Exploring Root-mediated Erwinia amylovora Invasion Mechanism in Korla fragrant pear (Pyrus sinkiangensis)

Erwinia amylovora , a Gram-negative bacterium in the genus Erwinia , responsible for fire blight in rosaceous plants, has long been studied for its aerial infection pathways. However, the root-mediated transmission of E. amylovora remains enigmatic. This study bridges this critical knowledge gap through integrated greenhouse and field experiments on two model systems, i.e. seed-propagated potted birch-leaf pear ( Pyrus betulifolia ) sapling in a greenhouse and grafted Korla fragrant pear ( Pyrus sinkiangensis YÜ) trees using birch-leaf pears as the rootstocks in orchards located in Xinjiang, China. By combining controlled root wounding regimes (fibrous roots/lateral roots/taproots) and soil drenching or embedded E. amylovora -infected branches, we found that taproot-wounded specimens exhibited higher disease incidence (57.4±3.1%) than lateral root- (34.4±2.1%) and fibrous root-wounded (12.3±0.6%) specimens with 10 ⁸ CFU/mL E. amylovora suspension at 15 dpi. Field trenching trials demonstrated depth-dependent epidemiology, and 40-cm deep tillage compromising taproots (30−40 cm) caused significant disease incidence versus 0% disease incidence in 20-cm trenching. Based on the findings, we proposed a root-aware tillage protocol, including controlling restrict depth (shallow depth ≤ 20 cm to protect taproots, or deep depth > 40 cm using vertical-shank subsoilers), and implementing dormancy-phase operations to leverage accelerated wound healing. Overall, this study not only first provided robust evidence demonstrating that E. amylovora can infect pear plants through the root system in China but also offered practical guidance for establishing fire blight-free cultivation practices in fragrant pears.