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William C. Johnson, William C. Johnson, Martin Goffinet, Mary J. Welser, Terence L. Robinson, H. Todd Holleran, Karl J. Niklas and Steve A. Hoying

An increased incidence of graft union failure of apple trees during high wind events has been noted by researchers participating in the NC-140 regional rootstock testing project for certain rootstock-scion combinations. By measuring the strength of graft unions in a survey of mature apple trees in multiple stock-scion combinations, we have determined that there are significant differences. These differences may be attributable to genotype specific characteristics of rootstocks, scions, and/or rootstock-scion interactions. We are presently exploring potential biophysical and anatomical differences related to weak graft unions of apple rootstock and scion varieties. As traits correlated with weak graft unions are identified, they will be useful to help growers avoid the rootstock-scion combinations that are particularly susceptible to tree failure.

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Umit Serdar, Bulent Kose and Fatma Yilmaz

We studied the anatomical structure of graft unions in European chestnut using several grafting methods. The work was done in the greenhouse during 2003–04. The grafting methods epicotyl, hypocotyl, and inverted radicle were used. The grafts were made with scions of clone SA 5-1 on clone SE 21-9 rootstock. The samples for examination were taken from the graft unions 2, 6, and 12 months after grafting, and fixed in a formalin–acetic acid–alcohol solution. The observation of the anatomical structure of the graft union area revealed that new cambium, xylem, and phloem tissues were formed in the samples two months after grafting. Further, it could be also observed that 6 months were necessary for continuous cambial connection.

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Sung Kyeom Kim, Duk Jun Yu, Ro Na Bae, Hee Jae Lee and Changhoo Chun

Grafted transplants are widely used for watermelon culture in Korea mainly to reduce the yield and quality losses caused by soil-borne diseases. It is normal practice to cure the grafted transplants under high relative humidity (RH) and low photosynthetic photon flux (PPF) conditions for a few days after grafting to prevent the wilting of the transplants. Transpiration rate (TR) and net photosynthetic rate (NPR), however, could be suppressed under those environmental conditions. In the present study, TR and NPR of the grafted watermelon transplants were compared during graft union formation under 18 environmental conditions combining two air temperatures (20 and 28 °C), three RHs (60%, 80%, and 100%), and three PPF s (0, 100, and 200 μmol·m-2·s-1). Percentages of graft union formation and survival were also evaluated. TR and NPR dramatically decreased just after grafting but slowly recovered 2 to 3 days after grafting at 28 °C. The recovery was clearer at higher PPF and lower RH. On the other hand, the recovery of TR and NPR was not observed in 7 days after grafting at 20 °C. Differences in TR and NPR affected by RH were nonsignificant. Percentage of graft union formation was 98% when air temperature, RH, and PPF were 28 °C, 100%, and 100 μmol·m-2·s-1, respectively, which was the highest among all the treatments. Percentage of survival was over 90% when air temperature was 28 °C and RH was higher than 80% (when vapor pressure deficit was lower than 0.76 kPa). In addition, higher PPF enhanced TR and NPR and promoted rooting and subsequent growth of grafted transplants. Results suggest that the acclimation process for grafted watermelon transplants can be omitted by properly manipulating environmental factors during graft union formation.

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Michele R. Warmund, Billy G. Cumbie and Mark V. Coggeshall

nutrients through the union ( MacDaniels, 1955 ; Weber and MacDaniels, 1969 ). Alternatively, it was hypothesized that low winter temperatures injured the developing tissues in the graft union ( MacDaniels, 1955 ). Others suggested that poor grafting

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Mercy A. Olmstead, N. Suzanne Lang, Gregory A. Lang, Frank W. Ewers and Shirley A. Owens

Dye transport through vascular pathways was examined in tissues surrounding the graft union of second-leaf, field-grown trees of `Lapins'/Gisela 5 (`Gi 5') (dwarfing) and `Lapins'/'Colt' (nondwarfing). Excavated, intact trees were allowed to take up xylemmobile dye via transpiration for 6 h before sectioning the tree into scion, graft union, and rootstock tissue. `Lapins'/'Gi 5' had a significantly larger stem cross-sectional area in the central graft union than did `Lapins'/'Colt'. Per unit cross section, dye transport of both `Lapins'/'Gi 5' and `Lapins'/'Colt' was significantly less in the graft union than in rootstock sections, with still less transported to scion tissues in `Lapins'/'Gi 5'. `Lapins'/'Gi 5' had a tendency to produce vascular elements oriented obliquely to the longitudinal axis of the tree. Dye was distributed more uniformly axially and radially across the graft union in `Lapins'/'Colt' than in `Lapins'/'Gi 5', with an apparent accumulation of dye in `Lapins'/'Gi 5' graft union. Xylem vessel diameters and vessel hydraulic diameters (VDh) were smaller overall in `Lapins'/'Gi 5' than in `Lapins'/'Colt'; however, graft unions in both had smaller VDh than did rootstock sections. These observations suggest reduced transport efficiency of xylem vessels in the graft union in `Lapins'/'Gi 5' may be due to smaller vessels, vascular abnormalities and/or increased amounts of callus and parenchyma tissue.

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K.V. Kommineni, J.M. Gillett and D.C. Ramsdell

In a greenhouse study, fifty 1-year-old `Stanley'/`Myrobalan 29C' plum (Prunus sp.) trees were inoculated with tomato ringspot nepovirus (ToRSV) by either nematode inoculation or slash inoculation to compare how inoculation effects the onset of the prune brown line (PBL) disease. In six tests (over 2 years), slash-inoculated trees had a higher percentage of ToRSV infection than nematode-inoculated trees when root and bark samples were tested by enzyme-linked immunosorbent assay (ELISA). ELISA differences between the two treatments were significant by chi-square analysis. None of the ToRSV positives by ELISA developed a brown line at the graft union. In a second experiment, five rootstock (`Myrobalan 29C', `Marianna 4001', `Marianna 2624', `Marianna GF8-1', and `St. Julian 655-2') and five scion (`Carolyn Harris', `New York 58.900.12', `Stanley', `Valor', and `70031') combinations (total combination = 25) were established in a field plot in Traverse City, Mich., and infected with ToRSV by slash and nematode inoculation. All five rootstocks were infected, with incidences of 40% to 60% ToRSV infections after 3 years. `Marianna 2624' had the lowest incidence of PBL (5%) compared to `Myrobalan 29C', which had the highest incidence (30%). The scion 70031 in combination with either `Myrobalan 29C' or `Marianna 4001' rootstocks, produced PBL in 100% of the trees. ToRSV was detected by ELISA and northern hybridization assays. ELISA consistently detected more positives when root or bark tissues were tested, and northern hybridization assay consistently detected more positives when rootstock sucker leaves were used.

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Craig E. Kallsen and Dan E. Parfitt

Similar scion and rootstock growth rates produce strong graft unions in fruit and nut trees. A SRR close to one provides a strong graft union as well as a uniform exterior surface for trunk-shaking harvesters. ‘Kerman’, which has been the standard

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Simon A. Mng’omba and Elsa S. du Toit

within 1 d and the grafting strips were kept intact onto the graft union interfaces until the end of the experiment. Fig. 1. Diagonal cut surface (100 mm long) of successfully grafted ( A ) Mangifera indica (mango), ( B ) Persia americana (avocado

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Simon A. Mng'omba, Elsa S. du Toit, Festus K. Akinnifesi and Helena M. Venter

and 32 °C ( Akinnifesi et al., 2004b ). Stem diameters of scions, stocks, and graft unions were measured using a pair of calipers. Bark thickness for both scions and stocks was also measured. Ten grafts of U. kirkiana trees, grafted by the splice

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Olfa Zarrouk, Pilar S. Testillano, María Carmen Risueño, María Ángeles Moreno and Yolanda Gogorcena

’/‘PM 105 AD’), and an incompatible heterograft (‘Summergrand’/‘Myrobalan GF 3–1’). Grafts were collected on 17 Feb. 2005, 157 d after grafting (about 5 months later). Histological examination. Three graft unions per combination were collected and