COMPARATIVE GROWTH RESPONSES OF Amaranthus spp. L. IN HUMUS AND FERRUGENOUS ULTISOLS USING PLANT GROWTH PROMOTING RHIZOBACTERIA

The need for an alternative to inorganic fertilizer is on the increase owing to the drawbacks associated with inorganic fertilizers. This study was therefore carried out to evaluate the bacteriological profile of digestates from different waste streams and the ability of the isolates to promote the growth of plants. Standard bacteriological methods were used to analyze digestates from different waste streams. Total heterotrophic bacterial count was obtained using pour plate method. The cultural, morphological and biochemical characteristics of the bacterial isolates were evaluated using standard differential media along with appropriate reagents. Plant growth promoting capacity of the isolates were evaluated using standard protocols for nitrogen fixation, phosphate solubilization, indole acetic acid and ammonia production. The results obtained from this study revealed that the total heterotrophic bacterial count (Log10 cfu/g) of digestate from different waste streams had values, which ranged from 4.91±0.02 for cattle rumen digestate to 4.41±0.03 for a combination of cattle rumen fruit and food waste digestate. The cultural, morphological and biochemical characteristics of bacterial isolates revealed the presence of Enterobacter cloacae, Escherichia coli, Pseudomonas aeruginosa, Salmonella enterica, Proteus mirabilis and Bacillus cereus. The distribution of bacterial isolates in the different waste streams revealed that E. coli was present in all digestates obtained from different waste streams. All bacterial isolates were found to possess plant growth promoting properties with 100 % capacity for nitrogen fixation and phosphate solubilization. While 66.7 % of the isolates had the ability to produce ammonia and indole acetic acid. The phosphate solubilization index of the isolates revealed that E. coli (5.97) and P. aeruginosa (5.76) had the highest solarization index amongst all tested bacteria in the study

The study was conducted to investigate the possibility that growth-promoting rhizobacteria would enhance plant growth capacities of Amaranthus hybrisus and A. viridis in ferruginous ultisols, comparative to their humus counterparts; given the negative impact the former has on cultivation of the plant species. To achieve this, the setup was divided into two groups; the first comprised of 2 weeks old plants that were inoculated the test rhizobacteria – Pseudomonas putida, P. fluorescence and a combination of both in the ratio of 1:1, in both humus (HMS) and ferruginous red (FRS) soils. The second consisted of seeds of the test plants bioprimed with the bacteria in filtrates of HMS and FRS respectively. Growth responses were observed and measured. Plant species sown in the ferruginous red soils (FRS) did not survive beyond 45 days notwithstanding the kind of microbial inoculant. They also did not attain a plant height of 3cm and as such were not reasonable for harvest. For plants sown in humus soil (HMS), height ranged from 30.1 – 39.2 cm in A. hybridus (p=0.293) and 35.3 – 41.6 cm (p=0.072) in A. viridis, notwithstanding the rhizo-inoculant used. For A. hybridus, Leaf area was significantly higher in the inoculated plants sown in HMS. No significant changes in leaf area was reported for A. viridis irrespective of exposure to rhizoinoculation (11.5 – 17.5 cm2, p=223). No significant differences in number of leaves per plant, stem girth, and internode was reported in both species irrespective of treatment. Qualitative assessment of phytochemicals showed presence of saponins, phenolic, tannins, terpenoids, alkaloids, and flavonoids in both species notwithstanding inoculation. The presence of glycosides in plants inoculated with P. pseudomonas was reported. Glycosides were absent in the control plants. Significant reduction in total phenols upon inoculation of plants with P. putida was also reported. Following the failure of FRS-exposed plants to subsist, in-vitro growth studies were conducted to compare seed growth response. Results showed that seeds sown in FRSfiltrates grew as better as those in HMS-filtrates. Germination percentage in the Pseudomonas- exposed seeds was better when seeds were primed for 24hthan ofr 3 h in both plant species