Isolation of bacterial strains for improved maize production
Olanrewaju, Oluwaseyi Samuel
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BACKGROUND-The ever increasing world population has led to a continued demand for food. If the increase and sustenance of available food crops are not taken seriously, then there might be a crisis of food shortage to sustain all. Maize happens to be an important food crop, as a matter of fact, it is the third largest staple food crop in the world. In South Africa, it is the largest staple crop produced for human consumption. Its importance is not only for food purposes, but also for other vital uses which ease the existence of mankind. Maize is used in the pharmaceutical industry, it is a major ingredient in poultry feed, used in energy industries, paper manufacturing, and brewing industries. The major problems hindering maize production arises from the unavailability of fertile land for good cropping systems caused by land shortage from urbanization and by land pollution mainly through contamination. In order to combat these problems, farmers resort to using chemical fertilizers on the available land. Although this helps to improve the yield to some extent, it is derogatory in the sense that it causes loss of soil fertility on the long run as well as becomes a hazard and a threat to the population it is meant to help. In other words, the advantages of using chemical inputs can never be compared to the destructive activities it causes to the ecosystem and health. This entails the need for a more reliable and safe alternative which is found in nature itself in the form of plant growth promoting rhizobacteria (PGPR). These PGPRs have been used over time as bio-fertilizers. The aim of this study is to identify some potent PGPRs and their synergistic effect to produce a “super” effect on maize crop yield on the farm. METHOD: This study was carried out using a randomized block design. Each treatment was used in triplicates with the control having no treatment. Treatments were used in single organisms, consortia of two organisms and three organisms. Length of leaves, roots, stem, plant heights, numbers of leaves and weight of 100 seeds were taken at 4 and 8 weeks. The readings were compared to the control. OUTPUT: In this study, 31 strains designated A1-A31 were isolated from the rhizospheric soil of maize plants grown in the North West University farm, Molelwane, South Africa. Morphological, biochemical and physiological characteristics of these isolates as well as their plant growth promoting abilities were carried out. 16S rDNA gene sequencing and the nucleotide sequence phylogenetic analysis were determined. 93.5% were able to produce ammonia and just 35.5% could produce indole (IAA). Based on these assays, 3 isolates that showed the most promising result as PGPR were finally selected from the 31 isolates. Three Streptomyces isolates designated NWU4, NWU14 and NWU198 which were also assayed with the 31 isolates that were also selected. All 6 isolates produced oxidase as well as catalase but not all could produce protease. Only A18 and NWU4 produced HCN. Antifungal and antibacterial assays were carried out on the 6 selected isolates. All showed antagonistic activity against the fungal pathogen Fusarium graminearum except A18 that was not effective. A1 and NWU198 were the most active against this pathogen showing more than 70% activity while NWU14, NWU4 and A29 were all moderate in their activities showing 50% and the last two showed 40% activity. Based on these assays, the isolates were categorized in groups of two and three as well as single organisms and were used to inoculate maize seeds which were then planted on the farm inside the university campus. Isolate A1 was screened for its metabolite production due to its high antifungal activity against the fungal pathogen. Metabolites such as phthalan, tropone, ethylbenzene etc were detected. This study demonstrates the potential benefits of using microbial consortia in plant growth promotion as compared to single inoculant treatments. Significant increase was observed in all the parameters compared to the control as well as between the consortia treatments. The study also demonstrates the screening of useful metabolites from one of the effective isolates. Lastly, the study showed that the use of microbial consortia can be of advantage in the eradication of low maize yield as well as serve as reliable alternatives to chemical fertilizers. CONCLUSION: Eradication of chemical fertilizers is becoming more realistic as potent biofertilizers are being discovered daily. These studies show that combination of microorganisms as consortia organisms can enhance all round growth yield in maize. These can be used as efficient PGPR for maize production in field as it is friendly and safe to the environment as well as cost effective.