Isolation and identification of antagonistic bacteria of Angelica root rot and their mechanism as biological control

Abstract

Fusarium avenaceum is the predominant pathogen associated with Angelica sinensis root rot, which results in mycotoxin contamination of Angelica, most prominently Enniatin B (ENN B). This study aimed to isolate bacteria capable of combating various phytopathogenic fungi and degrading ENN B to reduce Angelica root rot. Through co-culture with F. avenaceum, the bacterial strains YF and SY89 were isolated from Angelica rhizosphere soil for their antifungal activities. They were identified as Paenibacillus polymyxa and Bacillus tequilensis based on their morphological characteristics and phylogenetic trees constructed using the 16 S rDNA genes sequence. The strains YF and SY89 could produce antimicrobial substance such as surfactin, fengycin, iturin, polyketide synthases and non ribosomal polypeptide synthase detected by Polymerase Chain Reaction (PCR). In addition, strain P. polymyxa YF and B. tequilensis SY89 showed a prominent ability to inhibit synthesis and degrade ENN B in F. avenaceum suspensions and standard samples. The inhibition rate reached 61.93% and 77.64%, respectively, and the degradation rate reached 60.32% and 76.03%, respectively. Angelica pot experiments were conducted to further evaluate the strains YF and SY89 culture ability to promote plant growth and control Angelica root rot to assess its potential agricultural use. The results indicated that strains YF and SY89 could produce IAA and siderophores, which significantly promoted Angelica roots growth. In addition, strains YF and SY89 have the potential to increase the activity of resistant enzymes, thereby inhibiting F. avenaceum infection. The disease index of Angelica roots treated by strain YF and SY89 decreased by 65.38% and 61.54%, respectively. To further elucidate the antagonistic mechanism of YF and SY89, we examined their colonization pattern in the Angelica root using a green fluorescent protein (GFP) marker. The results indicated that YF and SY89 mainly colonized the root surface before migrating into the roots interior part. The present study demonstrated that P. polymyxa YF and B. tequilensis SY89 showed promising prospects for use as a biological control agent against Angelica root rot and ENN B inhibition under field conditions.