IDENTIFICATION OF SOME FUNGI ISOLATED FROM SOILS TREATED WITH HERBICIDES

ABSTRACT

Twenty three soil samples were characterized for the incidence of fungal strains from Herbicides treated agricultural soils. A total of 59 fungal strains were isolated and 33 fungi were characterized using various isolation and identification methods. Soil samples were also characterized for physiochemical properties. The isolated fungal strains were successfully identified belonging to the phylum ascomycota (7 genera), deuteromycota (2) and zygomycota (1). Alternaria, Aspergillus, Drechslera and Fusarium were predominant genera. Curvularia, Exserohilum, Humicola, Rhizopus and Torula were the most frequently isolated genera. Rests of the strains were not identified owing to the lack of sporulating structures under presently used incubation conditions. Such strains were designated as Mycelia sterilia. Further, these species will be used in biodegradation of commonly used Herbicides.

CHAPTER ONE

1.0             INTRODUCTION
The agrochemical spreading is a common and essential agricoltural practice to obtain high quality, large harvests.
Agrochemicals are classified according to the target organisms designed to be controlled (insects, weeds, fungi). Of all the target organisms, weeds cause by far the greatest economic loss due to their interference in crop production. It is not surprising therefore, that herbicides are the most common class of agrochemicals in the world (48% of the total expenditure) and in Europe (43%) outstripping fungicides (35%) and insecticides (14%). Europe, Asia, and the United States are the largest consumers of agrochemicals; in Europe, France has the biggest agricoltural areas, and is the highest-ranking country for pesticide consumption followed by Germany and Italy (see http://www.croplife.org/ and http://www.ecpa.be).
Bad agricoltural practice and accidental spreading of high doses of agrochemicals can determine toxic effects in humans and the environment; pesticides can accumulate in organisms and achieve critical concentrations for the human and ecosystem health.
Agrochemicals were used for the treatment of human diseases like malaria and typhus. However, high doses of some pesticides can be highly toxic to humans. Laboratory experiments have shown that the administration of high doses of pesticides to animals can cause cancer, mutagenesis, and even death; moreover, exposure to low doses can cause skin irritation and breathing problems. In the “infamous” case of DDT, for instance, which was introduced onto the market in 1940 for the malaria and typhus control, the central nervous system was attacked causing loss of memory, tremblings, and personality changes. Paraquat, a dipyridylic herbicide, is an extremely toxic systemic pesticide; it can enter in the body by inhalation, ingestion or direct contact. It is expecially toxic to the lungs, but can cause gastrointestinal apparatus, kidney, liver, and heart disorders and the weakening of other organs with vital functions.
Plants that are sensitive to pesticide molecules may show signs of growth inhibition and loss in biomass even as far as necrosis, but may be able to develop resistance to certain pesticides (see http://www.weedscience.org; Yuan et al, 2007). Agrochemicals may also have a toxic effect on nontarget plants (Madhun & Freed, 1990) when transported away from the treated site (soluble herbicides or surface erosion).
Soil and aquatic ecosystems contain a multitude of microorganisms. After pesticide spreading, microbic activity may be reduced. However, in some situations an enhancement in microbial activity may occur (Lewis et al., 1978; Pozo et al., 1994).
The leaching of soluble and highly mobile molecules, wilful discharge in underground wells and accidental dumping in water bodies contribute to water contamination. Carabias Martinez et al. (2000) monitored the concentration of fifteen herbicides selected owing to their frequency of use, the amounts used, their toxicity and their persistence in river basins in the provinces of Zamora and Salamanca (Spain). After six months, the presence of six out of the fifteen herbicides monitored, was detected at levels ranging from the detection limit  to 1.2 μg/L. The presence of these herbicides was related to agricultural activities as well as the kind of crop and its treatment period.
The prediction of herbicide movement and fate in soils represents an important strategy in limiting their environmental impact (Figure 1). Physical, chemical, and biological processes regulate herbicide mobility and degradation in soil: rainfall and irrigation water can move herbicides along the soil profile; sites negatively charged of clay mineral surfaces and/or organic matter can adsorb herbicides in their cationic form at soil pH; microbial activity can promote herbicide transformation. Different transfer and degradation processes which control the movement and the  pesticides in the environment are reported in the Table

Justification of the study 
Various  studies have identified some micro-organisms to be able to degrade soil. The degrading ability of these micro organisms have been determined using different methods. However it have been agreed on by researchers that more damage to the  soil is carried out by bacteria and fungi. This study scientifically justifies the use of fungi to degrade soil. This project was therefore carried out to determine the degrading ability of fungi isolated from soil-contaminated soil samples.

1.2             Objective of the study
The specific objectives of the study are to :
I.                        Isolate and identify fungi from soil-contaminated soil sample.
II.                        Screen the isolates from herbicide treated soils.
III.                        Assessment of the degrading abilities of the  fungi isolates

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Item Type: Project Material  |  Attribute: 54 pages  |  Chapters: 1-5
Format: MS Word  |  Price: N3,000  |  Delivery: Within 30Mins.
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