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Dennis R. Pittenger, Donald R. Hodel, and A. James Downer

Successful reestablishment of transplanted palms [members of the Arecaceae (Palmae)] depends on rapid regeneration of roots, avoiding injury and desiccation of the trees during transit and handling, and maintaining sufficient soil moisture around the root balls after transplanting. Since landscape contractors and nurserymen spend considerable resources and labor transplanting specimen palms, understanding the seasonality of palm root growth, how palm roots respond when trees are dug, and the effects of canopy manipulation during transplanting will enable them to adopt effective and rational transplanting practices. This manuscript provides a review of research findings that can be applied to maximize reestablishment of transplanted specimen palms.

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V.C. Baligar, N.K. Fageria, and M.A. Elrashidi

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Patrick E. McCullough, Haibo Liu, and Lambert B. McCarty

Ethephon is an effective growth retardant for suppressing Poa annua (L.) seedheads in creeping bentgrass putting greens; however, ethylene induction may cause bentgrass leaf chlorosis, reduced rooting, and quality decline. Two greenhouse experiments investigated the effects of nitrogen (N) fertility and ethephon applications on `L-93' creeping bentgrass over 9 weeks. Ethephon was applied at 0, 3.8, and 7.6 kg·ha–1 a.i. per 3 weeks and N was applied at 4 and 8 kg·ha–1·week–1. Ethephon applications linearly reduced bentgrass quality on every weekly observation. Increased N rate to 8 kg·ha–1·week–1 improved turf quality about 10% to 20% and 10% to 30% from ethephon applied at 3.8 and 7.6 kg·ha–1 per 3 weeks, respectively. Increased N rate to 8 kg·ha–1·week–1 enhanced shoot growth 30% but reduced root mass and length 12% and 11%, respectively. After 9 weeks, ethephon reduced root length by about 30% and root mass about 35% at both rates. From nine weekly samples, ethephon reduced dry clipping yield 10% and 16% at 3.8 and 7.6 kg·ha–1 per 3 weeks, respectively. From 2 to 9 weeks after initial treatments, ethephon linearly increased leaf water content. Increasing N fertility effectively reduced bentgrass leaf chlorosis from ethephon; however, repeat applications of ethephon and increased N may restrict bentgrass root growth. Chemical names used: [(2-chloroethyl)phosphonic acid] (ethephon).

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A.A. De Hertogh and M. Tilley

The Swaziland-grown Hippeastrum bulbs `Summertime' and `Sun Dance' reached the market and flowering stages of development in fewer days than the Dutch-grown bulbs `Apple Blossom' and `Red Lion'. `Sun Dance' was the quickest flower and `Red Lion' the slowest. The effects of the planting medium on days to market and flowering were variable and no medium appeared to be the best for this criterion. `Summertime' and `Red Lion' produced longer leaves at flowering than `Apple Blossom' and `Sun Dance'. Three media that led to the production of the longest leaves, a desirable trait, were: Sunshine no. 4, Fafard 3-B, and Sunshine Post-Harvest. `Apple Blossom' was the tallest cultivar followed by `Sun Dance', `Red Lion', and `Summertime'. Effects of the planting medium on total plant height were variable. The overall plant quality ratings for use as potted plants ranged from 3.4 to 3.8 out of 4 for `Summertime', `Sun Dance', and `Red Lion'. `Apple Blossom' was rated 3.0 because it was tall and had short leaves. It would be suitable as a cut flower. Regardless of the planting medium used, `Apple Blossom' lost the greatest amount of old basal roots. Consequently, it produced many new basal roots. The planting medium had variable effects on old and new basal roots and secondary root growth, depending on the cultivar. Based on all the flowering criteria and the rooting responses, the best media for all cultivars as potted plants were Fafard 3-B and Sunshine Mix no. 4. Fafard no. 2 was best for cut-flower usage since it produced taller plants with a good root system.

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Marc van Iersel

Various growth stimulators have been reported to improve plant growth. Some of these are formulated to improve root growth, which would be particularly beneficial for reestablishing transplants. Three commercially available plant growth stimulators—PGR IV (MicroFlo, Lakeland, Fla.), Roots2 (Lisa Products Corp., Independence, Mo.), and Up-Start (The Solaris Group, San Ramon, Calif.)—were tested to quantify their effect on post-transplant growth of petunia (Petunia × hybrida Hort. Vilm.-Andr.) and impatiens (Impatiens wallerana Hook.f.) seedlings and to assess their value for the greenhouse industry. Seedlings were transplanted from plug flats into larger 5.6-fl oz (166-cm3) containers and treated with 1.1 fl oz (31 mL) of growth stimulator per plant (22 fl oz/ft2). Applications were made immediately after transplant. None of the treatments affected root mass at any time. Up-Start (2 fl oz/gal) increased final shoot dry mass by ≈20% compared to the control plants. The increase in shoot growth by Up-Start most likely is caused by the fertilizer it contains. Up-Start also increased flowering of petunia from 34 to 40 days after transplant. PGR IV (0.5 fl oz/gal) and Roots2 (1.28 fl oz/gal) did not affect dry mass of the plants. PGR IV increased the number of flowers of petunia and impatiens, but this effect occurred well after the plants were marketable. Roots2 caused a small delay in early flowering and an increase in late flowering of petunia but had no effect on flowering of impatiens. Since the effects of the growth stimulators was either due their fertilizer content (Up-Start) or occurred after the plants would have been sold (PGR IV, Roots2), none of the growth stimulators appears to be beneficial for bedding plant producers.

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Eric Young

Dormant apple trees (Malus domestics Borkh., cv. MM. 111) were chilled at SC for O, 500, 1000, or 1500 hours and then forced at 10, 20, or 30C for 21 days. Budbreak and root growth were recorded after forcing, and shoot and root respiration was measured at 5, 10, 20, and 30C to determine Q10 and energy of activation values. Budbreak, root growth, and respiration generally increased with chilling and forcing temperature. The Q10 of shoot respiration increased significantly with increasing chilling when measured before forcing; however, after forcing, Q10 decreased with chilling. Root respiration Q10 was not as influenced as shoot respiration by chilling either before or after forcing. Energy of activation for shoot and root respiration decreased significantly with chilling after forcing at each temperature.

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Thomas Björkman, Lisa M. Blanchard, and Gary E. Harman

Sweet corn (Zea mays L.) varieties carrying the sh2 gene are in high demand, but such varieties have poor stress tolerance, especially during plant establishment. Trichoderma harzianum Rifai strain 1295-22 is a biocontrol fungus developed to provide season-long colonization of crop roots. It has the potential to reduce root rot and increase root growth. In the absence of detectable disease, colonization by Trichoderma increased root and shoot growth by an average of 66%. The enhancement was not uniform among the plants. Low- and intermediate-vigor plants were larger in the presence of Trichoderma, but high-vigor plants were not further enhanced by the fungus. Seeds that were subjected to oxidative stress with 0.05% NaOCI had much-reduced vigor; subsequent treatment with Trichoderma fully restored vigor. This result indicates that the damage caused by hypochlorite is specifically repaired by Trichoderma. Treatment of imbibed but unemerged seeds with cold (5/10 °C night/day) for varying periods reduced subsequent growth. Plants with Trichoderma-colonized roots were 70% larger at all durations of cold treatment. The absence of interation indicates the growth reduction due to cold and the growth enhancement due to Trichoderma are by different mechanisms. Allelopathic reduction in root growth by rye was mimicked by applying benzoxazolinone to the soil. Trichoderma-colonized roots grew faster, but the characteristic shortening of the radicle still occurred. There was no interaction between Trichoderma and allelopathy, indicating that these two treatments affect growth by independent mechanisms. The different ways that growth was enhanced by Trichoderma lead us to propose that this fungus acts, in part, by reversing injurious oxidation of lipids and membrane proteins. Root growth is markedly enhanced by colonization with Trichoderma harzianum. This enhancement can restore some stress-induced growth reduction and may directly reverse oxidative injury.

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Daniel I. Leskovar and Daniel J. Cantliffe

Shoot and root growth changes in response to handling and storage time in `Sunny' tomato (Lycopersicon esculentum Mill.) transplants were investigated. Transplants, 45 days old, were stored either in trays (nonpulled) or packed in boxes (pulled) for 0, 2, 4, 6, or 8 days at 5 and 15C. Also, 35-day-old nonpulled and pulled transplants were kept in darkness at 20/28C for 0, 1, 2, or 3 days. At SC, pulled transplants had longer and heavier stems, a higher shoot: root ratio, higher ethylene evolution, and lower root dry weight than nonpulled transplants. At 15C, pulled transplants had more shoot growth than nonpulled transplants. Nonpulled, initially 35-day-old transplants had heavier shoots and roots and higher (7.0 t·ha-1) yields of extra-large fruit than pulled transplants (4.1 t·ha-1), but there were no differences in the total yields of marketable fruits.

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Dilma Silva, Donald Cox, and Richard C. Beeson Jr

. Asbjornsen, H. 1995 Review of root dynamics in forest ecosystems grouped by climate, climatic forest type and species Plant Soil 187 159 219 Wilkin, M.F. Wright, N.A. Eakes, D.J. Ebel, B.C. 2006 The effect of drought on root growth of native shrub species