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Michel Carrier, André Gosselin, and Laurent Gauthier

A dynamic management strategy for supplemental lighting in greenhouses was developed. It makes use of a plant growth model and of a rule-based decisionmaking protocol within the framework of a generic greenhouse climate management software system. The model, an adapted version of SUCROS87, tracks plant growth and predicts dry weight production based on measured or estimated values of light intensity, temperature, and CO2 concentration. A set of logical predicates (rules) implements the strategy's behavior. Optimization of lamp use was conducted as a function of economic criteria that enable a comparison between the additional income associated with yield increases due to supplemental lighting and incurred cost increases. Although the model is not perfectly reliable in its predictions, the system can be used to simulate the effect of changes to economic parameters on the decisions of the management strategy. The dynamic strategy described here differs from conventional supplemental lighting scenarios in the sense that it increases the length of the period of supplemental lighting when the daily solar light integral is low, and reduces or eliminates the use of supplemental lighting when the weather forecast predicts that the daily solar light integral will exceed plant requirements.

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Patricia Garriz, Hugo Alvarez, and Graciela Colavita

Temperature has long been recognized as a major environmental factor affecting the net carbon exchange in the pear tree, as well as the growth of fruit. The objective of this work was to predict pear fruit growth as a function of accumulated growing-degree-days (DD) using a mathematical model. A crop of `Abbé Fetel' trees was studied at the Experimental Farm of the Comahue National University, Argentina (lat. 38°56'S; long. 67°59'W). Maximum fruit diameter (FD) measurements were carried out every 2 weeks during three growing seasons (2000–01, 2001–-02, and 2002–03). The range of sampling dates was 26 and 143 days after full bloom (DFB). An automated meteorological station, situated close to the orchard, collected temperature data, which were expressed on the basis of DD from time of full bloom to harvest, with critical temperatures at 4 and 35 °C. Equations were developed with SYSTAT procedure and model suitability was evaluated using goodness-to-fit measures. It was found that the following logistic regression provided the most satisfactory fit for the pooled data: FD (mm) = 71.62/[(1 + e^(1.7450-0.0027DD)], coefficient of determination = 0.96. The testing on an independent crop showed that predictions were accurate. Analyses of fruit growth, based on DD, did not improve data interpretation over that on a DFB basis. The average monthly temperature varied little between seasons. A remarkably consistent heat-unit accumulation function was obtained from year to year, with a 5% maximum variation in number of DFB to maturity, compared to a 6% variation in DD, occurring between the 2002 and 2003 commercial harvests. These results have important implications for cultural practices, such as fruit thinning and final size forecast.

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Carole L. Bassett, D. Michael Glenn, Philip L. Forsline, Michael E. Wisniewski, and Robert E. Farrell Jr

Reduced availability of water for agricultural use has been forecast for much of the planet as a result of global warming and greater urban demand for water in large metropolitan areas. Strategic improvement of water use efficiency (WUE) and drought tolerance in perennial crops, like fruit trees, could reduce water use without compromising yield or quality. We studied water use in apple trees using ‘Royal Gala’, a relatively water use-efficient cultivar, as a standard. To examine whether genes useful for improving WUE are represented in a wild relative genetically close to M. ×domestica, we surveyed Malus sieversii for traits associated with WUE and drought resistance using material collected from xeric sites in Kazakhstan. This collection has been maintained in Geneva, NY, and surveyed for various phenotypes and has been genetically characterized using simple sequence repeats (SSRs). These data suggest that most of the diversity in this population is contained within a subpopulation of 34 individuals. Analysis of this subpopulation for morphological traits traditionally associated with WUE or drought resistance, e.g., leaf size and stomata size and arrangement, indicated that these traits were not substantially different. These results imply that some of the genetic diversity may be associated with changes in the biochemistry, uptake, and/or transport of water, carbon, or oxygen that have allowed these trees to survive in water-limited environments. Furthermore, genes responding to drought treatment were isolated from ‘Royal Gala’ and categorized according to the biological processes with which they are associated. A large fraction of upregulated genes from roots were identified as stress-responsive, whereas genes from leaves were for the most part associated with photosynthesis. We plan to examine expression of these genes in the M. sieversii population during water deficit in future studies to compare their patterns of expression with ‘Royal Gala’.

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Jim Shrefler, Mike Bourne, John Damicone, Jonathan Edelson, S. Pair, Warren Roberts, and Merritt Taylor

Geographical dispersion of production hampers watermelon integrated pest management (IPM) information delivery in Oklahoma. Melon Pest Manager (MPM) was created to educate and provide advisory information on IPM. Available at www.lane-ag.org, the site emphasizes information relevant to the area. MPM was conceived as Internet availability grew and was recognized to have potential for enhancing IPM implementation. Survey of producers suggested the value of Web-based information may depend on how easily it can be accessed. MPM was designed to provide easy access to watermelon IPM information. Compared to printed literature, web-based format is easier to revise and suited to presentation of information that applies yearly as well as that which may change frequently. MPM provides general discussion of melon IPM tactics and pest-identification and time sensitive information such as pest advisories and pesticide registration changes. MPM offers opportunity for novel presentation of educational information such as the real-time posting of field demonstrations. An initial challenge was to balance site development, promotion and education. Promotion and education followed placement of watermelon IPM tactic information on MPM but preceded advisory and pest identification. Pest identification links to existing sources are enhanced by material prepared for MPM. Progress is slowed by the need for expert intervention and the availability of images and descriptive information. Education on use of advisory resources (e.g., disease forecasters) is a high priority. However, availability and applicability of such products is dependent on the home site. The original concept envisaged mapping of pest activity using grower, extension agent and expert input. Time demands of other components of the site delay development of this aspect. Pest alerts are posted and distributed to county extension offices.

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Ji Heun Hong, Douglas J. Mills, C. Benjamin Coffman, James D. Anderson, Mary J. Camp, and Kenneth C. Gross

Experiments were conducted to compare changes in quality of slices of red tomato (Lycopersicon esculentum Mill., cv. Sunbeam) fruit from plants grown using black polyethylene or hairy vetch mulches under various foliar disease management systems including: no fungicide applications (NF), a disease forecasting model (Tom-Cast), and weekly fungicide applications (WF), during storage at 5 °C under a modified atmosphere. In this study, we used the fourth uniform slice from the stem end and analyzed for firmness, soluble solids content (SSC), titratable acidity (TA), pH, electrolyte leakage, molds, yeasts and occurrence of water-soaked areas. With both NF and Tom-Cast fungicide treatments, slices from tomato fruit grown with hairy vetch mulch showed greater firmness than those from tomato fruit grown with black polyethylene mulch after 12 d of storage. Ethylene production of slices from tomato fruit grown using hairy vetch mulch under Tom-Cast was about 1.5- and 5-fold higher than that of slices from tomato fruit grown under the WF and NF fungicide treatments after 12 d, respectively. Within each fungicide treatment, slices from tomato fruit grown using hairy vetch mulch showed less chilling injury (water-soaked areas) than those from tomatoes grown using black polyethylene mulch. The percentage of water-soaked areas for slices from tomato fruit grown using black polyethylene mulch under NF was over 7-fold that of slices from tomato fruit grown using hairy vetch under Tom-Cast. These results suggest that, under our conditions, fruit from plants grown using hairy vetch mulch may be more suitable for fresh-cut slices than those grown using black polyethylene mulch.

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Carlos Miranda Jiménez and J. Bernardo Royo Díaz

Spring frosts are usual in many of Spain's fruit-growing areas, so it is common to insure crops against frost damage. After a frost, crop loss must be evaluated, by comparing what crop is left with the amount that would have been obtained under normal conditions. Potential crop must be evaluated quickly through the use of measurements obtainable at the beginning of the tree's growth cycle. During 1996 and 1997 and in 95 commercial plots of `Blanquilla' and `Conference' pear (Pyrus communis L.), the following measurements were obtained: trunk cross-sectional area (TCA, cm2), space allocated per tree (ST, m2), trunk cross-sectional area per hectare (TCA/ha), flower density (FD, number of flower buds/cm2 TCA), flower density per land area (FA, number of flower buds/m2 land area), cluster set (CS, number of fruit clusters/number of flower clusters, %), crop density (CD, number of fruit/cm2 TCA), fruit clusters per trunk cross-sectional area (FCT, number of fruit clusters/cm2 TCA), fruit clusters per land area (FCA, number of fruit clusters/m2 land area), fruit number per cluster (FNC), average fruit weight (FW, g), average yield per fruit cluster (CY, g), yield efficiency (YE, fruit g·cm-2 TCA), and tree yield (Y, fruit kg/tree). CS and average CY were related to the rest of the variables through the use of multiple regression models. The models that provided the best fit were CS = TCA/ha - FA and CY = -FA - FCT. These models were significant, consistent, and appropriate for both years. Predicted yield per land area was obtained by multiplying FA × CS × CY. The models' predictive ability was evaluated for 46 different plots in 2001 and 2002. Statistical analysis showed the models to be valid for the forecast of orchards' potential yield efficiency, so that they represent a useful tool for early crop prediction and evaluation of losses due to late frosts.

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Carlos Miranda Jiménez and J. Bernardo Royo Díaz

Spring frosts are usual in many of Spain's fruit-growing areas, so it is common to insure crops against frost damage. After a frost, crop loss must be evaluated, by comparing what crop is left with the amount that would have been obtained under normal conditions. Potential crop must be evaluated quickly through the use of measurements obtainable at the beginning of the tree's growth cycle. During the years 1998 and 1999 and in 62 commercial plots of `Golden Delicious' and `Royal Gala' apple (Malus ×domestica Borkh.), the following measurements were obtained: trunk cross-sectional area (TCA, cm2), space allocated per tree (ST, m2) trunk cross-sectional area per hectare (TCA/ha), flower density (FD, number of flower buds/cm2 TCA), flower density per land area (FA, number of flower buds/m2 land area), cluster set (CS, number of fruit clusters/number of flower clusters, percent), crop density (CD, number of fruit/cm2 TCA), fruit clusters per trunk cross-sectional area (FCT, number of fruit clusters/cm2 TCA), fruit clusters per land area (FCA, number of fruit clusters/m2 land area), fruit number per cluster (FNC), average fruit weight (FW, g), average yield per fruit cluster (CY, g), yield efficiency (YE, fruit g·cm-2 TCA), and tree yield (Y, fruit kg/tree). FCT and average CY were related to the rest of the variables through the use of multiple regression models. The models which provided the best fit were FCT = FD - TCA/ha - FD and CY= -FCA - FCT. These models were significant, consistent, and appropriate for both years. Predicted yield per land area was obtained by multiplying TCA/ha × FCT × CY. The models' predictive ability was evaluated for 64 different plots in 2001 and 2002. Statistical analysis showed the models to be valid for the forecast of potential yields in apple, so that they represent a useful tool for early crop prediction and evaluation of losses due to late frosts.

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D. Schwarz, H.-P. Kläring, K.T. Ingram, and Y.-C. Hung

Diurnal changes in microclimate in a greenhouse are often greater than changes in daily averages over weeks or months. Thus, one may hypothesize that changing the nutrient solution concentration supplied to plants at intervals less than one day would improve tomato yield and quality. To test this hypothesis research was conducted to compare four nutrient control strategies for their effects on plant growth, fruit yield, fruit quality, and root characteristics of `Counter' tomato [Lycopersicon esculentum (L.) Mill.]. The four strategies were 1) ECvariable, adjustment of nutrient solution electrical conductivity (EC) at 15-min intervals according to greenhouse microclimate over the previous 15-min and empirical models of photosynthesis and transpiration; 2) ECdaily, daily adjustment of nutrient solution EC based on each morning's 24-hour weather forecast; 3) EC3.7, supply of a single high nutrient solution of 3.7 dS·m-1; or 4) EC1.5, low nutrient solution EC of 1.5 dS·m-1 for the entire growth period. Mean effluent EC levels were 1.8 dS·m-1 for treatment EC1.5, 5.1 dS·m-1 for treatment EC3.7, 3.6 dS·m-1 for treatment ECdaily, and 3.4 dS·m-1 for treatment ECvariable. Except for fresh weight (FW) of roots, growth characteristics did not differ significantly among treatments. Total production averaged 12.2 kg·m-2 FW and 1.0 kg·m-2 dry weight (DW); and fruit yield averaged 6.7 kg·m-2. Dry matter content, yield loss to blossom-end rot, and firmness responded linearly to treatment EC. In general, ECdaily yielded higher fruit quality and ECvariable lower fruit quality than that predicted by linear regression. Although our strategy of short-term dynamic changes of nutrient solution EC according to changes in climate variables did not increase yield, daily adjustment of nutrient solution EC improved external fruit quality characteristics and may be practical for grower adoption.

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Bridget K. Behe, Kristin L. Getter, and Chengyan Yue

make that season longer or shorter ( Cawthorn, 1998 ). Revenue forecasting can help manage uncertainty in sales and incorporating weather into these forecasting models improves prediction accuracy ( Aghazadeh, 2007 ; Sivillo and Reilly, 2004

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Luis A. Ribera, Marco A. Palma, Mechel Paggi, Ronald Knutson, Joseph G. Masabni, and Juan Anciso

levels; and the associated revenue reductions to the United States and the supplying countries’ producers. To estimate the impacts of these foodborne illness outbreaks on each produce subsector, we forecasted domestic shipments, imports, and prices that