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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.

Open access

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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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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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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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.

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W.H. Gabelman, I.L. Goldman, and D. N. Breitbach

Aster yellows, an insect-vectored disease caused by a mycoplasmalike organism, limits vegetable crop production in the Midwestern U.S.A breeding effort was initiated in 1982 to develop aster yellows resistance in carrot. A synthetic population (AYSYN) composed of 5 open-pollinated varieties and 4 inbreds was assembled in 1982. Inbred lines and hybrids were extracted from AYSYN using a variety of methods. Selection in artificially-infected field sites was carried out from 1982 until 1989. Twenty-three inbreds and 3 hybrids were developed from AYSYN during the selection process. Replicated field experiments were conducted in 1990, 1991, and 1993 to determine the relative aster yellows resistance of these lines and hybrids in comparison with 6 check cultivars. Averaged over years, significant differences were detected for percent aster yellows infection among genotypes. Lines selected for resistance had a mean of 12% infected plant per plot as compared to 24% infection for standard cultivars. Results demonstrate the effectiveness of inbreeding and field selection for aster yellows resistance. This breeding effort represents the first report of aster yellows-resistant carrot germplasm.

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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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M.A. Dalbó, G.N. Ye, N.F. Weeden, W.F. Wilcox, and B.I. Reisch

The efficiency of marker-assisted selection for powdery mildew (Uncinula necator (Schw.) Burr) resistance in grapes (Vitis L. sp.) was studied using molecular markers associated with a major QTL (quantitative trait loci) for this trait. Initially, genetic maps were constructed from a segregating population of the cross `Horizon' × Illinois 547-1 (a hybrid between V. rupestris Scheele and V. cinerea Engelm.). A major QTL from Ill. 547-1, the resistant parent, explained 41% of the variation. One RAPD (randomly amplified polymorphic DNA) marker and one AFLP (amplified fragment length polymorphism) marker, obtained by bulked segregant analysis, showed the highest association with powdery mildew resistance in the mapping population. Segregation of the QTL was followed in different crosses by CAPS (cleaved amplified polymorphic sequence) markers developed from these two markers. An allele-specific amplified polymorphism that segregates as present/absent was also developed from the CS25b locus. Powdery mildew resistance was evaluated visually on a 1 to 5 scale in four different seedling populations. Two populations originated from crosses using Ill. 547-1 as the resistant parent. Two other populations were from crosses with NY88.0514.03, a resistant seedling from the original `Horizon' × Ill. 547-1 mapping population. Segregation ratio distortions were observed in some crosses. In these cases, the allele associated with the QTL for powdery mildew resistance was less frequent than the alternate allele. In all crosses, the markers were closely associated with resistance. If selection were based on markers, the percentage of susceptible individuals (classes 4 and 5) would decrease from 24% to 52% to 2% to 18%. Selection efficiency was greatest in crosses where segregation distortion was most intense.

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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.