Fungal pathogens cause severe yield losses in lettuce production worldwide. We developed transgenic lettuce lines overexpressing the ch5B chitinase gene from Phaseolus vulgaris under the regulation of the rbcS1 promoter. Molecular characterization confirmed stable transgene integration and expression across the selected lines. In vitro assays demonstrated that transgenic leaf extracts significantly inhibited R. solani mycelial growth. Furthermore, challenges in both seedlings and adult plants showed a significant reduction in lesion areas compared to non-transgenic (NT) controls. Finally, two events were evaluated in field trials, both showing substantial equivalence to the NT variety satisfying international biosafety frameworks for commercial development. Among them, line 3-4 appears as the most promising candidate for further studies, as it showed slightly higher fresh and dry weight compared to the control line under field conditions.

Fungal pathogens cause severe yield losses in lettuce production worldwide. We developed transgenic lettuce lines overexpressing the ch5B chitinase gene from Phaseolus vulgaris (bean) under the regulation of the rbcS1 (ribulose-1,5-bisphosphate carboxylase small subunit) promoter. Molecular characterization confirmed stable transgene integration and expression across the selected lines. In vitro assays demonstrated that transgenic leaf extracts significantly inhibited Rhizoctonia solani mycelial growth. Furthermore, inoculation assays in both seedlings and adult plants in the greenhouse showed a significant reduction in lesion areas compared to non-transgenic (NT) controls. Finally, two lines were evaluated in field trials, both showing agronomic substantial equivalence to the NT, satisfying international biosafety frameworks for commercial development. Among them, the ch5B 3-4 line appears to be the most promising candidate for further studies, as it showed slightly higher fresh weight compared to the NT under field conditions.: