Investigation of the physiological responses in soybean and common bean to water deficit

Drought causes considerable reduction of legume productivity and significantly threatens the food security, and this situation is expected to be aggravated due to climate change. In soybean and common bean, water resource capturing through plant root architectural plasticity and the role of symbiotic nitrogen fixation have not been investigated in greater detail yet. This study was therefore conducted to identify and apply useful morphological and physiological performance markers (traits) for selection of drought-tolerant common bean and soybean cultivars under both controlled phytotron and field conditions that might be applicable as markers in future legume breeding programs. In soybean, traits related to above ground performance, such as photosynthesis, biomasses, and stomatal conductance, were related to parameters for nitrogen acquisition in nodules. The ability to maintain vigorous shoot growth under drought-induced nitrogen limitation was identified as an important trait that can be used to select for improved drought tolerance. Further, experiments carried out growing different common bean inbred lines under controlled phytotron conditions revealed the importance of growth and gas exchange parameters as well as nitrogen fixing ability as performance markers to select superior performing bean lines for growth under drought. As a further result, the strong association of symbiotic nitrogen fixation with CO2 assimilation and stomatal conductance was also ascertained. In field experiments the effective use of water through enhanced lateral root development and maintaining the water status of the plant was found to be crucial for enhanced productivity under drought, with root morphology traits (root length, area and volume) as well as root architectural traits (first whorl angle, basal root number and adventitious root branching density) significantly related to seed yield. Measurement of these traits might be added to future bean varietal improvement programs. Further, a direct relationship between both water use efficiency (WUE) estimated using carbon isotope discrimination (CID) and nitrogen fixation (15N abundance) with root morphological and architectural traits (root length, area and volume, basal root number, 1st as well as 2nd whorl angles) was identified. CID (WUE) and 15N abundance (SNF ability) had a direct relationship with each other and also with productivity traits (seed yield and pod harvest index). Soybean field experiments verified the importance of root system architecture and morphology for providing drought tolerance with root architectural traits, tap and lateral roots (diameter and branching density) and morphological traits (root length, surface area and volume) contributing to better performance under drought. Moreover, the strong association of CID (WUE) with ä15N (SNF), root traits as well as seed yield in soybean exposed to drought was ascertained. Findings suggested that higher performance in CID under drought stress may be due to higher CO2 assimilation and better N2 fixation resulting in better root system architecture and morphology of the drought-tolerant cultivar through maintenance of the water status of the plant for efficient biological activity. Overall the study has generated new knowledge about the use of physiological markers (traits) that can be used widely for legume evaluation under drought suitable for both phytotron and field studies.Thesis (PhD)--University of Pretoria, 2012.Plant Scienceunrestricte

Identification and Application of Phenotypic and Molecular Markers for Abiotic Stress Tolerance in Soybean

Neurology & clinical neurophysiolog

High-density DArTSeq SNP markers revealed wide genetic diversity and structured population in common bean (Phaseolus vulgaris L.) germplasm in Ethiopia

Abstract Introduction Common bean is one of the widely consumed food security crop in Africa, Asia, and South America. Understanding genetic diversity and population structure is crucial for designing breeding strategies. Materials Two hundred and eighty-nine germplasm were recently collected from different regions of Ethiopia and introduced from CIAT to estimate genetic diversity and population structure using 11,480 DArTSeq SNP markers. Results The overall mean genetic diversity and polymorphic information content (PIC) were 0.38 and 0.30, respectively, suggested the presence of adequate genetic diversity among the genotypes. Among the geographical regions, landraces collected from Oromia showed the highest diversity (0.39) and PIC (0.30). The highest genetic distance was observed between genotypes collected from SNNPR and CIAT (0.49). In addition, genotypes from CIAT were genetically more related to improved varieties than the landraces which could be due to sharing of parents in the improvement process. The analysis of molecular variance revealed that the largest proportion of variation was due to within the population both in geographical region (63.67%) and breeding status (61.3%) based classification. Model-based structure analysis delineated the 289 common bean genotypes into six hypothetical ancestoral populations. Conclusions The genotypes were not clustered based on geographical regions and they were not the main drivers for the differentiation. This indicated that selection of the parental lines should be based on systematic assessment of the diversity rather than geographical distance. This article provides new insights into the genetic diversity and population structure of common bean for association studies, designing effective collection and conservation for efficient utilization for the improvement of the crop

Role of fixing nitrogen in common bean growth under water deficit conditions

In common bean (Phaseolus vulgaris L), limited information is available if potential of nodulation and symbiotic nitrogen fixation is associated with the expression of traits that confer better adaptation to drought conditions. Adaptive traits were therefore measured in N‐fixing bean lines BAT 477, DOR 364, and PAN 185 and in nonnodulating lines BAT 477‐NN and DOR 364‐NN. Drought affected growth in all bean lines and decreased chlorophyll content but more in DOR 364‐NN and BAT 477‐NN, and also reduced nodule size with highest reduction in DOR 364 (21.6%). Loss of nitrogen fixation under drought conditions was further associated with lower water use efficiency, measured as carbon isotope ratio of 13C/12C, and lower %N in shoots when compared to capability to fix nitrogen. Loss of symbiotic nitrogen fixation in mutant bean lines DOR 364‐NN and BAT 477‐NN negatively affected root architectural traits under drought. Under drought conditions, line BAT 477‐NN had about 50% lower values for all root architectural traits, such as root angle, strongly emphasizing an association of capability to fix nitrogen with root development. An association between capability to fix nitrogen and maintaining a better harvest index and seed yield was also found in the study. Under well‐watered conditions, all N‐fixing lines had a higher harvest index and seed yield (2.6–2.8 t of seed yield/ha) in comparison with the two nonfixing bean lines (1.4 t/ha). Although the harvest index and seed yield declined due to drought in all tested lines, this decline was only significant for line DOR 364‐NN (harvest index) and lines DOR 364‐NN and BAT 477‐NN (seed yield). Our study has overall demonstrated an important association between the capability of maintaining atmospheric N‐fixation and expression of traits conferring better adaptation to drought conditions with any change in nitrogen fixation affecting these traits

Role of fixing nitrogen in common bean growth under water deficit conditions

In common bean (Phaseolus vulgaris L), limited information is available if potential of nodulation and symbiotic nitrogen fixation is associated with the expression of traits that confer better adaptation to drought conditions. Adaptive traits were therefore measured in N‐fixing bean lines BAT 477, DOR 364, and PAN 185 and in nonnodulating lines BAT 477‐NN and DOR 364‐NN. Drought affected growth in all bean lines and decreased chlorophyll content but more in DOR 364‐NN and BAT 477‐NN, and also reduced nodule size with highest reduction in DOR 364 (21.6%). Loss of nitrogen fixation under drought conditions was further associated with lower water use efficiency, measured as carbon isotope ratio of 13C/12C, and lower %N in shoots when compared to capability to fix nitrogen. Loss of symbiotic nitrogen fixation in mutant bean lines DOR 364‐NN and BAT 477‐NN negatively affected root architectural traits under drought. Under drought conditions, line BAT 477‐NN had about 50% lower values for all root architectural traits, such as root angle, strongly emphasizing an association of capability to fix nitrogen with root development. An association between capability to fix nitrogen and maintaining a better harvest index and seed yield was also found in the study. Under well‐watered conditions, all N‐fixing lines had a higher harvest index and seed yield (2.6–2.8 t of seed yield/ha) in comparison with the two nonfixing bean lines (1.4 t/ha). Although the harvest index and seed yield declined due to drought in all tested lines, this decline was only significant for line DOR 364‐NN (harvest index) and lines DOR 364‐NN and BAT 477‐NN (seed yield). Our study has overall demonstrated an important association between the capability of maintaining atmospheric N‐fixation and expression of traits conferring better adaptation to drought conditions with any change in nitrogen fixation affecting these traits.Tropical legume II (TL II) through International Centre of Tropical Agricultural (CIAT) Cali, Colombia, and CIAT‐Africa/ Pan Africa Bean Research Alliance (PABRA), Uganda, and NRF South Africa.http://wileyonlinelibrary.com/journal/fes3am2020Plant Production and Soil ScienceForestry and Agricultural Biotechnology Institute (FABI

Identification of putative CLE peptide receptors involved in determinate nodulation on soybean

CLAVATA3/EMBRYO SURROUNDING REGION (CLE) peptides tightly control the balance between stem cell proliferation and differentiation in several plant developmental processes. Transmission of the CLE peptide signal has been shown to be rather complex. Despite their recent identification, little is known about the receptors by which nodulation-specific CLE peptides, which were identified in soybean, are perceived. Genetic analysis has indicated that the leucine-rich repeat receptor-like kinase NARK of soybean (Glycine max) and its orthologs in other legumes are possible candidates. However, more receptors need to be identified because CLE peptides are often detected by heteromultimeric complexes. Here, we identified two additional putative CLE peptide receptor pairs in the soybean genome with a nodulation-related expression pattern, GmRLK1-GmRLK2 and GmRLK3-GmRLK4, and discuss their role in CLE peptide perception during nodulation

Association of nodule performance traits with shoot performance traits of common bean under drought stress

The effect of drought stress on the association of nodule performance traits with shoot performance traits was studied using six common bean lines with contrasting differences in their adaptation to drought and low phosphorus (P) availability in soil. Drought stress reduced leaf water potential and gas exchange characteristics (CO2 assimilation, stomatal conductance) in all lines tested but two drought-tolerant lines, BAT 477 and BT_34-1,-1 were superior in their ability to adjust their leaf water status under drought. These two lines were also superior in root growth, rate of CO2 assimilation, vegetative biomass production, and nitrogen fixing ability under drought stress. A direct relation between symbiotic nitrogen fixation and nodule fresh weight with gas exchange traits as well as biomass production existed suggesting that relative growth of shoot vs. root depends on the provision of nitrogen by symbiotic nitrogen fixation and photosynthetic carbon assimilation. Overall, differences found in nodule, root and shoot performance traits indicated that the P-efficient bean line (BT_34-1-1) was superior than the other lines in terms of adaptation to drought. Results showed marked association of nodule performance traits with shoot performance traits under drought stress. We suggest that nodule characteristics and SNF ability should be included with above and below ground traits as phenotypic markers in germplasm evaluation and breeding programs that are aiming for improving drought tolerance in common bean.Tropical legume II (TL II) through International Centre of Tropical Agricultural (CIAT) Cali, Colombia and Pan Africa Bean Research Alliance (PABRA), Uganda.http://www.tandfonline.com/loi/wcim20hb201

erq426 1..13

Abstract CLE peptides are potentially involved in nodule organ development and in the autoregulation of nodulation (AON), a systemic process that restricts nodule number. A genome-wide survey of CLE peptide genes in the soybean glycine max genome resulted in the identification of 39 GmCLE genes, the majority of which have not yet been annotated. qRT-PCR analysis indicated two different nodulation-related CLE expression patterns, one linked with nodule primordium development and a new one linked with nodule maturation. Moreover, two GmCLE gene pairs, encoding group-III CLE peptides that were previously shown to be involved in AON, had a transient expression pattern during nodule development, were induced by the essential nodulation hormone cytokinin, and one pair was also slightly induced by the addition of nitrate. Hence, our data support the hypothesis that group-III CLE peptides produced in the nodules are involved in primordium homeostasis and intertwined in activating AON, but not in sustaining it

Search for nodulation-related CLE genes in the genome of Glycine max

CLE peptides are potentially involved in nodule organ development and in the autoregulation of nodulation (AON), a systemic process that restricts nodule number. A genome-wide survey of CLE peptide genes in the soybean glycine max genome resulted in the identification of 39 GmCLE genes, the majority of which have not yet been annotated. qRT-PCR analysis indicated two different nodulation-related CLE expression patterns, one linked with nodule primordium development and a new one linked with nodule maturation. Moreover, two GmCLE gene pairs, encoding group-III CLE peptides that were previously shown to be involved in AON, had a transient expression pattern during nodule development, were induced by the essential nodulation hormone cytokinin, and one pair was also slightly induced by the addition of nitrate. Hence, our data support the hypothesis that group-III CLE peptides produced in the nodules are involved in primordium homeostasis and intertwined in activating AON, but not in sustaining it

Chapter Identification and Application of Phenotypic and Molecular Markers for Abiotic Stress Tolerance in Soybean

Neurology & clinical neurophysiolog