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Steven H. Schwartzkopf

The use of computerized environmental control systems for greenhouses and plant growth chambers is increasing in frequency. Computerized systems provide the potential for more accurate environmental control, while at the same time allowing changes to be made more easily than with hard-wired mechanical control systems. The ease of changing allows switching sensor types, relocating sensors and resetting control parameters without significantly affecting the overall system design. Another advantage of computerized control systems is that they provide a method for recording environmental data as they simultaneously implement their programmed control algorithms. This data can subsequently be transferred to other computers for further processing and analysis. Computerized controls also support the possibility of implementing environmental control based on either mathematical models which simulate plant growth, or on actual monitored plant performance data such as nutrient uptake or leaf temperature. This paper discusses in detail these and other advantages of using computerized environmental control systems, as well as describing the problems and disadvantages associated with their implementation and use.

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Esther E. McGinnis, Alan G. Smith, and Mary H. Meyer

Environmental control of flowering in some northern Carex species Ann. Bot. (Lond.) 79 319 327 Heide, O.M. 2002 Climatic flowering requirement of bipolar sedges Carex spp. and the feasibility of their trans-equatorial migration by mountain-hopping Oikos 99

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Royal D. Heins

Environmental control computers allow regulation of greenhouse environments based on some model driven factor or factors other than fixed heating and cooling setpoints. A quantitative understanding of how environmental factors influence rate of plant development, flower initiation, and plant morphology is necessary to develop models for environmental control. The major limitation to the use of models for greenhouse climate and crop control is the lack of quantitative models. Examples of model development for environmental control will be discussed.

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T.M. DeJong

For the last several years, research in my laboratory has been focused on studying the developmental and environmental control of dry matter partitioning in peach trees based on the concept that plants grow as collections of semi-autonomous, but interacting, organs. This concept assumes that plant genotype, triggered by developmental and environmental signals, determines current organ specific growth potentials and that environmental conditions dictate conditional growth capacity and respiration (both growth and maintenance) requirements of each organ at any specific time. Dry matter partitioning at any given time is then determined by the availability of resources to be partitioned, the conditional growth capacity and maintenance requirements of each organ, and the relative ability of each organ to compete for the resources. In this presentation, I will demonstrate how developmental patterns of various organs influence dry-matter partitioning within the tree over time, how organ number can influence the amount of dry-matter partitioned collectively to an organ type, and propose an hypothesis for how environmental conditions may influence partitioning on a diurnal basis.

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Rina Kamenetsky, Idit London Shafir, Hanita Zemah, Amalia Barzilay, and H.D. Rabinowitch

An understanding of temperature and photoperiod effect on garlic (A. sativum L.) growth and florogenesis might solve the enigma of garlic sterility and provide environmental tools for flowering regulation and fertility restoration. The effect of storage temperature and growth conditions on the interactive relationships between the developing vegetative and reproductive organs was studied. A long photoperiod for more than 2 weeks was required for both dormancy induction of the axillary buds and clove formation. In contrast, combination of low temperatures with short photoperiod resulted in sprouting of the axillary buds. Four phases were recognized in the florogenesis of garlic, including: transition of the apical meristem, scape elongation, inflorescence differentiation, and completion of floral development. In garlic accession #2091, meristem transition is autonomous and occurs in growing plants under a variety of storage and growth conditions. A long photoperiod triggers the initial elongation of the scape in post-transitional plants. The temperature effect was quantitative: low storage and growth temperatures combined with long photoperiod promoted scape elongation, whereas warm temperatures and long photoperiod promoted the translocation of reserves to the cloves, and the degeneration of the developing inflorescence. Differentiation of topsets followed flower formation and was dominated by and required lengthy exposure to long photoperiod. Hence, under short photoperiod with only short interruption of long photoperiod, normal development of fertile flowers occurred. We conclude that in bolting garlic genotypes, manipulation of the environment, both before and after planting, can regulate the development of flowers and regain fertility. Normal flowering cannot be achieved if any of the four developmental stages of florogenesis mentioned above is inhibited.

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D. Zhang, A.M. Armitage, J.M. Affolter, and M.A. Dirr

Dense-flowered loosestrife is a quantitative long-day (LD) plant. Plants given a LD photoperiod (16 hours) flowered 21 and 34 days earlier than plants given 12- and 8-hour photoperiods, respectively. Plants under LDs produced significantly more flowers than those under 8- and 12-hour photoperiods. Only 1 week of LD was needed for 100% flowering; however, optimum flower count and size were produced with 3 weeks of LD. Plant dry weight did not differ significantly among treatments; however, LDs produced fewer but larger leaves, particularly those subtending the inflorescence. Total plant growth increased as temperature increased, but lower temperature (10C) decreased flower initiation and prevented flower development. High temperature (26C) reduced the persistence of open flowers. The optimum temperature for dense-flowered loosestrife growth was ≈20C. Flowering was accelerated and dry weight production increased as irradiance levels increased from 100 to 300 μmol·m–2·s–1.

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Harry W. Janes and Richard J. McAvoy

In this paper we review our research of light effects on tomato production. It was demonstrated that, during the production of greenhouse tomatoes, the total fruit yield, as well as time of harvest, was related to light. The date of harvest was inversely correlated with the amount of light the crop received during the seedling phase of growth, while fruit weight was positively correlated with light during the production phase. Additionally, we present information that shows that light was most effective in promoting fruit development between 15 and 45 days after flowering. Some of these relationships were quantified and used to develop a predictive model to help a grower plan a tomato crop to meet market demand. The concept of the Single-cluster Tomato Production System was developed, and the rewards of using our understanding of plant-environment interactions to control plant growth and, therefore maxim&profits were shown. Furthermore, the need to create a more dynamic model and the methods for doing so were discussed.

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Yuki Sago and Airi Shigemura

Environmentally controlled closed cultivation systems with artificial lighting, such as plant factories, are becoming important for stable vegetable production because they allow continuous cultivation of crops and protect crops from the weather and

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D. Zhang, A.M. Armitage, J.M. Affolter, and M.A. Dirr

Achillea millefolium `Summer Pastels' is a qualitative long-day plant with a critical photoperiod between 12 and 16 hours at 18C. Plants grown under a 16-hour photoperiod flowered after 27 days, while those under 8 hours remained vegetative. Shoot dry weight was not affected by photoperiod. Low temperature (10C) delayed the time of flower bud formation and anthesis by ≈20 days. Low irradiance (100 μmol·m–2·s–1) delayed flowering and resulted in lower shoot dry weight, while moderate shading (200 μmol·m–2·s–1) did not significantly affect flowering time and growth compared with high irradiance levels (300 μmol·m–2·s–1).