Unfruitfulness in temperate fruits
- Unfruitfulness is a serious problem in apple, cherry, almond and walnut and is associated with both internal and external factors.
- The sterility is mainly due to (i) Impotence, (ii) incompatibility and (iii) abortion of embryo.
(1) Impotence : It relates to the condition when either one or both the sex organs fail to develop to required stage and fails to form flowers or abortion of male and female flower organs occur.
(2) Incompatibility: It relates to the condition, where both male and female flowers develop and their organs are functional but sterility is due to the incompatibility.
(3) In some cases both the male and female flowers are formed and function but embryo abortion occur.
- Sterility associated with internal functions may be related to evolutionary tendencies due to factors associated with constitution of protoplasm, genetic influence and physiological reasons,
A. Evolutionary tendencies:
a. Defective flowers:
- Self fertilization is not possible in many temperate fruit species due to imperfect flowers, heterostyly, dichogamy and pollen impotence.
- In most of temperate fruit plants like apple, pear, stone and nut fruits, flowers are perfect and present on the same plant (monoecious) but problem of unfruitfulness still occur due to incompatibility ( apple, cherry and almond) and dichogamy (walnut , pecan nut and chestnut).
- In kiwifruit the male and female flowers are present on different plants which restrict self pollination.
- In apple, cherry and almond the cross incompatibility results in unfruitfulness.
- Some varieties of persimmon are staminate constant ( bear staminate flowers every year) and pistillate constant
- The presence of short styles with long filaments or long styles and short filaments is dimorphism, a type of heterostyly and basal gap between filaments is more which allow the bees to enter without touching the stigma to collect nectar ( in some apple varieties) results in unfruitfulness.
Abortiveness leading to impotence:
- Interference either in the development of flowers or in the full development of sex elements and their functions may lead to unfruitfulness.
- In certain varieties of plum pistil is degenerated and unfruitfulness results. In pecan and walnut the terminal clusters consisting of pistillate flowers fall off before pollination leads to unfruitfulness.
- In strawberry also late flowers are abortive and no fruit set occurs in these flowers.
- In some temperate fruits there are some varieties having defective pistil (plum), defective embryo and embryo-sac (apple) which also leads to unfruitfulness.
Non-viable pollen:
- When the pollen is not viable the production of fruit is not possible. Pollen of some varieties of plum, peach, pear and cherry are non-viable due to their abortion leads to unfruitfulness in these fruits.
Genetic factors:
- Hybridity is associated with sterility as well as unfruitfulness. Hybridity is also responsible for seedlessness in some varieties of temperate fruits.
- Hybridity and incompatibility are two type of sterility which are directly due to genetic factors.
- Self sterility depends on inheritance but its development is controlled by environment. Peach- pium hybrids known as Blackman are completely sterile. Similarly, Peach- sour cherry hybrid Kamdesa is completely sterile. Pyronia (Pear x quince) flowers and fruits freely but is always seedless.
- Incompatibility between pollen and ovule is one of the causes of unfruitfulness in apple, cherry, almond, pear, apricot,plum .
Physiological causes:
- Poor growth rate of the pollen tubes in the styles, possibly due to hormonal or chemotropic control ( apple, pear, cherries) is known.
- The pollen tube growth is slow due to low temperature.
- Unfruitfulness can also results from difference in the stage of maturity of pollen grain vis a vis the pistil and embryo.
- The proper development of the flowers, its maturity and fertilization leading to development of a fruit with viable seeds is controlled by the abortive condition within plant existing at the time of pre-blooming and post-blooming stages.
- The nutritive status of the plant determines the time taken by the pollen to fertilize. Fertilization takes in shorter time in strongly vegetative condition then those in poorly vegetative condition.
- Defective pistils are formed in exhausted or weakned trees caused by overbearing, drought and poor nutrition.
External factors:
(1) Environment: the climatic conditions at the time of flowering affect pollen germination, pistil formation and transfer of pollen , pollen tube growth and ultimately on fruit set. Low temperature and rainfall at the time of flowering adversely affect the transfer of pollen and pollen tube growth thereby results in poor fruit set in most of temperate fruits.
(2) Nutrition: Proper nutrient supply affect fruit setting as well as unfruitfulness. Jonathan apple which is self sterile become self fruitful in rich soils having optimum level of nutrients in the soil. Infect high nitrogen content in plant at the time of flowering encourages fruitfulness.
(3) Pruning: Moderate heavy pruning induces good setting and yield.
(4) Age and vigour of plant: Very young and vigorous tree set less fruits than the moderate vigorous and old trees.
(5) Water relations: Moisture stress promote the formation of abscission layers leading to flower and fruit drop.
Control :
- Pollination management by planting pollinizing varieties, placement of bee-hives .
- Proper nutrient management
- Irrigation
- Proper pruning
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