Evaluating severity of leaf spot of lettuce, caused by <em>Allophoma tropica</em>, under a climate change scenario

Abstract

Climate changes, particularly increases in temperature and CO₂,are seriously challenging agriculture, and are one of the main factors that should be considered in the emergence of new diseases and their potential spread. Six trials were carried out to evaluate the effects of increased temperature and CO₂ on the severity of leaf spot of lettuce, caused by Allophoma tropica (syn. Phoma tropica), a pathogen that was first observed on lettuce in northern Italy in 2011. Temperature, CO₂ and their interactions were significant factors (P<0.0001) influencing incidence and severity of leaf spot on lettuce. Temperatures between 22 and 26°C were the most favourable to the pathogen, and increased disease incidence and severity. Reductions in disease incidence and severity were observed at lower (18–22°C) and higher (26–30°C) temperatures. Concentrations of CO₂ ranging from 800 to 850 ppm increased disease incidence and severity at all the temperature ranges tested, and these effects were greatest at 22-26°C. Analysis of these results could be useful for mid-term agricultural planning at a regional scale, so that crops and their varieties can be adapted to anticipated future climate trends.