Coffee leaf rust (CLR), caused by Hemileia vastatrix, is a major disease affecting
coffee production worldwide. In this study, an in-depth analysis of the photosynthetic performance of
coffee leaves challenged or not with H. vastatrix and sprayed with either
epoxiconazole (EPO) or
pyraclostrobin (PYR) was performed by combining
chlorophyll a fluorescence images, photosynthetic pigment pools and the activities of
chitinase (CHI), β-1,3-glucanase (GLU),
peroxidase (POX) and
catalase (CAT). The CLR severity was higher in the control plants, but reduced in plants sprayed with both PYR and EPO. Also, the CLR severity was reduced in plants sprayed with PYR compared with plants sprayed with EPO. Plants sprayed with either EPO or PYR showed maximal
photosystem II quantum efficiency (Fv/Fm) values ranging from 0.78 to 0.80, which were quite similar to those obtained with inoculated plants (values ranging from 0.74 to 0.77). The decreases in the Fv/Fm ratio values and parallel increases in the F0 values in the inoculated plants, which were not observed in the control plants (sprayed with water) and were confirmed by images of the initial fluorescence (F0) and Fv/Fm parameters in the regions of the leaf tissue containing pustules and in the asymptomatic leaf tissue, indicated that photosynthesis was negatively impacted. When effective
photosystem II quantum yield (Y(II)) values approached zero with a high photosynthetic photon flux density, high values of quantum yield of regulated energy dissipation (Y(NPQ)) in association with a high
carotenoid concentration were noted in the inoculated plants sprayed either with PYR or EPO. The increased CLR severity in inoculated plants in contrast to inoculated plants sprayed with either PYR or EPO was associated with greater POX activity and a reduced photosynthetic pigment concentration. POX and CAT activities were increased in inoculated plants sprayed with either EPO or PYR when compared with control plants. CHI and GLU activities were maintained at high levels in the leaves of inoculated plants, regardless of the fungicide sprayed, indicating that CHI and GLU are less important for
coffee resistance against CLR. The results of the present study clearly demonstrated that plants sprayed with either EPO or PYR showed milder CLR symptoms with adequate photosynthetic performance and optimal conditioning of their
antioxidant systems.