Physiological and biophysical alterations in maize plants caused by Colletotrichum graminicola infection verified by OJIP study

Anthracnose caused by Colletotrichum graminicola (Ces.) Wils is among the most aggressive maize diseases worldwide, considerably hindering crop productivity. To investigate the responses underlying the host–pathogen interaction involved in anthracnose infection, we conducted two field experiments in some of the main grain producing areas of the State of Tocantins, in Brazil. Four maize hybrids (with differential tolerance to C. graminicola) were sown in February and March, 2017. Chlorophyll fluorescence measures were performed according to the OJIP protocol; additionally, SPAD readings were conducted and productivity components were assessed. Inoculation with the fungus spore suspension affected the response curve of the chlorophyll fluorescence transient, SPAD index, and productivity components. Anthracnose stalk rot caused 20–25% reduction in grain weight, 6–8% reduction in maize ear size, and 20–23% reduction in ear weight. Furthermore, plants experiencing C. graminicola rot showed reduced SPAD index and a 24–34% reduction in the activity indicator of PSII (PITotal). These changes in the photosynthetic apparatus were successfully observed via chlorophyll fluorescence measurements.