Brief Summary of Minutes of Annual Meeting

Accomplishments: Linkages were developed between NC-140 members and a project aimed at identifying the causes of the apple postharvest disorder bitter pit in ‘Honeycrisp’ and recommendations are being developed to reduce the severity of the disorder. NC140 members are continuing to work with nursery growers to propagate promising new rootstock selections more rapidly so they can be included in multi-state trials to quickly identify strengths and weakness of the new selections. NC140 members are collaborating with the Midwestern Apple Improvement Association to evaluate new varieties on dwarfing rootstocks.

      The WSU pear rootstock breeding program is moving forward. About 200 seedlings have been planted and some were budded to ’d’ Anjou’. Based on genetic mapping, a genetic locus for dwarfing was mapped on the chromosome 15 of Mustafabey.

Short-term Outcomes: After 5 years the Organic Apple rootstock trial has revealed some of the difficulties associated with organic apple production. Issues include inability to maintain soil nitrogen levels for adequate tree growth, difficulty in controlling some insect pests and weeds, lack of fruit thinning techniques. 

Outputs: NC-140 trials on research farms and on commercial farms are valuable outreach tools because growers can observe the trees. Results from NC-140 trials are used to develop rootstock and tree training/pruning recommendations for North American deciduous tree fruit growers. NC-140 is the primary source of information on rootstocks and training systems for the North American tree Fruit industries.   

Milestones:

• Some of the Geneva apple rootstocks are sensitive to latent viruses. Members of the Cornell/USDA-ARS rootstock breeding program are characterizing the sensitivity of several rootstocks to viruses, and they initiated a virus therapy program to obtained virus-free rootstocks.
• Early results from the 2013 Pear Orchard Systems trial indicate that choosing the specific combination of training system, spacing, and rootstock is critical to obtaining early production and fruit quality and these trials must be continued for 10 years to observe changes over time at different sites.
• The 2015 Organic ‘Modi’ Apple Trial has revealed several challenges for growing apples with organic practices. At some locations poor weed control resulted in poor tree growth and in other areas it resulted in tree loss due to vertebrates. Organic orchards will require rootstocks with more vigor than conventional orchards.  
• For the first time, a complete range of vigor-controlling peach rootstocks is currently under evaluation in coordinated trials. Relationships between peach canopy architectural variables and diffusion of vigor (to achieve reproductive/vegetative balance) are under concomitant study to provide insights into appropriate evaluation trial designs for, and eventually strategies for successful adoption of, canopy training systems must be matched to rootstocks of various vigor levels.
• The dwarfing Controller 7 and 8 and Rootpac 20 peach rootstocks have performed well in California and some northeastern states, but in Georgia they lack adequate vigor and tree survival was poor. Guardian continues to perform well at most locations.
• At most sites, the 4 Vineland (numbers 1, 5, 6 and 7) apple rootstocks are too vigorous for intensive orchards, and they are less productive than most dwarfing rootstocks. These rootstocks may produce appropriate size trees with weak-growing cultivars on nonfertile soils.
• The widespread planting of agronomic crops that are resistant to herbicides has led to horticultural crop injury due to herbicide drift. When young apple trees were sprayed with dicamba and glyphosate at driftable rates, tree growth, flowering and fruit yield were adversely affected for at least three years. Young trees on B.9 rootstock suffered multi-year yield loss following drift exposure.
• The MSU cherry rootstocks are dwarfing, but some may be too dwarfing for commercial tart cherry orchards. In Michigan, the rootstocks Cass, Clare and Crawford are more dwarfing for tart cherry than the standard Mahaleb. Clinton had higher yields than Clare or Lake.
• After 5 years, for sweet cherry, the rootstock Clinton is more dwarfing and more productive than Gi5.
• Several sweet cherry trials evaluating production systems using multi-leader initial tree development are being evaluated at several sites in Michigan.
• Summaries for the first 5 years of two multistate apple rootstock trials were published. ‘Honeycrisp’ was tested on 17 rootstocks from Russia, Cornell-Geneva, and Vineland, Ontario as well as the commercial standards, M.9-T337 and M.26. ‘Fuji’ was budded onto 14 rootstocks. Trees on G.214, B.10, G.11 and G.41 were smaller than M.9-T.337. Trees on V.1, V.5, V.6, V.7, G.890 and G.30 were larger than trees on M.26. Cumulative yield efficiency was greatest for G.935 and G.214.  
• Two projects were conducted to evaluate the influence of rootstock on bitter pit severity on ‘Honeycrisp’ apple. In Michigan 43 orchards were sampled and as part of the Root-2- Fruit project apples were collected from sites with the 2014 ‘Honeycrisp’ rootstock trial. Data relating fruit peel tissue nutrient levels to bitter pit are being analyzed.