GENERAL INTRODUCTION OF SUGARCANE IN ASPECT OF BANGLADESH:

        
         Sugarcane is one of the major industrial cash crops in Bangladesh. It is the principal sugar-yielding crop from which white sugar and molasses are produced. It is an important source of income and employment for the farming community of the country and essential item for industries like sugar, chipboard, paper, confectionery, chemicals, plastics, paints, synthetics, fibers, insecticides and detergents. Sugarcane production in our country has been decreasing for a long time. Total world sugar production is about 110 million tons (total from sugarcane and sugarbeet) having a breakup of the ratio sugarcane and sugarbeet of 65:35% respectively. This crop covers about 0.17 million hectares producing approximately 0.2 million tons sugar and 0.3 million tons molasses per annum in Bangladesh. Sugarcane is a crop with long life cycle and remains in the field for 12 to 15 months. As such the crop is vulnerable to many diseases throughout the growing period of the year. The climatic conditions of our country are very favorable for the growth and multiplication of pathogens. Naturally the diseases occur abundantly, cause serious damages to sugarcane and sometimes become a real threat for cultivation of the crop.

Habitats are usually not homogeneous; frequently local variations occur to constitute what ecologists call microhabitats. Each species of plants has its own pattern of distribution on local scale and does not grow equally in all types of habitats and microhabitats. The aim of sugarcane eco-pathology is to understand the factors that affect the growth, yield, development and distribution of different sugarcane populations and communities.

A set of biotic and abiotic habitat factors that determine the distribution, growth and reproduction of species. Physiochemical i. e. abiotic factors are fundamentally important. They vary from place to place. For each abiotic factor, a species possesses an amount of tolerance within which it can grow and reproduce. Different sugarcane varieties display different sets of tolerance ranges and these are reflected in their forms and functions i.e. in their vegetative organs. That is why ecologists pay greater attention to the vegetative parts of plants than to their floral ones, as the floral parts remain unchanged even under diverse habitat conditions.

According to Moore et al. (1986) any adaptation of sugarcane to any environment induces morphological, anatomical, pathological and physiological changes.

According to Stocker (1960) the structural modifications occur in nature due to the scarcity of water. Water and light greatly influence the external and internal structure of sugarcane as well as their physiological process. Sugarcane varieties that prefer wet/or moist habitats are hygrophytes and those that can adjust to drier habitats are xerophytes. Most of the xerophytes are sun loving and are known as heliophytes, while most of the hygrophytes are shade loving and are known as sciophytes.

Species without any ecophenic and/or ecotype variations are adapted only to a fixed combination of environmental factors and have very narrow ecological amplitude, while those with much variation can fit into a wide range of habitat conditions and hence have wide ecological amplitude (Daubenmire, 1959). Wild uncultivated-sugarcane appears to have broad ecological amplitude.

About 300000 species of plants have so far been identified in our planet, while tens of thousands more remain undiscovered. Of these only 1500 species (about 0.5%) are nurtured for food, fodder, fibre, timber, medicine, sugar, beverage and flowers. The rest (95.5%) are still wild-they grow, develop and die uncared (Ahmed, 1997). These vast wild plant populations are really the central nerve system of the earth’s environment and the main source of carbon and oxygen for all living beings. But it is unfortunate that man has been destroying these silent life support systems along with his science and technological achievement.

A plant population is a group of plants that normally interbreed, live together and belong to the same species. A plant community is composed of all the plant populations growing, reproducing and living together in a particular habitat. Plant communities are aggregations of plants - trees, shrubs and herbs having mutual relationships among them and to the environment (Oosting, 1956). On the other hand, an ecosystem that both plant and animal communities are interrelated consists of the living communities tougher with the nonliving factors of the environment. The general climate, altitude and latitude of the region influence both macro environment and microenvironment. The microenvironment is the environment that is closed enough to an organism or a group of organisms to be influenced by it. It shows variation from one microhabitat to another within a macro environment due to different types of local variation. There is usually more than one microhabitat within a macro environment or macro habitat. Ecologists are convinced that the microhabitats are as important for plant growing as the macro environment (Ambasht, 1974).

A community that includes two or more life forms of plants is called a complex community. In natural habitats communities met with are usually complex ones with different life forms of plants growing and developing together.

In a broad sense a plant community including all its organisms, is like a machine in that it is a system of interacting parts using and transforming energy. On the other hand, an ecosystem with which both plant and animal communities are interrelated consists of the living community plus the nonliving factors of environment.

In any biological organization plants and animals are very closely related and interdependent and at a particular site plants and animals are influenced by the same set of habitat conditions. That is why modern biologists use the term biotic community instead of plant or animal community (Odum, 1959).

In the last two million years of occupancy of the earth, man has been molding the plant to his own designs. As a result, habitats of plants are being deteriorated almost all over the world. In fact, for centuries, a lot of derelict/ fallow lands have been used as dumping grounds for human sewage and grazing land for herbivore animals. For these reasons many areas are not suitable for any type of vegetation. Besides these, the suitable natural environment can no longer survive without positive action by man to conserve it. Man has the capacity to do so. Due to these changes of the environmental conditions as experienced by different species of plants their growth, reproduction and survival of individual plants have changed and along with that the communities and ecosystems of which they are parts are also getting badly affected. It is also added that green plants which are the primary producers of the whole biotic ecosystem can not adapt well into changed unfavorable environmental conditions and the whole dynamic system would collapse.

Natural sugarcane communities are considered as indicating integrated responses to the variations of environmental conditions by their constituent species. The variations may be of different kinds. In fallow lands, mostly weeds are dominants, but when crop cultivation is practiced on them, periodic ploughing and weeding usually bring about spectacular changes in the structure of the weed species. The changes may be of different degrees and magnitude depending upon the adaptability of the species concerned.

Correlations between sugarcane populations and the changing habitat conditions can be made on careful ecological studies. In developing countries with growing human population, work on changing habitat conditions is becoming more important in land use as well as plant community development (Whitmore, 1967). Moreover, in the field of environmental biology increasing attention is being paid to the number, range and/or types of ecological niches for plant populations (Hall and Swaine, 1976).

A plant community is more than a mere grouping of individual plants (Weaver and Clements, 1938). It can be defined as an assemblage of plants growing together in a particular location and may be characterized either by its common species or by the combination of structural and functional characters that are expressed in the appearance or physiognomy of vegetation (Moore and Chapman, 19386).

In general, plant community is the sum total of plants with interrelations among them covering an area. It arises from the coming together of individual plants and their interactions upon each other. Vegetation is the largest category of plant communities. Vegetation like all organisms not only undergoes development but also possesses structure. The vegetation of an area is not uniform throughout. Depending upon climate and soil, it is differentiated into different natural units (Weaver and Clements, 1938).

The effect of plants upon the place in which they live and their influence upon each other are especially significant. Structure and development of plant populations and communities and the manner in which these are affected by the factors of the environment should be studied with the same care and thoroughness as are individual plants (Weaver and Clements, 1938).

It is noteworthy that in an ecosystem it is impossible to modify the number of available niches for one species without affecting the number of niches for others. For this reason all the sugarcane populations belonging to the ecosystem seldom occur in niches that supply their optimum habitat conditions. Since the habitat conditions and sugarcane populations are interrelated, the structure and floristic composition of a community are determined by the net effect of the habitat conditions. So work on the gradual change of those habitat conditions is essential.

This type of gradual change in habitat conditions, no doubt leads to gradual increase or decrease of individuals of a species. This in turn leads to plant succession. Population ecology involves studies on competition and interaction of a species or groups of associated species as related to habitat variations (Whitmore, 1967).

Saccharum species differs in their tolerance of and requirements from the environment so that their distribution or abundance varies along environmental gradients. This central concept in eco-pathology has been widely demonstrated in distribution maps of species (Perring and Walters, 1962; Cadbury et al. 1971; Hall and Swaine, 1976; Sarker and Rahman, 1987; Whitmore 1967) which often show clear associations between species occurrence and known environmental conditions.

The increased emphasis on sustainable sugarcane cultivation and an increasing world population (now 5.25 billion), coupled with the continued loss of prime sugarcane cultivated land to vegetable, housing and industry, signify that will be have to sugar more people than ever existed in the history of Mankind. There is basically three ways to increase the world sugar supply that one can cultivate “new” land, increase per unit crop yields or multi use of land.