Vine Biology and Function Presented by Mary Retallack for - - PowerPoint PPT Presentation

Vine Biology and Function

Presented by Mary Retallack for

Recommended Reading

We will cover the following topics

• Cell structure and function
• Types of plant tissues (meristematic, dermal, photosynthetic,

cortex and vascular)

• Grapevine Anatomy (roots, shoots, buds, leaves, flowering,

fruit development)

• Photosynthesis, Translocation, Transpiration, Respiration

And how this relates to vineyard management!

Introductions

• What would you like to find out more about today?

What is currently happening in the vineyard?

Growth (Meristematic) tissue

• Meristematic cells divide to make more cells, allowing the

vine to grow.

• They occur in the buds, root tips and shoot tips.

Growth (Meristematic) tissue

• The cambium layer of the vine stem is an example of a

secondary meristem because it enables organs to grow in

• thickness. When it is cut (damaged) it produces callus

tissue.

Wood (inner) and Bark (outer) Cells

Wood contains two main cell types

• Xylem cells, through which water and nutrients flow
• Ray (parenchyma) cells, which store food (starch

and proteins) Bark contains two different cell types

• Phloem through which sugars and other nutrients

move from one part of the vine to another

• Cork (phellum) cells which protect the vines inner

tissues.

Protection (dermal cells)

• Outermost layer of cells (epidermis)
• The bark of the vine protects the inner

cells from physical damage, pest invasion and winter loss.

• The epidermis of leaves and stems may

contain guard cells and hairs.

Photosynthetic Tissue

• Chloroplasts are the sugar producing cells (mainly found in

leaves).

• The chlorophyll in

these cells enables the process of photosynthesis to

• ccur.

Parenchyma (storage cells)

• Living cells with large central

vacuoles (storage of substances) and thin but flexible cell walls

• They form the cortex and pith
• f stems, the cortex of roots,

the pulp of fruits and the mesophyll of leaves (containing chloroplasts).

Collenchyma (living outer most cells)

• These cells form a complete

cylinder around the stem

• Elongated cells with thicker

cell walls (cellulose) providing strength and flexibility to stems and leaves

Sclerenchyma (support cells)

• Similar to collenchyma cells

but have additional lignin fibres in their cell walls which add strength and support to the plan body.

• As these fibres mature and

die they leave a hard skeleton of lignin fibres.

Vascular (conducting tissue) Xylem

• Xylem Conveys water and dissolved

minerals upward from roots into the shoot

• Consisting of elongated cells called

tracheids and vessel elements along with supporting fibres and parenchyma cells.

• The vessel walls contain perforations

connected to the next vessels in the line (which facilitate the movement of water and dissolved substances).

Vascular (conducting tissue) Phloem

• Phloem is the food or sugar conducting

tissue located on the inside of the bark.

• Vertical rows of sieve tubes along with

supporting fibres and parenchyma cells.

• A sieve tube plates connect each sieve tube

and controls the direction and flow of dissolved substrates.

• The movement of this sugar is always away

from the production site to a ‘sink’ or where it is to be utilised.

Dormant Ramsay cutting

• Section showing the small, thin

walled cells of the cambium

• The large sieve tube cells and the

thick-walled fibre cells of the phloem and xylem,

• The ray cells which in the xylem

contain starch grains and

• The large water-conducting xylem

vessel cells.

Anatomy of Vitis vinifera cane (A) and root (B)

• Although the internal structure of the

vascular cylinder (phloem, xylem and pith) is similar in Vitis stems and roots, the relations of the various tissues in the vascular cylinder differ considerably.

rh – rhytidoma (dead bark); co – dead cortex; ca – cambium; pe – periderm; phf – phloem fibres; pefi – perivascular fibres; ph – phloem; x – xylem; pi – pith, 11 – medullary ray; and px – residues of the primary xylem

Anatomy of Vitis vinifera cane (A) and root (B)

The anatomy of one year old cane (A) can easily be distinguished from that of one year

• ld root (B)
• Its strikingly larger pith
• It’s numerous and narrower medullary rays
• Its narrower phloem section
• The presence of perivascular fibres outside

each vascular bundle

• The presence of a thick dead bark

rh – rhytidoma (dead bark); co – dead cortex; ca – cambium; pe – periderm; phf – phloem fibres; pefi – perivascular fibres; ph – phloem; x – xylem; pi – pith, 11 – medullary ray; and px – residues of the primary xylem

pith Medullary rays phloem perivascular fibres bark

Support and Vascular tissue of a stem/cane

Support and Vascular tissue of root

Root distribution and function

• Main roots, lateral roots and

feeder roots.

• Feeder roots are formed

regularly during the growing season, short lived, and provide the large absorption surface needed to supply the vine with its nutrients and water.

Root distribution and function

Each root has at its end a yellow coloured region less than 2.5 cm long containing the absorption zone below this is the

• zone of elongation
• growing point
• root cap

Zone of maturation Zone of elongation Zone of cell division

The Casparian strip controls water movement into the vascular cylinder of the root

Root functions

Anchorage Water and nutrient absorption

• Dissolved nutrients in the soil solution are absorbed by the

roots and diffuse into the vascular tissue (xylem)

• Uptake of these nutrients depends on their concentration and

mobility in the soil, the uptake rate of the particular grape variety and the soil temperatures (optimum 25-30oC).

• Role of mychorrizal fungi

Arbuscular mycorrhizal root system and hyphae

• Beneficial organisms that

colonize plant roots

• Assist in the update of

nutrients (Phosphorous)

• Improve drought

tolerance

• Improve resistance to

certain fungal diseases

Root functions

Storage of reserves

• In late summer and autumn, carbohydrates are transferred for

storage in the root system to provide food reserves for the future season’s growth. Hormone production

• Hormone production (gibberellin and cytokinin) by the roots

influences growth and development of the shoots and clusters

• f the grapevine.

6

Root Distribution

• Most of the roots are

concentrated in the top metre of the soil directly under the vine canopy.

Shoots

• A shoot is the succulent stem

bearing the leaves, tendrils and flower clusters (inflorescences) all

• f the information required to

grow a shoot is contained within a bud.

Apical meristem

Leaf Function

• Leaves undergo a gradual transition from

importing photosynthetic products to export (at approximately 30-50% of the maximal size). Full leaf expansion may take between 30 to 40 days.

• Photosynthetic products from grapevine leaves are exported to the developing

apex and clusters.

• Following harvest/fruit removal, the majority of photosynthates are directed

towards and stored in the roots.

• Leaf fall or senescence normally begins in late autumn when minerals are

translocated (remobilised) back into the canes and trunk.

Compound and prompt buds

• Each compound bud contains three partially

developed shoots (primary, secondary and tertiary latent buds) enclosed in small leaf like structures called bracts which develops in the leaf axil.

• A lateral shoot (summer lateral) grows from a

prompt bud in the leaf axil.

• The prompt bud will grow into a lateral shoot in the

same season that it completes its development. The lateral shoot develops soon after the leaf at the same node has expanded.

Grapevine reproductive development

A) A developing latent bud showing an early stage of uncommitted primordium production. B) A later stage showing an uncommitted primordium, a leaf-

• pposed primordium, that has

separated from the shoot apical meristem. C) A dormant latent bud with an inflorescence primordium on the flank of the shoot apex. D) A dissected shoot tip with an immature tendril showing two branches. E) The structures found in the axil of a grape leaf. F) The typical architecture of Vitis Vinifera shoots originating from latent buds (Gibbard et al, 2003 pg 594).

Formation of grapevine flowers (3 stages) - Anlagen

• Anlagen (uncommitted primordia)
• May develop into inflorescence primordia,

tendril primordia or shoot primordia.

• Hormones
• Giberellin (GA) applied to inflorescence

primordia can convert them to tendril like structures.

• Cytokinin can be used to induce inflorescence

formation in place of tendrils.

• The formation of inflorescence primordia takes place if the

anlage undergoes repeated branching to develop many rounded branch primordia.

Formation of grapevine flowers (3 stages)

• Inflorescence primordia

Stages in inflorescence development, May 2006 (left) and August 2006 (right) (Heaslewood, PowerPoint Presentation)

• The final stage is

flower formation when the inflorescence primordia differentiate to form the flowers.

Formation of grapevine flowers (3 stages) – Flower formation

A) Young floral stage showing sepal/calyx development and petal primordia. B) Immature flowers with sepals covering the developing petals. C) Mature flowers with fused petals forming the cap. D) A longitudinal section of a grapevine flower prior to flowering and capfall. E) A hermaphroditic grapevine flower just after capfall. F) Young berries forming by the expansion of the pistil after pollination (Gibbard et al, 2003, pg 595).

Grapevine growth stages

• Bud burst occurs in early spring when the average daily

temperatures reach about 10oC.

• A period of slow growth for several weeks is followed by the

‘grand period of growth’ when shoot growth is very rapid (eg 2

• 3 centimetres per day).
• It is important to ensure you start the season with a ‘full’ soil
• profile. Check soil moisture monitoring equipment if winter

rainfall has been lower than average and apply sufficient water early in the season to avoid vine stress.

Grapevine growth stages

• Flowering is the next stage as the caps fall; this usually occurs about

eight weeks after bud burst.

• Cold rainy weather at flowering may reduce cap fall and subsequent fruit set.

Transition from an ovary to a berry (Dry, PowerPoint Presentation). Pollen tube growth in the grapevine flowers of Cabernet Sauvignon (Collins, 2004).

Poor set can be caused by a number of factors

To be able to manage fruit set in the vineyard, growers need to consider what factors affect fruit set at a particular site/vineyard, for example

• Varietal susceptibility
• Excess/lack of vigour
• High and low temperatures
• Exposure to wind
• Nutrient deficiencies
• Water stress
• Good carbohydrate reserves may

help to buffer against the impacts

• f poor weather conditions
• An adequate supply of

carbohydrates from photosynthesis may be more important for achieving good fruit set.

Poor set - Terminology

• Coulure occurs when many flowers fail to develop into

berries and drop (shatter) from the cluster within 10 days

• f opening.
• Hen and Chicken is a condition where there are a high

proportion of ‘chicken’ berries on a bunch.

• Millerendage is a condition characterised by berries

arrested at different stages of development and of different berry sizes on the same bunch.

They may include but are not limited to live green ovaries (LGOs), chickens or a combination of both. Bunches affected by millerendage tend to be loose.

Management options for overcoming Poor set

Some management options available to growers to manipulate fruit set include

• Shoot-tipping (at the start of flowering)
• Application of plant growth regulators (cycocel applied 3 weeks pre-flowering)
• Protective measures (wind breaks, cover crops, trees, physical barriers)
• Time of pruning (late pruning to shift flowering into a warmer period)
• Avoidance of water stress
• Nutrient applications (B, P, Zn and Mo can affect fruit set)
• Carbohydrate availability

Seeded berry development follows three clearly defined stages

Stage 1: Rapid Growth (40 to 60 days)

Muscat Gordon Blanco cell division and expansion

• The seed increases in size.
• There is a rapid increase in

berry size to cell division in the first two weeks, and some expansion

• The berry remains hard, acid is

high and sugar levels almost constant.

Seeded berry development follows three clearly defined stages (plus engustment)

Stage 2: A lag stage of nil or slow growth (7 to 40 days)

• The ‘lag phase’ is a period when either less growth or no growth in volume
• ccurs. The boundary between stage 2 and 3 is often unclear.

Stage 3: Growth resumes & maturation begins (approx 35 to 55 days)

• The onset of Stage 3 is signalled by veraison, the point of sudden change in

colour as green berries become yellow or red depending on the variety.

• During this stage, the berry softens, acid levels decrease, sugar is

accumulated, varietal flavours and aromas develop.

• The rapid increase in berry volume is due to cell enlargement.

Berry Development

Appearance of berries at 10 day intervals revealing the two successive sigmoid growth curves of a grape berry, named ’berry formation‘ and ‘berry ripening’. Three generalised x-axes are shown, days after flowering, approximate juice Brix values during ripening and developmental growth stages using the modified E-L system. The key growth stages and the approximate timing

• f the accumulation of major solutes are shown.

Top sketch indicating the relative activity of phloem and xylem transport into the berry. At bottom, scale drawings of anatomical features in the longitudinal sections of developing grape seeds at days, 4, 14, 28, 42 and 98 days after flowering

(Coombe and Iland, 2004).

Berry Anatomy

• The grape berries are made

up of skin, pulp, and seeds.

• The skin of grape berries

acquires different colours at differing stages in the growth cycle.

• Pigments in the outer layer

called anthocyanins are responsible for this colouring

Photosynthesis

• Photosynthesis occurs in chloroplasts
• Chloroplasts contain photosynthetic pigment which is

capable of absorbing energy from sunlight.

Photosynthesis

• Light energy is used along with

water and carbon dioxide to produce sugars and starch which can be used to power plant growth.

6H2O + 6CO2 + light energy (in the presence

• f chlorophyll) > C6H12O6+ 6O2

Six molecules of water plus six molecules of carbon dioxide produce one molecule of sugar plus six molecules of oxygen.

Photosynthesis

• The upper and lower surfaces of

the leaf are covered by the

• cuticle. This is resistant to the

diffusion of water and gases.

• The epidermis is below the cuticle

and chloroplasts are located below the upper epidermis.

• The epidermis contains the

stomata which are small openings in the leaf surface

What Affects the Rate of Photosynthesis

Light intensity, quality (wavelengths) and duration

• A single leaf in direct sunlight will absorb about 90% of

the sun’s radiation.

• Stomata open and close in relation to sunlight.
• They begin to open soon after dawn and are fully open at PAR
• f about 200µEm-2S-1. In grapevines no photosynthesis occurs

at low light levels, below about 30µEm-2S-1. Or about 1.5% of full sunlight.

• As light intensity increases so does photosynthesis until about

1/3 full sunlight is reached or 700 µEm-2S-1 (light saturated).

• Temperature – The optimum temperature for photosynthesis is generally

between 20 and 30C (and optimally at about 24C). Below 10C there is virtually no photosynthesis and it declines rapidly above 35C. Vine DNA denatures at about 50 C.

• Leaf age – The rate of photosynthesis increases rapidly in a young

grapevine leaf during the period of rapid leaf expansion.

• When it is one third its full size it exports more food than it uses and begins to contribute

to vine growth.

• When the leaf reaches its full size (about 30 to 40 days after unfolding) it is

photosynthesising at its peak.

• The rate of photosynthesis then gradually declines until the leaf becomes senescent.

What Affects the Rate of Photosynthesis

Seasonal movement of photosynthates

5th leaf starts to transport Shoot tipping at the start

• f flowering may help to

improve fruit set

Water Status – Water availability affects the opening and closing of the stomata and thus the entry of carbon dioxide into the leaves. The amount of water available for photosynthesis is determined by,

• The rate of transpiration (the capacity of the vine to replace lost moisture),
• Humidity (the lower the humidity or the higher the wind speed, the greater

the water loss),

• Mineral availability (especially nitrogen, iron and magnesium) which are

required to maintain leaf colour (if leaf chlorosis occurs then the photosynthetic capacity will be reduced),

• Stomata aperture (the opening and closing of stomata).

What Affects the Rate of Photosynthesis

Practical considerations

• The level of light reaching the leaves beneath the outer layer of the vine

canopy is generally less than required for maximum photosynthesis.

• When trellising grapevines, the grower should be aiming to maximise the number of

leaves exposed to direct sunlight.

• Vines carrying a heavy crop are able to photosynthesise at a higher rate

than vines carrying low crops.

• Beyond this limit, growth, fruit maturity and carbohydrate reserves are reduced.
• Vines that are stressed and wilt usually need some time to recover their

normal photosynthetic rate.

• This is probably because wilting causes some structural damage to the leaf cells.

Translocation

• Translocation is the process by which chemical materials and

nutrients are moved in the vine.

• Sugars can be exported to the shoot tip, the grape cluster, the root

system and/or other permanent parts like the trunk for storage (sinks).

• Stored foods flow in the phloem from the leaves to other parts of the

vine.

• Mineral salts, water, etc, absorbed by the roots, flow upwards in the

xylem.

General grapevine ‘plumbing system’

Water moves through the vine inside the xylem vessels carrying nutrients in solution.

Sugars and mobile nutrients move both up and down the vine in the living system of the phloem

Water and nutrients move into the vine via the roots Water is lost to the atmosphere via the transpiration process

Nutrient movement in grapevines

All minerals entering the vine roots from the soil must be in a water solution (some ions are absorbed more readily than others) Mobile nutrients (redistributed from old leaves to

the growing tip and deficiency symptoms evident on old leaves first) N, P, K, Mg, Mn

• Immobile nutrients (distributed in the xylem in
• ne direction only, to the growing tip and deficiency

symptoms are often evident on younger leaves first)

Ca, B, Fe,

• Variably mobile S, Cu, Mo, Zn

Nitrates quickly move to the leaves where they are converted into amino acids by chloroplasts. Magnesium, iron and nitrogen are needed by the leaves to produce chlorophyll. A shortage of these minerals can cause a yellowing (chlorosis) of the leaves.

Transpiration

• Water absorbed by the roots is drawn

into the leaves from where it evaporates in a process known as

• transpiration. Nearly all vine

processes are dependent on water.

• Up to 98% of water escapes from the

leaves and the stem as water vapour (natural cooling process).

• About 1% is used via photosynthesis

and another 1% is needed to keep the cells firm (turgid).

Factors affecting transpiration

• Humidity; Transpiration decreases as the humidity surrounding the leaves
• increases. Conversely, a rise in humidity will slow transpiration.
• Temperature; A rise in leaf temperature will increase transpiration.
• Light Intensity; The temperature of the leaf is increased as the light

intensity increases and this increases the rate of transpiration.

• The light level determines whether the stomates are open or closed. They are open in

the light and closed in the dark. They may also close on very hot windy days.

• Wind; The wind movement over the leaf takes with it the layer of water

vapour accumulated near the surface thus increasing transpiration.

Factors affecting transpiration

• Water content; Transpiration is influenced by both the water content of

the soil and the rate at which roots can absorb water.

• The loss of water from the leaves in transpiration increases the power of the

roots to absorb water (water intake will only occur if their are feeder roots present).

• If water is limited for a considerable time, the vine stops growing, the older

leaves yellow and drop and the fruit becomes susceptible to sunburn.

• Inadequate soil aeration slows down the water absorption rate of the roots.

This results in slow root growth and if conditions persist, the roots disintegrate.

Stomata: CO2 and Transpiration

• CO2 enters the leaf through

the stomata

• Closing stomata reduces

transpiration but also reduces the uptake of CO2

• The rate of photosynthesis

is dependent on the CO2 concentration within the leaf

• Water loss and carbon gain

are directly linked

Respiration

• Involves the breakdown of sugars (formed during

photosynthesis) and starch to release energy.

Glucose + Oxygen (in the presence of many enzymes) is converted to Carbon Dioxide + Water + Energy

The released energy is used by the vine for growth/fruit development and maintenance of the vine itself (shoots, leaves and roots)

C6H12O6 + 6O2 > 6CO2 + 6H2O + Energy

Respiration enables

• Synthesis of complex molecules
• Growth and repair of cells
• Active transport of materials across

cell membranes

• Extra energy for specials cells to

function

• Transport of materials in the phloem

Comparison between photosynthesis and respiration

The process of photosynthesis and respiration may appear to be the reverse of each other. They are not.

• The series of enzymes used in each process is different and the order of

reactions is not the reverse of each other.

Photosynthesis and respiration occur at the same time and are

interdependent. In photosynthesis, energy is stored and in respiration, energy is released.

Comparison between photosynthesis and respiration

Photosynthesis Respiration Produces sugars from energy Burns sugars for energy Energy is stored Energy is released Occurs only in cells with chloroplasts Occurs in most cells Oxygen is produced Oxygen is used Water is used Water is produced Carbon dioxide is used Carbon dioxide is produced Requires light Occurs in dark and light

Relating grapevine biology to vineyard management – vine stress

Visual indicators of water stress in vines

• The physiological reaction of a vine to water stress will depend on the

timing and level of stress during the season.

• If an exposed vine leaf feels cool to touch the vine is transpiring water

through the stomata (when vines are stressed, stomata partially or completely close, so transpiration ceases and the leaf feels warm).

• On a particularly hot day, the leaves may fold to avoid the sun, and tendrils

will appear to wilt.

• Berries may become less firm and start to shrivel

Relating grapevine biology to vineyard management – vine stress

Degree of Stress Vine Vigour Vine Appearance None Vine healthy and shoot tips growing vigorously (early in season) Shoot tip leaves light, bright green. Other leaves dull green. Tendrils not wilting at midday. Slight Slowing of vine vigour and shortening of inter node length. Shoot tip leaves light, bright green. Other leaves dull green. Tendrils wilting at midday. Moderate to High Shoot growth stopped. All leaves (including shoot tip leaves) dull light green. Tendrils and shoot tips drooping. High Vine canopy growth ceased Leaves folding, with backs to sun on hot days. Exposed basal leaves yellow. Shoot tips dead. High to Very High Leaves folded, light green with burnt margins, shoots

• drooping. Exposed basal leaves missing. Tendrils dead and

some missing.

Relating grapevine biology to vineyard management – vine water requirements

Growth Stage Water use requirement Budburst to flowering Dry condition prior to budburst and up to flowering may result in short or stunted shoot growth and fewer flowers on the inflorescences. Flowering As vines go through flowering, pollination and setting, they are extremely sensitive to water stress and set will be poor if vines are allowed to dry out during this critical phase of development. Set to veraison After flowering has concluded the vine canopy continues to grow until its maximum development. It is at this time that Regulated Deficit Irrigation practices may be employed to reduce berry cell division and subsequent cell elongation. Veraison to harvest Grapevines can endure some stress during this period however try to minimise water stress up until to harvest to ensure even ripening conditions. If the leaves are stressed they wilt and older leaves may fall to the ground exposing the fruit zone. Despite these outward appearances of moisture stress the berries will continue to increase in sugar. Harvest to dormancy After harvest the amount of moisture required by the vine is considerably lower but maintaining adequate moisture levels is critical for the vine to accumulate carbohydrate reserves into the maturing

• canes. Try to maintain active leaf function without encouraging new shoot growth.

Relating grapevine biology to vineyard management – heatwaves

What is your strategy for heat waves?

• Allocate a certain percentage of your irrigation budget for extreme weather events.
• Vines planted on sandy soils will dry out quickly. Risk of crop loss is high. Vines may shut

down resulting in delayed or uneven ripening.

• To minimise water used during heatwaves, make sure vines have water before the hottest

part of the day. Water at night or early in the morning.

• Be willing to sacrifice a small part of the block to get the majority through without

creating excess vigour.

• Be prepared to act quickly. You may need to forego a post-harvest irrigation to save this

season’s crop.

% of grapevine water requirements throughout the growing season (NSW Ag 2004)

9% 6% 35% 36% 14% 0% 5% 10% 15% 20% 25% 30% 35% 40% Budburst to flowering Flowering to Fruit set Fruit set to Veraison Veraison to Harvest Harvest to Leaf fall

Relating grapevine biology to vineyard management – drought conditions

Drought Related Issue Impact on Vine Biology Vineyard Management Considerations Lack of early season soil moisture Soil profile not full at the end of Winter Significant reduction in vine vigour and fruit set is likely if vines are stressed at the start of the growing season. Monitor soil moisture during winter months and in the lead up to budburst. Apply an early season irrigation to ensure the soil profile is full from budburst if required.

Relating grapevine biology to vineyard management – drought conditions

Drought Related Issue Impact on Vine Biology Vineyard Management Considerations Less water available Less water in dams, rivers, lakes and aquifers and allocations of irrigation water may be reduced Reduced water availability may result in vine stress early in the growing season Careful timing and use of available irrigation water is critical to vine health. Do not grow a large canopy if you do not have the water to ripen a large crop or maintain the additional shoot area. Match the shoot length to the fruit volume to be ripened (while providing sufficient leaf area to protect the fruit). Develop an irrigation budget and determine if additional water needs to be purchased (if available and cost benefit warrants additional purchase). Monitor vine growth carefully ensuring irrigation is applied at key times without encouraging excessive shoot length.

Relating grapevine biology to vineyard management – drought conditions

Drought Related Issue Impact on Vine Biology Vineyard Management Considerations Salinity Irrigating with saline water (or where soil salinity is high). All irrigation water contains dissolved salts at some concentration, as water is transpired by the vine these salts are left behind in the soil. If saline irrigation water is applied this is another source of salt entering the soil. Depending on level of water salinity and the build up of salts in the root zone, this may reduce vine vigour and adversely impact

• n vine health and fruit quality.

Consider applying an additional leaching irrigation in winter following a rainfall event (if possible) and apply (pulse) irrigation applications during the growing season to regularly push the salts

• utside the root zone.

Minimise the use of fertilisers which may add to the ‘salt load’ being added to the root zone (some nutrients may be needed to encourage vine vigour and maintain vine health). Mound undervine to provide a larger area for roots to explore (above an existing water table) and apply mulch undervine to minimise water loss. If replanting your vineyard consider planting onto salt resistant rootstocks.

Relating grapevine biology to vineyard management – drought conditions

Drought Related Issue Impact on Vine Biology Vineyard Management Considerations Wind Often more wind with greater evaporation Stomata will close frequently in windy

• conditions. Winds of 11 to 14 km/hr are

sufficient to cause the closure of stomates. This will reduce the level of transpiration and will also limit the production of

• photosynthates. Prolonged exposure to

windy conditions may result in shorter shoot length and an adverse impact on vine health. Install windbreaks; apply undervine mulch to maintain soil moisture.

Relating grapevine biology to vineyard management – drought conditions

Drought Related Issue Impact on Vine Biology Vineyard Management Considerations Frost Intensity of frost events may be higher due to dry soils, leading to consumption of water for frost mitigation. Frost events can cause severe damage to emerging shoots and dormant buds if it is cold enough. If the primary bud (or shoot) is damaged the secondary shoot may grow to takes its place (the fruitfulness is likely to be lower). You may find buds burst from ‘non count’ positions and they will need to be removed either shoot thinning during the growing season or at pruning time. Frost mitigation strategies (moist soil surface, vegetation slashed, frost fans, overhead sprinklers, use of tiny tags to monitor temperature). Post frost management strategy?

Relating grapevine biology to vineyard management – drought conditions

Drought Related Issue Impact on Vine Biology Vineyard Management Considerations Carbohydrate reserves Vine’s stored carbohydrate (sugars and starch) reserves are lower Grapevines rely on stored carbohydrate reserves early in the season for root and shoot growth (until leaves are 1/3 full size and can contribute to the vines energy requirements). Low vine carbohydrate reserves will impact on vine vigour and capacity to grow fruit. Avoid significant vine stress as this will reduce the vine photosynthesis (and carbohydrate production). Maintain the functioning leaf area post-harvest so the vines can produce and store carbohydrate reserves (this is particularly important for higher yielding varieties). Apply sufficient water and fertiliser early in the season to assist the vines in replenishing carbohydrate reserves early in the growing season

Relating grapevine biology to vineyard management – drought conditions

Vine Issues (related to drought conditions) Impact on Vine Biology Vineyard Management Considerations Poor root distribution The majority of vine roots are concentrated in the top metre of soil directly under the vine canopy. Wide dripper spacings may create ‘silos’ of alternating wet and dry areas along the undervine

• area. This may result in the root area being

naturally ‘pruned’ due to the dry conditions. Vine roots produce a plant hormone called abscisic acid (ABA) in response to stress. This signals for the rest of the vine to ‘shut down’ until conditions improve. Install drippers with closer emitter spacings or install additional drippers to maintain a wetted ‘strip’ undervine. This will encourage greater root exploration (mulch to retain water for longer).

Relating grapevine biology to vineyard management – drought conditions

Vine Issues (related to drought conditions) Impact on Vine Biology Vineyard Management Considerations Short shoots Shoot growth may be less with fewer functional leaves to ripen the crop. The potential for an unbalanced (over cropped) vine resulting in longer term vine health issues and poor fruit quality. Apply irrigation to grow sufficient shoot area to ripen crop. If the shoot length (or leaf function) is reduced then reduce the crop load accordingly.

Relating grapevine biology to vineyard management – drought conditions

Vine Issues (related to drought conditions) Impact on Vine Biology Vineyard Management Considerations Flowering conditions changed Flowering may occur earlier in a drought year than in a normal year. Frost, dry and windy conditions during flowering are not conducive for optimal set. High and/or prolonged low temperatures can also reduce set. Ensure vines are not moisture stressed up to and during flowering. Be ready to apply pre-flowering nutritional sprays at optimal timing (Boron, Zinc etc).

Relating grapevine biology to vineyard management – drought conditions

Vine Issues (related to drought conditions) Impact on Vine Biology Vineyard Management Considerations Vine canopy stress Stress may result in significant basal leaf loss, increasing the risk of sunburn of the fruit. Basal leaf defoliation will reduce the photosynthetic capacity of the vines (if the basal leaves are still functioning). Lack of fruit protection may result in uneven ripening, lower fruit quality (sunburn, phenolics characters, berry shrivel) and lower yield. Ensure vines are not stressed to the point of basal leaf loss. If hot weather (a heat wave) is forecast start irrigating several days prior (preferably at night) to reduce the level of vine stress experienced. Maintain irrigation application throughout hot weather (keep an eye on soil moisture monitoring results or use a ‘dig stick’ to determine how deep the irrigation is going down the profile).

Relating grapevine biology to vineyard management – general considerations

Vine Issues (related to drought conditions) Impact on Vine Biology Vineyard Management Considerations Vineyard development Site potential, Row direction (wind) Match vines (variety and clone) to the site to realise their full potential (soil, topography, aspect). Some vineyard sites are particularly windy and vines will struggle to grow well. Soil type may also be limiting. Carry out a thorough site assessment prior to planting. Plant vines parallel to the prevailing wind and/or install (or plant) a suitable windbreak to protect the vines.

Relating grapevine biology to vineyard management – general considerations

Vine Issues (related to drought conditions) Impact on Vine Biology Vineyard Management Considerations Root distribution and health Root distribution and health will be reduced in dry conditions, shallow root zones, nematodes, waterlogged environments (lack of aeration), impervious soil layers etc. This will adversely impact on vine health. Manage the rooting environment so it is conducive to optimal root growth (encourage roots to explore the soil profile available to them, deep rip hard pans, apply mulch to maintain soil moisture and reduce surface heat/reflection).

Relating grapevine biology to vineyard management – general considerations

Vine Issues (related to drought conditions) Impact on Vine Biology Vineyard Management Considerations Nutrient application Application of fertiliser Vines appear to have one main peak of root growth coinciding 4 to 6 weeks after budburst (near flowering). A second flush of root growth may occur post-harvest but not to the same extent as earlier in the growing season. If fertilisers are mobile in the soil and applied prior to the development of feeder roots they may be leached through the profile prior to the vines taking them up (nitrogen). Consider the best way to apply fertiliser. Macro nutrients are needed in larger quantities (broadcast or fertigate – time with irrigation application) and micronutrients are needed in smaller quantities (foliar application). Some nutrients are highly mobile and some are less immobile this will affect the method of application. Micro nutrients are best applied to the vine canopy. Some foliar nutrients need to be applied at key times ie during spring and/or pre-flowering.

Relating grapevine biology to vineyard management – general considerations

Vine Issues (related to drought conditions) Impact on Vine Biology Vineyard Management Considerations High temperatures Elevated tissue temperatures due to warming by sunlight are most

• bvious on sunny and calm days. For example grape berries exposed

to bright sunlight on clam days can be warmed up to 15C above the air temperature. Wind cools because it removes some of the stored heat from the surface of the berry. In contrast grapevine leaves do not warm as much as berries as they are cooled by transpiration. Ambient leaf temperatures above about 50C are hot enough to denature the leaf DNA causing irreversible damage to the leaf resulting in death and defoliation. Photosynthesis inhibition is usually seen about 10C lower than the lethal temperature. Vines with sufficient leaf area to provide protection, a deep root system tend to cope with heat better than weak vines with poor vigour. Ensure sufficient irrigation is applied leading up to an during periods of high temperatures. Recovery from heat stress is rapid (2 to 5 days) if tissue damage is avoided

Relating grapevine biology to vineyard management – general considerations

Vine Issues (related to drought conditions) Impact on Vine Biology Vineyard Management Considerations Post harvest care Getting ready for the next growing season Vines will export nutrients with the fruit produced. It is important to maintain vine health and build up the vines carbohydrate reserves prior to senescence. Vines will continue to function normally while actively functioning leaves are present. A second (smaller) flush of root growth may occur after harvest. Maintain water application until leaf senescence (while there are functioning leaves the vine will be transpiring and producing carbohydrates). Apply post harvest fertiliser if functional leaves are present to replace nutrients removed at harvest. Post harvest uptake of nitrogen and phosphorous is important and to a lesser extent potassium, magnesium and calcium. Ensure you do not encourage new shoot growth at this time of year. You will lose the opportunity to build the vines carbohydrate reserves if the growing season is cut short unexpectedly ie due to frost or extreme stress (defoliation).

Acknowledgements

The Advanced Viticulture series has developed on behalf of: Funding for the Advanced Viticulture series has been provided by: