Sorghum Roots Research Articles

Halotropism Is a Response of Plant Roots to Avoid a Saline Environment

Tropisms represent fascinating examples of how plants respond to environmental signals by adapting their growth and development. Here, a novel tropism is reported, halotropism, allowing plant seedlings to reduce their exposure to salinity by circumventing a saline environment. In response to a salt gradient, Arabidopsis, tomato, and sorghum roots were found to actively prioritize growth away from salinity above following the gravity axis. Directionality of this response is established by an active redistribution of the plant hormone auxin in the root tip, which is mediated by the PIN-FORMED 2 (PIN2) auxin efflux carrier. We show that salt-induced phospholipase D activity stimulates clathrin-mediated endocytosis of PIN2 at the side of the root facing the higher salt concentration. The intracellular relocalization of PIN2 allows for auxin redistribution and for the directional bending of the root away from the higher salt concentration. Our results thus identify a cellular pathway essential for the integration of environmental cues with auxin-regulated root growth that likely plays a key role in plant adaptative responses to salt stress.

Effects of arbuscular mycorrhizal fungi on maize (Zea mays L.) and sorghum (Sorghum bicolor L. Moench) grown in rare earth elements of mine tailings

Rare earth elements (REE) of mine tailings have caused various ecological and environmental problems. Revegetation is one of the most cost-effective ways to overcome these problems, but it is difficult for plants to survive in polluted tailings. Arbuscular mycorrhizal fungi (AMF) can provide biotic and abiotic stress tolerance to its host plant and has widely adopted for the revegetation of degraded ecosystems. However, little is known about whether AMF plays role in facilitating the revegetation of REE of mine tailings. The objective was to investigate the uptake of nutrients and REE when plants are inoculated with AMF. A greenhouse pot experiment was conducted on the effects of Glomus mosseae and Glomus versiforme for the growth, nutritional status, and uptake of REE and heavy metals by maize (Zea mays L.) or sorghum (Sorghum bicolor L. Moench) grown in REE of mine tailings. The results indicated that symbiotic associations were successfully established between AMF and the two plant species. G. versiforme was more effective than G. mosseae at promoting plant growth by significantly increasing the uptake of nitrogen (N), phosphorus (P), and potassium (K) and decreasing carbon:nitrogen:phosphorus (C:N:P) stoichiometry. The shoot and root dry weights of the two plant species were increased by 211–387% with G. versiforme inoculation. Maize and sorghum exhibited significant differences in the REE concentrations in response to the colonization by AMF. The shoot and root lanthanum (La), cerium (Ce), praseodymium (Pr), and neodymium (Nd) concentrations of the maize inoculated with G. versiforme were decreased by approximately 70%, whereas those in the roots of sorghum were increased by approximately 70%. G. mosseae only significantly decreased the La, Ce, Pr, and Nd concentrations in the maize shoots. Inoculation with AMF also significantly decreased the concentration of certain heavy metals in the shoots and roots of maize and sorghum. These findings indicate that AMF can alleviate the effects of REE and heavy metal toxicity on plants and enhance the ability of plants to adapt to the composite adversity of REE in mine tailings.

Response of millet and sorghum to a varying water supply around the primary and nodal roots.

Cereals have two root systems. The primary system originates from the embryo when the seed germinates and can support the plant until it produces grain. The nodal system can emerge from stem nodes throughout the plant's life; its value for yield is unclear and depends on the environment. The aim of this study was to test the role of nodal roots of sorghum and millet in plant growth in response to variation in soil moisture. Sorghum and millet were chosen as both are adapted to dry conditions. Sorghum and millet were grown in a split-pot system that allowed the primary and nodal roots to be watered separately. When primary and nodal roots were watered (12 % soil water content; SWC), millet nodal roots were seven times longer than those of sorghum and six times longer than millet plants in dry treatments, mainly from an 8-fold increase in branch root length. When soil was allowed to dry in both compartments, millet nodal roots responded and grew 20 % longer branch roots than in the well-watered control. Sorghum nodal roots were unchanged. When only primary roots received water, nodal roots of both species emerged and elongated into extremely dry soil (0.6-1.5 % SWC), possibly with phloem-delivered water from the primary roots in the moist inner pot. Nodal roots were thick, short, branchless and vertical, indicating a tropism that was more pronounced in millet. Total nodal root length increased in both species when the dry soil was covered with plastic, suggesting that stubble retention or leaf mulching could facilitate nodal roots reaching deeper moist layers in dry climates. Greater nodal root length in millet than in sorghum was associated with increased shoot biomass, water uptake and water use efficiency (shoot mass per water). Millet had a more plastic response than sorghum to moisture around the nodal roots due to (1) faster growth and progression through ontogeny for earlier nodal root branch length and (2) partitioning to nodal root length from primary roots, independent of shoot size. Nodal and primary roots have distinct responses to soil moisture that depend on species. They can be selected independently in a breeding programme to shape root architecture. A rapid rate of plant development and enhanced responsiveness to local moisture may be traits that favour nodal roots and water use efficiency at no cost to shoot growth.

Effects of Jasmonates on Sorgoleone Accumulation and Expression of Genes for Sorgoleone Biosynthesis in Sorghum Roots

This study investigated the roles of jasmonates in the regulation of sorgoleone accumulation and the expression of genes involved in sorgoleone biosynthesis in sorghum roots. Both methyl jasmonate (MeJa) and jasmonic acid (JA) substantially promoted root hair formation, secondary root development, root weight, and sorgoleone accumulation in sorghum roots. Sorgoleone content varied widely depending on the concentration of JA or MeJa and the duration of their application. Root weight and sorgoleone accumulation were highest after the application of JA or MeJa at a concentration of 5.0 μM, and then declined with increasing concentrations of jasmonates. At 5.0 μM, JA and MeJa increased sorgoleone content by 4.1 and 3.4-fold, respectively. Transcript accumulation was apparent for all genes, particularly for the O-methyltransferase 3 gene, which increased in expression levels up to 8.1-fold after a 36-h exposure to MeJa and 3.5-fold after a 48-h exposure to JA. The results of this study pave the way for more effective biosynthesis of sorgoleone, an important and useful allelochemical obtained from a variety of plant species.

Diversity and fertility of Fusarium sacchari from wild rice (Oryza australiensis) in Northern Australia, and pathogenicity tests with wild rice, rice, sorghum and maize

Research was undertaken to identify Fusarium spp. associated with an endemic wild rice (Oryza australiensis) community in northern Australia and determine the incidence of species reported as pathogens of tropical grain crops. A total of 92 isolates representing six Fusarium species were recovered from O. australiensis. Taxa were delimited based on morphological and phylogenetic (TEF-1α sequence) characters and identified as F. incarnatum-equiseti species complex (55 %), Gibberella fujikuroi species complex (GFSC, 27 %), F. longipes (14 %) and an unidentified Fusarium sp. (3 %). F. sacchari was dominant in the GFSC, a reported mycotoxin (beauvericin, fumonisin) producer and pathogen of sugarcane and sorghum. No isolates were identified as F. fujikuroi, the cause of Bakanae disease of rice in south-east Asia and other rice growing regions. Morphological, phylogenetic and phenetic (AFLP) analyses were in accordance, differentiating all F. sacchari isolates from other Fusarium taxa. The ratio of F. sacchari mating types (15 MAT-1:9 MAT-2) in the O. australiensis population was not significantly different from that expected under random mating (1:1). The effective population number (Ne) based on mating type (Ne(mt)) was 94 % of the count (total population). In contrast, that based on female-fertile isolates (Ne(f)) was 15 %, implying low frequencies of sexual reproduction among F. sacchari isolates. Pathogenicities of three F. sacchari genotypes were assessed against O. australiensis and commercial cultivars of rice, sorghum and maize. All F. sacchari isolates significantly (P < 0.001) reduced emergence of O. australiensis and rice, but not sorghum or maize. Isolation frequencies of all genotypes from sorghum and maize and one isolate from O. australiensis were significantly (P < 0.001) greater than the controls. There were no significant differences in F. sacchari re-isolation among rice treatments. Thus, F. sacchari is presumed to be a pre-emergent ‘damping off’ pathogen, endophyte or weak parasite of O. australiensis and rice and a root and crown pathogen of sorghum and maize.

The bioconversion of 5-deoxystrigol to sorgomol by the sorghum, Sorghum bicolor (L.) Moench

Strigolactones, important rhizosphere signalling molecules and a class of phytohormones that control shoot architecture, are apocarotenoids of plant origin. They have a structural core consisting of a tricyclic lactone connected to a butyrolactone group via an enol ether bridge. Deuterium-labelled 5-deoxystrigol stereoisomers were administered to aquacultures of a high sorgomol-producing sorghum cultivar, Sorghum bicolor (L.) Moench, and conversion of these substrates to sorgomol stereoisomers was investigated. Liquid chromatography-mass spectrometry analyses established that 5-deoxystrigol (5-DS) and ent-2'-epi-5-deoxystrigol were absorbed by sorghum roots, converted to sorgomol and ent-2'-epi-sorgomol, respectively, and exuded out of the roots. The conversion was inhibited by uniconazole-P, implying the involvement of cytochrome P450 in the hydroxylation. These results provide experimental evidence for the postulated biogenetic scheme for formation of strigolactones, in which hydroxylation at C-9 of 5-DS can generate sorgomol.

Isolation and characterization of a glyphosate-degrading rhizosphere strain, Enterobacter cloacae K7

Plant-growth-promoting rhizobacteria exert beneficial effects on plants through their capacity for nitrogen fixation, phytohormone production, phosphate solubilization, and improvement of the water and mineral status of plants. We suggested that these bacteria may also have the potential to express degradative activity toward glyphosate, a commonly used organophosphorus herbicide. In this study, 10 strains resistant to a 10mM concentration of glyphosate were isolated from the rhizoplane of various plants. Five of these strains – Alcaligenes sp. K1, Comamonas sp. K4, Azomonas sp. K5, Pseudomonas sp. K3, and Enterobacter cloacae K7 – possessed a number of associative traits, including fixation of atmospheric nitrogen, solubilization of phosphates, and synthesis of the phytohormone indole-3-acetic acid. One strain, E. cloacae K7, could utilize glyphosate as a source of P. Gas–liquid chromatography showed that E. cloacae growth correlated with a decline in herbicide content in the culture medium (40% of the initial 5mM content), with no glyphosate accumulating inside the cells. Thin-layer chromatography analysis of the intermediate metabolites of glyphosate degradation found that E. cloacae K7 had a C–P lyase activity and degraded glyphosate to give sarcosine, which was then oxidized to glycine. In addition, strain K7 colonized the roots of common sunflower (Helianthus annuus L.) and sugar sorghum (Sorghum saccharatum Pers.), promoting the growth and development of sunflower seedlings. Our findings extend current knowledge of glyphosate-degrading rhizosphere bacteria and may be useful for developing a biotechnology for the cleanup and restoration of glyphosate-polluted soils.

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.

Detection of a plant enzyme exhibiting chlorogenate-dependant caffeoyltransferase activity in methanolic extracts of arbuscular mycorrhizal tomato roots

When Glomus intraradices-colonised tomato roots were extracted in methanol at 6 °C, chlorogenic acid (5-caffeoylquinic acid), naturally present in the extract, was slowly converted by transesterification into methyl caffeate. The progress of the reaction could be monitored by HPLC. The reaction only occurred when the ground roots were left in contact with the hydro-alcoholic extract and required the presence of 15-35% water in the mixture. When the roots were extracted in ethanol, chlorogenic acid was transformed to ethyl caffeate in the same conditions. The reaction was also detected in Glomus mosseae-colonised tomato root extracts. It was also detectable in non-mycorrhizal root extracts but was 10-25 times slower. By contrast it was undetectable in extracts of the aerial parts of tomato plants, which also contain high amounts of chlorogenic acid, whether or not these plants were inoculated by the arbuscular mycorrhizal fungus. We found that this transesterification reaction is catalysed by a tomato enzyme, which remains active in hydro-alcoholic mixtures and exhibits chlorogenate-dependant caffeoyltransferase activity in the presence of methanol or ethanol. This transferase activity is inhibited by phenylmethanesulfonyl fluoride. The 4- and 3-caffeoylquinic acid isomers were also used as substrates but were less active than chlorogenic acid. Highest activity was detected in mycorrhizal roots of nutrient-deprived tomato plants. Surprisingly this caffeoyltransferase activity could also be detected in hydro-alcoholic extracts of G. intraradices-colonised roots of leek, sorghum or barrel medic.

Sorghum Allelopathy—From Ecosystem to Molecule

Sorghum allelopathy has been reported in a series of field experiments following sorghum establishment. In recent years, sorghum phytotoxicity and allelopathic interference also have been well-described in greenhouse and laboratory settings. Observations of allelopathy have occurred in diverse locations and with various sorghum plant parts. Phytotoxicity has been reported when sorghum was incorporated into the soil as a green manure, when residues remained on the soil surface in reduced tillage settings, or when sorghum was cultivated as a crop in managed fields. Allelochemicals present in sorghum tissues have varied with plant part, age, and cultivar evaluated. A diverse group of sorghum allelochemicals, including numerous phenolics, a cyanogenic glycoside (dhurrin), and a hydrophobic p-benzoquinone (sorgoleone) have been isolated and identified in recent years from sorghum shoots, roots, and root exudates, as our capacity to analyze and identify complex secondary products in trace quantities in the plant and in the soil rhizosphere has improved. These allelochemicals, particularly sorgoleone, have been widely investigated in terms of their mode(s) of action, specific activity and selectivity, release into the rhizosphere, and uptake and translocation into sensitive indicator species. Both genetics and environment have been shown to influence sorgoleone production and expression of genes involved in sorgoleone biosynthesis. In the soil rhizosphere, sorgoleone is released continuously by living root hairs where it accumulates in significant concentrations around its roots. Further experimentation designed to study the regulation of sorgoleone production by living sorghum root hairs may result in increased capacity to utilize sorghum cover crops more effectively for suppression of germinating weed seedlings, in a manner similar to that of soil-applied preemergent herbicides like trifluralin.

Effect of Nitrification Inhibitors on Yield and Yield Attributes of T. Aman Rice Varieties

A pot experiment was carried out in the greenhouse at Bangladesh Agricultural University, Mymensingh, during the T. aman season of July to November, 2011 to investigate the effect of natural [methyl 3-(4-hydroxyphenyl) propionate (MHPP)] and synthetic [3,4-dimethylpyrazole phosphate (DMPP)] nitrification inhibitors on yield and yield attributes of three T. aman rice cultivars (BINA dhan7, BRRI dhan39 and BR11). The three concentrations of both natural and synthetic nitrification inhibitors were 0, 100, and 250µM. The experiment was laid out in two factorial completely randomised design where each treatment was replicated three times. Nitrification inhibitors were applied as foliar spray at 15, 30 and 55 DAT. The results of the experiment revealed that both natural and synthetic nitrification inhibitors have positive effect in increasing the yield and yield contributing characters of T. aman rice cultivars by reducing the N loss from soil and supply nitrogen in steady state throughout the growing season. The cultivar BR11 showed better response to the nitrification inhibitors than the other varieties. The use of both natural and synthetic inhibitors at a concentration of 250µM showed increase in the number of tillers per hill, number of filled grains, 1000-grains weight, grain yield, and harvest index (%) because there is a steady uptake of nitrogen throughout the growing season. Nitrogen content in rice grains, straw and soil was found to be significantly higher in treatments where both natural and synthetic nitrification inhibitors were used than other treatments. From this experiment it can be concluded that methyl 3-(4-hydroxyphenyl) propionate has positive effect in inhibiting the nitrification process in soil which is similar to the recognised synthetic nitrification inhibitor DMPP when considering the yield and yield contributing characters of rice varieties. As DMPP is an expensive NI, MHPP which is produced from the sorghum root exudates can be used instead as an alternative. If the rice-sorghum-rice cropping pattern is followed, rice plant can grow with lesser amount of nitrogen supply compared to the recommended dose in the soil. Keywords: Nitrification inhibitors, root exudates, T. aman.

Effect of methyl 3-4-hydroxyphenyl propionate, a Sorghum root exudate, on N dynamic, potential nitrification activity and abundance of ammonia-oxidizing bacteria and archaea

It has been reported that root exudates of Sorghum bicolor can inhibit nitrification in a bioassay using Nitrosomonas, and methyl 3-(4-hydroxyphenyl) propionate (MHPP) was identified as one of the nitrification inhibiting compounds. Therefore, we have investigated the effects of this compound on nitrogen dynamic, potential nitrification activity and on soil microorganisms. We conducted soil incubation experiments using synthetic MHPP to evaluate its effect on changes in inorganic soil nitrogen pools, on nitrification activity and on abundance of ammonia-oxidizing bacteria and archaea. Addition of MHPP at two concentrations equivalent to 70 and 350 μg C g−1 soil was compared to glucose as a carbon source and to the commercially available nitrification inhibitor dicyandiamide (DCD). Soil amended with the high dose of MHPP and with DCD showed reduced nitrate content and low nitrification activity after 3 and 7 days of incubation. This was mirrored by a 70 % reduction in potential nitrification activity compared to a nitrogen-only control. None of the incubation treatments affected non-target microbial counts as estimated by 16S rRNA gene copy numbers, however, the high dose of MHPP significantly reduced the abundance of ammonia-oxidizing bacteria and archaea. These findings suggest that MHPP is capable of suppressing nitrification in soil, possibly by reducing the population size and activity of ammonia-oxidizing microorganisms.

Synthesis of 3-Aryl-1H-Indazoles and Their Effects on Plant Growth

Indazoles are valuable because of their biological activities. A series of 3-aryl-1H-indazoles have been synthesized by condensing bisulfite adduct of aromatic aldehydes with phenyl hydrazine in good yield. Different concentrations of indazoles were employed to check their effects on seed germination and early growth. The arylindazoles were proved to be growth inhibitors of root and shoot lengths of wheat and sorghum, especially at a high concentration (100 ppm). At lower concentrations growth inhibition was found to be less prominent. Seed germination and early growth of plantlets also depended on the nature of substitution on the aryl group.

Evaluation of the activity of dhurrin and sorghum towards Meloidogyne incognita

The epidermal cells of leaf and roots of sorghum (Sorghum bicolor), sudangrass (S. sudanensis) and sorghum-sudangrass hybrids (S. bicolor × S. sudanensis) contain the cyanogenic glucoside dhurrin, which can degrade into hydrogen cyanide (HCN), well known for its toxicity to many organisms, including nematodes. In vitro bioassays were carried out with the aim of evaluating the nematicidal and the nematistatic effects of dhurrin concentrations on second-stage juveniles (J2) of Meloidogyne incognita, and the effectiveness of dhurrin in decreasing or preventing hatching of M. incognita. Furthermore, Sorghum hybrid cv. Super Dolce 10, selected for its dhurrin content, and Eruca sativa sel. Nemat were used in two glasshouse experiments to study the host-nematode relationship and the development of M. incognita life cycle in the roots. In the in vitro bioassays, Sorghum hybrid cv. Super Dolce 10 showed an inhibitory effect on hatching, a slow nematicidal effect on J2 and no nematistatic activity. In the glasshouse experiments, both Sorghum hybrid cv. Super Dolce 10 and E. sativa sel. Nemat proved to be a poor to non-host of M. incognita, with reproduction factor (R) always &lt;1, compared with Solanum lycopersicum cv. UC82, an excellent host (R = 43). In both bioactive accessions two generations were completed in 15 weeks (four cycles in S. lycopersicum), but with the production of very few egg masses, while root infestation was also always very low, with gall index (G.I.) &lt; 1, compared with S. lycopersicum (G.I. = 4). In this study, the effectiveness of E. sativa sel. Nemat in controlling M. incognita confirmed data from previous work.

Interplay among NH 4 + uptake, rhizosphere pH and plasma membrane H+-ATPase determine the release of BNIs in sorghum roots – possible mechanisms and underlying hypothesis

Aims and background The ability to suppress soil nitrification through the release of nitrification inhibitors from plant roots is termed ‘biological nitrification inhibition’ (BNI). Earlier, we reported that sorghum roots release higher BNI-activity when grown with NH4+, but not with NO3- as N source. Also for BNI release, rhizosphere pH of 7.0. This study is aimed at understanding the inter-functional relationships associated with NH4+ uptake, rhizosphere-pH and plasma membrane H+-ATPase (PM H+-ATPase) activity in regulating the release of BNIs (biological nitrification inhibitors) from sorghum roots.

Tissue specific reactions of sorghum roots to the mycoherbicide Fusarium oxysporum f. sp. strigae versus the pathogenic F. proliferatum

Fusarium oxysporum f. sp. strigae (Foxy 2) is a mycoherbicide against Striga hermonthica. To ensure the safe use of this biocontrol agent, and as part of the risk assessment, this study was aimed at providing cytological evidence that Foxy 2 does not possess pathogenic behavior towards the non-target host sorghum. Therefore, we compared the infection processes and sorghum root tissue reactions towards the pathogenic F. proliferatum to that of Foxy 2 using light- and transmission electron microscopy. Given that during the growth process, hyphae could get into the central cylinder, tissue specific reactions of sorghum to Foxy 2 were also investigated by wounding the roots (exposing the vascular system), and testing for proliferation of hyphae within the vessels. Results showed that 2 weeks after sowing, F. proliferatum had invaded and destroyed all cell types including the central cylinder while Foxy 2 hyphae were located around the outer endodermal layer and were not able to penetrate the latter. There was an increase in blue autoflourescence in the central cylinder and especially the endodermis, probably due to increased phenolics in Foxy 2 infected roots which was not the case for F. proliferatum. This might contribute to the inability of Foxy 2 to penetrate the endodermis. Transmission electron microscopy showed extensive degradation of endodermis and vessel walls into thin translucent layers by F. proliferatum but not by Foxy 2. In the mechanically wounded and infected roots, Foxy 2 could invade the central cylinder close to the wound but was not identified a few millimeters away from the wound. This implies that it was not able to grow within or destroy the central cylinder even when already present within it; probably due to the observed increased phenolics. Thus, exposure of the vascular system did not serve as a route for the invasion of Foxy 2 which therefore could not further cause tracheomycosis. Therefore, Foxy 2 could be seen as a fungus well suited for biocontrol.

Sorgoleone, a sorghum root exudate: Algicidal activity and acute toxicity to the ricefish Oryzias latipes

The discovery of natural and natural-based compounds has resulted in its application as an alternative to synthetic algicides to control harmful algae in aquatic systems. Of the many natural-product-based algicides, sorgoleone, a natural plant product from Sorghum bicolor root exudates has been investigated for its controlling effect on different algal species and its acute fish toxicity. Growth of the blue green algal species Microcystis aeruginosa Kützing was completely inhibited by the crude methanol extract of sorghum root at 20μgmL−1. The most noticeable inhibition was observed in the bioassay of n-hexane soluble extract, where 98% growth inhibition occurred in M. aeruginosa at the concentration of 1.25μgmL−1. Sorgoleone very effectively controlled blue green algae inhibiting 97% of M. aeruginosa at 0.5μgmL−1 and 99% of Anabaena affinis Lemmermann at 4μgmL−1. In contrast, inhibition of the green algae species Chlorella vulgaris Beijerinck and Scenedensmus spp. at 16μgmL−1 sorgoleone was 87 and 68%, respectively. There were no mortalities or adverse effects observed in any of the fish exposed to water control, solvent control, and a nominal concentration of 1μgmL−1 during the test period. The no observed effect concentration (NOEC) value was 1.5μgmL−1 for the tested fish (O. latipes). Sorgoleone can be considered as an effective and an ecologically and environmentally sustainable approach to controlling harmful algae.

Biocontrol of charcoal-rot of sorghum by actinomycetes isolated from herbal vermicompost

A total of 137 actinomycetes, isolated from 25 different herbal vermicomposts, were characterized for their antagonistic potential against Macrophomina phaseolina by dual-culture assay. Of them, eight most promising isolates (CAI-17, CAI-21, CAI-26, CAI-68, CAI-78, KAI-26, KAI-27 and MMA-32) were characterized for the production of siderophore, chitinase, protease, hydrocyanic acid (HCN), indole acetic acid (IAA) and further evaluated for their antagonistic potential against M. phaseolina by blotterpaper assay and in greenhouse. All the eight isolates produced HCN and IAA, seven produced siderophore (except CAI-78) and protease (except KAI-27) and four produced chitinase (CAI-26, KAI-26, KAI-27 and MMA-32). In the blotter-paper assay, no charcoal-rot infection was observed in KAI-26 and KAI-27-treated sorghum roots, indicating complete inhibition of the pathogen, while the other isolates showed 47 to 88% lesser charcoal-rot infection compared to the control. In the antifungal activity test against M. phaseolina (in greenhouse on sorghum), all the isolates increased in shoot dry mass by 28 to 53% and root dry mass by 5 to 21%, over the control. In order to confirm the plant growth promoting (PGP) traits of the isolates, the green house experiment was repeated, but in the absence of M. phaseolina . The results further confirmed the PGP traits of the isolates as evidenced by 15 to 34% increase in shoot dry mass on six isolates (except CAI-26 and KAI-27), 14 to 57% increase in root dry mass on five isolates (except CAI-68, KAI-26 and KAI-27), 17 to 60% increase in root length on five isolates (except CAI-17, CAI-21 and CAI-68) and 10 to 64% increase in root volume on six isolates (except CAI-17 and CAI-68). Culture filtrate of three potential actinomycetes (CAI-21, CAI-26 and MMA32) at 0.5% inhibited the growth of M. phaseolina, indicating that the metabolites of these actinomycetes were responsible for the inhibition. The sequences of 16S rDNA gene of the isolates matched with Streptomyces but with different species in BLAST analysis. This study indicates that the selected actinomycetes have the potential for PGP and control of charcoal-rot disease in sorghum.

Arbuscular mycorrhizal colonization of Sorghum vulgare in presence of root endophytic fungi of Myrtus communis

A total of 150 isolates of endophytic fungi were obtained from roots of Myrtus communis grown in the Mediterranean area. Seven different endophytic fungi taxa, all belonging to the Ascomycota phylum were found. Arbuscular mycorrhizal (AM) fungi, belonging to the Glomus genus, were also present in roots of M. communis. None of the root endophytic fungi tested, except Drechslera sp., colonized the root of sorghum. Among all fungi tested, only Phoma schachtii and Cylindrocarpon destructans significantly increased the shoot dry weight of sorghum grown in sterilized soil. Phomopsis columnaris, P. schachtii, Eucasphaeria sp. and Cylindrocarpon pauciseptatum increased the dry matter of sorghum grown in unsterilized soil. The percentage of AM colonization of sorghum was increased significantly only when Ph. columnaris, P. schachtii, the two strains of Bionectria ochroleuca, Eucasphaeria sp. and C. pauciseptatum were applied to unsterilized soil. The number of CFUs of endophytic fungi inoculated in sorghum rhizosphere was similar throughout the experiment, except B. ochroleuca-1 whose population increased at the end of the experiment either in sterilized or in unsterilized soil. No significant effect of the endophytic fungi isolated from M. communis on shoot and root P, K, Ca, Na, Mg, Cu and Zn concentrations of plants grown in sterilized or unsterilized soils, except Eucasphaeria sp. which increased the shoot P concentration of sorghum grown in unsterilized soil.

Functional annotation of the transcriptome of Sorghum bicolor in response to osmotic stress and abscisic acid

BackgroundHigher plants exhibit remarkable phenotypic plasticity allowing them to adapt to an extensive range of environmental conditions. Sorghum is a cereal crop that exhibits exceptional tolerance to adverse conditions, in particular, water-limiting environments. This study utilized next generation sequencing (NGS) technology to examine the transcriptome of sorghum plants challenged with osmotic stress and exogenous abscisic acid (ABA) in order to elucidate genes and gene networks that contribute to sorghum's tolerance to water-limiting environments with a long-term aim of developing strategies to improve plant productivity under drought.ResultsRNA-Seq results revealed transcriptional activity of 28,335 unique genes from sorghum root and shoot tissues subjected to polyethylene glycol (PEG)-induced osmotic stress or exogenous ABA. Differential gene expression analyses in response to osmotic stress and ABA revealed a strong interplay among various metabolic pathways including abscisic acid and 13-lipoxygenase, salicylic acid, jasmonic acid, and plant defense pathways. Transcription factor analysis indicated that groups of genes may be co-regulated by similar regulatory sequences to which the expressed transcription factors bind. We successfully exploited the data presented here in conjunction with published transcriptome analyses for rice, maize, and Arabidopsis to discover more than 50 differentially expressed, drought-responsive gene orthologs for which no function had been previously ascribed.ConclusionsThe present study provides an initial assemblage of sorghum genes and gene networks regulated by osmotic stress and hormonal treatment. We are providing an RNA-Seq data set and an initial collection of transcription factors, which offer a preliminary look into the cascade of global gene expression patterns that arise in a drought tolerant crop subjected to abiotic stress. These resources will allow scientists to query gene expression and functional annotation in response to drought.