QSE-21 cell-free supernatant primes resistance and outperforms live cells in controlling on tomato.

INTRODUCTION

Biological control agents (BCAs) offer an environmentally friendly alternative to chemical pesticides for plant disease management. However, the efficacy of live microbial BCAs is often compromised by ecological constraints. Cell-free supernatants (CFSs), derived from BCA fermentation, contain most active biocontrol compounds responsible for disease suppression and can be directly applied without introducing living organisms into the environment. Our prior work demonstrated that CFS from QSE-21 (CFS-Q) directly inhibits the growth and development of . This study investigates CFS-Q-induced systemic resistance in tomato plants and fruits against .

METHODS

Tomato seedlings were foliar-sprayed with CFS-Q or controls. Systemic resistance was assessed by challenging distal leaves with . Comparative transcriptomics analyzed gene expression (RNA sequencing) in treated vs. untreated plants, with/without pathogen inoculation. Tomato fruits were sprayed with CFS-Q, live QSE-21 cells (Cell-Q), or LB medium (control group), followed by inoculation.

RESULTS

Application of CFS-Q triggered immune responses in tomato seedlings, conferring enhanced local and systemic resistance against without direct pathogen contact. Comparative transcriptomics revealed that CFS-Q treatment activated multiple immune signaling pathways in tomato, regardless of inoculation. This immune priming effect translated into significantly faster and stronger defensive reactions against attack. Crucially, compared to spraying live QSE-21 cells, spraying CFS-Q exhibited superior efficacy in controlling on tomato fruits.

DISCUSSION

CFS-Q operates via a dual mechanism: direct antagonism (established previously) and induced systemic resistance (ISR), evidenced by immune pathway activation. The priming effect ensures rapid defense mobil.