Since many of us might have heard saying,’ this year there is not much flowering or fruiting in mango like that of previous year’. This phenomenon is called alternate bearing.
Alternate bearing, also known as biennial bearing, is a common phenomenon in mango (Mangifera indica) and many other fruit trees where the tree produces one year of optimum or heavy fruiting (on year) followed by an year of little or no fruiting (off year). It indicated the yield variations in alternate years.This pattern can have significant implications for orchard management and fruit production.
This is one of the most burning problems, since it reduces mango cultivation, less remunerative to the growers. This is mainly a varietal character governed by genetic makeup and this tendency starts exhibiting in mango plants even at the second year of fruiting. However, different factors adverse the conditions.
Probable causes of alternate bearing :
Climatic factors :
Although climatic conditions do not directly cause basic biennial bearing but their adverse effects convert an on year into off year promoting the disease incidence like, anthracnose, powdery mildew. Likewise, frequent frost and low temperature during the flowering period adversely affect the fruit set.
Growth patterns :
In the alternate bearing variety, there will be no new growth after fruit harvest. Poor vegetative growth in the on season results in poor flowering in the off season and the profuse vegetative growth in the off season results in profuse flowering in the off year.
Age and size of shoots :
It is generally found that a certain amount of physiological maturity is prerequisite to flowering in mango trees. Shoots of 8-10 months old of maturity are more productive than early flushing.
Carbohydrate-Nitrogen ratio :
It is generally indicated that higher starch reserve, total carbohydrates and C:N ratio favours flower bud initiation. High carbon/moderate N encourages flower bud formation (30-40).
Hormonal control of flower formation :
The presence of high level of auxins induces more number of flowers. Higher levels of auxin and inhibitor-like substances i.e. abscisic acid and lower levels of gibberellins like substances were found to be vital for a flowering shoot.
Varieties :
Varieties with axillaries fruit bearing habit posses less than terminal bearing likewise, many commercial varieties are irregular bearers but Totapuri, Neelum, Amrapali, and other hybrids in which Neelum is involved as one of the parents are regular bearers.
Measures to overcome biennial bearing
Scientific management of orchard:
- Planting regular bearing varieties like Amrapali, Bangalora and Neelum.
- A proper schedule of manuring and fertilisation, intercultural operation, irrigation, plant protection, etc. help in reducing the irregularities of bearing.
• Manures and fertilizers may be applied in September-October after harvesting.
Pruning :
Light pruning is necessary after the fruit harvest. After harvesting the fruits, troop off branches to open the centre. Also remove dead, deformed, decayed, weaker, and criss-cross branches to allow sunlight through the canopy.
De-blossoming:
Heavy flowering and fruiting makes the off year in next year. The excessive number of flowers or fruits lets (before attaining pea size) should be thinned out.
Smudging :
Creation of gaseous atmosphere around the orchard is called smudging which is helpful to induce flowering.
Use of PGR :
Spraying of NAA, 2,4,5-T and ethrel (200ppm) favours flower initiation.
Paclobutrazol
It is a promising chemical for flower induction in mango. Soil drenching with paclobutrazol (5g-10g/tree) results in minimum outbreak of vegetative growth during Sep – Nov giving an early and profuse flowering.
Understanding and managing the factors associated with the alternate (biennial) bearing producers can work towards achieving a more stable and consistent mango production.