Quinoa leaf spot is an important fungal disease that limits quinoa yield and quality. This study aimed to evaluate the pathogenicity of isolates associated with quinoa leaf spot in Qinghai, China, and to screen multifunctional biocontrol bacteria with potential for further development. Pathogenicity assays conducted on healthy quinoa leaves showed that isolates Alternaria alternata AF15 and A. tenuissima AF18 induced typical leaf spot symptoms. The corresponding fungi were successfully re-isolated from the resulting lesions, confirming the pathogenicity of both isolates. Two highly effective biocontrol bacteria, Serratia liquefaciens CB82 and Bacillus velezensis CB316, were subsequently selected through dual-culture assays. Their maximum inhibition rates against the two fungal pathogens reached 56.00% and 57.00%, respectively. Both biocontrol strains exhibited broad adaptability to different temperatures, pH, and NaCl conditions, produced protease, amylase, and cellulase, and showed phosphate-solubilizing activity. Metabolite extraction and fractionation revealed that the antifungal substances were predominantly enriched in the n-butanol fractions, which caused severe shrinkage, surface roughening, breakage, and deformation of the pathogen hyphae. In addition, both strains exhibited strong biofilm-forming capacity and successfully colonized quinoa leaves. Their culturable populations peaked on day 3 after inoculation, reaching 5.58 × 10⁷ and 6.06 × 10⁷ CFU/mL, respectively. In seed germination pouch assays, the bacterial suspensions promoted quinoa root elongation, whereas the fermentation broths increased seedling biomass accumulation in pot experiments. Overall, this study confirmed the pathogenicity of fungal isolates associated with quinoa leaf spot in Qinghai, China, identified two promising biocontrol bacterial strains, and preliminarily characterized their antifungal substances. These findings provide valuable microbial resources and a research basis for the future development of biological control strategies against quinoa leaf spot.

Potato dry rot, induced by pathogenic Fusarium species, is a prevalent postharvest fungal disease that leads to significant economic losses. This research illustrates the biocontrol efficacy of Bacillus velezensis strain 2-1-9-CJK-2 against potato dry rot. The strain successfully inhibited disease progression, diminished oxidative damage in potato tubers, and augmented the activity of essential defense-related enzymes. It effectively colonized potato tubers and sustained consistent inhibitory activity under diverse environmental challenges. And its cell-free supernatant (CFS) retained consistent inhibitory activity. The crude lipopeptides (CLs) produced by this strain induced hyphal deformation, fragmentation, and cytoplasmic leakage in Fusarium solani. Transmission electron microscopy (TEM) further revealed that CL treatments triggered organelle degradation in the pathogen, with mitochondrial disintegration being particularly prominent. Transcriptomic analysis indicated that CLs upregulated genes linked to mitochondrial autophagy in the pathogen and stimulated plant defense mechanisms, notably the MAPK signaling cascade, in potatoes. The findings were additionally corroborated by qRT-PCR. B. velezensis strain 2-1-9-CJK-2 is a promising biocontrol agent and a great resource for the development of antifungal formulations to enhance sustainable potato production.