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William M. Randle

Sixty onion (Allium cepa L.) entries were evaluated for nonstructural water-soluble carbohydrates (NWSC) under high (4.0 meq·liter-1) and low (0.1 meq·liter-1) S nutrition. Significant differences were detected among entries for sucrose, fructose, glucose, total fructans, total NWSC, and soluble solids content (SSC). Sucrose, total fructans, and SSC were highly correlated with total NWSC although deviant NWSC concentration was detected. Since a significant S × entry interaction was found for all NWSC concentrations tested. selection should be conducted at S concentrations indicative of targeted production areas.

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Robert C. Ebel, Bryan Wilkins, David Himelrick, Tom Beckman, Andy Nyczepir, and Jim Pitts

Twelve peach rootstocks including `Lovell', `Nemaguard', `Flordaguard', `14DR51', five `Guardian' (BY520-9) selections, and three BY520-8 selections, were evaluated under field conditions to determine their effect on performance of `Cresthaven' peach. The trees were planted in 1994. Trunk cross-sectional area of BY520-8 selections SL1923 and SL4028 was 28% larger than the rest of the rootstocks, which were similar. There was no crop in 1996 due to late spring frost. Yield in 1997 and 1998 was higher for SL1923 because of higher cropload than the rest of the rootstocks, which were similar. Yield efficiency varied across years and rootstocks. Fruit weight varied among rootstocks but all were commercially acceptable. Harvest date was advanced by two days for some rootstocks compared to Lovell and none were delayed. Percent red blush, soluble solids and firmness varied among rootstocks, but none demonstrated superior quality in all of these parameters as compared to Lovell. Ring nematode population densities were above the threshhold considered to be critical for onset of PTSL for all rootstocks in 1997 and 1998. Tree survival was at or above 86% for all rootstocks and death was not correlated with ring nematode density No trees developed symptoms characteristic of Peach Tree Short Life disease complex. Guardian selections performed adequately compared to the commonly used commercial rootstocks in this study, however, the yield date are from 2 years only.

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Donald R. Scott

Abstract

Plant resistance to insects of the genus Lygus Hahn has been reported in bean (4), alfalfa (1) and cotton (2). The level of resistance of carrot (Daucus carota L.) to lygus bugs (L. hesperus Knight, L. elisus van Duzee) varies within and among cultivars (3). I carried out the present study to ascertain if the resistance level could be increased by inbreeding and selection.

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W.J. van der Burg, J.W. Aartse, R.A van Zwol, H. Jalink, and R.J. Bino

Studies based on X-ray photographs were conducted to predict the morphology of tomato (Lycopersicon esculentum Mill.) seedlings at transplanting stage. Currently, seed-lot quality of tomato seeds for growing commercial transplants is determined with grow-out tests in the greenhouse because the standard germination test fails to predict the percentage of normal or usable transplants (UTs). These grow-out tests, however, are difficult to standardize. An X-ray evaluation procedure is presented as an alternative. X-ray images nondestructively provide information on embryo size and morphology and the amount of endosperm and the area of free space. These parameters correlate well with the morphology of 14-day old seedlings. Cotyledon morphology has the highest correlation with the percentage of UTs. A test based on the evaluation of X-ray images, classifying the cotyledon morphology and seed free space, predicts the percentage of UTs more accurately than the currently used germination test. A second method based on an equation that uses the probabilities of all X-ray categories proportionally predicts the percentage of UTs of primed seeds more accurately than the first method. Selecting individual seeds based on X-ray images has the potential to raise the percentage of UTs of seed lots. On the average, the percentage of UTs of control seeds was 22% higher after hand selection based on X-ray evaluation. Primed seeds gave 12% higher results. Hence, X-ray analysis can predict seedling performance and enable the selection of high-quality seeds.

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Jocelyne Kervella, Loïc Pagès, and Michel Génard

Genotypic variations in the length-diameter relationship of branches among peach and nectarine [Prunus persica (L.) Batsch.] cultivars were investigated. The length and basal diameter of all undamaged first-order shoots from 1-year-old trees of 14 cultivars and one accession were measured. Statistical analysis of the allometric relationship between length and basal diameter of shoots provided evidence of genotypic differences for that relationship, although the diameter of very short shoots did not differ between genotypes. A gradient existed from `Armking' with thin shoots (9 mm in diameter for 85.5-cm-long shoots) to `Flavorcrest' with thick shoots (16.4 mm in diameter for 85.5-cm-long shoots). Early selection for shoot thickness should be possible in breeding programs. The likely consequences of observed shoot thickness variations on the mechanical and hydraulic properties of shoots are discussed.

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Patrick J. Conner and Ray E. Worley

The Coastal Plain Experiment Station has been evaluating pecan [Carya illinoinensis (Wangenh.) K. Koch] cultivars for over 75 years. Using annual yield data from this program, the alternate bearing intensities (I) of 66 pecan cultivars and numbered U.S. Dept. of Agriculture (USDA) selections were determined. Values ranged from 0.19 to 0.93 in young trees, and from 0.27 to 0.91 in mature trees under high-input production practices. The adoption of fungicides, insecticides, and irrigation during the last 30 years has reduced the average I value from 0.70 to 0.55. I was negatively correlated with both nut yield and nut weight. All but one cultivar recommended for commercial production in Georgia have I values lower than the average of 0.57 for all cultivars in this test. Values calculated early in a tree's productive life cycle were highly correlated with those of mature trees.

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Raymond O. Miller, Paul D. Bloese, James W. Hanover, and Robert A. Haack

A test of Michigan half-sib progeny of paper birch (Betula papyrifera Marsh.) and European white birch (B. pendula Roth.) was conducted in Michigan to examine species variation in growth, bark color, and resistance to bronze birch borer (Agrilus anxius Gory). Paper birch was superior to European white birch in height and borer resistance at age 12 years from seed. Families of paper birch were identified that grew exceptionally well, had developed white bark within 6 years, and exhibited borer resistance. The magnitude of additive genetic variance and narrow-sense family heritability estimates for paper birch indicated that sufficient genetic variation and inheritance exist to support selection and breeding for height. Paper birch may be an acceptable substitute for European white birch as a landscape species in northeastern North America.

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Karen H. S. Taylor, Dr. Greg Cobb, and Dr. Jayne Zajicek

Designing a landscape involves the selection of plants with certain characteristics such as height, color, hardiness zone, bloom time, etc. A Hypercard stack, which is a specific type of software application for Macintosh computers, was developed to aid landscapers in the location of plants with the desired characteristics. This Hypercard stack, called the “Plant Stack”, is based on the book, Identification Selection and Use of Southern Plants for Landscape Design, by Dr. Neil Odenwald and James Turner. The stack is also useful as an educational tool; for example, it can be used as a set of flash cards. Use of the software for selecting southern plants will be discussed as will use of the same software as an educational tool.

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J.C. Cousineau, A.K. Anderson, H.A. Daubeny, and D.J. Donnelly

Isoenzyme staining of horizontal starch gels was used to characterize 23 cultivars and three advanced selections of red raspberry (Rubus idaeus L.). The genotypes were separable using the enzymes malate dehydrogenase, phosphoglucoisomerase, phosphoglucomutase, and triose phosphate isomerase. In addition, staining for isocitrate dehydrogenase and shikimate dehydrogenase revealed polymorphisms in some cultivars. By combining these results with those obtained for 78 previously tested cultivars, 75 of the 104 (72%) genotypes tested were uniquely characterized using the six isoenzymes.

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Marvin L. Baker

In North America, cultivation of Mayhaws (Crataegus opaca L.) is rare; most commercial harvest is taken from the wild. Crataegus opaca is distributed in northeast Texas, east Texas and southeast Texas along the flood plains of the Angelina and Neuches rivers and their watersheds. Mayhaws are difficult to define due to unusual factors relating to reproduction, including apomixis, or the development of an embryo from cells other than sex cells. Mayhaws are valued for economic use as food, medicine and ornamentals. Since the hawthorn has shown extremely low toxicity in every animal tested, the discovery of isolated constituents thru research has caused pharmacological interest. A small orchard plot of selections with ripened fruit measuring larger than 2.5 cm up to 3.1 cm with bright red or pink color is being established for selecting possible cultivars for medicinal or food uses.

Five Crataegus opaca selections were collected due to showing spurtype, large fruits and thornlessness. Yearly production of fruit was noted for five years (even after late freezes) while selections grew in Taggert's Flat, Neuches river bottom, Angelina County. Seedlings are being grafted for further evaluations and uses in sustainable agricultural ecosystems.