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ARS Home » Northeast Area » Geneva, New York » Plant Genetic Resources Unit (PGRU) » Research » Publications at this Location » Publication #344115
Title: Effect of scion and graft type on transpiration, hydraulic resistance and xylem hormone profile of apples grafted on Geneva®41 and M.9-NICTM29 rootstocks

Author
item ADAMS, STUART - Willow Drive Nursery
item LORDAN, JAUME - Cornell University
item Fazio, Gennaro
item BUGBEE, BRUCE - Utah State University
item FRANCESCATTO, POLIANA - Cornell University
item ROBINSON, TERENCE - Cornell University
item BLACK, BRENT - Utah State University

Submitted to: Scientia Horticulturae
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/26/2017
Publication Date: 10/3/2017
Citation: Adams, S., Lordan, J., Fazio, G., Bugbee, B., Francescatto, P., Robinson, T., Black, B. 2017. Effect of scion and graft type on transpiration, hydraulic resistance and xylem hormone profile of apples grafted on Geneva®41 and M.9-NICTM29 rootstocks. Scientia Horticulturae. 227:213-222.

Interpretive Summary: This research was aimed at understanding the role of vascular connections through the graft union on the strength of the union. Some of the most promising apple rootstocks appear to have weak or brittle graft unions with certain apple varieties. We hypothesized that the strength of graft unions may be related to the amount of vascular connections between graft partners, and poor vascular connections may cause increased hydraulic resistance. We found that there was no correlation between graft union strength and whole tree transpiration rate or leaf area-specific transpiration rate. The hydraulic resistance of the weaker forming rootstock was not significantly different than the strong graft union rootstock and was more closely correlated with overall size of the root system. However, hydraulic resistance of the scion and graft union was small relative to root system resistance, making it difficult to detect differences in graft union resistance among scion-rootstock combinations. We observed differences in the hormone profile of xylem exudate among rootstock genotypes and among graft types. This data will enhance our ability to select more efficient apple rootstocks that form stronger graft unions.

Technical Abstract: New highly productive apple rootstocks resistant to fire blight and crown rot can improve orchard profitability. However, some of the most promising rootstocks appear to have weak or brittle graft unions that are susceptible to breakage in the nursery and in the field. Flexural strength of graft unions may be related to the amount of vascular connections between graft partners, and poor vascular connections may cause increased hydraulic resistance. We sought to determine if transpiration rate and hydraulic resistance were correlated with graft union strength by comparing Geneva® 41 with the strong graft-forming Malling 9 selection NIC™ 29. The primary goal of this study was to compare weak and strong graft unions by measuring whole-tree transpiration, as well as hydraulic resistance using the pressure chamber method. The effects of rootstock and grafting method on xylem hormone concentrations were also compared. There was no correlation between graft union strength and whole tree transpiration rate or leaf area-specific transpiration rate. The hydraulic resistance of the weaker forming rootstock was not significantly different than the strong graft union rootstock and was more closely correlated with overall size of the root system. However, hydraulic resistance of the scion and graft union were small relative to root system resistance, making it difficult to detect differences in graft union resistance among scion-rootstock combinations. Conversely, we observed differences in the hormone profile of xylem exudate among rootstock genotypes and among graft types.