RESUMO
AIM: The aim was to characterize cold-adapted bacteria by testing their PGP features and antagonistic activity against Macrophomina phaseolina, both in vitro and coating soybean seeds (Glycine max [L.] Merr.). METHODS AND RESULTS: Burkholderia gladioli MB39, Serratia proteamaculans 136 and Serratia proteamaculans 137 were evaluated. In vitro tests showed that S. proteamaculans 136 and 137 produce siderophore and indole-acetic acid (IAA), solubilize phosphate and fix nitrogen. Additionally, B. gladioli MB39 and S. proteamaculans 137 showed hydrolase activity and potent antifungal effects. The biocontrol efficacy over soybean seeds was evaluated using in vitro and greenhouse methods by immersing seeds into each bacterial suspension. As a result, S. proteamaculans 136 has improved the performance in all the seed germination evaluated parameters. In addition, S. proteamaculans 137 and B. gladioli MB39 strongly inhibited M. phaseolina, reducing the infection index values to 10% and 0%, respectively. CONCLUSION: Serratia proteamaculans 136, 137 and Burkholderia gladioli MB39 showed plant growth promotion features and inhibition of Macrophomina phaseolina infection by producing different antifungal compounds. SIGNIFICANCE AND IMPACT OF THE STUDY: Our results reinforce the application of cold-adapted Serratia proteamaculans and Burkholderia gladioli bacterial strains as candidates for developing microbial formulation to promote plant growth and guarantee antifungal protection in soybean crops.
Assuntos
Glycine max , Doenças das Plantas , Glycine max/microbiologia , Doenças das Plantas/microbiologia , Sideróforos , Antifúngicos/farmacologia , Serratia , Sementes , Nitrogênio , Fosfatos , Acetatos , HidrolasesRESUMO
Charcoal rot, caused by the fungus Macrophomina phaseolina, is an economically important disease of soybean (Glycine max) worldwide. Objectives of the present research were to (i) study the genetic and pathogenic diversity in a collection of M. phaseolina isolates from Argentina and Paraguay and (ii) develop an improved in vitro phenotyping method to evaluate disease response of soybean genotypes to M. phaseolina isolates. Cluster analysis showed no clear association among simple sequence repeat profiles, year of collection, pathogenicity, and geographical origin of the isolates from Argentina and Paraguay. Subsequently, the response of four soybean genotypes against seven M. phaseolina isolates was evaluated in the field and the results were confirmed using the in vitro assay developed. This assay, which is based on root disease development on soybean seedlings, allowed the detection of a differential level of aggressiveness among the isolates on four soybean genotypes. The results suggest the existence of specific interactions among soybean genotypes and M. phaseolina isolates. In addition, cultivar Munasqa RR showed a superior response against M. phaseolina compared with DT 97-4290 (moderately resistant), thus becoming a novel source of resistance to charcoal rot.
Assuntos
Ascomicetos/patogenicidade , Resistência à Doença/genética , Glycine max/genética , Doenças das Plantas/genética , Argentina , Genótipo , Paraguai , Fenótipo , Doenças das Plantas/microbiologia , Glycine max/microbiologiaRESUMO
Currently, fungicide application in soybean production accounts for an important amount of global pesticide use, and it is therefore most desirable to find new healthier and more environmental friendly alternatives for the phytosanitary management in this crop. In this study, we present convincing evidence for effective induction of disease protection by the agricultural biostimulant PSP1, a formulation based on the plant-defense eliciting activity of the fungal protease AsES (Acremonium strictum elicitor subtilisin), in multiple field trials in Argentina. PSP1 was shown to combine well with commercial spray adjuvants, an insecticide, a herbicide and fungicides used in Argentinian soybean production without losing any defense-inducing activity, indicating an easy and efficient adaptability to conventional soybean production and disease management in the region. Results from multiple soybean field trials conducted with different elite genotypes at several locations during two consecutive growing seasons, showed that PSP1 is able to induce an enhanced pathogen defense which effectively reduced late season disease (LSD) development in field-grown soybean. This defense response seems to be broad-range as disease development was clearly reduced for at least three different fungi causing LSDs in soybean (Septoria glycines, Cercospora kikuchii and Cercospora sojina). It was noteworthy that application of PSP1 in soybean alone gave a similar protection against fungal diseases as compared to the commercial fungicides included in the field trials and that PSP1 applied together with a fungicide at reproductive stages enhanced disease protection and significantly increased grain yields. PSP1 is the first example of an elicitor-based strategy in order to efficiently control multiple fungal diseases under field conditions in the soybean crop. These results show the feasibility of using induced resistance products as complements or even full-good replacements to currently used chemical pesticides, fulfilling a role as important components of a more sustainable crop disease management system.
RESUMO
Background Asian soybean rust (SBR) caused by Phakopsora pachyrhizi Syd. & Syd., is one of the main diseases affecting soybean and has been reported as one of the most economically important fungal pathogens worldwide. Knowledge of the genetic diversity of this fungus should be considered when developing resistance breeding strategies. We aimed to analyze the genetic diversity of P. pachyrhizi combining simple sampling with a powerful and reproducible molecular technique. Results We employed Amplified Fragment Length Polymorphism (AFLP) technique for the amplification of P. pachyrhizi DNA extracted from naturally SBR-infected plants from 23 production fields. From a total of 1919 markers obtained, 77% were polymorphic. The high percentage of polymorphism and the Nei's genetic diversity coefficient (0.22) indicated high pathogen diversity. Analysis of molecular variance showed higher genetic variation within countries than among them. Temporal analysis showed a higher genetic variation within a year than between years. Cluster, phylogenetic and principal co-ordinate analysis showed that samples group by year of collection and then by country sampled. Conclusions The study proposed combining a simple collection of urediniospore with a subsequent analysis by AFLP was useful to examine the molecular polymorphism of samples of P. pachyrhizi collected and might have a significant contribution to the knowledge of its genetic diversity. Also, AFLP analysis is an important and potent molecular tool for the study of genetic diversity and could be useful to carry out wider genetic diversity studies.