Doenças foliares na produção de biomassa e sólidos solúveis totais em sorgo sacarino (Sorghum bicolor (L.) Moench)

Abstract

Sorghum cultivars have been studied as potential biofuels sources due to their large potential to produce sugar and biomass. However, some features may influence the viability of biomass or sugar production from sorghum, for example plant diseases. The aim of this study was evaluate leaf diseases of two different sweet sorghum cultivars treated or not with fungicides, and the correlation between the fungicides applications and the sorghum biomass and the total soluble solids. The trial was conducted under field conditions at the Agriculture Science Experimental Farm (FAECA) at the Federal University of Grande Dourados (UFGD). Two sorghum cultivars (BRS 506 and BRS 511) were evaluated in two sowing seasons: November 25, 2014, and March 2, 2015. The experimental design was completely randomized, with four replications, in a 2x4 factorial design (cultivars x treatments). The treatments consisted in applications of Epoxiconazole + Pyraclostrobin with theses days: 0 – control (nor application), 1- one fungicide application at 45 days after the sorghum emergence, 2 – two fungicide applications at 45 and 66 days after the sorghum emergence, 3- three fungicide applications at 45, 66 and 87 days after the sorghum emergence. A second field trial was set up in March using a completely randomized design, in a factorial design (2x2) with four replications. The treatments consisted of Prothioconazole + Trifloxystrobin applications at the following application arrangement: first application at 45 days after sorghum emergence followed by four applications applied every 14 days, and another treatment with no fungicide application. The parameters evaluated were disease severity, stem diameter, plant height, broth volume, green biomass content and total soluble solids content were evaluated in the experiment. The data were submitted to analysis of the variance, and once significant were performed in the means tests. The correlation analysis between disease severity data and agronomic characteristics was performed. There are differences among cultivars regarding susceptibility to the target spot. The application of epoxiconazole + pyraclostrobin has a positive effect on the foliar diseases control, biomass accumulation and decrease the loss of total soluble solids. The fungicide prothioconazole + trifloxystrobin decreased the severity of anthracnose, cercosporiosis and rust; however, did not showed results in the control of helmintosporiosis and target spot and did not resulted in an increase of the biomass and sugars. Foliar diseases are negatively correlated with the production of biomass and total soluble solids in sweet sorghum.