Lecture 33
Avocado

Avocado: Persea americana, Lauraceae

  • Name comes from Spanish aguacata derived from the Aztec ahuacatl.
  • A high oil fruit, protein also high for fruit crop.
  • Myrtle family (Lauraceae).
  • Aromatic woody plants.
  • 40 genera, 1000 species.
    •

    Cinnamomium zeylandicum Cinnamon
    Cinnamomium camphora Camphor tree
    Laurus nobilis Laural or bay tree
    Persea american Avocado
    Sassafrass spp. Sassafras
    Umbellularia californica Oregon myrtle

    		 fig. 01

    Avocado: 2001 World Production
    Continent 1000 tonnes Chief countries
    World 2,553  
    Africa     213 S. Africa (81), Cameroon (50), Congo (27)
    North America 1,373 Mexico (903), USA (205), Dominican Republic (111)
    South America     524 Colombia (133), Chile (120), Peru (90)
    Asia     329 Indonesia (130), Israel (86), China (75)
    Europe       74 Spain (60), Portugal (13), Greece (1)
    Oceania       39 Australia (24), New Zealand (13), Samoa (2)

    Three Horticultural Races

    Mexican, Guatemalan, West Indian

  • Mexican
  • Native to highlands of Mexico, Andes to Chile, 2400 to 2800 m
  • Fruits ripen 6-8 months (rapid development)
  • Leaves are "anise" scented
  • Fruits are small
  • Trees found in higher elevations, hardy
  • Up to 30% oil
    •

  • Guatemalan Race
  • Native to highlands of Central America to Ecuador and Mexico, 800 to 2400 m
  • Large fruit, rough skin
  • Fruits mature 9–14 months, winter cultivar
  • Important commercial race; seeds are small, tight in cavity
  • Trees cold resistant
  • Hybrids of Guatemalan race most useful commercially
  • 7.5 to 18% oil
    •

  • West Indian Race
  • Native to lowlands of Central and South America, only introduced into West Indies.
  • Quite sensitive to cold
  • Fruit size variable, skin thin and smooth
  • Early maturing, 6 to 9 months (summer variety)
  • Seeds loose, can shake in fruit
  • Cotyledons rough
  • 5–7% oil

    • Character West Indian Guatemalan Mexican
    Origin Tropical lowlands Tropical highlands Tropical highlands
    Foliage No odor No odor Anise-scented
    Blooming season Feb.–March March - April Jan.–Feb.
    Maturity season May–Sept. Sept.–Jan. June–Oct.
    Development period 5–8 months 10–15 months 6–8 months
    Seeds Large Small Relatively large
    Fruit size 1–5 lbs ½ - 5 lbs Not over 1 lb
    Skin texture Leathery-smooth Woody-rough Papery-smooth
    Fruit oil content Low Med. to high Med. to high
    Cold hardiness
    Young trees 28–30ºF 26–28ºF 24–26ºF
    Mature trees 28–30ºF 21–25ºF 18–25ºF

    Flowering

  • Enormous flower production
  • 1000 per fruit
  • 5000 per 'Fuerte' fruit
    •
  • Flowers very small
  • Perfect (12 stamens, 9 functional, each having 4 pollen chambers)
  • Single pistil, 1 carpel = 1 seed
  • Fruit considered a single seeded berry.
  • Some fruits development without embryo (very small fruit)
  • Fruits are high oil and relatively high protein
  • One of few fruits to enlarge by cell division rather than expansion.

    		•  fig. 02

    Avocado in Bloom

    Hybrids High Variability

  • Fuerte
  • Considered hybrid between Mexican × Guatemalan
  • Dark green, somewhat pyriforom, attractive, high oil
  • Popular cultivar in California
  • Some call it a new race.
    •
  • Hass
  • Guatemalan type
  • Black skin, round, very good flavor, high oil
  • Gaining in popularity in California

    		•  fig. 03

    Avocado & Citrus, Indonesia

    fig. 04

    Avocado cultivars, Israel

    		 fig. 05

    Avocados

    fig. 06

    Giant Avocado

    		 fig. 07

    Avocado hybrids

    Fruit Maturation

  • Sugar contents is low 1.5 to 3.4% before maturity.
  • At maturity carbohydrates declines to 0.25 to 1.8 % as oil content increases.
  • Oil content in California higher than Florida
  • Fuerte:
  • 25% California
  • 13–17% Florida
    •
  • In California, standards are based on oil, but flavor not correlated with oil.
  • Florida avocados generally have much lower oil than California types.

    • Pollination & Fruit Set

  • Protogynous dichogamy with synchrynous daily complimentarity
  • Protogynous = pistil receptive first
  • Dichogamy = differential maturation of stamens and stigma

    • Two Classes of Cultivars

    Class A

  • New flowers open daily, sometimes in the morning, exact time depends on cultivar
  • They do not shed pollen in the morning
  • Pistil is mature, and receptive so flower functions as female
  • Closes at noon and stays closed until the afternoon of following day
  • Reopens and acts as male
  • TODAY AM             female
  • TOMORROW PM   male
    •

    Class B

  • Flowers open first time in the afternoon but pollen does not shed and close in the evening
  • In the afternoon, pistil is receptive, thus acts as female
  • Reopen the following day in the morning and sheds pollen, acts as male
  • TODAY PM             female
  • TOMORROW AM   male
    •
  • Thus to get good pollination and fruit set avocado grower has to have more than one cultivar of which some are Type A and some are Type B.

    • Propagation

  • Most avocados grafted
  • Ungrafted, 7–10 years to bear
  • Grafted 1–3 years to bear
  • In California used Mexican or Guatemalan root stocks
  • In Florida use Waldin stocks, sturdier and faster growing

    		•

    Planting Distance

  • 20–35 ft spacing within rows
  • 35–40 ft between rows

    		•
    fig. 08

    Planting the avocado tree as it is delivered from the nursery.

    		 fig. 09

    The planter is removing the building-paper pot which has surrounded the plant in the nursery.

    fig. 10

    Soil is filled around the set tree.

    		 fig. 11

    After the hole is filled with soil the planter will tamp the soil with a wood stick or his feet to compact the soil around the ball of the tree.

    fig. 12

    Soil is added around the tree from the surrounding area in order to have sufficient soil to build a water-holding basin.

    		 fig. 13

    After the basin is completed a mulch is placed in the basin and a paper protector is placed around the tree.

    fig. 14

    A newly planted avocado orchard on a terraced hill location.

    		 fig. 15

    This view shows the furrow irrigation system where the water is conserved by only using the one furrow nearest the trees.

    fig. 16

    This orchard is using the "brown arm" system of irrigation.

    		 fig. 17

    Avocado trees on unterraced land.

    fig. 18

    A two year old tree.

    		 fig. 19

    Growers practice different methods of soil management. Shown here is a cover crop that is periodically mowed.

    fig. 20

    A permanent sod culture, one of the four methods of caring for orchard soil

    		 fig. 21

    A natural cover crop of weeds and grasses.

    fig. 22

    Non-cultivation is the most popular method of soil management. Herbicides or oil are used to prevent weeds from becoming established.

    		 fig. 23

    Another grove where furrow irrigation and non-cultivation is practiced by the grower.

    fig. 24

    A non-tillage grove where low volume sprinklers are used.

    		 fig. 25

    One commercial variety of avocado is 'Zutano'. Shown here is the typical upright growth. The fruit is green and of medium quality, ripening late in the fall. Because Zutano avocados are more tolerant of frost they are recommended for locations where frost may be a problem.

    fig. 26

    'Zutano' fruit, which is rather large and has a relatively large seed. The fruit is considered of medium quality and is picked from October to February.

    		 fig. 27

    'Zutano' fruit

    fig. 28

    'Zutano' fruit on the left is cracked on the blossom end due to over maturity on the tree. The fruit on the right has been damaged by wind. The scar develops when the fruit rubs against another fruit or branch.

    		 fig. 29

    'Bacon' avocado growth habit, which is similar to 'Zutano' and is also used for windbreaks and in colder locations. The fruit is of medium quality ripening from December to March.

    fig. 30

    A cluster of 'Bacon' avocados showing their smooth green skin.

    		 fig. 31

    'Bacon' avocado. Note the large size of the seed.

    fig. 32

    Growth habit of 'Hass' avocado, which is a medium spreading tree. It is the number two commercial variety acreage wise. It produces a dark, rough skinned fruit of high quality. 'Hass' is less resistant to frost damage than 'Zutano' or 'Bacon'. It Should be planted in a warm location only.

    		 fig. 33

    A cluster of 'Hass' avocados. Note the rough exterior texture of the fruit. Hass turns dark at maturity and is picked from. April to October. It has a long storage life on the tree.

    fig. 34

    'Hass' fruit. The yellow flesh and the dark green band immediately under the skin are very desirable characteristic. Note also that the seed is small.

    		 fig. 35

    'Rincon' avocado. This tree is small, low, and spreading. It is no longer recommended because of the poor shipping qualities of the fruit and its tendency to produce poorly. Growers with this variety may increase their production by top-working their trees to a more desirable variety.

    fig. 36

    'Rincon' fruit. Note the large seed and the dark areas in the flesh which are "strings". This is a medium quality fruit. It is harvested during march to May.

    		 fig. 37

    'McArthur' avocado is a variety that is no longer recommended because of the poor quality of the fruit. Note the stringy fibers in the exposed section of the fruit.

    fig. 38

    'Fuerte' avocado. This is the most popular fruit in general planting. The variety upon which the avocado industry was built. It has excellent flavor, texture, and shipping qualities.

    		fig. 39

    'Reed' avocado. A new variety, now under field test. It is a cross between the Anaheim and Nabal varieties. It appears to be a high quality fruit, with a small seed, ripening in the summer.

    fig. 40

    An orchard of 'Fuerte' trees that are being top-worked to another variety which will produce more fruit because of the location of the property. The trees are dehorned, as shown, in the fall and then are top-worked with the new variety in February or march.

    		 fig. 41

    A newly top-worked tree showing the two sciens and the stakes to support them. The paper protects the stump from sunburn and the entry of water into the cracks in the stump.

    fig. 42

    An orchard that has been top-worked to 'Hass'. The larger trees were top-worked a year earlier and show the vigorous growth that takes place within a short time because of a large root area available to nourish the small scions.

    		fig. 43

    A closer view of one of the recently top-worked trees showing how the paper is placed to protect the trunk.

    fig. 44

    A close view of the top-worked tree showing the two scions.
    The left scion is permitted to grow while the scion on the right is suppressed by diligent pruning. This is necessary to encourage the closing of the stump by the growth of the cambium layer from two sides. Eventually the scion on the right will be removed leaving only one scion to produce the new tree.

    		fig. 45

    An avocado tree showing the effects of root rot. Note the sparseness of the foliage, off color of the leaves, and their wilted appearance. This is the most serious disease affecting avocados and is caused by a soil born organism called Phytophthora cinnamoni. Once an orchard is infected with this disease there is little that can be done except to plant alternate crops.

    fig. 46

    An avocado tree that has root rot. It is being inarched with disease tolerant seedling trees that have been planted around the tree in an attempt to develop a new root system that will tolerate the fungus.

    		 fig. 47

    Zinc deficiency in an avocado tree an indicated by the dieback of the older growth, the off color of the new growth, and the rosetting of the new leaves. Easily corrected by a zinc spray.

    fig. 48

    Zinc deficiency as compared to a normal twig. Note that the leaves are smaller, narrower, yellower, and rosetted. Note also that the fruit is round instead of elongated.

    		 fig. 49

    Zinc deficient 'Hass' avocado fruit on each side as compared with the normal fruit in the center of the picture.

    fig. 50

    Iron deficiency in a young avocado as indicated by the yellow appearance of the leaves.

    		 fig. 51

    Iron deficiency as compared to the normal leaf. Note that the blade area between the veins is yellow and the veins are green.

    fig. 52

    Tip burn caused by high salt in the soil or water. Irrigation practices can alleviate the problem.

    		 fig. 53

    Damage to avocados due to the instars of the omnivorous looper (Sabulodes caberata).

    fig. 54

    Avocado brown mite which collects along the ribs of the leaf causing the brown appearance of the leaves.

    		 fig. 55

    Close up of the avocado brown mite (Oligonychus punicae).

    fig. 56

    Latania scale on the twig of avocado. This is not an important pest and control is not recommended.

    		 fig. 57

    Latania scale on the same twig with the waxy exoskeleton lifted to one side, exposing the insect.

    fig. 58

    One latania scale on the center of a 'Hass' fruit. The other spots are the lenticels

    		 fig. 59

    Spray rig with a hand gun. One type of equipment used on many agricultural crops for pest control work.

    fig. 60

    The Selma Tree Farmer is a mechanical aid for pruning or harvesting of fruit.

    		 fig. 61

    Avocado fruit arrives at the packing house in field boxes stacked one on top of another. This machine unstacks the boxes and feeds them into a dumping machine.

    fig. 62

    Automatic weighing machine where three boxes of fruit are weighed at one time.

    		 fig. 63

    Fruit is inspected for defects.

    fig. 64

    After the fruit is graded it is placed in cups ahead of the stamping machine which places the packing house trade name on the fruit.

    		 fig. 65

    The stamping machine which places the name on the fruit.

    fig. 66

    Another type of stamping machine showing the rotating drum that has the rubber stamps fastened to its circumference.

    		 fig. 67

    Each fruit is automatically weighed and all like fruit is conveyed to a bin for packing.

    fig. 68

    A general view of the hand packing area. The boxes above are empty awaiting the needs of the packers. Two sizes of boxes are available with single cartons above and double cartons on the second shelf.

    		 fig. 69

    Layers of fruit are placed on top of styrofoam liners and when full are pushed onto the conveyer belt shown to the right of the tub.

    fig. 70

    Each carton passes this weighing station where the total weight is adjusted to a uniform total weight by either adding or taking away of fruit.

    		 fig. 71

    The boxes pass into this machine which automatically applies glue and folds down the flaps holding them for a sufficient time for the glue to set.

    fig. 72

    Boxes of fruit are placed on pallets for easy moving about the packing house. They are either shipped to market or held in storage.

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