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Michael W. Smith, William D. Goff, and M. Lenny Wells

unproductive. Wood et al. (2004a , 2004b ) conclusively demonstrated that mouse-ear was caused by nickel deficiency. Routine foliar application of a commercially available nickel product eliminated this problem. Crown gall has the broadest host range of any

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Ali A. Almehdi and F.A. Bliss

Crown gall incited by Agrobacterium tumifaciens is an important problem for nursery and field production of stone fruit and nut crops. Genotypes reportedly differ for crown gall reaction, but there is little information about resistance of Prunus accessions used as rootstocks. From among four wild-type strains of A. tumifaciens-virulent on apricot and almond, K12 was selected for inoculation of 6-month-old seedlings of cherry, plum, peach, almond, apricot, and miscellaneous species. The large majority of seedlings were very susceptible to crown gall, but some had few or no galls. Cherry, especially some lines of P. mahaleb, showed the most resistant or moderately resistant seedlings, while some accessions of plum, especially P. cerasifera, P. angustifolia, and P. insititia had the most resistant seedlings. Plants with different reactions were propagated to determine adult plant resistance and to study the heritability of crown gall reaction.

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F.A. Bliss, P.L. Schuerman, A.A. Almehdi, A.M. Dandekar, and N. Bellaloui

Crown gall is an important disease of many fruit and nut crops, but little is known about sources of resistance. We screened germplasm from Prunus armeniaca L., P. angustifolia Marsh., P. argentia L., P. avium L., P. besseyi Bailey, P. bokhariensis Schneid., P. brigantica L., P. cerasifera Ehrh., P. cerasus L., P. dulcis (Mill.) D.A. Webb, P. fruiticosa Pall., P. hortulana Bailey, P. insititia L., P. japonica Thunb., P. mahaleb L., P. persica (L.) Batsch, P. serotina Ehrh., P. simonii Carr., P. sogdiana L., and P. webbii (Spach) Vieh. When either main stems or lateral branches of seedlings were inoculated with strains K12 and C58 of Agrobacterium tumefaciens (Smith and Townsend) Conn., the incidence of resistance was less than 10% except in some accessions of P. mahaleb L. where up to 30% of the plants were resistant. Some resistant plants were identified in other species, with P. insititia L. being the most promising. Symptoms based on presence and size of galls should be allowed to develop for up to 90 days after inoculation to reduce the likelihood of misclassifying plants as resistant when they are slightly susceptible.

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E.W. Stover and C.S. Walsh

Trees of each of five rootstock genotypes (M.7a, M.9, M.26, MM.111, Mark,) were inoculated above and below ground with three strains of Agrobacterium tumefaciens. These were compared to controls that were uninoculated or inoculated with sterile deionized water. All rootstocks tested were quite susceptible to crown gall, but M.9 and Mark were consistantly among the most susceptible genotypes. Percent of inoculated sites forming galls above ground ranged from 43% in M.7a to 77% in M.9 and the mean size of galls that formed ranged from 3.7 mm in M.26 to 7.7 mm in M.9. All rootstocks except M.9 formed galls at a higher percentage of inoculated sites that were below ground. Percent of below ground inoculations forming galls ranged from 67% in MM.111 to 100% in Mark while mean size of galls underground ranged from 4.2 mm in MM.111 to 15.3 mm in M.9. The proportion of inoculated sites forming galls below ground in M.7a was twice as high as in above ground sites For rootstock × strain means, each measure of crown gall susceptibility above ground was significantly correlated with corresponding below ground data at the 0.01 level. to three rootstocks, some trees inoculated with sterile deionized water also produced apparent galls at sites below the soil line (100% in Mark, 60% in M.7a, 22% in M.26) although none of the above ground control inoculations produced galls. Uninoculated controls showed no gall formation.

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James R. McKenna and Lynn Epstein

Marsteller Street, West Lafayette, IN 47907-2033. We thank the following: S. Bassein for statistical advice; G. McGranahan for initiating and coordinating the Paradox Diversity Study; M. Schroth and B. Teviotdale for advice on crown gall; M

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William H. Olson and Richard P. Buchner

English walnut (Juglans regia) producers in California compete with many insect and disease pests to produce an acceptable crop. Traditional control strategies work reasonably well for most pests. However, environmental concerns, loss of certain pesticides and new or impending regulations threaten the use of many traditional techniques for control of many of the pests. Codling moth (Cydia pomonella), walnut husk fly (Rhagoletis completa), and walnut aphid (Chromaphis juglandicola) are the major insects that affect California walnut production. Control strategies that use integrated pest management programs, beneficial insects, mating disruption, insect growth regulators, improved monitoring techniques and precise treatment timing based on the insect's life cycle are leading edge techniques currently available for insect control in walnuts. Major diseases include walnut blight (Xanthomonas campestris pv. juglandis), crown gall (Agrobacterium tumefaciens) and crown and root rot (Phytophthora spp). Both copper resistant and copper sensitive strains of the walnut blight bacterium are best controlled with combinations of copper bactericides and maneb instead of copper materials alone. A new computer model, Xanthocast, used to forecast the need for walnut blight treatment is under evaluation. Crown gall is managed using a preplant biological control agent and a heat treatment to eradicate existing galls. Phytophthora crown and root rot is dealt with primarily by site selection, irrigation management and rootstock selection.

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Fengge Hao, Lirong Wang, Ke Cao, Xinwei Wang, Weichao Fang, Gengrui Zhu, and Changwen Chen

, 2004 ; van Loon et al., 1998 ). Agrobacterium tumefaciens , a soil-borne bacterium, causes formation of crown galls in many plant species. During infection, a specific segment of the tumor-inducing plasmid, the transfer DNA (T-DNA), is transferred from

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Karen L. Thies and Clinton H. Graves Jr.

A meristem micropropagation system was developed to produce Agrobacterium -free muscadine grape. Meristems were cultured on a modified Woody Plant Medium (mWPM) supplemented with 0.45 μm BAP. After 2 weeks, cultures were transferred to mWPM containing 8.92 μm BAP to enhance shoot proliferation. Propagules were subsequently subdivided and transferred to fresh medium at 2- to 4-week intervals. New shoots were excised and inserted in mWPM supplemented with 0.57 μm IAA to promote root formation. This method has been successfully used to produce Agrobacterium -free plants of muscadine cultivars Carlos, Doreen, Jumbo, Magnolia, and Sterling for research purposes and for a foundation planting in Mississippi. Chemical names used: benzylaminopurine (BAP); indole3-acetic acid (IAA).

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Thomas J. Burr, Cheryl L. Reid, Barbara H. Katz, Maria Elisabetta Tagliati, Carlo Bazzi, and Deborah I. Breth

Agrobacterium radiobacter (Beijerinc and van Delden) Conn strain K-84 failed to control raspberry (Rubus idaeus L.) crown gall caused by A. tumefaciens (E.F. Smith and Townsend) Conn. Agrobacterium tumefaciens strains isolated from galls on plants that had been treated with K-84 were not sensitive to agrocin 84 in vitro. These strains were isolated from `Titan' and `Hilton' raspberry in New York state and from `Himbo Queen' and `Schönemann' raspberry in Italy. Almost all strains were identified as A. tumefaciens biovar 2. Raspberry crown gall was not controlled by K-84 in three field experiments in New York state. In two of the experiments, plants were produced by micropropagation and were known to be pathogen-free. The other plant source was shown to be contaminated with the pathogen before treatment with K-84. Crown gall was not controlled either on raspberry in a greenhouse experiment or on Kalanchoe diagremintiana (Hamet. and Perrier) plants that were coinoculated with K-84 and strains of A. tumefaciens isolated from galls on raspberry.

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F.A. Bliss and Ali A. Almehdi

Seedlings of Prunus mahaleb are often used as rootstocks for sweet cherry (P. avium) scion cultivars in commercial orchards. While they are desirable based on ease of propagation and economical production of nursery stock, seedlings may be variable resulting in nonuniform compound trees, and they are susceptible to several important diseases. Seedling sources have shown substantial variability for population uniformity of plant growth, and reaction to crown gall, powdery mildew and Phytophthora root rot. Segregating families also vary for pollen fertility, inbreeding response and control of scion growth. Multiple screening for favorable trait combinations is underway to develop improved sources of cherry rootstocks.