FUNGI

Agricultural Uses

Fungi, an important group of microflora, are eukaryotes. These are achlorophyllous (which means lacking chlorophyll) thallophytes and have or possess somatic (physical) structures which are generally filamentous and branched. They have cell walls with prominent nuclei. The reproduction of fungi is by both sexual and asexual means. Fungi find their place in the kingdoms Protista and Fungi.
Kingdom Protista is further classified into two divisions - myxomycota and oomycota. Fungi belonging to these divisions have heterotrophic or autotrophic modes of nutrition. The fungi classified under both these divisions are slime moulds having plasmodial feeding stage. The mycelial fungi under oomycota bear aseptate hyphae, forming asexual spores called zoospores (sexual spores called oospores, are resting spores).
Kingdom Fungi contains the true fungi, that is mycelial or yeast fungi, which have absorptive, heterotrophic nutrition. These are classified into chytridiomycota( primitive fungi with flagellated asexual spores); zygomycota (aseptate hyphae, sexual spores called zygospores, are resting spores; asexual spores formed in sporangia); ascomycota (mycelial fungi or yeasts, sexual spores called ascospores formed in asci; asexual spores called conidia are abundant in some groups); and basidiomycota (sexual spores called basidispores formed on basidium, asexual spores abundant in some members, large fruiting bodies are common).
With advances in ultrastructural, biochemical and molecular biology, some mycologists established phylogenies and now, fungi are classified into three different kingdoms. These are Chromista, Fungi and Protozoa. Of the three, only kingdom Fungi consists exclusively of true fungi. The kingdoms Chromista and Protozoa mainly consist of non-fungal phyla.
Fungi are abundant in soils and perform many functions. Yeasts, moulds, mildews and mushrooms are some well known fungi. The presence of chitin in the cell wall is one of the major distinguishing features of the organisms in the kingdom Fungi. Fungi may be parasites, (many of these cause crop diseases) or saprophytes, but they are important in the release of nutrients to the soil from dead plants and animals. Fungi range in size from microscopic (lower fungi) to visiblespecimens (higher fungi, such as mushrooms as in Fig.F.25). Microscopic fungi exist in soil in abundance, about a million per gram of soil. They contribute to the mass of soil organic matter more than any other organism in acid soils.
Fungi are prevalent in soils rich in plant residues. Fungal population declines rapidly as the readily decomposable material disappears. Fungi generally produce spores, which help them survive in adverse conditions. They are heterotrophic and aerobic and produce a filamentous growth under neutral or slightly alkaline conditions. The filamentous body, known as mycelium, extends to many centimeters in the soil and even much longer in undisturbed forest soils (for example, mycorrhizal fungi).
Fungal mycelium spreads over surfaces and helps bind mineral particles, turning them into aggregates. They are sensitive to waterlogging or wet soil conditions. They have a very high efficiency of energy utilization in that 50% of the carbon is converted into the cell material while the rest is released as carbon dioxide. In comparison, bacteria convert only 20% of carbon into cell material. Fungi are, hence, of great importance in humus formation and nutrient recycling. Ecologically, fungi play an essential role as decomposers.
Other than angiosperms, fungi are the most economically important group in ways which are both, beneficial and deleterious. In addition to edible mushrooms, fungi are used in fermentation processes for the production of bread, alcoholic beverages, many cheeses (e.g., yeasts like Succhuromyces spp.) and many antibiotics (e.g., Penicillium chrysogenum in the production of penicillin). On the other hand, pathogenic fungi are responsible for devastating crop losses that have, in the past, impacted human history, and for debilitating diseases of humans and domestic animals. Rust fungi and smut fungi are examples of damaging pathogens harmful to cereal crops.