Biocontrol efficacy of Pseudomonas fluorescens and Bacillus subtilis on fusarium wilt and yield performance of cowpea varieties

Abstract

Combined action of microbes for biological control may help improve the efficacy of these microbes action both in vitro and in vivo. This study evaluated the effects of different concentrations of Pseudomonas fluorescens and Bacillus subtilis on the growth and yield of three cowpea varieties (Aloka local, IT89KD-288 and Kanannado Brown) commonly grown in northern Nigeria under pathogen stress. The screen house experiment was carried out in a Randomized Complete Block Design (RCBD) containing 12 treatments (B1(10⁹ ), B2 (10⁸ ), B3 (10⁷ ), B4 (10⁶ ), P1(10⁹ ), P2 (10⁸ ), P3 (10⁷ ), P4 (10⁶ ), C1(10⁹ ), C2 (10⁸ ), C3 (10⁷ ) and C4 (10⁶ ) CFU/ml) with three replications. The pathogen (Fusarium oxysporum) was isolated from infected cowpea plant obtained from the field and identified based on morphological appearance. Pseudomonas fluorescens and Bacillus subtilis were isolated from healthy cowpea rhizosphere soil and were identified using biochemical test. The Screenhouse experiment confirmed the effectiveness of microbial treatments, C1 and C2 consistently enhanced plant height, leaf number, chlorophyll content, root length, flower and pod production, and yield, with soil amendment outperforming foliar spray and control. C1-treated plants achieved the highest yield (8.43 g) and root length (10.52 cm), while untreated controls recorded the poorest growth performance. Among cowpea varieties, Kanannado Brown and IT89KD-288 responded better to microbial inoculants than Aloka Local, although varietal differences were not always significant. However, high-concentration combinations of P. fluorescens and B. subtilis, especially when applied as soil amendments, were most effective in improving cowpea performance. The findings underscore the potential of these bioagents as eco-friendly alternatives to chemical control in cowpea cultivation.