Streptomyces sp. 30702 composite chitosan alleviates continuous cropping obstacles in Chinese yam by improving rhizospheric soil microbial environment: A field study in Hainan

Abstract

Yam is a vital medicinal plant, yet its cultivation faces increasing challenges, particularly due to pathogenic diseases linked to continuous cropping obstacles. This study examines the effects of Streptomyces sp. 30702 and Chitosan on anthracnose and soil microbial communities across four treatment groups: CK (control), SP (Streptomyces sp. 30702), CTS (chitosan), and SC (combined Streptomyces sp. 30702 and Chitosan) within a continuous yam cropping system. The yam was watered every 20 days with 0.25 g plant⁻¹ of chitosan and 4.2 × 10⁵ CFU plant⁻¹ of Streptomyces sp. 30702. Notably, the SC treatment significantly reduced the disease index by 41.31 %, cut root-knot nematode populations by 95.40 %, and boosted yield by 205.45 % compared to CK (P > 0.05). SC treatment also increased soil levels of available nitrogen, phosphorus, potassium, and urease activity. High-throughput sequencing highlighted the dominance of three bacterial phyla (Acidobacteriota, Proteobacteria, and Actinobacteriota) and three fungal phyla (Ascomycota, Basidiomycota, and unidentified Fungi) at harvest. At the bacterial genus level, Bacillus showed a significant increase in SC compared to CK, while LEfSe analysis identified five marker microorganisms in CTS (including Flavobacterium) and four in SC at the fungal genus level. Importantly, SC management reduced the relative abundance of Colletotrichum, the primary cause of anthracnose, by 42.27 % compared to CK. In the Hainan yam continuous cropping system, four Amplicon Sequence Variants (ASVs) were identified as bacterial connectors, two as module hubs, and two as fungal connectors, underscoring their roles in decomposition and environmental adaptability. The results of the Redundancy Analysis (RDA) indicate that available phosphorus in the soil significantly affects the composition of bacterial and fungal communities, with the greatest influence. Additionally, available potassium, available nitrogen, and root-knot nematodes significantly influence the bacterial community, while available nitrogen and root-knot nematodes significantly affect the fungal community (P < 0.05). Overall, the combination of Streptomyces sp. 30702 and chitosan proved to be an effective bio-agent duo, regulating soil microbial communities, reducing anthracnose, and providing a theoretical basis for addressing continuous cropping challenges in yam cultivation.