Persea americana Mill
Origin and races
• Family: Lauraceae • Genus: Persea • Species: americana • Latin name: Persea americana Mill. • Origin: Central America – Mexico and Guatemala
Origin and races
Avocado = (Aztec ) Ahuacatl Another names: Palta (Inca) ,Custard apple (Africa), abogado (Spain), avocat (France)
Origin and races
History of the crop http://www.avocado.org/about-california-avocados/
Avocado has grown wild in Mexico for ca. 10,000 years, and cultivated for ca. 2,500 years 500 years ago, avocado began to be distributed to other countries.
Origin and races Origin: Central America – Mexico and Guatemala
West Indian (plain(
Guatemalan (mountains)
Mexican (high mountains)
Origin and races
The avocado is divided into 3 types, called races. The 3 races differ in: • Thickness of the exocarp • Time between flowering and fruit maturation • The "anise" (licorice) smell of their leaves Other differences include: sensitivity to frost, resistance to salinity, etc.
Origin and races
Variation in colour and shape Variation in West Indian race avocados obtained from a seedling grove in the Yucatan, Mexico.
Origin and races
Seedling fruit of avocado from: San Jerรณnimo, Costa Rica, April 1997.
Birnbaum et al., 2003
Origin and races Variation in seed size and fruit shape of some avocado seedling
Whiley et al., 2002
Origin and races
Main characteristics of the 3 races Race
Topography Anise smell
exocarp
Time from Resistance Resistance flowering to to frost to salinity fruit maturation 5-7 High Low
Mexican
High mountains
+
Thin
Guatemalan
Mountains
-
Thick
9-12
Medium
Medium
West Indian
Tropical valleys
-
Medium
6-8
Low
High
Origin and races
• There are many hybrids of these 3 races. • Some hybrids are natural occurrences and others from artificial hybridization. • 'Nabal' belongs to the Guatemalan race, but 'Hass', 'Fuerte' and 'Ettinger' are hybrids of 2 different races.
'Hass' and 'Fuerte' are hybrids between Guatemalan and Mexican races. 'Ettinger' is a hybrid between West Indian and Mexican races
Origin and races
Natural hybreeds anise scent
Mexican
Guatemalan
Mexican x Guatemalan
Reproductive biology
Reproductive biology
To set fruit, the tree has to pass through 5 steps: 1. Differentiation to flowering 2. Normal flower development – male and female 3. Pollination – pollen movement between flowers 4. Fertilization – pollen (n) tube growth in the style until the male gamete conjugates with the female gamete – egg cell (n) to create the zygote (2n) 5. Fruit development
Differentiation
• During the fall/winter – 3 to 5 months before flowering (in deciduous plants – 9 months before bloom)
Differentiation
• In a heavy crop load ("On" year) reduction of differentiation, especially in 'Hass' • The main reasons: 1. Lots of fruit many seeds/tree high synthesis of gibberellin reduction of differentiation potential 2. Competition between the fruits and buds for assimilates less C to the buds less differentiation
Differentiation
How can we reduce "alternate bearing"? 1. Thin some of the fruit ď § reduction of competition 2. Inhibit the fall vegetative flush (which needs a lot of carbohydrates) using growth retardants ('Kultar', 'Magic')
Flower development
Bloom ď § first step for obtaining fruit
Flower development
• Usually, there are no problems with avocado flowers. • A very cold winter (<0°C) or a very hot spring (>35°C) can harm the female and male flower organs.
Reproductive biology
Pollination The honeybee is responsible for the pollination process (transfer of pollen grains from one flower to another).
Pollination
• To understand the pollination of avocado flowers, we need to be familiar with the flower's structure and its suitability to honeybees. • Avocado flowers are very small (5 mm diameter) and they are carried on big inflorescences with hundreds of flowers. • Each mature tree contains ca. 1 million flowers. • The single flower is bisexual – contains male and female organs in the same flower.
Pollination and fertilization
Avocado flower
stigma
petal sepal
10 mm
style
staminodes stamens ovary
Pollination and fertilization
• To reduce the potential for self-pollination (encourage cross-pollination), a unique mechanism has developed in the avocado tree, termed "protogynous dicogamy“. Dicogamy – Male and female organs do not mature at the same time. Protogynous – The stigma (female organ) is receptive before the anthers release their pollen (the gynoecium = female part is the first to open) • Avocado flowers open twice: 1. Female opening on day 1 2. Male opening on day 2
First opening (1st day): Female Stigma â&#x20AC;&#x201C; receptive Stamen â&#x20AC;&#x201C; closed and "tightened down"
At night the flower is closed
Second opening (2nd day): Male Stigma â&#x20AC;&#x201C; not receptive Stamen â&#x20AC;&#x201C; erect and open
Pollination and fertilization
Pollination and fertilization
Flowering groups/types • All avocado cultivars belong to one of two flowering types – A or B. • 50% of cultivars belong to A and 50% to B.
Pollination and fertilization
Flowering groups/types
Pollination and fertilization
Pollination and fertilization
Pollination usually occurs between cultivars belonging to 2 different flowering types. For example â&#x20AC;&#x201C; cross-pollination of 'Hass' (A) by 'Ettinger' (B).
Pollination and fertilization
B (‘Ettinger’)
A (‘Hass’)
Afternoon
Morning
Morning
Afternoon
Pollination and fertilization
Is pollination a limiting factor for yield? • Avocado tree has ca. 1 million flowers. • Good yield = 500 fruit/tree (0.05%). • Heavy yield = 1,000 fruit/tree (0.1%). • Since many flowers are abnormal and there are many problems with fertilization, we need to pollinate many flowers (200-300 thousand) to obtain 500 fruits. • To achieve this, we need a lot of pollination (10,000 flowers/tree per day) .
Pollination and fertilization
Closed pollination Sometimes there is overlap between male flowers and female flowers on the same tree, so they can fertilize each other (a type of "self-pollination" occurring within the same tree) but not with the same flower.
Pollination and fertilization
Closed pollination
Pollination and fertilization
Cross-pollination is preferred 1. Reduction in yield as the distance from the pollenizer increases. 2. Manual cross-pollination gives better fruit set and yield than self-pollination.
Pollination and fertilization Influence of distance from pollenizer on yield of 'Hass' avocado 250 200 150 לעץFruit/tree מספר פירות
100 50 0
1
5 ממפרהpollenizer שורה Row from
Kobayashi et el., 2000. Scientia Hort. 86, 135-149
15
Pollination and fertilization How do the honeybees act as pollinators? Honeybee is the ideal pollinator: 1. Needs nectar + pollen 2. Has a lot of hair on its body ď § collects and transfers the pollen grains Hair on the leg
HB on avocado flower HB with pollen pellets on its legs
שלב Femaleנקבי stage
Male stage
HB collects nectar and touches stamens+ stigmas
Ish Am & Eisikowitch, 1993
Pollination and fertilization
Pollinating avocado with bumble bees
Summary of pollination in avocado Self pollination Flower types
B ‘Ettinger’
A ‘Hass’
6:00
12:00
18:00
Summary of pollination in avocado Cross pollination
Flower types
B ‘Ettinger’
A ‘Hass’
6:00
12:00
18:00
Summary of pollination in avocado Closed pollination
Flower types
B ‘Ettinger’
A ‘Hass’
6:00
12:00
18:00
Pollination and fertilization
Cross-pollination
‘Hass’
‘Ettinger’
Pollination and fertilization
Cross-pollination Possible movement of honeybees in the orchard
Self- pollination Self- pollination
Self- pollination
Cross- pollination
Pollination and fertilization
Orchard-design Couples of pollenizers
Rows direction
Pollination and fertilization
Orchard-design Pollenizers at the end of the row
Rows direction
Pollination and fertilization
Orchard-design Pollenizer at 1:6 ratio
Rows direction
Pollination and fertilization
Pollenizer at 1:9 ratio
Rows direction
Pollination and fertilization
Summary of pollenizers in avocado 1. We need pollenizers in the orchard (a solid block of one cultivar is not desirable). 2. The distance between cultivars must be minimal. 3. The overlap between cultivars' flowering must be good.
Pollination and fertilization The importance of insects/bees to avocado pollination:
• In closed trees (net) – very low yield • Wind pollination – almost no yield • Conclusion – avocado needs insect pollination
Pollination and fertilization
Competing flowers â&#x20AC;˘ During March and April ď § many competing flowers outside the avocado orchard (citrus, mustard, etc.). â&#x20AC;˘ Honeybees prefer the competing flowers, which are rich in nectar (citrus) or pollen (mustard).
Pollination and fertilization
Recommendations • 5-10 honeybees/tree per minute • Introduction of hives at 10% bloom • Density of 2.5-5 hives/ha • Distance between hives – not more than 150 m
The movies Avocado Flowering (A-Type)
Self pollination: How does Pollination Work? The mysteries of the avocado flower How Avocados Are Made
How To Super Pollinate Avocado Trees
Fertilization
Germination of a pollen grain on the stigma growth of pollen tube (with 2 generative nuclei) toward the ovule to create "double fertilization": 1. The egg cell zygote (2n) embryo
2. The polar nuclei endosperm (3n)
Fertilization
Fertilization
Longitudinal section of the pistil (schematic)
Fertilization
Longitudinal section of the ovule (anatomic)
Fertilization
(SEM)
Fertilization
Fertilization
to make a zygote (2n)
Fruit development
Zygote ď § cell division ď § embryo and fruit development
Longitudinal section of a young fruitlet (3 weeks): a. exocarp; b. mesocarp+endocarp (flesh); c. seed coat; d. endosperm; e. embryo
Fruit development
Fruit set • Transition from flower to fruit • After successful fertilization: 1. Fast growth of the ovary beginning of fruit development 2. Petal and stamen fall
Citrus (example)
Fruit development
Seasonal changes during fruit development
Increase in fruit size (A) and total mass (B), but decrease in water content
Fruit development
Typically to avocado: cell division all over the fruit growing season
Fruit development
Possible reasons for small fruit 1. Heavy crop load 2. High temperature and low humidity 3. Small number of cells/fruit The difference between small fruit and big fruit is in cell number and not cell size (Irihimovich et al., Planta 2010)
Cell no.
Fruit development
Cell size (Âľm2)
Days after bloom
Days after bloom Irihimovich et al., Alon Hanotea, 64: 13-18 (2010)
The limiting factor, which inhibits cell division in avocado, is probably abscisic acid (found at high levels in small fruit).
Fruit development
Reasons for heavy abscission of flowers and fruitlets: 1. Abnormal flowers (lacking female organs such as the embryo sac, egg cell, synergids, etc., or containing defective pollen grains) 2. Low pollination ratio 3. High temperatures during bloom (>33°C) 4. Low temperatures during bloom (<8°C)
5. Embryo abortion after successful fertilization (very high temperatures in May ca. 40°C) 6. Competition with young vegetative flush
Fruit development
Embryo abortion
Fertilization and fruit development Techniques for inhibiting abscission and increasing yield:
1. Improve cross-pollination (more honeybees, add bumblebees or other insects): out-crossed progeny develop better and are more resistant to abscission than progeny of self-pollination 2. Search for best pollenizers for each cultivar (for example, 'Ettinger' as best pollenizer for 'Hass')
3. Inhibit the young vegetative flush emerging from the inflorescence using growth retardants ('Magic', Cultar' etc.)
Fertilization and fruit development
The effect of cutting young flush on fruit no. of cv. ‘Fuerte’ Orchard
Fruit no. control
1
35
Flush cutting 304
2
22
385
Fertilization and fruit development
Effect of ‘Kultar’ (PB) on cv. ‘Hass’ yield
Fertilization and fruit development More techniques for inhibiting abscission and increasing yield:
4. Reduce high temperatures by using sprinklers above the canopy 5. Avoid abscission of mature leaves during bloom
6. Optimize irrigation and fertilization to achieve a balance between vegetative growth and fertility
Harvest
• The fruit is ready to pick when its dry matter (DM) is at least 20% • Avocado fruit can remain on the tree for long periods without softening or abscission • The problem: the percentage of DM increases and postponed harvest can reduce the following year's bloom and yield (the potential of alternate bearing is increased, especially in 'Hass')
Harvest
Mature fruit that is ready to harvest consists of: 1. Seed with 2 huge cotyledons 2. Mesocarp = edible flesh 3. Fruit peel
Mature fruit contains 10-20% oil (depending on the cultivar). Today, harvest is based on the percentage of dry matter (should be >20%). 'Fuerteâ&#x20AC;&#x2122;
Harvest Effect of the harvest time on alternate bearing
The movies Avocado harvesting UC Irvine Avocado Collection
UC Irvine Avocado Collection part two
Irrigation
Origin of avocado •Central American highlands •Deep, well drained volcanic soils •Soil surface mulch of leaf litter •Well structured soils, high in organic matter •Avocado is still a ‘young’ crop: •1911: First release of a selected, propagated variety •1940s: First attempt at rootstock selection
Irrigation
The conundrum 1) Avocados have a high water requirement 2) Avocado are sensitive to water stress but they are : a) Inefficient at extracting moisture from the soil b) Sensitive to over watering
Irrigation
Moisture stress = excessive fruit drop
Water stress = ringneck (incomplete fruit abscission)
Irrigation Water stress = death of seed coat = small fruit
Irrigation Water stress in first 11 weeks after fruitset = poor shelf life due to low calcium levels
Irrigation Water stress = poor quality fruit Vascular browning
Irrigation
Special Challenges in Avocado Irrigation â&#x20AC;˘ 80-90% of the feeder root length is located in the upper 20 cm of the soil profile
Irrigation
Shallow feeder root system
Irrigation
Special Challenges in Avocado Irrigation â&#x20AC;˘ 80-90% of the feeder root length is located in the upper 20 cm of the soil profile â&#x20AC;˘ Inefficient at absorbing water (few root hairs)
Irrigation
No root hairs
Irrigation
Special Challenges in Avocado Irrigation • 80-90% of the feeder root length is located in the upper 20 cm of the soil profile • Inefficient at absorbing water (few root hairs) • Avocados are heavy water users, water is expensive, most people irrigate less than is required for optimum yields
Irrigation
1) feeder roots have a high oxygen requirement (trees die after 48 hours)
Irrigation
Drowned avocado tree
Irrigation
1) feeder roots have a high oxygen requirement (trees die after 48 hours) 2) roots are susceptible to Phytophthora root rot
Irrigation
Healthy vs. Phytophthora infected roots
Irrigation
Healthy vs. root rot infected tree
Irrigation
What we can do? A focussed and responsive approach irrigation and moisture monitoring
Irrigation How can we do it? 1) Plant only on well drained soil 2) Install an irrigation system that delivers water and fertiliser evenly to every tree and does not leak when turned off 3) Install an accurate & reliable soil moisture monitoring system 4) Follow weather forecasts to be prepared for peak demand 5) Monitor soil moisture several times a day in warmer months
Irrigation
How can we do it? 6) aim to keep soil moisture between the Full (-8kPa) and Refill (-20kPa) points 7) Respond immediately to irrigation needs, but â&#x20AC;Ś donâ&#x20AC;&#x2122;t exceed Full Point 8) Irrigate several times a day if necessary
Irrigation
Soil moisture monitoring Full point
Refill point
Irrigation 6) aim to keep soil moisture between the Full (8kPa) and Refill (-20kPa) points
7) Respond immediately to irrigation needs, but â&#x20AC;Ś donâ&#x20AC;&#x2122;t exceed Full Point
8) Irrigate several times a day if necessary 9) Use mulch to create a more hospitable root
environment, reduce evaporation, increase soil organic matter and help combat root rot
Irrigation
Mulching avocado trees
Irrigation
Mulching avocado trees
Irrigation 6) aim to keep soil moisture between the Full (-8kPa) and Refill (-20kPa) points
7) Respond immediately to irrigation needs, but â&#x20AC;Ś donâ&#x20AC;&#x2122;t exceed Full Point 8) Irrigate several times a day if necessary 9) Use mulch to create a more hospitable root environment, reduce evaporation, increase soil organic
matter and help combat root rot 10) Use overhead misters for cooling during heat waves
Irrigation
Overhead misters
Irrigation
Typical avocado irrigation system • Tree spacing 5x 4m
• Under-tree mini sprinklers or drip irrigation • Systems deliver 80 to 120 L/tree/hour
• About 60% of orchard floor is wetted • Precipitation rates about 2mm/hour in wetted area
• Systems must be capable of meeting peak demand days
Irrigation
Irrigation Scheduling â&#x20AC;˘ The most important cultural operation in the grove â&#x20AC;˘ Need to know both frequency of irrigation and how much water to apply during an irrigation event
Irrigation
Frequency • Irrigate when 30% of soil moisture is lost (decomposed granite soils) or when 50% of soil moisture is lost (clay soils) • Therefore, you must check soil moisture content – Shovel – Tensiometer 30% moisture
Irrigation
Tensiometers • Must be within the wetted area of the minisprinkler or dripper • Should be placed 2-3 feet away from the sprinkler • Set one tensiometer 30 cm below the soil • Set another tensiometer 60 cm deep - this helps to know when to turn off the water or to irrigate for a longer period of time if it remains too dry
Irrigation
Tensiometers • Maintain them on a regular basis – Fill with water – Pump out air bubbles – Replace cork once a year
• Protect them from the pickers • If the soil gets too dry the clay cup breaks
Irrigation Measuring Soil Moisture – Simple and Cheap Methods Tensiometers – Labor intensive to collect data – Requires regular maintenance – Can be inaccurate in extremely wet or dry soils – Not accurate in very sandy soils – Indicates when to apply, not how much to apply
Irrigation
More Expensive Methods • Capacitance probes – Measure change in dielectric constant in the soil
• Neutron probes – Used only by researchers and irrigation consultants
Irrigation
Things to Remember 1) Avocados use water all year long. If it rains in the winter, calculate â&#x20AC;&#x153;effectiveâ&#x20AC;? rainfall, extra rain is lost by gravity and run-off. 2) Water use changes constantly according to temperature, light, humidity, and wind. Setting a timeclock is dangerous because it encourages you not to re-set it each week 3) Water use changes according to the number of leaves
Irrigation
Things to Remember 4) Control weeds â&#x20AC;&#x201C; they also use water 5) Historical water tables are somewhat useful, but dangerous. (the weather changes a lot!)
Irrigation
Soils and Irrigation 1) Irrigation water requirement is driven by the weather, not the soil type. Soil is important, however, because soil stores the water. 2) Sandy soils (coarse soils) hold less water than clay soils. Thus trees on sandy soils need to by irrigated more often.
Irrigation
Water Supply Avocado is the a very sensitive to salts in water. The Electrical Conductivity of Water (Ec) EC is a quick way to measure the total salts in the soil, both 'good' salts for the irrigator like nitrate and potassium and 'bad' salts like sodium and chloride. Many people find salt or EC measurement complicated because there are so many different ways of measuring how much salt is in a water sample.
Irrigation
Water Supply EC and yield? Ec 0.9 = no loss in yield Ec 1.2 = 10% loss in yield Ec 1.7 = 25% loss in yield Ec 2.4 = 50% loss in yield From R. S. Ayers, Journal of Irrigation and Drainage, ASCE Vol. 103, June 1977
Irrigation
What does Salinity do to Avocado? 1. Osmotic potential in soil increases, making it difficult for roots to extract water from soil. 2.
Water may leave the roots, even during an irrigation (This would happen at an EC = 4)
3. Sodium may accumulate in soil replacing calcium and magnesium, destroying soil structure. 4. Chloride uptake causes â&#x20AC;&#x153;tip-burnâ&#x20AC;? in leaves. These leaves must drop and be replaced. Tree focuses energy on leaf replacement and not flowering and fruiting
Fertilization
Chloride Tip-Burn Not a mineral deficiency, but an excess of salinity due to: 1) Saline irrigation water (wells or reclaimed water) 2) Poorly leached soils (salt accumulates in the rootzone) 3) Under-irrigation 4) Over application of manures and fertilizers
Irrigation
Chloride Tip Burn on Avocado
Fertilization
Avocado Fertilization
Fertilization
Introduction 1) Avocados have few mineral deficiencies 2) Surface feeder roots are efficient at recycling nutrients back into the tree 3) Nitrogen should be applied every year, occasionally zinc and sometimes phosphorus, potassium and calcium (maybe) 4) Leaf analysis is normally used to determine mineral deficiency or excess 5) Liquid fertilizer injection is the normal way to apply fertilizers
Fertilization
Required Mineral Nutrients • • • • •
16 mineral nutrients C, H, O N, P, K (primary macro-nutrients) Ca, Mg, S (secondary macro-nutrients) Micro-nutrients….Zn, Fe, Mn, Cu, B, Mo, Cl
Fertilization
Sampling
Leaf Analysis
1) Leaves taken in August-October period 2) 5-7 month-old leaves sampled 3) Non-fruiting branches 4) Sample good blocks vs. poor blocks in separate
Fertilization
• Hass avocados usually require 0.5 – 1.0 Kg actual nitrogen per tree per year • Usually applied as a liquid fertilizer divided between 6 to 9 applications per year
• Nitrate (NO3-) is mobile in the soil and is absorbed readily into roots, leaches readily • Ammonium (NH4+) is bound to the surfaces of soil particles and is not leached readily, slowly converts to nitrate (NO3-) • Most fertilizers are a combination of nitrate and ammonium
Fertilization
Nitrogen Deficiency 1) Lack of vegetative vigor
2) Pale, green small leaves 3) Reduced yields 4) Premature defoliation 5) Leaves with yellow veins (severe deficiency)
Fertilization Nitrogen Deficiency â&#x20AC;&#x201C; General Yellowing of leaf and Reduction in Yield of Fuerte
Fertilization Nitrogen Application Timing research from Dr Carol Lovatt, UC Riverside
â&#x20AC;˘ Control trees: nitrogen was applied at 1.25 lb/tree/year, divided into 0.25 lbs in January, February, April, June, Nov. â&#x20AC;˘ Treatments: the same but there was an extra 0.25 lb applied in each of these months
Fertilization
Four-year trial by Lovatt N applied
Control trees (1.25 lbs/year) Jan extra 0.25 lb Feb extra 0.25 lb April extra 0.25 lb June extra 0.25 lb Nov extra 0.25 lb
average wt/tree of fruit
128.7lb 123.4 123.4 158.0 117.0 168.3
The best yield occurred when the extra N was applied in April or in November
Fertigation â&#x20AC;˘ Fertigation is the injection of fertilizers, soil amendments, and other water-soluble products into an irrigation system.
Fertilization
Advantages of Fertigation 1) Most groves have low volume irrigation
systems 2) Water is distributed uniformly, good fertilizer distribution 3) Manager has flexibility in timing applications 4) Less fertilizer needed because all of the fertilizer is applied to the wetted area, where the roots are located 5) Labor costs are lowered
Fertilization
Injection Equipment 1) Differential pressure tanks (Batch Tanks) 2) Venturi devices 3) Positive displacement pumps • Also needed: – Backflow prevention device – Tanks that can hold chemical fertilizers
Fertilization
Zinc • Avocado has a small but essential requirement for zinc • Leaf mottling between veins, small rounded fruit, shortened internodes • Zinc deficiency can be a chronic problem in organic groves where high phosphorous manures are used
Fertilization
Zinc Deficiency
Fertilization
Zinc Deficiency
Fertilization
Zinc • Leaves are mottled, showing yellowing between the veins • Small leaves • Zinc sulfate can be – Through the irrigation system – hand applied around each tree every 3-5 years
The movies Why People Fail at Avocado Trees Avocado Tree Growing Mistake Watering
Grafting and seedling You can grow avocado tree from seed but: 1. long juvenile period. 2. donâ&#x20AC;&#x2122;t know what you avocado will be like! The favorite method to propagate avocado is by grafting!