Potential role of photosynthesis-related factors in banana metabolism and defense against Fusarium oxysporum f. sp. cubense

Photosynthesis-related factors play a crucial role in plant metabolism and could be involved in defense against pathogens. To investigate the interaction between photosynthesis and defense response, hydroponic experiments with Fusarium oxysporum f. sp. cubense (FOC) infection or without the pathogen were conducted in greenhouse. During the early stage of disease development (after 8 days infection), Fusarium-infected banana seedlings exhibited decreases in photosynthesis rate and stomatal conductance without damage to Photosystem II (PSII). As disease progressed (after 10 days infection), the maximum quantum efficiency of PSII photochemistry decreased. Simultaneously, decreases in the maximum carboxylation efficiency and the chlorophyll content of infected plants were observed. In addition, an increased photorespiration rate and defense reactions were detected in banana plants at the same infection stage. Also, the activity of defense enzymes increased notably, which was associated with the accumulation of phenolic acid and lignin. H2O2 and malate, peaked following FOC infection. A decreased photorespiration rate following exposure to weak light was probably related to the earlier chlorosis of infected plants. Our results demonstrate that early FOC infection induced a decrease in net photosynthetic rate, which mainly resulted from stomatal limitation, and the damage to chloroplasts also contributed to the reduction in the photosynthetic capacity of banana plants in the later stages of infection. The increased photorespiration rate was possibly involved in the resistance of banana plants in the later stages of infection, suggesting an interaction between host plant resistance and the pathogen associated with photosynthesis.