Sclerotinia sclerotiorum is a necrotrophic parasitic fungus that causes Sclerotinia stem rot (SSR), which is currently one of the most difficult agronomic crop diseases to control. A number of plants of the Brazilian Cerrado biome have been shown to be important sources of symbiotic microorganisms with biotechnological potential, so we decided to test the potential of bacteria isolated from the dwarf jelly palm, Butia archeri (Arecaceae) for the control of the pathogenic effects provoked by S. sclerotiorum. For this, we bioprimed seeds and evaluated the effects of this biopriming on the OJIP transient patterns prior to and following infection by the phytopathogen. Plants treated with the BA48R strain of Enterobacter sp., and in particular, those treated with the BA88R strain of Bacillus cereus presented the best results in terms of the loss/gain of the physiological and symptomatological variables evaluated. The plants bioprimed with BA88R presented high post-infection levels of total chlorophyll (33.35 FCIs) and chlorophyll a (26.39 FCIs), maintained a high Nitrogen Balance Index (NBI = 18.87), and synthesized low concentrations of flavonoids (1.39). These plants also maintained high levels of PIABS (1.111) and PITOTAL (1.300) following infection, and low levels of Di0/RC (0.602), which indicates that, in the presence S. sclerotiorum, the efficiency of the photosynthesis in the plants treated with these bacteria was less affected in the reaction centers, as confirmed by the negative amplitude recorded in the L band. The present study reconfirms the importance of the use of chlorophyll fluorescence for the diagnosis of disease and conditions of stress in crop plants, in addition to demonstrating the effectivenesss of the BA48R bacterial strain and, in particular, the BA88R strain on systemic resistance induction and suppression of S. sclerotiorum in Glycine max plants, with enormous potential for the development of more sustainable agricultural processes.
The heavy metal Cd accumulates in trophic chains, constituting a toxic element for photosynthesizing organisms, including the algal photobionts of lichen. Thus, as lichens respond differently to heavy metal toxicity, we hypothesized that the species Parmotrema tinctorum and Usnea barbata, commonly sampled in the Cerrado ecoregion, could be sensitive to Cd and, therefore, be used to biomonitor the dispersion of this metal. We also aimed to indicate the responsiveness of biological markers to Cd in these species by exposing the thalli to simulated rainfall with increasing metal concentrations. We observed that both lichen species are responsive to Cd stress; however, different pathways are accessed. The synthesis of carotenoids by P. tinctorum and the production of antioxidant enzymes by U. barbata seem to constitute relevant response strategies to Cd-induced stress. The lichen morphoanatomy, cell viability, photobiont vitality index, chlorophyll a fluorescence, and chlorophyll a synthesis were efficient biomarkers for the effects of increasing Cd exposure in P. tinctorum, being the variables primarily associated with damage to the photobiont. For U. barbata, the lichen morphoanatomy, photochemistry, and antioxidant enzyme activity (catalase, superoxide dismutase and ascorbate peroxidase) were essential to reflect Cd toxicity. However, the species P. tinctorum was characterized as the most sensitive to Cd toxicity, constituting a good bioindicator for the presence of this metal. It can be used in the diagnosis of air quality in urban and industrial areas or even in forest areas influenced by Cd in phosphate fertilizers.
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