Relationships between leaf pigments and photosynthesis in common bean plants infected by anthracnose

The objective of this study was to: first, evaluate the infection effects caused by Colletotrichum lindemuthianum pathogen (race 2047) on photosynthetic pigments and gas exchanges in Phaseolus vulgaris plants (cv. Mexico 222); and, second, determine infection effects on leaf pigments and their consequences on photosynthesis rate. A completely randomized design with a factorial scheme was used, combining two treatments (control and inoculated) and three evaluation periods (4th, 8th and 12th day). Carotenoid levels presented decreases of 28.3% and 35% during the 8th and 12th day after infection, when control and inoculated plants were compared. Correlation analysis demonstrated the direct relationship between carotenoids and photosynthesis rate (r = 0.84). Total chlorophyll in infected plants had progressive reductions of 6.4%, 20.6% and 21.3% on the 4th, 8th and 12th day, respectively, when treated and untreated plants were compared. Total chlorophyll with photosynthesis (r = 0.85) also revealed a significant and linear correlation. The photosynthetic rate in infected plants decreased by 22%, 49.9% and 77.3% on the 4th, 8th and 12th days after the inoculation, respectively. Anthracnose infection also induced negative effects concerning stomatal conductance, transpiration, photosynthesis and water use efficiency. Our results demonstrate that leaf pigment reduction as a result of pathogens was the main cause of lower gaseous exchanges in infected plants.