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.
Abstract
There are various problems associated with hot-callusing graft unions of dormant fruit and nut trees. Since the whole plant is exposed to elevated temperatures, growth is promoted not only at the graft union, but also from the scion buds and the roots. Translocation demands are placed on the graft union once growth of scion buds starts and leafing out occurs. Scion buds and leaves will desiccate if a callus bridge between rootstocks and scion is inadequately formed (1).
Abstract
Comparative studies of clonal anatomy revealed visible differences in medullary ray cell diam in juniper cultivars with different chromosome numbers. Histological studies, made at 10-day intervals for 60 days after grafting showed no differences in developmental sequence but only differences in rate at which each stage occurred. Callus tissue form ation began 10 - 20 days after grafting; first in ‘Fountain’ and last in ‘Pfitzeriana Kallay’. Isodiametric cells from uninjured cambia appeared by the 20th day except with ‘Pfitzeriana Kallay’ scions. By an alternating series of radial and tangential divisions, these cells overwalled the injured graft surfaces, but was less pronounced in closely fitted grafts. Overwalling cells did not occur in ‘Pfitzeriana Kallay’ until 30 days after grafting. By 40 - 50 days, overwalling cells began, by radial divisions to produce organized cells which filled voids between graft partners and crushed intervening callus. Mixing of newly formed cells between stock and scion cambia occurred 50 - 60 days after grafting. These cells assumed the spindle-shape of typical tracheids and were oriented into a “cambial bridge.” New, normally oriented xylem subsequently formed from this new cambial tissue. In typical grafts, most new tissue arose from the understock prior to the 50th day after grafting. At 60 days, contribution from stock and scion were equivalent. Adjacent walls of mixed graft tissue were found to be unmodified and appeared as paired structures each with a middle lamella and secondary wall thickenings. Abnormally large numbers of pits were observed at the graft union.
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.
Abstract
Using heat pulses the apparent velocity of the transpiration stream was measured in apple (Malus sylvestris Mill.) grafted on French seedlings (M. baccata Desf.), and several cultivars of peach (Prunus persica Sieb. and Zucc.) and Japanese plum (Prunus triflora Roxb.) grafted on almond (Prunus amvgdalus Batsch.) rootstock. The trees varied in compatibility with their respective rootstocks, as established by visual observation and gross morphology of the zone of union. Velocity of the transpiration stream was measured in 3 regions of each tree: the rootstock stem, the zone of union, and the scion stem. In definitely defective unions velocity of the transpiration stream in the zone of union exceeded that in both rootstock and scion. The possible use of this method as a tool for identifying poor graft unions in orchards is evaluated.
Abstract
Five apple species were grafted onto East Mailing VII, IX and 26 and Mailing Merton 104, 106 and 111 and 3 cherry species were grafted onto Mazzard F12/1 rootstock (a virus indexed clone) and grown in the field for one season. Determinations were made on graft success and plant response in the field. In October, representative graft unions of the 33 combinations were prepared, sectioned, and examined microscopically in an effort to find a rapid test for compatibility. The results of these microscopic examinations were correlated with the field results to see if one or more abnormalities could be found consistently in a significant number of grafts. Only a few grafts showed incompatibility characteristics which could be correlated to the field tests thus eliminating a quick microscope test. Anatomical abnormalities appeared to be the result of secondary influences suggesting that the biochemical factors probably control the compatibility or incompatibility of graft unions.
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.
Abstract
The role of scion water relations was studied using Colorado blue spruce (Picea pungens Engelmann ‘Hoopsi’) scions on Norway spruce [Picea abies (L.) Karst.] rootstocks grown either in a greenhouse or in a covered, unheated lath house. In greenhouse-grown grafts, total water potential (ψT) and relative water content (RWC) of the scions declined rapidly the first 2 weeks. Thereafter, both ψT and RWC were maintained or gradually increased in successful grafts. With scion budbreak, ψT rapidly increased to −1.0 MPa. This increase occurred 1 to 2 weeks after tracheid connections matured, based on dye movement through the graft union. At the same time, the ψT and RWC of unsuccessful grafts declined rapidly. Osmotic potentials (ψw) increased 3 weeks prior to budbreak in successful grafts. However, ψπ declined in unsuccessful grafts more rapidly than ψT, resulting in increased calculated turgor pressures with graft failure. Lath house-grown grafts had higher scion ψT and higher graft success than those in the greenhouse, but required more time for union development. Based on this data and previous work, an hypothesis relating changes in ψT, maturation of connecting tracheids, and scion budbreak to graft success or failure is presented.
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
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