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James F. Harbage and Dennis P. Stimart

Many physiological responses in plants are influenced by pH. The present chemiosmotic hypothesis suggests that auxin uptake into plant cells is governed by pH. Since auxin is used widely to enhance rooting, the influence of pH on 1H-indole-3-butyric acid (IBA) induced adventitious root formation was examined. Roots were initiated aseptically in 5 node apical shoot cuttings of micropropagated Malus domestica 'Gala'. Initiation was induced using a four day pulse in IBA and 15 g/L sucrose at pH 5.6 and 30C in the dark. Observations showed pH rose to 7.0 or greater within 1 to 2 days from microcutting placement in unbuffered initiation medium. Root numbers from shoots in media containing 1.5 μM IBA buffered with 10 mM 2[N-morpholino] ethanesulfonic acid (MES) to pH 5.5, 6.0, 6.5 or 7.0 with KOH resulted in average root numbers of 14.2, 10.9, 8.7, and 7.1, respectively, while unbuffered medium yielded 7,6 roots per shoot. Comparison of MES buffered medium at pH 5.5, 6.25 or 7.0 in factorial combination with IBA at 0, 0.15, 1.5, 15.0, and 150.0 μM resulted in a significant pH by IBA interaction for root number. At 0, 0.15 and 1.5 μM IBA root numbers were greatest at pH 5.5. At 15.0 μM IBA, pH 6.25 was optimal and at 150.0 μM IBA all three pH levels produced equivalent root numbers. A calorimetric assay to measure IBA removal from the initiation medium by microcuttings of `Gala' and `Triple Red Delicious' showed more IBA removal at pH 5.5 than at pH 7.0. Possible reasons for the effect of pH on adventitious root formation will be discussed.

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Fuad Gasi, Silvio Simon, Naris Pojskic, Mirsad Kurtovic, Ivan Pejic, Mekjell Meland and Clive Kaiser

. Talaie, A. Oraguzie, C.N. Fatahi, R. Hajnajari, H. Wiedow, C. Gardiner, S.E. 2009 Genetic identity and relationships of Iranian apple ( Malus × domestica Borkh.) cultivars and landraces, wild Malus species and representative old apple cultivars based

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Jan Bizjak, Nika Weber, Maja Mikulic-Petkovsek, Ana Slatnar, Franci Stampar, Zobayer Alam, Karl Stich, Heidi Halbwirth and Robert Veberic

mechanism, by which P-containing compounds affect the red coloration of apples. Materials and Methods Plant materials. The experiment was carried out in 2011 on 10-year-old trees of striped ‘Braeburn’ ( Malus domestica Borkh.) cultivar clone Hillwell

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S. Mantha, H. Desilets, J.-A. Rioux, S. Gagne, S. Parent and P. Moutoglis

Two experiments with Malus domestica sp. were planted in 1997 at the Laval Univ. experimental farm located south of the St. Lawrence river near Quebec City. These experiments examined the association of the mycorrhizal fungus Glomus intraradices with Malus domestica sp. The first experiment compared the vegetative growth of `McIntosh' apple trees on M.106 rootstock in presence or absence of a commercial inoculum of G. intraradices (Premier Tech, Riviere-du-Loup, Quebec) under three levels of phosphorus fertilization (P) to the soil (0%, 50%, and 100% of the usual recommandation for this crop). After two seasons, all the treatments had better growth than the control (0% P without G. intraradices). The best treatment was achieved with 100% of the P associated with mycorrhizal inoculation. The second experiment compared the vegetative growth of three apple rootstocks Bud.9, M.26, and M.106, inoculated with G. intraradices under the same three P levels as the preceding experiment. Uninoculated rootstocks receiving the usual phosphorus fertilization served as control. Two roostocks, M.26 and M.106, increased growth with G. intraradices, while the third one, Bud.9, did not respond to the presence of mycorrhizal fungus.

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M.E. Garcia and Linda A. Boccuzzo

Hardiness testing of the wood of deciduous fruit trees has been conducted using a variety of techniques. In our studies, the objective was to determine an efficient method of determining freezing injury for apple (Malus × domestica Borkh.) wood. We tested 1-year old wood of two cultivars: Liberty and RedMax. The wood was tested over the course of 2 years (1998 and 1999). Collection began in the late fall and continued throughout the winter (until it was determined full hardiness had been achieved) and then again in the early spring. The wood was cut into 1-cm sections and frozen. The artificial freezing was conducted in an ethanol bath, with the temperature lowered at 5 °C/h. Samples were removed in 3-min intervals. After freezing, the wood was acclimated to 4 °C for 12 h. Three tests were conducted to determine the hardiness/injury to the tissues. The tests used were: discoloration, callus growth and vital staining (with 2,3,5-triphenyltetrazolium chloride). This was a split block design with samples collected randomly from each tree. Four replicates (12 trees) of each cultivar were tested. Results showed that the callus test predicted the same LT50 as the other two tests, discoloration and vital staining. Discoloration was not easy to differentiate and was the most time-consuming. The callus grown by the apple wood was easily formed and distinguished. The callus test does not require the tetrazolium stain; therefore, one less step was needed in comparison to the vital staining test. This reduced testing time by over 6 h.

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Shiow Y. Wang, Miklos Faust and Michael J. Line

The effect of Indole-3-acetic acid (IAA) on apical dominance in apple (Malus domestica Borkh.) buds was examined by studying changes In proton density (free water) and membrane lipid composition in lateral buds. Decapitation induced budbreak and enhanced lateral bud growth. IAA replaced apical control of lateral bud paradormancy. Maximal inhibition was obtained when IAA was applied immediately after the apical bud was removed. Delaying this application weakens the effect of IAA. An increase in proton density in lateral buds was observable 2 days after decapitation, whereas the change in membrane lipid composition occurred 4 days later. Decapitating the terminal bud induced an increase in membrane galacto- and phospholipids. and the ratio of unsaturated to corresponding saturated fatty acids. Decapitation also induced a decrease in the ratio of free sterols to phospholipids in lateral buds. Application of IAA to the terminal end of decapitated shoots inhibited the increase of proton density and prevented changes in the membrane lipid composition of lateral buds.

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Edwin J. Reidel*, Brian G. Ayre, E. Robert Turgeon and Lailiang Cheng

Sorbitol (d-glucitol) is the major end product of photosynthesis in apple (Malus domestica Borkh.), as well as the predominant phloem-translocated carbohydrate. The mechanism by which sorbitol is phloem-loaded for transport to heterotrophic sink tissues is unknown. We hypothesized that a plasma membrane-bound H+/sorbitol symporter mediates apoplastic phloem-loading of sorbitol. To discover genes potentially encoding sorbitol transporters, a cDNA library was constructed from mature `Gala' apple leaves. A homologous probe was synthesized via PCR with primers were designed against the cherry fruit sorbitol transporter, PcSot1, and using library lysate as template. From an initial plating of approximately 5 × 105 clones, twelve positives were identified after three rounds of hybridization screening. Following single-pass, 5' end sequencing, the clones were sorted into four contiguous sequences. One clone was chosen from each contig for complete sequencing. The four clones, provisionally named MdSOT1-4 (Malus domesitca Sorbitol Transporter), potentially encode full-length cDNAs for sorbitol transporters: Translated-BLAST searching (blastx) revealed that the open reading frames encode the complete Pfam sugar transporter domain, and the most significant alignments are with sequences encoding known- and putative polyol and sugar transporters.

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Q. Liu, S. Salih, J. Ingersoll, R. Meng, L. Owens and F. Hammerschlag

Transgenic `Royal Gala' apple (Malus × domestica Borkh.) shoots were obtained by Agrobacterium-mediated gene transfer using the plasmid binary vector pGV-osm-AC with a T-DNA encoding a chimeric gene consisting of a secretory sequence from barley-amylase joined to the modified cecropin MB39 coding sequence. Shoots were placed under the control of a wound-inducible, osmotin promoter from tobacco. The integration of the cecropin MB39 gene into apple was confirmed by Southern blot analysis. The transformation efficiency was 1.5% when internodes from etiolated shoots were used as explants and 2% when leaf explants were used. Both non- and transgenic tetraploid plants were produced by treatment of leaf explants with colchicine at 25 mg·L-1, and polyploidy was confirmed by flow cytometry. Of the diploid transgenics, three of seven were significantly more resistant to Erwinia amylovora than the non-transgenic `Royal Gala' control. Also, in one instance, a tetraploid transgenic was significantly more resistant than the diploid shoot from which it was derived.

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Mekjell Meland and Clive Kaiser

‘Summerred’ apples (Malus domestica Borkh.) are highly susceptible to biennial bearing if not properly thinned. This results in erratic yields and also affects fruit quality adversely. Between 2003 and 2005, ‘Summered’/‘M9’ trees were treated with ethephon at concentrations of 250, 375, and 500 mg·L−1 when most king flowers opened (≈20% bloom) or at concentrations of 500, 625, and 750 mg·L−1 when the average fruitlet size was 10 mm in diameter. The experiment was conducted with 2.5-m height slender spindle trees sprayed to the point of runoff with a hand applicator only when temperatures exceeded 15 °C. Within 2 weeks after the second application, fruit set was reduced linearly with increasing concentrations of ethephon to less than one fruitlet per cluster at the highest concentrations used. Most thinning treatments reduced fruit set significantly compared with unthinned trees. Fruit numbers per tree decreased significantly with increasing ethephon concentrations, and the highest concentrations of ethephon applied during bloom or when the average fruitlet size was 10 mm in diameter resulted in overthinning. Yield results confirmed the fruit set response in which yield reductions were significant at the highest concentrations of ethephon (2.1 kg/tree) compared with hand-thinned trees (7.3 kg/tree) in 2005. All thinning treatments resulted in higher percentage of fruits larger than 60 mm diameter compared with unthinned control fruit. Thinning resulted in significantly higher soluble solid contents, and this was especially so for hand-thinned trees. Other fruit quality parameters like yellow–green background color did not show a clear response to thinning. Return bloom was, however, improved on all thinned trees. It is recommended that ethephon be applied at a rate of 375 mg·L−1 when king flowers open or at a rate of 625 mg·L−1 when the average fruitlet size is 10 mm in diameter. This thins ‘Summerred’ apples to a target of approximately five fruits/cm2 per trunk cross-sectional area or 50 to 70 fruits per 100 flower clusters without impacting on fruit quality, yield, or return bloom the next year.

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Neal Mays, Curt Richard Rom, Kristofor R. Brye, Mary C. Savin and M. Elena Garcia

soil erosion ( Carter, 2002 ; Karlen et al., 1992 ; Kemper and Rosenau, 1986 ). Surface crusting and erosion may be reduced or eliminated in orchards with application of non-living groundcover mulches. Mulches useful for organic apple ( Malus