmelon) and Myrothecium roridum were investigated by evaluating six populations: the parents, F1, F2, BCP1 and BCP2 of crosses between `Hales Best' (tolerant), `Perlita' (intermediate) and `Iroquois' (susceptible). A spore inoculation bioassay with detached-leaves was used to determine levels of resistance. Resistance was determined by measuring necrotic lesion diameter, chlorotic plus necrotic lesion diameter, and a subjective rating score. Parents and F1s had consistent performance while the segregating generations were inconsistent. Factors contributing to the response will be discussed.

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W.A. Mackay, T.J Ng and F.A. Hammerschlag

Genetics of the host-pathogen interaction between Cucumis melo L. (muskmelon) and Myrothecium roridum were investigated by evaluating six populations: the parents, F1, F2, BCP1 and BCP2 of crosses between `Hales Best' (tolerant), `Perlita' (intermediate) and `Iroquois' (susceptible). A spore inoculation bioassay with detached-leaves was used to determine levels of resistance. Resistance was determined by measuring necrotic lesion diameter, chlorotic plus necrotic lesion diameter, and a subjective rating score. Parents and F1s had consistent performance while the segregating generations were inconsistent. Factors contributing to the response will be discussed.

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W.A. Mackay, T.J Ng and F.A. Hammerschlag

Cucumis melo L. (muskmelon) is susceptible to Myrothecium roridum at all stages of growth with no known source of resistance. Screening of regenerants from long-term cotyledonary-derived callus cultures of muskmelon cv. Hales Best (tolerant), Iroquois (susceptible), and Perlita (intermediate) was carried out to determine if novel plants with increased levels of resistance could be obtained. A detached-leaf bioassay was used to screen greenhouse-grown regenerants and seedlings of the three cultivars. Resistance was determined by measuring necrotic lesion diameter and chlorotic plus necrotic lesion diameter. No change in the level of resistance to M. roridum has thus far been observed. Thus, screening for somaclonal variation may not be aviable approach to recover resistance in muskmelon to M. roridum.

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Jennifer L. Boatright, J.M. Zajicek and W.A. Mackay

A study was conducted to test the ability of hydrophilic polymers to retain moisture in annual bedding plant beds in addition to reducing NO3 and NH4 leaching. Petunia plants were transplanted into raised concrete benches containing a drainage pipe that allowed for excess leachate to be collected. Beds that were treated with 0 or 366 g·m–2 of hydrogel and 0 or 186 g of ai N. Watering of beds followed a strict irrigation schedule and soil moisture was monitored daily. At termination, plant dry weight was measured and analyses of plant tissue and leachate were conducted for NO3 and NH4 concentrations. Results from this study demonstrated that, under suboptimal conditions of minimal irrigation and fertilization, polymer incorporation had a significant effect on water, NH4, and NO3 retention in soils. Water leaching was decreased by 17%; NH4 retention was increased by 83%; and NO3 retention, where additional N was added, was increased by 64% due to polymer incorporation. In addition, a 47% reduction in NO3 concentration of water leachate was detected when polymer was incorporated under minimal fertilization. Growth or N levels of petunia were not significantly affected by polymer incorporation.

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Jennifer L. Boatright, J.M. Zajicek and W.A. Mackay

Two experiments were conducted in which a polyacrylamide gel (Hydrosource, Western Polyacrylamide) was incorporated into 56 × 38-cm, raised, concrete beds, 20 cm deep, with a drain pipe in the center of each bed. In Expt. 1, treatments included (in grams of i.a. N) 0, 186, 372, or 558 plus 0 or 366 g hydrogel/m2, for a total of eight treatments. Each treatment was replicated three times. Petunia plants were transplanted into each plot for a total of 30 plants per treatment. Plants were kept well watered. Polymer incorporation had no effect on soil water retention, soil NO3 or NH4 retention, or plant growth. Expt. 2 included treatments of 0 or 186 g of ai N and 0 or 366 g hydrogel/m2. Each treatment was replicated six times with 10 plants per replication, resulting in a total of 60 plants per treatment. Minimal irrigation was imposed on treatments. This study demonstrated that under suboptimal conditions of minimal irrigation and fertilization, polymer incorporation significantly increased soil moisture (17%), NH4 retention (83%), and NO3 retention where additional N was added (64%) compared to soils without polymer.

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W.A. Mackay, D. Sankhla, T.D Davis and N. Sankhla

Racemes of Big Bend bluebonnet (Lupinus havardii Wats.), a winter annual native to far west Texas with attractive blue flowers, are currently being produced commercially as a specialty cut-flower crop. Our studies indicated that the key determinants of postharvest longevity and performance are flower abscission and flower senescence, both of which can be influenced by ethylene. Therefore, this study was undertaken to evaluate the role of some ethylene biosynthesis inhibitors (aminooxy acetic acid = AOA; cobalt = CO++; salicylic acid = SA) and an ethylene action inhibitor (silver thiosulfate = STS) on flower abscission and flower senescence of bluebonnet racemes. Depending on the concentration used (10 μM - 1 mM), AOA and CO++ exhibited variable effects on flower abscission, flower senescence and vaselife. SA (10-100 μM) slightly delayed senescence but did not affect abscission, while higher levels of SA (500 μM - 2 mM) slightly promoted abscission and also significantly enhanced the senescence of flowers on cut racemes. The effects of SA were found to be pH-dependent. However, STS nearly eliminated flower abscission and enhanced vaselife. The results also demonstrated that the abscission of bluebonnet flowers, in particular, is highly sensitive to ethylene.

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Shelley A. McReynolds, J.M. Zajicek, W.A. Mackay and J. L. Heilman

A study was conducted to explore how different mulches affect water use of landscape plants. Plots 4.9 m × 7.3 m, were covered with 5cm pine bark, cypress, white rock, or clay aggregate. 3 potted plants of Ligustrum japonicum (wax-leaf ligustrum) and Photinia × fraseri (red tip photinia) were placed in each plot so that the top of each pot was at ground level. 1 plant of each species was planted directly into each plot. Water loss was measured on a daily basis, both gravimetrically and using heat balance stem flow gauges, during both the 1992 and 1993 growing seasons. Stomatal conductance was measured periodically during each growing season. Surface, air, and soil temperatures at two depths were recorded. During 1992, pine bark mulched plants consistently used more water than the other treatments, as opposed to summer 1993 when the most water was used by plants over white rock. Surface temperatures of pine bark, cypress and clay aggregates were higher than those of white rock both years, by as much as 20C, while temperatures under the mulch varied as much as 5C between pine bark and white rock.

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Mario Valenzuela-Vázquez, Geno A. Picchioni, Leigh W. Murray and Wayne A. Mackay

The raceme of Lupinus havardii Wats. (Big Bend bluebonnet) is a new greenhouse specialty cut flower, but postharvest life is limited by ethylene sensitivity. The authors studied the effects of 160 nL·L−1 1-methylcyclopropene (1-MCP) with 0 to 6 days exposure to a 50-μm vase solution of ethephon [(2-chloroethyl) phosphonic acid, CEPA] on raceme postharvest quality indices and mature flower cell membrane permeability. With no CEPA, 1-MCP delayed postharvest losses in fresh weight and mature flower retention, and extended vase life longevity (VLL) by 1 to 4 days relative to a non-1-MCP control. With 2 days or more of CEPA, 1-MCP deferred raceme fresh weight loss and the abscission of both mature and newly opened flowers from 3 days to 5 days. There was a relatively strong protective effect of 1-MCP on raceme fresh weight, flower retention, and newly opening flowers in the presence of CEPA compared with the absence of CEPA. The greatest raceme VLL (7.2 days) was obtained for 1-MCP-treated racemes that did not receive CEPA in the vase. Although VLL was reduced by CEPA, VLL was consistently greater (by ≈2 days) after 1-MCP treatment relative to no 1-MCP treatment and irrespective of CEPA's duration. As expected, electrolyte leakage increased with individual flower development and between 1 day and 6 days in the vase. Unexpectedly, however, the 5-day postharvest increase in leakage was intensified by 1-MCP treatment if the racemes were exposed to 1 hour of CEPA in the vase solution. Electrical conductivity measurements suggested that, in the latter treatment (+1-MCP, +CEPA), increased levels of diffusible electrolytes that had yet to be exported to the expanding apical meristem (delayed raceme development) contributed to the higher leakage. Results also demonstrate good potential for quality maintenance of L. havardii racemes by using 1-MCP, and that in addition to flower retention, raceme fresh weight and flower opening should be considered in developing VLL criteria for this new specialty crop.

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Tim D. Davis, Steven W. George, Wayne A. Mackay and Jerry M. Parsons