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-plant-atmosphere 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

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 long-term 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.

Linking abiotic stress to horticultural performance of tree

fruit in Washington State

Lee Kalcsits, Assistant Professor

Department of Horticulture

Washington State University

Tree Fruit Research and Extension Center

Wenatchee, WA

What is abiotic stress?

• An non-living external force that negatively affects the growth, productivity and health of a plant (light, heat, water, nutrient, cold, etc.)

Cold

Mechanical Injury

Air PollutionLight

Heat

Water

Salinity

Plant Responses to Abiotic Stress

Summer Growing Season in the Pacific North-West (East of

the Cascades)

• Average daily maximum temperature in July and August (91 F)

• High light intensity (>2000 umol m-2 s-1 PAR)

• We live in a desert

• Water restrictions are forcing the use of wells

• Sudden cold periods

Plant Responses to Abiotic Stress

How stress interacts with the tree

• Sudden changes in temperature or irrigation failure• Heat or cold

• Duration• How long the stress event lasts for, -20 F for one hour or below -10 F for 1 week?• Time with water stress

• Number of exposures• How frequent stress events are? Can the plant recover between events

• Combination of stresses• Water stress with salinity? • Cold with biotic stress• Heat with light in the summer

Plant Responses to Abiotic Stress

What affects how a plant responds?

• Affected location of the plant• Roots are less cold hardy than stems which are less cold hardy than buds

• Fruit is more susceptible to sunburn than leaves

• The developmental stage• Each stress affects the plants differently at different stages

• Genetic differences• Each scion/rootstock shows different responses to abiotic stress.

• Some are more drought tolerant/cold tolerant

• Some are less susceptible to sunburn

• Some rootstocks are more cold hardy

Plant Responses to Abiotic Stress

How does a plant respond?

• Tolerance – The stress affects the plant but it does not lead to death

• Resistance – The plant has mechanisms in place to limit damage caused by stress

• Increased Susceptibility to Pests and Disease – Damage caused by abiotic stress can increase the risk of insect and disease attack

• Death

Brunner et al. 2015. Frontiers in Plant Sciences

Plant Response - Stress Sensing

Reactive Oxygen Species (ROS)

• Chemically reactive molecules containing oxygen. Examples include H2O2, O2

-, OH-, and O-.

• These are fine at normal rates but increase under stress and can cause damage.

• Plants respond by scavenging ROS throughout the plant• Antioxidants

• Secondary metabolites

Hormonal Responses• Absiscic Acid – ABA

• ABA-mediated signaling also plays an important part in plant responses to environmental stress

• ABA concentration increases under stress that affects molecular, metabolic and developmental processes.

• Jasmonic Acid – JA• The major function of JA and its various metabolites is regulating plant

responses to abiotic and biotic stresses as well as plant growth and development.

• Changes in plant development with JA include growth inhibition, senescence, flower development and leaf abscission.

• Ethylene• Increased levels of ethylene under environmental stresses • Often unable to grow and proliferate to any great extent, at least until the

stress is removed and the ethylene level is lowered.

Morphological and Developmental Responses

Horticultural Responses

• Manipulation of growth

• Manipulation of flowering

• Crop load/size

• Postharvest quality/storability