Assessment of Actinomyces and Pseudomonas species on Meloidogyne incognita population and growth of carrot plants in disparate soils

Synthetic nematicides play an important role in the limitation of Meloidogyne incognita on agricultural fields. However, the reliance on synthetic nematicides has made them a threat to the environment due to their toxic nature. Application of rhizobacteria could reduce excessive dependency on their use. In view of the foregoing, an attempt was made to isolate and characterize growth-promoting bacterial strains through morphological and molecular methods. The 16 S rRNA gene sequencing exhibited identity with Streptomyces pseudogriseolus NRRL B-3288, Actinomyces hongkongensis H_KU8, Actinomyces liubingyangii VUL4_1, Pseudomonas amygdali AL1, Pseudomonas aeruginosa DSM 50,071 and Pseudomonas otitidis MCC10330. The growth-promoting ability of the isolated organisms was evaluated in sandy-loam, silty-loam and clay-loam soils planted with carrots in the screenhouse. This was compared with sole carbofuran and soil devoid of treatment. Their potency on M. incognita population was accessed simultaneously with the vegetative growth of carrot plants for 120 days. A probable degradation activity of the included organisms was also appraised. On the field, the organisms were assessed individually in sandy-loam soil. In the screenhouse, the organisms acted differently in disparate soils on their impact on M. incognita population and vegetative growth of carrot plants. Significant (p < 0.05) increase in vegetative growth and yield of carrot plants was noticed with inclusion of Actinomyces sp., in all soil classes. Pseudomonas sp., was not as effective as Actinomycetes sp., with regards to M. incognita population management and increase in yield. Nonetheless, Pseudomonas amygdali in sandy-loam soil exhibited a remarkable action on M. incognita population contrary to carbofuran alone. Secondly, on the field Actinomycetes sp., notably controlled M. incognita population and a remarkable reduction of egg mass and root galls was realized with an increase in yield. Evaluation of probable degradation of carbofuran with HPLC analysis revealed the presence of metabolites such as 3-hydroxy-carbofuran, 3-keto-carbofuran and carbofuran-phenol which implies that there was considerable degradation by the organisms. The growth-promoting attributes and nematicidal potential of S. pseudogriseolus, A. hongkongensis, A. liubingyangii , and P. amygdali have been established. These organisms are regarded as an excellent option in the management of M. incognita and they could be employed as part of the soil regimen in carrot production to reduce environmental contamination of synthetic nematicides.