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M.D. White, D.S. Tustin, K.F. Foote, R.K. Volz, J. Stokes, J. Campbell, R. Marshall, and C. Howard

ReTain™ is a plant bioregulator containing the active ingredient aminoethoxyvinylglycine (AVG), which inhibits the ethylene biosynthesis pathway. In 1997, the first efficacy studies on `Royal Gala' apple with ReTain™ were conducted under New Zealand conditions in Hawkes Bay. ReTain™ was applied 4 weeks before the anticipated start of harvest on `Royal Gala' at 850 and 1700 g·ha–1 with or without adjuvants. ReTain™ application delayed the onset of `Royal Gala' fruit maturation between 1 and 2 weeks, resulting in enhanced fruit size and fruit flesh firmness at harvest. The optimum response for delaying the onset of fruit maturation was achieved using ReTain™ at 850 g·ha–1 if applied in combination with a wetter. Fruit were also graded for fruit quality and air-stored at 0.5 °C. Fruit after 10 weeks of storage showed no difference in fruit flesh firmness, but all ReTain™ treatments had fruit with less yellow background colour compared with untreated fruit. In 1998, efficacy studies were undertaken in three geographical locations on `Royal Gala'. ReTain™ was applied at a rate of 830 g·ha–1 in combination with Silwet L-77 at 0.1%. All trees with the exception of `Royal Gala' grown in the Hawkes Bay had not received any ReTain™ previously. In all regions, seasonal changes in background color and starch pattern index were delayed by ReTain™ treatment. A concurrent delay of an increase in soluble solids concentration and retention of higher flesh firmness were also induced by ReTain™ treatment.

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Alan W. Meerow, Sven E. Svenson, and Michael E. Kane

DCPTA is a synthetically produced tertiary amine bioregulator with potential for increasing crop productivity at high light intensities. DCPTA reduces the number of days from planting to maturity in various potted ornamental crops, including `Fortune' daffodil (Narcissus L.), `Sonora' tulip (Tulipa L.), and `Jan Bos' hyacinth (Hyacinthus orientalis L.). Our objective was to examine how light intensity and DCPTA application influence growth and flowering of amaryllis (Hippeastrum hybridum Hort.). Flowering size bulbs of a micropropagated amaryllis clone were treated with 30 μm or no DCPTA and grown in full sun or 63% shade for 1 year. Number of scapes produced, flowers per scape, change in bulb fresh weight, number of bulblets produced, and bulblet weight were recorded and analyzed. There were no significant differences in days to first flowering or in number of flowers produced per scape among the treatments. DCPTA application at the recommended rate significantly reduced number of emergent inflorescences and the bulb biomass increase of hybrid amaryllis. Additionally, the interaction between light level and DCPTA appeared weak for amaryllis, and was only slightly significant relative to bulblet production. Chemical name used: 2-(3,4-dichlorophenoxy)triethylamine (DCPTA).

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Victor W. Winkler

A U.S. Environmental Protection Agency (EPA) voluntary program encourages the registration of pesticides that represent reduced risk to human health and the environment. A “reduced risk” designation for a pesticide depends on how its use will affect human health and the environment, pesticide resistance, and pesticide management. Prohexadione-Ca is a bioregulator being developed by BASF Corporation to control vegetative growth in apples with the effect of improving fruit production. BASF will petition the EPA to register prohexadione-Ca as a reduced risk pesticide in 1997 based on the following properties associated with its use: Prohexadione-Ca exhibits a very low mammalian toxicity and a low propensity for crop residues. Prohexadione-Ca rapidly dissipates in soil as a result of microbial metabolism and causes no detrimental ecological effects. There is no other hazard associated with the compound and no health risk for user or consumer is indicated. The use of prohexadione-Ca reduces the incidence of fireblight (and helps control this disease). The use of prohexadione-Ca reduces tree row spray volumes of other pesticides up to 25%. With these beneficial characteristics, prohexadione-Ca will fit exceptionally well into an Integrated Pest Management (IPM) program, providing another “reduced risk” justification for the registration of prohexadione-Ca. The current situation of accepting prohexadione-Ca as a reduced risk pesticide and its registration status will be discussed.

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Mostafa M. Qrunfleh, Dawud M. Al-Eisawi, and Moh'd I. Hozain

Three experiments were performed to establish rooting procedure of Amygdalus arabica Oliv. Two-centimeter shoots grown in vitro on MS medium supplemented with IBA at 0.01 mg/L, BA 0.2 mg /L, sucrose 30.0 g/L, and agar 6.0 g/L were used in rooting microcuttings using three experiments: 1) IAA, IBA, and NAA at concentrations of 0.5, 1.0, and 1.5 mg/L during the whole experiment with 4 days of dark period; 2) effect of dark and light conditions and IBA and NAA treatments during root induction period (4 days), then shoots were transferred onto free plant bioregulators (PBR), MS medium until end of the experiment; 3) Rooting microcuttings after quick dipping in different NAA concentrations (0.0, 250, 500 ppm) or induced for 6 days in root induction medium (MS) with 3.0 mg/L NAA, then shoots were transferred onto containers containing 200 ml of peatmoss, perlite, or peatmoss: perlite mixture (1:1, v/v). Results of the first experiment showed that best rooting was obtained with NAA, followed by IBA. In the second experiment, dark treatments improved rooting percentage and root length. NAA was superior to IBA in root number. Higher IBA and NAA (3.0 mg/L) concentrations gave the best rooting. In the third experiment, induced shoots transferred to perlite gave better root number and rooting percentage followed by peatmoss: perlite mixture. Regardless of rooting medium, insignificant differences between 250 and 500 ppm NAA in root number and rooting percentage were obtained. In the quick dip method, NAA was superior to the in vitro root induction method. The highest rooting percentage (86.7%) was obtained with perlite at either 250 or 500 ppm, replacing by that the traditional in vitro rooting and obtaining plantlets that are more ready to grow under in vivo conditions.

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Zhen Zhang and Zong-Ming Cheng

Jasmonates are a group of native plant bioregulators that occur widely in the plant kingdom and exert various physiological activities when applied exogenously to plants. We investigated the effect of free jasmonic acid (JA) on stem and root growth and tuberization of potato in vitro nodal culture. Nodal cuttings of three potato cultivars, Norchip, Red Pontiac, and Russet Burbank, were cultured in 2.5 × 15 cm test tubes containing either nodal culture (MS with 2% sucrose) or tuber-inducing (MS with 8% sucrose and 11.5 μm kinetin) medium. The media were supplemented with JA at 0, 0.1, 0.5 1.0, 5.0, 10.0 and 50 m. The cultures were maintained under a 16-hour photoperiod at 24°C for 6 weeks. Potato cultivars showed different sensitivities to JA in stem growth. Norchip is the most and Red Pontiac the least sensitive cultivar. On the nodal culture medium, stem length of Norchip was promoted at 0.1–5 μm, and inhibited at 10–50 μm of JA, but that of Red Pontiac was promoted by JA at all concentrations tested. The number of nodes increased significantly on media with JA than that on medium without JA. The number of adventitious roots did not, but the lateral roots increased significantly when JA was added to the medium. On tuber-inducing media, stem length and node number did not appear to be affected by addition of JA to the medium. The number of axillary shoots increased significantly on the media with low concentrations of JA (0.1–5 μm). No microtubers formed on both media from all three cultivars in 6 weeks.

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Anish Malladi and Peter M. Hirst

Peach production is significantly reduced and severely limited by frost injury in regions frequently exposed to late spring freeze conditions. Peach flower buds become increasingly susceptible to low-temperature damage from the period of completion of rest through fruit set. Delaying dehardening and/or flower bud development is an effective way to avoid frost damage. Bio-regulator applications, affecting dormancy or bud development, can delay flowering and dehardening of the buds and can help in avoiding spring freeze injury. Spring applications of AVG and dormant oils on 8-year-old `Redhaven' peach trees were evaluated. AVG applications effectively delayed bloom by 2 to 5 days. The most effective treatment was two applications of 2000 ppm AVG, which delayed bloom by almost 5 days. Repeat applications of AVG were more effective than the single dosage treatments. The 1000 ppm, repeat application delayed bloom by 4 days. A single application of 5000 ppm AVG resulted in severe phytotoxicity. The wetting agent levels were also varied and AVG applications were most effective in combination with 0.2% `Sylgard'. AVG, apparently, delayed bloom by delaying bud development following the completion of rest. The dormant oil sprays were ineffective in achieving bloom delay. The specific leaf weight characteristics of the treated trees were not affected except for the 5000-ppm AVG application, which reduced SLW. Fruit characteristics such as maturity, weight, and soluble sugar concentration were not affected by any of the spring applications (except for the 5000-ppm AVG application, which was phytotoxic). Our studies indicate that AVG is effective in delaying bloom in peaches by up to 5 days. This has the potential to substantially increase peach yields in years with a late spring freeze.

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Hameed J. Aljuburi, Hasan. Al-Masry, and Saeed A. Al-Muhanna

Date palm trees are among the most plentiful fruit trees in the Arabian Gulf States. Bioregulators have been used for the improvement of quality and productivity of date plam tree fruits. Application of gibberellic acid (GA3), naphthalene acetic acid (NAA), and ethephon, separately or in a mixture, has significant effects on fruit set, fruit dry matter percentage, fruit soluble percentage, fruit ripening, and yield of date palm trees. A study was conducted to assess relative effectiveness of GA3, NAA, ethephon, and a mixture of growth regulators on some fruit characteristics, and productivity of `Barhee' date plam trees. Five uniform female `Barhee' date palm trees were pollinated on 5–15 Mar. 1994, 1995, and 1996 by placing eight fresh male strands on female spadix centers (flower cluster). Ten flower clusters were used on each tree, and every two flower clusters were subjected to one of the following treatments: control (water), 150 mg·L–1 GA3, 100 mg·L–1 NAA, 1000 mg·L–1 ethephon, and a mixture of growth regulators. The fruit set (%), dry matter (%), total soluble solids (°Brix), fruit ripening (%), and fruit weight (kg per bunch and per tree) were measured. The data showed that the application of GA3 or ethephon on flower clusters of `Barhee' date palm trees had no constant effect on fruit characteristics and productivity of trees. NAA or a mixture of growth regulators reduced fruit dry matter percentage, fruit ripening percentage, and increased fruit weight per bunch and per tree. Spraying `Barhee' date palm flower clusters with NAA or a mixture of growth regulators 20 days after pollination decreased dry matter percentage, fruit ripening, and increased fruit flesh percentage and tree yield.

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Roberto Nuñez-Elisea and Jonathan H. Crane

Carambola (Averrhoa carambola L.) is native to the humid tropics of southeastern Asia, where it bears fruit year-round. In south Florida, winter conditions (strong winds and night temperatures below 15 °C) repress growth and flowering of the main commercial cultivar, Arkin, and fruit is produced from July to February. Off-season fruit would reach premium prices. We have previously demonstrated that selective pruning stimulates flowering of carambola at any time of the year. However, flowers produced during cool, windy weather have consistently failed to set fruit. This study was conducted in 1994–1995 to determine whether protected cultivation would help obtain off-season fruit. Four-year-old `Arkin' trees growing in 80-L containers were placed in a glasshouse or outdoors and pruned in November or December to force flowering during December–January. Glasshouse night temperatures during the winter were above 20 °C. All trees flowered in response to pruning. Outdoor trees produced less than one fruit per tree in late March to late April. Glasshouse trees produced 2.3 to 6.1 fruit per tree, 2 to 3 weeks earlier than trees outdoors. In the glasshouse, more than 98% of fruit were seedless, whereas all fruit produced outdoors were seeded. Production of seedless fruit indoors was achieved in the absence of insect pollinators, and yields were low compared to those of outdoor trees during the summer (at least 25 fruit per tree). We speculate that, under protected cultivation, the use of synthetic bioregulators during anthesis and insect pollinators may help increase production of off-season seedless and seeded fruit, respectively.

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Torrance R. Schmidt, Don C. Elfving, James R. McFerson, and Matthew D. Whiting

reduce russet in ‘Golden Delicious’ was later confirmed by Meador and Taylor (1987) and Elfving and Allen (1987) . Reuveni et al. (2001) reported similar reductions in fruit russet from three different commercial bioregulator formulations containing

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Duane W. Greene

of these were devoted to mulching, irrigation, pruning, pollination, and harvest. Although spray application and the use of plant bioregulators (PBRs) have been mentioned in previous books and reviews, in Blueberries all of Chapter 7 was devoted to