Avocado Breeding

1. Avocado Breeding
Mandeep Kaur
Ph.D. Fruit Science

2. Introduction & Importance
• The word "avocado" comes from Nahuatl word ahuacatl (which means ‘testicle’,
a reference to shape of the fruit). Avocados were known by the Aztecs as ‘fertility fruit’.
• Avocado (Persea americana Mill., 2n=24) belongs to family Lauraceae.
• It is also known as Butter fruit (English) & Makhan Fal (Hindi).
• The fruit of the plant, also called an avocado (or avocado pear or alligator pear), is
botanically a large berry containing a single large seed.
• The fruit is tasteless & have a green-skinned, fleshy body that may be pear-shaped, egg-
shaped, or spherical. Fruit size & skin texture vary with the cultivar (Brickell, 1992).
• Avocados have become more than a staple food in the American diet; they have proven to
be a key ingredient in many recipes.
• According to the Hass Avocado Board, as of 2015, avocado consumption in the United
States doubled since 2005 and quadrupled since 2000.

3. Composition & Health Benefits of Avocado
Nutritional values per 100 g of edible parts
Energy 670 kJ
Carbohydrates 8.53 g
Sugars 0.66 g
Dietary fiber 6.7 g
Fat 14.66 g
Saturated 2.13 g
Monounsaturated 9.80 g
Polyunsaturated 1.82 g
Protein 2 g
Vitamin B₁ 0.067 mg
Vitamin B₂ 0.130 g
Vitamin B₃ 1.738 mg
Vitamin C 10 mg
*Source: Bergh 1992

4. Origin, Domestication & Distribution
• Avocado appeared approximately 12,000 years ago.
• Avocado is native to state of Puebla in Mexico & from
here, avocado dispersed to the south eastern part of the
U.S., to a large part of South America: Colombia,
Venezuela, Brazil, Peru, Bolivia, and Chile.
• It was 1st reported in Florida in 1833 & in California in
1856.
• In India, avocado is not a commercial fruit crop. It have
been introduced in the south and west coasts of India
about 50-75 years ago from Ceylon.
• In India, it is centered on hill slopes of Tamil Nadu,
Kerala, Coorg and in selected regions of Karnataka and
Maharashtra.

5. 44%
14%
10%
7%
7%
5%
4%
3%
3% 3%
World Production of Avocado in 2016-17
Mexico
Dominican Republic
Peru
Indonesia
Colombia
Brazil
Kenya
Chile
Venezuela
USA
*Source: http://www.fao.org/faostat/en/#data/QC/visualize
Country Production
(millions of tonnes)
Mexico 1959620
Dominican Republic 619518.5
Peru 461076
Indonesia 334047.5
Colombia 304332
Brazil 204731.5
Kenya 185162
Chile 137097
Venezuela 132106
USA 128795

6. Taxonomy
• Genus Persea, name has been derived from ancient Greek
name of an Egyptian tree with sweet fruits, derived probably
from Perseus.
• Kopp (1966) studied 81 species and grouped them into two
subgenera: Eriodaphne and Persea, based on morphology and
hybridization and graft incompatibility.
• Persea is one of about 50 genera in this family.
• All Persea spp. have 24 chromosome number, excepting Persea
hintonii (2n = 48) (Garcia, 1975).
• Commercial avocado (Persea americana Mill.) belongs to family
Lauraceae & the sub-genus Persea that also contains two other
important species, Cinnamon (Cinnamonum zeylanicum) &
Campor (Cinnamonum camphora).
Kingdom Plantae
Phylum Angiosperms
Class Magnoliids
Order Laurales
Family Lauraceae
Genus Persea
Species P. americana

7. Races of Avocado
• P. americana is a polymorphic species containing several separate taxa that are considered to be
botanical varieties, more commonly referred to as horticultural races (Scora et al., 2002).
• According to Bergh (1975), all members of Persea subgenus are best named as a Persea americana Mill.
and three races (subspecies) are identified within P. americana and are given varietal status within the
species.
• These three subspecies are:
a. P. americana var. drymifolia (Mexican race)
b. P. americana var. guatemalensis (Guatemalan race)
c. P. americana var. americana (West Indian race)
• Each race has unique ecological adaptation & identifiable characteristics (Bergh,1975; Kight, 1980).
Although inter racial hybrids do occur, that are of horticultural & commercial importance now.
• These races are also described as semitropical, subtropical and tropical respectively, on the basis of
increasing cold hardiness and general climatic adaptation. Their naming signifies the ecological
requirements rather than origin.

8. P. americana var. drymifolia
(Mexican race)
• Grown in more elevated and cooler habitat
with 6-8 month winter-spring dry period.
• Very thin skin, which makes it susceptible to
diseases.
• Large seed and smaller fruit.
• Crushed leaves have a distinct anise
(licorice) smell, unique to this race.
• Matures in 6 months.
• Varieties: Duke, Topa.

9. P. americana var. guatemalensis
(Guatemalan race)
• Similar to Mexican race in oil content and flavor.
• Skin is thicker and seed is smaller.
• Highest quality among other three races.
• Needs more time to mature i.e. more than 12
months.
• Hybrids with other two, helps to bridge the race
maturity gap.
• Varieties: Lula, Hass, Green.

10. P. americana var. americana
(West Indian race)
• Found in Central American forests.
• Largest fruits with light green skin.
• Well adapted to lowland tropical regions.
• Lowest oil content.
• Matures in 5 months.
• Varieties: Pollock, Purple.

11. Character Mexican race Guatemalan race West Indian race
Native Mexico Guatemala Low land of Central America
Climatic adaptation Semi-tropical Sub-tropical Tropical
Cold tolerance Most Intermediate Least
Salinity tolerance Least Intermediate Most
Fruit size Tiny-medium Small-large Medium to very large
Fruit shape Mostly elongated Mostly round Variable
Skin colour Usually purple Black or green Pale green/maroon
Oil content Highest (30%) Medium (7-18%) Low (5-7%)
Seed/fruit ratio Large Small Large
Distinct flavour Common Less common Intermediate
Surface Smooth Smooth Rough
*Source: Bergh 1975

12. Race Cultivars
Mexican (M) Gottfried, Topa – Topa, Aquila, Duke , Pernod, Cholula, Mayo, Indio, Jalna,
Mexicola
Guatemalan (G) Sharwil, Hass, Banik, Nabal, Gwen, Criollo, Tonnage, Hayes, Taylor,
Anaheim, Edranol, Hazzard, Reed, Green, Hopkins, Rzamna, Dickinson,
MacDonald
West Indian (W) Black Prince, Simmonds, Waldin, Tentima, Pollock, Day, Novillero, Purple
M X G Shepherd, Fuerte, Rincon, Ryan, Wurtz, Sharwil, Irving, Creelman, Corona,
Bacon
G X W Fairchild, Long, Hall, Lula, Idi, Booth-7, Booth-8, Monroe, Ixopo, Gema
M X W Robusta
Related Persea species P. hintonii, P. floccosa , P. nubigenea, Persea sciedeana
Important avocado cultivars & species

13. Cultivar Origin Group
Cultivars for Sub-tropical climate
Bacon M × G B
Fuerte M × G B
Hass G with some M
genes
A
Reed G A
Cultivars for Tropical climate
Beta G × WI B
Hall G × WI B
Lisa WI × M B
Black Prince G × WI A
Bernecker WI A
Loretta G × WI B
Different cultivars
of
Avocado

14. HassFuerte
Pollock Lula
Conti…

16. New released Avocado cultivars
Cultivar Characteristics
TKD-1 Semi spreading, suitable for HDP and high fat content (23.8%). It is selection
made at Horticulture Research Station, Thadiyankudisai, Tamil Nadu.
Iriet Outcross of Hass, flesh is green yellow, buttery in texture, excellent nut like
flavour and a very small seed. It is harvested from mid winter to the following
mid summer in Israel.
Eden Cross of Pinkerton and NISI-2 in Israel. Fruit is yellow, buttery and free from
fibers with nut like flavour.
Gowen Derived via open pollination in Hass. Highly precocious with a semi dwarfing
upright habit. It produce high quality medium size fruit.

17. Iriet Gwen
Eden

18. Genetic resources
• Natural selection over thousands of years has produced sizeable number of desirable types suited to agro-
ecological situations.
• Lamberts and Crane (1990) have reported 63 commercial cultivars in Florida (USA). These are either West
Indian or West Indian x Guatemalan hybrids. Of these, Booth-8, Hall, Lula, Monore, Pollock and Simmonds
are most important in commerce. The Florida cultivars are better suited to the tropics.
• In Texas, 'Lula' is the best cultivar producing good high quality crops (15 t/ha). Its fruit is pear shaped and
has creamy, sweet flesh (Duke, 1978).
• In California, cultivars like "Bacon", "Zutano", "Nabal" and "Hass" are more popular.
• Israel's main cultivars are Ettinger, Fuerte, Hass, Nabal, Reed and Benik (Shachar, 1982).
• In Australia, important cultivars are: Bacon, Fuerte, Hass, Hazzard, Nabal, Pinkerton, Reed, Rincon, Ryan,
Sharwil, Shephard, Wurtz, Zutano and Gwen (Cull & Lindsay 1995).
• The Mexican race originating from the Mexican highlands is most tolerant to cold. Unfortunately, the fruits
of pure Mexican race background are the least desirable, being small and soft skinned with large seeds.
• Cross-bred cultivars are of more value. Fuerte and Zutano are Mexican x Guatemalan hybrids. They have
medium-sized fruit with smooth skins. 'Fuerte' shows some hardiness to frost.

19. Country Cultivars
USA (California) Furete, Hass, Zutano, Bacon, Reed, Gwen, Pinkerton
USA (Florida) Pollock, Booth 8, Lula, Hardee, Ruehle, Hall, Hickson, Monroe
Australia Zutano, Sharwil, Bacon, Furete, Hass, Green Gold
New Zealand Fuerte, Zutano, Hayes, Hopkins, Hass, Pollock, Booth, Simmonds, Reed
Israel Fuerte, Hass, Nabal, Ettinger, Horshim, Wurtz, Ardith, Adi, Iriet, Gil
Brazil Fuerte, Hass, Nabal, Ryan, Edranol, Corona, Solano, Quintal
South Africa Fuerte, Hass, Rayn, Hayes, Pollock
Mexico Fuerte, Hass, Bacon, Reed, Criollor, Zutano
Spain Hass, Bacon, Furete, Reed, Sutano, Gwen
India Green Type, TKD-1, Nabal, Linda
Major Avocado cultivars growing areas

20. • Cultivars belonging to Mexican race (Duke-7) have shown tolerance to Phytophthora
root rot.
• In general, Mexican race rootstocks are cold tolerant and of low vigour (Cull and
Lindsay, 1995).
• Resistance to salinity is most common in the West Indian race and most rare in the
Mexican race (Bergh, 1975).
• Zentmyer et al. (1965) indicates that the Mexican race has more genetic resistance to
canker and Verticillium wilt.
• The Guatemalan rootstocks appear to have better nutrient absorption ability
particularly for boron.
• Possible sources of dwarfing rootstocks include 'Mt 4' (Bergh and Whitsell, 1962),
'Jalna', 'Wurtz' and 'Nowels' and Persea americana botanical varieties floccosa, or
nubigena (Bergh, 1975).
• Barrientos-Priego et al. (1992) have suggested that cv. Colin V-33 is an effective
dwarfing rootstock for avocado.
Conti…

21. Genetic variation in colour, shape and seed size

22. Seedless avocado
• Seedless avocado fruits (the result
of stenospermocarpy) often set but
do not reach the normal size of
fruits with seeds.
• The seedless fruits are usually
curved and elongated and are
commonly known as ‘cukes’ or
‘cocktail avocados’.

23. Flowering Physiology
• The avocado flowering behavior is typical in many ways.
• The inflorescence is compound panicle of raceme having two
types of growth i.e. indeterminate & determinate.
• In indeterminate inflorescence (A), terminal of the shoot that
bears the flowers will end with a vegetative bud.
• Whereas in determinate inflorescence (B), the tip of the shoot
that bears the flowers will end in a floral bud.
*Source: http://dx.doi.org/10.1016/j.scienta.2013.09.051

24. Main Phenological Growth Stages of
‘Hass’ Avocado
*Source: http://dx.doi.org/10.1016/j.scienta.2013.09.051

25. Flowering Behaviour
• The avocado has unique flowering behaviour, named as Protogynous diurnal synchronous
dichogamy (Bergh 1969).
• While dichogamy indicates that female & male parts mature at different times, but it
synchronizes in such a way that all the open flowers on a tree are female at one time & male at
another time.
• The synchronization is diurnal for each tree, flower is functionally female at one part of the day &
functionally male during another part of the same day (i.e. flowers which were female in
morning on 1st day of anthesis, they would behave as male in the afternoon of the next day &
vice versa).
• The dichogamy is also protogynous, which means the pistil will mature earlier than stamen.
• While avocado flower is structurally bisexual, but it is functionally unisexual.

26. • Based on flower type cultivars, it is classified into 2 groups:
• Group A: The first opening (i.e. female) starts in the morning & ends before noon. Second opening
(i.e. male) occurs in the afternoon of the next day.
• Group B: The first opening (i.e. female) occurs in the afternoon and male opening next morning.
• Mixed plants of cultivars is desirable to avoid unfruitfulness.
• Honey bees are chief pollinating agents.

27. Ripening

28. Conventional Breeding Problems
• Highly heterozygous crop resulting in unpredictable progeny.
• Poor fruit setting
• Alternate or irregular bearing habit of the trees
• Monopodial growing habit & large sized trees.
• Long juvenile phase
• Fruit rot & root rot disease
• Susceptibility to Anthracnose, Cercospora spot and Verticillium wilt

29. Avocado Ideotype
• The Ideotype must be a regular, prolific bearer with good fruit setting ability and endowed with
high quality, medium size fruits (250-300 g) of uniform shape, a small seed, thick and smooth skin
to protect the flesh in transit.
• It will have a high oil content of >18 per cent.
• The seed should be tightly held in its cavity, with pulp free from fibres.
• The growth habit of the tree should be spreading type rather than being upright (Bergh, 1975).
• The fruit on the tree should mature over a relatively short time.

30. Breeding Objectives
• The first and foremost objective is to breed for high yield and regular bearing tendency.
• As regards rootstock breeding, emphasis is laid on developing strains that can impart dwarfness
to scion.
• Development of rootstocks that can impart resistance to root-rot disease (due to fungus
Phytophthora cinnamomi Rands).
• Resistance to Anthracnose, Cercospora spot and Verticillium wilt either through rootstock or
scion breeding.
• In frost prone areas, a stock that enhances cold hardiness would be highly desirable.
• Resistance to salinity is sought in the areas having excessive salt concentration in the soil.
• Heavy bearing of the scion (Bergh, 1975).
• Extend the harvest season.

31. Selection
• Majority of old, established cultivars of avocado
are chance seedlings selected on the basis of
superior yield and fruit quality.
• Some notable examples are: Fuerte, Hass,
Bacon, Zutano, Benik, Nabal, Sharwil and
Ettinger.
• The avocado's unique mating system based on
synchronized dichogamy insures considerable
cross pollination, and considerably, a high
degree of heterozygosity.
• Some commercially successful avocado cultivars
developed in California through selection are
given in the table.
Cultivar Parent
Mexican race
Reed Nabal seedling
Jim Bacon seed
Creelman Fuerte × Hass
Teague Fuerte × Duke
Ettinger Fuerte
West Indian race
Simmonds Pollock
Ruehle Waldin
Gautemalan race
Tonnage Taylor

32. Hybridization
• There are no sterility barriers between the three varieties and thus numerous attempts have
been made in the past to develop superior strains through intervarietal hybridization.
• In tropical and near tropical areas, only americana is well adapted, but hybrids of it with
guatemalensis (e.g. the Booth selections) are performing well and are valuable for extending the
harvest season.
• In less tropical regions, hybrids of guatemalensis with drymifolia predominates.
• Genetic constitutions vary largely from drymifolia (Ettinger, Zutano) through approximately equal
proportions (Fuerte, Sharwil) to guatemalensis (Hass).
• ‘Hass’, a G x M hybrid, is a black-skinned (when ripe), ovate cultivar whose fruit weighs 140 to 300
gm. ‘Hass’ accounts for about 75% of the production in Mexico and California, and is also
important in other countries.
• Tri hybrids of all the three varieties have been developed in Hawaii and University of California
breeding programme.

33. • Due to absence of sterility, hybridization occurs readily in nature, wherever trees of
different races are growing in proximity.
• This has led to evolution of several natural hybrids that happen to be present cultivars.
Cultivar Parent
Fuerte Mexican x Guatemalan hybrid
Booth 7 Guatemalan and West Indian races
Booth 8 Guatemalan and West Indian races
Creelman Fuerte × Hass
Teague Fuerte × Duke
Hass Mexican x Guatemalan hybrid
In rootstock breeding, attempts have been made to develop strains (or stocks) that can
impart resistance against root rot caused by Phytophthora cinnamomi.

34. Polyploidy
• Tetraploidy has been induced with colchicine in ‘Fuerte’ & ‘Mexicola’.
• Typical gigas characteristics were observed in the vegetative organs but
fruit set was reduced to almost nil (Bringhurst, 1956).

35. Mutation
• Spontaneous mutations occur in nature in avocado over a long period of
cultivation.
• Although natural mutants of Fuerte, Hass and Jim have been recognized,
deviations in fruit characters or tree morphology appear to be unstable and
has proven unimpressive economically.
• To enhance moderate root rot resistance, ‘Duke’ scions were irradiated with
fast neutrons in the California. One resulting selection, ‘D9’, was tested as a
commercial stock because of its considerable root rot resistance & also some
dwarfing effects. ‘D9’ was found more productive than ‘Martin Grande’
(Arpaia et al., 1992).

36. Obtaining of new genotypes from avocado
‘Hass’ variety by mutation breeding
• Alper Arslan is working on mutation breeding project of avocado in Turkey in the year 2015-
2020.
• Optimal mutation doses via gamma ray were detected as 13-17 Gy on ‘Hass’ cultivar in Mexico (E.
De La Cruz T: and M.Rubi A., 1995).
• This project is aimed to select for higher yield, bigger fruit size and better quality then that of
‘Hass’ cultivar after irradiation, and to improve the first native cultivars in Turkey.
• With these aims, the scions of ‘Hass’ cultivar will be irradiated with 15, 20 and 25 Gy using by
gamma ray from a source of Co ⁶⁰ and then M1V3 generation will be created in growth apex of
scions.

37. Biotechnology
• Several reports have appeared on different aspects e.g. cell culture techniques
(Witjaksono et al., 1998), taxonomic characterization (Davis et al., 1998) & genetic
transformation (Cruz-Hernandez et al., 1998).
• Protoplast fusion techniques have utility for making new combinations of nuclear
and cytoplasmic genes.
• Recently, DNA markers were applied to analysis of avocado genome.
• Restriction fragment length polymorphism (RFLP) markers were used to study
genetic relationship in Persea genus (Fumier et al., 1990).
• DNA fingerprint (DFP) markers were used for identification purposes and genetic
analysis (Levi et al., 1991 a) as well as detecting a genetic association between DFP
bands and agronomically important traits (Mhameed et al., 1995).
• Simple sequence repeat (SSR) markers were applied for identification of genotypes
and their genetic analysis (Lavi et al., 1991).

38. Developing a cryopreservation protocol for avocado
(Persea americana mill.) shoot tips
• O’Brien conducted a research trail with following objectives:
To overcome oxidation/browning and improve shoot tip regrowth during the cryo-procedure.
To develop an in vitro cryopreservation protocol for shoot tips of Persea species.
• Various treatments; polyvinylpyrrolidone (PVP), and the antioxidants ascorbic acid, citric acid and
melatonin, were applied to reduce browning of cv. ‘Reed’ shoot tips.
• Shoot-tips were scored for browning at 0, 2, 3 and 4 weeks.
• Shoot-tip survival and regrowth were scored at 8 weeks.

39.  Results
• Ascorbic acid at 100 and 250 mg/L, reduced browning of shoot tips.
• PVP at 1.5 g/L showed normal growth and reduced browning.
• Citric acid at 40 and 55 mg/L controlled browning, but resulted in abnormal growth and vitrification.
• Melatonin at 0.2 μM controlled browning but shoots were stunted and lacked vigor.
 Conclusion
• Ascorbic acid at 100, 250 mg/L and PVP at 1.5 g/L best controlled browning and displayed normal
growth. These will be useful in subsequent steps in cryopreservation protocol.
Figure: Shoot tips
after 8 weeks in
regrowth media

40. Application of genomic tools to avocado (Persea americana) breeding:
SNP discovery for genotyping and germplasm characterization
• Kuhn et al. (2019) describe the development of the first set of avocado genetic markers based on
single-nucleotide polymorphism (SNP) variation in expressed genes.
• RNA sequencing was used both to build a reference transcriptome from 'Hass', the most widely
grown avocado cultivar worldwide, and to identify SNPs by alignment of RNA sequences from the
mapping population parents to the ˈHassˈ transcriptome.
• This study provides a new genomic tool for the avocado community that can be used to assess
the genetic diversity of avocado germplasm worldwide and to optimize avocado breeding and
selection programs by complementing traditional breeding methods with molecular approaches,
thus increasing the efficiency of avocado genetic improvement.

41. Conclusion
• Molecular techniques have provided a deeper and more precise
understanding of gene action and inheritance (Dopico et al., 1993; Cass et
al., 1990; Sharon et al., 1997, 1998) and have also helped in generating
genetic linkage maps (Lewis, 1992).
• With such deepened understanding, hybridization and selection of
avocado via standard sexual procedures will be planned and executed
with greater vision and economy in future.