Abstract:
This study investigated 13-commercial biofertilisers for their microbial contents and potential functional capabilities using a culture-based approach. Isolates obtained were identified by sequencing the partial I6S rRNA gene
and ITS 1 and 2 regions and screened for plant growth-promoting capabilities. A total of 58 bacterial and three
fungal isolates were obtained from all biofertilisers, with major genera being Bacillus, Rhizobium, Pseudomonas,
Candida and Aspergillus. Five of the biofertilisers had the microbes (all or some) listed in the label detected while
eight products had none detected. All the products had more microbes than that declared in the labels, suggesting
the presence of potential contaminants. Generally, all the identified microbes, including the potential contaminants, had different beneficial capabilities. Approximately 40% of the isolates showed potential for nitrogenfixation, while 27% exhibited high phosphate-solubilisation ability. Additionally, 87% of the isolates produced
indole acetic acid in the range of 0.1–114.4 μg/mL. High levels of siderophore production were mainly observed
amongst Bacillus and Pseudomonas genera. The potential of the microbes, including those not listed in the label, to
fix nitrogen and produce acid phosphatase, indole acetic acid and siderophore, was highest in four products. This
suggests the products have multiple functional abilities in improving crop productivity. However, other qualities
of biofertiliser, such as viable cell count and level of contamination, must always be within the acceptable
standards. This will guarantee high product quality as well as efficiency when applied in the field. Overall, the
results show that there is a high correlation between microbial compositions and potential capability of biofertilisers for plant-growth promotion.
