Alternate Bearing in Fruit Trees
Authors: B. Shiva and K.Usha
Division of Fruits and Horticultural Technology, IARI, New Delhi
Alternate bearing or biennial bearing is one of the major problems in many fruit crops. Each fruit tree in commercial bearing does not bear equal crop year after year, which makes fruit cultivation less remunerative to the growers and fruit traders.
A biennial cycle is very usual so that on year is followed by off year and so sequence of several years. An alternate bearing plant or branch or orchard is the one that does not bear a regular crop year after year, rather heavy yields are followed by extremely light yield and vice versa. Alternate bearing is a widely spread phenomenon, occurring in both deciduous and evergreen fruit plants. It is a problem in most polycarpic fruit crops. Olive shows extreme alternation even more than mango, which is considered as a highly alternate bearer fruit crop in India.
An alternate bearing cycle are due to genetical and environmental and orchard management practices resulting in either an exceptionally heavy or a very poor crop in young trees. In certain fruit crops during the fruit development processes high amount of photosynthates are required to be transferred from leaves to the fruits. Such enhanced photosynthetic rates of leaves near fruits cannot compensate for the high fruit carbon (energy) demands therefore less carbon reserves are left for vegetative renewal and also development of new fruiting sites/fruit bud differentiation processes essential for the next seasons fruiting. The result is no or very low fruiting or off crop.
The bearing behaviour of a crop can be affected by environmental conditions, cultivar and rootstock, and management. Phenomenon of alternation is more prominent in the perennial fruit crops particularly Anacardiaceae (Mango, Pistachionut), Carylaceae(Hazelnut), Oleaceae(Olives), Rosaceae (Apple , Pear, Plum , Apricot etc.), Rutaceae(Orange ,Tangor, Satsuma etc.,) and also in tamarind and Jamun etc. Within a tree species some cultivars are regular while others are alternate bearer, e.g. in Mango Amrapali is regular while Langra is strongly alternate bearer.
Horticultural traits associated with alternate bearing:
a) Genetic control : Family, Genera, and Species,.cultivar differences
b) Effect of rootstocks
c) Effect of tree age and vigor
d) Flowering habit
e) Autonomy of branches
Two types of situations may bring alternate bearing in fruit plants
• An off year either due to poor flowering , poor fruit set or excessive flower or fruit drop, and
• An on year, due to excessive flowering, high fruit set, very less extent of flower and fruit drop.
Causes of Alternate bearing
Environmental triggers
• Climatic stresses
• Spring frost
• Temperature
• Atmospheric RH
• Rains
• Edaphic stresses
• Insect Pest & Diseases
Endogenous factors
• Effects of growing fruits on flower inhibition
• Hormonal imbalance
• Effects of pollination on fruit set
• Effects of seeds on fruit drop
• Effects of leaves
• Competition between vegetative and reproductive sinks
• Carbon: Nitrogen ratio
• Cultural practices
• Crop overload
Horticultural measures to overcome alternate bearing
• Proper orchard maintenance
• Regulation of flowering
• Use of chemicals like paclobutrazol
• Smudging
• Girdling
• Deblossoming
• Thinning of fruits
• Selective pruning
• Early harvesting
• Growing regular bearing cultivars
• Use of dwarfing rootstocks
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Alternate Bearing in Fruit Trees
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