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Jeff Olsen

Hazelnuts in Oregon are grown on 30,000 acres by ≈1000 orchardists in the Willamette Valley. Their annual production accounts for 3% to 5% of the world's hazelnut tonnage. The trees are grown in a single trunk system wrtb an average spacing of 20 feet between trees. Mechanical harvestihg is done in October. The industry employs an Integrated Pest Management approach, utilizing combinations of scouting, trapping, and biological control. The main insect pests are filbertworm, filbert leafroller, obliquebanded leafroller, and filbert aphids. The aphid parasite Trioxys pallidus was imported from Europe and successfully established in Oregon. Eastern Filbert Blight, Anisogramma anomala, a fungus disease, is the most serious disease problem in the industry. Annual applications of nitrogen to the soil and boron applied to the foliage are routine for Oregon's hazelnut growers. OSU research has quantified the importance of good light distribution in the tree canopy for increased nut production. OSU recommends a 5-year rotational pruning program. Some growers use mechanical hedging instead of hand pruning. OSU is home to the world's largest hazelnut breeding program. `Barcelona' is still the main, cultivar grown, while `Ennis' is the main in-shell variety. There is growing interest in planting varieties with a high percent kernel, such as `Casina', `Willamette', and `Lewis'.

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T.E. Thompson and L.J. Grauke

Precocity of pecan [Carya illinoinensis (Wangenh.) C. Koch] seedlings (year of first fruit production) was studied in relation to original seed measurements (nut weight, buoyancy, volume, and density) and in relation to growth index (GI) measurements of seedling trees for 4 years. A total of 2,071 pecan seedlings, representing nine controlled-cross families, were studied. Original seed measurements were not related to precocity of resultant seedling trees; but seed weight, buoyancy, and volume were significantly correlated with seedling growth rates. Nut density was negatively related to growth of seedlings. These relationships show the importance of original seed measurements and seed parentage in determining seedling growth, and have direct relevance in pecan nursery operations to increase general rootstock seedling vigor. Seedling growth rate was significantly correlated to precocity levels, with measurements taken in the later years of the study showing the highest correlations with precocity. This strong growth-precocity relationship may have negative genetic implications since a common breeding objective is to produce more precocious cultivars that maintain smaller tree size in mature orchards.

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Takaya Moriguchi, Kazuyuki Abe, Tetsuro Sanada, and Shohei Yamaki

Japan. Contribution no. A-281 of the Fruit Tree Research Station. We thank S. Hayashi for assistance in conducting the present study and members of Breeding 2nd Laboratory for kind suggestions. The cost of publishing this paper was defrayed in part by

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John A. Muir and Richard S. Hunt

Introductions of white pine blister rust (WPBR, causal fungus: Cronartium ribicola J.C. Fischer) to eastern and western North America before 1915 caused such extensive damage that western white pine (Pinus monticola D. Don) was essentially abandoned as a manageable forest tree species for over 60 years. Recent results from WPBR resistance selection and breeding programs, and from field trials of tree spacing, pruning and bark excision treatments have supported efforts to increase establishment and to intensively manage western white pine. Western white pine is a desirable component in many forested areas because of its faster growth and much higher value compared to many other associated tree species. It also has a low susceptibility to armillaria root disease caused by Armillaria ostoyae (Romagnesi) Herink and laminated root rot, caused by Phellinus weirii (Murr.) Gilb. Some regulations, e.g., Forest Practices Code of British Columbia (BC) Act, require anyone who harvests timber on provincial forestland and uses western white pine for reforestation to either plant genetically resistant western white pine stock or prune susceptible young trees for protection. Risks of increased WPBR associated with increased commercial cultivation of gooseberries and currants (Ribes L.) have yet to be determined. However, major threats appear to include 1) increase in local amounts of spores for nearby infection of pines; and 2) possible introductions or development of new, virulent races of C. ribicola, particularly from eastern to Pacific northwestern North America. In view of these possible threats, we recommend that existing regulations and legislation should be amended, or possibly new measures enacted, to permit propagation and commercial cultivation only of varieties of Ribes that are immune or highly resistant to WPBR.

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J. D. Norton

The Chinese chestnut (Castanea mollissima) has been cultivated in China for more than 1000 years. During this period, indigenous cultivars and traditional cultivation practices have been used. China is the leading producer of Chinese chestnut (Castanea mollissima) with 37% of the world' s production. In the last 4 years, improved cultivars and improved cultural practices have resulted in marked increases in production.

The leading provinces in Chestnut production are Hopei, Hubei, and Shandong. Severe injury, crop losses and tree mortality have resulted from the chestnut gall wasp in China Yields have increased greatly in Hubei province through cooperative breeding and developmental research between the Department of Horticulture Auburn University and the Hubei Academy of Agricultural Sciences. Two resistant seedlings from Auburn University are being utilized to save the chestnut industry in China and possibly worldwide.

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J.D. Norton, G.E. Boyhan, and B. Tangsukkasemsan

Plum leaf scald (PLS) caused by the organism Xylella fastidiosa is one of the most serious diseases of plum. After X. fastidiosa was identified as the causal agent for PLS, a feral source (Starcher no. 1) was used extensively in the breeding program. Microscopic (phase contrast) examinations of vacuum extracts and petiole squashes and later ELISA were used to determine PLS infection and later were correlated with a rating index for PLS and tree longevity. Cultivars, species, and their progeny, including Prunus americana, P. angustifolia, P. cerasifera, P. munsoniana, P. salicina, P. simoni, P. bullata, and P. triflora were evaluated. Observations indicate that resistance is heritable and controlled by recessive genes. ELISA and visual observation indicated that an Auburn Univ. seedling (CD 122) was free from this disease.

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Jocelyne Kervella, Loïc Pagès, and Michel Génard

Genotypic variations in the length-diameter relationship of branches among peach and nectarine [Prunus persica (L.) Batsch.] cultivars were investigated. The length and basal diameter of all undamaged first-order shoots from 1-year-old trees of 14 cultivars and one accession were measured. Statistical analysis of the allometric relationship between length and basal diameter of shoots provided evidence of genotypic differences for that relationship, although the diameter of very short shoots did not differ between genotypes. A gradient existed from `Armking' with thin shoots (9 mm in diameter for 85.5-cm-long shoots) to `Flavorcrest' with thick shoots (16.4 mm in diameter for 85.5-cm-long shoots). Early selection for shoot thickness should be possible in breeding programs. The likely consequences of observed shoot thickness variations on the mechanical and hydraulic properties of shoots are discussed.

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Duane W. Greene and Wesley R. Autio

77 POSTER SESSION 10 (Abstr. 90-621) Tree Fruits/Nuts: Culture & Management

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Robert D. Belding

The potential mechanism of susceptibility of apple (Malus ×domestica Borkh.) fruit to sooty blotch due to carbohydrate leachates was examined. Fruit received applications of 0.5% apple juice to the fruit cuticle in order to mimic leachates. Nine cultivars of apple were selected from a variety block of potentially disease resistant breeding stock. Intact fruit on selected limbs received 0.5% apple juice applications on eight evenly spaced occasions during development. Trees received a minimal fungicide program only. Leachate samples from the fruit cuticles were collected monthly by immersion of whole, detached fruit in dH2O for 60 min. At harvest, fruit were evaluated for skin roughness, fruit rots, sooty blotch, sooty mold, flyspeck, and insect injury. Despite drought conditions, sooty blotch and sooty mold showed strong increases in disease intensity ratings, while flyspeck and skin texture damage showed moderate increases in intensity due to the dilute juice applications. Fruit rots and insect damage were unaffected by the juice applications.

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Jude W. Grosser

Citrus protoplast technology has advanced to where several practical applications in variety improvement and plant pathology are routine. We will report on progress in the following areas: somaclonal variation—`Valencia` and `Hamlin' sweet orange protoclones have been selected for improved juice color, higher soluble solids, seedlessness, and altered maturity dates; somatic hybridization for scion improvement—allotetraploid breeding parents have been created from numerous combinations of elite parental material, and are now being used as pollen parents in interploid crosses to produce seedless triploid varieties; somatic hybridization for rootstock improvement—numerous somatic hybrids combining complementary rootstock germplasm are under commercial evaluation and several look promising for wide adaptation, improved disease resistance, and tree size control; transformation—an alternative protoplast-based transformation that utilizes EGFP for selection has been developed; virus resistance assays—a protoplast-based assay is being used to screen varieties and candidate sequences for resistance to citrus tristeza virus at the cell level, saving time and greenhouse space.