Bacterial leaf spot (BLS) of lettuce is a sporadic and destructive foliar disease that poses an economic threat to farmers, particularly those within Florida due to the subtropical environmental conditions. The disease is caused by the bacteria Xanthomonas hortorum pv. vitians (Xhv), which has three races. There are no chemical interventions that can effectively control this pathogen, creating a significant challenge for farmers to manage BLS. Additionally, most commercial lettuce cultivars are susceptible to BLS, emphasizing the need to improve host resistance. Resistance to Xhv race-1 has been identified in heirloom lettuce PI 358001-1 and ‘La Brillante’, and PI 667690. To facilitate and accelerate modern plant breeding techniques and the introgression of resistance into new cultivars, the identification of resistance genes is crucial. However, a detailed description on how these genes is regulated in the lettuce genome remains unknown. To aid in the understanding of the interaction between lettuce and Xhv, a gene expression study was conducted. A total of 180 plants each of La Brillante (R), PI 358001-1 (R), PI 667690 (R), and Okeechobee (S) were grown in laboratory conditions for 21 days. Half of the plants were mock inoculated with buffer, and the remaining plants were inoculated with Xhv race-1 isolate L7. Leaf samples were collected at 24-, 72-, and 144-hours post-inoculation, and RNA was extracted for sequencing using the Illumina NovaSeq 6000 platform. The analysis of differentially expressed genes and their associated pathways revealed distinct reactions upon interaction with Xhv. Additionally, similar reactions were observed in other crops and their respective Xanthomonas pathovars, such as the upregulation of peroxidases, chitinases, and proteases, were observed between inoculated and mock-inoculated plants, such response was time point dependent. Primers will be designed and validated for these candidate genes using qPCR with additional time points to confirm their expression across key plant development stages. These findings provide valuable insights into the molecular resistance of lettuce to BLS, unlocking new opportunities for molecular breeding techniques, identification of chemical compounds within the plant that control BLS, and the development of new resistant cultivars. This knowledge will benefit not only the UF/IFAS lettuce breeding program, but also be disseminated to other research groups working to breed BLS-resistant lettuce cultivars.
