Three Factors Responsible for Unfruitfulness in Fruit Crops are: A.
External Factors , B. Internal Factors and C. Physiological Factors !
Orchardists
are concerned with the profits from the fruit crop. Sometimes orchard’s
efficiency of bearing is low in spite of the abundant blossom.
The
conditions under which fruit trees do not set fruit to a desired extent
are known as unfruitfulness. These conditions may be external or
internal. External factors are not related to the fruit trees. Internal
factors are specific to the fruit plant.
A. External Factors:
The
environmental conditions govern the life cycle of a fruit plant. These
conditions greatly influence the flowering and fruit setting in the
fruit plant. Factors like nutrition, pruning, water supply, rootstock
used, temperature, insect pests and diseases affect the fruiting in
fruit trees.
1. Climate:
I. Temperature:
This
is one of the most important factor, which governs the flowering,
fruiting and fruit development. Temperature requirements are species
specific. Variation in day and night temperature or extreme
fluctuations, or continuously hot temperature adversely affects the
pollination and fruit set in most of the fruits. For example, cloudy
weather at full-bloom stage affect the pollination and fruit set in soft
pears and plum. Poor setting in Sapota fruit is due to drying of
flowers. Temperature affects the bee activity in an orchard. Bees help
in the pollination and fruit setting.
II. Rainfall:
Rainfall
is very important to maintain the underground level of water. It also
helps in improving the quality of fruits particularly in peaches,
patharnakh and mango. Rain at full bloom washes away the pollen,
stigmatic fluid and keeps the pollinisers away, hence affecting the
fruit set.
III. Winds:
There are many fruits
which get pollinated through wind (Anemophily). For these plants
movement of air at the time of flowering is necessary to affect
pollination. Most of the fruit plants are insect-pollinated
(entomophilous). In such plants, wind hinders rather than helping in
pollination.
Hot wind (too) during May-June in North India desiccate the flowers or newly set fruits. Winds along with rain is more harmful.
IV. Frost/Freeze:
It
is the most important factor for deciding the fruitfulness in an
orchard. Frost injury can convert a regular bearing cultivar into an
irregular bearing. Even orchards may not produce any fruit for two to
three years continuously due to killing of branches caused by severe
frost. Even set fruits nearing maturity in Guava were spoiled by severe
frost which occurred during, December 2007 and January 2008.
V. Hail Storm:
Hail
storm has been found to be very harmful in hilly areas. Most of the
apple crop was damaged by hails at fruit set. Hails kill flower buds and
blossoms. There are areas which are prone to hails and freezes every
year. Some areas are almost free from these hazards in the same zone.
VI. Cloudy Weather:
Cloudy
weather is more dangerous than hails. The humidity makes the conditions
most favorable to spread fungal diseases. Powdery mildew in mango and
Umran ber usually appears in cloudy weather.
VII. Intensity of Light:
Light
also plays a major role in the fruitfulness of an orchard. Strawberry
plants develop pistils only when these are exposed to specific light
intensity. In overgrown litchi and mango plantations due to overlapping
shade the fruit set is reduced. Closely planted kin now ’10 by 10′ or
’10 by 20′ at full growth stage bear poorly due to poor light
penetration. Even fruits do not develop proper color at maturity.
2. Disturbed Moisture in Soil:
Soil
moisture is one of the key factors to production of fruits. The excess
soil moisture as well as low soil moisture conditions at the time of
flowering and fruit set encourage abscission layer formation, leading
flower and fruit drop. Growing cover crops or mulching the basins can
overcome the low soil moisture. Flooding of the orchards at flowering
time should be avoided.
3. Nutrition:
When
balanced nutrition is not given the plant’s growth and development is
affected. The practice of application of fertilizers at the time of
flowering/fruit set should be avoided. The manures and fertilizers need
to be applied one to two months before flowering and in split doses
after fruit setting.
Imbalance in the nutrients certainly cause
unfruitfulness or flower drop. Higher does of fertilizers render many
kinds of fruit plants more vegetative and without flowers or produce
abnormalities in the flowers. Excess of nitrogenous fertilization
induces barrenness in plants.
4. Rootstocks:
Rootstocks
affect the scion cultivars physiologically. Quince rootstock induces
dwarfing in pear due to formation of inverted bottleneck, whereas D-4
produces very vigorous pear plants. Trifoliate orange and its hybrids
Troyer and Carrizo produced dwarf citrus plants than on Jatti Khatti and
Kharna Khatta. The grafted plants produce early crops than those raised
through seeds, this way fruiting is affected by the rootstocks. Use of
inter-stock reduced the juverule period by two years in ‘Leconte’ and
other soft pears. Patharnakh (Pyrus pyrifolia) inter-stock was better
than root suckers (Pyrus calleryana).
5. Pruning:
The
deciduous trees are judiciously pruned each year. Un-pruned grapes bear
little crop with small bunches as compared to pruned vines. Un-pruned
peaches bear little fruit and are prone to limb breakage. To improve
fruiting, right pruning is given every year. Similarly, summer dormant
ber is pruned in May-June to get more fruit. The intensity of prurning
varies from cultivar to cultivar and species to species.
6. Plant Age:
Some
fruit plants have long juvenile period than others. These plants cannot
be made to bear fruit early. The Citrus medical and C. jambhiri plants
bear only male flowers in the first few years. Slowly hermaphrodite
flowers appear with age. Young grape vines produce less pollen than the
aged vines of the same cultivar. Very healthy plants bearless flowers
than semi- healthy plants. Declining plants bear profusely than healthy
trees.
7. Chilling Requirements:
Some
fruit trees need desired chilling hours requirement for spur formation
and flowering. Bartlette and conference pears do not flower in plains;
whereas low chilling requiring ‘Leconte’ and other pears bear heavy
fruit. Apple remains vegetative for long in lower hills than higher
altitudes. Southern cultivars of mango shoots get killed due to frost or
low temperature in north hence no fruiting. In ‘Leconte’ pear profuse
flowering is observed every year but fruit set is irregular due to
change in season.
8. Spraying at Full-bloom:
Normally
insecticide sprays at flowering time are not recommended. However,
sometimes due to prolonged flowering particularly in litchi, mango and
pear, it becomes necessary to control aphids, etc. Hence, insecticide is
sprayed, which adversely affect the fruit set. In mango a disease
‘Jhumka’ has surfaced due to poor pollination. Fungicides normally do
not affect pollination. Insecticide sprays should be avoided on full-
bloom. Spray may be advanced or delayed for a week or so.
B. Internal Factors:
Some
fruit species produce abundant flowers arid set little fruit. Sometimes
there may not be any fruit on a tree. Pollination failure, sterility or
deficiency of nutrients may be the major cause of unfruitfulness.
The internal factors are:
(1) Impotency, (2) Incompatibility, and (3) embryo abortion. Some other factors are related to flower structure and form.
These are:
1. Dicliny or Uni-sexuality:
The stamens and carpels lie in separate flowers. Male or female flowers borne on same or different trees.
(a) Male and female flowers on the same plants are called monoecious, e.g., walnut, pecan nut, chestnut, banana and coconut.
(b) Dioecious:
The
male and female flowers are borne on two different plants. Hence, to
set more fruit male flowers from male plants are placed close to female
flowers on the other plant, e.g. Date palm and papaya.
Papaya has 8 types of flowers:
(1)
Pure pistillate flowering plants (2) Pure staminate (3) Both staminate
and perfect flowers (4) Plants with sterile pollen (Pseudo
hermaphrodite) (5) Plants producing staminate and perfect flowers but
neither pollen nor pistil is fertile (Sterile hermaphrodite) (6) Plants
producing staminate, pistillate and perfect flowers (7) Plants with
staminate and perfect flowers (8) Plant with pistillate and perfect
flowers.
2. Dichogamy:
In many bisexual
flowers the anthers and stigma mature on different times. This condition
is known as dichogamy. It acts as a barrier to self-pollination hence;
unfruitfulness in such plants is the result. When the gynoecium matures
earlier than the anthers of the same flower the condition of the flower
is protogyny.
On the other hand when the anthers mature first and
discharge their pollen earlier than the stigma of the same flower, the
condition is protandry. Avocado flowers are protogynous in nature and in
mango stigma are receptive for two hours but pollen is available for
longer period hence such a situation is termed as protandry. Coconut can
be another such example.
3. Self-sterility:
In
such flowers the pollen does not fertilize the ovule of the same flower
through stigma; this leads to unfruitfulness in many fruits. This can
also be termed as incompatibility. In incompatibility, both pollen and
ovule are fertile but fail to unite due to some reason. The
self-sterility has been found in pear, apple, plum, almond citrus and
mango cultivars. Bartlett pear is self-sterile. Commercial cultivars of
loquat are self- incompatible. In plum cultivars pollinizer Kala
Amritsari have been recommended due to self-incompatibility.
4. Heterostyly:
In
this condition the flowers have short styles and long filaments
(stamens) and other flowers on the same tree or species have long style
and short stamens/filaments. This is known as dimorphic heterostyly.
Similarly there can be trim-orphic heterostyly, i.e., stamens and styles
of three different lengths, example pomegranate, litchi, sapota and
almond. Hence, poor fruit set may be due to heterostyly.
C. Physiological Reasons:
It is difficult to assign the particular reason for unfruitfulness in some of the situations.
These physiological factors are:
1. Pollen Tube Growth:
The
rate of pollen tube growth through the style is so slow that it does
not reach the ovule. It is usually so in heterostyly condition. Poor
rate of pollen tube growth has been found in pear and mandarin.
2. Poor Pollen Germination:
Sometimes
due to physiological reasons pollen does not germinate on the stigmatic
surface. This situation may bring unfruitfulness.
3. Delayed Pollination:
Sometimes
flowers abscise because of delay in pollination, for example, if kangji
kalan lemon flowers are not pollinated from outside source, all flowers
fall down due to self-incompatibility. Hence, to get good crop
synchronizing in pollen cultivar with that of lemon cultivars should be
included as pollinator.
4. Nutrition:
When
fruit plants over-bear in one season and get depleted in nutrition,
there may be no crop in the coming year. Nutrition affects the pistils
and pollen productivity both. For example, plums and peaches may not
produce any crop in one year after a heavy crop in the previous year.
Carbohydrate deficiency has been reported for coulure or blossom
abortion and flower drop in grapes. Twenty percent sucrose spray at full
bloom stage improves fruit set in soft pears.
Further information: germination
Seeds and spores can be used for reproduction (through e.g. sowing). Seeds are typically produced from sexual reproduction within a species, because genetic recombination
has occurred. A plant grown from seeds may have different
characteristics from its parents. Some species produce seeds that
require special conditions to germinate, such as The seeds of many Australian plants and plants from southern Africa and the American west require smoke or fire to germinate. Some plant species, including many trees
do not produce seeds until they reach maturity, which may take many
years. Seeds can be difficult to acquire and some plants do not produce
seed at all. Some plants (like certain F1/F2 hybrids and GMO plants) may produce seed, but not fertile seed.
In certain cases (like with GMO's), this is done to prevent the
accidental spreading of these plants (which are generally non-native
crops), for example by birds and other animals.
Techniques for vegetative propagation include:
Further information: germination
