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  • Author or Editor: Ian J. Warrington x
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Abstract

A survey experiment was carried out to examine the effect of five growth regulators on the vegetative growth of Boronia megastigma. Promalin, daminozide, and chlormequat chloride were shown to have potential for modifying plant growth in the development of a commercial pot plant. Promalin restricted plant height and promoted lateral branch formation; concentrations of 0.5 and 1.0 g·liter–1 restricted height by ≈40% while branch number doubled. Daminozide significantly restricted plant height at concentrations of 5 and 10 g·liter–1. Plants that received a single application of daminozide also showed an increase in branch number. Dikegulac-sodium completely inhibited vegetative growth even at the lowest concentration used (2.5 g·liter–1) while chlormequat chloride, applied as a foliar spray (3 and 6 g·liter–1), restricted both height growth and plant dry weight. Chlormequat chloride and paclobutrazol, applied as root drenches, were ineffective. Chemical names used: butanedioic acid mono(2,2-dimethylhydrazide)(daminozide); N-(phenyImethyl)-1H-purine-6-amine and GA4+7 (Promalin); Na 2,3:4,6-bis-O-(1-methylethylidene)-α-l-xylo-2-hexulofuranosonic acid (dikegulac-sodium); 2-chloro-N,N,N-trimethylethanaminium chloride (chlormequat chloride); (2RS,3RS)-1-(4-chlorophenyl)-4,4-dimethyl-2-(1,2,4-triazol-l-yl) pentan-3-ol (paclobutrazol).

Open Access

In New Zealand, harvest maturity for kiwifruit is determined by the soluble solids concentration (SSC) of juice (minimum 6.2%). Commercial maturity differs in various regions of the country within each season and between years and may be due to differences in temperatures during growth.

Mature `Hayward' kiwifruit vines were grown in controlled environment temperature treatments of 14/8, 18/8, 22/8, 26/8, 14/12 and 22/12C to determine whether the increase in SSC at low night temperatures recorded in a related study was a result of the mean temperature, the min. daily temperature, or the magnitude of the max./min. temperature difference. Measurement was made of fruit size, firmness, starch and total sugar concentrations in the fruit at 10 day intervals.

SSC increased fastest with the coolest mean temperature irrespective of the min. temperature or max./min. difference. In the coolest treatment the concentration of starch decreased rapidly with a rise in total sugar, in the warmest treatment the change in the carbohydrate components was slower. Data will be used to predict harvest date at commercial orchard sites based on field temperature measurements.

Free access

The early growth responses of apple fruit to temperature were studied under controlled environment conditions. Growth of fruit on young trees of `Fuji'/M.9 `Golden Delicious'/M.9, and `Harold Red Delicious'/M.9 was frequently measured, over a 30-day period commencing 10 days after full bloom, under daily maximum/minimum temperatures of 22/12, 19/9, 16/6 and 13/3C. All other environmental conditions were maintained constant across all temperature treatments. Fruitlet diameter growth rate was approximately constant over the treatment period within each temperature regime and ranged from 0.24 mm day-1 at 13/3C to 0.85 mm day-1 at 22/12C. The growth responses to temperature were similar among cultivars but expansion rates were highest for `Fuji' and lowest for `Golden Delicious'. Cell division rates and durations, using flow cytometry, were measured over the treatment period and could be related to diameter growth rates. The impacts of temperature-induced differences in early fruit growth rates on final fruit sire will be described.

Free access

Abstract

Fruiting laterals were tagged within the inner and outer canopy zones of the basal, mid, and upper tiers of dormant, mature central-leader ‘Granny Smith’ apple (Malus domestica Borkh.) trees and were classified into pendant (>120°), horizontal (30°-120°), and vertical (0°-30°) types. Transmission of photosynthetic photon flux (PPF) to spur sites on tagged laterals was measured in mid-season and fruits from these sites were harvested at commercial maturity for assessment of fresh weight, soluble solids concentration (SSC), starch pattern index, and background color. Pendant laterals produced fewer, smaller, and greener fruit per flowering spur than horizontal or vertical laterals. Fruit fresh weight and soluble solids concentration increased with increasing height in the canopy and were higher in the outer compared with the inner horizontal canopy position. Background color followed a trend opposite to that of fresh weight and soluble solids concentration, with fruit from the lower inner canopy regions being greenest. Both fresh weight and SSC showed highly positive correlations with the percentage transmission of PPF. Fruit set showed a positive correlation with PPF, although the relationship was weaker than that for fresh weight or SSC. PPF penetration was lower to pendant laterals than to horizontal and vertical laterals and declined from upper to lower and from outer to inner canopy positions. Pendant fruiting laterals received < 15% of PPF, irrespective of location within the canopy.

Open Access

The government-funded horticulture extension service, which provided a free service to New Zealand growers for nearly 50 years, was privatized in the late 1980s as part of major reforms to the primary production sector. That service had provided one-on-one on-farm visits, budget advice, provision of technical information, and facilitation of field days, workshops and discussion groups throughout the country. This government-funded service also provided policy advice, acted as an interface between industry and the research and development (R&D) sector, and responded to biosecurity incursions. A decade following privatization, the number of people involved in equivalent consultancy activities has almost halved with very little recruitment of new people into the profession. The emphasis is now much more towards providing advice on the overall management of an individual enterprise to ensure its financial viability, with less emphasis on technical transfer. Large horticultural businesses are increasingly employing specialists in-house who can provide technical solutions and advice on balance sheet management. Private consultancy companies now tend to work more at a local or regional level rather than at a national level and links with R&D providers have markedly weakened as research organisations are increasingly protecting intellectual property for their own commercial advantages and as information provision is now largely on a user-pays basis. In addition, biosecurity incursions over the past decade appear to have increased as a result of a weakened surveillance effort. Nonetheless, horticultural exports from New Zealand continue to grow at around 10% per annum and many sectors remain very competitive on world markets.

Full access

The relationships between temperature and light on vegetative growth of the foliage house plants Epipremnum aureum (Linden and Andre) Bund, and X Fatshedera lizei (Guillaum) were investigated in a controlled environment study during the exponential growth phase. Responses were examined under conditions with a constant day temperature (30°C) in combination with constant night, split-night or sliding night temperatures with means of either 15° or 20°C. Two PFDs of 150 and 320 μmol·s-1·m-2 were included in each temperature treatment. Growth parameters (including dry matter increase, shoot elongation rate and leaf production rate) were all influenced by species but not by each temperature profile within the same temperature integral (ie all growth responses were directly related to mean night temperature). Growth rates were highest under the high PFD conditions but dry weight accumulation per unit of PFD was markedly higher at low PFD than at high PFD. The optimum temperature for vegetative growth of Epipremnum aureum was higher than that for X Fatshedera lizei and Epipremnum aureum was particularly sensitive to temperatures below 10°C.

Free access

Photosynthetic activity of individual leaves of Zantedeschia Spreng. `Best Gold' aff. Z. pentlandii (Wats.) Wittm. [syn. Richardia pentlandii Wats.] (`Best Gold'), were quantified with leaf expansion and diurnally, under a range of temperature and photosynthetic photon flux (PPF) regimes. Predictive models incorporating PPF, day temperature, and percentage leaf area expansion accounted for 78% and 81% of variation in net photosynthetic rate (Pn) before, and postattainment of, 75% maximum leaf area, respectively. Minimal changes in Pn occurred during the photoperiod when environmental conditions were stable. Maximum Pn (10.9μmol·m-2·s-1 or 13.3 μmol·g-1·s-1) occurred for plants grown under high PPF (694 μmol·m-2·s-1) and day temperature (28 °C). Acclimation of Pn was less than complete, with any gain through a greater light-saturated photosynthetic rate (Pmax) at high PPF also resulting in a reduction in quantum yield. Similarly, any gain in acclimation through increased quantum yield under low PPF occurred concurrently with reduced Pmax. It was concluded that Zantedeschia `Best Gold' is a shade tolerant selection, adapted to optimize photosynthetic rate under the climate of its natural habitat, by not having obligate adaptation to sun or shade habitats.

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Dry matter accumulation and partitioning in plants of Zantedeschia Spreng. `Best Gold' aff. Z. pentlandii (Wats.) Wittm. (syn. Richardia pentlandii Wats.) were quantified under a range of temperature and photosynthetic photon flux (PPF) regimes using plant growth analysis. The relative rate of dry matter accumulation [relative growth rate (RGRM), g·g-1·d-1] was highly correlated with the partitioning of the daily increment of dry matter into leaf tissue [leaf matter partitioning (LMP), g·d-1 per g·d-1]. In contrast, a poor correlation existed between RGRM and net assimilation rate (NAR, g·m-2·d-1). Maximum values of RGRM increased linearly with increasing temperature (from 13 to 28 °C), with a base temperature of 2.1 ± 2.7 °C. The optimum temperature for growth was PPF dependent with maximum total plant dry mass occurring under high PPF (694 μmol·m-2·s-1) at 25 °C. However, as the plant responded to PPF by altering LMP, final total plant dry mass was actually greater under the low PPF regime (348 μmol·m-2·s-1) at temperatures <22 °C. The optimum temperature for dry matter accumulation was close to the average daily air temperature during the growing season for the natural habitat of the parent species. Similarly, the greater dry matter accumulation under the combination of either low PPF and cooler temperatures or high PPF and warmer temperatures was paralleled by the diversity of PPF habitats in the natural open grassland and forest margin the parent species occupies. It is therefore suggested that Zantedeschia `Best Gold' is well adapted to optimize growth under these environmental conditions.

Free access

The characteristics of 1-year-old vegetative spurs growing on 2-year-old branches were measured on 28 `Delicious' apple (Malus domestica Borkh.) strains growing on M.7 rootstocks at Clarksville, Mich., and on 23 strains of `Delicious' on M.7a rootstocks at Kearneysville, W.Va. Spur-type strains typically had densities >20 to 21 spurs/m, and high spur leaf numbers, leaf areas per spur, leaf areas per leaf, and terminal bud diameters, whereas values for standard strains were generally lower. However, for most spur quality characteristics, there was a continuous range of values between the extremes rather than any distinct grouping into either spur or standard type. At both sites, spur density was significantly and positively correlated with yield efficiency. In a related study, the spur characteristics of `Starkspur Supreme' were measured on nine rootstocks: M.7 EMLA, M.9 EMLA, M.26 EMLA, M.27 EMLA, M.9, MAC 9, MAC 24, OAR 1, and Ottawa 3. Spur leaf number and spur leaf area were both high with vigorous rootstocks, whereas spur density was low. The rootstocks MAC 9, M.9, and M.9 EMLA had the highest yield efficiencies.

Free access