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Chang-Hoo Lee, N. I. Hyung, and S. E. Kim

Experiments were conducted to investigate the factors influencing mesophyll protoplast isolation in `Fuji' apple. Half an hour pretreatment in 0.6M mannitol gave the highest protoplast yield.The enzyme solution containing 2% Cellulase Onozuka R-10 and 0.5% macrozyme R-10 with CPW 0.6M mannitol at pH 5.5 was most effective for protoplast isolation from leaf. Effective incubation time for the enzyme treatment was found to be 15-20 hrs at 25°C in the dark. Use of 1.0-2.0% PVP and 0.5mM MES was essential for higher yield and viability of protoplast. Supplementation of BA and IBA to the shoot culture media gave the higher yield of viable protoplast. From these protoplast, new cell walls were regenerated and 4 cell structures developed from one protoplast by cell division in K8P medium supplemented with 3A and NAA. Planting density higher than 10 protoplasts/ml was required for cell division from protoplast in liquid or 0.5% agarose culture.

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James Luby, Philip Forsline, Herb Aldwinckle, Vincent Bus, and Martin Geibel

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Dorcas K. Isutsa, Ian A. Merwin, and Bill B. Brodie

Orchard replant disorder (ORD) is a widespread soilborne disease complex that causes stunting and poor establishment of replanted fruit trees. Chemical and cultural control of ORD provide effective, but short-term, control. More-sustainable strategies would involve ORD-resistant rootstocks not yet identified in apple. We tested `Bemali', G11, G13, G30, G65, G189, G210, and G707 clones from the apple rootstock breeding program at Geneva, N.Y., for their response to ORD in a composite soil collected from New York orchards with known replant problems. Clones were tested in the greenhouse in steam-pasteurized (PS), or naturally infested field soils (FS) with about 900 Pratylenchus penetrans and 150 Xiphinema americanum per pot. Plant dry mass, height, root necrosis, and nematode populations were determined after 60 days under optimal growing conditions. Stunting, reduced plant dry mass, and root necrosis were more severe in FS than in PS for most of the clones (P ≤ 5%), but G30 and G210 were substantially more tolerant to replant disorder than smaller ones, but this toleratnce might not be sustained in fields with greater or more prolonged nematode infestations. There is sufficient variation in apple rootstock resistance or tolerance to ORD to suggest that genetic resistance may be identified and developed for better management of orchard replant problems.

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Adriana C. de M. Dantas, Gerson R. de L. Fortes, Sergio D. dos Anjos e Silva, and João Baptista da Silva

This work aimed to evaluate apple rootstock somaclones by characterizing the genetic variability among them. The isoenzymatic systems were used for analyzing variability as follows: FAC (acid phosphatase), PRX (peroxidase), and 6-PGD (6-phosphogluconate dehydrogenase). The migration were performed by applying a potential difference around 10 volt/linear cm. A data matrix was built so that the genotypes were placed in the lines and the bands in the columns. The scores were attributed as follows: band present (1) and band not present (0). By the gel analyses in relation to the presence/absence and band intensity, we observed marked differences among the somaclones and within somaclones as well. In the peroxidase system a higher band polyimorphism was detected with 18 enzymatic patterns. The group analyses for the 73 apple somaclones revealed a large variability through the enzymes (18 peroxidases, 8 FAC, and 6 6-PGD), which were classified into two groups. Group I was represented by M.7 somaclones with seven subgroups with 43% similarity among the clones. Differences among M.9 and M.111 cultivars and two clones referred to as M9b and M925 were fitted within somaclones M.111. The remaining somaclones of cultivar M.9 showed a higher variability bearing 43 subgroups. Clones M929, M930 and M932 presented 100% similarity.

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Michael J. Perry, Preston K. Andrews, and Robert G. Evans

`Fuji' apples grown in the high light intensity of arid eastern Wash. are prone to sunscald damage. Evaporative cooling with over-tree sprinklers has become a commercially acceptable method for reducing the incidence of sunscald damage. A computer-controlled, over-tree evaporative cooling system was installed in a 3-yr-old commercial `Fuji'/M.9 orchard near Walla Walla, Wash. Over-tree sprinklers (Nelson R10 Mini Rotators) applied 280 or 560 1·min-1·ha-1 (30 or 60 GPM/A) when core temperatures were ≥33C (91.4F). Fruit skin and core temperatures were monitored with thermocouples. Fruit growth was not different between treatments. Skin color was improved by cooling, but the incidence of sunscald was low in all treatments. Commercial pack-out was measured and culls were evaluated. Fruit quality was analyzed at harvest and after 14 weeks storage. Titratable acids and soluble solids were higher in the 560 1·min-1·ha-1 treatment at harvest.

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Frank Cheng, Norman Weeden, and Susan Brown

The ability to pre-screen apple populations for fruit color at an early seedling stage would be advantageous. In progeny of the cross `Rome Beauty' × `White Angel' red/yellow color variation was found to be highly correlated with the genotype at Idh-2, an isozyme locus that was heterozygous in both parents. We postulate that the red/yellow color variation was produced by a single gene linked to I&-2 and also heterozygous in both parents. This population was also screened with over 400 primers to detect randomly amplified polymorphic (RAPD) markers for fruit color. DNA extraction procedures were developed for bark, and DNA was extracted from bark samples and leaves. Red and yellow fruited individuals were examined in bulk. Several markers have been found that are linked to red color. A high density map is being constructed in this region. These markers are being examined in other crosses segregating for fruit color. The application of these markers will be discussed in relation to the inheritance and manipulation of fruit color.

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Stan C. Hokanson, James R. McFerson, Philip L. Forsline, Warren F. Lamboy, James J. Luby, Aimak D. Djangaliev, and Herb S. Aldwinckle

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James F. Harbage, Dennis P. Stimart, and Ray F. Evert

Anatomical events of adventitious root formation in response to root induction medium, observing changes during induction and post-induction stages, were made with microcuttings of `Gala' apples. Shoot explants on root induction medium containing water, 1.5 μm IBA, 44 mm sucrose, or 1.5 μm IBA + 44 mm sucrose after 4 days of treatment averaged 0, 0.2, 2.2, and 11.9 meristemoids per microcutting, respectively. Meristemoids formed in response to sucrose were confined to leaf gaps and traces. Time-course analysis of root induction with 1.5 μm IBA + 44 mm sucrose over 4 days revealed that some phloem parenchyma cells became densely cytoplasmic, having nuclei with prominent nucleoli within 1 day; meristematic activity in the phloem was widespread by 2 days; continued division of phloem parenchyma cells advanced into the cortex by 3 days; and that identifiable root primordia were present by 4 days. Cell division of pith, vascular cambium, and cortex did not lead to primordia formation. Meristematic activity was confined to the basal 1 mm of microcuttings. Time-course analysis of post-induction treatment revealed differentiation of distinct cell layers at the distal end of primordia by 1 day; primordia with a conical shape and several cell layers at the distal end by 2 to 3 days; roots with organized tissue systems emerging from the stem by 4 days; and numerous emerged roots by 6 days. Root initiation was detectable within 24 hours and completed by day 4 of the root induction treatment and involved only phloem parenchyma cells. Chemical names used: 1 H -indole3-butryic acid (IBA).

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Roberto Hauagge and James N. Cummins

Apple seedlings have a shallow dormancy, as has been observed in many other species. The length of bud dormancy in high-chilling-requirement seedlings does not reflect their genetic constitution well if dormancy is induced before they are 200 days old. Seedling populations sprayed with paclobutrazol and/or ethephon displayed bud dormancy periods resembling those of older populations of similar genetic constitution. Terminal bud formation and dormancy could not be induced by continuously exposing apple seedlings to low temperature (8 ± 1C) and short photoperiod, even after extended periods. Stomate operation may not be completely functional under these conditions. Terminal bud formation was induced by holding apple seedlings above 20C. Additional exposure to low temperature (8 ± 1C) induced leaf fall. These findings suggest the existence of an active regulatory factor that induces terminal bud formation and dormancy and is either turned on or synthesized above 15 to 17C. Chemical names used: β- [(4-chlorophenyl)methyl]- α -(1,1-dimethylethyl)-1H-1,2,4-triazole-1-ethanol(paclobutrazol);(2-chloroethyl)phosphoric acid (ethephon).

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

The effect of IAA on apical dominance in apple buds was examined in relation to 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 buds and maintained paradormancy. Maximal inhibition was obtained when IAA was applied immediately after the apical bud was removed; delaying application reduced the effect of IAA. An increase in proton density in lateral buds was observed 2 days after decapitation, whereas the change in membrane lipid composition occurred 4 days later. Removing the terminal bud increased membrane galacto- and phospholipids and the ratio of unsaturated to corresponding saturated fatty acids. Decapitation also decreased the ratio of free sterols to phospholipids in lateral buds. Applying thidiazuron to lateral buds of decapitated shoots enhanced these effects, whereas applying IAA to the terminal end of decapitated shoots inhibited the increase of proton density and prevented changes in membrane lipid composition in lateral buds. These results suggest that change in water movement alters membrane lipid composition and then induces lateral bud growth. IAA, presumably produced by the terminal bud, restricts the movement of water to lateral buds and inhibits their growth in apple.