No description available.

Greenbug is one of two key insect pests of sorghum, and biotype evolution hinders the long-term usefulness of resistant sorghums. The current study sought to identify plant resistance mechanisms, plant damage characteristics, and greenbug fitness in sorghum/greenbug interactions. Choice tests were conducted to elucidate resistance mechanisms displayed by four sorghum genotypes towards several greenbug biotypes and isolates. Results indicated all three resistance modalities (antibiosis, antixenosis, tolerance) were identified in sorghums, with some genotypes displaying two or more modalities towards some biotypes. This suggests some sorghum genotypes do not select for greenbug biotypes, and the sorghum genotypes cultivated may have relatively long-term resistance. Non-choice tests were used to determine plant damage associated with greenbug feeding. Four sorghum genotype, Johnson grass, and five greenbug biotype combinations were used to elucidate plant characteristics associated with visible plant damage. Fluid loss and plant stunting were significantly associated with visible plant damage, and were also observed in some plants not incurring heavy visible damage. Additionally, some biotypes avirulent to cultivated sorghum caused significant damage to Johnson grass. These results suggest visible plant damage, routinely used in damage studies, reflects underlying causes that could lead to poor agronomic performance. Additionally, Johnson grass may harbor greenbug biotypes not commonly found in sorghum fields. Greenbug colony and individual fitness were determined by reproduction rates of five biotypes on four sorghum genotypes and Johnson grass in non-choice tests. Generally, colony and individual fitness estimates were not different within genotype/biotype combinations. Also, biotypes did best on more susceptible and worst on more resistant sorghum genotypes. Colonies and individuals of all biotypes had lowest fitness on Johnson grass. These results suggest virulent biotypes may have a fitness advantage over avirulent ones, at least in the presence of the cultivated host. The results presented herein reflect the diversity of sorghum/greenbug interactions, and underscore the need for further understanding of the nature of greenbug biotypes, and how they interact with cultivated and non-cultivated host plants.

Sorghum downy mildew (SDM) of maize is caused by the oomycete Peronosclerospora sorghi (Weston and Uppal) C. G. Shaw. The disease can cause devastating yield losses in maize (Zea mays L.). Quantitative trait loci (QTLs) mediating resistance to SDM were mapped using both restriction fragment length polymorphisms (RFLPs), and simple sequence repeats (SSRs) in 220 F2 individual maize progeny derived from a cross between two extremes; highly susceptible inbred parent SC-TEP5-19-1-3-1-4-1-1 (white) and highly resistant inbred P345C4S2B46-2-2-1-2-B-B-B (yellow). The phenotypic expression was assessed on F2:3 families in a wide range of environments under natural field infection and in a controlled greenhouse screening method. Heritability estimates of disease reaction ranged from 93.3% in Thailand sit 1 to 48% in Thailand sit 2. One hundred and thirty three polymorphic markers were assigned to the ten chromosomes of maize with LOD scores exceeding 4.9 covering about 1265 cM with an average interval length between markers of 9.5 cM. About 90% of the genome was located within a 10 cM distance to the nearest marker. Three putative QTLs were detected in association with resistance to SDM in different environments using composite interval mapping. Despite environmental and symptom differences, one QTL on chromosome 2 bin 9 had a major effect in all trials and explained up to 70% of the phenotypic variation in Thailand where the highest disease pressure was experienced. Two other QTLs on chromosome 3 bin 5 and chromosome 9 bin 2 had a minor effect, each explaining no more than 4% of the phenotypic variation. These results revealed one major gene and two minor genes that control sorghum downy mildew resistance. These markers should be very useful in breeding programs in facilitating the introgression of the resistance genes into commercial varieties. Marker-assisted selection for these loci should be useful in incorporating SDM resistance genes in maize across environments, even in the absence of the pathogen.

Sorghum contains many phenolic compounds which have potential antioxidant, anti-inflammatory, and chemopreventive properties as well as natural colorants in foods. Phenolic compounds of stalks, sheaths, leaves, glumes and grains from tan (ARTx631/RTx436), red (Tx2911) and purple (Tx3362) sorghum plants were characterized by UPLC-MS/MS. Antiproliferative properties of selected sorghum extracts were evaluated using HT-29 colon cancer cells and absorption of their polyphenolics was determined by a Caco-2 in vitro model system. Phenolic acids, flavones, 3-deoxyanthocyanidins and chalcones were found in all plant components. Phenolic acids were predominant in the stalks, sheaths and grains of all sorghum types. Flavone glycosides were predominant in leaves, sheaths and stalks while flavone aglycones in glumes and grains. 3-Deoxyanthocyanidins and chalcones were mostly found in sheaths, leaves, glumes and grains of Tx2911 (red) and Tx3362 (purple) genotypes. Sorghum leaves showed high levels of flavone glycosides while glumes had high levels of flavones aglycones. Glume extract of ATx631/RTx436 (tan) and Tx2911 genotypes had the strongest antiproliferation activity (IC_(50) = 85-178 µg/ml), these extracts had also the highest levels of flavone aglycones (19.6-49.8 mg/g). Absorption of flavones (30.4-42.3 %) was higher than 3-deoxyantocyanidins (1.4-11.3%), while absorption of methoxylated 3-deoxyanthocyanidins (11.3%) was higher than non-methoxylated 3-deoxyanthocyanidins (1.4 – 1.6 %). Flavones had high absorption compared to other sorghum phenolics suggesting that sorghum flavone aglycones are more bioavailable than other sorghum phenolic compounds. Consequently, sorghum glumes could be used as used as a source of phytochemicals to increase value of sorghum crop.

Consumption of whole grains has been linked to reduced risk of colon cancer. This study determined estrogenic activity of sorghum phenolic extracts of different phenolic profiles and identified possible estrogenic compounds in sorghum in vitro, as well as evaluated the potential of estrogenic sorghum phenolic extracts to prevent colon carcinogenesis in vivo. The thermal stability of sorghum 3-deoxyanthocyanins was also studied, to determine their suitability as functional food colorants. White and TX430 (black) sorghum extracts showed estrogenic activity in cell models predominantly expressing estrogen receptor-α (ERα) or ERβ at 5 and 10 µg/mL, respectively. The same treatments led to induction of apoptosis in cells expressing ERβ. The red TX2911 sorghum did not possess these activities. Compositional analysis revealed differences in flavones and flavanones. Flavones with estrogen-like properties, i.e. luteolin and apigenin, were detected in White and TX430 (black) sorghum extracts, but not in red TX2911 extract. Naringenin, a flavanone known to antagonize ERα signalling, was only detected in the red TX2911 extract. Additional experiments with sorghum extracts of distinct flavones/flavanone ratio, as well as with pure apigenin and naringenin, suggested that flavones are the more potent ERβ agonists in sorghum. On the other hand, 3-deoxyanthocyanins were probably not estrogenic. Estrogenic white and black sorghum phenolic extracts (fed at 1% level in the diet) reduced the number of azoxymethane induced colon premalignant lesion (aberrant crypt foci) by 39.3% and 14.7%, respectively, in ovariectomized mice. Further studies are needed to elucidate the protective mechanisms induced by these sorghum extracts. Sorghum 3-deoxyanthocyanins retained good color stability after 30 minutes of heat treatment at 121 °C under pressure: More than 80% of color retained in pH 1 and 2 HCl and citric acid solutions, and 39-84% retained from pHs 3-7. Formic acid negatively affected the color stability at pH 1 and pH 2 due to its reducing capacity. Methoxylation decreased the thermal stability of 3-deoxyanthocyanins. The heat stability of 3-deoxyanthocyanins indicates good potential for food use. Overall, the inherent estrogenic activity of specific sorghum phenolic extracts is a likely mechanism for colon cancer prevention. Further studies are needed to assess physiologically relevant dietary level of sorghum phenolics for prevention of colon cancer, and effect of food processing on the activity and bioavailability of the chemopreventive components.

Recently designated as a bioenergy crop, Sorghum is rather unique as it can produce large quantities of cellulose or sugar which can be used to produce advanced biofuels or compounds. Sweet sorghum contains high levels of sugars and biomass sorghums consist primarily of ligno-cellulosic biomass. Improvement of both sorghum types is essential for maximizing production and conversion efficiency. Photoperiod sensitive sorghum is thought to maximize biomass production yet maturity influence on biomass production and composition is not fully understood. Utilizing sorghum for sugar production has increased efforts to develop sweet sorghums with sugar yields similar to sugarcane. Hybridization of these species has been investigated with, until recently, little success. Testing newly developed intergeneric hybrids and improvement of parents used in their creation will determine their feasibility and improve hybrid performance. Objectives of this research are multifaceted. First, analyze photoperiod sensitive sorghum in varying day length environments to determine maturity effects on plant phenotype, composition, and QTL detection. Second, analyze intergeneric sorghum × sugarcane hybrids to determine agronomic performance in relation to sugarcane. Lastly, introgress the iap allele into sweet sorghum females for use in intergeneric hybrid creation. Photoperiod sensitive sorghum RILs were evaluated in College Station and Weslaco, Texas and Puerto Rico which caused differential expression of plant maturity. Genetic control of trait expression was high for each location. Results indicate gradual induction of plant maturity increases detection of phenotypic QTL and detection of compositional QTL increases when maturity effects on plant phenotype are reduced. Intergeneric sorghum × sugarcane F_1 hybrids were compared to sugarcane in Weslaco, Texas in 2011. Each hybrid expressed agronomic traits similar or better than that of the sugarcane variety. High levels of repeatability and genetic influence on trait expression were observed. Overall performance of the sugarcane variety was better than any individual hybrid tested. Introgression of iap into sweet sorghum was successful and generated seventeen new sweet sorghum female genotypes possessing the allele. Only two genotypes exhibited higher brix readings and both were later maturing than Tx3361. Height and maturity of all developed genotypes varied and desirability of developed lines was similar to Tx3361.

No description available.

Sorghum [Sorghum bicolor (L.) Moench] is a major food security crop for millions of people in sub-Saharan Africa and the fourth most important crop in Africa. The potential sorghum yields are limited due to a number of abiotic, biotic and socio-economic constraints. Among the biotic stresses is the parasitic weed, Striga hermonthica, which inflicts yield losses ranging from 30-100%. Various control options have been recommended to reduce levels of Striga damage. However, these techniques need to be integrated for effective control and to boost sorghum productivity. A series of experiments was conducted to integrate host resistance improvement and the use of a biological control agent, Fusarium oxysporum f.sp. strigae to control Striga hermonthica. These studies were also focused on improving breeders‟ awareness of the traits that farmers‟ desire, on the assumption that farmers‟ variety preference traits are the missing link in technology development and adoption process for S. hermonthica management. The objectives of the study were to: 1) determine farmers‟ views on sorghum production opportunities; threats; indigenous knowledge and perceptions; breeding priorities; Striga infestation; and the coping mechanisms of farmers in the north eastern and north western Ethiopia, 2) evaluate sorghum genotypes for compatibility to F. oxysporum inoculation where grown in Striga infested soil in controlled environments, 3) determine field responses of sorghum genotypes and F. oxysporum compatibility for integrated Striga management (ISM), 4) determine the variability present among selected sorghum genotypes exhibiting S. hermonthica resistance, and compatibility with the biological control agent using phenotypic and simple sequence repeat (SSR) markers, 5) identify F. oxysporum compatible sorghum parents and hybrids with high combining ability for grain yield, yield components, and Striga resistance for ISM, and 6) undertake farmers‟ participatory assessment, and identify their preferred traits for sorghum genotypes under ISM, simultaneously with the breeders‟ evaluation. A participatory rural appraisal (PRA) research was conducted involving 315 farmers in nine districts of three administrative zones within two provinces in Ethiopia. Sorghum landraces were preferred by >85% of participants rather than previously improved released varieties. The participating farmers listed and prioritized their sorghum production constraints. In the North Shewa and North Wello zones drought was the most important constraint, followed by Striga. In the Metekel zone Striga was the number one constraint followed by a lack of genotypes with high grain quality. Controlled environment experiments were conducted involving greenhouse and laboratory tests in order to evaluate 50 sorghum genotypes for their compatibility with F. oxysporum and for possible deployment of the bio-control agent to control Striga. Striga population was reduced by 92% through the application of F. oxysporum, resulting in yield increment of 144%. Twelve sorghum genotypes were identified as promising parents for breeding and to control Striga through integration of host resistance and F. oxysporum seed treatment. During field and sick plot plot evaluations differential responses to F. oxysporum application among the sorghum genotypes were observed for various attributes including Striga plant height. Most traits showed highly significant (p<0.001) genotype X site interactions. Similarly, the main effects of F.oxysporum application were highly significant (p<0.001) across sites for most of the traits. The genotype and genotype X environment biplot identified 13 genotypes that consistently performed well following Fusarium application. The variability present among 14 selected sorghum genotypes exhibiting S. hermonthica resistance, and compatibility with a biological control agent, Fusarium oxysporum, were determined using phenotypic and 20 polymorphic simple sequence repeat (SSR) markers. Highly significant (p<0.001) differences were detected among genotypes for phenotypic traits. Principal component analysis showed three components that accounted for 73.99% of the total variability exhibited among genotypes. Cluster analysis allocated the genotypes into two major groups, one with a further two subgroups based on morphological traits, showing clear demarcations between the genotypes. The SSR markers revealed high levels of polymorphisms among genotypes, with the mean number of alleles per locus being 6.95 and the mean polymorphic information content being 0.80. The observed genetic diversity was relatively wide, with the allele sizes ranging from 203.6-334 bp. The SSR markers allocated genotypes into two distinct clusters close to the phenotypic markers. Forty sorghum hybrids were developed through a line by tester mating design involving 10 lines selected for their compatibility with F. oxysporum and high agronomic performances and four Striga resistant tester parents. The F1s and their parents were field evaluated with complementary in-vitro tests. Field evaluations were conducted at two locations: Kobo and Shewa Robit in Ethiopia, which are well known for their severe Striga infestation. Significant (p<0.05) general combining ability (GCA) effects were observed among testers and lines at both sites for days to 50% flowering and maturity, plant height, biomass, number of Striga plants and Striga plant height. Furthermore, significant (p<0.05) specific combining ability (SCA) effects were detected for days to 50% flowering, biomass, grain yield and number of Striga plants. From the complementary in-vitro experiment, highly significant variation (p<0.01) was exhibited due to line x tester interaction for maximum Striga germination distance. The study identified paternal parents with high GCA effects including SRN-39 and Birhan and maternals 235761, 2384443, IC9830, 235466, 237289,235763, and 235929 to be useful for breeding for ISM in sorghum. At Kobo, cross 235763 x N-13 and Shewa Robit IC9830 x SRN-39 had significantly negative SCA effects for the numbers of Striga plants. Progenies of these crosses will be selected in the Striga resistance breeding program. In the participatory sorghum genotypes assessment, farmers were invited to assess and select the genotypes based on their preferences at maturity and harvesting. The standard agronomic traits and Striga parameters relevant for breeding were collected by the breeders. Earliness, Striga resistance, high yield and high grain quality and threshability were the most important farmers‟-preferred traits for sorghum genotypes. Comparative analyses between farmers‟ and breeders‟ evaluations revealed highly significant correlations (p<0.01) except between Striga resistance and Striga damage and pest resistance and insect damage. Repeatability of scoring genotypes among farmers was consistent (>0.80) for all traits except Striga and pest resistance. The prioritized traits through farmers‟ participation are important for further breeding program. Overall, the study established farmers‟ preferred traits, the effectiveness of ISM to boost sorghum productivity, and identified useful parents and crosses for effective sorghum breeding to control Striga in Ethiopia. / Thesis (Ph.D.)-University of KwaZulu-Natal, Pietermaritzburg, 2013.

The aim of this research was to study the influence of altered water availability on stomatal patterns of leaves. A baseline study of leaves stomatal indices, (stomatal as a proportional of all epidermal cells) stomatal density, (number of stomatal per unit area of epidermis) epidermal cell density, epidermal cell length and stomatal length and width was made in wheat, and sorghum cultivars; Saudi Red, Funk, Indian White, Morgon 854, Morgon 856 and Pioneer 8ss in relation to water limitation. Seedlings of wheat and sorghum cultivars grown under water limitation showed increases in their stomatal density, epidermal cell density and trichome index in response to reduced watering frequency. Stomatal index of the two species, however, were not altered in the same way. In sorghum there was no apparent change in stomatal index in relation to water limitation treatment but stomatal density and trichome index increased. In wheat there was a marked reduction in the stomatal index in response to water limitation but there were increases in trichome indices and stomatal densities of all parts of the leaves. Wheat plants grown under water limitation imposed by polyethylene glycol (PEG) treatments to roots showed marked reductions in their growth compared with controls. Stomatal density was found to increase in response to PEG treatments while stomatal index decreased. Incubation of newly-germinated wheat seedlings in PEG resulted in an inhibition of growth of coleoptiles. However, the density of stomata decreased, unlike what was seen in leaf tissues. When wheat coleoptiles were subjected to conditions of limited water availability guard mother cell (GMC) production appeared not to be influenced by water status of the tissues. Wheat coleoptiles grown under different periods of light showed slight decreases in stomata density compared to the controls. Abscisic acid treatment was able to substitute for water limitation treatments by reducing stomatal index in both leaves and coleoptiles whilst increasing the production of trichomes in leaves. However, in coleoptile the same treatment reduced both the GMC index as well as stomata index. Salinity treatments, inhibited seed germination and were found to decrease stomatal index. Incubation of wheat seedlings in PEG resulted in a yellow pigmentation of the roots. The pigment was tentatively identified. However, it was not possible to distinguish whether the pigment was a specific metabolite of PEG in the roots or was produced by a non-biological conversion of PEG.

Harnessing the control of flowering time in sorghum bicolor has been essential to programs committed to the development and improvement of this crop. The success of such programs was dependent on the utilization of six Maturity Loci, photoperiod- responsive floral repressors discovered through classic heritability studies. However, the identities of the genes underlying these loci have remained largely unknown. The elucidation of these genes allows for accelerated marker-assisted breeding programs and contributes to the understanding of flowering time in short day plants. Thus, in these studies, two Maturity Loci were identified using a map-based cloning approach, and alleles of each were sequenced in the germplasm. Expression analysis of individual genes by qRT-PCR and the transcriptome by RNAseq was utilized to characterize their response to photoperiod. Maturity Locus 1 (Ma1), the most effective of the loci, was identified as PSEUDORESPONSE REGULATOR 37, a component of the circadian clock. Sequence analysis revealed an allelic series at this locus, each conferring photoperiod insensitivity to varying degrees. It was demonstrated that the expression of this gene is regulated by the circadian clock, yet also highly dependent on light. Moreover, PRR37 was found to up-regulate floral repressors while down-regulating activators, providing a mechanism of flowering control consistent with the external coincidence model. Maturity Locus 6 (Ma6) also generated interest through its genetic interaction with Ma1, and was identified as Grain Yield, Plant Height and Heading Date 7 (Ghd7). Sequence analysis of Ghd7 revealed several severe mutations and these were traced through several Milo maturity standards, sweet and bioenergy varieties, as well as the pedigree of lines used heavily in the conversion of tropical sorghum to early flowering types. The expression of Ghd7 mirrors that observed for PRR37 and is also regulated by both light and the circadian clock. PRR37 and Ghd7 together confer greater repression of floral activators than either alone, but do so independently via pathways that converge on the same downstream "florigen". Thus in sorghum varieties with functional alleles of both, floral initiation is delayed indefinitely in long day photoperiods. The identification of these two genes provides a novel perspective on flowering in short day plants, while also accelerating breeding efforts that ultimately result in improved sorghum varieties for food, forage, and biofuels.