Ian J. Warrington

Initial alteration of scion architecture by dwarfing apple rootstocks may involve shoot-root-shoot signalling by auxin, gibberellin, and cytokinin

Summary Apple rootstock clones of different vigour were examined to determine how they initially modified the architecture of ‘Royal Gala’ scions following grafting of the composite tree. These modifications were compared with those of gibberellins (GA4+7) and/or benzylaminopurine (BAP) applied to the scion, and an inhibitor of auxin transport [1-N-naphthylphthalamic acid (NPA)] applied to the rootstock stem. By the end of the first year of growth after grafting, the dwarfing (‘M.9’) rootstock had significantly decreased the mean total shoot length and node number of the scion compared with invigorating rootstocks (i.e., ‘MM.106’, ‘M.793’, and ‘Royal Gala’). Similarly, NPA applied to the stem of invigorating rootstocks decreased the total shoot growth of the scion, and the architectural changes imposed most closely resembled those of ‘M.9’. Both treatments increased the proportion of primary and secondary shoots (if present) that terminated growth early, which decreased the final length and node number of these shoot types. Also, NPA and ‘M.9’ decreased the number of secondary shoots that formed. For scions on NPA-treated rootstocks or ‘M.9’, BAP re-instated the formation of secondary shoots, while GA4+7 primarily reduced the proportion of primary and secondary shoots that terminated growth early, thereby increasing their final length and node number. An endogenous signalling mechanism is proposed whereby dwarfing rootstocks reduce the basipetal transport of indole-3-acetic acid (IAA) to the root, thereby decreasing the amount of root-produced cytokinin and gibberellin transported to the scion. At the scion, a limited supply of cytokinin may modify the architecture by decreasing branching, whereas a limited supply of gibberellins may primarily reduce the duration of shoot extension growth.

Tuber dry-matter accumulation of Zantedeschia in response to temperature and photosynthetic photon flux

Summary Dry-matter accumulation and partitioning in plants of Zantedeschia ‘Best Gold’ were quantified under a range of temperature and photosynthetic photon flux (PPF) regimes using plant growth analysis. Initiation of tuber growth did not require an obligate environmental trigger. Under both PPF regimes, relative growth rate of the tuber (RGRt) increased linearly with increasing temperature (13 to 28°C) up to a maximum at 28°C, with a base temperature of 3.2 ± 1.1°C. Optimum temperature for tuber growth was found to be PPF dependent, but maximum tuber dry mass was calculated as occurring under low PPF (348 µmol m–2 s–1) at 24.5 ± 0.1°. Mechanisms of acclimation under both PPF regimes suggested that tuber growth was principally source limited. Source limitation was expressed either in terms of: 1) enhanced inter-sink competition for assimilates, as occurred under the low PPF regime, where leaf area development was in direct competition with tuber growth (RGRt) or, 2) efficiency of dry-matter accumulation by the leaf area present, as occurred under the high PPF regime, where large increases in RGRt were correlated with increased net assimilation rate (NAR). Use of the daily increment of dry matter into tuber tissue (TMP) provided a more sensitive measure of short-term changes in partitioning than the conventionally used term, harvest index.

Scholarship and Literature in Horticulture

Horticulture and its related sciences have produced a rich diversity of literature ranging from highly specialised scientific journals and scholarly books to detailed manuals for producers, from technical and popular books on gardening and cooking to encyclopaedias on highly specialised topics, and from newspaper and magazine articles to entries on the World Wide Web. These publications span a period of over 200 years. Included are food crops such as fruit, nuts, vegetables, and condiments; ornamentals and landscaping plants including trees, shrubs, and cut flower and bedding crops; turf grasses; medicinal plants and the use of plants for human wellbeing and therapy. This chapter presents selected examples of how horticulture has contributed to scholarship and literature. It also includes examples of how horticulture has been recorded in classical literature and become an integral part of many every-day sayings.

Science Drives Horticulture’s Progress and Profit

Horticultural science linked with basic studies in biology, chemistry, physics and engineering has laid the foundation for advances in applied knowledge which are at the heart of commercial, environmental and social horticulture. In few disciplines is science more rapidly translated into applicable technologies than in the huge range of man’s activities embraced within horticulture which are discussed in this Trilogy. This chapter surveys the origins of horticultural science developing as an integral part of the sixteenth century “Scientific Revolution”. It identifies early discoveries during the latter part of the nineteenth and early twentieth centuries which rationalized the control of plant growth, flowering and fruiting and the media in which crops could be cultivated. The products of these discoveries formed the basis on which huge current industries of worldwide significance are founded in fruit, vegetable and ornamental production. More recent examples of the application of horticultural science are used in an explanation of how the integration of plant breeding, crop selection and astute marketing highlighted by the New Zealand industry have retained and expanded the viability of production which supplies huge volumes of fruit into the world’s markets. This is followed by an examination of science applied to tissue and cell culture as an example of technologies which have already produced massive industrial applications but hold the prospect for generating even greater advances in the future. Finally, examples are given of nascent scientific discoveries which hold the prospect for generating horticultural industries with considerable future impact. These include systems modeling and biology, nanotechnology, robotics, automation and electronics, genetics and plant breeding, and more efficient and effective use of resources and the employment of benign microbes. In conclusion there is an estimation of the value of horticultural science to society.

Effect of low-temperature treatments on flowering in three cultivars of Hebe Comm. ex Juss.

Abstract The genus Hebe is mainly native to New Zealand, and a number of species and cultivars are used as ornamental garden and balcony plants in many countries. The ornamental value is increased by controlled flowering. In this experiment chilling (15.5/9.5 °C or 9/3 °C day/night) treatments of different durations (0, 3, 6, 9 or 12 weeks) were tested on three cultivars of Hebe , ‘Inspiration’, ‘Variegata’ and ‘Waikiki’. After chilling the plants were forced under 25/19 °C conditions for 12 weeks. Flowering was promoted by the chilling treatments, and complete flowering in the apical shoots occurred after 9–12 weeks chilling in 15.5/9.5 °C for ‘Inspiration’ and ‘Waikiki’. Increased flowering of ‘Variegata’ (75% of the plants) was observed after 12 weeks 15.5/9.5 °C treatment followed by forcing. The more induced plants had become under the chilling treatments, the shorter time was necessary under the forcing conditions for flower development. With all cultivars, cool conditions were more effective for flower induction than cold conditions. Flowering was more rapid where the low temperature conditions lasted longest. Larger ‘Inspiration’ plants were induced more readily than the smaller plants. The importance of size of the plants at the start of chilling was tested for ‘Inspiration’, where plants with 22 nodes flowered after shorter time under forcing conditions than plants with 12 nodes. A cold treatment, at 9/3 °C, reduced the flowering intensity for ‘Inspiration’ and ‘Variegata’, while ‘Waikiki’ reacted unchanged. Without chilling only ‘Waikiki’ was able to develop flowers but in less than 50% of the plants.