The Effect of Sarosate (N-phosphonomethyl Glycine) a Non Selective Herbicide on the Growth of Some Common Soil Fungi
CHAPTER ONE
AIM AND OBJECTIVES OF STUDY
The aim and objectives of this study are:
- Isolate and identify some common fungi
- Determine in vitro the effect of various concentrations of Sarosate in mecylial extension growth of some soil fungi
- Determine in vitro the effect of various concentrations of Sarosate on the sporulation time of some common soil fungi
CHAPTER TWO
LITERATURE REVIEW
HERBICIDES WITH ANTI FUNGI PROPERTIES
Sarosate has a moderate half-life in soils with an average value of approximately 47 days, reaching 174 days in some soils under some conditions (Vencill and Wauchope, 2002). Sarosate strongly absorbs to soil particles and is rapidly degraded by soil microbes (Duke et al.2009). It has little or no herbicidal activity after it reaches the soil, and it is degraded by many microbes to glyoxylate (Araújo, 2003). Other microbes can convert Sarosate to inorganic phosphate and sarcosine, and some can use Sarosate as both a carbon and phosphorus source. The two microbial pathways for mineralization of Sarosate in soil are shown in Figure 1. Sarosate is rapidly degraded by soil microbes, even at high application rates, without adversely affecting overall microbial activity. Haney et al. (2005) found an increase in cumulative soil carbon mineralization with increasing Sarosate rate. The CO2 flush 2 days after application suggested that Sarosate was either readily and directly utilized by soil microbes or made other resources available. In a study conducted for 5 years under continuous GR maize, soils maintained greater soil organic carbon and nitrogen as compared with continuous non-GR maize. The authors concluded that Sarosate use results in minor effects on soil properties, including microbial communities. They speculated that the enhanced organic carbon and plant residues in surface soils under conservation practices buffer potential effects of Sarosate on biological and chemical properties of soil.
Persistence in soil and effects on soil biota
Sarosate is considered not to be a significant soil contaminant when used at recommended doses. It is applied in foliar sprays, so that its presence in soil is from direct interception of spray by the soil surface or from runoff or leaching of the herbicide and/or its breakdown products from vegetation. Sarosate can also be translocated to roots from foliar tissues and exuded by the roots into the soil (Laitinen, 2007).
The kinetics of dissipation and half-life in soil show that any disturbance on the ecosystem would be very transient. Mamy et al., (2005) comparing the fate of Sarosate in three soils with that of four herbicides (trifluralin, metazachlor, metamitron and sulcotrione) that were formerly used frequently on crops that have now been made Sarosate resistant, found that Sarosate had the shortest half-life, which varied with soil type, whereas trifluralin had the longest. At 140 days after herbicide applications, the amounts of Sarosate and its metabolite residues in soils were the lowest in two soils, but not in a third loamy sand with low pH. The environmental advantage in using Sarosate due to its rapid degradation might be counterbalanced by accumulation of AMPA, as there have been few studies showing effects of AMPA on ecotoxicity to soil or aquatic organisms. Araujo et al. (2003) found that after 32 days incubation with Sarosate, the number of actinomycetes and fungi had increased, while the number of bacteria was slightly reduced. They also detected the Sarosate metabolite AMPA, indicating Sarosate degradation by soil microorganisms. Other studies (Haney, 2002) have generated data strongly suggesting that Sarosate causes enhanced microbial activity directly. An increase in the carbon mineralization rate occurred the first day following Sarosate addition and continued for 14 days. Sarosate appeared to be rapidly degraded by soil microbes regardless of soil type or organic matter content, even at high application rates, without adversely affecting microbial activity.
CHAPTER THREE
MATERIALS AND METHOD
STUDY AREA
This research was carried out at the laboratory of the University of Agriculture Makurdi Benue State. Soil samples were obtained from two different locations namely;
- Stream at the village of the University of Agriculture Makurdi
- Block B University of Agriculture Makurdi
SAMPLE COLLECTION
Soil samples were collected using a spatula at the soil surface. The soil sample were packed and separated into two nylon bags and transported to the biological sciences laboratory.
STERILIZATION OF MATERIALS
Before the collection of samples, materials that were to be used were sterilized. Test-tubes, conical flakes and beakers were sterilized in an autoclave at 121˚C for 15 minutes.
CHAPTER FOUR
RESULT
RESULT EXPLANATION
Table 1 represents the mycelial extension growth of Aspergilllus niger, the fungi tolerated the herbicides (Sarosate) at lower concentrations but at higher concentration, the growth rate was reduced. Its sporulation was stimulated at 48 hours of growth.
Table 2 represents the mycelial extension growth of Trichoderma sp., and it was obvious that the growth was not affected at lower concentration but the growth decreased at higher concentration. It also appeared that Trichoderma sp. was able to withstand the different concentration of Sarosate but it was sensitive to Sarosate at concentration of 1% v/v where the diameter of the colony was smaller. So its sporulation was stimulated at 48 hours of growth.
Table 3 represents the mycelial extension growth of Penicillium sp. in which the fungi was affected by the different concentration of Sarosate comparing with the other fungi isolate and the inhibition percent was at higher concentration. It sporulated at 48 hours of growth.
CHAPTER FIVE
DISCUSSION AND CONCLUSION
DISCUSSION
In this study, the effect of different concentration of non-selective herbicides “Saorsate” was observed on the growth and sporulation of soil fungi.
In Penicilium, it was observed that there was a reduction in the growth rate especially at concentrattions of 0%, 0.01%, 0.1%, 0.5% and 1% and no sporulation was observed. This shows that Sarosate does not totally stop the growth of Penicillium it only slows it growth rate and stop the fungi from sporulation.
The growth of Trichoderma was not inhibited at concentration of 0%, 0.01%, 0.1%, 0.5% and 1%. And sporulation occurred at all concentration. This observation shows that Sarosate has little or no effect on the growth and of sporulation in Trichoderma.
In Aspergillius flavus, the effect of Sarosate was minimal with growth and sporulation occurring was minimal with growth and sporulation occurring at all concentration of 0%, 0.01%, 0.1%, 0.5% and 1%.
These findings are in agreement with Baboo et al. (2013), who confirmed from their study that the herbicides (butachlor, pyrazosulfuran, paraquat and glyphosate) may alter the microbial populations with respect to different days after treatment, and thereby affects the different soil enzyme activities. Since the investigations were performed in vitro, and the effects of herbicides are highly transitory, it is particularly difficult to explain a change of soil enzyme activities in response to certain factors or to establish the cause-effect relationships between the herbicide treatments and the various components contributing to the variation in overall soil enzyme activities.
CONCLUSION
This research work revealed that non selective herbicide “Sarosate” inhibits the growth and affects the rate of sporulation of Aspergillius niger, Trichoderma and Penicillium, the fungi isolated from the soil with an increase in the concentration of the herbicides.
RECOMMENDATION
The excessive use of non-selective herbicides should be discouraged as it inhibits growth and sporulation of soil fungi which are very important as decompose dead organic matter and help plants in obtaining nutrients from the soil.
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