Effect of elevated atmospheric CO2 and temperature on disease severity of Fusarium oxysporum f.sp. lactucae on lettuce plants

• We examine the development of the FOL-caused disease in lettuce in phytotrons.
• Microbial count, enzymatic assays, and PCR-DGGE were performed.
• High temperatures can cause a modification in the development of disease.
• The total bacterial abundance was reduced at elevated CO2 concentration.
• The microbial enzyme activity was not affected by the elevated CO2.

Climate change effects on Fusarium oxysporum f.sp. lactucae (FOL) on lettuce plants grown under simulated climate change were studied. An artificial growing substrate was infested with FOL to reach a final concentration of 1 × 104 CFU g−1 of substrate. A non infested tank was used as control.Subsequently, 32 pots (2 l each) were prepared from the infested tank and other 32 pots were prepared from the non infested tank (control). Lettuce plants were then transplanted into the pots and grown in phytotrons under four simulated environmental conditions: (1) 800 ppm CO2, 22–26 °C; (2) 800 ppm CO2, 18–22 °C; (3) 400 ppm CO2, 22–26 °C and (4) 400 ppm CO2, 18–22 °C. Substrate samples were collected from each phytotron at 7, 14, 21 and 28 days after transplanting. Plate counts, enzymatic assays, and polymerase chain reaction denaturing gradient gel electrophoresis (PCR-DGGE) analyses were performed to evaluate the effect of climate change on the microbial population. The abundance of Fusarium spp. and the severity of Fusarium wilt of lettuce varied significantly as a consequence of increased temperature (22–26 °C). Increased CO2 levels showed no effect on the severity of Fusarium wilt of lettuce and on the abundance of Fusarium spp. On the other hand, the total bacterial abundance was reduced at elevated CO2 concentration (800 ppm). PCR-DGGE fingerprints of the ascomycete community obtained from DNA directly extracted from infested substrate samples did not change as a consequence of elevated temperature and CO2.Enzymatic activities were not affected by the elevated CO2 level. Our study indicates that the CO2 concentration used in our experiment had no detectable impact on Fusarium wilt of lettuce. Only temperature influenced all observed parameters, but did not affect the fungal species diversity. Other factors, such as nutrient limitation and the effect of plant species needs further study.