Breeding Principles
- Evolving superior and heavy yielding strains or varieties of coconut by breeding
does not appear to have received the attention that it deserves.
- Methods
for coconut improvement consist of
- Introduction of better varieties and
strains.
- Artificial self-pollination and selection in self-fertilised
lines.
- Hybridisation-natural or artificial.
- Mass selection and
strain building.
- Close and line breeding, etc.
- Plant-to-row
method.
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Plant-To-Row Method
- 'Plant-to-row method' in the breeding of crops has led to a great improvement
in the production of quality seed material in crops open for cross pollination.
- This method of improvement of the coconut from a practical point of view
as an adjunct to the 'close breeding' methods of establishment of isolated seed
gardens.
- In undertaking this method, seed-nuts of progeny are selected
from palms which appeared to be superior or as indicated by the various criteria
used for selection of good palms or preferably by previous yield records.
- Seednuts
are sown in nurseries with progeny of single palms in separate lines for comparision
in respect of growth and vigour of seedlings.
- This sowing in rows makes
it possible to eliminate rows of seedlings which are inferior in performance.
- After rejecting such rows, planting materials from the other rows, viz.,
vigorous seedlings satisfying all the pre-requisites, are selected.
- These
seedlings are planted side by side under optimum conditions, so that the heredity
of progeny of individual parents could be judged to some extent from the very
early stage of growth onwards.
Top Mass selection
- The majority of world coconuts are derived from mass selection, informally
done by growers.At the end of the 19th century, large plantations were established
by planting fruits imported from a region known for its production.
- In
most cases, seednuts were selected according to their own characteristics: some
preferred large and heavy fruits, others medium-sized fruits, preferably roundish
.
- The genetic structure of the coconut populations was modified by successive
selection of fruit characteristics.
- The system of selection of the best
trees within the best plots began to be applied more recently. In this period,
all research stations involved with coconut breeding have used this mass selection
system.
- In most cases, the selection criteria include the yield of copra
per tree or one of its components such as number of fruits produced or nut copra
content; various authors have included resistance to disease (which can be the
main limiting factor), drought tolerance, or certain vegetative and reproductive
characteristics.
- Thus, there are three variants of mass selection, differing
according to the reproduction system used: mass selection using open pollination,
selfing, or intercrossing.
- Mass selection using open pollination has
been practised most. The advantage of the method is its simplicity: seednuts are
collected from trees which show attractive characteristics at a certain moment
or over a certain period. Progenies resulting from open pollination are the basis
of an improved population, which will then undergo other selection cycles.
- The
other variants of mass selection consist either of selfing the selected trees,
or intercrossing them.
- These methods, more cumbersome because they require
hand pollination, were less often used.
Top Close And Line
Breeding - The expression 'close breeding' was derived from the fact
that, as far as possible, the pollen produced by individual palms in one population
was meant to fertilise the flowers of the palms belonging to the same population,
all of which were derived from nuts harvested from the same individual mother
tree.
- In practice it would be difficult to prevent the intermixing of
the pollen of the several members of the population but some precautions are indicated
to eliminate this possibility as far as possible.
- Close breeding would
permit of the elimination of inferior strains after each generation until finally
only the best strains as determined by performance of yield or any other character
under observation are perpetuated.
- Such a process of elimination, really
amounted to 'strain building' and did not preclude the building up of other improved
seed plots from the best strains, at any time, without interfering with the programme
of improvement and without loss of vigour in the resultant progeny.
- This
method gives the quickest means of improvement which can be increased with each
generation of further selection.
- Under this method, seed-coconuts derived
from open-pollinated flowers of selected individual palms are collected and numbered.
- The seednuts from each individual palm are kept in separate plots in
the nursery. The seedlings are selected in the nursery before planting them out.
- The selected seedlings are planted in distinct and separate plots in
the field so that the population derived form each individual palm constitutes
separate small square blocks in the field.
- It should prove possible to
remove the inflorescence from the palms on the borders of each individual plot
and thus prevent fruiting.
- Even by observational methods, many inferior
populations could be recognised.
- These could be cut out and eliminated
so that any outside crossing which does occur would be with individuals of superior
populations.
- Plant seednuts from these together in separate plots in
new areas.
- The close-bred plants are sufficiently heterozygous as not
to lose vigour after continued selection in the close breeding plots.
Top Pollination
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- There is considerable difference of opinion among workers as to the nature
of pollination taking place in the coconut.
- Some workers believed that
it was wind-pollinated, while others maintained that it was insect pollinated.
| - According to a few others it was essentially
a cross pollinated plant through the agency of wind and insects.
- Yet
some others showed that self-pollination was of common occurrence in the coconut.
- The production of a large quantity of pollen, a distinct exposure of
anthers and stigma to the air designed to scatter the pollen to the wind, the
three pointed stigmatic teeth standing erect at the stage of fertilisation, its
complete separation of sex with staminate and pistillate flowers distributed separately
in the same inflorescence are other factors to facilitate cross-pollination.
- The
fact that the female flowers in the coconut generally attain receptivity some
time later than completion of the period of anthesis of the staminate flowers
also provides evidence in this direction.
- In most of the cases, the staminate
flowers fall off before the pistillate flowers become receptive.
- In a
few trees, and particularly in January, April and August, there is the possibility
for self-pollination through overlapping of spadices.
- The coconut is,
therefore, not entirely cross-pollinated as is generally supposed. There are fair
chances for self-pollination in April.
Top Self Pollination
- the coconut palm is a cross fertilised plant, it has almost certainly accumulated
by mutation unopposed by selection, a large number of deleterious recessives and
these would come to light on selfing.
- The deleterious recessives would
also occur in paired crosses, since the parents might be heterozygous for the
same recessive gene.
- The dwarf variety of coconut generally bred true
to type because of the fact that it was commonly self-fertilised.
- In
the dwarf variety, self pollination is the general rule due to the overlapping
of the female and male phases in the same inflorescence.
- Self pollination
occurs in certain seasons in the tall variety also.
- In terms of performance
of seedlings from selfed, cross-pollinated and naturally polinated seednuts, the
selfed progenies are least vigorous, while seedlings from natural and cross-pollinated
nuts are definitely superior in vigour.
- Different varieties of coconuts
will respond to selfing in different ways and to different extent.
Top Hybridization
- Hybridization is possible by controlled pollination to make hybrids where
both the mother and father are known, designated as a 'paired cross', which formed
the basis of a new method of tree breeding as some of the high yielding paired
crosses have given a yield more than twice the average.
- Re-sowing of
proved high yielding pairs resulted in a gain of 30 per cent over the unselected
commercial material and further cycle of paired cross between the best of the
paired crosses have given still further increase in yield.
- Breeding in
coconuts differed from other annuals in that once a pair of trees has been established
for crossing to give uniformity high yielding off springs when crossed, that pair
can be subjected to further crossing for the production of seedlings, which, after
screening for undesirable seedling characters, can be used for commercial distribution.
- Once a maternal transmitter is identified it can continuously be used
in paired crosses, self-fertilisation and as male parent in extensive crosses
with high yielding mother palms.
- The process of identifying male transmitters
can be speeded up by the use of dwarf palms as females since they are largely
self pollinated and reasonably homogeneous.
Top Introduction
Of Varieties And Strains - The Governments of some of the countries
where coconut is extensively cultivated had adopted the policy of introducing
varieties of the coconut from outside, with the object of raising better plantations.
- The old New Guinea company had introduced selected coconut varieties
from outside sources to their plantations in Madang.
- There is evidence
to show that there was frequent interchange of coconut planting material between
New Guinea and Solomon Islands from very early times.
- Different varieties
of Coconut from New Guinea, Cochin-China, Java, Siam, Philippines, Fiji, Ceylon,
Laccadives, etc., were planted at the Coconut Research Station, Pilicode, by the
Madras Agricultural Department.
- Of these, the introductions from Laccadives,
Cochin-China, Java, Siam, etc., appear to be desirable for multiplication under
South Indian conditions.
- The former Cochin Department of Agriculture
had introduced varieties from Malaya, Sea Island, Philippines, Malaya, Borneo,
Solomon Islands, Seychelles, Panama, East Africa, West Indies, Andamans, Laccadives
and from different regions in India have been planted at the Central Coconut Research
Station, Kasaragod to study their comparitive performance under the conditions
prevailing in Kerala.
- The introduction of even outstanding varieties
of forms from distant countries for large scale plantations has to be done with
circumspection because many coconut varieties are not cosmopolitan and so they
might not perform equally well in another country with different ecological conditions.
- It is also necessary that new introductions should be restricted to varieties
which are distinct and superior because, many of the varieties met with in different
lands may turn out to be only duplications of existing ones.
- In spite
of the limitation pointed out above, the introduction of varieties still occupies
an important place in coconut improvement.
Top Combination Breeding
A. Dwarf X Dwarf
B. Tall X Dwarf 1. Tall (female) x Dwarf ( Male)
2. Dwarf (female) X Tall (male)
3. Tall X Tall. A.
Dwarf (female)X Dwarf (male) - Crossing between the Malayan dwarf and
N'uleka an indigenous dwarf from the Fiji Islands, formed a distinct group with
inflorescence differing in many respects from the Malayan dwarf.
- In hybrids,
N'uleka characters are predominate but with considerable variation. Some progenies
of these hybrids were observed to be high yielding.
B.
Tall X Dwarf hybrids - Crosses between the ordinary tall and the dwarf
varieties occurred in nature which showed hybrid vigour and proved superior whether
the dwarf parent was male or female.
- The inclusion of the dwarf element
in hybridisation was found to have hastened the early exhibition of the character
of early splitting of leaves in the hybrids.
- The general characters of
these hybrids included early fertility with the production of nuts of intermediate
size.
1.Tall (female) X Dwarf (male) hybrids
- When the tall variety was used as the female and the dwarf as the male parent
,then the hybrids are more vigorous.
2. Dwarf (female)
X Tall (male) hybrid - The general characters of the hybrids from this
combination were showing early fertility with nuts of intermediate size and distinct
male and female phases.
- The first generation (F1), was very homogeneous
and did not show the undesirable weakness of the dwarf varieties.
- The
hybrids, of which were proved to be vigorous as the tall coconut and fruited earlier.
- Therefore, hybrids are growing under circumstances where early fruit
bearing was of prime importance as in the new settlements.
- The crosses
with these parents had shorter height measurements compared with the tall type
while the reciprocal crosses were similar to the tall in this respect.
3. Tall (female)X Tall (male) hybrid - This combination
breeding produce progenies which would yield the maximum amount of copra.
- Cyclic
crosses involving all important economic characters of the ordinary variety viz.,
high yields of nuts, high production of female flowers, high setting percentage,
thick kernel and large sized nuts.
Top Development Of
The Fruit - After fertilisation, the growth of the fruit follows with
pericarp developing most rapidly at the basal region which remains soft and whitish
until the fruit is nearly mature.
- The endocarp is already differentiated
as a soft, creamy, white structure long before the time of fertilisation.
- As
the fruit develops and matures, the embryo-sac increases in size, leaving a large
vacuole at the centre.
- The embroy-sac is at first rounded and then it
elongates and widens until near maturity.
- The fruit loses its conical
shape in the early part of the elongating period and becomes spheroidal to orbicular
as it matures.
- When the fruit is young, the mesocarp comprises the major
portion of the pericarp, being wider near the stigmas and sides and very narrow
at the portion which attaches the fruit to the rachilla.
- During its development,
the mesocarp up to maturity increases in thickness in the region opposite the
stigmas or near the micropylar end of the ovules.
- The exocarp always
remains tough and hard and loses its green colour when old, the final colour varying
with the variety.
- The pericarp undergoes differentiation long before
the ovules are formed, into
- an outer single layer of squarish to elongated
cells comprising the exocarp
- the large isodiametric cells of the mesocarp;
and
- the small isodiametric cells of the endocarp.
- There are
three eyes , and when only one embryo is developed , one eye become functional
and the other two are non-functional.
- The fertile eye appearing to be
a depression which is due to the failure of the endocarp to lignify.
- The
remainder of the covering of the eye , is composed of spongy parenchymatous tissue
which morphologically belongs to the endocarp and the fertile eye which became
covered only by a very thin plate of lignified cells formed from the palisaded
layer of the endocarp and from the outer integument of the fertile ovule.
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