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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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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

with that of the rootstock, a graft resulted in a compatible union and in the restoration of vascular connection. In contrast, when it was different, callus formation was impaired and graft incompatibility occurred ( Santamour, 1988c ). Moreover, other

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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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Xin Zhao, Qianru Liu, M. Tatiana Sanchez and Nicholas S. Dufault

ended at 32 and 28 days after transplanting in 2015 and 2016, respectively. Longest vine length, stem diameter (measured at plant crown area above the soil line and below the graft union for grafted plants and at similar height above the soil line for

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Tomomi Eguchi and Chieri Kubota

seedlings. However, vegetable grafting as an alternative to soil fumigation with methyl bromide is now attracting growing interest in the United States ( Colla, 2010 ). In vegetable grafting, the position of the grafted union must be high enough to prevent

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Sahar Dabirian, Debra Inglis and Carol A. Miles

that included the crown, and above the graft union for grafted plants, was surface sterilized using a 10% bleach solution and rinsed with deionized water. Each sample was cut in half longitudinally with a sterile knife to expose the vascular tissue

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Guo-qing Song, Aaron E. Walworth and Wayne H. Loescher

part (scion or rootstock) of the grafted plant, translocation of signal MTP (e.g., proteins/peptides, RNAs, and hormones) across the graft union will occur and could thus enable the strategy of using the transgene product from the transgenic part to