The apple rootstock ‘Geneva® 41’ (‘G.41’), is desirable for its resistance to fire blight, Erwinia amylovora, while producing high yields. However, ‘G.41’ and other Geneva® selections tend to form weak graft unions in the nursery that are susceptible to breaking in the wind, at harvest, or during shipment. In order to understand and remedy this graft union weakness, six scions (‘Fuji’, ‘Gala’, ‘Honeycrisp’, ‘McIntosh’, ‘Pink Lady’, and ‘Scilate’) by seven rootstocks (‘G.41’, ‘G.935’, ‘G.214’, ‘G.11’, ‘M.9-NIC 29’, ‘B.9’ and ‘EMLA 26’), by two grafting methods (chip bud and saddle graft) in a factorial design were tested for graft union flexural strength and flexibility. Additionally, plant growth regulators (PGR) were applied to trees with ‘G.41’ as rootstock as a solution to overcome graft union weakness. Transpiration rate and hydraulic resistance were measured for comparison of a weak graft forming rootstock (‘G.41’) to a strong graft forming rootstock (‘M.9-NIC 29’). ‘G.41’ consistently formed a weaker graft union regardless of scion or grafting method. Scions such as ‘McIntosh’ and ‘Pink Lady’ formed stronger graft unions, while ‘Scilate’ and ‘Honeycrisp’ form weaker graft unions. Saddle grafting did not improve graft union strength. Nurseries that graft on ‘G.41’ should choose scions that form stronger graft unions. Benzyl adenine (BA) in a latex paint increased the strength and flexibility of the graft union relative to scion cross sectional area (SCSA), but further research is needs to identify more efficient methods of application. Rootstock effect on transpiration rate was different between years. No detectable differences were found for hydraulic resistance through the graft union of different rootstocks, suggesting weaker graft unions did not limit hydraulic conductance or transpiration rate. Thus graft union weakness is not an indicator of poor vascular connection.
| Identifer | oai:union.ndltd.org:UTAHS/oai:digitalcommons.usu.edu:etd-6102 |
| Date | 01 December 2016 |
| Creators | Adams, Stuart W. |
| Publisher | DigitalCommons@USU |
| Source Sets | Utah State University |
| Detected Language | English |
| Type | text |
| Format | application/pdf |
| Source | All Graduate Theses and Dissertations |
| Rights | Copyright for this work is held by the author. Transmission or reproduction of materials protected by copyright beyond that allowed by fair use requires the written permission of the copyright owners. Works not in the public domain cannot be commercially exploited without permission of the copyright owner. Responsibility for any use rests exclusively with the user. For more information contact Andrew Wesolek (andrew.wesolek@usu.edu). |
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