Alterações fisiológicas e bioquímicas em plantas de cevada supridas com silício e tratadas com fungicida contra Bipolaris sorokiniana

Abstract

Spot blotch on barley, caused by the fungus Bipolaris sorokiniana (Sacc. In Sorok) is one of the main diseases that occur in the crop, reducing yield and grain quality for the brewing industry. The disease management include strategies such as the reduction of initial inoculum, use of cultivars with partial resistance, complemented with fungicide applications, which aim to attenuate the rate of disease progress. Thus, other management measures can be useful to complement and/or increase the control efficiency. Searching for additional management measures, the objective of this study was to investigate the effects of silicon (Si) amendment in the soil to barley plants of the cultivars AnaG01 and BRS Cauê, combined with the preventive application of the fungicide fluxapiroxade + pyraclostrobin + epoxiconazol at 7 or 15 days before inoculation with B. sorokiniana, in the reduction of the spot blotch intensity and on the biochemical defense mechanisms (Article 1), and on the physiological alteration resulting of the process of infection by B. sorokiniana in the leaves (Article 2). The results showed a reduction in disease severity, for both cultivars supplied with Si, up to 41%, as well as reduction in the rate of lesion expansion (21 – 36%) and in the area under the disease progress curve (15 – 34%). The superoxide dismutase enzyme had the greatest activity in inoculated plants and supplied with Si. Plants supplied with Si also showed a higher concentration of phenolic compounds and lignin-thioglycolic acid derivatives, and reduced electrolyte leakage. Regarding photosynthetic responses, in inoculated plants, there was a reduction in net assimilation of CO2 (A), and 10 days after inoculation there was a decrease in stomatal conductance (gs), internal CO2 concentration (Ci), and transpiration rate (E). The concentrations of total chlorophyll, chlorophyll a and carotenoids increased, while chlorophyll b has been reduced in the leaves of inoculated plants. The supply of Si ameliorated the damage on the gas exchange variables (A and gs) and on the concentration of pigments. The association of Si and fungicide provided a greater reduction of disease intensity and maintenance of a better physiological state of the plant when challenged with B. sorokiniana. The results of this study demonstrated the potential of Si to increase the resistance of barley plants to spot blotch, through the potentiation of biochemical defense responses or the reduction of physiological damage caused by the pathogen infection.