Vine Biology and Function. Presented by Mary Retallack for

Transcription

1 Vine Biology and Function Presented by Mary Retallack for

2 Recommended Reading

3 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!

4 Introductions What would you like to find out more about today?

5 What is currently happening in the vineyard?

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8 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.

9 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.

10 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.

11 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.

12 Photosynthetic Tissue Chloroplasts are the sugar producing cells (mainly found in leaves). The chlorophyll in these cells enables the process of photosynthesis to occur.

13 Parenchyma (storage cells) Living cells with large central vacuoles (storage of substances) and thin but flexible cell walls They form the cortex and pith of stems, the cortex of roots, the pulp of fruits and the mesophyll of leaves (containing chloroplasts).

14 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

15 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.

16 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).

17 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.

18 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.

19 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

20 Anatomy of Vitis vinifera cane (A) and root (B) perivascular fibres The anatomy of one year old cane (A) can easily be distinguished from that of one year old 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 phloem pith Medullary rays 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

21 Support and Vascular tissue of a stem/cane

22 Support and Vascular tissue of root

23 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.

24 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

25 Zone of maturation Zone of elongation Zone of cell division

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

27 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 o C). Role of mychorrizal fungi

28 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

29 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 of the grapevine.

30 6 Root Distribution Most of the roots are concentrated in the top metre of the soil directly under the vine canopy.

31 Apical meristem Shoots A shoot is the succulent stem bearing the leaves, tendrils and flower clusters (inflorescences) all of the information required to grow a shoot is contained within a bud.

32 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.

33 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.

34 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 leafopposed 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).

35 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.

36 Formation of grapevine flowers (3 stages) - Inflorescence primordia The formation of inflorescence primordia takes place if the anlage undergoes repeated branching to develop many rounded branch primordia. Stages in inflorescence development, May 2006 (left) and August 2006 (right) (Heaslewood, PowerPoint Presentation)

37 Formation of grapevine flowers (3 stages) Flower formation The final stage is flower formation when the inflorescence primordia differentiate to form the flowers. 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).

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39 Grapevine growth stages Bud burst occurs in early spring when the average daily temperatures reach about 10 o C. 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.

40 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).

41 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 of poor weather conditions An adequate supply of carbohydrates from photosynthesis may be more important for achieving good fruit set.

42 Poor set - Terminology Coulure occurs when many flowers fail to develop into berries and drop (shatter) from the cluster within 10 days of 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.

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44 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

45 Seeded berry development follows three clearly defined stages Stage 1: Rapid Growth (40 to 60 days) 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. Muscat Gordon Blanco cell division and expansion

46 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 occurs. 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.

47 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 of 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).

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49 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

50 Photosynthesis Photosynthesis occurs in chloroplasts Chloroplasts contain photosynthetic pigment which is capable of absorbing energy from sunlight.

51 Photosynthesis Light energy is used along with water and carbon dioxide to produce sugars and starch which can be used to power plant growth. 6H 2 O + 6CO 2 + light energy (in the presence of chlorophyll) > C 6 H 12 O 6 + 6O 2 Six molecules of water plus six molecules of carbon dioxide produce one molecule of sugar plus six molecules of oxygen.

52 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

53 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 of about 200µEm -2 S -1. In grapevines no photosynthesis occurs at low light levels, below about 30µEm -2 S -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 -2 S -1 (light saturated).

54 What Affects the Rate of Photosynthesis 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.

55 Seasonal movement of photosynthates Shoot tipping at the start of flowering may help to improve fruit set 5 th leaf starts to transport

56 What Affects the Rate of Photosynthesis 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).

57 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.

58 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.

59 General grapevine plumbing system Water is lost to the atmosphere via the transpiration process 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

60 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 one 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.

61 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).

62 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.

63 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.

64 Stomata: CO 2 and Transpiration CO 2 enters the leaf through the stomata Closing stomata reduces transpiration but also reduces the uptake of CO 2 The rate of photosynthesis is dependent on the CO 2 concentration within the leaf Water loss and carbon gain are directly linked

65 Respiration Involves the breakdown of sugars (formed during photosynthesis) and starch to release energy. C 6 H 12 O 6 + 6O 2 > 6CO 2 + 6H 2 O + 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)

66 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

67 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.

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

69 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

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

71 Relating grapevine biology to vineyard management vine water requirements Growth Stage Budburst to flowering Flowering Set to veraison Veraison to harvest Harvest to dormancy Water use requirement Dry condition prior to budburst and up to flowering may result in short or stunted shoot growth and fewer flowers on the inflorescences. 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. 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. 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. 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.

72 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.

73 % of grapevine water requirements throughout the growing season (NSW Ag 2004) 40% 35% 30% 35% 36% 25% 20% 15% 10% 14% 5% 9% 6% 0% Budburst to flowering Flowering to Fruit set Fruit set to Veraison Veraison to Harvest Harvest to Leaf fall

74 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.

75 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.

76 Relating grapevine biology to vineyard management drought conditions Drought Related Issue Salinity Irrigating with saline water (or where soil salinity is high). Impact on Vine Biology 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 on vine health and fruit quality. Vineyard Management Considerations 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 outside 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.

77 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.

78 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?

79 Relating grapevine biology to vineyard management drought conditions Drought Related Issue Carbohydrate reserves Vine s stored carbohydrate (sugars and starch) reserves are lower Impact on Vine Biology 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. Vineyard Management Considerations 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

80 Relating grapevine biology to vineyard management drought conditions Vine Issues (related to drought conditions) Poor root distribution Impact on Vine Biology 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. Vineyard Management Considerations 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).

81 Relating grapevine biology to vineyard management drought conditions Vine Issues (related to drought conditions) Short shoots Shoot growth may be less with fewer functional leaves to ripen the crop. Impact on Vine Biology The potential for an unbalanced (over cropped) vine resulting in longer term vine health issues and poor fruit quality. Vineyard Management Considerations 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.

82 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).

83 Relating grapevine biology to vineyard management drought conditions Vine Issues (related to drought conditions) Vine canopy stress Stress may result in significant basal leaf loss, increasing the risk of sunburn of the fruit. Impact on Vine Biology 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. Vineyard Management Considerations 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).

84 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.

85 Relating grapevine biology to vineyard management general considerations Vine Issues (related to drought conditions) Root distribution and health Impact on Vine Biology 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. Vineyard Management Considerations 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).

86 Relating grapevine biology to vineyard management general considerations Vine Issues (related to drought conditions) Nutrient application Application of fertiliser Impact on Vine Biology 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). Vineyard Management Considerations 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.

87 Relating grapevine biology to vineyard management general considerations Vine Issues (related to drought conditions) High temperatures Impact on Vine Biology Elevated tissue temperatures due to warming by sunlight are most obvious 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. Vineyard Management Considerations 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

88 Relating grapevine biology to vineyard management general considerations Vine Issues (related to drought conditions) Post harvest care Getting ready for the next growing season Impact on Vine Biology 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. Vineyard Management Considerations 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).

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