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


About Author / Additional Info: