Sorghum Flowering Research Articles

Sorghum SbGhd7 is a major regulator of floral transition and directly represses genes crucial for flowering activation.

Molecular genetic understanding of flowering time regulation is crucial for sorghum development. GRAIN NUMBER, PLANT HEIGHT AND HEADING DATE 7 (SbGhd7) is one of the six classical loci conferring photoperiod sensitivity of sorghum flowering. However, its functions remain poorly studied. The molecular functions of SbGhd7 were characterized. The gene regulatory network controlled by SbGhd7 was constructed and validated. The biological roles of SbGhd7 and its major targets were studied. SbGhd7 overexpression (OE) completely prevented sorghum flowering. Additionally, we show that SbGhd7 is a major negative regulator of flowering, binding to the promoter motif TGAATG(A/T)(A/T/C) and repressing transcription of the major florigen FLOWERING LOCUS T 10 (SbFT10) and floral activators EARLY HEADING DATE (SbEhd1), FLAVIN-BINDING, KELCH REPEAT, F-BOX1 (SbFKF1) and EARLY FLOWERING 3 (SbELF3). Reinforcing the direct effect of SbGhd7, SbEhd1 OE activated the promoters of three functional florigens (SbFT1, SbFT8 and SbFT10), dramatically accelerating flowering. Our studies demonstrate that SbGhd7 is a major repressor of sorghum flowering by directly and indirectly targeting genes for flowering activation. The mechanism appears ancient. Our study extends the current model of floral transition regulation in sorghum and provides a framework for a comprehensive understanding of sorghum photoperiod response.

Sorghum bicolor INDETERMINATE1 is a conserved primary regulator of flowering.

A fundamental developmental switch for plants is transition from vegetative to floral growth, which integrates external and internal signals. INDETERMINATE1 (Id1) family proteins are zinc finger transcription factors that activate flowering in grasses regardless of photoperiod. Mutations in maize Id1 and rice Id1 (RID1) cause very late flowering. RID1 promotes expression of the flowering activator genes Early Heading Date1 (Ehd1) and Heading date 1 (Hd1), a rice homolog of CONSTANS (CO). Mapping of two recessive late flowering mutants from a pedigreed sorghum EMS mutant library identified two distinct mutations in the Sorghum bicolor Id1 (SbId1) homolog, mutant alleles named sbid1-1 and sbid1-2. The weaker sbid1-1 allele caused a 35 day delay in reaching boot stage in the field, but its effect was limited to 6 days under greenhouse conditions. The strong sbid1-2 allele delayed boot stage by more than 60 days in the field and under greenhouse conditions. When sbid1-1 and sbid1-2 were combined, the delayed flowering phenotype remained and resembled that of sbid1-2, confirming late flowering was due to loss of SbId1 function. Evaluation of major flowering time regulatory gene expression in sbid1-2 showed that SbId1 is needed for expression of floral activators, like SbCO and SbCN8, and repressors, like SbPRR37 and SbGhd7. These results demonstrate a conserved role for SbId1 in promotion of flowering in sorghum, where it appears to be critical to allow expression of most major flowering regulatory genes.

Genome-wide association mapping identifies an SNF4 ortholog that impacts biomass and sugar yield in sorghum and sugarcane.

Sorghum is a feed/industrial crop in developed countries and a staple food elsewhere in the world. This study evaluated the sorghum mini core collection for days to 50% flowering (DF), biomass, plant height (PH), soluble solid content (SSC), and juice weight (JW), and the sorghum reference set for DF and PH, in 7-12 testing environments. We also performed genome-wide association mapping with 6 094 317 and 265 500 single nucleotide polymorphism markers in the mini core collection and the reference set, respectively. In the mini core panel we identified three quantitative trait loci for DF, two for JW, one for PH, and one for biomass. In the reference set panel we identified another quantitative trait locus for PH on chromosome 6 that was also associated with biomass, DF, JW, and SSC in the mini core panel. Transgenic studies of three genes selected from the locus revealed that Sobic.006G061100 (SbSNF4-2) increased biomass, SSC, JW, and PH when overexpressed in both sorghum and sugarcane, and delayed flowering in transgenic sorghum. SbSNF4-2 encodes a γ subunit of the evolutionarily conserved AMPK/SNF1/SnRK1 heterotrimeric complexes. SbSNF4-2 and its orthologs will be valuable in genetic enhancement of biomass and sugar yield in plants.

A sorghum gigantea mutant attenuates florigen gene expression and delays flowering time.

GIGANTEA (GI) is a conserved plant‐specific gene that modulates a range of environmental responses in multiple plant species, including playing a key role in photoperiodic regulation of flowering time. The C4 grass Sorghum bicolor is an important grain and subsistence crop, animal forage, and cellulosic biofuel feedstock that is tolerant of abiotic stresses and marginal soils. To understand sorghum flowering time regulatory networks, we characterized the sbgi‐ems1 nonsense mutant allele of the sorghum GIGANTEA (SbGI) gene from a sequenced M4 EMS‐mutagenized BTx623 population. sbgi‐ems1 plants flowered later than wild type siblings under both long‐day or short‐day photoperiods. Delayed flowering in sbgi‐ems1 plants accompanied an increase in node number, indicating an extended vegetative growth phase prior to flowering. sbgi‐ems1 plants had reduced expression of floral activator genes SbCO and SbEHD1 and downstream FT‐like florigen genes SbFT, SbCN8, and SbCN12. Therefore, SbGI plays a role in regulating SbCO and SbEHD1 expression that serves to accelerate flowering. SbGI protein physically interacts with the sorghum FLAVIN‐BINDING, KELCH REPEAT, F‐BOX1‐like (SbFFL) protein, a conserved flowering‐associated blue light photoreceptor, and the SbGI‐SbFFL interaction is stimulated by blue light. This work demonstrates that SbGI is an activator of sorghum flowering time upstream of florigen genes under short‐ and long‐day photoperiods, likely in association with the activity of the blue light photoreceptor SbFFL.Significance StatementThis study elucidates molecular details of flowering time networks for the adaptable C4 cereal crop Sorghum bicolor, including demonstration of a role for blue light sensing in sorghum GIGANTEA activity. This work validates the utility of a large publicly available sequenced EMS‐mutagenized sorghum population to determine gene function.

Colinearity of putative flowering gene in both sugarcane and sorghum

Sugarcane (Saccharum spp.) and sorghum (Sorghum spp.) have become increasingly important crops for biofuels production. Sugarcane has an autopolyploid complex genome, whereas sorghum has a diploid simple genome. Flowering is one of the sugar-related agronomic traits in both species. Here, we obtained cDNA of inflorescences at 0–15 cm from S. spontaneum using cDNA-amplified restriction fragment length polymorphisms to develop flower transcriptome profiling with 26 primer combinations. A total of 183 transcript-derived fragments (TDFs) were screened and 96 TDFs were sequenced. Out of 96 TDFs, 26 were selected as putative flowering genes to study collinearity with the sorghum genome. For gene collinearity, a genetic linkage map with 169 SSR co-dominant markers and 12 TDF marker loci were mapped to 14 linkage groups collectively spanning 1077.8 cM and corresponding to the 10 sorghum chromosomes. Interestingly, 9 TDF marker loci could be mapped to 5 linkage groups. In this study, we successfully identified the homologous location of sugarcane flowering TDFs in the sorghum genome and found that 4DS_1X and 2DS_3E TDFs may serve as candidate specific markers linked to flowering in both sorghum and sugarcane.

Integrating genetic analysis and crop modeling: A major QTL can finely adjust photoperiod-sensitive sorghum flowering

In West Africa Sudano-Sahelian zone, sorghum sensitivity to photoperiod is a major trait for flowering adjustment toward the end of the rainy season. This trait ensures that conditions for crop development are optimal. Improving the understanding of the genetic control of flowering time in sorghum is thus an important step toward breeding climate resilient varieties for meeting the challenge of climate smart agriculture. In the wake of green revolution, most sorghum breeders eliminated photoperiod sensitivity to develop early maturing varieties. The evidence is now that simultaneous improvement of production, yield stability and grain quality requires the development of photoperiod-sensitive varieties.A segregating sorghum population derived from a cross between two photoperiod sensitive elite parents was evaluated in three different locations and five environments. CERES crop model was applied to decompose the flowering time of each genotype into basic vegetative phase, critical photoperiod and photoperiod sensitivity. Phenology and model derived variables were used for genetic analysis.The three model parameters were controlled by specific genomic regions. A major QTL affecting critical photoperiod was identified, whereas only independent minor QTLs were found for basic vegetative phase and photoperiod sensitivity. Candidate gene analysis in the major QTL region allowed us to propose a candidate gene (ELF3) involved in the circadian clock as a key regulator of flowering time in photoperiod-sensitive sorghum. Our findings provide critical information supporting the development of photoperiod-sensitive genotypes specifically adapted to climate variability encountered in Sudano-Sahelian zone.

Meteorological Influences on Pheno–Morpho–Yield Data of Grain Sorghum Varieties in Central Italy

Core Ideas Solar radiation was the first greatest forcing variable for the sorghum flowering. Water table during summer and past fruit setting represented a limiting factor. Sorghum morphological development was deeply influenced by precipitation. Medium and long season sorghum varieties showed a yield homogeneity. Brenus and Marcus varieties manifested low relationships with water soil and good yield performance. Sorghum (Sorghum bicolor L. Moench) is widely grown in many arid and semiarid areas of the world due to its ability to yield well under rainfed or water‐limited conditions. In the present study some sorghum varieties (medium‐long season) have been studied in relationship with the principal meteorological variables considering also the drought effect in a favorable groundwater situation. The phenological adaptation, morphological and productive features during 11 yr of investigations from 2005 to 2015 in central Italy were evaluated. In the study area the soil water availability from emergence to flowering was high for all the varieties development considering that no significant phenological differences were evidenced also after flowering between the groups of sorghum cultivars. The plant vegetative development and in particular the flag leaf height was influenced by the low precipitation volumes recorded during 2007 and 2015 spring periods such as plant height particularly affected by extremely low rain volumes from May to July during the last study year. Moreover, seed numbers may be reduced if drought stress occurs immediately after seed set as a result of embryo abortion and the quite absent precipitations during summer 2007 (above all during August when average sorghum flowering is recorded) resulted in a reduction of kernel weight for almost all the varieties. The highest groundwater depth (conditioned by low precipitation volumes) recorded during 2015 determined a high water stress that may have influenced above all panicle size and consequently the number of seeds per panicle.

Effects of different crop rotations on growth of continuous cropping sorghum and its rhizosphere soil micro-environment.

The effects of crop rotation on sorghum [Sorghum biocolor (L) Moench] growth, rhizosphere microbial community and the activity of soil enzymes for successive crops of sorghum were evaluated. Five years of continuous monoculture sorghum as the control (CK) was compared to alfalfa and scallion planted in the fourth year. The results showed that incorporation of alfalfa and scallion into the rotation significantly improved sorghum shoot growth. Specifically, sorghum grain yield increased by 16.5% in the alfalfa rotation plots compared to the CK. The rotations also increased sorghum root system growth, with alfalfa or scallion rotation increasing sorghum total root length by 0.3 and 0.4 times, total root surface area by 0.6 and 0.5 times, root volume by 1.2 and 0.6 times, and root biomass by 1.0 and 0.3 times, respectively. Alfalfa rotation also expanded sorghum root distribution below the 10 cm soil depth. A Biolog analysis on biome functions in the sorghum flowering period indicated significantly higher microbial activity in the rotation plots. The alfalfa and scallion rotation increased the Shannon index by 0.2 and 0.1 times compared to the CK, and improved the sucrose activity in the rhizosphere soil. It was concluded that including alfalfa in rotation with sorghum improved sorghum rhizosphere soil environment, enhanced soil microbial enzyme activity, alleviated the obstacle of continuous cropping and thus increased the sorghum yield.

Three FLOWERING LOCUS T-like genes function as potential florigens and mediate photoperiod response in sorghum.

Sorghum is a typical short-day (SD) plant and its use in grain or biomass production in temperate regions depends on its flowering time control, but the underlying molecular mechanism of floral transition in sorghum is poorly understood. Here we characterized sorghum FLOWERING LOCUS T (SbFT) genes to establish a molecular road map for mechanistic understanding. Out of 19 PEBP genes, SbFT1, SbFT8 and SbFT10 were identified as potential candidates for encoding florigens using multiple approaches. Phylogenetic analysis revealed that SbFT1 clusters with the rice Hd3a subclade, while SbFT8 and SbFT10 cluster with the maize ZCN8 subclade. These three genes are expressed in the leaf at the floral transition initiation stage, expressed early in grain sorghum genotypes but late in sweet and forage sorghum genotypes, induced by SD treatment in photoperiod-sensitive genotypes, cooperatively repressed by the classical sorghum maturity loci, interact with sorghum 14-3-3 proteins and activate flowering in transgenic Arabidopsis plants, suggesting florigenic potential in sorghum. SD induction of these three genes in sensitive genotypes is fully reversed by 1 wk of long-day treatment, and yet, some aspects of the SD treatment may still make a small contribution to flowering in long days, indicating a complex photoperiod response mediated by SbFT genes.

Parallel Domestication of the Heading Date 1 Gene in Cereals.

Flowering time is one of the key determinants of crop adaptation to local environments during domestication. However, the genetic basis underlying flowering time is yet to be elucidated in most cereals. Although staple cereals, such as rice, maize, wheat, barley, and sorghum, have spread and adapted to a wide range of ecological environments during domestication, it is yet to be determined whether they have a common genetic basis for flowering time. In this study, we show, through map-based cloning, that flowering time in sorghum is controlled by a major quantitative trait locus (QTL) Heading Date 1 (HD1), located on chromosome 10. The causal gene encodes the CONSTANS gene family which contains a CCT domain. A 5-bp deletion of a minor allele present in the coding sequence leads to a gene frameshift that delays flowering in sorghum. In contrast, in foxtail millet, association mapping of HD1 showed a common causal site with a splicing variant from "GT" to "AT" that was highly correlated with flowering time. In addition, the rice HD1 gene is known to harbor several causal variants controlling flowering time. These data indicate that the major flowering time QTL HD1 was under parallel domestication in sorghum, foxtail millet, and rice. The pattern of common mixed minor, or even rare, causal alleles in HD1 across different species may be representative of the genetic basis of the domestication syndrome. Furthermore, large DNA sequence analysis of HD1 revealed multiple origins for domesticated sorghum and a single origin for domesticated foxtail millet.

Sorghum phytochrome B inhibits flowering in long days by activating expression of SbPRR37 and SbGHD7, repressors of SbEHD1, SbCN8 and SbCN12.

Light signaling by phytochrome B in long days inhibits flowering in sorghum by increasing expression of the long day floral repressors PSEUDORESPONSE REGULATOR PROTEIN (SbPRR37, Ma1) and GRAIN NUMBER, PLANT HEIGHT AND HEADING DATE 7 (SbGHD7, Ma6). SbPRR37 and SbGHD7 RNA abundance peaks in the morning and in the evening of long days through coordinate regulation by light and output from the circadian clock. 58 M, a phytochrome B deficient (phyB-1, ma3R) genotype, flowered ∼60 days earlier than 100 M (PHYB, Ma3) in long days and ∼11 days earlier in short days. Populations derived from 58 M (Ma1, ma3R, Ma5, ma6) and R.07007 (Ma1, Ma3, ma5, Ma6) varied in flowering time due to QTL aligned to PHYB/phyB-1 (Ma3), Ma5, and GHD7/ghd7-1 (Ma6). PHYC was proposed as a candidate gene for Ma5 based on alignment and allelic variation. PHYB and Ma5 (PHYC) were epistatic to Ma1 and Ma6 and progeny recessive for either gene flowered early in long days. Light signaling mediated by PhyB was required for high expression of the floral repressors SbPRR37 and SbGHD7 during the evening of long days. In 100 M (PHYB) the floral activators SbEHD1, SbCN8 and SbCN12 were repressed in long days and de-repressed in short days. In 58 M (phyB-1) these genes were highly expressed in long and short days. Furthermore, SbCN15, the ortholog of rice Hd3a (FT), is expressed at low levels in 100 M but at high levels in 58 M (phyB-1) regardless of day length, indicating that PhyB regulation of SbCN15 expression may modify flowering time in a photoperiod-insensitive manner.

Energy sorghum--a genetic model for the design of C4 grass bioenergy crops.

Sorghum is emerging as an excellent genetic model for the design of C4 grass bioenergy crops. Annual energy Sorghum hybrids also serve as a source of biomass for bioenergy production. Elucidation of Sorghum's flowering time gene regulatory network, and identification of complementary alleles for photoperiod sensitivity, enabled large-scale generation of energy Sorghum hybrids for testing and commercial use. Energy Sorghum hybrids with long vegetative growth phases were found to accumulate more than twice as much biomass as grain Sorghum, owing to extended growing seasons, greater light interception, and higher radiation use efficiency. High biomass yield, efficient nitrogen recycling, and preferential accumulation of stem biomass with low nitrogen content contributed to energy Sorghum's elevated nitrogen use efficiency. Sorghum's integrated genetics-genomics-breeding platform, diverse germplasm, and the opportunity for annual testing of new genetic designs in controlled environments and in multiple field locations is aiding fundamental discovery, and accelerating the improvement of biomass yield and optimization of composition for biofuels production. Recent advances in wide hybridization between Sorghum and other C4 grasses could allow the deployment of improved genetic designs of annual energy Sorghums in the form of wide-hybrid perennial crops. The current trajectory of energy Sorghum genetic improvement indicates that it will be possible to sustainably produce biofuels from C4 grass bioenergy crops that are cost competitive with petroleum-based transportation fuels.

CONSTANS is a photoperiod regulated activator of flowering in sorghum.

BackgroundSorghum genotypes used for grain production in temperate regions are photoperiod insensitive and flower early avoiding adverse environments during the reproductive phase. In contrast, energy sorghum hybrids are highly photoperiod sensitive with extended vegetative phases in long days, resulting in enhanced biomass accumulation. SbPRR37 and SbGHD7 contribute to photoperiod sensitivity in sorghum by repressing expression of SbEHD1 and FT-like genes, thereby delaying flowering in long days with minimal influence in short days (PNAS_108:16469-16474, 2011; Plant Genome_in press, 2014). The GIGANTEA (GI)-CONSTANS (CO)-FLOWERING LOCUS T (FT) pathway regulates flowering time in Arabidopsis and the grasses (J Exp Bot_62:2453-2463, 2011). In long day flowering plants, such as Arabidopsis and barley, CONSTANS activates FT expression and flowering in long days. In rice, a short day flowering plant, Hd1, the ortholog of CONSTANS, activates flowering in short days and represses flowering in long days.ResultsQuantitative trait loci (QTL) that modify flowering time in sorghum were identified by screening Recombinant Inbred Lines (RILs) derived from BTx642 and Tx7000 in long days, short days, and under field conditions. Analysis of the flowering time QTL on SBI-10 revealed that BTx642 encodes a recessive CONSTANS allele containing a His106Tyr substitution in B-box 2 known to inactivate CONSTANS in Arabidopsis thaliana. Genetic analysis characterized sorghum CONSTANS as a floral activator that promotes flowering by inducing the expression of EARLY HEADING DATE 1 (SbEHD1) and sorghum orthologs of the maize FT genes ZCN8 (SbCN8) and ZCN12 (SbCN12). The floral repressor PSEUDORESPONSE REGULATOR PROTEIN 37 (PRR37) inhibits sorghum CONSTANS activity and flowering in long days.ConclusionSorghum CONSTANS is an activator of flowering that is repressed post-transcriptionally in long days by the floral inhibitor PRR37, contributing to photoperiod sensitive flowering in Sorghum bicolor, a short day plant.

Evaluation of Sorghum Genotypes Compatibility with Fusarium oxysporum under Striga Infestation

ABSTRACTCombined use of host resistance and Fusarium oxysporum as a biocontrol agent may provide enhanced management of Striga hermonthica (Delile) Benth. in sorghum [Sorghum bicolor (L.) Moench]. The objective of this study was to identify sorghum genotypes compatible with F. oxysporum and to determine the potential of this biocontrol agent for controlling Striga. Fifty sorghum genotypes were evaluated in the greenhouse in Striga‐infested soils with and without inoculation by F. oxysporum. A supplementary laboratory study was conducted to investigate the growth and proliferation of F. oxysporum in the soil and sorghum roots. Data were recorded on crop growth parameters, Striga incidence and colonization, and the persistence of F. oxysporum in the soil and on plant roots, using samples taken at 45 and 60 d after planting. Inoculation with F. oxysporum significantly shortened days to maturity compared to noninoculated plants. Plant height, biomass, panicle length, and seed yield per plant were higher in F. oxysporum treated pots. Striga emergence was delayed and vigor and overall incidence of the parasite was significantly reduced in Fusarium‐treated pots. The number of Fusarium colony forming units obtained from soil and plant samples were significantly different between genotypes. Three principal components (PCs) contributed to 67.31% of the total variation among the genotypes. Principal component 1, PC2, and PC3 contributed 27, 23, and 18%, respectively, to the total variance. Days to Striga emergence and Striga count and height correlated with PC1 while sorghum panicle length and plant height with PC2 and days to sorghum flowering and maturity with PC3. Thus, 12 promising sorghum lines were identified with farmer‐preferred agronomic traits and with F. oxysporum compatibility. This result is valuable in the development of Striga control in sorghum through integration of host resistance and F. oxysporum inoculation.

Genetic control and comparative genomic analysis of flowering time in Setaria (Poaceae).

We report the first study on the genetic control of flowering in Setaria, a panicoid grass closely related to switchgrass, and in the same subfamily as maize and sorghum. A recombinant inbred line mapping population derived from a cross between domesticated Setaria italica (foxtail millet) and its wild relative Setaria viridis (green millet), was grown in eight trials with varying environmental conditions to identify a small number of quantitative trait loci (QTL) that control differences in flowering time. Many of the QTL across trials colocalize, suggesting that the genetic control of flowering in Setaria is robust across a range of photoperiod and other environmental factors. A detailed comparison of QTL for flowering in Setaria, sorghum, and maize indicates that several of the major QTL regions identified in maize and sorghum are syntenic orthologs with Setaria QTL, although the maize large effect QTL on chromosome 10 is not. Several Setaria QTL intervals had multiple LOD peaks and were composed of multiple syntenic blocks, suggesting that observed QTL represent multiple tightly linked loci. Candidate genes from flowering time pathways identified in rice and Arabidopsis were identified in Setaria QTL intervals, including those involved in the CONSTANS photoperiod pathway. However, only three of the approximately seven genes cloned for flowering time in maize colocalized with Setaria QTL. This suggests that variation in flowering time in separate grass lineages is controlled by a combination of conserved and lineage specific genes.

Association analysis of photoperiodic flowering time genes in west and central African sorghum [Sorghum bicolor (L.) Moench

BackgroundPhotoperiod-sensitive flowering is a key adaptive trait for sorghum (Sorghum bicolor) in West and Central Africa. In this study we performed an association analysis to investigate the effect of polymorphisms within the genes putatively related to variation in flowering time on photoperiod-sensitive flowering in sorghum. For this purpose a genetically characterized panel of 219 sorghum accessions from West and Central Africa was evaluated for their photoperiod response index (PRI) based on two sowing dates under field conditions.ResultsSorghum accessions used in our study were genotyped for single nucleotide polymorphisms (SNPs) in six genes putatively involved in the photoperiodic control of flowering time. Applying a mixed model approach and previously-determined population structure parameters to these candidate genes, we found significant associations between several SNPs with PRI for the genes CRYPTOCHROME 1 (CRY1-b1) and GIGANTEA (GI).ConclusionsThe negative values of Tajima's D, found for the genes of our study, suggested that purifying selection has acted on genes involved in photoperiodic control of flowering time in sorghum. The SNP markers of our study that showed significant associations with PRI can be used to create functional markers to serve as important tools for marker-assisted selection of photoperiod-sensitive cultivars in sorghum.

Coincident light and clock regulation of pseudoresponse regulator protein 37 (PRR37) controls photoperiodic flowering in sorghum.

Optimal flowering time is critical to the success of modern agriculture. Sorghum is a short-day tropical species that exhibits substantial photoperiod sensitivity and delayed flowering in long days. Genotypes with reduced photoperiod sensitivity enabled sorghum's utilization as a grain crop in temperate zones worldwide. In the present study, Ma(1), the major repressor of sorghum flowering in long days, was identified as the pseudoresponse regulator protein 37 (PRR37) through positional cloning and analysis of SbPRR37 alleles that modulate flowering time in grain and energy sorghum. Several allelic variants of SbPRR37 were identified in early flowering grain sorghum germplasm that contain unique loss-of-function mutations. We show that in long days SbPRR37 activates expression of the floral inhibitor CONSTANS and represses expression of the floral activators Early Heading Date 1, FLOWERING LOCUS T, Zea mays CENTRORADIALIS 8, and floral induction. Expression of SbPRR37 is light dependent and regulated by the circadian clock, with peaks of RNA abundance in the morning and evening in long days. In short days, the evening-phase expression of SbPRR37 does not occur due to darkness, allowing sorghum to flower in this photoperiod. This study provides insight into an external coincidence mechanism of photoperiodic regulation of flowering time mediated by PRR37 in the short-day grass sorghum and identifies important alleles of SbPRR37 that are critical for the utilization of this tropical grass in temperate zone grain and bioenergy production.

Leaf Discs as a Source Material for Plant Tissue Culture Studies of Sorghum bicolor (L.) Moench.

Sorghum bicolor is one of the most difficult plant species to manipulate for tissue culture and genetic transformation; on the other hand Sorghum crop improvement through biotechnology requires efficient plant tissue culture protocols. In the present study a protocol has been optimized for Sorghum callus induction and regeneration from leaf tissue by optimizing the suitable explant, photoperiod and media composition. In Sorghum generally inflorescence tissue was used as explants for initiating callus cultures. Conversely, Sorghum flowering occurs only once in its life time and for few days only, thereby providing a small window of opportunity to provide source material or explant to initiate callus. Hence it is essential to identify a suitable explant, which can be available at any season. In the present study efficient callus induction was achieved on media supplemented in combination with 2 mgl -1 2,4,5-T plus 1 mgl -1 NAA and 0.5 mgl -1 ZN. Among the different combinations and concentrations of plant growth regulators tried for regeneration, 2.5 mgl -1 TDZ plus 1.0 mgl -1 BAP and 0.5 mgl -1 IAA showed better shoot regeneration frequency with 62.2±4.6 shoots per explant after 4 weeks of culture. Similarly, root induction was obtained from shoots with 1.0 mgl -1 NAA followed by their transfer to half strength MS medium which produced an average of two roots per shoot. Among the six genotypes tested, genotype ‘IS3566’ displayed superior results. Because of the reproducibility and the easy of accessibility of leaf tissue, the plant regeneration from leaf tissue provides a foundation for genetic transformation of Sorghum; this is of significant importance for improving important traits such as biomass, protein and sucrose content.

Weed control with selected herbicides in acetolactate synthase-resistant sorghum

The recent development of grain sorghum hybrids with resistance to acetolactate synthase (ALS)-inhibiting herbicides has allowed for the use of several post-emergence applied (POST) ALS-inhibitors to control weeds in the crop. Field experiments were conducted at four sites in Kansas in 2008 to evaluate the efficacy of nicosulfuron and nicosulfuron + rimsulfuron applied alone or in combination with dicamba, metsulfuron methyl, and atrazine. All POST treatments slightly injured sorghum 2 weeks after treatment (WAT) at Garden City and Hesston, whereas at Hays and Manhattan, only treatments that included dicamba caused injury. Nicosulfuron + rimsulfuron applied alone provided 41, 83, 74, and 93% control of grasses 4 WAT at Garden City, Hays, Hesston, and Manhattan, respectively. However, to obtain the highest level broadleaf weed control, nicosulfuron or nicosulfuron + rimsulfuron need to be applied with other broadleaf herbicides. POST treatment of nicosulfuron + metsulfuron methyl + dicamba + atrazine provided 90% or greater control of all broadleaf weeds at sorghum flowering. Sorghum grain yield was greater following all herbicide treatments compared with the weedy check. The POST treatment that provided the highest yield at Garden City was nicosulfuron + rimsulfuron + atrazine, whereas in Hesston and Manhattan, nicosulfuron + metsulfuron methyl + dicamba + atrazine provided the highest yields. This research showed that many grasses can be effectively controlled with POST applications of nicosulfuron or nicosulfuron + rimsulfuron in ALS-resistant sorghum. The research also indicated that broadleaf weed control is greater when nicosulfuron or nicosulfuron + rimsulfuron are applied with other broadleaf-control herbicides such as dicamba, metsulfuron methyl, and atrazine.

Efficacy of Herbicide Seed Treatments for Controlling Striga Infestation of Sorghum

Witchweed (Striga spp.) infestations are the greatest obstacle to sorghum [Sorghum bicolor (L.) Moench] grain production in many areas in Africa. The objective of this study was to evaluate the efficacy of herbicide seed treatments for controlling Striga infestation of sorghum. Seeds of an acetolactate synthase (ALS) herbicide–tolerant sorghum hybrid were treated with two ALS‐inhibiting herbicides. Treatments included three rates of imazapyr (IMI), three rates of metsulfuron‐methyl (MET), and an untreated control group. In greenhouse trials, observations at 32, 46, and 60 d after planting showed that seeds treated with the highest herbicide rates had the fewest Striga attachments and the greatest delay in attachment. All plants in the untreated group died at or before sorghum flowering; however, herbicide seed treatments, particularly metsulfuron, reduced Striga emergence and significantly increased sorghum grain yield and dry matter production. Field studies comparing seed treatments produced similar results with delayed Striga emergence and fewer emerged Striga plants in herbicide‐treated plots. These studies indicate that herbicide seed treatments may provide a highly effective tool for managing Striga in sorghum.