NC_OLD140: IMPROVING ECONOMIC AND ENVIRONMENTAL SUSTAINABILITY IN TREE-FRUIT PRODUCTION THROUGH CHANGES IN ROOTSTOCK USE
Statement of Issues and Justification
The NC-140 Regional Research Project is designed to address a number of high-priority areas within the North Central Region as well as other parts of North America. This project seeks to enhance economically and environmentally sustainable practices in temperate fruit production by focusing on rootstocks. The NC-140 project meets the guidelines presented by the North Central Regional Association (NCRA) in Guidelines for Multistate Research Activities (May 2001). Specifically, this project addresses high priorities defined by NCRA, within the crosscutting research areas of agricultural production, processing, and distribution, genetic resource development and manipulation, integrated pest management and economic development and policy. The project involves researchers from multiple states and is multidisciplinary. Researchers involved in this project have leveraged Federal and state dollars to add significant resources to address this research area. Lastly, outreach is integral to the project and includes electronic information transfer through web sites, written material for growers and other stakeholder groups, and numerous educational programs in individual states and at national and international grower and scientific meetings.With the competitive international market, the demand for high quality fruit by consumers, the strong pressure to reduce chemical use, and a need to enhance the economic efficiency of production, tree-fruit growers must look to alternative, economically and environmentally sustainable management schemes of production. Growers who want to stay profitable must establish high-density plantings with much smaller trees using new cultivars. These high-density plantings may cost 10 to 20 times more to establish than low-density plantings, thus greatly enhancing the economic risk. Potential returns of high-density plantings, however, far exceed those of low-density plantings, particularly during the first 10 years after planting, often returning the growers initial investment much sooner than the initially less-costly, low-density plantings. The central component of high-density systems is the rootstock, the part of the tree which provides size control to allow for high-density plantings. As part of the tree, the rootstock influences many factors in addition to tree size, particularly productivity, fruit quality, pest resistance, stress tolerance, and ultimately profitability.
As the industry moves from low- to high-density plantings, several rootstock-related problems must be addressed. New pome- and stone-fruit rootstocks cannot be recommended unless there is sustained research investigating soil and climatic adaptability, root anchorage, size control, precocity, productivity, pest resistance, and propagation. In general, field testing of rootstocks in an orchard setting requires a minimum of eight years to accurately assess the potential for improved profitability, reduction of external farm inputs, and enhancement of production efficiency. With year-to-year variation in weather, this time span is necessary to obtain a true indication of rootstock performance across multiple environments.
With the establishment of the NC-140 technical committee, researchers from the North Central region were able to develop a coordinated research effort in apple rootstock research through the uniform testing of rootstocks and multiple genetic systems, and to discuss, evaluate, and coordinate other rootstock research. As the project has continued, multiple temperate-zone fruit tree crops have been evaluated. With cooperators in various geographical regions across the country these research efforts allow the results from NC-140 studies to be interpreted directly. Since NC-140 is the only regional committee focusing on rootstock research, researchers from around the country, along with Canadian provinces, and Mexico (see table of participants) have joined and continue to participate.
A stable tree-fruit industry based on economically and environmentally sustainable orchard systems is one of the primary goals of NC-140 research. Prior to organization of NC-140, knowledge of rootstock and multiple genetic system performance and adaptability had to be obtained from a number of unrelated studies. The lack of common planting materials, spacing, and cultural procedures made comparison of the results of these studies difficult, and slowed the accumulation of knowledge that could be applied by orchardists. These difficulties coupled with the industry shifting to smaller trees with closer spacing resulted in serious planning and management errors leading to loss in revenue. Also, such unrelated studies were incomplete or slow in evaluating rootstock tolerances to biological, environmental, and edaphic stresses. Through the uniform cooperative testing undertaken by NC-140, new rootstocks are exposed quickly and systematically to widely varying soil and climatic conditions to shorten the time necessary for thorough evaluation.
Management systems
Any newly developed rootstock must exist ultimately as an integrated orchard-management system. Current economic trends make production efficiency of multi-genetic combinations under various management systems one of the most important factors that must be evaluated thoroughly before specific combinations are recommended for large-scale plantings by fruit growers. Uniform trials replicated within sites and across varying climatic and edaphic conditions have been established by the NC-140 Committee for many of the temperate-zone fruit trees.
Orchard systems, focusing on the rootstock, must be designed to meet the specific needs of each temperate-zone tree fruit crop. In northern Europe, where labor is expensive and new land is unavailable, the apple and pear industries have developed orchard systems with a high number of trees per acre, with all tree maintenance occurring from the ground by using size controlling rootstocks. In past years, the free-standing, central-leader system has been very profitable for North America, particularly with the weak, spur-type Delicious cultivar. As labor became more expensive and the list of profitable cultivars has changed, North American growers converted to smaller, high-density orchard systems on size controlling rootstocks. However, no system can be taken in its entirety from one area and implemented in another without modifications. Growth characteristics of rootstocks under North American conditions are much different than in northern Europe where most high density systems were developed. Also, tree response under a particular management system in different areas in North America can vary greatly. These problems require that various rootstocks be tested under many North American climates and that modifications of training and pruning techniques be developed to match local growing conditions. Rootstock development and improvement
If the temperate-zone fruit industry is going to continue to remain competitive in international markets and meet the needs of the consuming public, new genetic material will need to be incorporated into existing material to enhance performance of rootstocks. Through traditional plant breeding and novel genetic engineering methods including gene transfer, researchers can incorporate insect and disease resistance into existing rootstock material, as well as develop rootstocks with enhanced horticultural performance. Obtaining genetic material from research programs from throughout the world and testing those new rootstocks through the NC-140 cooperators has been an integral part of the project. Clonal materials of different rootstocks have been obtained from many countries since the inception of the NC-140 project and will continue. Rootstocks developed with new genetic engineering techniques can also be tested efficiently and effectively within the committee structure. One of the major roadblocks that stands in the way of testing these new rootstocks is the very slow propagation time that is characteristic of clonal rootstocks. Usually new rootstocks are available in small numbers, because it takes several seasons (years) to propagate. Research on alternative ways of quick propagation of rootstocks is very much needed to shorten the time when these rootstocks will have a major positive impact on the industry
Genetics and developmental physiology
Knowledge of the physiological characteristics of newer rootstocks and the potential interactions with scion cultivars is important. The mechanism of how rootstocks control size either through genetic or physiological means needs to be studied at a basic level for the trait to be maximized in the orchard setting. Research on incompatibility between cultivars and rootstocks is a continuing need. Some promising temperate-zone fruit tree rootstocks cannot be considered for commercial production because of potential incompatibility. Understanding the mechanism of these incompatibilities will ultimately increase rootstock options for growers. In addition, techniques must also be developed to screen plant material early for desirable characteristics such as disease and insect resistance.
With many new rootstocks available for growers and nurseries, the need to be able to identify these plants via morphological and molecular methods is imperative. Some rootstocks stand out morphologically because of a difference in bark and leaf characteristics, but most do not. Developing methods for use in the laboratory and in the field will help all who use rootstocks to decrease the likelihood of planting mistakes.
Biotic and abiotic stresses
Low temperatures, soil adaptability, and susceptibility to pests limit the use of some existing rootstocks, and potentially will limit the adaptability of some new rootstocks within the North Central Region and across North America. Understanding how different rootstocks respond to biotic and abiotic stresses can lead to recommendations for use or non-use under certain orchard conditions. Such studies must include factors contributing to stress tolerance, development of practical means for controlling various stresses, or development of rapid means for screening potential rootstock candidates for susceptibility to various stresses. A better understanding of the physiological mechanisms behind these responses may allow for development of cultural practices which can relieve the detrimental effects of stress.
Cooperative testing of new and existing rootstocks by NC-140 researchers continues to generate interest and support from the fruit and nursery industries. This interest has resulted in industry financial support for the establishment of cooperative plantings, grants for state rootstock research, and propagation of trees for several of the NC-140 plantings. It is estimated that over the term of the current project (2002-2007), nearly $2,000,000 will be received to support NC-140 research from sources other than universities, Hatch funds, and RRF funds, and more than one half of this total will come from grower organizations. A compelling need exists to continue the present coordinated studies and to initiate new studies on a regional basis for temperate-zone fruit tree rootstocks as new plant materials are made available. Continued testing will provide a thorough evaluation of promising rootstocks, multiple genetic systems, and planting and training system efficiencies. This research project has led and will lead to sound recommendations to growers and nurseries based on widespread knowledge of adaptability and performance of the plant material.
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