Nghiên cứu kỹ thuật nhân giống vô tính cây đu đủ (carica papaya l ) cv ‘tainung no 2’ and ‘red lady’

國國國國國國國國國國國國國國國國國國
Department of Tropical Agriculture and International Cooperation
National Pingtung University of Science and Technology
國國國國國國
Ph.D. Dissertation
國國 2 國國國國國國國(Carica papaya L.)國國國國國國國
Studies on asexual propagation techniques of papaya (Carica
papaya L.) cv. ‘Tainung No.2’ and ‘Red Lady’

國國國國 Advisors: 國國國 國國 (Chung-Ruey Yen, Ph.D.)
國國國 國國 (Ching-Hsiang Hsieh, Ph.D.)
國國國 Student: 國國國 (Nguyen Van Hong)

國國國國 107 國 10 國 30 國
October 30, 2018


INTRODUCTION
The cultivated papaya (Carica papaya L.) is the most economic
important species in the family Caricaceae. Papaya grows year-round, is an
elongated berry of various sizes with a smooth thin skin and a greenishyellow color (Paull 2011). Its flesh is thick with a color ranging from yellow
to red and offers a pleasant, sweet, mellow flavor (Devitt 2006, Fuggate
2010). Papaya is considered to be one of the most important sources of
vitamins (A, B, C) (Bose 1990, Watson 1990), minerals, several proteins, and
the industrially important enzyme papain

(Barret 1985, Bose 1990, El

Moussaoui 2001). Papaya fruit is low in sodium, fat, and calories, and contain
no starch (Sampson 1986 ). Papain, whose proteolytic action is similar to that
of pepsin and trypsin, is employed as a meat tenderizer in applications in the

food industry, as well as in the textile, pharmaceutical, and cosmetic
industries (Villegas 1997, Su 2009).
Papaya is one of the most economically important fruit crops in many
tropical and subtropical countries. In 2016, total areas for fruit cultivation
were 441,964 ha in the world which produced 13,050,749 tonnes (t) of fruit
(Faostat 2017). In Taiwan, papaya is one of the top ten fruits of production
(Fig.5). In 2015, papaya area harvested and production were 2,500 ha and
115,115 tonnes (Faostat 2017). Recently, the papaya production is affected by
destructive diseases, specially, papaya ringspot (PRS). PRS is one the most
destructive diseases of papaya and occurs in every region where papaya is
grown. It has been reported to be a major limiting factor for commercial
papaya production particularly in Hawaii, areas of Thailand, Taiwan, India,
Mexico, Bangladesh, the

Philippines, and the southern region of China

(Chang 2003, Jayavalli 2011).
Papaya is a polygamous species with many forms of inflorescences.
The species has three sex types: Staminate, pistillate and hermaphrodite
(Dinesh 2001, Paull 2011). Papaya is one of the few fruit crops still mostly
1


propagated by seed for commercial production. Papaya seedlings propagated
from seed is hindered by problems because of the sex reversal, inherent
heterozygosity and dioecious nature of the crop (Teixeira 2007, Clarindo
2008). In the commercial plantations of most producing countries, male plants
are useless and only hermaphrodite individuals are agreed by growers (Usman
2002, Hsu 2012). However, it was found that undesirable male plants prevail
as high as 30% and sometimes over 50 % of trees planted in papaya fields

(Jordan 1983). So, in actual commercial production, three or four seedlings
are planted at each position, and when their sexes are determined, only
hermaphrodites are kept. There are cases in which none of them are
hermaphrodites. In addition, the plants grown from seeds show considerable
variations in disease susceptibility, fruit quality, and yield (Reuveni 1990,
Allan 1995, Teixeira 2007).
The main advantage of vegetative propagation is the certainty of
keeping the characteristics of the mother plant (Hartmann 2002, Hartmann
2011). It had been reported the possibility of developing materials highly
productive and resistant to diseases, which can be spread safely keeping intact
the characteristics of the papaya mother plants through asexual propagation
(San Jose 1988). Additionally, one can reduce transmissible diseases by
choosing mother plants carefully. The case of gynodioecious cultivars, the
bisexual types which produce fruits with shape, size, and flavor are preferred
to round fruits of female plants as they fetch premium price in the market
(Reuveni 1990, Teixeira 2009). Up to now, asexual propagation techniques,
such as rooting of cuttings, grafting and micropropagation have been
successful in papaya cultivars (Airi 1986 , Ramkhelawan 1998 , Teixeira
2007, Chong 2008 , Wu 2012, Setargie 2015).
The success of assexual propagation by cutting, grafting, tissue culture
depends on numerous factors, among them the zone environment, the material
and technique application, and the genotype (Hartmann 2002, Soundy 2008,
Hartmann 2011, Mabizela 2017). In addition, the results can not apply to all
2


varieties and in all climatic conditions. So, scientists need conduct much more
research on each variety under certain conditions.
In Taiwan, the papaya is mainly propagated by seed and by a method
designed to reduce damage from viruses of insects. To date, there is hardly

any information on cuttings, grafting and tissue culture propagation of the
hybrid papaya cultivars ‘Tainung No.2’ and ‘Red Lady’. The ‘Tainung No.2’
papaya is the major cultivar with 90% of growing area and ‘Red Lady’
papaya is potentially one for spreading with fruit weigh of 1.5-2 kg, good fruit
quality (flesh is thick, red, with 13% sugar content, and aromatic) and
preferred by the local market (Agriculture and Food Agency, Council of
Agriculture, Executive Yuan, R.O.C). So, on purpose of cloning good quality
papaya varieties, we conducted researches on propagation of two papaya
varieties (‘Tainung No.2’ and ‘Red Lady’) by grafting, cutting and tissue
culture. The aims of this study were to investigate the effects of grafting,
cutting and micropropagation techniques on commercial asexual propagation
in 'Tainung No.2' and 'Red Lady' papaya. The specific objectives were:
• Research on grafting propagation of ‘Tainung No.2’ and
‘Red
Lady’ papaya.
• Research on cutting propagation of ‘Tainung No.2’ and ‘Red
Lady’
papaya.
• Research on tissue culture propagation of ‘Tainung No.2’ and
‘Red
Lady’ papaya.

3


LITERATURE REVIEW
1. General of papaya plant
Papaya (Carica papaya L.) is a popular fruit native to tropical America.
Papaya plant is grown for its melon-like fruit. It is a herbaceous perennial
plant, bearing fruit continuously at the leaf axils spirally arranged along the

single erect trunk. The papayas have common names, such as papaya, papaw
or pawpaw, papayer (friench), melonenbaum (German), lechosa (Spanish),
mamao (Portuguese), mugua (Chinese), and dudu (Vietnamese) (Paull 2011).
1.1. Taxonomy
Carica Papaya L., is the most important economic fruit, belongs to the
Carica Genus, Caricaceae family. Caricaceae is a small family of
dicotyledonous plant with five genera of tropical American origin (Carica,
Jarilla, Jacaratia, Horovitzia and Vasconcella) and one from equatorial
Africa (Cylicomorpha) (Paull 2011). There are 32 species described with
distribution: Carica, 1 species, Jarilla, 3 species, Jacaratia, 5 species,
Horovitzia, 1 species, Vasconcella, 20 species, and Cylicomorpha, 2 species.
Carica and Vasconcella species are dioecious, except for the
monoecious Vasconcella monoica (Desf.) and some Vasconcella pubescens
and the polygamous C. papaya. Most species are herbaceous, single-stemmed
and erect (Paull 2011).
1.2. Origin, distribution and production
Upto now, scientist has not found Carica papaya wild in nature. It is
evidenced in distantly relation to the Vasconcella species by isozyme and
AFLP analysis (Paull 2011). It is believed that Carica papaya is native to
tropical America, Its origin region is southern Mexico and neighbouring
Central America (Morton 1987). In the 16th century, spanish took papaya to
the Caribbean and South East Asia. In the accounts of 18th century, seeds of
4


papaya had been taken from the Caribbean to Malacca and on to India ( Paull
2011). Subsequent historical records indicate that from Malacca or
Philippines the papaya distribution continued throughout Asia and to the
South Pacific region. The factors such as a large number of the seeds in the
fruit and their long viability have contributed to the wide geographical

distribution of the fruit (Paull 2011).
In the past decade, papaya has attained great popularity because it can
be intensively cultivated, its rapid returns and the increased demand for the
fresh fruit as well as its processed products. Papaya is commercially
cultivated between 23o North and 32o South latitude (Paull 2011), an area
which includes many tropical and sub-tropical countries of the world. From
2006 to 2016, Papaya area harvested and production had been developing
quickly in the world (Figure (Fig.) 1). The highest papaya production was
obtained in Asia (49%) followed by Americas (37.7%) and by Africa
(13.2%). The lowest production (0.2%) is recorded Oceania (Fig.2). Top ten
countries of papaya production (2006-2016) are India, Brazil, Indonesia,
Negeria, Mexico, Dominican Republic, Democratic Republic of the Congo,
Kenya, Thailand, Colombia, Philippines (Fig.3) (Faostat 2017).
Area harvested

Production (Tonnes)

14000000

500000
450000
400000
350000
300000
250000
200000
150000
100000
50000
0

12000000
10000000
8000000
6000000
4000000
2000000
0

Area harvested (ha)

Production

Years

Figure 1. Production of papaya in the world 2006-2016 (Source: Faostat,
2017)

5


Asia

Americas

Africa

Oceania

Oceania

0.2 %

Africa
13.2 %

Asia 49%
Americas
38.7%

Production (tonnes)

Figure 2. Production share of papaya by region (Source: Faostat, 2017).
5
4.5
4
3.5
3
2.5
2
1.5
1
0.5
0

Production (Tonnes)

Figure 3. Top papaya production countries (Source: Faostat, 2017)
Papaya production in Taiwan
In 17th century, papaya travelled from the west Indies to Asia where at
the end of the Qing Dynasty it was introduced to Taiwan and be developed

forcefully upto now. In 2016, papaya area harvested and production achieved
2,584 ha and 118,661tonnes, respectively (Faostat 2017). Periods of 19942016, papaya area harvested and production were varied in Taiwan and they
were increasing trend in 2014-2016 (Fig. 4). Papaya is in top 10 fruit growing
in Taiwan with 4% of fruit production in 2013 (Fig.5).


Area harvested

160000
140000
120000
100000
80000
60000
40000
20000
0

3500
3000
2500
2000
1500
1000

Area harvested (ha)

Production (tonnes)

Production

500
0
2006 2007 2008 2009 2010 2011 2012 2013 2014 2015
2016
Years

Figure 4. Area harvested and production of papaya in Taiwan (Source:
Faostat, 2017)
Wax Apple
4%

Pear
4%

Other fruits
24%

Papaya
5%
Betel nut
5%
Guava
7%
Mango
8%

Citrus
20%
Pineapple

16%

Banana
7%

Figure 5. Fruit production in Taiwan in 2013 (Source: COA, TIER, 2014)
1.3. Characteristic of papaya plant
* Stem
The papaya plant is a large, mono-axial herbaceous plant with an erect
stem terminating with a crown of large leaves and can attain by 9 m heights
(Fig. 6). Although there are occasional lines or cultivars that produce and


abundance of lateral branches, especially during the juvenile period, the main
stem normally growth of the axillary branches does occur when the trees
become 3-5 years old (Paull 2011). The stem is semi-woody and hollow and a
major site of starch storage. The bark is smooth, grayish, with large and
prominent leaf scars. When the stem is wounded, a thin milky sap oozes from
the wound (Fig. 6).
After transplanting, shoot growth is initially slow, though considerable
root growth is taking place, extending out well beyond the canopy drip line.
Stem growth is then rapid up to flowering, increasing in circumference up to 2
mm per day (Paull 2011). Growth rate peaks at flowering then declines as the
tree starts bearing. The rate of growth is influenced by nitrogen and
phosphorus supply, irrigation and temperature (Paull 2011).

Figure 6. Vegetative parts of the papaya plant. (a) Cross section of a 1-yearold papaya stem: periderm (pe), fiber sheath (fs), phloem (ph),
cambium (c), xylem rays (xr), pith (p). (b) Leaf lamina and petiole.
(c) Longitudinal section of a 3-month-old papaya stem showing
hollow pith cavity. (d) Longitudinal section of a 1-year-old papaya

stem showing complete pith cavity. (e) Stem of a 1-year-old papaya
plant showing conspicuous petiole scars.


* Leaves
A cluster of leaves occurs at the apex of the plant and along the upper
part of the stem and makes up the foliage of the tree (Fig. 6). New leaves are
constantly formed at the apex and old leaves senesce and fall. Leaves are
palmately lobed with prominent veination and can measure 40-50 cm or more
in diameter and have an individual leaf area of 1625 cm2, with 15 mature
leaves per plant (Paull 2011). In the tropics, new leaves appear two to three a
week (Chan 1984). Petioles are cylindrical, hollow and length of 60 – 90 cm,
depending upon the cultivar. The most recently matured leaf’s fresh weight
(about 10th leaf from 2.4 cm juvenile leaf) varies from ca 50 to 170 g. The leaf
petiole dry mass increases at a rapid rate until flowering the increases more
slowly, peaking after fruit bearing starts (Paull 2011).
* Floral organization and flowers
Papaya has three types of distinctly different flowers, male, female and
hermaphrodite, which give rise to fruits (Bose 1990) (Fig. 7). The flowers are
found in the auxiliary pendulous in the inflorescence. Male flowers are
yellowish, 2-4 cm long with petals fused to form a long tube, with 10 fertile
stamens and a rudimentary ovary (Fig.7 A, D). Female inflorescence is much
shorter, 3-4cm long and sits alone or in small groups in leaf axils. Female
flowers are larger, usually white or cream in color, with five free petals and a
large ovary with 5 fan shaped stigmas without stamens (Fig. 7 C, F).
Hermaphrodite flowers have either 5 or 10 stamens and a prominent ovary
(Fig. 7 B, E).
Five major floral structures namely pistillate, pentandria, elongate,
staminate and intermediate have been identified of papaya (Bose 1990).

Figure 7. Papaya flowers with one petal removed to show internal parts (A–C)
and inflorescences (D–F). (A) Staminate flower showing stamens
(st), pistillode (pi) and corolla tube (ct). (B) Perfect flower showing
st, ct, stigmata (sa), petal (p) and an elongated ovary (o). (C)
Pistillate flowers showing sepals (sp), petals and round ovary (o). (D)
Long male inflorescence with dozens of staminate flowers. (E)
Andromonoecious cyme showing one dominant perfect (pf) and five
secondary staminate flowers (sf). (F) Female cyme with three
pistillate flowers
* Fruits
Papaya fruits are usually born auxiliary on the main stem often as
single and rarely in small clusters. They are generally melon-like (oval to
nearly round) or somewhat pyriform or elongated club shaped with a waxy
skin. The flesh is yellow – orange to salmon at maturity and pale yellow in
unripened ones. The shapes of the fruits vary according to the sex and the
variety of papaya qualifying sex as an important trait in papaya (Parasnis
1999).


The fruit is rich in carbohydrates, fats, proteins, fiber minerals and
vitamins and is also a good source of iron calcium, vitamins A, B and C. The
unripe hard green fruit contain white latex, which is rich in papain (Rubens
Monti 2000). The yellow, orange or reddish succulent flesh in the ripe fruit
underneath the thick wall of the fruit is aromatic, juicy and sweetish and
harbors seeds lightly by soft, white, fibrous tissue.
* Seeds
The papaya seeds are black, corrugated, ovoid, peppery and coated with
a transparent gelatinous coat. The structure of the seeds concludes the seed
coat, endosperm, embryo.

Figure 8. Seed and seedling. A. Mature dried seeds, T.S. (transverse section)
and L.S. (longitudinal section). B. Endosperm cells. C. Ovule wall
of developing seed. (em) embryo, (en) endosperm, (mt) mesotesta
ridge, (vb) vascular bundle, (ii) inner integument, (oi) outer
integument, (sad) sarcotesta (Source: Fisher 1980)
Seed coat: The outer region is fleshy and becomes a gelatinous
sarcotesta at maturity (Fig. 8C). It is derived from the multiple outer
epidermis of the outer integument of the ovule. The mesotesta is compact,
consisting of a series of sculptured, spongy, and hydroscopic longitudinal
ridges, derived chiefly from subepidermal layers of the outer integument (Fig.
8A). The inner epidermis of the outer integument remains unchanged except
for development of druses. The inner integument produces thin, inner,
sclerotic layers of the seed coat with the inner epidermis tanniniferous and


subepidermis fibrous. The funicle is stout, its head occasionally enlarged and
fleshly as a short aril (Fisher 1980). The funicular vascular bundle extends
into the inner integument at the chalazal end where it subdivides.
Endosperm: Cells are thin-walled with abundant oil and aleurone
grains; starch is absent at maturity (Fig. 8B ).
Embryo: The embryo is straight and median with ovoid and flattened
cotyledons (Fig. 8A ).
* Root system
Young

roots

show

well-differentiated

epidermis,

cortex,

and

endodermis, enclosing an exarch vasculature in which six xylem and six
phloem poles alternate. Cambium formation in a concentric ring triggers
secondary growth and root thickening while maintaining succulence. The
papaya root is predominately a non-axial, fibrous system, composed of one or
two 0.5–1.0 m long tap roots. Secondary roots emerge from the upper sections
and branch profusely (Fig. 9 a, b). Healthy roots are whitish cream and no
laticifers have been observed in them (Marler 1997, Carneiro 2009).

a

b

Figure 9. Root system. (a) Side view of an excavated 5-month-old papaya root
system, showing the main and secondary roots. (b) Upper view of the
same root system, showing horizontal distribution of secondary
roots.


Phenotypic plasticity of roots is high. Size, number, distribution, and
orientation of plant roots adjust readily across the soil profile, to various soil
conditions, and throughout the life of the plant (Marler 1997, Carneiro 2009).
Plants dependent on mycorrhizas for their nutrition and benefit from

soil mulching and appropriate drainage that facilitate biotic interactions in the
rhizosphere and water and nutrient uptake. Mycorrhizal interactions of male
and female papaya plants may differ: females seem more responsive to
changes in soil fertility and readily adjust mycorrhizal colonization
accordingly (Vega-Frutis 2009).
1.4. Sex characteristics of papaya
Papaya crop is polygamous in nature. The sex of dioecious papaya
plants only can be defined after they attain reproductive maturity (6–8
months) (Bose 1990). Normally, 50% of the population in a field is composed
of unfruitful male plants and almost 45% of these have to be uprooted at the
flowering stage (Parasnis 1999). This unnecessary cultivation of unwanted
males leads to wastage of resources, which can be avoided if the sex of the
plant is determined at juvenile stage. Morphological and cytological studies
conducted so far have failed to differentiate between the various sex forms of
papaya (Parasnis 1999). Papaya exhibits wide morphological and biological
diversity of sex types with prominent specific characters. The papaya plants
can be either dioecious with male or female flowers occurring in separate
plants or monoecious with male and female parts falling in the same flower
(Yon 1994).
Three sex forms (female, male, and hermaphrodite) are regulated by an
incipient X–Y chromosome system. Papayas can be either dioecious (with
male and female plants) or gynodioecious (with hermaphrodite and female
plants). Several studies suggested that the Y chromosome contains a small
specific region that controls expression of male (Y) or hermaphrodite (Y h )
types. Female plants are of the XX form. All combinations among the Y


and/or Y h chromosomes are lethal; therefore, the male and hermaphrodite
types are heterozygous (XY and XY h , respectively) (Ming 2007).
In papaya the change of sex occurs in some trees at high temperature,

where short stalked male flowers are produced instead of usual perfect
flowers (Chan 2009).

Male or bisexual plants changing completely too

female plants after being beheaded and some “all male” plants occasionally
producing small flowers with perfectly pistils leading to abnormally slender
fruits are also instances of change of sex in papaya (Sujitha 2012).
Chay-Prove (Chay-Prove 2000) and OECD (Organization for
Economic Cooperation and Development 2003) showed that: Changes in
functional gender in response to environmental viriables have been used
advantageously in papaya breeding programs and to help select the most
appropriate varieties for commercial cultivation in particular regions.
* The environmental factors affect papaya sex expression.
The basic sex types in papaya are genetically determined. The pistillate
or female is phenotypically very stable. However, certain male and
hermaphrodite trees have been known to undergo sex reversal under the
influence of various environmental changes (Ming 2007 )
Temperature
Cool temperatures in the winter months appear to promote more
femaleness in hermaphrodite trees (Allan 1987). Cooler temperature reduces
the number of stamens, as described previously is brought about by fusion of
the stamens to the ovary (Jain 2009). The warm temperatures tend to promote
the production of hermaphrodite flowers resulting in the sterility of the trees.
When such conditions persist over a length of time, a production gap along
the trunk is clearly visible.


Allan et al. (Allan 1987) in a study on environmental effects on clonal
female and male papaya plant found that cool night temperatures of about 12

o

C and short daylengths appeared to be critical in causing sex reversal from

the sterile staminate to fertile, elongata type hermaphrodite flowers.
Moisture
Moisture levels probably affect the growth and development of the
trees and indirectly bring about the reversal in sex (Jain 2009). High moisture
regime promotes femaleness in papaya. For hermaphrodite plant, consistently
high moisture levels will promote the production of hermaphrodite flowers
with reduction of stamen number and low soil moisture regime tend to
produce more elongate type hermaphrodite flowers (Jain 2009).
Nitrogen
Application of nitrogen promoted greater tendency towards femaleness
in hermaphrodite trees ( Jain 2009). Manipulation of nitrogen levels applied to
the plants able to control the expression of sex (Teixeira 2009).
Growth regulators
Ethylene promotes femaleness in papaya (Pet Roey 2014). Papaya
seedlings of a dioecious cultivar treated by Ethephon (a conversion from
ethylene) exhibited a significantly higher percentage of female trees at
maturation. This percentage was over 90% when applications were
continuously given at 15-day or 30 day intervals until emergence of flowers.
2. Propagation in papaya
2.1. Sexual propagation in papaya
Papaya propagation by seed plays a particularly important role in the
production of plantlets and have been considering as a major method in
commercial propagation (Senthilkumar 2014, Abdel 2016, Omar Schmildt


2016) . Seeds can be obtained from natural pollination or artificial pollination.

Seeds are produced in seedling centers by controlling process in parental
pollination. Seeds of some papaya verities are easily reproducible while some
require elaborate pollination procedures.
The ratio of female, hermaphrodite and male offspring are predictable,
as summarized in Table No. 1 (Jain 2009) and as follows:
(1) Pistillate flowers pollinated by staminate flowers give equal
numbers of male and female progeny
(2) Pistillate flowers pollinated by pollen from bisexual flowers give
equal numbers of female and bisexual progeny
(3) Bisexual flowers either self or cross-pollinated with other bisexuals
give a ratio of one female to 2 bisexual
(4) Bisexual flowers pollinated by staminate ones produce equal
numbers of female, male and bisexual progeny.
Table 1. Summary of gender ratios following pollinations between male (M),
Felmale (F) and bisexual (B) C. papaya gender forms
P N N
l o. o.
na of of
F
1
F
1
M
B
1
M
1

S
d

See
3 an
dti yare placed into cup or vessel with fresh and room temperature water and
seeds


soak them for 24 hours. The sink seed can be used for germination and the
remaining seeds is continued to soak in fresh water for more 24 hours. Then,
the sink seeds are used for germination and discard the rest (bad seeds).
During the soaking phase, we must ensure to use very clean water.
Once the seeds have been saturated with clean water they can be
germinated in several ways. The two most common methods to germinate
seeds are by using sterile potting medium or a cloth sling. Either way, the
medium containing the seed needs to be sterile and kept moist at all times.
The optimum temperature for germination is about 25 oC. Seeds germinate in
2 to 5 weeks.
Some methods such as removing

seed sarco-testa (Chow 1991),

soaking in growth regulators (Tawfik 2002) or in potassium nitrate (Montejo
2002) or in magnetized water (Espinosa 1997) or in leaf extract and powder
(Ananthakalaiselvi 1998), putting seeds in temperature extremes (Salomao
2000, Wood 2000), treating matri-conditioning (Andreoli 1993), and in vitro
germination (Bhattacharya 2001) were successful to improve papaya seed
germination.
Production seedlings:
Dry papaya seeds are relatively light, weighing about 14.5 g per 1,000
seeds. The density of the crop is at 2,000 trees/ha. For establishing a hectare
of papaya need about 3,000 seeds (50 g) (Chan 1994). If multiple seedlings

per position are practised, amount of seeds weigh could be increased to 75–
100 g.
Seeds germinated are transplanted in containers or polythene bags for
seedlings. Seedlings by 6 – 8 inches (15.24 – 20.32 cm) high are replanted in
the field.
Papaya plants propagate from seeds only can be defined after they
attain reproductive maturity (6–8 months) (Bose 1990). So, to ensure plant


density in the production plantation, growers plant three or four seedlings at
each position before extracting tree having unwanted sex characteristics.
* Advantages and disadvantages of propagation by seed
Advantages of propagation by seed
Seed propagation is a common and conventional method of propagation
in papaya. It is very simple and easy method of propagation that does not
much advanced or complicated techniques. Farmers generally collect fruits of
good quality from their orchards and the extract seeds for subsequent
plantings. So farmers or growers can apply it in their gardens or orchards.
According to recommendation of seed manufacture in market, the
germination rate is over 75% (Chauhan 2014). In cases of other propagations
that are difficult to implement or ineffective due to lack of facilities and
equipment for in-vitro culture, and inadequate materials for cutting
propagation, seed propagation seems to be a suitable and effective tool for
seedling multiplication.
The cost of seedlings from seeds are cheaper than cost of seedlings
from cuttings, grafting and tissue culture. According to my investigation in
Taiwan, the cost of a seedling propagated by seeds is about 3-15 TWD
(Taiwan dollar) belong to variety and planting season and be cheaper than
cost of seedling propagated by asexual method (25-50 TWD with grafting).
Seedlings propagated by seeds have strong roots. It is advance for

growth of plant when papaya plant in the field. The seedling plants are long
lived and are resistant to water stress. Specially, strong root system of papaya
helps plant coping with frequently storm in sub-tropic and tropic.
Hybrid seed production needs to be developed by this method,
especially creating new hybrid generation.


Transmission of viruses can be prevented by seedling method.

In

polyembryonic seeds, the apospory form, which maintains the genetic
systems similar to their mother plants, is a valuable material source for
seedling or micro-propagation due to free diseases.
Due to more efficiency of root activities, seed propagation is used to
produce root stocks for budding and grafting. Seed can be transported and
stored more convenient and for longer time for propagation.
Disadvantages of propagation by seed
Propagation is hindered with problems associated with inherent
heterozygosity and dioecious nature of the plant (Manshardt 1992,
Bhattacharya 2001, Paull 2011). Seeds derived from open pollinated flowers
can produce plants with considerable variation in sex types (a mix of male,
female and hermaphroditic plants) which is highly undesirable when this
results in variation in disease susceptibility, fruit quality and yield (Allan
1995, Teixeira 2007). Heterozygous and a cross pollinated crop, sexual
propagation has resulted in immense variation among populations for growth
duration, yield, size, shape, quality of fruit and disease susceptibility leading
to production of non-true-to-type plants (Panjaitan 2007). The disadvantage of
dioecious varieties is that unproductive male plants prevail as high as 30%
and some times over 50% of the total in commercial plantation (Jordan 1983).

This makes the wastage of money, time and labours for the problem of truesex plant density leads to a reduction in production efficiency.
Marin and Silva (Marin 1996) stated that the possibility of maintaining
original characteristics of the parent plants of papaya does not occur in the
conventional system of production where seeds are harvested in majority of
cases, from commercial open pollinated orchards.


In addition, as the same as other fruit crops, seedlings propagated by
seeds have a more juvenile period than those propagated by vegetative
propagation (Hartmann 2011).
The use of seeds for papaya production has both positive and negative
facets. Numerous seeds are available from one papaya fruit, but seed
germination can be slow and sporadic (Perez 1980). Reyes et al. (Reyes 1980)
and Yahiro and Yoshitaka (Yahiro 1982) isolated “germination inhibitors” in
the sarcotesta and inner seed coat but not in the embryo and endosperm. In
addition, the occurrence of inhibitory substances present in the aril, extraction
and conservation of seeds may cause germination loss in relatively short
periods (Couto 1983).
2.2. Asexual propagation in papaya
Vegetative propagation of plants is their reproduction from vegetative
organs: stems, roots, leaves, buds, even single cells. Through vegetative
propagation or cloning, show exact copies of the ‘mother plant’ are produced,
a process that can – in theory – be repeated indefinitely. The phenomenon of
vegetative propagation is based on the ‘omnipotence’ of plant cells, meaning
that any plant cell, unlike most animal cells, has the potential to regenerate
into a functioning organism. Vegetative propagation as opposed to sexual
propagation (by seed) offers a range of benefits in tree domestication as well
as in conservation efforts.
Papaya is one of the fruit crops, which to date, have defied attempts to
clonally propagate by vegetative means. In current papaya asexual

propagation, main applied methods are cutting, grafting, and tissue culture
(Paull 2011).
As other crop asexual propagation, vegetative propagation methods in
papaya produce new plants from vegetative parts of the original plant, such as
the buds, stems, and leaves etc. In asexual propagation, only a single parent is


required and thus t is no need propagation mechanisms such as pollination,
cross pollination etc. In this process, no exchange of genetic information
takes place as the offspring is formed through material of a single parent
(Hartmann 2002, Teixeira 2007, Paull 2011). Thus the resultant plants formed
contain the genetic material of only one parent, so they are essentially clones
of the parent plant.
Vegetative propagation becomes imperative for the production of
standard varieties from the most outstanding local types, those developed
through breeding programs.
There are many environmental factors affecting papaya asexual
propagation such as light (irradiance, daylength, light quality), temperature,
gases and gas exchange, media and nutrition (Muhamad Hafiz 2014, OforiGyamfi 1998, Tchinda 2013, Wendling 2002, De Oliveira 2017, John 1997,
Loach 1986, Adugna 2015,

Jordan 2010, Muhammad 2006, Owuor 2009,

Baltunis 2010, McIvor 2014). In addition, papaya genotype is the factor make
large differences to vegetative propagation process (Husen 2003, Teixeira
2007, Baltunis 2010, Rambaran 2013, McIvor 2014, Setargie 2015).
* Advantages and disadvantages of papaya asexual propagation:
Advantages of asexual propagation
One advantage of asexual propagation is that the sex is determined
from selection mother plant (plant material propagation). Plantlets formed

through asexual process are genetically identical, useful traits can be
preserved among them (Hartmann 2011, Paull 2011).
The use of vegetative propagation techniques can produce a large
number of true to type high quality planting material is an essential
requirement in papaya cultivation (Teixeira 2007, Hartmann 2011).


The plants also bypass the immature seedling phase and therefore reach
the mature phase sooner in vegetative propagation (Hartmann 2002). Plants
grown through vegetative propagation bear fruits early, lower fruiting height,
greater fruit weight, longer cropping span and improved yield over plants
grown from seeds (Li- Hung 2004, Allan 2013).
It was reported that the possibility of developing materials highly
productive and resistant to viruses, which can be spread safely keeping intact
the characteristics of the mother plants of papaya through asexual propagation
(San Jose 1988, Dhekney 2016).
According to Reuveni et al. (Reuveni 1990) the clonal propagation
technique of selected mature female and male plants in papaya is highly
desirable for commercial practice, especially in subtropical areas, as the
dioecious lines exhibit considerable variation in shape, size and flavor of the
fruit and disease susceptibility.
Injured plants can be recovered or repaired through techniques involved
in asexual propagation (Bose 1990, Ramkhelawan 1998 , Hartmann 2002,
Abdel 2016, Dhekney 2016).
Asexual propagation methods have been applied significantly in papaya
breeding. They help clone propagation only male or female in crossbreeding
(Chan 2009) and in embryo rescue (Magdalita 1996).
Disadvantages of asexual propagation
Papaya is one of the fruit crops, which to date, have defied attempts to
clonally propagate by vegetative means. Like most other higher plants papaya

has an indeterminate mode of growth in which the leaf axils contain
subsidiary meristems, each of which is capable of growing into a shoot that is
identical to the main axis. Axillary branching under natural conditions is
inhibited by apical dominance. This natural growth habit of papaya plant
representsa major hurdle for the vegetative propagation. Mechanical and


chemicalinduction of branching has been accomplished to avail planting
materials for vegetative propagation (Allan 1995, Tawfik 2002).
Vegetative propagation methods for some papaya cultivars have been
described in the literature (Allan 1995, Ramkhelawan 1999, Tawfik 2002) but
none is suitable for rapid production of large numbers of clonal transplants of
desired papaya cultivars for commercial plantations. Furthermore, these
techniques are often slow, time consuming, tedious, impractical, need high
technical know-how, and are not widely known by growers in many papaya
growing countries (Ramkhelawan 1999).
Vegetative propagation of trees is easily achieved when juvenile
sources of propagation materials are used. A major limitation is the need to
use juvenile tissues from young trees since maturation is usually associated
with a declining regenerative capacity (Babu 2002):
In addition, as propagation of other crops, diversity is lost in asexual
propagation which is the main reason behind occurrence of diseases in future
plant species; papayas produced through this asexual propagation (cutting and
grafting) have shorter life-span than those grown through sexual process;
Papaya tree involved in this process are less likely to resist pests and diseases
(Hartmann 2011).
2.2.1. Grafting propagation
* General of grafting:
Grafting is the combination of a root system (rootstock) with an
appropriate crown part (scion). Grafting techniques have three main purposes:

To propagate species otherwise not easily propagated; to substitute a part of a
plant with that of another; and to join plants that were specifically selected
for different purposes such as disease resistance, adaptability to certain
environmental constraints, productivity.


Grafting methods are labor intensive and need good training before
they can be successfully applied. However, grafting has become the most
used way to improve high-value fruit trees. Grafting combines two
independent individual plants, and produces one functioning individual. The
process of graft union formation is regulated by a complicated balance of
plant hormones and enzymes. Five stages have been defined (Hartman 1986):
Lining up the vascular cambiums of rootstock and scion; Wounding response,
callus bridge formation, wound-repair xylem and phloem, and production of
secondary xylem and phloem.
The important requirements for successful grafting operation,
producing a plant:
•
•

The stock and scion must be compatible.
The cambial region of the scion must be placed in intimate
contact
with that of the stock.
• The grafting operation must be done at a time when stock and scion
are in the proper physiological stage.
• Immediately after the grafting operation is completed, all cut
surfaces must be protected from desiccation.
• Proper care must be given the grafts for period of time after
grafting.

The methods of plant grafting:
There are many methods of grafting, some very specific for a particular
species. According to Hartmann et al. (Hartmann 2002), there are many
methods of grafting such as whip grafting, splice grafting, side grafting, cleft
grafting, wedge grafting, bark grafting, inarching, and bridge grafting. Cleft
grafting is a good choice for species that callus readily produced and is one of
the popular methods used for papaya propagation. Steps in cleft grafting were
presented following: