Cross-tolerance as an ecological paradox: a hypothesis-driven systematic review of Leersia hexandra as both remediator and pathogen reservoir.

Leersia hexandra, a perennial grass widely distributed in rice agroecosystems, presents a striking ecological paradox. It is simultaneously recognized as an asymptomatic reservoir for Xanthomonas spp. the causal agent of Bacterial Leaf Blight (BLB), and as a potent ecoremediation agent capable of hyperaccumulating heavy metals such as chromium. This hypothesis-driven systematic review, conducted in accordance with PRISMA guidelines, addresses this dual identity by integrating findings from phytopathology and environmental sciences through the lens of the cross-tolerance hypothesis. We propose that the physiological mechanisms enabling tolerance to chronic abiotic stress also modulate the plant's interaction with biotic pathogens. Based on a synthesis of 30 primary studies, we suggest that the physical traits of L. hexandra (e.g., iron plaque formation) and its internal biochemical defenses, primed by long-term abiotic exposure, may create a tightly regulated host-pathogen equilibrium. This containment does not eliminate the pathogen but may allow sustained, asymptomatic colonization, positioning L. hexandra as a potential cryptic reservoir. The very traits that enable pollutant remediation may inadvertently facilitate pathogen survival, rendering this species a persistent "green bridge" for BLB epidemics. These findings highlight the need for integrated management strategies that reconcile environmental resilience with disease risk and invite experimental validation of the proposed framework.