“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.
- 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.
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.
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.
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.
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.
- 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.
- 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.
- 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.
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.
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).
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.
- 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.
- 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.
- 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.
- 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.
- Dicliny or Uni-sexuality:
The stamens and carpels lie in separate flowers. Male or female flowers borne on same or different trees.
- Male and female flowers on the same plants are called monoecious, e.g., walnut, pecan nut, chestnut, banana and coconut.
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.
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.
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.
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.
- Physiological Reasons:
It is difficult to assign the particular reason for unfruitfulness in some of the situations.
These physiological factors are:
- 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.
- Poor Pollen Germination:
Sometimes due to physiological reasons pollen does not germinate on the stigmatic surface. This situation may bring unfruitfulness.
- 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.
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 coulor or blossom abortion and flower drop in grapes. Twenty percent sucrose spray at full bloom stage improves fruit set in soft pears.
Remedies to Control Unfruitfulness
1) Evolutionary Factors:
Unfruitfulness due to evolutionary factors is mainly associated with pollination, following fertilization and by ensuring the cross pollination in such plants fruit set can be achieved or unfruitfulness can be avoided to some extent and thus promo of pollens can be effected in several ways
- i) Hangmg or tymg wire netted basket containing pollenizer’s .flower at different places in the orchard. Pollination of smaryna fig with sporifics is effected in this manner.
- ii) Shoots of pollenizer’s plants can be top worked on the orchard trees. These can serve permanently as pollinizer.
iii) Pollenizers trees may be inter planted in the orchard/in suitable numbers in different pockets. 10% of male plants of papaya is required for Hood fruit set.
- iv) Rearing of honeybees colony will be effective for transfer of poleis.
Some varieties are sterile, self unfruitful cross sterile, in such cases block of other varieties which provide compatible pollens should be established.
- i) By application of plant growth regulator growth rate of pollen tube in toe style can be enhanced.
- ii) By maintaining the proper nutritive health of the plant and attending CCC/NN ratio, will produce optimum fruitfulness.iii) Special horticultural practices like bahar treatments ringing .may improve fruit set by bringing the plant in C / N ratio.
- i) Timely application of manures and fertilizers with adequate quantities will improve the health of the plant and ultimately retention of fruits.
- ii) The varieties which are suitable to particular climate may be grown.
iii) Wind breaks should be planted on south – west side of orchard to protect the plant from high wind velocity with high temperature and low humidity. This will avoid-the drying of stigmatic fluid and shedding of flowers and fruits.
- iv) Cloudy weather, low temperature fig .and. high humidity, are the conditions favorable for breeding of certain pest and spread of certain diseases. Timely control of pest and diseases during this period may protect toe plant from low fit. set or failure of crop.
- v) Excessive moisture supply, deficient moisture supply or fluctuating moisture at the critical stage of flowering and fruit set may try to crop into failure one hence adequate and timely irrigation frequencies be maintain to regulate moisture supply.
- vi) Deep ploughing at flowering be avoided for obtaining good fruit set. Pruning is necessary in fig. Grape, falsa for obtaining good fruit set.