Tolerant Sorghum Research Articles

Comparative Physiological, Biochemical and Transcript Response to Drought in Sorghum Genotypes

Sorghum [Sorghum bicolor (L.) Moench] is considered as an important staple crop in the tropical regions. However, the productivity of this useful crop is hindered by drought which contributes to significant yield reduction. The present study aimed to decipher the effects of drought stress on physiological, biochemical and gene expression changes in sorghum genotypes and to ascertain the differences in their response to drought stress. To achieve these objectives, six sorghum genotypes were grown in pot culture in a greenhouse, in a randomized complete block design and exposed to water stress treatment for 10 days. From the study, drought stress caused a significant (P < .05) reduction in plant height, leaf water and chlorophyll contents while the proline, malondialdehyde (MDA), soluble sugar, electrolyte leakage (EL), hydrogen peroxide (H2O2) and antioxidant enzymes activity increased significantly (P < .05) and differentially in all sorghum genotypes. Among the genotypes investigated, PI 585456 showed enhanced performance and was considered as the most tolerant to drought in relation to plant growth and water relation, membrane status, photosynthetic activity, ROS and osmolytes accumulation and antioxidant enzymes activity. Furthermore, the transcript expression analyses of different categories of drought-responsive genes, viz; antioxidant-related, osmolytes biosynthesis-related, dehydrin-related, photosystem-related and transcription-related were differentially upregulated in sorghum genotypes investigated. The results revealed the differences in metabolic response to drought among the genotypes, which accentuated the physiological, biochemical and molecular mechanism related to a specific response that may play a vital role in drought tolerance in sorghum.

Sorghum genotypes evaluation in drought-prone land of East Flores agroecosystem for biomass improvement with liquid organic fertilizer application

Drought tolerant sorghum varieties cultivation on dryland areas is one of the potential sources of plant biomass to be used for bioethanol production. East Nusa Tenggara which has a short month of rainfall and mainly consists of drought-prone areas is suitable for sorghum to thrive where most other food crops simply withered. Eleven sorghum genotypes were evaluated on the dry land of East Flores in East Nusa Tenggara with treatment in the different applications of organic liquid fertilizer. Results showed that genotypes values were significantly different in all traits observed, and the interaction factors between fertilizer and genotypes had a significant effect on all traits except panicle length and width. The application of liquid organic fertilizer, however, did not significantly affect traits in both plant and stem biomass. Super 2 genotype showed the highest stem biomass value and differed significantly compared to other genotypes, even though fertilized treatment obtained less yield (29.87 t.ha−1) compared to without fertilizer (44.11 t.ha−1). Pearson correlation between all observed traits showed that stem biomass was significantly highly correlated to various traits, such as number of internodes (r = 0.77), plant height (r = 0.74), stem diameter (r = 0.72), and plant biomass weight (r = 0.97).

Exogenous jasmonic acid and humic acid increased salinity tolerance of sorghum

AbstractSalinity limits germination and plant growth and development in 45 million ha worldwide. Techniques to overcome this problem are needed. This project investigated the effects of jasmonic acid (JA) (0, 5, and 10 mM JA) and humic acid (HA) (0, 3, and 6 g HA kg−1 soil) on growth and physiological parameters of forage sorghum (Sorghum bicolor L. Moench) under different NaCl salinity levels (0, 100, and 200 mM NaCl, with an equivalent electrical conductivity (EC) of 0.12 dSm−1 as control treatment, 3.22, and 5.78 dSm−1, respectively). NaCl salinity reduced emergence percentage, emergence rate, salt tolerance index and seedling vigor index, all seedling growth parameters, ascorbate peroxidase (APX) activity, chlorophyll a, b and total chlorophyll content. Proline content and soluble protein content were increased with salinity. At the 200 mM salinity level, seeds treated with 10 mM JA had a positive effect on emergence percentage, emergence rate, shoot length, total fresh weight, salt tolerance index, seedling vigor index, chlorophyll a and total chlorophyll content. At 200 mM NaCl salinity level, seeds treated with 6 g HA kg−1 soil had increased root length, total dry weight, salt tolerance index, seedling vigor index, shoot length, protein content, APX, chlorophyll b, and total chlorophyll in seedlings. The application of 5 mM JA combined with 6 g HA kg−1 soil was most effective in minimizing salinity stress. Our study suggested that the appropriate combined application of HA and JA could efficiently protect early seedlings from salt stress damage and alleviate abiotic stress.

QTL analysis of salt tolerance in Sorghum bicolor during whole‐plant growth stages

AbstractTo study the salt tolerance genetics of sorghum, 181 recombinant inbred lines (RILs) were used to locate quantitative trait loci (QTLs) underlying salt stress adaptability. Six traits, namely, plant height (PH), stem diameter (SD), total biomass (TB), stem fresh weight (SFW), juice weight (JW) and Brix, were investigated under normal and salt stress conditions in two years. A total of 53 QTLs for the six traits under both conditions and their corresponding salt tolerance index (STI) were detected and phenotypic variation explained (PVE) ranged from 4.16% to 20.42%. Six of the QTLs, qTB6, qSFW9, qJW9, qBrix2, qBrix10 and qSTI‐Brix9, were the main effect QTLs controlling salt tolerance and had a PVE more than 10%. qSFW9 and qJW9 colocalized in the same marker interval as SB5069‐UGSM18 and had PVEs of 17.70% and 14.20%, respectively, with positive effects from L‐Tian. QTL clusters controlling PH, TB, STI‐TB, SFW and JW were consistently mapped in the marker interval of Xcup19‐SB4177 on chromosome 7. These locations might serve as target sites for marker‐assisted selection (MAS) in improving salt tolerance of sorghum.

Multi-trait PGP rhizobacterial endophytes alleviate drought stress in a senescent genotype of sorghum [Sorghum bicolor (L.) Moench

Root-tissue colonizing bacteria demonstrated with multiple PGP traits from sorghum plants were identified as Ochrobactrum sp. EB-165, Microbacterium sp. EB-65, Enterobacter sp. EB-14 and Enterobacter cloacae strain EB-48 on the basis of 16S rRNA gene sequencing. Here, the in vivo experiments using ½-MS media and ½-MS media + 15% PEG 8000 (for inducing drought stress) indicated stress tolerance imparting ability of these rhizobacterial endophytes in a non-stay green and senescent genotype (R-16) of sorghum. In the experiment with sterile soilrite mix base, seed bacterization with these isolates showed improved plant growth specifically the roots, in terms of root length (~ 44.2 to 50.8% over controls), root dry weight (~ 91.3 to 99.8% over controls) and root surface area (~ 1 to 1.5 fold over controls) under drought stress. Rhizobacterial endophytes were successful, not only in providing better cellular osmotic adjustment in leaves (≥ 1-fold increase in proline accumulation over controls), but favorable physiological responses like Relative Water Content (RWC) and cell Membrane Stability Index (MSI) in the inoculated plants during the drought stress induction. Up-regulation of drought responsive genes like sbP5CS2 and sbP5CS1 was observed in these endophytes-treated plants as compared to untreated control and Escherichia coli DH5α (negative control)-treated plants. Interestingly, the stress imparting traits of rhizobacterial endophytes, including up-regulation of specific genes, were observed during sorghum seedling growth only under drought stresses. The results of this study lead to the conclusion that the potential endophytic rhizobacterial interactions can contribute to plant growth promotion as well as induced stress tolerance in sorghum.

Genetic Architecture of Chilling Tolerance in Sorghum Dissected with a Nested Association Mapping Population.

Dissecting the genetic architecture of stress tolerance in crops is critical to understand and improve adaptation. In temperate climates, early planting of chilling-tolerant varieties could provide longer growing seasons and drought escape, but chilling tolerance (<15°) is generally lacking in tropical-origin crops. Here we developed a nested association mapping (NAM) population to dissect the genetic architecture of early-season chilling tolerance in the tropical-origin cereal sorghum (Sorghum bicolor [L.] Moench). The NAM resource, developed from reference line BTx623 and three chilling-tolerant Chinese lines, is comprised of 771 recombinant inbred lines genotyped by sequencing at 43,320 single nucleotide polymorphisms. We phenotyped the NAM population for emergence, seedling vigor, and agronomic traits (>75,000 data points from ∼16,000 plots) in multi-environment field trials in Kansas under natural chilling stress (sown 30–45 days early) and normal growing conditions. Joint linkage mapping with early-planted field phenotypes revealed an oligogenic architecture, with 5–10 chilling tolerance loci explaining 20–41% of variation. Surprisingly, several of the major chilling tolerance loci co-localize precisely with the classical grain tannin (Tan1 and Tan2) and dwarfing genes (Dw1 and Dw3) that were under strong directional selection in the US during the 20th century. These findings suggest that chilling sensitivity was inadvertently selected due to coinheritance with desired nontannin and dwarfing alleles. The characterization of genetic architecture with NAM reveals why past chilling tolerance breeding was stymied and provides a path for genomics-enabled breeding of chilling tolerance.

Assessment of agro-morphological variability of dry-season sorghum cultivars in Chad as novel sources of drought tolerance

Dry-season sorghum is a type of sorghum whose establishment ends at the end of the rainy season and its development takes place during the dry and cold harmattan period. Its root system is particularly well developed with deep penetration for water withdrawal. This study was conducted to assess the level of genetic diversity present among dry-season sorghum in Chad’s Sudanese zone using phenotypic traits, and to identify new sources of drought tolerance that could be used in sorghum breeding programs. A high variability in qualitative traits was observed except for the botanical race which showed that all cultivars were of durra race. It was also observed that most cultivars had compact panicles (66.67%), mostly black glumes (66.67%), glume hairiness (58.33%) and did not have aristation (91.67%). Most qualitative traits showed a coefficient of variation of less than 30%, and the analysis of the variance showed that at 0.1% probability, there were significant differences between cultivars for all traits except botanical race. It was observed that the potential productivity of dry-season sorghum of this collection was strongly related to their staygreen characteristic; a trait of enormous importance in breeding for postflowering drought tolerance in sorghum. Plant height was highly heritable (91.9%), followed by the peduncle length (90.2%), panicle length (87.5%) and the internodes number (86.5%). Structuring of diversity separated the cultivars into four statistically distinct groups; with group 2 clustering cultivars with panicle productivity, early maturity and high staygreen, and other traits that contribute to the performance of cultivars. The findings will help to enhance the selection and production of dry-season sorghum in Chad and also provide alternative sources for staygreen introgression into the larger sorghum breeding community.

Rhizobacteria-induced systemic tolerance against drought stress in Sorghum bicolor (L.) Moench

Induction of systemic tolerance in sorghum [Sorghum bicolor (L.) Moench] against drought stress was studied by screening a large collection of rhizobacterial isolates for their potential to exhibit this essential plant growth-promoting trait. This was done by means of a greenhouse assay that measured the relative change in both plant height and -biomass (roots and shoots) between rhizobacteria-primed versus non-primed (naïve) plants under drought stress conditions. In order to elucidate the metabolomic changes in S. bicolor that conferred the drought stress tolerance after treatment (priming) with selected isolates, untargeted ultra-high performance liquid chromatography-high definition mass spectrometry (UHPLC-HDMS)-based metabolomics was carried out. Intracellular metabolites were methanol-extracted from rhizobacteria-primed and naïve S. bicolor roots and shoots. Extracts were analysed on a UHPLC-HDMS system and the generated data were chemometrically mined to determine signatory metabolic profiles and bio-markers related to induced systemic tolerance. The metabolomic results showed significant treatment-related differential metabolic reprogramming between rhizobacteria-primed and naïve plants, correlating to the ability of the selected isolates to protect S. bicolor against drought stress. The selected isolates, identified by means of 16S rRNA gene sequencing as members of the genera Bacillus and Pseudomonas, were screened for 1-aminocyclopropane-1-carboxylate (ACC) deaminase activity by means of an in vitro assay and the presence of the acdS gene was subsequently confirmed by PCR for strain N66 (Pseudomonas sp.). The underlying key metabolic changes in the enhanced drought stress tolerance observed in rhizobacteria-primed S. bicolor plants included (1) augmented antioxidant capacity; (2) growth promotion and root architecture modification as a result of the upregulation of the hormones gibberellic acid, indole acetic acid and cytokinin; (3) the early activation of induce systemic tolerance through the signalling hormones brassinolides, salicylic acid and jasmonic acid and signalling molecules sphingosine and psychosine; (4) the production of the osmolytes proline, glutamic acid and choline; (5) the production of the epicuticular wax docosanoic acid and (6) ACC deaminase activity resulting in lowered ethylene levels. These results unravelled key molecular details underlying the PGPR-induced systemic tolerance in sorghum plants, providing insights for the plant priming for abiotic stress.

Transcriptomic analysis of a Sorghum bicolor landrace identifies a role for beta-alanine betaine biosynthesis in drought tolerance

Sorghum is indigenous to Africa and a remarkably drought tolerant cereal crop. In this study, the genetic response mechanisms involved in sorghum's tolerance to progressive water deficit and re-watering were investigated in a South African landrace (designated LR6), using cDNA microarrays comprising 35,899 transcript probes. Significant differential expression of 902 transcripts, including 128 transcripts with currently unknown functions, was altered in response to progressive water stress and re-watering. The modulated sorghum genes had homology to proteins involved in growth, regulation, and protection. Gene Ontology (GO) analysis identified significant enrichment of 26 genes involved in the ‘response to abiotic stimulus’ GO category during severe stress. The expression of two genes associated with beta(β)-alanine betaine biosynthesis was validated with quantitative RT-PCR. Importantly, the detection of β-alanine betaine in sorghum leaf extracts using NMR spectroscopy, and the significant increase in relative abundance during severe stress supports the microarray and qRT-PCR findings, thereby highlighting a role for β-alanine betaine biosynthesis in drought tolerance of sorghum. In future, crop improvement initiatives that consider metabolic engineering of the β-alanine betaine biosynthesis pathway should be explored.

A high throughput method for screening deep-seeding tolerance in sorghum

Low soil moisture is a major abiotic stress wide spread in arid and semi-arid regions, limiting both seed germination and seedling establishment. Deep-seeding technique allows seeds to use the moisture in deep soil, however, most sorghum seeds cannot penetrate soil layer of 10 cm or deeper. To develop sorghum varieties tolerant to deep-seeding, it is necessary to identify promising accessions with good agronomic traits and tolerance to deep-seeding. A high throughput hydroponic method was developed to screen sorghum accessions with long mesocotyl under dark conditions. This method revealed large genetic variations for mesocotyl length in the panel of 105 sorghum accessions, which were validated by soil culture and deep-seeding experiments. The lines with long mesocotyl under hydroponic culture had good seedling establishments in deep-seeding experiments, while the lines with short mesocotyl length could not emerge. Compared to conventional sand or soil cultural methods, the hydroponic culture was highly efficient that requires less time, space, and labor. The mesocotyl lengths of screened sorghum accessions under the newly developed hydroponic method were highly correlated with soil culture and germination rate under deep-seeding in soil. As an efficient screening tool for the mesocotyl lengths under soil culture and the seedling emergence rates from deep soil layer, the hydroponic culture method can be easily integrated in breeding programs targeting deep-seeding tolerance. Breeding for long mesocotyl sorghum varieties may lead to good seedling establishments under arid and semi-arid regions.

Evaluation of Morphological and Biochemical Characteristics of Sorghum [Sorghum bicolor [L.] Moench] Varieties in Response Salinity Stress

Salinity is among the most severe and widespread environmental constrains to global crop production, especially in arid and semi-arid climates and negatively affecting productivity of salt sensitive crop species. Breeding and selection of salt tolerant crop varieties is therefore necessary for sustainable plant productivity. Given that germination and seeding phases are the most critical phase in the plant life cycle, this study aimed to evaluate seed germination potential and associated traits under salt stress conditions as a simple approach to identify salt tolerant sorghum varieties [Gadam, Sc Sila and Serena] which are adaptated to various agroecological regions. Salinity stress was applied by addition of NaCl at three different levels of stress [100, 200 and 300 mM NaCl], while plants irrigated with water were used as control. Evaluation of tolerance was performed on the basis of germination percentage, shoot and seed water absorbance, shoot and root length, leave water content, seedling total chlorophyll content and morphologic abnormality. Our results showed that salinity stress significantly impacts all features associated with germination and early development of seedlings. Our results indicated that salinity stress substantially affects all traits associated with germination and early seedling growth, with the effect of salinity being dependent on the variety used and level of salinity stress applied. Among the tested sorghum varieties, Gadam was established to the most salt tolerant variety, suggesting its potential use for cultivation under salinity stress conditions as well as its suitability for use as germplasm material in future sorghum breeding programmes. For a greater insight into comprehensive mechanisms of salinity tolerance in sorghum, we suggest further research on genomic and molecular analysis.

Reproductive Cold Stress Tolerance in Sorghum F1 Hybrids is a Heterotic Trait

The sensitivity of sorghum to pre-flowering cold stress, resulting in reduced pollen viability and poor seed set, is a major constraint for expanding growing areas into higher altitudes and latitudes. Nevertheless, compared to juvenile cold tolerance, reproductive cold tolerance in sorghum has received much less attention so far, and very little is known about its inheritance in F1-hybrids. We have composed a representative factorial (n = 49 experimental F1-hybrids) for a comprehensive study on heterosis and combining ability for crucial tolerance traits as spikelet fertility (panicle harvest index), seed yield and pollen viability, using field trials in stress- and control environments in Germany and Mexico as well as climate chamber experiments. Our results indicate a heterotic and rather dominant inheritance of reproductive cold tolerance in sorghum, with strong effects of female general combining ability (GCA) on F1-hybrid performance in our material. These findings, together with the comparatively low contribution of specific combining ability (SCA) effects and high heritability estimates, suggest that robust and efficient enhancement of reproductive cold tolerance is feasible via hybrid breeding.

Transcriptomic profiling of sorghum leaves and roots responsive to drought stress at the seedling stage

Drought stress affects the growth and productivity of crop plants including sorghum. To study the molecular basis of drought tolerance in sorghum, we conducted the transcriptomic profiling of sorghum leaves and roots under drought stress using RNA-Seq method. A total of 510, 559, and 3 687 differentially expressed genes (DEGs) in leaves, 3 368, 5 093, and 4 635 DEGs in roots responding to mild drought, severe drought, and re-watering treatments were identified, respectively. Among them, 190 common DEGs in leaves and 1 644 common DEGs in roots were responsive to mild drought, severe drought, and re-watering environment. Gene Ontology (GO) enrichment analysis revealed that the GO categories related to drought tolerance include terms related to response to stimulus especially response to water deprivation, abscisic acid stimulus, and reactive oxygen species. The major transcription factor genes responsive to drought stress include heat stress transcription factor (HSF), ethylene-responsive transcription factor (ERF), Petunia NAM, Arabidopsis ATAF1/2 and CUC2 (NAC), WRKY transcription factor (WRKY), homeodomain leucine zipper transcription factor (HD-ZIP), basic helix-loop-helix transcription factor (bHLH), and V-myb myeloblastosis viral oncogene homolog transcription facotr (MYB). Functional protein genes for heat shock protein (HSPs), late-embryogenesis-abundant protein (LEAs), chaperones, aquaporins, and expansins might play important roles in sorghum drought tolerance. Moreover, the genomic regions enriched with HSP, expansin, and aquaporin genes responsive to drought stress could be used as powerful targets for improvement of drought tolerance in sorghum and other cereals. Overall, our results provide a genome-wide analysis of DEGs in sorghum leaves and roots under mild drought, severe drought, and re-watering environments. This study contributes to a better understanding of the molecular basis of drought tolerance of sorghum and can be useful for crop improvement.

Molecular genetic studies on abiotic stress resistance in sorghum entries through using half diallel analysis and inter-simple sequence repeat (ISSR) markers

BackgroundWater deficit stress is considered as one of the most important environmental stresses which is more harmful to strategic crops, as it reduces the final crop yield by up to 40%. Therefore, the aim of this research is to evaluate some promising and superior sorghum entries for water stress tolerance and determine the most agro-morphological parameters and reasons responsible for drought tolerance in this regard.ResultsFifteenth sorghum genotypes (five parents and their ten F1 crosses resulting from half diallel analysis) were used in this investigation under two levels of irrigation (normal and drought experiment). The recent genotypes were estimated through some physiological parameters related to water stress tolerance in sorghum; besides that, eight inter-simple sequence repeat (ISSR) primers were used to identify among the five sorghum parents and the highest five crosses resistance to water deficit conditions depending on the data calculated from all studied traits under both conditions. The following genotypes P1, P2, P3, P1 × P2, P1 × P3, P2 × P3, P2 × P4, and P3 × P4 confirmed high resistance to water deficit conditions under the drought treatment compared with the control. This high resistance was affirmed through the calculated data for all studied traits. The ISSR profile analysis showed 151 fragments as taxonomic divisions among the ten sorghum genotypes (38 of them were monomorphic and 113 polymorphic with 74.83% polymorphism).ConclusionThe entries (P1, P2, P3, P1 × P2, P1 × P3, P2 × P3, P2 × P4, and P3 × P4) were succeeded in achieving the highest concept of water deficit resistance under both conditions. Therefore, this work will be the nucleus for producing resistant sorghum varieties for drought stress in the future.

Transcriptome analysis reveals candidate genes related to phosphorus starvation tolerance in sorghum

BackgroundPhosphorus (P) deficiency in soil is a worldwide issue and a major constraint on the production of sorghum, which is an important staple food, forage and energy crop. The depletion of P reserves and the increasing price of P fertilizer make fertilizer application impractical, especially in developing countries. Therefore, identifying sorghum accessions with low-P tolerance and understanding the underlying molecular basis for this tolerance will facilitate the breeding of P-efficient plants, thereby resolving the P crisis in sorghum farming. However, knowledge in these areas is very limited.ResultsThe 29 sorghum accessions used in this study demonstrated great variability in their tolerance to low-P stress. The internal P content in the shoot was correlated with P tolerance. A low-P-tolerant accession and a low-P-sensitive accession were chosen for RNA-seq analysis to identify potential underlying molecular mechanisms. A total of 2089 candidate genes related to P starvation tolerance were revealed and found to be enriched in 11 pathways. Gene Ontology (GO) enrichment analyses showed that the candidate genes were associated with oxidoreductase activity. In addition, further study showed that malate affected the length of the primary root and the number of tips in sorghum suffering from low-P stress.ConclusionsOur results show that acquisition of P from soil contributes to low-P tolerance in different sorghum accessions; however, the underlying molecular mechanism is complicated. Plant hormone (including auxin, ethylene, jasmonic acid, salicylic acid and abscisic acid) signal transduction related genes and many transcriptional factors were found to be involved in low-P tolerance in sorghum. The identified accessions will be useful for breeding new sorghum varieties with enhanced P starvation tolerance.

Exogenous spermidine enhances expression of Calvin cycle genes andphotosynthetic efficiency in sweet sorghum seedlings under salt stress

Salinity adversely affects plants resulting in disruption to plant growth and physiology. Previously, it has been shown that these negative effects can be alleviated by various exogenous polyamines. However, the role of spermidine (Spd) in conferring salinity tolerance in sorghum is not well documented. The effect of exogenous Spd on the responses of sweet sorghum (Sorghum bicolor L.) seedlings to salt stress (150 mM NaCl) was investigated by measuring photosynthetic carbon assimilation, Calvin cycle enzyme activities, and the the expression of respective genes. Application of 0.25 mM Spd alleviated the negative effects of salt stress on efficiency of photosystem II and CO2 assimilation and increased the activities of ribulose 1,5-bisphosphate carboxylase/oxygenase (Rubisco) and aldolase. Salt stress significantly lowered the transcriptions of genes encoding Rubisco large subunit, Rubisco small subunit, 3-phosphoglyceric acid kinase, glyceraldehyde-3-phosphate dehydrogenase, triose-3-phosphate isomerase, fructose-1,6-bisphosphate aldolase, fructose-1,6-bisphosphate phosphatase, and sedoheptulose-1,7-bisphosphatase. However, transcriptions of genes encoding phosphoribokinase and Rubisco were up-regulated. The Spd application enhanced expressions of most of these genes. It appears Spd conferred salinity tolerance to sweet sorghum seedlings by enhancing photosynthetic efficiency through regulation of gene expressions and activities of key CO2 assimilation enzymes.

The leaf-air temperature difference reflects the variation in water status and photosynthesis of sorghum under waterlogged conditions.

Waterlogging stress is one of the most important abiotic stresses limiting sorghum growth and development. Consequently, the responses of sorghum to waterlogging must be monitored and studied. This study investigated changes in the leaf water status, xylem exudation rate, leaf anatomical structure, leaf temperature and photosynthetic performance. Waterlogging-tolerant (Jinuoliang 01, abbreviated JN01) and waterlogging-sensitive (Jinza 31, abbreviated JZ31) sorghum cultivars were planted in pots. The experiment was carried out using a split block design with three replications. Waterlogging stress was imposed at the sorghum five-leaf stage. The leaf free water content (FWC) and relative water content (RWC) decreased under the waterlogged condition. The leaf thickness was thinner under the waterlogged condition, and the main changes occurred in the upper epidermal and mesophyll cells. Gas exchange parameters and the xylem exudation rate were also restrained by waterlogging; however, greater responses of these parameters were observed in JZ31. JZ31 had a higher leaf-air temperature difference (ΔT) than JN01. We found that changes in ΔT were always consistent with changes in the RWC and the gas exchange parameters. ΔT was significantly associated with the leaf RWC, photosynthetic rate (Pn) and transpiration rate (Tr). The results suggest that ΔT may be an indicator reflecting the water status in leaves and can be used to evaluate the tolerance of sorghum to waterlogging.

New candidate loci and marker genes on chromosome 7 for improved chilling tolerance in sorghum.

Sorghum is often exposed to suboptimal low temperature stress under field conditions, particularly at the seedling establishment stage. Enhancing chilling tolerance will facilitate earlier planting and so minimize the negative impacts of other stresses experienced at later growth stages. Genome-wide association mapping was performed on a sorghum association panel grown under control (30/20 °C; day/night) and chilling (20/10 °C) conditions. Genomic regions on chromosome 7, controlling the emergence index and seedling (root and shoot) vigor, were associated with increased chilling tolerance but they did not co-localize with undesirable tannin content quantitative trait loci (QTLs). Shoot and root samples from highly contrasting haplotype pairs expressing differential responses to chilling stress were used to identify candidate genes. Three candidate genes (an alpha/beta hydrolase domain protein, a DnaJ/Hsp40 motif-containing protein, and a YTH domain-containing RNA-binding protein) were expressed at significantly higher levels under chilling stress in the tolerant haplotype compared with the sensitive haplotype and BTx623. Moreover, two CBF/DREB1A transcription factors on chromosome 2 showed a divergent response to chilling in the contrasting haplotypes. These studies identify haplotype differences on chromosome 7 that modulate chilling tolerance by either regulating CBF or feeding back into this signaling pathway. We have identified new candidate genes that will be useful markers in ongoing efforts to develop tannin-free chilling-tolerant sorghum hybrids.

Genetic gain of Al tolerance and contribution of agronomic traits on Al tolerance in the early stage of sorghum breeding program

ABSTRACT Genetic gain (GG), heritability and contribution of the agronomic traits on Al tolerance are precious information for selection strategy in the breeding of Al-tolerant sorghum. The objectives of this study were (i) to estimate the GG of Al tolerance in sorghum and (ii) to determine the direct effect of agronomic traits on Al tolerance through path analysis. Evaluation of agronomic characters used F2, and F3 sorghum progenies in field experiment and screening of Al tolerance used the hematoxylin-staining method. Three sorghum populations showed the low GG of Al tolerance (GG = 0.558–1.108). This result indicates that high allocation of progenies in the early stages of the Al-tolerant breeding program and high selection differential (sd) of Al tolerance should be applied to obtain a higher gain of Al tolerance. Selection pressure for early maturity (sd = −2.942) and short plant height (PH) (sd = −38.165) resulted in lower improvement of GG for Al tolerance. The high dry weight and tall PH provided a more genetic contribution to the advancement of Al tolerance. Based on the overall path analysis data, the increase of plant biomass, the significant number of progenies in the early stage of breeding and strong sd of Al tolerance would be more appropriate to improve the Al tolerance in sorghum.

Physiological and Biochemical Analyses of Sorghum Varieties Reveal Differential Responses to Salinity Stress

ABSTRACT Salinity is among the most severe and widespread environmental constrains to global crop production, especially in arid and semi-arid climates and negatively affecting productivity of salt sensitive crop species. Breeding and selection of salt tolerant crop varieties is therefore necessary for sustainable plant productivity. Given that germination and seeding phases are the most critical phase in the plant life cycle, this study aimed to evaluate seed germination potential and associated traits under salt stress conditions as a simple approach to identify salt tolerant Sorghum varieties. There Sorghum varieties whose adaptation to various agroclimatic conditions is not well elucidated. Salinity stress was applied by addition of NaCl at three different levels of stress (100, 200 and 300 mM NaCl), while plants irrigated with water were used as controls. Evaluation of tolerance was performed on the basis of germination percentage, shoot and seed water absorbance, shoot and root length, leave water content, seedling total chlorophyll content and morphologic abnormality. Our results showed that salinity stress significantly impacts all features associated with germination and early development of seedlings. Our results indicated that that salinity stress substantially affects all traits associated with germination and early seedling growth, with the effect of salinity being dependent on the variety used and level of salinity stress applied. Among the tested Sorghum varieties, Gadam was established to the most salt tolerant variety, suggesting its potential use for cultivation under salinity stress conditions as well as its suitability for use as germplasm material in future Sorghum breeding programmes. For a greater insight into comprehensive mechanisms of salinity tolerance in Sorghum, we suggest further research on genomic and molecular analysis.