How biological and chemical fungicides impact the maize microbiome, Fusarium verticillioides populations and fumonisins content

Abstract

Plant diseases go beyond economic damage and physiological damage. Some pathogens such as Fusarium verticillioides can produce secondary metabolites, which are toxic to humans and animals, known as mycotoxins. The productions of these toxins, in the case of F. verticillioides, better known as fumonisins are a socioeconomic problem. Thus, alternatives that reduce the production of fumonisins are emergencial needs, mainly within the maize crops, where this toxin is usually present. The objectives of this work were: (1) to evaluate the dynamics of the maize phyllosphere microbiome under the combination of foliar treatment with fungicide (azoxystrobin+cyproconazole) and biological control agent (Bacillus subtilis) (2) to evaluate new integrated management techniques , using the fungicide compatibility with biological control agent against F. verticillioides and (3) to evaluate the economic costs in two production systems, one with only the application of fungicides and others with the combination of fungicides and the biological control agent in the reduction of fumonisin losses. Tests with maize plants were carried out in two different areas as part of the ears was collected in two times for analysis of bacterial populations (16S) and fungi (ITS) by next-generation sequencing (NGS). The amounts of pathogen present cycles (qPCR) and fumonisin content (LC-MS / MS) on plants treated and inoculated with F. verticillioides was also analyzed. In the second part the sensitivity of 20 isolates of F. verticillioides to 10 active fungicides (azoxystrobin, pyraclostobin, captan, thiabendazole, fluatriafol, carbendazim, propiconazole, tetraconazole, tebuconazole and cyproconazole) was evaluated in different concentrations (0; 0,1; 1; 10 e 100 ppm) besides that bacteria (30 strains) and fungi (30 strains) antagonists of the maize phylloplane to cyproconazole and azoxystrobin. Finally, the production cost in two production systems, conventional system (two fungicide applications) and proposed system (fungicide application combined with biological control agent), analyzing the system productivity (ton/ha), nutritional quality between the two systems (NIR) and fumonisin losses (LC-MS/MS) in the production systems. Statistical analyzes was performed using the Tukey test (p<=0.05) and analysis of the maize phyllosphere microbiome by bioinformatics procedures. Changes were observed in the communities of bacteria and fungi between the treatments. There were more copies of F. verticillioides DNA and higher fumonisin content in the treatment with two fungicide applications. Regarding the sensitivity of F. verticillioides strains against fungicides, tebuconazole and tetraconazole were the most active ingredients among the population. There have also been isolated antagonists to F. verticillioides compatible with cyproconazole and azoxistorbin. In relation to the cost/yield, a better relation was observed in the treatment with two fungicide applications, but the accumulated fumonisin content was higher in the ratio of 8:1 (conventional system/proposed system). It is possible to conclude the importance of integrated management within the maize-F. verticillioides-fumonisins pathosystem as an allied tool in the reduction of fumonisins. The best moments of application of the biological control agents for greater gains in yield must be worked on in this system.