Harnessing microalgal inoculants for integrated damping-off management and growth promotion in Phaseolus vulgaris

Abstract Background The common bean ( Phaseolus vulgaris L.) is a legume of significant nutritional and economic value. Fungal diseases, especially damping-off, greatly reduce its yield and threaten sustainable production. The study aimed to evaluate the efficacy of algal inoculants individually and in combinations as a biological control approach for managing seedling damping-off diseases and enhancing the growth of common bean crops. Results The virulence of four Rhizoctonia solani isolates were tested on common bean ( cv. Nebraska ) under greenhouse conditions, and all isolates caused damping –off with varying degrees. The species isolated from Beni-Suef was the most virulent, causing the highest pre-emergence damping-off (66.6%) and lowest plant survival (26.6%), and was therefore selected for further studies. Soil inoculation with microalgal inoculants (MI) based on Desmodesmus abundans NA1 ( D. abundans NA1), Nostoc paludosum NA2 ( N. paludosum NA2), and Tildeniella torsiva NA3 ( T. torsiva NA3), individually or combined, significantly suppressed damping-off in common bean and enhanced plant growth ( P < 0.05). The most effective treatment was the 20% triple microalgal inoculant (MI) combination, which reduced pre-emergence damping-off by 1.7-fold and entirely suppressed post-emergence damping-off. At the same time, it increased plant survival by 14-fold compared to the control. A remarkable 33-fold increase in overall yield per feddan was also noted, along with notable improvements in yield parameters such as increases of 1.7-fold in pods per plant, 3.1-fold in seeds per plant, 3.6-fold in seed weight per plant, and 1.6-fold in 100-seed weight. To our knowledge, This study is the first to investigate the combined application of D. abundans NA1, N. paludosum NA2, and T. torsiva NA3, determining their innovative role in controlling damping-off disease and acting as biofertilizers that improve the growth and yield of common bean plants. Conclusion These results highlight the potential of algal bioformulations as promising sustainable biocontrol and biofertilization agents in legume cultivation.