Contribution of organic amendments to soil properties and survival of Stenocarpella on maize stalk

The incorporation of organic matter to the soil not only improves nutrient content, but also reduces the survival of Stenocarpella, the causal agent of stalk rot, Diplodia ear rot, and grey leaf spot, in maize stubble. We evaluated the effect of organic waste incorporation on Stenocarpella survival in maize stalks, the activity of suppressiveness-related enzymes, and nutrient contents. We conducted the assays in the municipalities of Lavras and Sete Lagoas, Minas Gerais State, Brazil. Maize stalks infested with Stenocarpella were kept in field conditions for three months after poultry litter, swine manure, fish hydrolysate, compost sewage sludge, and urea application. Infested stalks, without residue amendment, were kept on surface or incorporated into the soil, representing negative and positive controls. Stenocarpella concentration in stalks was assessed using qPCR expressed as cycle threshold number. Sewage sludge, buried stalks, and stalks retained on the surface showed reduction of pathogen inoculum. Swine manure and urea did not reduce the quantity of DNA. In the experiment conducted in Lavras, poultry litter stimulated β-glucosidase, urease and hydrolysis of fluorescein diacetate activities when compared to the negative control. Sewage sludge, poultry litter, and swine manure increased Ca in the soil by 44 %, 38 % and 36 %, respectively, in the experiment conducted in Lavras. Poultry litter increased Ntotal three months after application. The results indicate that organic wastes are promising in improving nutrient content, activity of hydrolysis-related enzymes, but Stenocarpella inoculum dynamics should be taken into consideration when deciding on the specific organic amendment

Repeated exposure of wheat to the fungal root pathogen Bipolaris sorokiniana modulates rhizosphere microbiome assembly and disease suppressiveness

Abstract Background Disease suppressiveness of soils to fungal root pathogens is typically induced in the field by repeated infections of the host plant and concomitant changes in the taxonomic composition and functional traits of the rhizosphere microbiome. Here, we studied this remarkable phenomenon for Bipolaris sorokiniana in two wheat cultivars differing in resistance to this fungal root pathogen. Results The results showed that repeated exposure of the susceptible wheat cultivar to the pathogen led to a significant reduction in disease severity after five successive growth cycles. Surprisingly, the resistant wheat cultivar, initially included as a control, showed the opposite pattern with an increase in disease severity after repeated pathogen exposure. Amplicon analyses revealed that the bacterial families Chitinophagaceae, Anaerolineaceae and Nitrosomonadaceae were associated with disease suppressiveness in the susceptible wheat cultivar; disease suppressiveness in the resistant wheat cultivar was also associated with Chitinophagaceae and a higher abundance of Comamonadaceae. Metagenome analysis led to the selection of 604 Biosynthetic Gene Clusters (BGCs), out of a total of 2,571 identified by AntiSMASH analysis, that were overrepresented when the soil entered the disease suppressive state. These BGCs are involved in the biosynthesis of terpenes, non-ribosomal peptides, polyketides, aryl polyenes and post-translationally modified peptides. Conclusion Combining taxonomic and functional profiling we identified key changes in the rhizosphere microbiome during disease suppression. This illustrates how the host plant relies on the rhizosphere microbiome as the first line of defense to fight soil-borne pathogens. Microbial taxa and functions identified here can be used in novel strategies to control soil-borne fungal pathogens