This document summarizes information about breeding in avocados. It discusses the taxonomy and genetic resources of avocados, focusing on the three main races: Mexican, Guatemalan, and West Indian. The breeding objectives are outlined as developing high yielding cultivars with regular bearing, dwarfing rootstocks, and disease resistance. Breeding methods discussed include selection of superior cultivars, hybridization between the races to extend harvest seasons, and induced polyploidy, though fruit set is reduced with polyploidy.

1. BREEDING IN AVOCADO
SHARVESH, S.,
M.Sc. HORTICULTURE,
DEPARTMENT OF HORTICULTURE,
FACULTY OF AGRICULTUR,
ANNAMALAI UNIVERSITY.

2. INTRODUCTION
• The word “avocado” comes from Nahuati word ahuacati.Which means
‘testicle’, a reference to shape of the fruit.
• Avocados were known by the Aztecs as ‘fertility fruit’.
• Avocado 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.
• Otherwise also known as poor man’ butter.
• Origin is state of Puebla in Mexico.
• Chromosome number is 2n=2x=24.
• It is a self pollinated crop.

3. • Avocado appeared approximately 12,000 years ago.
• It was 1st reported in Florida in 1833 & in California in 1856.
• 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.
• In india is cultivated at himalayan areas and followed by north eastern
areas of indi.
• 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.

4. • Genus Persea, name has been derived from ancient Greek
name of an Egyptian tree with sweet fruits, derived probably
from Perseus.
• It have 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).
• Commercial avocado (Persea americana Mill.) is belongs to
family Lauraceae & the sub-genus Persea that also contains
two other important species, Cinnamon (Cinnamonum
zeylanicum) & Campor (Cinnamonum camphora).

5. TAXONOMY
Persea americana is a polymorphic species containing several
separate taxa that are considered to be botanical varieties, more
commonly referred to as horticultural races.
• 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)

6. Persea 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.

7. Persea 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.

8. Persea 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.

9. FLORAL BIOLOGY
The perianth includes both sepals and petals.
Sepals are green colour and Petals are bright coloured.
The stamens are 9 in number, arranged in an outer circle of 6 and an
inner circle of 3.
The inner 3 have a basal pair of nectar-secreting “nectaries” and
alternate with 3 nectar-secreting “staminodes”. Each stamen has 4
pollen sacs which release the mature pollen through valves hinged at
the top. The pistil is in the center of the flower.
The flowers are grouped in compound inflorescences of a few to
several hundred flowers each.

12. 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).

13. • 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.

14. • In California, cultivars like “Bacon”, “Zutano”, “Nabal” and “Hass” are
more popular.
• 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.
• Israel’s main cultivars are Ettinger, Fuerte, Hass, Nabal, Reed and
Benik

15. 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.

16. 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.

17. FLOWER TYPES
• Based on flower type 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.
• Honey bees are chief pollinating agents

18. 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.
• The fruit on the tree should mature over a relatively short time.

19. 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.

20. BREEDING METHODS
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.

21. 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 exten
• 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 programmeding the harvest
season.

22. • 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.

23. 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).

24. 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’

25. • 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.
• 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.

26. BIOTECHNOLOGY
• Several reports have appeared on different aspects e.g. Cell culture
techniques& genetic transformation .
• 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.
• DNA fingerprint (DFP) markers were used for identification purposes and
genetic analysis as well as detecting a genetic association between DFP
bands and agronomically important traits.
• Simple sequence repeat (SSR) markers were applied for identification of
genotypes and their genetic analysis.

27. APPLICATION OF GENOMIC TOOLS TO AVOCADO 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.

28. 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

29. CONVENTIONAL BREEDING PROBLEM
• 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