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  • Author or Editor: William Reid x
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The nuts of 10 pecan cultivars were used to produce rootstock trees for the propagation of two scion cultivars—Posey and Pawnee. Seed sources included: `Chickasaw', `Colby', `Dooley', `Giles', `Greenriver', `Major', `Mohawk', `Peruque', `Posey', and `Shoshoni'. Leaf analysis performed in 1994 and 1996 revealed that rootstock influenced K and Zn concentrations. Scions propagated on `Posey' seedlings contained the greatest amount of K, while scions propagated on `Greenriver' seedlings contained the least. Zn levels were highest in trees with `Chickasaw' seedling rootstocks and the least in `Major' seedlings. Yield and nut quality was influenced by a major drought during the late summer and fall of 1995. Nuts produced by trees with `Chickasaw' and `Colby' rootstocks had the highest kernel percentage, while trees grown on `Major' and `Posey' had the lowest. The greatest yields, during the drought year, were produced from scion cultivars grafted on `Giles' and `Chickasaw' seedling rootstocks. `Major' and `Greenriver' seedlings produced trees with the smallest yields.

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Field resistance to the black-margined pecan aphid [Monellia caryella (Fitch)] was evaluated for 12 pecan [Carya illinoinensis (Wangen.) K. Koch.] cultivars in 1995 and 19 cultivars in 1999. Each year, aphid populations were sampled from four trees of each cultivar by counting the number of aphids on 10 mid-shoot leaves per tree each week throughout the growing season. On leaves of several cultivars, populations of black-margined aphids peaked above the economic threashold level (20 aphids/leaf) during the month of August in both years. `Pawnee' and `Greenriver' demonstrated field resistance to aphids by maintaining fewer than 10 aphids/leaf throughout the season. `Hirschi' and `Posey' maintained among the highest aphid populations in both years—2 to 5 times higher than threashold levels. By avoiding cultivars susceptible to aphid feeding, growers can avoid aphid-induced yield reductions.

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Pecans (Carya illinoinensis) are produced under a wide array of environmental conditions—from the warm humid southeastern states, to the continental climate of the central plains, to the arid climates of the American west. In addition, pecan cultural systems vary from the low-input management of native stands of seedling trees to the intensive management of single-cultivar pecan orchards. This wide diversity of pecan agroecosystems has fostered the development of innovative, site-specific approaches toward pecan pest management. Current pecan pest management programs require an intimate knowledge of orchard ecology. Growers use monitoring methods and prediction models to track pest populations. Biological control agents are conserved by habitat manipulation and/or augmented through inoculative releases. Selective pesticides are used to control target pests while conserving natural enemies. Four pecan cultural systems are described in detail to illustrate how ecological principles are applied to widely diverse pecan agroecosystems.

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Pecan trees, Carya illinoensis, often exhibit a strong alternate bearing pattern. The presence of a heavy seed crop inhibits terminals from fruiting the following season. This study was developed to discover at what point in the development of the pecan fruit does this inhibition take place. Six nut removal times were evaluated: (1) after pollination but before fertilization, (2) one-half ovule expansion, (3) full ovule expansion or water stage, (4) dough stage, (5) 3 weeks after the initiation of the dough stage, and (6) no fruit removal until harvest. The cultivar `Mohawk' was used for this randomized block experiment.

Return bloom was significantly enhanced by the removal of fruit prior to the initiation of kernel filling (dough stage). Less than 10% of terminals that supported pecans through the dough stage were able to produce distillate flowers the following year. Twig mortality was significantly higher for terminals that completed kernel filling. These results indicate that nut thinning prior to the water stage may reduce the alternate bearing tendency in pecan.

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Over 10,000 metric tons of eastern black walnut, Juglans nigra L., are harvested annually in the U.S. This production is based entirely on hand harvested nuts from seedling trees growing in native stands throughout the midwest and northeast. Significant improvement in nut quality and yield could be made for black walnut through the selection and propagation of superior clones. Cultivars have been identified that exhibit one or more of the important genetic traits needed for crop improvement. These traits include: lateral bud fruitfulness, late leafing, resistance to Gnomonia leptostyla (Fr.) Ces. & de Not., precocity, thin shell thickness, high percent kernel, ease of shelling, and light colored kernels. Cultivars that bear nuts on lateral branches and produce nuts with more that 30% kernel are currently available. If planted in an orchard situation, these cultivars could have an immediate impact on the black walnut industry. Commercial black walnut orchards based on thin shelled cultivars have not been developed due to the lack of cultivar performance data and undemonstrated crop profitability. Large trial plantings that become financial successful will be necessary to stimulate a black walnut orchard industry. The incorporation of additional positive traits into walnut cultivars will only be made after an established walnut industry demands further crop improvement.

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Excellent table quality is an essential characteristic of commercial sweet corn (Zea mays) and commonly held paramount as a selection criterion. As a consequence, breeding for improved agronomic performance in sweet corn has been limited in comparison with United States dent corn breeding efforts. The narrowness of genetic diversity within modern sweet corn germplasm suggests potential exists for yield enhancement through new heterotic combinations and introgression of sources of improved agronomic performance. The objective of this study was to examine the results of incorporating nonsweet germplasm in the development of improved temperate sweet corn cultivars. Five inbreds derived from crosses between nonsweet germplasm and temperate supersweet (shrunken2, sh2) inbreds were crossed with three temperate sh2 testers to make 15 experimental hybrids. The hybrids were evaluated in four environments with three replications per environments. Experimental entry Wh04038V × Tester2 yielded 18.1 Mg·ha−1 in 2009 and 16.6 Mg·ha−1 in 2010, significantly out-yielding the top producing commercial control, ‘Overland’, in both years. An additional six entries derived from exotic-by-temperate crosses yielded significantly more than all commercial checks in 2009. Four specific experimental entries consistently exhibited superior resistance to root lodging, northern corn leaf blight (Exserohilum turcicum), and Maize dwarf mosaic virus (MDMV) compared with ‘Marvel’ and ‘Supersweet Jubilee Plus’. Ten of the 15 experimental entries exhibited similar quality for flavor relative to ‘Marvel’ and ‘Overland’, however ‘Supersweet Jubilee Plus’ outperformed all entries for both flavor and tenderness, suggesting that while incorporation of nonsweet germplasm in sweet corn breeding programs may provide valuable contributions for yield and agronomic performance, flavor and tenderness must be carefully regarded.

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Abstract

Seasonal changes in deep supercooling and cold-hardiness of stem tissue and apical buds of pecan [Carya illinoensis (Wang enh.) C. Koch] cultivars were studied. All the pecan cultivars showed supercooling in stem and apical buds. Supercooling in stem and apical buds was maximal in early January and least in early spring. A good correlation between killing temperatures and freezing of supercooled water was found in apical buds. Similar results were observed for stem samples collected during early spring. Apical buds appeared to be more prone to injury during spring than stem tissue in all the pecan cultivars. In early April, stem samples of pecan cultivars were killed at or below –20.1C, whereas apical buds were killed at –16C or above. Apical buds of ‘Posey’ showed greater cold-hardiness than those of other pecan cultivars in midwinter and early spring.

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More than 93% of pecans [Carya illinoinensis (Wangenh.) K. Koch] produced in the United States are grown in the southeastern and southwestern states. However, the native range of the pecan tree extends northward into Kansas, Missouri, and Illinois. In these northern states, commercial pecan production is expanding as additional acres of native trees are brought under cultivation and orchards of short-season, cold-hardy cultivars are established. Native nut production dominates the northern pecan industry accounting for over 95% of nuts produced in the region. Cultural practices for native pecans have been developed for northern groves that feature low inputs and good yields. Pecan cultivars adapted to the north ripen their fruit in a climate that provides 155 to 200 frost-free days. Few generalizations can be made about northern cultivars. The nuts produced by these cultivars vary in size from small [4 g (0.14 oz)] to medium [8 g (0.28 oz)] with shelling percentages ranging from 44% to 59%.

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Can Carolina buckthorn (Rhamnuscaroliniana) persist north of its native habitat without becoming invasive? Its distribution (USDA zones 5b to 9b) suggests that genotypes vary in cold hardiness, and invasiveness of other Rhamnus sp. has been linked to unusually early budbreak each spring. Therefore, we investigated depth of cold hardiness and vernal budbreak of Carolina buckthorns from multiple provenances and made comparisons to the invasive common buckthorn (Rhamnus cathartica). Budbreak was recorded in Ames, Iowa, from 9 Apr. to 10 May 2002. Buds of common buckthorn broke earlier than those of Carolina buckthorn, and mulching plants of Carolina buckthorn hastened budbreak. Stem samples were collected in October, January, and April from a plot in Ames, Iowa (USDA zone 5a), of Carolina buckthorns from three provenances (Missouri, Ohio, and Texas) and of naturalized common buckthorns. A similar schedule was followed during the next winter, when two plot locations [Ames, Iowa, and New Franklin, Mo. (USDA zone 5b)], were compared, but Carolina buckthorns from only Missouri and Texas were sampled. Carolina buckthorn and common buckthorn survived midwinter temperatures as low as –21 °C and –24 °C, respectively. Provenance differences were minimal; Carolina buckthorns from Missouri were more hardy than those from Ohio and Texas only in April of the first winter. We conclude that its cold hardiness will permit use of Carolina buckthorn beyond where it is distributed in the southeastern United States. Delayed budbreak of Carolina buckthorn relative to that of common buckthorn may underscore the potential for Carolina buckthorn in regions with harsh winters and may lessen its potential to be as invasive as common buckthorn.

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Carolina buckthorn [Rhamnus caroliniana Walt. or Frangula caroliniana (Walt.) Gray] is an attractive and water-stress-resistant shrub or small tree distributed extensively in the southeastern United States that merits use in managed landscapes. Due to substantial climatic differences within its distribution (30-year normal midwinter minima range from 13 to -8 °C), selection among provenances based on differences in cold hardiness is warranted. Before selections are marketed, the potential of carolina buckthorn to be invasive also merits investigation. Ecological problems resulting from the introduction of Rhamnus L. species in the United States, most notably the dominance of R. cathartica L. (common buckthorn) over neighboring taxa, are due in part to early budbreak. Consequently, we investigated depth of cold hardiness and vernal budbreak of carolina buckthorn and common buckthorn. Stem samples of carolina buckthorn and common buckthorn collected in midwinter survived temperatures as low as -21 and -24 °C, respectively. Although the cold hardiness of carolina buckthorns from Missouri was greater than that of carolina buckthorns from Ohio and Texas on 2 Apr. 2003, there were no differences in cold hardiness of stems from Missouri and Texas on all three assessment dates in the second experiment. All plants survived at both field locations except for the carolina buckthorns from southern Texas planted in Iowa, which showed 0% and 17% survival in 2003 and 2004, respectively. Budbreak of both species with and without mulch in Ames, Iowa, was recorded from 9 Apr. to 10 May 2002. Mean budbreak of common buckthorn was 5.7 days earlier than budbreak of carolina buckthorn, and buds of mulched carolina buckthorns broke 4.2 days earlier than did buds of unmulched carolina buckthorns. We conclude that the cold hardiness of carolina buckthorn is sufficient to permit the species to be planted outside of its natural distribution. Populations of carolina buckthorn in Ohio and Missouri should be the focus of efforts to select genotypes for use in regions with harsh winters. Phenology of its budbreak suggests carolina buckthorn will not be as invasive as common buckthorn, but evaluation of additional determinants of invasiveness is warranted.

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