Floral Biology
Papaya is a polygamous plant three basic types of flowers viz. staminate, pistillate and hermaphrodite (bisexual). Of these, only pistillate is stable, whereas flowers of hermaphrodite and male vary in sex expression under different environmental conditions.
Fig: Papaya flowers withone
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
Staminate
flowers
Staminate flowers serve as pollinators.
These plants show 1 to 1.5 m long flower stalks hanging out from trunk. The individual
flower is small, tubular and contains stamens only.
Pistillate
Flowers
Pistillate flowers are large, yellow,
borne singly or in – group of three in the leaf axils close to the trunk. The
flowers have fine large twisted and fleshy petals that surround an ovary, which
swells and develops into papaya fruit. The fruits developed from pistillate
flower are spherical to oblong shaped having thick, yellow to orange coloured flesh in different cultivars with
large to small cavity in which numerous round wrinkled black seeds are
attached.
Hermaphrodite
or bisexual flowers
It has both male and female organs.
Individual flowers are 3.5 to 4.5 cm long with tubular base that widens into
goblet shape and then spreads out into 5 thick yellow coloured recurred petals.
In between these petals, male organs i.e. stamens are present and female organs
containing oblong ovary which develops into cylindrical fruits.
Hybridization: Techniques and
Consequences
The
mating or crossing of two plants or a line of dissimilar genotype is known as
hybridization. In plants, crossing is
done by placing pollen grains from one genotype, the male parent, on to the
stigma of flowers of the other genotype, the female parent. It is essential to prevent self-pollination
as well as chance cross-pollination in the flowers of the female parent. At the same time, it must be ensured that the
pollen from desired male parent reaches the stigma of female flowers for
successful fertilization. The seeds as
well as the progeny resulting from the hybridization are known as hybrid or
F1.
Intervarietal Hybridization: The parents involved in hybridization belong to the
same species; they may be two strains, varieties or races of the same
spiciest. It is also known as
intraspecific hybridization. In crop
improvement programmes, inter-varietal hybridizations the most commonly used. In fact, it is so common that it may often
appear to be the only form of hybridization used in crop improvement. An example would be crossing of two varieties
of papaya e.g. CO 3 (CO 2 x
Sunrise solo).
Papaya
is a polygamous nature of the fruit plant.
Therefore it is imperative to know the cross combination and its
segregation ration in the next generation prior to initiate the crossing
prgramme. The cross following cross combination and their segregations are
given below.
Hybridization procedure or steps
involved in hybridization
Details
of the following steps have to be known prior to initiating the any
hybridization programme in papaya.
1. Choice
or selection of parents: selection
of female and male parents
2. Emasculation:
it required normally in those cross combination where hermaphrodite flower used
as female parent.
4. Crossing or pollination: collect the pollen grains from
desired/selected male plants which dehisced recently. To cross-pollinate, one or 2 stamens from a bisexual flower
are placed on the pistil of a female flower about to open and a bag is tied
over the flower for a few days. At full opening, the stigma is dusted with
pollen from a selected male bloom and the bag quickly resealed and it remains
so for 7 days.
5. Bagging:
Immediately after emasculation of the flower enclosed with suitable bags of
appropriate size to prevent random cross pollination.Bags are tied over bisexual blossoms for several days to assure
that they are self-pollinated. Paper bags
has to be removed after two weeks of the selfing/crossing to facilitate the
fruit growth
6. Tagging: The flowers are tagged just after bagging. They are attached to the
flower with the help of thread. The following may be recorded on the tag with
pencil or high quality permanent markers.
·
Date of
emasculation (DOE):
·
Date of
pollination (DOP):
·
Parentage:
Parents:
·
No. of flowers
emasculated
·
Signature
6. Harvesting of
fruits for F1 seed
7. Isolation of F1 seed from
crossed fruits.
8. Raising F1 generation
Precautions
· Use needles and forceps carefully
otherwise latex will come out from ovary of the pistillate/hermaphrodite flower
which will lead flower drop.Do not select any virus infected plants
for crossing otherwise there is strong possibilities of the mechanical transfer
of the diesess.
·
Do not select first 3-4 flower for the
crossing which leads poor quality seed.