José Renato Bouças Farias

Drought Tolerance Characteristics of Brazilian Soybean Cultivars

Abstract Drought is one of the major constraints for soybean production in Brazil. Seed yield of ten Brazilian soybean cultivarssheltered from rain (drought stress) for one month after the first flowering was examined over two growing seasons in the field in Londrina, Brazil. The drought tolerance on the basis of seed yield varied with the cultivar, and the yield ranking among cultivars was nearly the same across two years. In cultivars with higher drought tolerance, crop growth rate (CGR)during the drought stress period was higher than in other cultivars. They also maintained a larger leaf area during the stress period. Although reproductive development was retarded by the drought stress, it tended to be retarded less in drought-tolerant cultivars. The information obtained in this research may be useful for breeding drought-tolerant cultivars or selecting diverse germplasms of soybean cultivars.

The soybean yield gap in Brazil – magnitude, causes and possible solutions for sustainable production

Brazil is one of the most important soybean producers in the world. Soybean is a very important crop for the country as it is used for several purposes, from food to biodiesel production. The levels of soybean yield in the different growing regions of the country vary substantially, which results in yield gaps of considerable magnitude. The present study aimed to investigate the soybean yield gaps in Brazil, their magnitude and causes, as well as possible solutions for a more sustainable production. The concepts of yield gaps were reviewed and their values for the soybean crop determined in 15 locations across Brazil. Yield gaps were determined using potential and attainable yields, estimated by a crop simulation model for the main maturity groups of each region, as well as the average actual famers’ yield, obtained from national surveys provided by the Brazilian Government for a period of 32 years (1980–2011). The results showed that the main part of the yield gap was caused by water deficit, followed by sub-optimal crop management. The highest yield gaps caused by water deficit were observed mainly in the south of Brazil, with gaps higher than 1600 kg/ha, whereas the lowest were observed in Tapurah, Jatai, Santana do Araguaia and Uberaba, between 500 and 1050 kg/ha. The yield gaps caused by crop management were mainly concentrated in South-central Brazil. In the soybean locations in the mid-west, north and north-east regions, the yield gap caused by crop management was 2000 kg/ha. For reducing the present soybean yield gaps observed in Brazil, several solutions should be adopted by growers, which can be summarized as irrigation, crop rotation and precision agriculture. Improved dissemination of agricultural knowledge and the use of crop simulation models as a tool for improving crop management could further contribute to reduce the Brazilian soybean yield gap.

Survival of pathogens on soybean debris under no-tillage and conventional tillage systems

n†A study was conducted in the subtropical area of Southern Brazil to determine the survival of pathogens in soybean residues under conventional and no-tillage cultivation systems from March to September of 1998 and 1999. The pathogens most frequently isolated were Colletotrichum truncatum, Phomopsis†spp., Cercospora kikuchii, Fusarium†spp., Macrophomina phaseolina, and Rhizoctonia solani. Other fungi isolated were Myrothecium roridum, Penicillium†sp., Chaetomium sp., Epicoccum†sp., Corynespora cassiicola and Trichoderma†sp. The percent of survival of each pathogen varied accord- ing to the month and the year. Survival of C.†truncatum, Phomopsis†spp. and C.†kikuchii were signifi- cantly reduced (p<0.05) from the first to the last evaluation either on buried debris or maintained on the soil surface. On†the other hand, M.†phaseolina and Fusarium†spp. were either not affected or fa- vored by burying the debris. The frequency of recovery of Fusarium†spp. increased specially in debris kept under the soil. The loss of biomass, measured by debris weight along the period of this study, showed a reduction of 44.4% in the conventional system and 34.9% in the no-tillage system in†1998, when rain was better distributed. In 1999, the reduction was 48.2% and 39.0% for the conventional and no-tillage system, respectively.

Expression patterns of GmAP2/EREB-like transcription factors involved in soybean responses to water deficit.

Soybean farming has faced several losses in productivity due to drought events in the last few decades. However, plants have molecular mechanisms to prevent and protect against water deficit injuries, and transcription factors play an important role in triggering different defense mechanisms. Understanding the expression patterns of transcription factors in response to water deficit and to environmental diurnal changes is very important for unveiling water deficit stress tolerance mechanisms. Here, we analyzed the expression patterns of ten APETALA2/Ethylene Responsive Element Binding-like (AP2/EREB-like) transcription factors in two soybean genotypes (BR16: drought-sensitive; and Embrapa 48: drought-tolerant). According to phylogenetic and domain analyses, these genes can be included in the DREB and ERF subfamilies. We also analyzed a GmDRIP-like gene that encodes a DREB negative regulator. We detected the up-regulation of 9 GmAP2/EREB-like genes and identified transcriptional differences that were dependent on the levels of the stress applied and the tissue type analyzed (the expression of the GmDREB1F-like gene, for example, was four times higher in roots than in leaves). The GmDRIP-like gene was not induced by water deficit in BR16 during the longest periods of stress, but was significantly induced in Embrapa 48; this suggests a possible genetic/molecular difference between the responses of these cultivars to water deficit stress. Additionally, RNAseq gene expression analysis over a 24-h time course indicates that the expression patterns of several GmDREB-like genes are subject to oscillation over the course of the day, indicating a possible circadian regulation.

Natural Occurrence of the Entomopathogenic Fungi Metarhizium, Beauveria and Paecilomyces in Soybean Under Till and No-till Cultivation Systems

A ocorrencia de fungos entomopatogenicos Metarhizium, Beauveria e Paecilomyces foi estudada em condicoes de semeadura direta e convencional da soja. Foi determinada a densidade de unidades formadoras de colonia por g de solo e por cm2 de foliolos de soja. Verificou-se que no solo sob semeadura direta ocorreu maior incidencia dos entomopatogenos, mas sobre os foliolos essa diferenca nao ocorreu, proporcionando as mesmas possibilidades de infeccao nos insetos da parte aerea suscetiveis que ocorrem nas duas condicoes de cultivo.

Subtractive libraries for prospecting differentially expressed genes in the soybean under water deficit

Soybean has a wide range of applications in the industry and, due to its crop potential, its improvement is widely desirable. During drought conditions, soybean crops suffer significant losses in productivity. Therefore, understanding the responses of the soybean under this stress is an effective way of targeting crop improvement techniques. In this study, we employed the Suppressive Subtractive Hybridization (SSH) technique to investigate differentially expressed genes under water deficit conditions. Embrapa 48 and BR 16 soybean lines, known as drought-tolerant and -sensitive, respectively, were grown hydroponically and subjected to different short-term periods of stress by withholding the nutrient solution. Using this approach, we have identified genes expressed during the early response to water deficit in roots and leaves. These genes were compared among the lines to assess probable differences in the plant transcriptomes. In general, similar biochemical processes were predominant in both cultivars; however, there were more considerable differences between roots and leaves of Embrapa 48. Moreover, we present here a fast, clean and straightforward method to obtain drought-stressed root tissues and a large enriched collection of transcripts expressed by soybean plants under water deficit that can be useful for further studies towards the understanding of plant responses to stress.

Progress of soybean charcoal rot under tillage and no-tillage systems in Brazil

The increase in incidence of charcoal rot caused by Macrophomina phaseolina on soybeans (Glycine max) was followed four seasons in conventional and no-till cropping systems. In the 1997/98 and 2000/01 seasons, total precipitation between sowing and harvest reached 876.3 and 846.9 mm, respectively. For these seasons, disease incidence did not differ significantly between the no-till and conventional systems. In 1998/99 and 1999/00 precipitation totaled 689.9 and 478.3 mm, respectively. In 1998/99, in the no-till system, the disease incidence was 43.7% and 53.1% in the conventional system. In 1999/00 the final incidence was 68.7% and 81.2% for the no-till and conventional systems, respectively. For these two seasons, precipitation was lower than that required for soybean crops (840 mm), and the averages of disease incidence were significantly higher in the conventional system. The concentration of microsclerotia in soil samples was higher in samples collected in conventional system at 0 - 10 cm depth. However, analysis of microsclerotia in roots showed that in years with adequate rain no difference was detected. In dry years, however, roots from plants developed under the conventional system had significantly more microsclerotia. Because of the wide host range of M. phaseolina and the long survival times of the microsclerotia, crop rotation would probably have little benefit in reducing charcoal rot. Under these study conditions it may be a better alternative to suppress charcoal rot by using the no-till cropping system to conserve soil moisture and reduce disease progress.

Transcriptome-Wide Identification of Reference Genes for Expression Analysis of Soybean Responses to Drought Stress along the Day.

The soybean transcriptome displays strong variation along the day in optimal growth conditions and also in response to adverse circumstances, like drought stress. However, no study conducted to date has presented suitable reference genes, with stable expression along the day, for relative gene expression quantification in combined studies on drought stress and diurnal oscillations. Recently, water deficit responses have been associated with circadian clock oscillations at the transcription level, revealing the existence of hitherto unknown processes and increasing the demand for studies on plant responses to drought stress and its oscillation during the day. We performed data mining from a transcriptome-wide background using microarrays and RNA-seq databases to select an unpublished set of candidate reference genes, specifically chosen for the normalization of gene expression in studies on soybean under both drought stress and diurnal oscillations. Experimental validation and stability analysis in soybean plants submitted to drought stress and sampled during a 24 h timecourse showed that four of these newer reference genes (FYVE, NUDIX, Golgin-84 and CYST) indeed exhibited greater expression stability than the conventionally used housekeeping genes (ELF1-β and β-actin) under these conditions. We also demonstrated the effect of using reference candidate genes with different stability values to normalize the relative expression data from a drought-inducible soybean gene (DREB5) evaluated in different periods of the day.

Characterization of Molecular and Physiological Responses Under Water Deficit of Genetically Modified Soybean Plants Overexpressing the AtAREB1 Transcription Factor

Drought is one of the major factors limiting crop productivity worldwide. Currently, the techniques of genetic engineering are powerful tools for the development of drought-tolerant plants, once they allow for the modification of expression patterns of genes responsive to drought. Within this context, transcription factors recognize specific DNA sequences in the regulatory region of target genes, and thereby regulate their expression. AREB is a transcription factor in the basic leucine zipper family, which binds to the ABRE element in the promoter region of genes induced by abscisic acid and drought. In this study, soybean plants transformed with the 35S:AtAREB1 construct were submitted to drought under greenhouse conditions. AtAREB1 expression was observed in the transgenic lines 1Ea2939 and 1Eb2889, but not in the event 1Ea15 and, under control of the CaMV 35S promoter, did not cause dwarfism and resulted in a higher survival rate of transformed plants after drought and rehydration. Moreover, 1Ea2939 and 1Eb2889 plants presented a greater total number of pods and seeds and increased dry matter content of seeds. The best performance of the transgenic lines 1Ea2939 and 1Eb2889 relative to BR 16 plants (wild type) and to event 1Ea15 might be related to mechanisms of drought prevention through reduced stomatal conductance and leaf transpiration under control conditions. Changes in the expression profile of phosphatases and kinases may also be involved. Such results suggest that the constitutive overexpression of the transcription factor AtAREB1 leads to an improved capacity of the soybean crop to cope with drought with no yield losses.

Characterization of Soybean Genetically Modified for Drought Tolerance in Field Conditions

Drought is one of the most stressful environmental factor causing yield and economic losses in many soybean-producing regions. In the last decades, transcription factors (TFs) are being used to develop genetically modified plants more tolerant to abiotic stresses. Dehydration responsive element binding (DREB) and ABA-responsive element-binding (AREB) TFs were introduced in soybean showing improved drought tolerance, under controlled conditions. However, these results may not be representative of the way in which plants behave over the entire season in the real field situation. Thus, the objectives of this study were to analyze agronomical traits and physiological parameters of AtDREB1A (1Ab58), AtDREB2CA (1Bb2193), and AtAREB1 (1Ea2939) GM lines under irrigated (IRR) and non-irrigated (NIRR) conditions in a field experiment, over two crop seasons and quantify transgene and drought-responsive genes expression. Results from season 2013/2014 revealed that line 1Ea2939 showed higher intrinsic water use and leaf area index. Lines 1Ab58 and 1Bb2193 showed a similar behavior to wild-type plants in relation to chlorophyll content. Oil and protein contents were not affected in transgenic lines in NIRR conditions. Lodging, due to plentiful rain, impaired yield from the 1Ea2939 line in IRR conditions. qPCR results confirmed the expression of the inserted TFs and drought-responsive endogenous genes. No differences were identified in the field experiment performed in crop season 2014/2015, probably due to the optimum rainfall volume during the cycle. These field screenings showed promising results for drought tolerance. However, additional studies are needed in further crop seasons and other sites to better characterize how these plants may outperform the WT under field water deficit.