Session 1 Pome Fruit Physiology 101

Transcription

1 Session 1 Pome Fruit Physiology 101 Session Manager Karen Lewis Objective: Understand basic physiology of apple and pear including growth and development, floral initiation and the role of hormones. Presentations: Plant Growth and Development Matthew Whiting Endogenous Hormones Duane Greene Floral Initiation Matthew Whiting

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3 PLANT GROWTH AND DEVELOPMENT Whiting, M.D. Department of Horticulture, Irrigated Agriculture Research and Extension Center, Washington State University, Prosser, WA KEYWORDS Fruit, shoots, roots, carbohydrate metabolism, partitioning, light interception, orchard system, cultivar, rootstock, meristem ABSTRACT Understanding how, why, and where trees, branches, fruit, and buds, are formed is fundamental for managing and manipulating growing points and canopy resources for profit. Every management practice, every limb manipulation, each decision to intervene in the natural growth and fruiting habit of trees should be done with a thorough understanding of tree growth and developmental processes. Orchardists have evolved to be master manipulators able to reshape and refine tree growth and fruiting with exceptional precision. This is done to maximize tree productivity, with an understanding of the delicate balance between fruit quantity and quality, and the tree s ability to perennially produce. Often narrow developmental windows exist to elicit an effect: from growth regulators that are strategically applied during key developmental stages to improve fruit cell division or manage vegetative growth, to targeted thinning processes that account for pollen tube growth and fertilization rate. To be sure, an understanding of tree growth and development is fundamental to adopt precision management practices that are essential in today s high-input-high-output production models. This presentation will provide an overview of apple and pear canopy growth and developmental processes, highlighting the 12-month developmental timeline, the canopy s acquisition and distribution of growth resources, and setting the stage for subsequent, more specific presentations.

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7 PLANT HORMONES 101 Greene, D. University of Massachusetts, Stockbridge School of Agriculture, Amherst, MA KEYWORDS Plant growth regulators, Plant hormones, auxins, gibberellins, cytokinins, abscisic acid, ethylene, directors of plant growth and development, naturally occurring compounds. ABSTRACT The growth and development of a plant is directed and guided by hormones produced by the plant. Plant hormones generally do not participate directly in the growth of a plant but they do send the signals that lead to gene expression and gene activation, enzyme activation and/or synthesis that ultimately results in developmental changes. There are five universally recognized major classes of hormones: auxins, gibberellins, cytokinins, abscisic acid and ethylene. There are two hormones that have a less dominant role in the regulation of plant growth and development: brassinosteroids and the jasmonates. Major Hormones Auxins: This group of hormones was the first to be discovered in the 1930s. Indole-3- acetic acid is the primary endogenous auxin found in most plants. While it is limited in the number of field uses it is probably has the greatest influence on how trees are grown and managed. Auxins do promote cell elongation. Apical dominance. Auxins are produced in the apical buds of shoots and diffuse downward inhibiting the growth and development of bud below. If the apical bud is removed or pruned off then inhibition of growth is lifted and lateral buds start to develop. These buds develop until they become dominate and reestablish the apical dominance. Growth of lateral buds are allowed due to the buildup of sugars and the presence of cytokinins. Leaf abscission. Auxins produced in the leaf diffuse downward and prevent abscission. As long as sufficient auxin is reaching the abscission zone abscission will not occur. Phototropism and geotropism. Plants tend to bend and grow toward light and response to gravity because of the movement of auxin resulting in asymmetric distribution of auxin. Auxin mediated ethylene production.

8 Gibberellins (GA): This is a group of hormones that is largely responsible for stem elongation and growth of shoots. A major goal in tree fruit production is to find cultural and chemical means to reduce and counteract the growth-stimulating effects GAs have on plants. There are over 135 known naturally occurring GAs. Each plant species has just a few GAs that are particular to that plant. GA 4 and GA 7 are dominant GAs in apple. Growth promotion. Limiting GA production in apple is often a goal in pome fruit production. Flower bud formation. GAs are known to be natural inhibitors of flower development in pome fruit. It is largely accepted that GAs produced in the seeds play a major role in inhibiting return bloom. GA 7 is particularly inhibitory in apple. Elongation of fruit. GAs as well as cytokinins are known to influence the shape (elongation) of apples. Cytokinins: This is a group of hormones that participates in many physiological processes but their effects are less dramatic than observed for other hormones. They are cell division factors and they help counteract stress in the plant and inhibit senescence. Cytokinins interact with auxins in the regulation of apical dominance; auxins reinforcing apical dominance and cytokinins help overcoming it. Abscisic Acid: While abscisic acid does promote abscission it is far more dominant and plays a more important role in other physiological events. Stomatal Movement and Transpiration. ABA plays a dominant role in regulating stomatal movement which in turn largely determines the rate of transpiration and water loss from a plant. Stress and Senescence. ABA is produced when plants are placed under stress. This may lead to abscission and accelerate senescence. Ethylene: Because ethylene is a gas its acknowledgement as an important plant hormone was ignored for many years. Advance fruit ripening. When fruit ripen they give off ethylene. The start of significant ethylene production (or CO 2 evolution) generally signals the physiological marker that indicates that fruit are ripe. This ethylene then speeds the ripening process. Controlling ethylene production and action is key to regulating ripening, fruit quality and storage potential. Promote Abscission. Exogenous application of ethylene or ethylene production in the plant in response to stress will promote abscission. Controlling heat, water and cold stress will alleviate premature leaf abscission.

9 Auxin induced ethylene production. Elevated rates of auxin increase ethylene production in plants. Some responses attributed to auxins may be cause by ethylene such as epinasty. Less Known Plant Hormones Brassinosteroids are required for vegetative growth and pollen tube growth, promote cell division and cell expansion and are required for plant morphological development. Jasmonates are best known for inducing plant defenses against injury due to insect diseases of mechanical injury.

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13 FLORAL INITIATION Whiting, M.D. Department of Horticulture, Irrigated Agriculture Research and Extension Center, Washington State University, Prosser, WA KEYWORDS meristem, fertilization, yield, fruit set, pollination biology, hormones ABSTRACT Floral initiation is the first step in the processes of flowering and fruit development that take place over two years, culminating with harvest. For fruit crops, floral initiation is arguably the single most important event the density and distribution of floral clusters largely determines management practices for the year considering the inextricable connection between fruit quantity and quality and their importance in orchard profitability. Floral initiation includes all biological developments required for the commitment by the developing meristem to produce an inflorescence. This occurs about 50 days after full bloom in apple and pear. In these crops, the cycle of flower development from initiation to harvest often lasts from 9 to 10 months, placing great import on the short lapse of time during which meristem fate is determined (i.e., the appearance and formation of the floral primordia in summer) as well as the the final formation of flower parts in spring. Flowers are initiated during the growing season before winter dormancy, and anthesis occurs in the spring when the chilling requirement of winter dormancy has been satisfied and temperatures are suitable for growth. The apple inflorescence is a determinate raceme which generally has five flowers (Figure1). Floral initiation in apple and pear is dependent on factors including vegetative development in the growing season before anthesis, Figure 1. Apple floral bud before (A, illustrated) and after bud break (B). Source: Foster et al., Ann. Bot. 92 (2): the effect of the environment, as well as hormones,

14 plant growth regulators, and carbohydrates. Research investigating floral initiation in apple implicates seasonal developmental processes and hormonal relationships as the major factors driving floral initiation as opposed to specific environmental stimuli. Clearly, an improved understanding of endogenous and exogenous factors controlling floral initiation will offer insights into practicable mechanisms for manipulating flowering and fruit load. This presentation will review the processes of floral initiation and flower development, and describe how growers may manipulate them via pruning/training and with growth regulators.

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17 Session 2: The Dynamic Nature of Nutrient and Water Relations and the Importance of Roots in Modern Orchard Systems Session Manager Lee Kalcsits Objective: Understand roots and their relationship with canopy growth and productivity. Presentations: Roots General Session Lee Kalcsits Nutrient Uptake and Distribution Massimo Tagliavini Irrigation and Nutrient Management Denise Nielsen

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19 ROOTS ARE IMPORTANT TOO: ROOT PHYSIOLOGY AND FUNCTION IN THE ORCHARD Kalcsits, L lee.kalcsits@wsu.edu Department of Horticulture, Washington State University, Wenatchee, USA Tree Fruit Research and Extension Center, Wenatchee, USA KEYWORDS Rootstocks, nutrient uptake, drought tolerance, root tips, root architecture, soil temperature, soil ph, soil water content. ABSTRACT Root health affects orchard performance, yield potential and quality. The most recognizable effect that roots have on growth of fruit trees is from using dwarfing rootstocks that promote precosity, reduced shoot vigor and limit overall tree size. This habit allows for more efficient management of the canopy and increased planting densities. The presence of dwarfing rootstocks have allowed the development of modern, trellised orchard systems to support high fruit production. However, some dwarfing rootstocks have slow or limited root growth potential. The impact of this limited root growth on water and nutrient uptake and resistance to soil-borne pathogens is relatively unknown. During planting and establishment of new orchards, this can be a challenge, particularly in poor soil environments where water and nutrients are being supplied almost exclusively through drip or microsprinkler irrigation and root vigor is restricted. Poor root establishment and slow root growth can limit canopy establishment in early years and increase the susceptibility of roots to periodic environmental stress because of the small, shallow root systems. When an orchard is first planted, early growth depends on root establishment to provide the water and nutrients required for the canopy to fill the space in the orchard. Early growth and development is critical to the productive success of an orchard. There are two primary types of roots, foraging or fibrous roots and structural roots that are responsible for forming the root architecture that fibrous roots branch off of and forage in the soil. Pioneer roots are less affected by short-term fluctuations in environment. Fibrous root systems regularly die and regenerate in trees during the course of a season or from one season to the next.

20 Roots are responsible for water and nutrient uptake from the soil. Water and nutrients can follow two pathways of movement through the root into the xylem to be transported to the aboveground parts of the tree, either between the cells (apoplastic pathway) or through the cells (sympastic pathway) (Figure 1). Apoplastic movement requires less within cell transport and is therefore a more rapid path to uptake of water and nutrients to the xylem. In roots, fine white root tips are responsible for most of the water and nutrient uptake Figure 1. Uptake pathway of water in roots from the soil (Figure 2). As root tips mature, a waxy layer forms in the hypodermis and endodermis of roots that limits water and nutrient uptake. Therefore, to have good water and nutrient uptake, there needs to be constant generation of white root tips. Soil interacts with roots and soil chemical and physical characteristics can affect root growth, managing orchard soil to be well drained, uniform and with a balanced ph are the first steps to promote healthy root growth. Figure 2: Diagram of a root tip. Source: biology.tutorvista.com Root growth starts early in the spring prior to bud flush as soil temperatures warm. This provides early water uptake to supply the developing flowers and leaves. Early season nutrient requirements are largely met by stored nutrients in the roots and wood. As the growing season progresses and the energy sink of the plant switches from growing roots and stems to developing fruit, root growth decreases. High soil temperatures (above 25 C or 80 F) can be a significant source of stress for roots. For dwarfing rootstocks with shallow, small root systems, the impact of temperature is greater. Increased stress may cause root mortality and/or decreased root tip growth leading to a reduced capacity to take up water and nutrients from the soil. Sources of stress may include disease, drought, heat, ph, salinity, and flooding among others.

21 Unlike aboveground growth, roots do not become dormant and will continue growing as long as conditions remain favorable and there is an energy reserve that can be used. Therefore, root growth can continue long after the upper part of the tree has gone dormant and can scavenge nutrients later in the season to store for growth and development the following season. Under conditions that lead to root death during the summer, the autumn can act as a period to catch up and re-establish an active root system for the following season. Maintaining an environment that promotes root growth throughout the season and limits below ground stress ensures that the trees can access water and nutrients at times during the season when the demand for those resources is high. As planting densities continue to increase and technology allows for more precise control of orchard systems, it is critical to manage the timing of nutrient and water uptake.

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25 NUTRIENT UPTAKE AND DISTRIBUTION Tagliavini, M 1, Zanotelli, D 1 massimo.tagliavini@unibz.it 1 Faculty of Science and Technology, Free University of Bozen-Bolzano, Italy KEYWORDS Calcium, dynamics of nutrient uptake, magnesium, nitrogen, nutrient partitioning, phosphorus, potassium, tree growth, uptake rate, yields. ABSTRACT Annual uptake of nutrients from the soil, and sometimes from the leaves, at desired rates and timings, is necessary for apple and pear trees to successfully complete their vegetative and reproductive cycle, produce high quality fruits, and become economically viable. Nutrient uptake provides for an optimal concentration of nutrient in tree organs to sustain growth, yields, flower bud formation, and the building of nutrient reserves. Nutrient uptake occurs with rates and dynamics depending on tree factors like growth rate (Figure 1) and yields, but also on environmental factors and nutrient availability. Figure 1 Example of total annual new biomass (NPP tot ) produced by apple trees and its partitioning to fruits (NPP fruits ). Data are in t D.W. per hectare and refer to cv. Fuji on M9 with fruit yields around t fresh weight ha -1 (27-29 t/acre)

26 Our quantitative knowledge about the amounts of absorbed nutrients under field conditions is derived either by 1) quantification of new biomass produced every year and its nutrient concentration or 2) by stable isotope techniques. For mature fruit trees, regularly subjected to pruning, it is often assumed that the increment of biomass of the framework of adult trees could be approximated to the amount of pruning wood, as secondary growth is considered low and negligible. Under these situations, nutrient uptake can be estimated by considering the amount of nutrients in the yield, in the pruning wood and in the abscised leaves (Table 1). Calcium (Ca), nitrogen (N) and potassium (K) are often the most absorbed nutrients. The partitioning of the absorbed nutrients within tree organs depends on their relative growth (Figure 1) and on specific nutrient needs. Most absorbed N is allocated to shoots and leaves, while most absorbed Ca is partitioned to leaves and woody organs. Pome fruits have low protein content and relatively low N requirements, while contain relatively high potassium. Therefore, the higher the yields the higher the K uptake and the need for K fertilizers. The rate of nutrient uptake varies along the season with dynamics that differs according to the nutrient. In apple, the uptake rate of N, phosphorus (P), Ca and magnesium (Mg) increases along the spring, slightly decreases in summer and markedly decreases approaching fruit harvest; K uptake rate, on the contrary, decreases only slightly in summer and approaching fruit harvest. Predicting annual amount and dynamics of the nutrient uptake, and their distribution in organs is a fundamental step for developing rational fertilization strategies in apple and pear orchards. Table 1 Example of nitrogen uptake, assumed equal to the nitrogen content in fruits, abscised leaves and woody organs yearly produced. Tree organ Biomass (t D.W. ha -1 ) N concentration (% D.W.) N content (kg N ha -1 ) Abscised leaves Fruit Woody organs yearly produced Total

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29 IRRIGATION AND NUTRIENT MANAGEMENT IN TREE FRUIT PRODUCTION SYSTEMS Neilsen, D 1, Neilsen, G 1, Forge T 1 denise.neilsen@agr.gc.ca 1 Agriculture and Agri-Food Canada, Summerland, B.C. Canada KEYWORDS Irrigation and nutrient management are linked; micro-irrigation; irrigation scheduling; available soil moisture; automated irrigation systems; nutrient availability in the root zone; matching nutrient demand and supply. ABSTRACT In irrigated production systems water management often controls nutrient availability. For apple, the change to dwarfing rootstocks and increasing tree density has provided the opportunity to focus water and nutrient inputs into the root zone, but this means that management needs to be more precise. As rootstock vigor decreases, the volume of soil accessed by the roots decreases Retention of nutrients in the root zone for as long as possible improves the chance of root uptake, increasing nutrient use efficiency and reducing fertilizer costs. This can be achieved by conservative water management and by applying fertilizer at the right time, rate and placement to meet plant requirements. Water management options include micro-irrigation systems which are well-engineered to meet peak demand and correctly designed for the crop/soil combination; mulches to reduce soil evaporation and irrigation scheduling. The amount of water required, depends on the stage of crop development, the amount of evapo-transpiration or precipitation that has occurred since the last irrigation and soil type. The lower the frequency of irrigation (subdaily to several day intervals), the more important soil type becomes. Improving water management by scheduling irrigation to meet crop demand has the benefit of saving water (Figure 1) nutrients and potentially improving fruit quality. Figure 1. Water and nitrogen retention in the root zone is determined by irrigation scheduling and timing of N applications. Losses are higher when irrigation is not scheduled to meet plant demands.

30 The most effective way to schedule irrigation is through fully automated monitoring systems based on estimates of evapo-transpiration and soil moisture measurements, which can then be used to control the irrigation system. The most effective way to match nutrient requirements to plant demand is through fertigation (applying nutrients through the irrigation system), which works best with drip and small radius micro-sprinkler. Nitrogen (N) is particularly suited for this as it is very mobile in soil and water, but because of that it is also difficult to control. In this case it is best to apply small amounts frequently (e.g. daily) and match the timing of application to plant demand. For apple and other tree fruits, it has been shown that there is little uptake from the soil until bloom as N which has been stored over-winter in the tree is used for early spring growth. Applying N during fruit cell division (approximately 6 weeks after bloom) promotes fruit and canopy development. Later N applications may have detrimental effects on fruit quality. If low, tree N status may be improved by postharvest foliar urea applications just before leaf senescence. Boron (B) is another mobile nutrient, like N, which can be fertigated. Phosphorus (P) is particularly important for tree root growth and early establishment. It can be applied pre-plant as a granular fertilizer and fertigated early in the season. A single large application is more effective than multiple small ones and should not be mixed with other fertilizers. Potassium (K) can become depleted under drip irrigation and fertigation or if ammonium N sources are used in other systems, particularly in coarse-textured (sandy) soils. Fruit removal of K can be double that of N, and if leaf K approaches deficiency, K applications do not negatively affect fruit storage quality.

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33 ROLE OF SOIL MICROBIOLOGY IN ORCHARD SYSTEM FUNCTION & PRODUCTIVITY Mazzola, M mark.mazzola@ars.usda.gov USDA-Agricultural Research Service, Wenatchee, WA KEYWORDS microbiome, rhizosphere, suppressive soils, soil-borne pathogens, nutrient cycling, system resilience, soil health ABSTRACT Soil microbiology significantly influences the function, efficiency, resilience, sustainability and productivity of all crop production systems including tree fruit orchards. These contributions may be positive, for instance in the cycling and retention of nutrient inputs, or may be negative as is the case for plant/soil-borne pathogen interactions. The composition and activity of the soil and rhizosphere microbiome (entire microbial community) will be determined by numerous factors including environment, management practices and the plant host. However, the microbiology that directly influences root health, and therefore most directly plant productivity, resides in the rhizosphere, a habitat which encompasses the narrow region of soil that is directly influenced by root exudates. The rhizosphere microbiome is vastly different from the same community found in bulk soil (non-rhizosphere soil) in terms of both composition and function. As such, while the management of the rhizosphere microbiome may depend upon indirect actions such as the application of a soil amendment, it can also rely on direct management through selection of the appropriate plant genotype. Our knowledge of how management, or host, influences the form and function of the rhizosphere microbiome has been advanced by novel technologies that enable us to see and monitor the entire community whereas in the recent past we were limited to those organisms that could be cultured or were more obvious in their function. As a result, we are well aware of the importance of the well-studied mycorrhizal fungi which extends function of the root by developing relationships that increase phosphorus availability to the plant and may also contribute to root health by limiting pathogen attack. Additional less well known but important components of the rhizosphere microbiome have been shown to enhance drought tolerance, induce flowering, and stimulate root formation. Benefits resolved from active management of the rhizosphere microbiome are most evident in terms of utilizing this microbiological resource for the control of soil-borne plant diseases. The use of biologically active soil amendments and employment of a specific host genotype (rootstock) can result in the recruitment of a specific rhizosphere microbiome which acts as the first line of defense against attack by root infecting pathogens. The capacity to effectively utilize the microbiology resident to orchard soil ecosystems will rely upon clearly defining management goals and greater understanding of the identity and function of the innumerable microorganisms that reside in the plant rhizosphere.

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37 Session 3 Manipulation of Tree Growth with Pruning and Plant Growth Regulators Session Manager Stefano Musacchi Objective: Understand the applied techniques available to manipulate physiological cycles in fruit trees. Presentations: Apple and Pear Tree Architecture Pierre-Eric Lauri Competition Among Vegetative and Reproductive Cycles and Role of Pruning Stefano Musacchi Plant Growth Regulators in Tree Manipulation Duane Greene

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39 APPLE AND PEAR TREE ARCHITECTURE A WAY TO IMPROVE ORCHARD MANAGEMENT Lauri, PÉ lauri@supagro.inra.fr INRA, Joint Research Unit SYSTEM (Tropical and Mediterranean Cropping System Functioning and Management), Montpellier, France KEYWORDS apple, architectural type, bourse-over-bourse, branching, centrifugal training system, flowering spur desynchronization, extinction, fruiting, pear, pruning, return-bloom, salsa training system, vegetative growth ABSTRACT Between 1960 and 1970, tree architecture evolved as a scientific discipline in tropical forests. First to synthetize knowledge on the form of trees and how it develops with time (ontogenesis), and second to analyze relationships between tree development and the dynamics of forests (sylvigenesis). Since 1989, the idea was developed at INRA, France, to implement architectural concepts on fruit trees with the objectives to analyze genetic diversity and to improve training and pruning. According to Lespinasse s typology, apple trees can be classified between two extreme types: type I (columnar type and spur type) cultivars, characterized by upright scaffold branches with dense spur branching, lateral fruiting and alternate bearing, and type IV cultivars with pendant laterals, long fruiting shoots, terminal fruiting and more regular bearing. Our objectives were to get more insights into these tree forms, and especially to analyze the relationships between vegetative growth and fruiting patterns. The first quantitative works were done on fruiting branches with cultivars of contrasting architectures. Figure 1 : Relationships between the number of leaves of flowering shoots (bourse and bourseshoot) on 1YW and flowering (top; from Lauri and Trottier, 2004) and fruiting (bottom) frequency in terminal position on that shoot on 2YW, for 2 apple cultivars, Pitchounette and Chantecler. Each symbol represents frequency on at least five shoots. Source: Lauri & Corelli-Grappadelli 2014

40 The methodology included the description of the fate and growth of all laterals across consecutive years. We showed that each cultivar can be characterized by a combination of architectural traits defining its endogenous architectural strategy. Especially, two main traits have been seen: bourse-over-bourse (the ability to string fruiting on a same shoot over consecutive years) and extinction (the death of a shoot). Across genotypes, bourse-over-bourse is curvilinearly related to shoot length (Figure 1). There is also a positive relationship between bourse-over-bourse and extinction supporting the idea that a higher ability to differentiate a flower bud in terminal position on a bourse-shoot is somehow related to a lower spur density on the branch due to extinction. The talk will explain how these findings opened to the concept that implementing artificial spur extinction in the ON-year on cultivars prone to alternate bearing is efficient to improve regular bearing. This technique has been initially developed on the Centrifugal Training System where it also aimed at improving the light climate for a better leaf functioning and fruit coloring (Figure 2). Based on results obtained in commercial orchards we are now progressing towards lessdemanding training and pruning systems. We consider that the search for both canopy porosity (partly related to natural or artificial extinction) and the physiological autonomy of the fruiting shoot (partly related to its length; see above) should be the objectives of manipulations done on the apple tree to improve regularity of bearing and fruit quality. Moreover, we propose to better adapt training to Figure 2: Evolution of tree architecture the natural ability of a given cultivar to be trained with a single trunk or as multiple-reiterative trunks. This latter concept is implemented in the Salsa Training System (Figure 2). Our experience in pear is strongly inspired by what was developed in apple. The talk will focus on two aspects, the influence on the entrance into production of the type of branching on the trunk in the first two years in the orchard, and the interest of artificial spur extinction of the vegetative shoots in the OFF-year.

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43 COMPETITION AMONG VEGETATIVE AND REPRODUCTIVE CYCLES AND ROLE OF PRUNING Musacchi, S. Washington State University, TFREC, Wenatchee, WA KEYWORDS pruning, dry matter (DM), competition, source, sink, flower bud, vegetative bud, thinning, anthesis, girdling, notching, bending, root pruning. ABSTRACT Vegetative and reproductive cycles in fruit trees overlap and generate a series of competitions among the various organs. Understanding the factors generating competition within the tree can improve the orchard management. The subjects covered in the presentation will be: physiological basis of vegetative and reproductive cycles, overlap of the two cycles, source-sink theory, dry matter (DM) partition, competitions among tree organs, and role of pruning in apple and pear orchards. Trees perform activities which are closely related such as: canopy and roots development, reproductive development (from flower bud differentiation up to fruit maturity) and reserves accumulation. Active growing organs (fruit and shoot tips) are typically strong attraction centers ( sink ) for photosynthesis products generated in the leaves ( source ) and nutrients. The sink strength seems to depend on the ratio between the different endogenous hormones involved. Pruning is a pool of practices that allow control of the tree growth and maximize the orchard income. Growth leads to a modification of the tree shape and/or dimension and occurs only when DM increases. Net total DM of an apple orchard is a function of incident solar radiation availability (independent of the production system) and light interception (training system-depending and the main factor limiting orchard productivity). The rootstock can affect the scion development by influencing various parameters: photosynthetic efficiency, speed and duration of growth, apical dominance, leaf area, leaf senescence, assimilates allocation and vigor. Main competitions between organs are: roots/shoots, shoots/buds formation, shoots/fruit, fruit development/shoots, seeds/flower buds, fruits in the same cluster, and shoots in a different position. Pruning can alter these competitions and therefore modify the gradient from vegetative to reproductive.

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47 IMPROVE TREE PERFORMANCE USING PLANT GROWTH REGULATORS Greene, D. University of Massachusetts, Stockbridge School of Agriculture, Amherst, MA KEYWORDS Growth control, Plant growth regulators, Prohexadione-calcium, chemical thinning, branching, ethylene inhibitors, Apogee, Kudos, AVG, harvest delay. ABSTRACT Plant growth regulators (PGRs) are compounds that regulate or direct specific physiological processes in the plant that improve fruit quality while helping to optimize production. It must be emphasized that PGRs can only be used effectively and profitably when applied to properly designed trees in a well-managed orchard. While they may help troubled orchards they are most effectively used in amplifying the value of fruit harvested in well managed orchards. Growth Control Effective growth control in is extremely important in today s well managed orchard. Prohexadione-calcium (Pro-Ca) has emerged as being the most important growth PGR in used in the orchard today. There are two formulations available (Apogee and Kudos) and these appears to perform comparably. Although Pro-Ca has been in use for many years we are still learning about how to use this most effectively. It requires 10 to 14 days after application for Pro-Ca to function fully as a growth retardant. Since trees in northern climates start to grow early and the most rapid growth is early, it is important to apply Pro-Ca as early as possible or when sufficient tissue has emerged to absorb it. When applied early repeat application(s) are generally necessary. The amount applied and the frequency of application depends on the amount initially applied and the propensity for the trees to grow. Pro-Ca can increase fruit set. This can be considered a positive effect when used on trees that will or have been blossom thinned. Generally, Pro-Ca treated orchards required a more aggressive thinning program to compensate for its tendency to reduced June drop. Delay in harvest and drop control Many commercial varieties suffer from moderate to severe preharvest drop. Consequently, controlling this malady as well as retarding ripening account for a very large portion of the total PGR use. While drop is less of an issue in Washington these same drop control products, ReTain and Harvista can be used to delay ripening. ReTain appears to be used much more frequently than is Harvista due in large part to the ability of the grower to apply what is needed at the proper time compared with application of Harvista which in most cases is done or directed by the company using

48 special application techniques or equipment. Response to ReTain is linear; the more you apply the greater the response. We generally use the maximum rate allowed per application on difficult varieties such as McIntosh. We use a third to half that amount on low ethylene producing varieties such as Honeycrisp and Gala. Although ripening is delayed as assessed by the starch test, treated fruit still loose firmness, so firmness must be monitored. Branching There has been an increase in the interest in increasing branching on trees in the orchard especially on trees grown as a tall spindle. The use of BA as the formulation MaxCel is the usual product used because of its effectiveness and the absence of GA to inhibit flower bud formation. Notching is also used to increase branching. When done together, prior to bloom a large percent of the treated bud break and develop into functional lateral shoots. Chemical thinning Crop load adjustment is one of the most important things and orchardist must do and it can influence the bottom line more than almost any other management decision. The use of PRGs is critical. Fruit may be thinned over at least a 3 week period. During this time a fruit is goes through changes that dictate the type of chemical approach that must be used. Initially at bloom caustic products or products that influence pollen germination of pollen tube growth are most useful. Hormone-type thinners such as NAA, Amid-Thin MaxCel or carbaryl may be used at petal fall but the mode of action as thinners at this time is unclear. As a fruit grows and develops it becomes a sink for photosynthates thus making them vulnerable to thinners that cause a stress in the trees by limiting available carbohydrate. It is at this stage that hormonal thinners are most effective.

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51 Session 4 Stress Physiology: The Good and The Bad Session Manager Tory Schmidt Objective: Understand the various environmental factors common in the Pacific Northwest that cause plant stress, their effects on various tree organs, and implications for orchard management strategies. Presentations: Basic Plant Stress Physiology Lee Kalcsits Heat and Light Stress/Sunburn Larry Schrader Management Strategies to Exploit Stresses Todd Einhorn Management Strategies to Mitigate Stresses Mike Robinson and Del Feigal (Presentation only)

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53 LINKING ABIOTIC STRESS TO HORTICULTURAL PERFORMANCE OF TREE FRUIT IN WASHINGTON STATE Kalcsits, L lee.kalcsits@wsu.edu Department of Horticulture, Washington State University, Wenatchee, USA Tree Fruit Research and Extension Center, Wenatchee, USA KEYWORDS Abiotic stress, light, temperature, water, salinity, cold, physiological responses, avoidance, tolerance. ABSTRACT In Washington State, abiotic stress such as heat, light, salinity, drought, cold and flooding stress can affect tree fruit orchards at some point during their productive life. Abiotic stress can be defined as a non-living factor that negatively affects plant growth, survival and its ability to reproduce. Abiotic stress causes changes in the soil-plantatmosphere continuum and can lead to reduced yields and decreased plant performance. These stresses are sensed in the plant and plants can either respond by increasing their tolerance to or using physiological avoidance to survive these events. These strategies lead to physiological and developmental changes that affect the productivity and growth of the tree. The severity, duration, frequency of exposure and combination with other stresses and its location of effect on the plant shape the type of response from the plant (Figure 1). Figure 2. Plant response scenarios to abiotic stress

54 Plants have the ability to sense the environment around them. They have signalling networks that quickly respond to changes in environment and, in turn, adjust protein activation, gene expression and cellular balance to tolerate or avoid abiotic stresses (Figure 2). Many abiotic stresses affect similar physiological pathways in plants and often similar mechanisms exist to tolerate abiotic stress, whether it is drought, cold, salinity or other stresses. Physiological responses include both immediate and longterm adjustments that include osmotic adjustment, cell wall permeability, protein adjustments, production of antioxidants and hormonal changes (Figure 2). For example, when water supply cannot meet the water demand by the plant, the plant is able to sense changes in water availability through ionic imbalance that lead to ion transport and concentration regulation which affect protein activity and gene expression. These biochemical changes shape how the plant acts and responds and ultimately affects the long-term productivity of the tree. Figure 3. Sensing external environmental changes in plants Although stress is defined as negatively affecting plant growth, productivity and survival, when properly managed, it can be used as a tool to manipulate growth and flower induction in horticultural crops. Timely water limitation or nutrient restrictions can induce responses that allow a grower to manipulate vegetative growth, dormancy induction, flower induction. However, there are other abiotic and biotic stresses that have negative effects on plant growth and performance. Here, the strategies of trees to survive abiotic stress events will be described in addition to the effects that these stresses have on tree performance, health and productivity.

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57 HEAT AND LIGHT STRESS/SUNBURN Schrader, L. Professor Emeritus, Washington State University, Wenatchee, WA KEYWORDS Apple; skin disorders; sunburn necrosis; sunburn browning; photo-oxidative sunburn; fruit surface temperature (FST); Fuji stain; lenticel marking; sunburn scald in Granny Smith; water core in Honeycrisp ABSTRACT Several fruit skin disorders are induced by heat and/or light stress in apples (Malus x domestica Borkh.). Some disorders appear on fruit prior to harvest, whereas others do not appear until after harvest and cold storage. Fruit do not utilize much light energy, so excess light energy is converted to heat injury. On a hot day, the fruit surface temperature (FST) of the sun-exposed side of apple can be 20 to 30 F above air temperature. Sunburn is usually the major cause of cullage. It appears before harvest and its incidence often provides an early signal that other disorders will appear later. Three types of apple sunburn have been characterized (Figure 1). One type (sunburn Necrosis Browning Type 3 Figure 1: Three types of fruit skin disorders induced by heat and/or light stress necrosis) is caused by heat alone. A high FST of ~126 F results in thermal death followed by necrosis. A second type (sunburn browning) occurs with high FST (115 to 120 F) and damaging UV-B radiation. A third type (photooxidative sunburn) appears to be caused by visible light alone and occurs on green peel (non-acclimated to light) that is suddenly exposed to full sunlight so that photobleaching occurs first, followed by necrosis. This third type results from photooxidative damage and can occur at much lower FST and without UV-B radiation. Another disorder that results from heat and light

58 stress is lenticel marking. Its incidence increases in fruit that have more severe sunburn. Fuji stain is a skin disorder that appears only after a period of cold storage. This stain disorder appears primarily in sunburned fruit, and its incidence rises sharply as the severity of sunburn increases. We have evidence that UV-B radiation is involved; incidence of stain is higher in orchards with excess Nitrogen. Another disorder that is enhanced by heat stress is bitter pit (especially in Jonagold). Although Calcium deficiency is reported to cause bitter pit, we observed increased bitter pit in Jonagold apples that were exposed to high temperatures and water stress as they neared maturity. Color of the peel did not develop normally, but had a blotchy appearance. High temperatures near maturity also increased water core in Honeycrisp. This physiological disorder is associated with internal moisture stress, and high temperatures cause premature conversion of starch to sugar and pronounced leakage from cells into intercellular spaces. Sunburn scald in Granny Smith develops during cold storage on the sun-exposed side of fruit that showed sunburn browning earlier in the season. If sunburn browning is prevented, the skin disorders listed above seldom appear. This suggests that management practices are needed to reduce absorption of UV-B radiation and to keep FST below critical temperatures at which sunburn browning occurs. Such practices include overhead evaporative cooling; sunscreen such as RAYNOX; sun blockers such as Eclipse or Surround WP; and photo-selective netting.

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61 MANAGEMENT STRATEGIES TO EXPLOIT STRESSES Einhorn, T. Oregon State University, Mid-Columbia ARC, Hood River, Oregon KEYWORDS Light, shade, fruit set, thinning, root pruning, return bloom, photosynthesis, carbon allocation, root pruning. ABSTRACT This presentation will focus on management strategies that either minimize or induce stress to optimize production of pome fruits with an emphasis on pear. Several topics will be discussed with attention paid to recent advances regarding the role of light (and shade), root pruning, and the application of plant growth regulators on flowering, fruit set, fruit growth, vigor relations and yield. Light management in fruit production is critical for optimizing dry matter production, initiating floral buds, and improving shoot renewal, fruit set and quality. Shade adversely affects fruit set by altering light quality and reducing the quantity of light necessary for photosynthesis to meet the carbon demands of developing fruitletshence, shade can potentially be managed to effectively thin fruits. Recent thinning studies will be used to demonstrate the efficacy of shade, alone, or in combination with specific plant growth regulators (PGRs) to induce fruit drop. The consequence of large, dense canopies on poor light distribution and non-uniform fruit set and fruit quality will also be discussed. Appropriate uses of reflective fabrics to improve canopy light interception and distribution, fruit set, fruit quality, and yield will be presented. Root pruning is a management strategy that invokes plant stress via production of stress hormones, reduction of growth-promoting hormones, and limited carbon supplies. Root pruning can also induce water and nutrient deficits which may further serve to alter growth and productivity. The objective of root pruning is to balance overly vigorous canopies characterized by delayed and/or poor productivity. Root pruning reduces vigor resulting in greater light penetration and distribution, improved carbon allocation to fruit buds, and increased return bloom and set the subsequent season. Hence, higher crop loads subsequently control vegetative growth. Root pruning has markedly improved apple and pear productivity; however, when applied improperly, severe stress can develop resulting in reduced fruit size and yield. Results from new pear trials will be presented outlining the appropriate use of this tool to optimize tree balance and productivity.

62 The application of PGRs is widely used to manipulate pome fruit growth and development. Several PGRs alter tree hormone balance and/or induce carbon stress to thin apples and pears. Positive results from two such compounds for thinning Bartlett pears will be presented. Alternatively, PGRs can be used to interfere with the production of natural growth inhibitors that might otherwise reduce productivity. For the low-setting cultivars Comice and d Anjou, the latter in the formative years, AVG can be used to inhibit the production of ethylene, which is partly responsible for abscission of flowers and young fruits; however, application timing is critical to success. A case will be presented for alternative AVG application timing based on the ethylene production of developing pear fruits. Finally, the use of auxin and ethylene-generating compounds to enhance flower initiation and improve return bloom will be presented.

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65 Session 5 Physiology of Fruit Maturation and Quality Session Manager Sara Serra Objective: Understand parameters of fruit maturation and pre-harvest practices to maintain high quality fruit from harvest through storage. Presentations: Fruit Maturity and Quality Jim Mattheis Optimizing Pre-Harvest Fruit Quality Sara Serra Pre-Harvest Growth Regulator in Pears Yan Wang Pre-Harvest Growth Regulator in Apples Dana Faubion

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67 FRUIT MATURITY AND QUALITY Mattheis, J. USDA, ARS Tree Fruit Research Laboratory, Wenatchee, WA KEYWORDS respiration, ethylene, ripening, color change, starch conversion, soluble solids, titratable acidity, softening, texture, aroma ABSTRACT Maturation is the process through which fruit develop marketable appearance and gain the capacity to ripen. Harvest ends the maturation process and maturity stage at harvest determines fruit quality after storage. Maturity has two important definitions. Physiological maturity is attained when fruit have the capacity to ripen after harvest. Horticultural maturity means fruit have developed marketable appearance and edibility. Fruit at physiological maturity typically have a long storage life but may not be horticulturally mature. This is commonly the case for red varieties where red color development lags behind the start of ripening. Physiologically immature fruit ripen poorly, do not develop typical flavor, and can be highly susceptible to shrivel, bitter pit, superficial scald, and external CO 2 injury during storage. Picking late in the maturation process when ripening has begun limits storage life due to softening, low acidity, and high susceptibility to chilling injury and internal CO 2 injury in susceptible varieties. Because maturation and ripening patterns vary among varieties, some varieties are best harvested before the fruit eats well while others should not be harvested until some typical flavor is detected. Ripening of apples and European pears requires ethylene gas. Ethylene is produced naturally by fruit but can also be applied from an external source to accelerate ripening. Ethylene production increases as maturation progresses and ethylene analysis is a means to assess physiological maturation. Fruit ethylene production is not always easily interpreted in part because the pattern of ethylene production varies considerably with cultivar and ethylene production trends vary from year to year. Other common indicators used to assess maturity include starch loss, peel ground color, firmness, soluble solids, and titratable acidity. Together these maturity indices provide an indication at harvest of where fruit is on its developmental path as well as what quality can be expected after storage. While changes in these attributes occur during maturation in all varieties, the patterns of change vary considerably among varieties. For example, starch index at optimum maturity for Red Delicious is very low compared to Honeycrisp.

68 Once harvested, the starch remaining is converted to sugar, softening and texture changes occur, chlorophyll breaks down, yellow pigments accumulate, aroma increases, the peel may become greasy, and acidity decreases as acid is used to fuel respiration. Many of these aspects of ripening require ethylene to proceed including softening, chlorophyll degradation, greasiness, and production of volatile compounds responsible for ripe aroma. The rate of acid loss is also an ethylene response. These processes all occur simultaneously but may not progress at the same rate, particularly when ripening is slowed due to use of postharvest technology. The beginning of physiological disorder development also occurs soon after harvest although visual symptoms of some disorders may not develop until months later. Figure 1. Ethylene production and respiration rate during maturation and ripening of apple fruit.