Genetic dissection of early-season cold tolerance in sorghum (<Emphasis Type="Italic">Sorghum bicolor</Emphasis> (L.) Moench)

Soil temperatures at 15°C or below limit germination and seedling establishment for warm season cereal crops such as sorghum (Sorghum bicolor (L.) Moench) during early-season planting. To better understand the genetics of early-season cold tolerance in sorghum, mapping of quantitative trait loci (QTL) associated with germination, emergence and vigor using a recombinant inbred mapping population was carried out. A mapping population consisting of 171 F₇–F₈ recombinant inbred lines (RILs) derived from the cross between RTx430 (cold-sensitive) and PI610727 (cold-tolerant) was developed and a genetic map was constructed using 141 microsatellites or simple sequence repeat (SSR) markers. The RILs were evaluated for cold and optimal temperature germinability in the laboratory, field emergence, and seedling vigor in two locations during early-season planting. Two or more QTL were detected for all traits, except for seedling vigor, with only one QTL was detected in the population. A QTL for cold germinability (Germ 12-2.1) showed the highest LOD value and was also associated with optimal germinability. One of the QTL for field emergence, Fearlygerm-9.3, a contribution from PI610727, was found significant in both locations used for the study. This study showed alignment of QTL in SBi1 (Fearlygerm-1.2 and FGerm30-1.2) with previously reported QTL associated with late field emergence identified from a different mapping population. This indicates that PI617027 shares some common loci with other known early-season cold-tolerant sorghum germplasm but also harbors novel QTL that could be useful in introgression of enhanced laboratory germination and early-season field emergence.     

Characterization,development and mapping of Unigene-derived microsatellite markers in sorghum [<Emphasis Type="Italic">Sorghum bicolor</Emphasis> (L.) Moench]

Molecular variation within known genes controlling specific functions provide candidate gene-based markers which are tightly linked with the trait of interest. Unigene-derived microsatellite markers, with their unique identity and positions, offer the advantage of unraveling variation in the expressed component of the genome. We characterized ≥12-bp-long microsatellite loci from 13,899 unique sequences of sorghum [Sorghum bicolor (L.) Moench] available in the NCBI unigene database for their abundance and possible use in sorghum breeding. Analysis of 12,464 unigenes (≥200-bp) using MISA software identified 14,082 simple sequence repeats (SSRs) in 7,370 unigenes, from which 1,519 unigene SSR markers were developed. The average frequency of SSR was 1 per1.6 kb and 1.0 per 1.1 unigene; hexamers followed by trimers were found in abundance, of which 33.3% AT-rich and CCG repeats were the most abundant. Of the 302 unigene SSRs tested, 60 (19.8%) were polymorphic between the two parents, M35-1 and B35 of a recombinant inbred line (RIL) mapping population. A mapping population consisting of 500 RILs was developed using the above two parents, and a subset of random 245 RILs was used for genotyping with polymorphic SSRs. We developed a linkage map containing 231 markers, of which 228 (174 genomic and 54 genic) were microsatellites and three were morphological markers. Markers were distributed over 21 linkage groups, and spanned a genetic distance of 1235.5 cM. This map includes 81 new SSRs, of which 35 (21 unigene and 14 genomic) were developed in the present study and 46 from other studies. The order of the SSR markers mapped in the present study was confirmed physically by BLAST search against the whole-genome shotgun sequence of sorghum. Many unigene sequences used for marker development in this study include genes coding for important regulatory proteins and functional proteins that are involved in stress-related metabolism. The unigene SSR markers used together with other SSR markers to construct the sorghum genetic map will have applications in studies on comparative mapping, functional diversity analysis and association mapping, and for quantitative trait loci detection for drought and other agronomically important traits in sorghum.     

Identification of quantitative trait loci for resistance to shoot fly in sorghum [<Emphasis Type="Italic">Sorghum bicolor</Emphasis> (L.) Moench]

The shoot fly is one of the most destructive insect pests of sorghum at the seedling stage. Deployment of cultivars with improved shoot fly resistance would be facilitated by the use of molecular markers linked to QTL. The objective of this study was to dissect the genetic basis of resistance into QTL, using replicated phenotypic data sets obtained from four test environments, and a 162 microsatellite marker-based linkage map constructed using 168 RILs of the cross 296B (susceptible) × IS18551 (resistant). Considering five component traits and four environments, a total of 29 QTL were detected by multiple QTL mapping (MQM) viz., four each for leaf glossiness and seedling vigor, seven for oviposition, six for deadhearts, two for adaxial trichome density and six for abaxial trichome density. The LOD and R ² (%) values of QTL ranged from 2.6 to 15.0 and 5.0 to 33%, respectively. For most of the QTL, IS18551 contributed resistance alleles; however, at six QTL, alleles from 296B also contributed to resistance. QTL of the related component traits were co-localized, suggesting pleiotropy or tight linkage of genes. The new morphological marker Trit for trichome type was associated with the major QTL for component traits of resistance. Interestingly, QTL identified in this study correspond to QTL/genes for insect resistance at the syntenic maize genomic regions, suggesting the conservation of insect resistance loci between these crops. For majority of the QTL, possible candidate genes lie within or very near the ascribed confidence intervals in sorghum. Finally, the QTL identified in the study should provide a foundation for marker-assisted selection (MAS) programs for improving shoot fly resistance in sorghum.     

Development of marker-free transgenic sorghum [<Emphasis Type="Italic">Sorghum bicolor</Emphasis> (L.) Moench] using standard binary vectors with <Emphasis Type="Italic">bar</Emphasis> as a selectable marker

We report an Agrobacterium-mediated transformation system that can generate marker-free transgenic sorghum [Sorghum bicolor (L.) Moench] from a public line [P898012] using standard binary vectors with bar as a selectable marker. Eight co-cultivation conditions were examined for their effect on transformation. The average transformation frequencies were 0.4 and 0.7% for pZY101-TC2 and pZY101-SKRS, respectively, derived from binary vector pZY102 and containing bar and target gene(s) in separate T-DNA regions. A low selection pressure (2.5 mg l⁻¹ DL-phosphinothrithin, PPT) was deployed during callus induction in combination with rapid selection to generate plants from 80 independent events, all but three of which were fertile and set seed. PCR and Southern analyses showed that 36 out of 80 events contained both bar and the target gene(s) (an average co-transformation frequency of 45%). Seedlings of the T1 generation transmitted T-DNAs with target gene(s) and bar gene independently, generating a fraction of progeny with only the target gene(s).     

Genetic diversity assessment in Somali sorghum (<Emphasis Type="Italic">Sorghum bicolor</Emphasis> (L.) Moench) accessions using microsatellite markers

In the north-western region of Somalia, bordering Ethiopia, sorghum represents an important resources for human and animal nutrition. The critical situation of Somalia is threatening the preservation of this valuable resource and it becomes urgent to develop a strategy of correct evaluation of the sorghum germplasm in order to promote conservation and preservation programs. Microsatellites, also known as Simple Sequence Repeats (SSRs), are reproducible molecular markers useful in assessing the level of genetic diversity of plants. A total of 5 sorghum SSR-specific primer pairs were used to assess the genetic diversity of Somali sorghum landraces. Extensive variation was found at the microsatellite loci analysed, except for a locus that resulted in a monomorphic for some accessions. Considerable differences were found between total and effective number of alleles indicating non uniform allele frequency. Moreover allele frequency at a single locus significantly changed among accessions. Total gene diversity calculated for each locus ranged from 0.44 to 0.79. Most of the genetic diversity occurred within accessions demonstrating that accessions are not under selection processes and/or there is a continuous exchange of genes between sorghum populations. In any case, the patterns of clustering were significantly affected by the presence/absence of some alleles with high discriminant weight. Accessions Carabi, Abaadiro, Masego Cas and Masego Cad represent distinct genotypes confirming finding observed in previous phenotypic studies. The results highlight the central role of local farmers in maintaining and shaping local germplasm.     

Arbuscular mycorrhizal fungi-parasite-host interaction for the control of<Emphasis Type="Italic"> Striga hermonthica</Emphasis> (Del.) Benth. in sorghum [<Emphasis Type="Italic">Sorghum bicolor</Emphasis> (L.) Moench]

Five Glomus species (G. intraradices, G. albidum, G. mosseae, G. fasciculatum, and G. etunicatum) were compared against a check [without arbuscular mycorrhizal (AM) fungi, plus Striga] and control (without AM fungi or Striga) treatments for the control of Striga in a tolerant sorghum variety (War-wara bashi) in an experiment carried out in 12-cm-diameter clay pots. The experiment was carried out in a controlled growth chamber. G. mosseae significantly reduced the number of Striga emerging per plant, increased plant growth, shoot and total dry matter yield of sorghum, did not affect the root dry matter compared with the other AM fungi species, but had a comparable effect to the control treatment. All the AM fungi except G. mosseae, and also the Striga-infested treatment, increased the root:shoot ratio compared to the control treatment. The percent reduction (62%) of Striga emergence after G. mosseae inoculation resulted in about a 30% increase in total dry matter yield of sorghum over the control, while the total loss in dry matter yield of sorghum due to Striga infestation was 36%. Root colonization of sorghum by AM fungi was highest for G. mosseae (44%) followed by G. intraradices (24%) and G. albidum (23%) then G. fasciculatum (18%), with the lowest recorded for G. etunicatum (14%). No colonization of Striga roots was observed. The potential of AM fungi to reduce or to compensate for Striga infestation could be important for soil management, especially in the tropics, and for the reduction of Striga-resistant varieties of sorghum which are mycorrhiza-responsive.     

Identification and validation of genomic regions that affect shoot fly resistance in sorghum [<Emphasis Type="Italic">Sorghum bicolor</Emphasis> (L.) Moench]

Shoot fly is one of the most important pests affecting the sorghum production. The identification of quantitative trait loci (QTL) affecting shoot fly resistance enables to understand the underlying genetic mechanisms and genetic basis of complex interactions among the component traits. The aim of the present study was to detect QTL for shoot fly resistance and the associated traits using a population of 210 RILs of the cross 27B (susceptible) × IS2122 (resistant). RIL population was phenotyped in eight environments for shoot fly resistance (deadheart percentage), and in three environments for the component traits, such as glossiness, seedling vigor and trichome density. Linkage map was constructed with 149 marker loci comprising 127 genomic-microsatellite, 21 genic-microsatellite and one morphological marker. QTL analysis was performed by using MQM approach. 25 QTL (five each for leaf glossiness and seedling vigor, 10 for deadhearts, two for adaxial trichome density and three for abaxial trichome density) were detected in individual and across environments. The LOD and R ² (%) values of QTL ranged from 2.44 to 24.1 and 4.3 to 44.1%, respectively. For most of the QTLs, the resistant parent, IS2122 contributed alleles for resistance; while at two QTL regions, the susceptible parent 27B also contributed for resistance traits. Three genomic regions affected multiple traits, suggesting the phenomenon of pleiotrophy or tight linkage. Stable QTL were identified for the traits across different environments, and genetic backgrounds by comparing the QTL in the study with previously reported QTL in sorghum. For majority of the QTLs, possible candidate genes were identified. The QTLs identified will enable marker assisted breeding for shoot fly resistance in sorghum.     

Fine Mapping of <Emphasis Type="Italic">qDor7</Emphasis>, a Major QTL Affecting Seed Dormancy in Sorghum (<Emphasis Type="Italic">Sorghum bicolor</Emphasis> (L.) Moench)

Seed dormancy is a key domestication trait for major crops, which is acquired in long-term systems development processes and enables the survival of plants in adverse natural conditions. It is a complex trait under polygenic control and is affected by endogenous and environmental factors. In the present study, a major seed dormancy QTL in sorghum (Sorghum bicolor (L.) Moench), qDor7, detected previously, was fine mapped using a large, multi-generational population. The qDor7 locus was delimited to a 96-kb region which contains 16 predicted gene models. These results lay a solid foundation for cloning qDor7. In addition, the functional markers tightly linked to the seed dormancy QTL may be used in marker-assisted selection for seed dormancy in sorghum.     

Molecular tagging and validation of microsatellite markers linked to the low germination stimulant gene (<Emphasis Type="Italic">lgs</Emphasis>) for <Emphasis Type="Italic">Striga</Emphasis> resistance in sorghum [<Emphasis Type="Italic">Sorghum bicolor</Emphasis> (L.) Moench]

Striga is a devastating parasitic weed in Africa and parts of Asia. Low Striga germination stimulant activity, a well-known resistance mechanism in sorghum, is controlled by a single recessive gene (lgs). Molecular markers linked to the lgs gene can accelerate development of Striga-resistant cultivars. Using a high density linkage map constructed with 367 markers (DArT and SSRs) and an in vitro assay for germination stimulant activity towards Striga asiatica in 354 recombinant inbred lines derived from SRN39 (low stimulant) × Shanqui Red (high stimulant), we precisely tagged and mapped the lgs gene on SBI-05 between two tightly linked microsatellite markers SB3344 and SB3352 at a distance of 0.5 and 1.5 cM, respectively. The fine-mapped lgs region was delimited to a 5.8 cM interval with the closest three markers SB3344, SB3346 and SB3343 positioned at 0.5, 0.7 and 0.9 cM, respectively. We validated tightly linked markers in a set of 23 diverse sorghum accessions, most of which were known to be Striga resistant, by genotyping and phenotyping for germination stimulant activity towards both S. asiatica and S. hermonthica. The markers co-segregated with Striga germination stimulant activity in 21 of the 23 tested lines. The lgs locus similarly affected germination stimulant activity for both Striga species. The identified markers would be useful in marker-assisted selection for introgressing this trait into susceptible sorghum cultivars. Examination of the sorghum genome sequence and comparative analysis with the rice genome suggests some candidate genes in the fine-mapped region (400 kb) that may affect strigolactone biosynthesis or exudation. This work should form a foundation for map-based cloning of the lgs gene and aid in elucidation of an exact mechanism for resistance based on low Striga germination stimulant activity.     

Method for Label-Free Quantitative Proteomics for <Emphasis Type="Italic">Sorghum bicolor</Emphasis> L. Moench

Sorghum (Sorghum bicolor L. Moench) is a rapidly emerging high biomass feedstock for bioethanol and lignocellulosic biomass production. The robust varietal germplasm of sorghum and its completed genome sequence provide the necessary genetic and molecular tools to study and engineer the biotic/abiotic stress tolerance. Traditional proteomics approaches for outlining the sorghum proteome have many limitations like, demand for high protein amounts, reproducibility and identification of only few differential proteins. In this study, we report a gel-free, quantitative proteomic method for in-depth coverage of the sorghum proteome. This novel method combining phenol extraction and methanol chloroform precipitation gives high total protein yields for both mature sorghum root and leaf tissues. We demonstrate successful application of this method in comparing proteomes of contrasting cultivars of sorghum, at two different phenological stages. Protein identification and relative quantification analyses were performed by a label-free liquid chromatography tandem mass spectrometry (LC/MS-MS) analyses. Several unique proteins were identified respectively from sorghum tissues, specifically 271 from leaf and 774 from root tissues, with 193 proteins common in both tissues. Using gene ontology analysis, the differential proteins identified were finely corroborated with their leaf/root tissue specific functions. This method of protein extraction and analysis would contribute substantially to generate in-depth differential protein data in sorghum as well as related species. It would also increase the repertoire of methods uniquely suited for gel-free plant proteomics that are increasingly being developed for studying abiotic and biotic stress responses.     

High copper levels improve callus induction and plant regeneration in <Emphasis Type="Italic">Sorghum bicolor</Emphasis> (L.) Moench

Summary A highly efficient protocol for callus induction and plant regeneration in Sorghum bicolor was developed by varying the concentrations of copper (0.1, 0.3, 0.5, 0.7, 1, 1.5, 2.5 μM) in Murashige and Skoog (MS) medium. The mature embryos of Sorghum bicolor were cultured on MS medium containing 2,4-dichlorophenoxyacetic acid (9μM), kinetin (2.3 μM), and 3% (w/v) sucrose for embryogenic callus induction. Plant regeneration from this callus occurred on MS medium containing kinetin (9.2 μM) and indole-3-acetic acid (2.85 μM). A much greater response was noted on these media with higher levels of copper. Frequency of plant regeneration and number of regenerants dramatically increased with an optimal amount of copper (2 μM) in the MS medium. Rooting of the regenerated shoots readily occurred on half-strength MS medium supplemented with α-naphthaleneacetic acid (10.7 μM) and 3% (w/v) sucrose. Well-developed plantlets were transferred to the field where 100% survival and normal seed setting was noted.     

Genome-wide identification and cadmium induced expression profiling of sulfate transporter (<Emphasis Type="Italic">SULTR</Emphasis>) genes in sorghum (<Emphasis Type="Italic">Sorghum bicolor</Emphasis> L.)

Sulfur is an essential element for all living organisms. Plants can convert inorganic sulfur into organic sulfur compounds by complex enzymatic steps. In this study, we conducted a genome-wide analysis of sulfate transporter genes (SULTRs) in the sorghum (Sorghum bicolor) genome and examined expression profiles of SbSULTR genes under 200 µM cadmium (Cd) exposure. As a result of sorghum genome analysis, 11 SULTR genes were identified, including SbSULTR1;1, SbSULTR1;2, SbSULTR1;3, SbSULTR2;1, SbSULTR2;2, SbSULTR3;1, SbSULTR3;2, SbSULTR3;3, SbSULTR3;4, SbSULTR3;5, and SbSULTR4. Given names are based on phylogeny and chromosomal locations. Except SbSULTR4, all SbSULTR proteins contained Sulfate_transp (PF00916), STAS (PF01740) domains and 12 trans-membrane domains. Phylogenetic analysis revealed that four major groups were identified such as SULTR1, 2, 3, and 4 groups and SULTR4 group was separated to other SULTR groups. In promotor sequences of SbSULTR genes, many diverse cis-acting elements were found mainly related with physiological processes such as light, stress and hormone responsiveness. The expression profiles of SbSULTR genes showed that SULTR1;2, 1;3, 3;3, and 3;5 genes up-regulated in root, while expression level of SULTR4 decreased under 200 µM Cd exposure. The predicted 3D structures of SULTR proteins showed some conformational changes, suggesting functional diversities of SbSULTRs. Finally, results of this study may contribute towards understanding SbSULTR genes and their regulations and roles in Cd stress in sorghum.     

Characterization of fragrance in sorghum (<Emphasis Type="Italic">Sorghum bicolor</Emphasis> (L.) Moench) grain and development of a gene-based marker for selection in breeding

Fragrance is one of the most important and valued quality characters in sorghum and other foods and attracts a premium price in local and global trade. The allele of the SbBADH2 gene in fragrant sorghum cultivar E228 was characterized. A 1441 bp deletion extending from exon 13 to 15 was found rather than a deletion from exon 12 to 15 as had been reported earlier. This allowed the development and validation of a new perfect PCR-based marker for identification of fragrant sorghum accessions in breeding. The concentration of 2-acetyl-1-pyrroline (2AP) in the grain of this cultivar was estimated to be 6.5 ± 0.4 ppb using headspace solid-phase microextraction (HS-SPME) coupled with GC-MS. Flavor components of fragrant sorghum accession E228 (IC 568489) were analyzed and compared with the non-fragrant M35-1 cultivar. PCA analysis revealed that 2AP, benzothiazole, 2,3,5-trimethylpyridine, (1E)-1-ethylidene-1H-indene, cedrene, 2,4-bis(2-methyl-2-propanyl)phenol, 2-hexyl-1-octanol, and 2-butyl-1-octanol were among 25 compounds that were found in sorghum grain that may be contributing toward the aroma of fragrant sorghum. Proline and methylglyoxal contents were found to be higher in E228 than in M35-1, while SbBADH2 expression in E228 was half that in M35-1, suggesting a similar 2AP biosynthetic mechanism to that found in fragrant rice and soybean.     

Molecular mapping of QTLs for resistance to the greenbug <Emphasis Type="Italic">Schizaphis graminum</Emphasis> (Rondani) in <Emphasis Type="Italic">Sorghum bicolor</Emphasis> (Moench)

Sorghum is a worldwide important cereal crop and widely cultivated for grain and forage production. Greenbug, Schizaphis graminum (Rondani) is one of the major insect pests of sorghum and can cause serious damage to sorghum plants, particularly in the US Great Plains. Identification of chromosomal regions responsible for greenbug resistance will facilitate both map-based cloning and marker-assisted breeding. Thus, a mapping experiment was conducted to dissect sorghum genetic resistance to greenbug biotype I into genomic regions. Two hundred and seventy-seven (277) F(2) progeny and their F(2:3) families from a cross between Westland A line (susceptible parent) and PI550610 (resistant parent) combined with 118 polymorphic simple sequence repeat (SSR) markers were used to map the greenbug resistance QTLs. Composite interval mapping (CIM) and multiple interval mapping (MIM) revealed two QTLs on sorghum chromosome nine (SBI-09) consistently conditioned the resistance of host plant to the greenbug. The two QTLs were designated as QSsgr-09-01 (major QTL) and QSsgr-09-02 (minor QTL), accounting for approximately 55-80%, and 1-6% of the phenotypic variation for the resistance to greenbug feeding, respectively. These resistance QTLs appeared to have additive and partially dominant effects. The markers Xtxp358, Xtxp289, Xtxp67 and Xtxp230 closely flanked the respective QTLs, and can be used in high-throughput marker-assisted selections (MAS) for breeding new resistant parents and producing commercial hybrids.     

Rapid and efficient <Emphasis Type="Italic">Agrobacterium</Emphasis>-mediated transformation of sorghum (<Emphasis Type="Italic">Sorghum bicolor</Emphasis>) employing standard binary vectors and <Emphasis Type="Italic">bar</Emphasis> gene as a selectable marker

Key message

A rapid and efficient Agrobacterium -mediated transformation system in sorghum has been developed employing standard binary vectors and bar gene as a selectable marker.

Abstract

Sorghum (Sorghum bicolor) is an important food and biofuel crop worldwide, for which improvements in genetic transformation are needed to study its biology and facilitate agronomic and commercial improvement. Here, we report optimization of regeneration and transformation of public sorghum genotype P898012 using standard binary vectors and bar gene as a selectable marker. The tissue culture regeneration time frame has been reduced to 7–12 weeks with a yield of over 18 plants per callus, and the optimized transformation system employing Agrobacterium tumefaciens strain AGL1 and the bar with a MAS promoter achieved an average frequency over 14 %. Of randomly analyzed independent transgenic events, 40–50 % carry single copy of integrated T-DNA. Some independent transgenic events were derived from the same embryogenic callus lines, but a 3:1 Mendelian segregation ratio was found in all transgenic events with single copy as estimated by Southern blots. The system described here should facilitate studies of sorghum biology and agronomic improvement.

     

Molecular mapping and candidate gene analysis of a new epicuticular wax locus in sorghum (<Emphasis Type="Italic">Sorghum bicolor</Emphasis> L. Moench)

Key message

A new epicuticular wax (bloom) locus has been identified and fine mapped to the 207.89 kb genomic region on chromosome 1. A putative candidate gene, Sobic.001G269200, annotated as GDSL-like lipase/acylhydrolase, is proposed as the most probable candidate gene involved in bloom synthesis/deposition.

Abstract

Deposition of epicuticular wax on plant aerial surface is one strategy that plants adapt to reduce non-transpiration water loss. Epicuticular wax (bloom)-less mutants in sorghum with their glossy phenotypes exhibit changes in the accumulation of epicuticular wax on leaf and culm surfaces. We report molecular mapping of a new sorghum locus, bloomless mutant (bm39), involved in epicuticular wax biosynthesis in sorghum. Inheritance studies involving a profusely bloom parent (BTx623) and a spontaneous bloomless mutant (RS647) indicated that the parents differed in a single gene for bloom synthesis. Bloomless was recessive to bloom deposition. Genetic mapping involving F₂ and F₇ mapping populations in diverse genetic backgrounds (BTx623 × RS647; 296A × RS647 and 27A × RS647) identified and validated the map location of bm39 to a region of 207.89 kb on chromosome 1. SSR markers, Sblm13 and Sblm16, flanked the bm39 locus to a map interval of 0.3 cM on either side. Nine candidate genes were identified, of which Sobic.001G269200 annotated for GDSL-like lipase/acylhydrolase is the most likely gene associated with epicuticular wax deposition. Gene expression analysis in parents, isogenic lines and sets of near isogenic lines also confirmed the reduced expression of the putative candidate gene. The study opens possibilities for a detailed molecular analysis of the gene, its role in epicuticular wax synthesis and deposition, and may help to understand its function in moisture stress tolerance and insect and pathogen resistance in sorghum.

     

Genetic structure and relationships within and between cultivated and wild sorghum (<Emphasis Type="Italic">Sorghum bicolor</Emphasis> (L.) Moench) in Kenya as revealed by microsatellite markers

Understanding the extent and partitioning of diversity within and among crop landraces and their wild/weedy relatives constitutes the first step in conserving and unlocking their genetic potential. This study aimed to characterize the genetic structure and relationships within and between cultivated and wild sorghum at country scale in Kenya, and to elucidate some of the underlying evolutionary mechanisms. We analyzed at total of 439 individuals comprising 329 cultivated and 110 wild sorghums using 24 microsatellite markers. We observed a total of 295 alleles across all loci and individuals, with 257 different alleles being detected in the cultivated sorghum gene pool and 238 alleles in the wild sorghum gene pool. We found that the wild sorghum gene pool harbored significantly more genetic diversity than its domesticated counterpart, a reflection that domestication of sorghum was accompanied by a genetic bottleneck. Overall, our study found close genetic proximity between cultivated sorghum and its wild progenitor, with the extent of crop-wild divergence varying among cultivation regions. The observed genetic proximity may have arisen primarily due to historical and/or contemporary gene flow between the two congeners, with differences in farmers’ practices explaining inter-regional gene flow differences. This suggests that deployment of transgenic sorghum in Kenya may lead to escape of transgenes into wild-weedy sorghum relatives. In both cultivated and wild sorghum, genetic diversity was found to be structured more along geographical level than agro-climatic level. This indicated that gene flow and genetic drift contributed to shaping the contemporary genetic structure in the two congeners. Spatial autocorrelation analysis revealed a strong spatial genetic structure in both cultivated and wild sorghums at the country scale, which could be explained by medium- to long-distance seed movement.     

Evaluation of salinity tolerance in sorghum (<Emphasis Type="Italic">Sorghum bicolor</Emphasis> L.) using ion accumulation,proline and peroxidase criteria

Salt tolerance of sorghum varieties in terms of fresh weight, ion accumulations, proline content and peroxidase activity was analyzed in this study. Three sorghum varieties, Payam, Kimia, and Jambo, differing in salt tolerance, were grown in a greenhouse-hydroponic culture with a complete nutrition solution to which 0, 50, 100, 150 and 200 mM NaCl was added. Plant roots and leaves were harvested at 15 and 30 days after treatment and subjected to analysis. Clear decline in K⁺ and Ca²⁺ concentrations and increase in Na⁺ and proline contents were observed in the root and leaf tissues at each NaCl concentration in all varieties during the NaCl treatment. The Ca²⁺ concentration in leaves was higher than in roots, and had the following order in the tested cultivars: Jambo, Kimia, and Payam. Total peroxidase activity increased under salinity stress and it was proportional with the salt concentration. Payam had the largest decrease (46.95%) in fresh weight caused by NaCl, while Jambo had the lowest decrease, 28.63%. Linear regression analysis revealed significant relationships between the estimated factors and fresh weight. The profiles of isoperoxidases were modified under stress conditions. Two isoforms, A1 and A2, were detected in all three varieties with different intensities. Under NaCl stress, isoperoxidases were strongly expressed and a third isoform, A3, was specifically found in variety Jambo suggesting that A3 is implicated in salt adaptation of this variety.