Skip to main content
ARS Home » Northeast Area » Geneva, New York » Plant Genetic Resources Unit (PGRU) » Research » Publications at this Location » Publication #330703

Research Project: Breeding Apple Rootstocks Tolerant to Abiotic Stresses and Resistant to Pests and Diseases

Location: Plant Genetic Resources Unit (PGRU)

Title: The effect of plant growth regulators on apple graft union flexural strength and flexibility

item ADAMS, STUART - Utah State University
item BLACK, BRENT - Utah State University
item Fazio, Gennaro
item ROBERTS, NICK - Utah State University

Submitted to: Journal of the American Pomological Society
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/15/2016
Publication Date: 1/15/2017
Citation: Adams, S., Black, B.L., Fazio, G., Roberts, N. 2017. The effect of plant growth regulators on apple graft union flexural strength and flexibility. Journal of American Pomological Society. 71:8-18.

Interpretive Summary: Commercial apple trees are usually made from two different types of apples: the top or fruiting section is called the scion, and the below ground section is called the rootstock. These two parts are joined together at the graft union, which is normally a few inches above ground. Depending on different combinations of scions and rootstock, the graft union may be weaker than normal, sometimes resulting in breakage of the tree. These experiments were aimed at using plant hormones to modify the strength of the graft union during the nursery phase of the tree. We found that some plant hormones were effective in increasing the strength of the graft unions, but more research is needed to increase efficiency of application methods.

Technical Abstract: The apple rootstock ‘Geneva® 41’ (‘G.41’) forms weak graft unions with multiple scions. Exogenous plant growth regulators (PGR) can influence vascular differentiation and wood formation, and thus may improve graft union strength. A series of commercial and experimental PGR formulations were applied to trees on ‘G.41’ rootstock over two seasons, and graft union strength and flexibility were measured. Benzyl adenine (BA) applied in paint solution to the graft union significantly increased the flexural strength per scion cross-sectional area and the flexibility of the union. Foliar applications of Prohexadione-Ca also increased graft union flexural strength and flexibility, but temporarily limited scion extension growth. Applying PGRs in the nursery to more brittle rootstock-scion combinations may be an option for improving graft union strength and preventing tree losses. However, more efficient methods of application are needed for this approach to be commercially viable.