Search Results

You are looking at 1 - 10 of 10 items for :

  • Author or Editor: B. W. Wood x
  • Journal of the American Society for Horticultural Science x
Clear All Modify Search
Author:

Alternately bearing `Cheyenne' pecan [Carya illinoensis (Wangenh.) K. Koch] trees were studied to assess the temporal aspects of previous season fruit development on several reproductive and vegetative traits of horticultural importance. Action spectra were generated and used to identify the relative sensitivities of these traits to the temporal aspects of fruiting. Based on date of maximum rate of change in sigmoidal models fitted to these action spectra, the relative sensitivity of certain important growth and developmental parameters to fruit removal time was number of distillate flowers per terminal shoot > number of distillate flowers per flower cluster on lateral shoots> length of terminal shoots > percentage of lateral shoots with fruit= catkins per terminal shoot at top of the tree> percentage of terminal shoots with fruit > catkins per standard terminal shoot> shoots produced per l-year-old branch> percentage of l-year-old shoot death. Maximum rates of change for these reproductive and vegetative parameters were typically during the dough stage of ovule development; however, substantial change also occurred for several parameters over a much wider developmental window. No evidence was found for a hormone-like translocatable factor from developing fruit that either promotes or inhibits flowering. Extending the time from nut ripening to leaf drop increased production of staminate and distillate flowers the following year and appeared to increase fruit set.

Free access
Author:

Abstract

Pecan [Carya illinoinensis) (Wangenh.) K. Koch] kernel development was characterized by an initial rapid localized expansion of testa and endosperm, which was closely associated with low levels of free and bound abscisic acid (ABA) and with high levels of gibberllin-like (GL) substances. Rapid cotyledon growth began with the termination of testa and endosperm expansion, which was subsequent to a sharp increase in both free and bound ABA. The rate of change for growth in kernel dry weight was highly correlated with the rate of change in levels of both free ABA (R 2 = 0.86) and bound ABA (R 2 = 0.88). Levels of GL substances (ng/g kernel), as measured by the dwarf pea and cucumber bioassays, were relatively low after the rapid accumulation of kernel dry weight, however, GL substances detected by the barley endosperm bioassay were high during the last 30 days of kernel development. Abscisic acid and GL substances seem to exercise a significant role in seed development.

Open Access
Author:

Abstract

The dynamics of indoleacetic acid (IAA), cis-trans abscisic acid (c,t-ABA), and gibberellin (GA)- and cytokinin-like compounds were measured in pecan [Carya illinoensis (Wang) K. Koch; cv. Desirable] buds following their release from imposed dormancy. Both bound and free ABA levels in apical and basal primary buds and in secondary buds declined 27 days prior to budbreak until the time of budbreak, with the exception of a steady rise in free ABA in secondary buds. During this period IAA initially dropped sharply, remained low, and finally increased again at budbreak. Cytokinin-like substances peaked after the drop in IAA but prior to the peak in gibberellin-like substances which occurred during bud swelling. The findings raise the possibility of a key regulatory role for IAA, possibly through its influence on regulation of bud cytokinin and gibberellin levels via their metabolism in roots. Growth regulator dynamics during pecan budbreak are discussed in relation to the hormonal theory versus tissue sensitivity to growth regulators.

Open Access
Authors: and

Abstract

Immature embryos were excised during kernel development from fruits of the pecan [Carya illinoensis (Wangenh.) C. Koch] cultivars Desirable and Stuart. The cotyledons were removed and the main embryo axes were used as explants. Explants were cultured in vitro on media containing various levels of cytokinins and auxins. Morphogenesis in ‘Stuart’ preceded that of ‘Desirable’ by 1 to 2 weeks. In both cultivars, the percentage of embryo axes forming shoots only or both shoots and roots increased until ≈4 to 6 weeks before nut maturity, as judged by shuck dehiscence. After this time, developmental responses declined. Production of normal plants was highest on a medium containing IBA, BA, and kinetin at 0.5, 4.4, and 9.3 μM, respectively. Shoots only were obtained on a medium containing cytokinin without auxin and roots only on a medium containing auxin with no cytokinin. Axillary shoots elongated from embryo axes of both cultivars. This response was greatest on a medium containing cytokinin as the only hormone for ‘Desirable’, but with both auxin and cytokinin for ‘Stuart’. Chemical names: indole-3-butyric acid (IBA); N-(phenylmethyl)-1H purin-6-amine (BA); N-(2-furanylmethyl)-1H-purin-6-amine (kinetin).

Open Access
Authors: and

Abstract

Starch and sugars were generally higher in bearing than in nonbearing shoots (wood and bark) of pecan (Carya illinoensis (Wang.) Koch). Decreases in shoot starch were reflected by generally simultaneous increases in either shoot or kernel sugars. Shoot starch fell to its lowest level during the liquid stage of ovule development. Leaf starch generally declined as the growing season progressed. Total sugar levels rose in the kernel, shuck, and shell during fruit enlargement and declined during kernel growth. Mature kernels had less sugar than mature shucks. Ovule sugar was highest during the liquid stage and decreased to very low levels at maturity. Ovule starch generally increased as kernels matured.

Open Access
Authors: and

Abstract

Sugars and fatty acids were measured during fruit development of ‘Moneymaker’ pecan [Carya illinoensis (Wang.)] Koch. Major sugars in the kernel, shell, and shuck were fructose, glucose, sucrose, and inositol; major fatty acids were oleate, linoleate, palmitate, linolenate, stearate, myristate, margarate, and arachidate. During endosperm expansion fructose and glucose rapidly accumulated and fatty acids were present in small concentrations. During embryo and cotyledon expansion fatty acids accumulated and reducing sugars and inositol declined while sucrose increased.

Open Access

Abstract

Feeding injury by pecan aphids on fully expanded pecan [Carya illinoensis (Wangenh) K. Koch] seedling foliage reduced net CO2 exchange within 2 weeks of infestation and was dependent upon aphid density and species. Increasing aphid population levels resulted in increasing reductions in net photosynthesis. Carbon exchange rates after a buildup and subsequent rapid decline of either Monellia caryella (Fitch) or Monelliopsis pecanis (Bissell) populations resulted in a 50% reduction in net photosynthesis and 25% reduction in dark respiration. This effect can persist at least 12 weeks after the cessation of aphid infestation. Such leaves exhibit aphid-induced clogging of the phloem with callose and other substances. Such clogging may be associated with the commonly observed aphid population decline in pecan orchards. Observations indicate that the influence of aphid feeding on leaf photosynthetic physiology may impair pecan productivity.

Open Access

Polyphenols were analyzed in expanding buds and developing leaves of pecan [Carya illinoensis (Wangenh.) C. Koch] cultivars with varying responses to Cladosporium caryigenum (Ell. et Lang. Gottwald), the organism causing scab. Plant tissue extracts were examined by high-performance liquid chromatography using a water: methanol gradient to separate polyphenolic components on a C-18 reversed phase column. A diode-array detector was used to identify profile components by retention times and computer matching of ultraviolet spectra to standard compounds in a library. Concentrations of these polyphenols were compared throughout the growing season in leaves of pecan cultivars with low (`Elliott'), intermediate (`Stuart'), and high (`Wichita') susceptibility to scab; during susceptibility to infection by Cladosporium caryigenum from 16 cultivars; and in `Wichita' leaf discs with and without scab lesions. The major polyphenolic constituent of tissues for all cultivars was identified as hydrojuglone glucoside, which was detected in intact buds and leaves throughout the growing season. Hydrojuglone glucoside concentration increased concomitantly with leaf expansion and then declined slowly. Juglone was barely, if at all, detectable, regardless of leaf age. No correlation was found between cultivar susceptibility to pecan scab and the levels of either juglone or hydrojuglone glucoside in the healthy leaves of 16 cultivars. Leaf tissue with scab lesions had significantly higher juglone and hydrojuglone glucoside levels than leaf discs without scab lesions. Chemical names used: 4-8-dihydroxy-1-naphthyl b-d-glucopyranoside (hydrojuglone glucoside); 1,5-hydroxy-naphthoquinone (juglone).

Free access

Polypeptides from pecan [Carya illinoensis (Wangenh.) C. .Koch] leaves were separated by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and visualized by silver staining. Pecan leaf protein profiles were similar irrespective of cultivar (Desirable and Stuart), leaflet position, reproductive status of the allied shoot, or seasonal leaf age relative to fruit development. The large subunit of ribulose l,5-bisphosphate carboxylase and the majority of the other polypeptides were consistently present. However, the most striking change in the polypeptide composition was the seasonal decline of a polypeptide with an approximate molecular mass of 24.5 kDa. This leaf polypeptide was present in leaves collected in June and July, coinciding with the periods of initial fruit elongation and rapid increase in fruit volume. A detectable decrease occurred by mid-August, when kernel development was initiated. Changes in the abundance of this polypeptide relative to other polypeptides were observed over two growing seasons. Cells of young leaves collected early in the growing season contained more ribosomes and starch granules, but fewer vesicles and smaller electron-dense osmophilic granules than old leaves collected late in the growing season.

Free access

Leaf water status, carbohydrate levels, net photosynthesis, stomatal conductance, ABA, dihydrozeatin riboside (DHZR), and trans-zeatin riboside (ZR) levels were determined in a greenhouse during rooting of stem cuttings of Acer rubrum L. `Red Sunset' taken on 3 Sept. 1987 and 28 May 1988. Leaf water status deteriorated before rooting and improved after root emergence. Leaf carbohydrate concentrations (glucose, sucrose, total soluble sugars, and total carbohydrates) increased until rooting and decreased after rooting, while changes in starch concentrations were trendless. ABA levels increased after insertion of cuttings into the rooting medium, but decreased before rooting. No correlation between timing of rooting and concentrations of the cytokinins ZR or DHZR was observed. Photosynthetic rates during rooting were higher for the Sept. 1987 cuttings and did not decrease to the compensation point as did those for May 1988 cuttings. Low photosynthetic rates and stomatal conductance of the cuttings during rooting were associated with water stress. The relationship between photosynthetic rates of such cuttings and cytokinin (CK) or ABA content was unclear. Chemical names used: [S-(Z,E]-5-(1-hydroxy-2,6,6-trimethyl-4-oxo-2-cyclohexen-1-yl)-3-methyl-2, 4-pentadienoic acid (abscisic acid, ABA); 2-methyl-4-(1H-purin-6-ylamino)-2-buten-1-ol (zeatin, Z).

Free access