February 8: India is the second largest producer of fruits in the world. But productivity per unit area compared with developed countries is abysmally low. The reason: inadequate pollination.Agricultural experts say pollination is acting as the main stumbling block for fruit cultivation in India. Himachal Pradesh has borne the brunt of this as it is known as the horticulture state of the country. Himachal's rural economy is largely dependent on the cultivation of fruit crops. The peculiar topography and agro-climatic conditions prevailing in this hill state are ideally suited for the production of different types of fruits ranging from temperate to sub-tropical. Out of total area of 190,000 hectares under fruit crops, apples occupy 40 per cent of the area but account for 80 per cent of total fruit production, generating about Rs 250 crore to Rs 300 crore of incomes in the state.
Apple productivity per unit of cultivated area is, however, very low as compared to the west. Experts at the Dr Y.S.ParmarUniversity of Horticulture and Forestry at Solan in Himachal Pradesh are unanimous in the view that pollination still remains one of the most critical, complex and less understood areas in fruit production. Although trees in Himachal produce abundant bloom they fail to set fruit due to the lack of pollination.
The vice-chancellor of this horticulture university, Prof. L.R.Verma, says that cross-pollination is mostly carried out by insects, especially honey bees. Wind plays a negligible role in cross-pollination because of the heavy and sticky nature of apple pollen. The university has done extensive work on apple pollination and the research has revealed that sterility is brought about by the failure of any of the processes concerned with the development of pollen, embryo and endosperms. Most of the commercial cultivars of apple are self "unfruitful" and poor fruit set often results from failure associated with pollen production, transfer and germination, tube development or fertility of ovules.
Thesexual incompatability, according to Prof K.K.Jindal of the department of Pomology at Parmar University, is due to the failure of even functional pollen to grow down the style and bring about fertilisation. This is most common in apple. Apple varieties like Red Delicious, Royal Red, Delicious, Top Red and Vance Delicious were completely self-incompatible. In self-compatibility, the germination of pollen and growth of pollen tube to the ovule is generally controlled by stigma-style-pollen interactions and transmitting tissue-style-pollen interactions.
There are about 1,000 species of insects that exist in nature but only a small number are useful in the pollination of apple orchards. Wild bees, particularly bumblebees, are efficient pollinators because of their large and hairy bodies.
The advantages of pollination by honebees are mainly:
Body parts are modified to pick up many pollen grains; Flower fidelity and constancy; Potential for long working hours; Honeybee populationcan be maintained easily; Stimulates germination of pollen on stigmas of flowers and improves selectivity in fertilisation; Improves fruit set in self-unfruitful apple; Reduces fruit drop and increases fruit yield; Improves size, shape and fruit quality.In addition, the recommended management practices in pollination can help increase apple yield, suggest the experts. For instance, when planning an apple orchard, eery third tree in every third row should be a polliniser. The flowering period of the polliniser variety should overlap with the flowering period of the main cultivar to be crosspollinated.
The polliniser variety, besides helping in cross-pollination, should also have commercial value. The experts say that two beehives of the "apis mellifera" variety per hectare of apple orchard provide adequate pollinator force and are recommended.
Also, significant increases in yields can be obtained by supplying apple orchards with deficient nutrient elements by suitablymanipulating the fertiliser. Contour planting in the middle of a terrace at appropriate spacing could give good results. The weeds should be checked either by handweeding or by chemical sprays of herbicides. Grass mulches of 10 cm thick or black alkathene mulch could effectively check weed growth and conserve soil moisture during stress period. Legumes could be introduced to improve soil fertility, to prevent soil erosion, check weed growth and to ease the pressure on soil. Around the orchards, such trees should be planted which act as good wind breaks.
A study conducted by two soil scientists, Uday Sharma and AR Bhandari, in Chamba district of Himachal Pradesh has also found that cross-pollination by bees brings about somatic, reproductive and adaptive heterosis effects in plant progeny and these bring several changes in plants. This stimulates germination of pollen on stigmas of flowers and improves selectivity in fertilisation, and increases the viability of seeds, embryos and plants.
The fruits arealso more nutritious and aromatic, while fruit set increases and fruit drop reduces.
Copyright © 1998 Indian Express Newspapers (Bombay) Ltd.
