The levels of pattern-triggered immunity in the root and stembase of tomato cultivars positively correlate with the resistance to Ralstonia solanacearum.

Abstract

Background: Bacterial wilt (BW), caused by Ralstonia solanacearum (Rs), is one of the most destructive diseases impacting a wide range of crops globally. The infection process is complex involving intricate interactions between the plant and Rs. Managing BW is challenging, and crop breeding remains the most effective strategy for disease control. Resistance to BW in crops is primarily associated with quantitative trait loci (QTLs), which are believed to correlate with the simultaneous activation of multiple defense mechanisms against pathogens. This study aimed to clarify the nature of BW resistance and determine whether pattern-triggered immunity (PTI) plays a role in this resistance.

Results: PTI can be triggered in tomato roots and stembases by an Rs hrpG^- mutant and by the cell wall extract (PiCWE) from the root-infected beneficial fungus Piriformospora indica (Pi). Among tomato plants with varying resistance levels to Rs, BW-resistant (BW^R) and moderate-resistant (BW^MR) cultivars exhibited higher levels of root and stembase PTI in response to Rs hrpG^- inoculation and PiCWE treatment than in BW-susceptible (BW^S) cultivars. Additionally, BW^R and BW^MR cultivars showed enhanced leaf PTI after inoculation with a Pseudomonas syringae pv. tomato (Pst) hrcC^- mutant. The BW^R cultivar Hawaii 7996 (H7996) also demonstrated high tolerance to several leaf pathogens.

Conclusions: Efficient systems for the analyses of PTI responses in tomato roots, stembases and leaves in response to patterns derived from root-infected pathogenic and beneficial microorganisms have been established. The levels of PTI in roots, stembases, and leaves are positively correlated with BW resistance in tomato plants. The BW^R cultivar H7996 also shows tolerance to various leaf pathogens. This study reveals a significant correlation between tomato PTI and resistance to Rs, provides valuable insights into the nature of BW resistance, and offers critical information for tomato breeding.