Differential efficacy of salicylic acid-induced resistance against bacterial blight caused by Xanthomonas oryzae pv. oryzae in rice genotypes

Salicylic acid (SA) serves as a pivotal signaling agent, activating defense mechanisms such as hypersensitive responses and systemic acquired resistance in various plants. This study aims to investigate the impact of SA application on bacterial blight (BB) resistance across diverse rice cultivars. The optimization of SA spraying involved testing three distinct methods: Method I (daily spraying with SA for 2 consecutive days before inoculation), Method II (spraying with SA once before inoculation and again 1 day after inoculation), and Method III (daily spraying with SA for 2 consecutive days after inoculation). Each method was evaluated using varying SA concentrations (0, 0.5, 1, and 2 mM) to determine their efficacy in susceptible rice cultivars. The most effective approach, Method I, was then extended to different rice cultivars to evaluate SA's influence on disease resistance induction and defense-related gene expression in "Phitsanulok 2" ("PSL2"), "IRBB21," and backcrossed lines ("PSL2-Xa21" BC5F6). The results revealed that Method I, with 2 mM SA applied before inoculation, significantly reduced lesion length by 4.6% in the susceptible "PSL2" cultivar compared to the H2O treatment. However, the impact was less pronounced in the resistant "IRBB21" and moderately resistant "PSL2-Xa21" cultivars, both carrying the Xa21 resistance gene. SA spraying up-regulated OsPal2 gene expression in the "PSL2" cultivar and enhanced OsXa21 gene expression in the "IRBB21" and "PSL2-Xa21" cultivars, compared to the H2O treatment control. These findings emphasize the potential of SA as a signaling molecule capable of activating defense mechanisms against BB disease in a range of rice cultivars, warranting further investigation into its application for BB management. Future research should focus on conducting field trials to assess the practical applicability of this approach under diverse agricultural settings. Additionally, investigating the molecular mechanisms underlying the interaction of SA and genetic resistance in rice will provide deeper insight into optimizing this strategy for effective disease control.