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Angela R. Davis, Charles L. Webber III, Wayne W. Fish, Todd C. Wehner, Stephen King, and Penelope Perkins-Veazie

as needed (at the first signs of water stress), and fertigated bimonthly. To assess environmental effects, 10 watermelon cultigens ( Table 2 ) were also grown at College Station, TX [Zack very fine sandy loam (fine, smectitic, thermic Udertic

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Daniela M. Segantini, Renee T. Threlfall, John R. Clark, Luke R. Howard, and Cindi R. Brownmiller

substantial number of sources of variation and dependent variables for primocane-fruiting blackberries. We found major year-to-year differences for several variables, and this indicates that environmental effects can be substantial and growers should be aware

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Marianne Andresen and Nina Cedergreen

scarce for natural growth enhancers as is information about the active components in the products, their physiological effects on plants, possible environmental effects, product stability under different environments, etc. Combining the scarce scientific

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J. N. Moore, Catherine Lundergan, and Elvin D. Brown

Abstract

Nine seedling populations involving small-, intermediate-, and large-seeded parental clones of tetraploid blackberries (Rubus sp., subgenus Eubatus) were evaluated for seed-size inheritance. All seedling progenies exhibited a wide range of seed sizes with high frequencies of transgressive segregation especially for small seed size The frequency distribution curves were skewed in the direction of small seed size. The data support a model for quantitative inheritance with partial dominance for small seed size. Calculations of heritabihty show an average maximum estimate of 97%, supporting previous observations of the lack of environmental effects on the expression of seed size in blackberries.

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J.W. Gonzales, D.P. Coyne, D.T. Lindgren, D. Schaaf, and K. M. Eskridge

The potato leafhopper (PLH), Empoasca fabae Harris is the most important Empoasca species attacking dry beans (Phaseolus vulgaris L.) in North America. The objective of this study was to determine the heritability (h2) of PLH injury based on parent-offspring regression analysis of F3 means on individual F2 plants derived from crosses of pinto `Sierra' (resistant) × great northern `Starlight' (susceptible), and black bean `Tacarigua' (resistant) × `Starlight' (susceptible). Low narrow-sense heritability values of 0.29 ± 0.06 and 0.28 ± 0.10, respectively, were obtained for the above crosses. The low narrow-sense heritability estimates indicated large environmental effects on the expression of PLH injury in dry beans. An allelic test showed that both resistant parents possessed the same genes for resistance.

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L. Carl Greve, Gale McGranahan, Janine Hasey, Ronald Snyder, Kathy Kelly, David Goldhamer, and John M. Labavitch

The variation in polyunsaturated fatty acid content of walnut (Juglans regia L.) oils was determined by analysis of samples isolated from specimens growing in four germplasm collections [California (55 cultivars), Washington (64 seedlings), China (12 cultivars), and France (20 cultivars)]. In addition, the impact of within-state geographic differences on oil composition was examined by comparing samples from three California cultivars (`Ashley', `Hartley', and `Franquette') grown in three locations. Local environmental effects on oil composition of `Chico' were also examined by comparing 1) samples collected from shaded and sun-exposed locations of the same trees and 2) samples collected from trees subjected to three irrigation regimes. Polyunsaturated fatty acid content, as a percentage of total fatty acids, ranged from 47.2% in nuts from PI 142323 from France to 81.0% in `Ashley' from California. However, our data indicate that environment, genotype, nut maturity, and their interactions all contribute significantly to variation in the degree of unsaturation of walnut oil.

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Hongzhan Huang, James Harding, and Thomas Bvrne

The effects of long-term genetic improvement are measured by selection response predicted from estimates of narrow-sense heritability. However, changes of population mean must be partitioned into genetic and environmental components-in order to accurately estimate selection response.

A long-term selection experiment for cut-flower yield in the Davis population of gerbera (Gerbera hybrida, Compositae) was conducted for sixteen generations. Breeding value was estimated for individual plants in the population using Best Linear Unbiased Prediction (BLUP). Genetic change was calculated from breeding values of individual plants in each generation. The results of this study indicate: the long-term selection experiment was successful and necessary for genetic improvement. Genetic change over sixteen generations was 33 flowers. Mean breeding values increased monotonously with an “S” shape pattern. Environmental effects fluctuated from generation to generation. Cut-flower yield in the Davis population of gerbera will continuously respond to selection.

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Lynn Ellen Doxon

When determining whether landscaping is sustainable, we should consider environmental, financial, and human factors. Environmental factors include the capacity of the landscape to damage or heal the system in which it is placed, the environmental effects of the cultural techniques and products used to install and maintain the landscape, and the ability of that landscape to endure without environmentally damaging inputs. Financial factors include the cost of the landscape compared to the economic return in terms of increased property values, the ability to attract and hold industry in the neighborhood, and user fees paid by people attracted to an area by the landscaping. Human factors include the effects on the landscape on mood, employee retention, and health and activity of the individuals who interact with the environment. The ideal landscape would be sustainable in all three of these areas, meaning there is more benefit than cost environmentally, financially, and humanly.

Open access

Roy M. Sachs and Wesley P. Hackett

Abstract

Chemical control of plant height has been achieved for many herbaceous and woody species. Horticultural practices in the greenhouse, orchard, and landscape have been altered to include the use of numerous compounds, the main function of which is to eliminate overgrowth. The problems encountered in selecting and using even the registered materials cannot be readily generalized since each compound presents special difficulties. Nevertheless, for the purpose of this review, 7 challenges to effective use usually presented by all compounds will be discussed, namely: 1) identifying the primary cause of inhibition of stem elongation; 2) timing the application of compounds to the appropriate stage of plant development; 3) determining the best method of application; 4) determining the optimum dosage, formulation, and frequency of application; 5) testing for cumulative phytotoxicity; 6) noting species specificity; and 7) taking note of potential environmental effects. Many chemicals have been made available for testing, but relatively few of them are registered expressly for control of overgrowth (Fig. 1).

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Lingxia Sun, Sunchung Park, Martin Bukovac, and Steven van Nocker

Abscission of leaves, floral organs, and fruit is a developmentally and environmentally regulated process initiated in specialized thin layers of cells within abscission zones (AZs). Very little is known about early molecular events that drive abscission, especially of fruit. Commercial apple production relies on the use of flower and fruit abscission-promoting and -inhibiting compounds to enhance fruit quality, control preharvest fruit drop, and maintain consistent annual bearing. The success of chemical treatments is strongly influenced by numerous factors, including environment, genotype, developmental stage of the fruit, and physiological state of the tree. Toward developing improved strategies for regulating fruit abscission, we carried out transcriptional profiling of competent-quiescent and activated abscission layers. We found that a decisive event in the sequential process of abscission layer development is the transcriptional activation of the MdPEL1 gene, encoding a plant pectate lyase protein and potentially involved in the degradation of the middle lamella of adjacent abscission layer cells. Additionally, regulatory elements of at least 12 homologous pectate lyase genes in Arabidopsis thaliana were found to direct expression in floral AZs and in dehiscence zones along valve margins, suggesting that these genes have evolutionary conserved function. This work identifies a novel role for pectate lyases in plants. Furthermore, many abscission-related genes identified in this study are being used to track biochemical and regulatory pathways that participate in abscission in response to chemical treatments or environmental effects.