ABSTRACT
Maydis leaf blight (MLB), caused by the necrotrophic fungus Bipolaris maydis, has caused considerable yield losses in maize production. The hypothesis that maize plants with higher foliar silicon (Si) concentration can be more resistant against MLB was investigated in this study. This goal was achieved through an in-depth analysis of the photosynthetic apparatus (parameters of leaf gas exchange chlorophyll (Chl) a fluorescence and photosynthetic pigments) changes in activities of defense and antioxidative enzymes in leaves of maize plants with (+Si; 2 mM) and without (-Si; 0 mM) Si supplied, as well as challenged and not with B. maydis. The +Si plants showed reduced MLB symptoms (smaller lesions and lower disease severity) due to higher foliar Si concentration and less production of malondialdehyde, hydrogen peroxide, and radical anion superoxide compared to -Si plants. Higher values for leaf gas exchange (rate of net CO2 assimilation, stomatal conductance to water vapor, and transpiration rate) and Chl a fluorescence (variable-to-maximum Chl a fluorescence ratio, photochemical yield, and yield for dissipation by downregulation) parameters along with preserved pool of chlorophyll a+b and carotenoids were noticed for infected +Si plants compared to infected -Si plants. Activities of defense (chitinase, ß-1,3-glucanase, phenylalanine ammonia-lyase, polyphenoloxidase, peroxidase, and lipoxygenase) and antioxidative (ascorbate peroxidase, catalase, superoxide dismutase, and glutathione reductase) enzymes were higher for infected +Si plants compared to infected -Si plants. Collectively, this study highlights the importance of using Si to boost maize resistance against MLB considering the more operative defense reactions and the robustness of the antioxidative metabolism of plants along with the preservation of their photosynthetic apparatus.
ABSTRACT
Strawberry (Fragaria x ananassa, Duch.) is an important crop worldwide. However, since it is a highly demanding crop in terms of the chemical conditions of the substrate, a large part of strawberry production implies the application of large amounts of fertilizers in the production fields. This practice can cause environmental problems, in addition to increases in the fruit's production costs. In this context, applying plant growth-promoting bacteria in production fields can be an essential strategy, especially thanks to their ability to stimulate plant growth via different mechanisms. Therefore, this study aimed to test in vitro and in vivo the potential of bacteria isolated from strawberry leaves and roots to directly promote plant growth. The isolates were tested in vitro for their ability to produce auxins, solubilize phosphate and fix nitrogen. Isolates selected in vitro were tested on strawberry plants to promote plant growth and increase the accumulation of nitrogen and phosphorus in the leaves. The tested isolates showed an effect on plant growth according to biometric parameters. Among the tested isolates, more expressive results for the studied variables were observed with the inoculation of the isolate MET12M2, belonging to the species Brevibacillus fluminis. In general, bacterial inoculation induced strain-dependent effects on strawberry growth. In vitro and in vivo assays showed the potential use of the B. fluminis MET12M2 isolate as a growth promoter for strawberries.
ABSTRACT
Botrytis cinerea causes the gray mold disease in a wide range of plant hosts, especially in post-harvest periods. The control of this phytopathogen has been accomplished through the application of fungicides. However, this practice can cause environmental problems and increase fruit production costs. In addition, this fungus species has developed resistance to conventional synthetic fungicides. In this context, plant growth-promoting bacteria have shown potential for application in agricultural production because they are able to stimulate plant growth through different mechanisms, including the biological control of phytopathogens (indirect growth promotion mechanism). The aim of this work was to evaluate in vitro and in fruits the potential for indirect plant growth-promotion of bacteria isolated from strawberry leaves and roots. Dual plate method and inverted plate method were used to verify the ability of controlling in vitro the growth of Botrytis cinerea via the production of diffusible and volatile antifungal compounds, respectively. The effect of six bacterial isolates that showed greater potential for biological control in vitro was evaluated by scanning electron microscopy. Antifungal compounds produced by these bacterial isolates were identified by liquid chromatography coupled with mass spectrometry. Six bacterial strains were tested on strawberry pseudofruits. Five selected strains belong to the genus Bacillus and one to the genus Pantoea sp. Selected strains were able to inhibit more than 80 % of the mycelial growth of B. cinerea by the production of diffusible compounds and 90 % by volatile antifungal compounds production. Scanning electron microscopy showed the intense degradation of fungal hyphae caused by the presence of all bacterial strains. Bioactive compounds (salycilamide, maculosin, herniarin, lauroyl diethanolamide, baptifoline, undecanedioic acid, botrydial, 8 3-butylidene-7-hydroxyphthalide and N-(3-oxo-henoyl)-homoserine lactone) were obtained from liquid culture of these strains and extraction with ethyl acetate. All six isolates tested in vivo reduced the incidence of gray mold in strawberry pseudofruits in postharvest. It is concluded that isolates 26, 29, 65, 69, 132 (Bacillus sp.) and MQT16M1 (Pantoea sp.) have potential application for the biological control of Botrytis cinerea in strawberry via the production of diffusible and volatile antifungal compounds.
