Samuel Julio Martins

Biological control of mycotoxin-producing molds

Mycotoxins are produced by the secondary metabolism of many fungi and can be found in almost 25% of the worlds agricultural commodities. These compounds are toxic to humans, animals, and plants and therefore, efforts should be made to avoid mycotoxin contamination in food and feed. Besides, up to 25% of all harvested fruits and vegetables are lost due to storage molds and/or mycotoxin contamination and many methods have been applied to mitigate these issues, but most of them rely on the use of fungicides. Although chemicals are often the first defensive line against mycotoxigenic fungi, the indiscriminate use of fungicides are awakening the public perception due to their noxious effects on the environment and human/animal health. Thus, there is an increasing public pressure for a safer and eco-friendly alternative to control these organisms. In this background, biological control using microbial antagonists such as bacteria, fungi and yeasts have been shown to be a feasible substitute to reduce the use of chemical compounds. Despite of the positive findings using the biocontrol agents only a few products have been registered and are commercially available to control mycotoxin-producing fungi. This review brings about the up-to-date biological control strategies to prevent or reduce harvested commodity damages caused by storage fungi and the contamination of food and feed by mycotoxins.

Essential oils for the control of bacterial speck in tomato crop

Bacterial speck (Pseudomonas syringae pv. tomato) is considered one of the major diseases of tomato crop worldwide and alternative methods to control it are desirable. The objective of this study was to evaluate the effect of essential oils (EOs) on P. syringae pv. tomato strain ufv-1 growth, in controlling bacterial speck in tomato plants, as well as to find the best application time of the EOs. The EOs used in this study were thyme (TH), eucalyptus (EU), tea tree (TT), clove (CL), cinnamon (CN), citronella (CI), and lemon grass (LE). An in vitro test using EOs were conducted to verify the ufv-1 inhibition, and two tests were carried out in a greenhouse to evaluate the effect of EOs before and after inoculation with Pst. Inhibition zones were observed for EU, CI, CL, and CN at a concentration of 1%. Plants pre-treated with EOs showed lower disease severity than that in plants post-treated with EOs (P<0.05), whereas higher efficacy was observed using acibenzolar-S-methyl and CI (91 and 83%, respectively). Regarding post-treatment, TT, TH, CI, EU, LE, and commercial fungicide, resulted in reducing disease severity by 8 to 40% compared to control (water). Results from this study showed the potential use of EOs in controlling bacterial speck in tomato and suggest the induced resistance as the major mode of action.

Contribution of host and environmental factors to the hyperparasitism of coffee rust under field conditions

Coffee rust is a devastating disease but its paratism by Lecanicillium lecanii is assumed as having little role in the disease progress. However, recent evidence showed that the ecology of the multitrophic interaction is more complex but the factors that contribute for Hemileia vastatrix parasitism have only started to be addressed. Surveys of rust and its parasitism in a coffee plantation where no fungicide was used were carried out to find out the contribution of the plant characteristics and environmental conditions on the dynamics of coffee rust and its parasitism by L. lecanii. Throughout the year, rust incidence/severity and hyperparasite presence were assessed monthly on leaves. The maximum parasitism was found in the dry season with high rates on the east-facing side of the plant rather than on the west-facing side. There was a positive correlation between hyperparasite incidence and rust incidence/severity, regardless of the plant parts or season and a stronger correlation in the upper part of the plant. H. vastatrix and L. lecanii were more frequently found at higher temperatures. The abiotic environmental factors as well as plant features play a strong role in epidemic rust and on its natural enemy. The results from this work showed that disease control strategies should take such factors and plant features into consideration in the integrated management of coffee rust, to rationally manage fungicide application and therefore both reduce production costs and the risk of the emergence of fungicide insensitive H. vastatrix populations.

Plant-associated bacteria mitigate drought stress in soybean

Agriculture accounts for ~ 70% of all water use and the world population is increasing annually; soon more people will need to be fed, while also using less water. The use of plant-associated bacteria (PAB) is an eco-friendly alternative that can increase crop water use efficiency. This work aimed to study the effect of some PAB on increasing soybean tolerance to drought stress, the mechanisms of the drought tolerance process, and the effect of the PAB on promoting plant growth and on the biocontrol of Sclerotinia sclerotiorum. PAB were isolated from soybean rhizosphere and S. sclerotiorum sclerotia. The strains identified as UFGS1 (Bacillus subtilis), UFGS2 (Bacillus thuringiensis), UFGRB2 and UFGRB3 (Bacillus cereus) were selected on their ability to grow in media with reduced water activity. Soybean plants were inoculated with the PAB and evaluated for growth promotion, physiological and molecular parameters, after drought stress. Under drought stress, UFGS2 and UFGRB2 sustained potential quantum efficiency of PSII (Fv/Fm), while a decrease was found in the control plants. Moreover, UFGS2 and UFGRB3 maintained the photosynthetic rates in non-stressed conditions compared to the control. UFGS2-treated plants showed a higher stomatal conductance and higher transpiration than the control, after drought stress. Some PAB-treated plants also had other beneficial phenotypes, such as increases in fresh and dried biomass relative to the control. Differential gene expression analysis of genes involved in plant stress pathways shows changes in expression in PAB-treated plants. Results from this study suggest that PAB can mitigate drought stress in soybean and may improve water efficiency under certain conditions.