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  • Author or Editor: Xia Xu* x
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Many biotypes of annual bluegrass (Poa annua L.) are found on golf course putting greens. Although normally considered an invasive weed, annual bluegrass can provide as good a putting surface as creeping bentgrass (Agrostis palustris Huds.). The most desirable biotypes of annual bluegrass are primarily vegetative and have a low flowering frequency. Whether the nutritional requirements of annual bluegrass biotypes differ from one another or from creeping bentgrass is unknown. The response of three flowering (FAB, high seedhead production) and three vegetative (VAB, low seedhead production) biotypes of annual bluegrass (AB), and the three parents of `Penncross' creeping bentgrass (CB) to varying levels of iron (Fe) in greenhouse sand culture was investigated. After establishment, clones were grown for 3 weeks and irrigated with a half-strength Hoagland's solution containing 0, 2, 4, 6, and 8 mg·L-1 Fe in citrate-Fe. Shoot and root responses to Fe were similar for the VAB and FAB biotypes. However, VAB had higher color ratings (darker green leaf color) with Fe treatment level at 4 mg·L-1 than did FAB or CB, which required 6 mg·L-1 Fe for acceptable color. Growth of creeping bentgrass was greater than that of annual bluegrass at every Fe level tested. Shoot dry weights of CB increased significantly with Fe treatment level up to 6 mg·L-1. Shoot dry weight of AB increased up to 4 mg·L-1 Fe and then declined at ≥6 mg·L-1. Root growth of CB increased up to 6 mg·L-1 Fe, but then decreased significantly at 8 mg·L-1 Fe. Root growth of AB increased slightly up to 4 mg·L-1 Fe and then declined at 6 and 8 mg·L-1. Shoot tissue concentrations of Fe were similar for AB and CB at each Fe rate tested except at 8 mg·L-1 Fe, where Fe levels in CB were significantly lower. Based on this work, creeping bentgrass and annual bluegrass respond differently to Fe nutrition, but different biotypes of annual bluegrass appear to respond similarly.

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Annual bluegrass (Poa annua L.) is becoming an important component of golf course putting greens. A greenhouse sand culture experiment was conducted to study the zinc (Zn) requirements of three genotypes of flowering annual bluegrass (FAB) and three genotypes of vegetative annual bluegrass (VAB), which were compared with the three parents of `Penncross' creeping bentgrass [Agrostis stolonifera L. (CB)]. Clonally propagated plants were grown in sand culture without Zn for 6 weeks prior to the initiation of the Zn treatments. The plants were then irrigated for 3 weeks with half-strength Hoagland's nutrient solution containing 0, 2.5, 5.0, or 40 mg·L-1 Zn from ZnSO4. Color was the only parameter affected by genotype; each genotype showed a significant quadratic response to increasing levels of Zn, with highest color ratings occurring at 2.5 mg·L-1. No genotypic differences were observed among CB, VAB, and FAB for shoot fresh and dry weight, root dry weight, or shoot tissue Zn concentrations. Shoot dry weight of all genotypes increased quadratically with Zn levels. Root dry weights of both VAB and FAB increased, while that of CB remained unchanged, as Zn level increased. Zinc concentrations in shoot tissue increased linearly as Zn level increased. Shoot Zn concentrations were higher in both VAB and FAB than in CB at each Zn level, but differences between VAB and FAB were insignificant. Maintaining shoot Zn concentrations below 109 mg·kg-1 in CB and 200 mg·kg-1 in VAB or FAB prevented Zn phytotoxicity from occurring.

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Pierce's Disease (PD) is a major factor limiting grape production in the southeast United State. This disease is caused by a bacterium, Xylella fastidiosa Wells et al., which is transmitted to the xylem system of the grapevines primarily by glassy-winged sharpshooters (Homalodisca coagulata Say). Once it is in the xylem, the X. fastidiosa will use the xylem sap as a nutrient source to multiply, colonize, and eventually plug the xylem vessels and cause the PD in susceptible cultivars. On the other hand, symptoms of PD in tolerant cultivars do not appear until fruit maturation, and symptoms are rarely observed in PD resistant cultivars. In order to understand the correlation between X. fastidiosa and PD symptom development, a study was initialed to monitor X. fastidiosa in xylem of resistant, tolerant, and susceptible vines on a monthly basis. Presence of X. fastidiosa was detected directly from xylem sap of field-grown vines by medium culture and confirmed by polymerase chain reaction (PCR). Xylella fastidiosa was detectable throughout the growing season in PD susceptible cultivar `Chardonnay', PD tolerant Florida hybrid grape `Blanc du Bois', and muscadine cultivar `Carlos'. The bacteria were also appeared in the dormant vines with high density in cultivars `Chardonnay' and `Blanc du Bios'. Although X. fastidiosa was also found in dormant canes of `Carlos', the density decreased throughout the late fall and winter months, and they were hardly found before June. The results indicated that X. fastidiosa were carried over from previous season in cultivars `Chardonnay' and `Blanc du Bois', while in PD tolerant cultivar `Carlos', they were newly acquired from the sharpshooter feedings during the growing season.

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Muscadine grape industry in the southeastern United Sates is expanding in recent years. To provide necessary information for the growing industry, 50 muscadine grape cultivars were evaluated for vigor and fruit characteristics at Florida A&M Univ., Tallahassee, Fla. Vine vigor was measured by winter pruning weight and varied from 5.4 lb/vine to 35.7 lb/vine. Among these cultivars, Triumph, Summit, and Tara were the least vigorous, while `Carlos', `Fry Seedless', and `Gold Isle' produced the most pruning weight. Dry scar ranged from 60.6% (Darlene) to 97.7% (Dixie Red). Among the most important table grapes, `Nesbitt', `Alachua', `Jumbo', `Fry', `Triumph', and `Scarlete' showed more than 70% of dry scars. Fruit rot ranged from 0.3% (Gold Isle) to 31.8% (Dixie Land). `Noble', `Scarlet', `Nesbitt', and `Carlos' were the important cultivars with less than 5% rotted fruits. Commercial fruit index were different significantly among the cultivars, ranged from 45.5% to 96.4%. Higher commercial fruit index of table grapes were found with `Magnolia', `Rosa', `Scarlet', and `Tara', while `Dixie Land' (45.5%) was the least. Seeds per fruit varied among the cultivars, ranging from 2.4 to 4.9. Fewer fruit seeds were found in `Fry' and `Nesbitt', while `Granny Val', `Senoria', `Darlene' and `Triumph' had more seeds per fruit than the others. Seed size also differed among the cultivars. `Sugar Pop' had the largest seeds (0.144 g/seed), which was twice as the size of the smallest seeds of `Welder' (0.056 g/seed). Fruit soluble solids content (SSC) ranged from 11.7% to 16.9% among the cvs. evaluated. Higher SSCs were found in `Welder', `Fry Seedless', `Scarlet', and `Cowart', while `Senoria' and `Jumbo' had relatively low SSC.

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`Pam' is a popular muscadine grape (Vitis rotundiforia) used for the fresh fruit market. It is characterized with large berry, nice appearance, good texture and flavor, and high disease resistance. This cultivar, however, requires pollinators because it is pistillate. To select a better pollinator for this pistillate cultivar, a 2-year study was conducted at Florida A&M University in 2003 and 2005. Fresh pollen of muscadine grape `Alachua', `Nesbitt', and `Noble' was used for pollination. `Nesbitt' pollen resulted in 100% of the pollinated clusters setting fruits in both years, while pollination with `Alachua' yielded 70% (2003) to 87% (2005) of fruiting clusters, and `Noble' pollen yielded 72% (2003) and 97% (2005) fruiting clusters, respectively. Fruit numbers per fruiting cluster also varied among pollen sources. `Alachua' pollen resulted in 7.2 (2003) and 8.1 (2005) fruits per cluster, while `Nesbitt' produced 10.1 (2003) to 10.5 (2005) fruits per cluster, and `Noble' produced 8.3 (2003) and 9.0 (2005) berries per cluster. Open pollinated `Pam' had 100% clusters set fruits, averaging about 11 fruits per cluster in both seasons. No difference of berry size was observed among fruits produced from different pollen sources. Both sugar contents and acids levels were a little bit higher in 2005 than that in 2003. However, no differences of sugar content and acid level were found among the fruits derived from different controlled pollen sources. These data suggested that `Nesbitt' is a better pollinator than `Alachua' and `Noble' for `Pam' muscadine grape.

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Low frequency of in vitro regeneration has hampered the adoption of genetic engineering technique for improving the quality of muscadine grape. This study is to develop a straightforward method for high-frequency regeneration of muscadine grapes in vitro. Leaves, petioles, and immature ovules of muscadine grapes were cultured on various media. Embryogenic callus, somatic embryos were formed after 9 weeks inoculated on embryo rescue (ER) medium. The somatic embryos were isolated and subcultured on fresh medium to promote enlargement and increase the number of uniformly sized somatic embryos. Of the medium tested (MS, NN, and ER), the ER medium was the best for somatic embryo growth and multiplication. The somatic embryogenic lines were maintained by transferring the embryos to the fresh ER medium every 4 weeks. Germination was achieved by transferring these embryos to woody plant medium or NN medium. The frequency of somatic embryogenesis of embryo germination appeared to be genotype dependent. The establishment of the somatic embryogenesis system in this study should be a step forward in directly transferring a foreign gene into muscadine grape.

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Ploidy level in grapevines varies, especially since in vitro techniques are employed in the breeding process and after plants are treated with either chemicals or radiation. Detection of ploidy level in grapevines by microscopic chromosome counting is complicated by their high number and the small size of chromosomes. Flow cytometry provides an accurate and rapid method in determining the ploidy level in plant tissue by measuring the nuclear DNA content in living cells and thus is a very useful tool in plant breeding or genetic studies. The objective of this research was to analyze the ploidy level of a selected group of muscadine vines that were different from normal diploid vines in morphology. These grapes were derived from either chemical treatment of known varieties or from controlled/open pollinations. Among the 26 grapevines investigated, 8 were found to be diploids, 11 were tetraploids, and 7 were chimeric aneuploids. Results of this study indicate that flow cytometry is a quick, reliable tool for determining ploidy levels of grapevines.

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Biotechnology has great potential for grape genetic improvement. However, successful implementations of grape biotechnologies, such as transformation and in-vitro selection, are based on a high yield productivity of synchronized somatic embryos as well as an efficient single-cell regeneration system. Suspension culture has been known as an ultimate approach to provide those requirements. We recently developed the highly repeatable protocol for PEM suspension culture of `Autumn Royal Seedless' (Vitis vinifera L.). In a following experiment, three factors, including activated charcoal (AC), darkness, and full- or half-strength MS medium were tested for their impact on grape embryogenesis of PEM suspension cells. All three factors proved to be important for grape somatic embryogenesis. Darkness was the most-influenced factor among the three. After 4 weeks on full-strength MS medium plus AC, suspension cells mostly grew friable callus and somatic embryos were rarely observed under 16-h light conditions, whereas numerous somatic embryos were fully developed in darkness. Strength of MS medium and AC also affected grape somatic embyogenesis. In every combination tested, full-strength MS media was all superior to half-strength, which was more obvious under darkness. The AC had a positive effect for promoting of somatic embryogenesis.

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Drought stress is a major factor in turfgrass management; however, the underlying mechanisms of turfgrass drought tolerance are not well understood. This greenhouse study was designed to investigate proline and hormone responses to drought stress in two tall fescue [Festuca arundinacea (Schreb.)] cultivars differing in drought tolerance. The two cultivars, Van Gogh (relatively drought-tolerant) and AST7002 (relatively drought-sensitive), were established and grown under either well-watered (maintaining 90% container capacity) or drought stress (≈26% container capacity) and then re-watered. Drought stress reduced turfgrass quality, relative leaf water content (LWC), leaf indole-3-acetic acid (IAA) and cytokinin zeatin riboside (ZR) content, and increased proline and abscisic acid (ABA) content. ‘Van Gogh’ had greater turfgrass quality rating, LWC, proline, ABA, and ZR content relative to ‘AST7002’ under drought stress conditions. At the end of drought stress, leaf proline, ZR, and ABA content were 32%, 43%, and 50% higher in ‘Van Gogh’ relative to ‘AST7002’, respectively. No cultivar difference was observed under well-watered conditions. The results of this study suggest that the proline, ABA, and ZR content are associated with drought tolerance. Selection and use of the cultivars with higher proline, ABA, and ZR content under drought stress may be a practical approach to improve tall fescue drought tolerance.

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Herbaceous peony (Paeonia lactiflora Pall.) is a well-known ornamental plant with abundant flower colors. However, our understanding of the underlying mechanisms of flower color formation is limited. In this study, a wild sample of herbaceous peony (collected from Heze, China) and eight cultivars with different colors were selected for experimental investigation. The Royal Horticultural Society Color Chart was used to determine flower color, and the anatomic structure; cell sap pH value; moisture content (MC); condensed tannin content (Ct); soluble sugar and soluble protein content of the petals; and content and composition of anthocyanin, flavonoids, and carotenoids in the petals were examined. 1) In the white, pinkish white, pale purple, purplish pink, and reddish purple cultivars, deeper color was associated with greater total amounts of anthocyanin (TA). Hypochromic effects were observed for kaempferol-7-O-glucoside (Km7G), myricetin-3-rhamnoside (My3R), and luteolin-7-O-glucoside (Lu7G). The accumulation of quercetin-3-O-glucoside (Qu3G) and lutein affected yellow color formation in the petals. 2) There are papillate epidermal cells in the petals of the wild P. lactiflora sample, ‘Lanyucangjin’, and ‘Dongjingnvlang’. 3) Cell sap pH and MC of the petals of white, pinkish white, pale purple, and purplish pink cultivars were greater than those of the purplish red and most of the reddish purple cultivars. 4) The Ct was greatest in the purplish red cultivars, whereas no condensed tannins were detected in the white, pinkish white, and pale purple cultivars. 5) There were no significant correlations among soluble sugar content, soluble protein content, and the other physiological indications.

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