Effect of Elevated Atmospheric CO(2) and Temperature on the Disease Severity of Rocket Plants Caused by Fusarium Wilt under Phytotron Conditions

The severity of F. oxysporum f.sp. conglutinans on rocket plants grown under simulated climate change conditions has been studied. The rocket plants were cultivated on an infested substrate (4 log CFU g(-1)) and a non-infested substrate over three cycles. Pots were placed in six phytotrons in order to simulate different environmental conditions: 1) 400–450 ppm CO(2), 18–22°C; 2) 800–850 ppm CO(2), 18–22°C; 3) 400–450 ppm CO(2), 22–26°C, 4) 800–850 ppm CO(2), 22–26°C, 5) 400–450 ppm CO(2), 26–30°C; 6) 800–850 ppm CO(2), 26–30°C. Substrates from the infested and control samples were collected from each phytotron at 0, 60 and 120 days after transplanting. The disease index, microbial abundance, leaf physiological performances, root exudates and variability in the fungal profiles were monitored. The disease index was found to be significantly influenced by higher levels of temperature and CO(2). Plate counts showed that fungal and bacterial development was not affected by the different CO(2) and temperature levels, but a significant decreasing trend was observed from 0 up to 120 days. Conversely, the F. oxysporum f.sp. conglutinans plate counts did not show any significantly decrease from 0 up to 120 days. The fungal profiles, evaluated by means of polymerase chain reaction denaturing gradient gel electrophoresis (PCR-DGGE), showed a relationship to temperature and CO(2) on fungal diversity profiles. Different exudation patterns were observed when the controls and infested plants were compared, and it was found that both CO(2) and temperature can influence the release of compounds from the roots of rocket plants. In short, the results show that global climate changes could influence disease incidence, probably through plant-mediated effects, caused by soilborne pathogens.