Date of Award

12-2008

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Legacy Department

Plant and Environmental Science

Advisor

Reighard, Gregory L

Committee Member

Bauerle , Williams L

Committee Member

Bielenberg , Douglas G

Committee Member

Rajapakse , Nihal C

Committee Member

Wells , Christina E

Abstract

The use of small trees in orchard systems reduces manual labor (pruning, thinning and harvesting), and induces precocity, thus making high-density plantations economically advantageous, which has elicited an interest in size-controlling rootstocks. However, the mechanisms involved in the reduction of scion growth by the rootstock are not well understood. The main objective of this study was to gain a better understanding of the dwarfing mechanism induced by size-controlling peach rootstocks. The relationship among different rootstocks (dwarfing to invigorating range) as to stored carbohydrates, tree water status, and interstem and grafting height was evaluated on young and mature `Redhaven' and `Redtop' peach trees in California, Georgia and South Carolina. The main rootstocks involved in the study were Cadaman® (vigorous), Lovell (control), Pumiselect® (semivigorous), Controller® 5 (semivigorous), and Krymsk® 1 (more size-controlling).
Greater concentrations of TNC were found in `Redhaven' and `Redtop' roots in California compared to the other two sites; however, shoot TNC did not differ significantly among sites. Concentration of TNC in roots were at least two fold compared to shoot TNC concentration. About 70% of total non-structural carbohydrates were accumulated in root tissues, where smaller roots accounted for most of the carbohydrates (>80%). The more vigorous rootstocks not only had the higher accumulation of dormant carbohydrates but also the highest root and shoot dry weight per tree, suggesting that the initial difference in new spring growth could be the result of these growth components.
Rootstock genotypes used as interstems and not the grafting height affected the size of `Redhaven' trees in the studied combinations. Krymsk® 1 and Pumiselect® interstem trees were 81% and 88%, respectively, the size of Lovell trees at the end of the first year, while Krymsk® 1 interstem trees were almost 50% of the control at the end of second year. Budding height did not affected significanltly scion growth, however a tendency was observed when trees on Krymsk® 1 had reduced growth when grafted at higher height. These data suggest the dwarfing mechanism in some Prunus rootstocks involves other plant tissues rather than roots.
There was a positive correlation between scion vegetative growth as affected by rootstock and tree water status. In addition, the results suggested that the seasonal changes in dry matter production and partitioning found in two peach cultivars may be influenced, at least in part, by seasonal variations in stem water potential, stomatal conductance and transpiration rates. Xylem vessel diameters of Lovell rootstocks were two fold greater than those of Krymsk® 1 rootstocks. The results also suggested that in peach rootstocks the main hydraulic resistance might be located at the root such as the case of Krymsk® 1 or graft union interface as in Pumiselect®; so, depending on genotype combinations.

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