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Raffi Stern
Main topics:
• Climate needs for growing subtropical fruit
trees
• Frost and protection from it
• Origin and distribution of species
• Reproductive biology (flowering, pollination,
fertilization, fruit development and maturity)
• Focus on avocado and litchi as representative
subtropical fruit trees (which also include
mango, date palm, banana, etc.)
Course syllabus: 1. Introduction to the subtropics: climate
adaptation, frost and protection from it
2. Avocado: origin and distribution, the 3 races of
avocado, reproductive biology – pollination
3. Avocado: reproductive biology – fertilization, fruit
set and development
4. Litchi: origin and distribution, differentiation, 3
flower types
5. Litchi: fruit development, fruitlet abscission,
vegetative propagation, cultivars
6. Field trip to avocado orchard (and
packinghouse)
1. Fruits of Warm Climate / J. Morton. Purdue Univ. USA, 1978.
2. Tropical Fruits / H. Nakasone and R. Paull. CABI, UK, 1998.
3. The Encyclopedia of Fruit and Nuts / J. Janick and R. Paull. CABI,
UK, 2008.
4. The Avocado: botany, production and uses / Whiley, Shaffer,
Wolstenholme. CABI Publishing, 2002.
5. The Mango; botany, production and uses / R. Litz. CABI Publishing,
(2nd ed.) 2009
6. Litchi and Longan: botany, production and uses / Menzel and Waite.
CABI Publishing, 2005.
1. Stern, R.A. & Gazit, S. (2003). The reproductive biology of the lychee.
Hort. Rev. 28: 393-453.
References : Books :
Article :
Book on
Subtropical Fruit Trees
http://www.hort.purdue.edu/newcrop/morton/index.html
Videos on Subtropical Fruit Trees (from Florida) Jonathan H. Crane
mango.htm-http://trec.ifas.ufl.edu/fruitscapes/video
http://trec.ifas.ufl.edu/tfphotos/
www.avocadosource.com
Climate
The temperatures and atmospheric
conditions (rain, humidity, wind,
radiation, etc.) prevailing in a certain
region over time
Climate is influenced by several
factors, such as: latitude, altitude,
geographic location (close to/far from
the sea), etc.
Subtropical and tropical regions
There are 3 main types of climate:
1. Tropical
2. Temperate
3. Arctic
Each region is generally divided into
several subclimates
Subtropical and tropical regions
The tropical region is defined schematically as lying between the tropics of Cancer (23.5° north) and Capricorn (23.5° south).
Subtropical and tropical regions
However, there are some exceptions:
•The Andes mountains at the equator.
• Israel, South Africa, California – at ca. 30° lat. and still subtropical
Subtropical and tropical regions
What are the climatic characteristics of
the tropical region?
I. Stable and high temperatures
1. Average annual temp. >25°C
2. Average temp. of coldest month >18°C
3. The difference between the hottest and coldest month is no more than 5°C
Subtropical and tropical regions
II. Heavy rain
1000-6000 mm annual rainfall
Near the equator there are 2 seasons:
1. Wet season (most of the year)
2. 2.Dry season (a few months)
Subtropical and tropical regions
III. Stable photoperiod
At the equator, daylength is always ca. 12 h.
North/south of the equator daylength changes:
The difference between longest day (summer) and
shortest day lengthens.
Subtropical and tropical regions
Nakasone and Paull, 1999
IV. Sun angle
At the equator the sun is at ca. 90° most of the
year.
Therefore, irradiation is high and stable
vegetative growth throughout the year (heavy
cloud cover reduces strong irradiation).
Subtropical and tropical regions
• 0° (Equator) - High and
stable irradiation most
of the year (minimum in
May)
• 20° - High irradiation
for 5 months (maximum
in May)
• 40° - High irradiation
for 3 months (maximum
in May)
• 60° - High irradiation
for 1 month (May)
Subtropical and tropical regions
V. High evaporation
High temp., heavy rain, long daylength and high
irradiation cause >80% relative humidity.
All 5 parameters result in high and stable
vegetative growth.
Subtropical and tropical regions
Subtropical region
Part of the tropics but more distant from the equator, roughly between latitudes 23.5° and
35°, even 40°.
There are a few sub-regions in the subtropical
region that have a: "Mediterranean Climate".
They include: Israel, California, South Africa
Subtropical and tropical regions
What are the climatic characteristics of
subtropical vs. tropical regions?
1. Hotter summer and colder winter.
2. Longer days in summer and shorter days in
winter.
3. Stronger irradiation (hot and dry summer
without clouds).
4. Lower humidity.
5. The average temp. in the coldest month is not lower than -3°C and not higher than 18°C.
Subtropical and tropical regions
Happens when the temperature drops to below 0°C.
When the temp. gets to -5°C there is
severe damage to trees such as avocado,
mango, litchi, banana, etc.
Subtropical orchards in Israel: Climate requirements
Frost damage in avocado trees
Subtropical orchards in Israel: Climate requirements
‘Ettinger’
(resistant)
Gaz
it, 1968
‘Nabal’
(sensitive)
How do we get such low temperatures in
the subtropics?
There are two reasons:
1. Frost
2. Freeze
Subtropical orchards in Israel: Climate requirements
1. Frost
Occurs on cold, dry, clear (no clouds) and
without wind during night.
Under these conditions, a phenomenon termed
"inversion" occurs: the hot air from the soil
rises to the sky (lighter than cold air) and the
cold (and heavy) air remains near the soil.
Subtropical orchards in Israel: Climate requirements
1. Frost
The cold air is heavy and accumulates close to
the ground in the orchard.
Tree damage will be much worse at site B than
at site A.
Subtropical orchards in Israel: Climate requirements
B
2. Freeze
Occurs with the penetration of a very cold air
mass (from Russia to Israel, for example).
Temperature quickly drops to below 0°C.
The freeze not only harms the lowlands: all
areas are affected.
Subtropical orchards in Israel: Climate requirements
Factors influencing the extent of the
damage from frost or freeze
1. Temperature – The lower the temp. <0°C
and/or the longer the low temperatures last, the
greater the damage.
2. Species sensitivity – very sensitive: banana and mango (0°C extensive damage);
sensitive: avocado and litchi (-3°C damage
begins); "resistant": citrus (-6°C damage
begins).
Subtropical orchards in Israel: Climate requirements
Factors influencing the extent of the
damage from frost or freeze
3. Cultivar – avocado: 'Hass' is the most sensitive (-2°C), followed by 'Fuerte' (-4°C) and 'Ettinger'
(-5°C); mango: 'Kit', 'Maya' are very sensitive
(-0°C), 'Hayden', 'Kent' are sensitive (-1°C); litchi:
'Mauritius' more sensitive than 'Floridian‘.
4. Tree age – young trees are more sensitive than
mature trees
Subtropical orchards in Israel: Climate requirements
Factors influencing the extent of the
damage from frost or freeze
5. Tree health – "Green" and healthy trees are
more resistant than weak and chlorotic ones.
6. Crop load in the previous year – higher crop
load higher sensitivity
7. Temperature prior to the frost – low temp. (down to 0°C) before the frost can confer
resistance to the tree.
Subtropical orchards in Israel: Climate requirements
How can we see frost damage?
From slight leaf burn, through damage to the
fruit tissue, to death of the entire tree.
Subtropical orchards in Israel: Climate requirements
Damage of mature leaves
Browning of fruit stem
Damage inside the
fruit (Phloem+ Xylem)
Damage of thin branches
Damage of thick branches
Serious damage of ‘Fuerte’ (sensitive), but less in ‘Ettinger’ (resistant)
Damage of the rootstocks
Frost-protection measures
A. Before planting
Choosing the appropriate region (not in high
mountains or deep valleys), on slopes where
the "drainage" of cold air is good.
Subtropical orchards in Israel: Climate requirements
Topoclimatic map of the
Upper Galilee region
Central valley (blue): long periods <0°C
Mountains on the left (red): short periods <0°C
Frost-protection measures
B. After planting
I. Before the frost event
1. Clear weeds – to allow quick passage of
the hot air from the deep soil to the soil
surface and to the tree canopy.
2. Protect the stem of the young trees,
including the graft union (0-40 cm from the
soil). We can use plastic, cardboard, etc.
around the stem.
Subtropical orchards in Israel: Climate requirements
Frost-protection measures
B. After planting
I. Before the frost event
3. Funnel cold air out of the orchard using
passes in the lower orchard levels
Subtropical orchards in Israel: Climate requirements
Frost-protection measures
B. After planting
II. During the night frost
1. Sprinkle over the top of the canopy –
start when the temperature goes down to +1°C and stop only after it comes back up
to +3°C and there is no longer any ice on
the trees.
Subtropical orchards in Israel: Climate requirements
Frost-protection measures
B. After planting
II. During the night frost
1. Sprinkle over the top of the canopy –
Subtropical orchards in Israel: Climate requirements
Frost-protection measures
B. After planting
II. During the night frost
2. Create air turbulence – using a
machine fixed at the center of the
orchard.
Subtropical orchards in Israel: Climate requirements
Frost-protection measures
B. After planting
II. During the night frost
3. Create air turbulence using a helicopter
– the same idea but much more expensive.
Subtropical orchards in Israel: Climate requirements
Treatment of the tree after damage from frost
A. Weak damage
1. Spray a white covering to protect the
branches from sunburn.
2. Prune – only a little pruning of the small dry
branches .
Subtropical orchards in Israel: Climate requirements
Treatment of the tree after damage from frost
B. Strong damage
1. New plantation.
2. Heavy pruning – only during the summer
after the new vegetative flush (if any).
3. Graft new scion after pruning.
4. Reduce amount of irrigation and
fertilization.
Subtropical orchards in Israel: Climate requirements
Treatment of the tree after damage from frost
Subtropical orchards in Israel: Climate requirements
Pruned and whitened trees after the frost