Effects of Epoxiconozale and Pyraclostrobin Fungicides in the Infection Process of Hemileia vastatrix on Coffee Leaves as Determined by Chlorophyll a Fluorescence Imaging

Coffee is the most traded commodity in the world, and Brazil is its largest producer. Coffee leaf rust, caused by the biotrophic fungus Hemileia vastatrix, is the most important coffee disease, reducing coffee yield by 35-50%. This study aimed to use the ratio of variable and maximum fluorescence of dark-adapted tissue (F-v/F-m) as a parameter to differentiate presymptomatic tissue from healthy tissue during disease development in plants sprayed with pyraclostrobin and epoxiconazole after 4days postinoculation. Visual severity was considered as an indicative of apparent disease and true severity as an indicative of both apparent and non-apparent disease. There was a significant linear relationship between the areas of true severity and visual severity, and for each additional unit in the visual severity, there was an increase of 1.53 units on the true severity. For the epoxiconazole and pyraclostrobin treatments, coffee leaf rust symptoms decreased according to both visual and F-v/F-m images. Pustules on the leaves sprayed with epoxiconazole were smaller in size than those on the leaves of non-sprayed plants but bigger than those sprayed with pyraclostrobin. The reduction in F-v/F-m values at the pustule epicentres present on the leaves of plants sprayed with epoxiconazole, and pyraclostrobin was greater than those of the non-sprayed plants. This finding was expected and reflects the importance of these fungicides in prohibiting the progress of coffee leaf rust. The photosynthetic capacity of Coffea arabica was affected by H.vastatrix infection, and the F-v/F-m parameter was able to show this effect before the visual symptoms were noticed.