Broccoli plants exposed to the combined threat of climate change and bacterial infection.

backgroundClimate change is expected to intensify plant diseases by altering both host physiology and pathogen behaviour, posing a growing risk to global food security. Brassica crops such as broccoli (Brassica oleracea var. italica), a key vegetable for human nutrition, are particularly vulnerable to black rot caused by Xanthomonas campestris pv. campestris (Xcc). To assess how future climates may influence this particular pathosystem, broccoli plants were cultivated under three environmental regimes: current climate conditions (CCC) and two late-century projections—an intermediate scenario (RCP 4.5: +3 °C and 650 ppm CO2) and an extreme scenario (RCP 8.5: +6 °C and 1000 ppm CO2). Plants were inoculated with Xcc races 1 and 4.

resultsThe moderate scenario (RCP 4.5) did not negatively affect plant fitness, whereas severe future conditions (RCP 8.5) markedly reduced vegetative growth and photosystem II efficiency. Black rot severity and bacterial growth kinetics depended on both pathogen race and environmental conditions: race 4 was most aggressive under CCC and RCP 4.5, while race 1 gained virulence under RCP 8.5 at later infection stages. Regardless of race, infection increased leaf temperature and lipid peroxidation and stimulated the accumulation of phenolics and other antioxidant metabolites, indicating a shift toward defence-related secondary metabolism. These metabolic changes mitigated oxidative damage but did not prevent the decline in photosynthetic performance under climate conditions.

conclusionsThese findings demonstrate that future climate scenarios will not only compromise broccoli physiology but also alter the performance of Xcc races selectively.