Molecular identification, pathogenicity assessment, and cellulase and protease production of fungi associated with root rot of cowpea (Vigna unguiculata L.)

Abstract

Cowpea (Vigna unguiculata L.) is a major grain legume whose productivity is severely limited by soil-borne root rot pathogens. This study isolated and identified the fungi associated with cowpea root rot and evaluated their pathogenicity and extracellular enzyme production. A total of 45 fungal isolates were recovered from naturally infected cowpea roots and identified as Fusarium solani, Fusarium oxysporum, Rhizoctonia solani, and Macrophomina phaseolina. F. solani was the predominant species, accounting for 33.33% of the isolates. Morphological identification was confirmed by ITS-rDNA sequencing, and the representative F. solani isolate was deposited in GenBank under accession number LC924504. Pathogenicity assays demonstrated significant differences among the tested fungi. F. solani exhibited the greatest virulence, reducing seed germination to 20% in the Petri dish assay and causing 100% disease incidence with a mean disease severity of 79.17% under greenhouse conditions. F. oxysporum ranked second in pathogenicity, whereas R. solani and M. phaseolina were comparatively less aggressive. Enzymatic analyses revealed that F. solani produced the highest cellulase (2.08 U mL^-1) and protease (5.09 U mL^-1) activities, indicating a strong association between extracellular hydrolytic enzyme production and fungal virulence. The elevated enzymatic activity corresponded closely with increased disease incidence, disease severity, and reduced seed germination. Overall, the findings identify F. solani as the principal causal agent of cowpea root rot and highlight the critical role of cell wall-degrading enzymes in disease development. These results provide a basis for developing effective disease management strategies and breeding resistant cowpea cultivars.