Fungal Diversity in the Rhizosphere and Rhizoplane of Okra (Abelmoschus esculentus L.) Moench. in Nsukka, Enugu State, Nigeria

Aim: The growth and development of economically important crops are usually affected positively or negatively by the microbes present in the rhizosphere and rhizoplane. Based on this, the study was carried out to determine the fungal diversity in the rhizosphere and rhizoplane of okra plant.

Methods: Okra seeds were purchased from an agricultural shop in Nsukka main market and were planted at Botanic garden, Department of Plant Science and Biotechnology, University of Nigeria, Nsukka. Physicochemical properties of the soil sample were evaluated prior to planting and as the plant aged. Rhizosphere and rhizoplane samples were collected at two weeks interval and dilution plate method was used in fungi isolation after which they were identified. The frequency of occurrence and the colony forming unit per gram of the sample (cfu/g) were evaluated.

Results: The Physicochemical properties of the soil samples fluctuated as plant aged at two weeks intervals. The pH was slightly acidic to neutral which is ideal for most plant to grow. The water retention capacity, moisture content and organic matter content increased from 11.47-27.90 ml/g, 5.03-21.07% and 2.35-3.68% respectively at two weeks interval but fluctuates at subsequent weeks. A total of eleven (11) fungi were isolated from the rhizosphere and were identified as, Aspergillus niger, Aspergillus fumigatus, Aspergillus flavus, Aspergillus bertholletius, Fusarium oxysporum, Galactomyces candidum, Helminthosporium solani, Rhizopus stolonifer, Mucor racemosus, Penicillium citrinum and Trichoderma viride. All fungi were present in the rhizoplane except Aspergillus bertholletius and Penicillium citrinum. Rhizosphere had a greater number of fungi than the rhizoplane. Aspergillus species were predominant in both the rhizosphere and rhizoplane. A. niger had the highest frequency of occurrence of 58.67% on the 6th week and 65.79% on the 4th week in rhizosphere and rhizoplane respectively. The colony forming unit (cfu/g) of Aspergillus niger was significantly different from all other isolates at P≤0.001 followed by Mucor racemosus and Fusarium oxysporum with significant differences at P≤0.05 and P≤0.01 respectively.

Conclusion: The rhizosphere and rhizoplane of okra plants has been shown to be rich in fungal diversity and a greater number were obtained from the rhizosphere. The data obtained from this work could be exploited by microbial ecologist to ascertain ecological associations and biomass increase by the fungal communities which also forms part of ecosystem. The fungi had no pathological effect on the plant which suggest positive effect on the growth and development of okra plant as the plant aged.