Plant Pathology and Insect Ecology Quiz

Plant Stresses

• Plant stress is anything that prevents a plant from reaching its full potential
• Plant stress responses show the characteristics observed when a plant detects stress
• Not all plants respond to all stresses in the same way
• Understanding plant responses to stress is important and challenging in plant research

Abiotic Plant Stress

• Abiotic plant stress is caused by non-living factors
• Examples include: cold, heat, nutrient deficiency, and salt content (NPKS)

Stress Caused by Salts

• Salts in soil deprive plants of water and dissolved nutrients
• Plant roots have a low water concentration which attracts water through osmosis
• Dissolved salts increase the osmotic pressure of the soil solution, reducing water intake by the roots
• If the soil solution is too concentrated, plants can die, even if water and nutrients are adequate

Salt Stress

• (Image of plants under salt stress)

Low Temperature

• Lower temperatures result in slow plant growth and development
• Every plant has an optimal temperature range
• Freezing can occur below 0°C, damaging cells
• Contents leak out and cells die
• Frozen plant tissue appears initially dark green and water-soaked but later becomes blackened and necrotic
• In dry conditions, the tissue may appear white as water evaporates

Frost Damage

• (Image of frost-damaged plant)

Frost Damaged Canola

• (Image of frost-damaged canola)
• Plant remains green when frost damage occurs and no water remains

Low Temperature (Perennial Species)

• Perennial species become dormant in preparation for winter
• However, these species can still be damaged by low temperatures

Winter Burn

• Winter burn (or winter desiccation) happens when absorption of water by roots cannot keep pace with moisture lost by foliage (transpiration)
• This is common in sunny/windy days with frozen soil, where plants cannot absorb water
• Injury shows as brown leaf margins on needle tips when warm weather begins

Winter Burn (Spruce)

• (Image of winter-burned spruce)
• Spruce are typically affected more frequently by winter burn when drought affects their water supply

High Temperature

• High temperatures can damage plant tissue
• Every plant has an optimal temperature range
• Cell proteins coagulate and the plant cell dies at high temperatures.

Wilting

• During warm weather, if plants cannot take up moisture, they wilt and die due to the Net Assimilation Rate being negative
• Respiration exceeds photosynthesis.
• To reduce water loss, the stomata closes
• This prevents plants from performing photosynthesis

Internal Leaf Structure

• The cuticle is the outer surface of the leaf and is non-cellular
• The cuticle may be waxy to reduce moisture loss
• Cuticle thickness varies between plants and is affected by environment
• Plant develop a thicker cuticle when conditions are hotter
• Cuticle thickness change can affect herbicide activity

Stomata

• Stomata are openings in plants that allow movement of gases (carbon dioxide, oxygen, water vapor)
• Vaporized water leaves and carbon dioxide enters through these openings
• Stomata of most plants open during the day for photosynthesis and close at night.

Guard Cells

• Guard cells are present in pairs in the epidermis (skin) of a plant
• Mostly found on the underside of the leaves
• Guard cells surround the stomata and regulate opening/closing

Guard Cells (Microscopic View)

• (Microscopic image of guard cells)

Turgor Pressure

• When conditions are hot/windy, plants experience water stress and wilt
• Reduced water pressure decreases the function of guard cells, which then close
• This action helps maintain water levels within the plant

Wilting (Image)

• (Image of wilted and healthy basil plants)

Why are weeds a problem?

• Weeds compete for light, water, and nutrients
• Weeds contaminate crops
• Weeds can cause downgraded quality
• Weeds can kill plants or animals
• Weeds can cause crop yield loss

Yield Loss

• Yield loss is due to weeds competing for essential plant growth resources (water, sun, and nutrients)

Canada Thistle (Cirsium arvense)

• (Image of Canada Thistle)

Wild Oats (Avena fatua)

• (Image of Wild Oats)

Contamination

• Weed seeds mixed with crop seeds lower the grade and value of grain
• Wild mustard seeds are similar to canola seeds in terms of size and shape, making separation impossible for conventional methods
• Contamination can reduce quality of crop products.

Contamination: Wild Mustard (Sinapis arvensis)

• (Image of Wild Mustard)

Harvest Losses

• Thick weed growth can make harvesting difficult
• Slower operation time and higher control costs lead to harvest losses
• Presence of dirt or other materials contaminates seed quality during harvest

Harvest Losses: Kochia (Bassia scoparia)

• (Image of Kochia)

Toxic Weeds

• Some weeds are toxic to animals and humans
• Death camas contain zygadenine alkaloid, more poisonous than strychnine
• Water hemlock toxins concentrate in rootstocks but are also present in leaves and stems
• Consuming poisonous plants can be fatal to animals and humans

Toxic Plants: Rhubarb (Rheum rhabarbarum) Leaves

• (Image of Rhubarb)
• Rhubarb leaves contain oxalic acid and glycosides, poisonous substances
• Consumption of rhubarb leaves may cause death
• Usually, death is incredibly rare when ingesting not substantial quantities

Why are weeds a problem?

• Weeds exhibit vigorous growth habits, competing with desired plants for resources and environment
• They are versatile, adapting to diverse environments, and creating competition for resources.
• Weeds have quick life cycles and produce copious amounts of seeds, enabling rapid dispersal and persistence.
• Effective seed dispersal and dormancy mechanisms of weeds further increase chances of survival and reproduction in different environments.

Specialized Stems

• Modified stems are frequent in plants
• These stem modifications often participate in vegetative reproduction, enabling the weed to remain persistent
• Modified stems can also serve as a food source for humans

Rhizomes

• Rhizomes are horizontal underground stems, serving as over-wintering organs for vegetative propagation
• Rhizomes create new shoots and roots at nodes, and grow into new plants, relying on nutrients from the parent plant for initial growth as example such as Purple Loose Strife and Canada Thistle.

Seed Distribution

• Weedy species are effective at seed dispersal
• Dandelion pappus is adapted for wind dispersal
• (Image of dandelion seeds)

Adaptations for Distribution

• Seeds and fruits are the plants way to propagate themselves.
• They can be distributed by wind (winged fruits like maple seeds, dandelion parachutes, or entire plant dispersal), water, or animals (barbed seeds like burrs)

Infectious Plant Diseases

• Infectious Plant Disease is caused by a living agent (pathogen), causing the disease to spread from one plant to another
• The majority of plant diseases are extremely contagious and hard to manage

Infectious Plant Disease Cycle

• Inoculation: pathogens transferred from a source plant
• Incubation: period from pathogen entering until the appearance of symptoms
• Infection: multiplication of pathogens and disease symptoms

Infectious Plant Diseases: Control Methods

• Control methods are most effective when conducted during the inoculation phase
• Plant diseases are often a significant cause of yield and quality losses in crops
• Prevention from diseases is more effective than treatment due to the difficulty and cost, and in times of favorable conditions

Causes of Infectious Disease

• Infectious diseases are caused by microorganisms
• Environment and agronomic conditions can influence the occurrence and severity of the disease, affecting plant health
• Unfavorable factors can make the disease more likely to worsen or spread, such as herbicide injury, nutrient deficiency, hail damage, deep seeding, or poor quality of seed.

Common Plant Disease-Causing Organisms in Western Canada

• Fungi are the most frequent (and important) plant disease causal organisms in Western Canada

Fungi

• Fungi reproduce through spores
• Spores can spread via air, water, machinery, insects, or contaminated seeds
• When moisture is present, spores germinate and grow along the plant surface; then the fungus penetrates plant tissues through wounds or stomata
• Spores survive in plant residues in the soil, or form overwintering bodies, ensuring the disease persists

How Plants React to Disease

• Plant diseases cause a reduction in yield and the deterioration of quality
• Symptoms include wilting, death of some or all plant parts, discoloration, or the appearance of lesions and tumors
• Identification of diseases may require lab testing due to the similarity between symptoms

Sclerotinia (White Mold)

• Sclerotinia stem rot, caused by the fungus Sclerotinia sclerotiorum, is a common disease
• It infects over 400 plant species
• Common crops affected include various legumes, canola, peas, and mustards
• Yield losses due to the disease vary between years based on the weather pattern - in Saskatchewan, higher risk areas experience greater moisture
• (Image of Sclerotinia on plants)

Ergot (Claviceps purpurea)

• Another fungal pathogen, Ergot (Claviceps purpurea), creates sclerotia (overwintering structures)
• It infects cereal and grasses, replacing the seed with a black mass of spores.
• The disease can be toxic to humans and animals
• (Image of ergot on wheat)

Ergot is Toxic

• Convulsive ergotism leads to nervous issues, pain, trembling, delusions, and hallucinations
• Gangrenous ergotism can result in loss of extremities due to restricted blood flow and subsequent infections with subsequent pain, and eventual tissue necrosis.

Aster Yellows

• Aster Yellows, caused by a phytoplasma, is transmitted by leafhoppers

• Symptoms lead to stunting, deformation, virescence (greening of flowers), phyllody (development of leaf-like flower petals), reddening of foliage, reduced root systems, and sterility

• (Image of disease on plant and diseased insect transmitting it)

Insects

• More species of insects exist than all other animals combined
• Insects are diverse and have various specializations

Beneficial Insects

• Insects benefit humans in their pollination, parasitism, and recycling nutrient roles.

Harmful Insects

• Harmful insects cause damage to crops, food, and buildings; and are resistant to various insecticides.

Insect Injury to Plants

• Insects can transmit diseases to plants directly, by feeding on plant tissues.
• Insects can cause damage, e.g. sucking juices, girdling stems, or chewing foliage of leaves, developing seeds and flowering parts

Insect Damage

• Insect damage extent dependent on insect population, plant growth stage, growing conditions , and weather patterns, and how effectively the plant recovers.
• Insect populations fluctuations are often cyclical

Insect Population

• Greater insect population sizes result in greater and faster crop damage.

Plant Growth Stage

• Smaller plants are more vulnerable to damage than mature, older plants.
• Planting dates can be modified to avoid specific insect damage

Growing Conditions

• Favorable growth conditions reduce insect damage impact
• Plants facing better growth conditions exhibit higher recovery rates after insect injury. Factors conducive to growth include adequate water, nutrients, and sufficient protection against environmental stresses

Weather

• Insect function varies with temperature. Some insects thrive in hot conditions, whereas others function better in cold conditions.
• Temperature can affect insect activity, and also inactivity, reducing insect impact on crops.

The Cyclical Nature

• Insect damage patterns often cycle based on the insect life cycle, including larval and adult stages of development
• Some insects have multiple generations per year while others only have one