|Authors: ||M.A. Olmstead, N.S. Lang, G.A. Lang, F. Ewers, S. Owens|
|Keywords: ||graft union, Gisela series, vessel diameter, confocal laser microscopy|
Interspecific hybrid rootstocks for sweet cherries (Prunus avium L.) have been introduced to reduce plant height and increase productivity.
Mechanisms of dwarfing in sweet cherry are not well understood, thus best management practices are difficult to delineate for all rootstock/scion combinations.
Historical work on apples (Malus spp.), citrus (Citrus spp.), and some Prunus species indicate possible mechanisms: graft incompatibility; presence of virus; incomplete formation of vascular elements during healing of graft wounds; and hormonal or phenolic interactions between scion and rootstock.
Trees were bud-grafted using ‘Rainier’ (scion) on Gisela 5 (Gi 5, 148/2; Prunus cerasus x Prunus canescens; most dwarfing), Gisela 6 (Gi 6, 148/1, P. cerasus x P. canescens), and Colt (P. avium x P. pseudocerasus, vigorous), rootstocks in late August 2001. Heterografts were prepared in three combinations: ‘Rainier’ x Gi 5, ‘Rainier’ x Gi 6, and ‘Rainier’ x Colt.
Homografts (rootstock bud-grafted on rootstock) were included to observe variation due to wounding effects.
These were: Gi 5 x Gi 5, Gi 6 x Gi 6, and Colt x Colt.
Six of each combination (hetero- and homograft) were double-budded to ensure success.
Graft unions were harvested monthly beginning one month after bud grafting for six months.
Graft unions were fixed in formalin-acetic acid (FAA) and sectioned into longitudinal (20 μm sections) and transverse sections (15 μm) with a sliding or rotary microtome and stained with safranin O or acridine orange.
A laser confocal microscope (Zeiss 210) was used to characterize vessel diameter, length, area and number.
Callus formation around the wounding site was visible two weeks after bud grafting.
Rootstock combinations did not affect vessel number and length; however area and diameter were affected by location and rootstock combination.
In addition, as rootstock vigor decreased, vessel area decreased.
There were also wounding effects observed in homograft combinations, as well as some natural variation in vessel area between ungrafted rootstocks.
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