Leaf spots caused by Colletotrichum sp. decrease photosynthesis rate and hamper the growth of açaí seedlings in nurseries. The objective of the study was to quantify the changes in the photosynthetic performance of açaí leaves inoculated with Colletotrichum sp. through measurements of gas exchange, chlorophyll a fluorescence, and photosynthetic pigments. The rate of net CO 2 assimilation, stomatal conductance, transpiration rate, chlorophyll a and b, ratio of chlorophyll a/b and total chlorophyll decreased, but the intercellular CO 2 concentration increased in inoculated plants compared with non-inoculated plants. Changes in chlorophyll a fluorescence began at 3 days after inoculation (dai) and increased with the number of injuries. The maximum photochemical efficiency ratio (F v /F m) declined sharply as well as other characteristics of chlorophyll a fluorescence, such as the photochemical quenching coefficient, effective quantum yield of PSII, quantum yield of non-regulated energy dissipation, and electron transfer rate. Infection by Colletotrichum sp. reduces the photosynthetic performance due to reduced light capture and assimilation of CO 2 in the mesophyll. Gas exchange and chlorophyll a fluorescence can describe reductions in photosynthetic capacity caused by anthracnose in leaves.

Leaf scald caused by Monographella albescens reduces the photosynthetic area, causing yield losses in rice. This study investigated the efficacy of the rhizobacteria Burkholderia pyrrocinia (BRM-32113) and Pseudomonas fluorescens (BRM-32111), combined with silicon (Si) fertilization, to reduce lesion size and the area under the disease progress curve (AUDPC), as well as to minimize the negative effects on gas exchange, chlorophyll a fluorescence, chlorophyll content and the activity of oxidative stress enzymes. The experiment used a completely randomized design with four replications and seven treatments. Compared with plants only fertilized with Si, plants fertilized with Si and treated with BRM-32113 showed reductions of 22% in scald lesion expansion and 37% in AUDPC, a 27% increase in the rate of CO 2 assimilation (A), a 33% decrease in the internal CO 2 concentration (C i ), and a 40% increase in ascorbate peroxidase activity. It was therefore concluded that the combination of BRM-32113 with Si fertilization reduces the severity of leaf scald, protecting the photosynthetic apparatus, thus representing a sustainable method of reducing the loss of income caused by leaf scald in rice.

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