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Joan Lordan, Miquel Pascual, Francisco Fonseca, Víctor Montilla, Josep Papió, Josep Rufat, and Josep M. Villar

that require long-term sampling, especially during periods of active growth when shape and size of the leaves change rapidly ( Baker et al., 1996 ). Other common methods to determine fruit tree growth and development include the measurement of TD and

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Andrew I. Samuelsen, Sumontip Bunnag, Ruth C. Martin, David W. S. Mok, and Machteld C. Mok

Two approaches are used to improve iron utilization of fruit trees under iron-limiting conditions: 1) selection of somaclonal variants; and 2) cloning and incorporation of genes encoding Fe(III) reductases. Two somaclonal variants of quince with tolerance to low iron availability have been selected from 2000+ shoots regenerated from leaf discs. In greenhouse tests, under iron stress conditions, the variant clones continued to show improved iron utilization, having significantly higher chlorophyll concentrations in the new leaves when compared to the quince control. Cloning of Fe(III) reductase genes is based on mutant rescue utilizing a yeast mutant deficient in Fe(III) reduction (Dancis et al., PNAS 89:3869, 1992). A shuttle vector is used to incorporate a tomato root cDNA library into the yeast mutant. Complementing cDNAs, restoring growth to wild-type levels, are selected for further analyses. Cloning of genes involved in iron utilization will eventually lead to transgenic plants with improved iron efficiency.

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Duane W. Greene

Monografia dei Portinnesti dei Fruttiferi (Book on Fruit Tree Rootstocks) . Carlo Fideghelli and Filberto Loretti (eds.). 2009. Agricultural Research Council, Via Nazionale 82 - 00184 Rome. 239 p. In recent years rootstocks are playing an

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Ahmed A. Obeidy and M.A.L. Smith

Micrografting is an effective technique for elimination of viruses, early diagnosis of grafting incompatibilities, rejuvenation of mature tissue, and bypassing the juvenile phase in fruit trees. Current micrografting procedures are difficult, impractical, expensive, and generally result in an inefficient rate of successful graft production. In order to alleviate some of these limitations, a unique apparatus was designed to splice the in vitro-derived scion and rootstock together during the micrografting process. The dual-layer device was constructed with a pliant outer layer to facilitate manipulation during the grafting of micro-scale plants, and a delicate, absorbent inner layer to cushion the plant tissue and retain hormones and other compounds. These chemicals are slowly released at the grafting zone to alleviate oxidation and enhance callus formation at the cut surface of scion and rootstock. After healing, it is easy to remove the grafting apparatus from the grafted plant without damaging the tissues. This apparatus may be used to unite a scion and a rootstock with different stem diameters. Shoot-tip cultures of `McIntosh' and `M-7' apple and `North Star' sweet cherry, and in vitro seedlings of lemon, orange and grapefruit were used as a source of in vitro scions and rootstocks. Successful graft unions were developed, and the grafted plants were transplanted into the greenhouse environment Micrografted plants were sectioned to determine the anatomical characteristics of the graft union.

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Ahmed A. Obeidy and M.A.L. Smith

Micrografting is au effective technique for elimination of viruses, early diagnosis of grafting incompatibilities, rejuvenation of mature tissue, and bypassing the juvenile phase in fruit trees. Current micrografting procedures are difficult, impractical, expensive, and generally result in an inefficient rate of successful graft production. To alleviate some of these limitations, a unique apparatus was designed to splice the in vitro-derived scion and rootstock together during the micrografting process. The dual-layer device was constructed with an outer layer of aluminum foil, with flexibility to facilitate manipulation during the grafting of micro-scale plants. A delicate, absorbent inner layer of paper toweling cushions the plant tissue. It also may be treated with hormones and other compounds. After healing, it is easy to remove the grafting apparatus from the grafted plant without damaging the tissues. This apparatus may be used to unite a scion and a rootstock with different stem diameters. Shoot-tip cultures of `McIntosh' and M.7 apple and `North Star' sour cherry, and in vitro seedlings of lemon, orange, and grapefruit were used as a source of in vitro scions and rootstocks. Successful graft unions were developed, and the grafted plants were transplanted into the greenhouse environment.

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Liu Runjin, Xu Kun, and Liu Pengqi

The study of mycorrhizas of fruit trees was carried out in the 1980s in China. More progress has been made in resources, taxonomy, anatomy and morphology, physiology, ecology, effects, and application of mycorrhizas in fruit trees. The present status and research trends in the study of fruit tree mycorrhizas in China were introduced, and the application prospects of mycorrhizas in fruit tree cultivation also were discussed.

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J. Farias-Larios, S. Guzman-Gonzalez, and A. Michel-Rosales

The productivity of marginal soils frequently found in the arid tropics might be improved by using VAM fungi as “biofertilizer” and as a tool of sustainable agricultural systems. Study of mycorrhizas of fruit trees was performed in 1987 in western Mexico. More progress has been made in resources, taxonomy, anatomy and morphology, physiology, ecology, effects, and application of mycorrhizas in fruit trees and ornamental plants production. Currently, five genera has been identified and inoculated plants showed significant difference in respect to plants not inoculated with mycorrhizal fungi. Citrus trees were highly dependent on mycorrhizae for normal growth and development, while the banana plants showed lower levels of root colonization by different strains of VAM fungi. The added endomycorrhizal inoculum significantly increased root fungal colonization in fruit trees and reduce the time in nursery. The current status and research trends in the study of fruit tree mycorrhizas in western Mexico are introduced, and the application prospects in sustainable agriculture also are discussed.

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Makki A. Al-Kahafaji

This study was conducted during two season (1993-1994) to formulate a suitable mathematical model to determine optimal chilling conditions for deciduous fruit trees from different areas of Iraq (Baghdad, Diyala, Karbala, and Naynawa). A hygrothermograph was utilized to record the average chilling temperature: Baghdad (571), Diyala (874), Karbala (548), and Naynawa (1206). Temperature information gathered 1982-1994 from weather forecasting records also proved beneficial to our study. The model designed for this project was then used to measure optimal chilling conditions of deciduous fruit trees in 11 areas of Iraq: 1000-1200 h in northern areas (Douhook, Sulaymaniyah, Arbeel Naynawa); 700-800 h in the north central areas (Al-Taameen, Salah al din, Diyala), 500-600 h in the middle and south centeral areas (Baghdad, Karbala, Babil, Al-Najaf, Wasit), and 200 h in the southern areas (Al Qadissiyah, Thi-qar, Misan, Basrah). The chilling temeperature differences recorded in the central areas were due primairly to variations in water surface and plant coverage. Temperature proved to be the determining factor for chilling hours accumulations recorded during the growing seasons.

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Freddi A. Hammerschlag, Ghazala Hashmi, Robin Huettel, Dennis Werner, and David Ritchie

One approach for obtaining useful genetic variation is to select for somaclonal variants generated by tissue culture techniques. Increased levels of resistance to bacterial leaf spot (Xanthomonas campestris pv. pruni) have been observed in toxin-selected and unselected peach regenerants in vitro, in the greenhouse and under field conditions. Peach regenerants have also demonstrated increased levels of bacterial canker (Pseudomonas syringae pv. syringae) and root-knot nematode (Meloidogyne incognita) resistance. Random amplified polymorphic DNA (RAPD) primers have been used to study genetic variation at the DNA level among the somaclonal variants. Sixty RAPD primers (10-mers) were screened and 10 proved useful as markers to detect polymorphisms, thus establishing a genetic basis for somaclonal variation. These studies demonstrate the feasibility of using tissue culture techniques to generate fruit trees with increased levels of disease resistance.

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Y. Wakasa, R. Ishikawa, M. Niizeki, T. Harada, S. Jin, M. Senda, and S. Akada

Sequencing of the sequence tagged site-DNA marker fragments linked to the fruit skin-color gene in apple revealed two fragments containing insertions that are associated with yellow skin color, and are alleles of the red skin gene (Rf). One fragment resulted from the insertion of a 76-bp inverted repeat, whereas the 163 bp in the other fragment was characterized as a mobile element because of the presence of target site duplication. A database search found this latter element in the 5' flanking regions or intron of six apple genes. DNA blot analysis revealed that the element is highly reiterated, with a copy number of between 5000-6000 in the genome of Maloideae (pome) fruit trees. We named this element Majin. Inter-transposon amplified polymorphism using primers from this element resulted in polymorphic bands among apple cultivars.