Flávio Henrique Vasconcelos de Medeiros

Transcriptional profiling in cotton associated with Bacillus subtilis (UFLA285) induced biotic-stress tolerance

Plant growth promoting rhizobacteria (PGPR) confer disease resistance in many agricultural crops. In the case of Bacillus subtilis (UFLA285) isolated from the cotton producing state of Mato Grosso (Brazil), in addition to inducing foliar and root growth, disease resistance against damping-off caused by Rhizoctonia solani was observed. The aim of this cotton study was to identify gene transcriptional events altered with exposure to the PGPR strain UFLA285 in infected plants. Global gene transcription was profiled using a commercially-available cotton gene chip; cotton plants with and without UFLA285-seed treatment were infected with R. solani 9-days after planting and harvested on day14. Microarray data of stem tissue revealed 247 genes differentially regulated in infected plants, seed treated versus untreated with UFLA285. Transcripts encoding disease resistance proteins via jasmonate/ethylene signaling as well as osmotic regulation via proline synthesis genes were differentially expressed with UFLA285 induction. Consistent with transcriptional regulation, UFLA285 increased plant-proline accumulation and dry weight. This study has identified transcriptional changes in cotton, induced by the beneficial soil bacterium UFLA285 and associated with disease control.

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.

Management of melon bacterial blotch by plant beneficial bacteria

Plant beneficial bacteria (PBB) have shown potential for disease control and are particularly important in the management of bacterial diseases, which are poorly controlled by conventional methods. In melon, bacterial fruit blotch caused by Acidovorax citrulli is a seedborne disease that is particularly destructive under certain conditions. PBB strains were screened for their ability to protect seeds and leaves from bacterial fruit blotch, and their antibiosis activity and plant colonization were studied. When Bacillus sp. RAB9 was applied to infected seeds, it reduced the area under the disease progress curve (AUDPC) by 47% and increased the incubation period (the time between inoculation and the first visible symptoms) by 35%. Three of the selected strains (JM339, MEN2 and PEP91) displayed antibiosis against A. citrulli. The RAB9Rif-Nal mutant colonized seeds epiphytically and roots and stems endophytically. Paenibacillus lentimorbus MEN2 sprayed on melon seedlings protected leaves, and when challenged with A. citrulli, it reduced the AUDPC (by 88%), disease index (by 81%) and incidence (by 77%). Given that the production of both melon seedlings and commercially grown greenhouse melons is increasing, biocontrol strategies may well be integrated into bacterial blotch management programs.

Augmenting iron accumulation in cassava by the beneficial soil bacterium Bacillus subtilis (GBO3).

Cassava (Manihot esculenta), a major staple food in the developing world, provides a basic carbohydrate diet for over half a billion people living in the tropics. Despite the iron abundance in most soils, cassava provides insufficient iron for humans as the edible roots contain 3–12 times less iron than other traditional food crops such as wheat, maize, and rice. With the recent identification that the beneficial soil bacterium Bacillus subtilis (strain GB03) activates iron acquisition machinery to increase metal ion assimilation in Arabidopsis, the question arises as to whether this plant-growth promoting rhizobacterium also augments iron assimilation to increase endogenous iron levels in cassava. Biochemical analyses reveal that shoot-propagated cassava with GB03-inoculation exhibit elevated iron accumulation after 140 days of plant growth as determined by X-ray microanalysis and total foliar iron analysis. Growth promotion and increased photosynthetic efficiency were also observed for greenhouse-grown plants with GB03-exposure. These results demonstrate the potential of microbes to increase iron accumulation in an important agricultural crop and is consistent with idea that microbial signaling can regulate plant photosynthesis.

Impact of Seed Exudates on Growth and Biofilm Formation of Bacillus amyloliquefaciens ALB629 in Common Bean

We aimed to unravel the events which favor the seed-rhizobacterium Bacillus amyloliquefaciens strain ALB629 (hereafter ALB629) interaction and which may interfere with the rhizobacterium colonization and growth on the spermosphere of common bean. Seed exudates from common bean were tested in vitro for ALB629 biofilm formation and bacterial growth. Furthermore, the performance of ALB629 on plant-related variables under drought stress was checked. Seed exudates (1 and 5% v/v) increased ALB629 biofilm formation. Additionally, the colony forming units for ALB629 increased both in culture and on the bean seed surface. The bean seed exudates up-regulated biofilm operons in ALB629 TasA and EpsD by ca. two and sixfold, respectively. The high-performance liquid chromatography (HPLC)-coupled with MS showed that malic acid is present as a major organic acid component in the seed exudates. Seeds treated with ALB629 and amended with malic acid resulted in seedlings with a higher bacterial concentration, induced plant drought tolerance, and promoted plant growth. We showed that seed exudates promote growth of ALB629 and malic acid was identified as a major organic acid component in the bean seed exudates. Our results also show that supplementation of ALB629 induced drought tolerance and growth in plants. The research pertaining to the biological significance of seed exudates in plant–microbe interaction is unexplored field and our work shows the importance of seed exudates in priming both growth and tolerance against abiotic stress.

Strains of the Group I Lineage of Acidovorax citrulli, the Causal Agent of Bacterial Fruit Blotch of Cucurbitaceous Crops, are Predominant in Brazil.

Bacterial fruit blotch (BFB), caused by the seedborne bacterium Acidovorax citrulli, is an economically important threat to cucurbitaceous crops worldwide. Since the first report of BFB in Brazil in 1990, outbreaks have occurred sporadically on watermelon and, more frequently, on melon, resulting in significant yield losses. At present, the genetic diversity and the population structure of A. citrulli strains in Brazil remain unclear. A collection of 74 A. citrulli strains isolated from naturally infected tissues of different cucurbit hosts in Brazil between 2000 and 2014 and 18 A. citrulli reference strains from other countries were compared by pulsed-field gel electrophoresis (PFGE), multilocus sequence analysis (MLSA) of housekeeping and virulence-associated genes, and pathogenicity tests on seedlings of different cucurbit species. The Brazilian population comprised predominantly group I strains (98%), regardless of the year of isolation, geographical region, or host. Whole-genome restriction digestion and PFGE analysis revealed that three unique and previously unreported A. citrulli haplotypes (assigned as haplotypes B22, B23, and B24) occurred in Brazil. The greatest diversity of A. citrulli (four haplotypes) was found among strains collected from the northeastern region of Brazil, which accounts for more than 90% of the countrys melon production. MLSA clearly distinguished A. citrulli strains into two well-supported clades, in agreement with observations based on PFGE analysis. Five Brazilian A. citrulli strains, representing different group I haplotypes, were moderately aggressive on watermelon seedlings compared with four group II strains that were highly aggressive. In contrast, no significant differences in BFB severity were observed between group I and II A. citrulli strains on melon and squash seedlings. Finally, we observed a differential effect of temperature on in vitro growth of representative group I and II A. citrulli haplotypes. Specifically, of 18 group II strains tested, all grew at 40 and 41°C, whereas only 3 of 15 group I strains (haplotypes B8[P], B3[K], and B15) grew at 40°C. Three strains representing haplotype B8(P) were the only group I strains that grew at 41°C. These results contribute to a better understanding of the genetic diversity of A. citrulli associated with BFB outbreaks in Brazil, and reinforce the efficiency of MLSA and PFGE analysis for assessing population structure. This study also provides the first evidence to suggest that temperature might be a driver in the ecological adaptation of A. citrulli populations.

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.

Defining plant growth promoting rhizobacteria molecular and biochemical networks in beneficial plant-microbe interactions

BackgroundOur knowledge of plant beneficial bacteria in the rhizosphere is rapidly expanding due to intense interest in utilizing these types of microbes in agriculture. Laboratory and field studies consistently document the growth, health and protective benefits conferred to plants by applying plant growth promoting rhizobacteria (PGPR). PGPR exert their influence on other species, including plants, in the rhizosphere by producing a wide array of extracellular molecules for communication and defense.ScopeThe types of PGPR molecular products are characteristically diverse, and the mechanisms by which they are acting on the plant are only beginning to be understood. While plants may contribute to shape their microbiome, it is these bacterial products which induce beneficial responses in plants. PGPR extracellular products can directly stimulate plant genetic and molecular pathways, leading to increases in plant growth and induction of plant resistance and tolerance. This review will discuss known PGPR-derived molecules, and how these products are implicated in inducing plant beneficial outcomes through complex plant response mechanisms.ConclusionsIn order to move PGPR research to the next level, it will be important to describe and document the genetic and molecular mechanisms employed in these interactions. In this way, we will be able to restructure and harness these mechanisms in a way that allows for broad-based applications in agriculture. A greater depth of understanding of how these PGPR molecules are acting on the plant will allow more effective development of rhizobacterial applications in the field.

Building soil suppressiveness against plant-parasitic nematodes

ABSTRACT Damage caused by plant-parasitic nematodes (PPNs) represents significant losses in agriculture worldwide. Sustainable and non-agrochemical practices have been sought out for the last few years aiming the reduction of PPN outbreaks, as such practices represent less interference in the soil health. In addition, certain soils naturally show high levels of suppressiveness against nematodes. Natural suppressive soils do not allow PPN increment by a balance in soil biotic and abiotic conditions. Such soils must be better understood by which components are responsible for their natural suppressiveness. Hence, keeping, stimulating or and even creating suppressive conditions in agricultural rhizosphere has been studied and applied to reduce PPN populations. There are many aspects that implicate in soil suppressiveness against PPN, such as microbiota activities, organic matter amount, chemical composition and physical constitution. However, any of those conditions is a single driver in suppressive soils against PPN. In this context, we intend to bring up an overview concerning the natural occurrence of suppressive soils against the most devastating PPNs worldwide and discuss the means used to induce suppressiveness in agricultural fields by sustainable management practices.