Wild Sorghum Research Articles

Agromorphological Characterization of Introgression Lines Derived from Wild and Exotic Sorghum Germplasm to Climate Change Challenges

Sorghum (Sorghum bicolor (L.) Moench) is vitally important for food security in semi-arid West Africa. The introgression of wild- and high transpiration efficiency genotypes may contribute genes for abiotic stress tolerance or novel traits. Characterizing the introgressed lines can help researchers in the process of varietal improvement. The objectives of this study are (i) To learn if introgression of wild sorghum (CWR) and high transpiration efficiency (HTE) lines into a very early maturing (photoperiod insensitive) local land-race variety can create useful variation for grain yield in drought-prone Sahelian environments, (ii) To determine if grain yield advantages (and putative drought tolerance traits) obtained from introgression of CWR and HTE germplasm are expressed differently in moderately to highly moisture-limited environments, and (iii) To understand the relationship between putative drought tolerance traits. These populations were developed from crosses between the CSM63E (Jakumbe, a high grains quality variety) and two wild parents (accessions) and five high transpiration efficiency (TE) sorghum accessions. Phenotyping was conducted using an alpha lattice design with three replications in two environments for agronomic traits (grain yield and components), flowering time and physiological traits (stay-green, chlorophyll content and lodging). A total of 669 BC1F5 progenies were developed. Genetic variation for grain yield and putative drought tolerant traits were evaluated. Both populations derived from wild parents exhibited in Cinzana a grain yield (>300 g/m2) greater than CSM63E (245 g/m2). In Bema, more than 75% of the progenies of all populations indicated a chlorophyll content at physiological maturity (>30 SPAD) higher than CSM63E (20 SPAD) chlorophyll content. The estimated broad sense heritability was generally high (≥0.50) for all traits. The results also showed a very significant interaction between genotype and environment for grain yield, flowering time, chlorophyll content, stay green and lodging. There was a strong correlation between stay green and chlorophyll content (0.60) on the one hand and between stay green and lodging (0.48) on the other. This great variability could help improve the grain yield of sorghum for farmers in the Sahelian zone.

Genome-Wide Association Study for Biomass Related Traits in a Panel of Sorghum bicolor and S. bicolor × S. halepense Populations.

The efficient use of sorghum as a renewable energy source requires high biomass yields and reduced agricultural inputs. Hybridization of Sorghum bicolor with wild Sorghum halepense can help meet both requirements, generating high-yielding and environment friendly perennial sorghum cultivars. Selection efficiency, however, needs to be improved to exploit the genetic potential of the derived recombinant lines and remove weedy and other wild traits. In this work, we present the results from a Genome-Wide Association Study conducted on a diversity panel made up of S. bicolor and an advanced population derived from S. bicolor × S. halepense multi-parent crosses. The objective was to identify genetic loci controlling biomass yield and biomass-relevant traits for breeding purposes. Plants were phenotyped during four consecutive years for dry biomass yield, dry mass fraction of fresh material, plant height and plant maturity. A genotyping-by-sequencing approach was implemented to obtain 92,383 high quality SNP markers used in this work. Significant marker-trait associations were uncovered across eight of the ten sorghum chromosomes, with two main hotspots near the end of chromosomes 7 and 9, in proximity of dwarfing genes Dw1 and Dw3. No significant marker was found on chromosomes 2 and 4. A large number of significant marker loci associated with biomass yield and biomass-relevant traits showed minor effects on respective plant characteristics, with the exception of seven loci on chromosomes 3, 8, and 9 that explained 5.2–7.8% of phenotypic variability in dry mass yield, dry mass fraction of fresh material, and maturity, and a major effect (R2 = 16.2%) locus on chromosome 1 for dry mass fraction of fresh material which co-localized with a zinc-finger homeodomain protein possibly involved in the expression of the D (Dry stalk) locus. These markers and marker haplotypes identified in this work are expected to boost marker-assisted selection in sorghum breeding.

Novel sources of drought tolerance from landraces and wild sorghum relatives

AbstractSorghum (Sorghum bicolor [L.] Moench) is the fifth most important cereal crop worldwide and second after maize (Zea mays L.) in Kenya. It is an important food security crop in arid and semi‐arid lands, where its production potential is hampered by drought. Drought tolerance can be measured by a plant's ability to resist premature senescence, often described as stay‐green. This study was carried out with the objective of identifying novel stay‐green trait among wild and landrace genotypes of sorghum. Forty‐four sorghum genotypes that included 16 improved, nine landraces, and 17 wild relatives of sorghum alongside known stay‐green sources, B35 and E36‐1, were evaluated under well‐watered and water‐stressed conditions in an alpha‐lattice design of three replications. Data was collected on plant height (PHT), flag leaf area (FLA), panicle weight (PWT), 100‐seed weight (HSW), relative chlorophyll content (RCC), number of green leaves at maturity (GLAM), days to 50% flowering (DFL), and grain yield (YLD). Genetic diversity was determined using diversity arrays technology (DArT) sequencing and quality control (QC) markers were generated using a java script. Lodoka, a landrace, was the most drought‐tolerant genotype, recorded the highest numbers of RCC and GLAM, and outperformed B35 and E36‐1 in yield under water‐stress and well‐watered conditions. The RCC was highly correlated with GLAM (r = .71) and with yield‐related traits, HSW (r = .85), PWT (r = .82), and YLD (r = .78). All traits revealed high heritability (broad‐sense) ranging from 60.14 to 98.4% for RCC and DFL, respectively. These results confirm earlier reports that wild relatives and landraces are a good source of drought tolerance alleles.

Genetic diversity analysis of geographically diverse landraces and wild accessions in sorghum

Landraces are highly dynamic populations with historical origins. Several factors have influenced the evolution of landraces and some of them were selection by farmers, natural selection, gene-flow from various neighboring populations, genetic drifts, etc. In this study, we phenotyped 36 landraces and wild populations of sorghum conserved at ICRISAT genebank, Hyderabad, India, to assess the diversity among the populations of sorghum. Since landraces are diverse populations, we phenotyped more plants (over 100 plants) in each accession for nine economically important quantitative traits, thus capturing the entire variability. Our study revealed that the clustering pattern based on D2 statistics grouped the 36 accessions into 5 clusters, in which cluster 1 holds the maximum number of 15 accessions and cluster 3 with the least (2 accessions). Minimal intra cluster distance (3.66) was observed in cluster 3 followed by cluster 5 (9.52), while the maximum intra cluster distance was found in cluster 2 (12.50). The highest inter cluster distance was found between clusters 1 and 4 (16.29) indicating the presence of wide diversity between accessions of these two clusters. Accessions in cluster 1 were early maturing (67 days after sowing, DAS) while those in cluster 4 were late maturing (129 DAS) and high yielding (36.9 g). Results from this study provide information about the diversity of landraces and wild sorghum populations for their utilization in crop improvement

Modelled distributions and conservation priorities of wild sorghums (Sorghum Moench)

AbstractAimTo fill knowledge gaps regarding the distributions, ecogeographic niches and conservation status of sorghum's wild relatives (Sorghum Moench).LocationThe study covered the potential native ranges of wild Sorghum taxa worldwide, including Australia, New Guinea, Asia, Africa and Central America.MethodsWe modelled the distributions of 23 wild Sorghum taxa, characterized their ecogeographic niches, assessed their conservation status both ex situ and in situ and performed preliminary threat assessments.ResultsThree taxa were categorized as “high priority” for further conservation based on their ex situ and in situ assessments, with a further 19 as “medium priority” and only one as “low priority”. The preliminary threat assessment indicated that 12 taxa may be Endangered, four Vulnerable and four Near Threatened. The taxa fill a wide range of climatic niches, both across and within taxa, including temperatures and precipitation.Main conclusionsTaxon richness hotspots, especially in northern Australia, represent hotspots for conservation action, including further seed collection and habitat protection, with Sorghum macrospermum E. D. Garber being the highest priority for increased in situ protection. Outside Australia, Sorghum propinquum (Kunth) Hitchc. stands out for further ex situ conservation, especially given its close relationship to the crop.

Wild Sorghum as a Promising Resource for Crop Improvement.

Sorghum bicolor (L.) Moench is a multipurpose food crop which is ranked among the top five cereal crops in the world, and is used as a source of food, fodder, feed, and fuel. The genus Sorghum consists of 24 diverse species. Cultivated sorghum was derived from the wild progenitor S. bicolor subsp. verticilliflorum, which is commonly distributed in Africa. Archeological evidence has identified regions in Sudan, Ethiopia, and West Africa as centers of origin of sorghum, with evidence for more than one domestication event. The taxonomy of the genus is not fully resolved, with alternative classifications that should be resolved by further molecular analysis. Sorghum can withstand severe droughts which makes it suitable to grow in regions where other major crops cannot be grown. Wild relatives of many crops have played significant roles as genetic resources for crop improvement. Although there have been many studies of domesticated sorghum, few studies have reported on its wild relatives. In Sorghum, some species are widely distributed while others are very restricted. Of the 17 native sorghum species found in Australia, none have been cultivated. Isolation of these wild species from domesticated crops makes them a highly valuable system for studying the evolution of adaptive traits such as biotic and abiotic stress tolerance. The diversity of the genus Sorghum has probably arisen as a result of the extensive variability of the habitats over which they are distributed. The wild gene pool of sorghum may, therefore, harbor many useful genes for abiotic and biotic stress tolerance. While there are many examples of successful examples of introgression of novel alleles from the wild relatives of other species from Poaceae, such as rice, wheat, maize, and sugarcane, studies of introgression from wild sorghum are limited. An improved understanding of wild sorghums will better allow us to exploit this previously underutilized gene pool for the production of more resilient crops.

Crop wild relatives as a genetic resource for generating low-cyanide, drought-tolerant Sorghum

Using a Sorghum bicolor cultivar and seven wild Sorghum species endemic to Australia as our experimental system, we monitored their different responses to drought by assessing growth and morphological, physiological and biochemical parameters. Drought stress significantly decreased height, biomass, the maximum potential quantum efficiency of photosystem II, photosynthetic rate and relative water content in S. bicolor, while several of the wild species were much more tolerant. Drought significantly increased dhurrin concentration in aboveground tissue in S. bicolor but not in the wild species. Root dhurrin content was unaffected by drought in S. bicolor, in contrast to the varied responses observed in the wild species. Sorghum macrospermum and S. brachypodum maintained relatively high growth and photosynthetic performance under drought, with negligible aboveground dhurrin content. These wild species are promising candidates for sorghum crop improvement.

First direct evidence of wild plant grinding process from the Holocene Sahara: Use-wear and plant micro-residue analysis on ground stone tools from the Farafra Oasis, Egypt

The excavation of the 8000-year-old Hidden Valley village has highlighted the importance of wild plant exploitation in the Mid-Holocene contexts of the Farafra Oasis. This site yielded high numbers of plant macro-remains, which were analysed during the early 2000s by A.G. Fahmy. Among these, Sorghum and other species of wild grasses, often found charred in the fireplaces of the site, prevail; together with the assemblage from E−75-6 (Nabta Playa) these represent the oldest evidence of wild Sorghum exploitation in the Eastern Sahara. Hidden Valley village has also yielded one of the largest assemblages of grinding implements for the whole of North Africa, which, until recent times, had been analysed only from a techno-typological perspective. The general assumption of a direct link between grinding tools and plant exploitation has been tested, and challenged using, for the first time for North African contexts, an integrated method, carried out on the actual tools, combining low- and high-power use-wear and plant micro-residue analyses. Firstly, micro-residues (mainly starch granules and phytoliths) were extracted from the Hidden Valley grinding tools, and analysed by means of a high magnification transmitted-light microscope. The identification of the plant micro-fossils was based upon the ‘visual matching’ of morphological characteristics with those of a purpose-built reference collection of modern starch granules and phytoliths. Then, tool micro-topography and use-wear traces were analysed both using a low- and high-power approach in order to detect the possible presence of macro- and micro-wear associated with plant exploitation. The grinding stones analysed showed very developed wear mainly consistent with plant processing activities. The same artefacts also yielded starch granules, sometimes in large quantities, together with a lower number of phytoliths. A number of plant tribes from the grass family Poaceae were represented in the micro-remain assemblage. Our results integrate and complement the previous archaeobotanical work carried out on the plant macro-remains from this site and stress the important role played by grinding tools in the processing activities of the variety of wild grasses that were consumed as staple food by Eastern Saharan communities during the Holocene.

Nutritional potential of wild sorghum: Grain quality of Sudanese wild sorghum genotypes (Sorghum bicolor L. Moench).

In the last decades, deficiency of macro‐ and micronutrients was considered as a serious problem associated with the increase in the human population. To meet the increased demand for food consumption, the wild relative plant might serve as an important source of new genetic material for increasing macro‐ and micronutrients. To investigate this, the variations in protein content, in vitro protein digestibility, tannin content, phytic acid content, total polyphenol content, and total and bioavailability of minerals were studied in grains of ten wild sorghums and two released sorghum cultivars. The results showed significant differences (p ≤ 0.05) in all quality tests among the genotypes. The highest percentage of total protein contents and in vitro protein digestibility were encountered in the grains of PQ‐434 (14.6%) and the released cultivar AG8 (49.8%), respectively, while the highest concentrations of total and bioavailable iron were found in the grains of Almahkara (3.17 mg/100 g) and Abusabiba (92.8 mg/100 g), respectively. The grains of wild sorghum genotype Adar Umbatikh grains were found to possess higher total zinc contents. The PCA identified only five components of eigenvalues greater than one and cumulatively accounted for 88% of the total variation. It could be concluded that Almahkara and PQ‐434 could be used as potential sources for iron and protein sorghum biofortification, respectively. Results from this study might be used in the development of new value‐added products from wild sorghum grains by‐products.

Risks Posed by Intercrops and Weeds as Alternative Hosts to Xanthomonas campestris pv. musacearum in Banana Fields.

Alternative host plants are important in the survival and perpetuation of several crop pathogens and have been suspected to play a role in the survival of Xanthomonas campestris pv. musacearum (Xcm) and perpetuation of Xanthomonas wilt (XW) disease of banana and enset. This study determined the potential risk posed by two weeds (Canna spp. and wild sorghum) and common banana intercrops (maize, millet, sorghum, taro, and sugarcane) as alternative hosts to Xcm. The study employed screenhouse experiments, laboratory procedures and diagnosis of banana fields in XW-affected landscapes. Typical XW symptoms were only observed in artificially inoculated Canna sp., with an incidence of 96%. Leaf lesions characteristic of xanthomonads occurred on millet (50%) and sorghum (35%), though the plants recovered. No symptoms occurred in maize, sugarcane, taro or wild sorghum. However, Xcm was recovered from all these plant species, with higher recoveries in Canna sp. (47%), millet (27%), sugarcane (27%), and wild sorghum (25%). Only isolates recovered from Canna sp., millet, sorghum and wild sorghum caused disease in banana plantlets. The presence and incidence of XW on-farm was positively associated with the presence of susceptible ABB Musa genotypes and negatively with number of banana cultivars on farm and household access to training on XW management. Only 0.02% of field sampled Canna spp. plants had Xcm. Risk posed by Canna spp. on-farm could be limited to tool transmission as it has persistent floral bracts that prevent insect-mediated infections. Given the high susceptibility, perennial nature and propagation through rhizomes of Canna sp., it could pose a moderate-high risk, thus warranting some attention in the management of XW disease. Sugarcane could offer a low-moderate risk due to its perennial nature and propagation through rhizomes while risk from maize, millet, and sorghum was deemed zero-low due to their annual nature, wind-mediated mode of pollination and propagation through seed. Understanding the interactions of a crop pathogen with other plants is thus important when diversifying agroecosystems. The study findings also suggest other factors such as cultivar composition and management of the disease at farm and landscape level to be important in the perpetuation of XW disease.

Sweet Sorghum Originated through Selection of Dry, a Plant-Specific NAC Transcription Factor Gene.

Sorghum (Sorghum bicolor) is the fifth most popular crop worldwide and a C4 model plant. Domesticated sorghum comes in many forms, including sweet cultivars with juicy stems and grain sorghum with dry, pithy stems at maturity. The Dry locus, which controls the pithy/juicy stem trait, was discovered over a century ago. Here, we found that Dry gene encodes a plant-specific NAC transcription factor. Dry was either deleted or acquired loss-of-function mutations in sweet sorghum, resulting in cell collapse and altered secondary cell wall composition in the stem. Twenty-three Dry ancestral haplotypes, all with dry, pithy stems, were found among wild sorghum and wild sorghum relatives. Two of the haplotypes were detected in domesticated landraces, with four additional dry haplotypes with juicy stems detected in improved lines. These results imply that selection for Dry gene mutations was a major step leading to the origin of sweet sorghum. The Dry gene is conserved in major cereals; fine-tuning its regulatory network could provide a molecular tool to control crop stem texture.

Genotypic and Pathogenic Diversity of Colletotrichum sublineola Isolates from Sorghum (Sorghum bicolor) and Johnsongrass (S. halepense) in the Southeastern United States.

Anthracnose caused by Colletotrichum sublineola is an important disease of cultivated sorghum (Sorghum bicolor) worldwide. Anthracnose is also common on the ubiquitous wild sorghum relative Johnsongrass (S. halepense). Analysis of repetitive molecular fingerprinting markers revealed that isolates of C. sublineola from both hosts in the southeastern United States were genotypically diverse, with relatively few haplotypes found in more than one location. With few exceptions, isolates recovered from S. bicolor belonged to a population that was genetically distinct from the population recovered from S. halepense. Twenty-three isolates from cultivated sorghum were all pathogenic to at least one of 13 heritage inbred lines of S. bicolor. In all, 4 of 10 isolates from S. halepense were also pathogenic to one or more of the lines, while the rest caused no disease in greenhouse assays. The four pathogenic isolates from S. halepense were less aggressive, on average, than isolates from S. bicolor, although the ranges overlapped. Pathogenicity tests involving 15 representative pathogenic isolates from S. bicolor and S. halepense on eight heritage inbred lines of S. bicolor identified 12 races. The combined results of this study demonstrated that C. sublineola comprises two separate host-associated subpopulations in the field, even though some isolates from S. halepense were able to cause disease on S. bicolor under ideal greenhouse conditions. Nonetheless, the apparent existence of infrequent cross-infection events in the field, indicated by molecular fingerprinting, suggests that Johnsongrass has the potential to serve as a refuge and an incubator for genetic diversity in C. sublineola, which can complicate efforts to develop and deploy resistant sweet sorghum varieties in the region.

Quantification of sorgoleone in sorghum accessions from eight southern African countries

Allelopathic effects of sorghum (Sorghum bicolor (L.) Moench) can ease weed pressure and improve grain yields if cultivars capable of producing high levels of natural chemicals effective in suppressing weeds of economic importance are identified. Three hundred and fifty three sorghum accessions fom Botswana, Malawi, Mozambique, Namibia, South Africa, Tanzania, Zambia and Zimbabwe were screened for sorgoleone content using high-performance liquid chromatography (HPLC) in 2016. Three replicates of seeds of each accession were germinated in petri dishes at the University of Zimbabwe. Roots of six-day-old seedlings were excised from shoots and immersed in methanol to extract sorgoleone. The crude extract was filtered, evaporated and dissolved in the mobile phase (1 mg mL−1) prior to HPLC analysis. One-way ANOVA showed that there were highly significant differences in sorgoleone production among the sorghum cultivars (p < 0.001). The South African landrace IS9456 yielded the highest sorgoleone (584.69 μg mg−1 root fresh weight). High levels of sorgoleone were also detected in accessions from Botswana as well as in wild sorghum from Zimbabwe. Improved sorghums had very little sorgoleone. It was concluded that some landraces and wild sorghum have high potential for use in allelopathic weed control.

Novel Grain Weight Loci Revealed in a Cross between Cultivated and Wild Sorghum

Grain weight has increased during domestication of cereals. Together with grain number it determines yield, but the two are often negatively correlated. Understanding the genetic architecture of grain weight and its relationship with grain number is critical to enhance crop yield. Sorghum is an important food, feed, and biofuel crop well-known for its adaptation to drought and heat. This study aimed to dissect the genetic basis of thousand grain weight (TGW) in a BCF population between a domesticated sorghum accession and its wild progenitor, subsp. and investigate its relationship with grain number. Thousand grain weight, grain number, and yield were measured in field trials in two successive years. A strong negative correlation between TGW and grain number was observed in both trials. In total, 17 TGW quantitative trait loci (QTL) were identified, with 11 of them exhibiting an opposing effect on grain number, implying the correlation between TGW and grain number is due to pleiotropy. Nine grain size candidate genes were identified within 6 TGW QTL, and of these 5 showed signatures of selection during sorghum domestication. Large-effect QTL in this study that have not been identified previously in cultivated sorghum were found to contain candidate genes with domestication signal, indicating that these QTL were affected during sorghum domestication. This study sheds new light on the genetic basis of TGW, its relationship with grain number, and sorghum domestication.

Assessment of Striga resistance in wild relatives of sorghum under field conditions

The witch-weeds (Striga spp.) are destructive root parasites of many crops. They result in considerable crop damage, especially in the semiarid tropic parts of the world. The parasite control is difficult due to the complexity of the parasite life cycle, and the large number of seeds produced by the parasite with prolonged viability. The most promising way of controlling the parasite is through the development of the resistant crop varieties. Identification of different sources of resistance will enhance breeding for resistant varieties. Wild relatives of sorghum are rich in genetic diversity and have a broad genetic base including novel and valuable traits like Striga and disease resistance. In this context, 55 wild sorghum lines were collected from three regions of Sudan including eastern Sudan (Gadaref), central Sudan (Gezira), and western Sudan (North Kordofan). The collected germplasm was assessed for Striga resistance using artificial infestation. The results showed a significant difference in the number of Striga emerged plants compared to the checks. Hence, the significant difference was observed in the number of days to 50% plants to reach flowering, plant height, and grain yield per hectare. The wild relatives were also morphologically characterized and the result showed 55 lines structured in six groups independently from their geographical regions.

Evidence for Sorghum Domestication in Fourth Millennium BC Eastern Sudan: Spikelet Morphology from Ceramic Impressions of the Butana Group

Since the 1970s, the quest for finding the origins of domesticated sorghum in Africa has remained elusive despite the fact that sorghum (Sorghum bicolor (L.) Moench. sensu stricto) is one of the world’s most important cereals. Recognized as originating from wild populations in Africa (Sorghum arundinaceum (Desv.) Stapf), however, the date and cultural context of its domestication has been controversial, with many scholars inferring an early Holocene origin in parallel with better-known cereal domestications. This paper presents firm evidence that the process of domesticating sorghum was present in the far eastern Sahel in the southern Atbai at an archaeological site associated with the Butana Group. Ceramic sherds recovered from excavations undertaken by the Southern Methodist University Butana Project during the 1980s from the largest Butana Group site, KG23, near Kassala, eastern Sudan, were analyzed, and examination of the plant impressions in the pottery revealed diagnostic chaff in which both domesticated and wild sorghum types were identified, thus providing archaeobotanical evidence for the beginnings of cultivation and emergence of domesticated characteristics within sorghum during the fourth millennium BC in eastern Sudan.

Domestication reduces alternative splicing expression variations in sorghum.

Domestication is known to strongly reduce genomic diversity through population bottlenecks. The resulting loss of polymorphism has been thoroughly documented in numerous cultivated species. Here we investigate the impact of domestication on the diversity of alternative transcript expressions using RNAseq data obtained on cultivated and wild sorghum accessions (ten accessions for each pool). In that aim, we focus on genes expressing two isoforms in sorghum and estimate the ratio between expression levels of those isoforms in each accession. Noticeably, for a given gene, one isoform can either be overexpressed or underexpressed in some wild accessions, whereas in the cultivated accessions, the balance between the two isoforms of the same gene appears to be much more homogenous. Indeed, we observe in sorghum significantly more variation in isoform expression balance among wild accessions than among domesticated accessions. The possibility exists that the loss of nucleotide diversity due to domestication could affect regulatory elements, controlling transcription or degradation of these isoforms. Impact on the isoform expression balance is discussed. As far as we know, this is the first time that the impact of domestication on transcript isoform balance has been studied at the genomic scale. This could pave the way towards the identification of key domestication genes with finely tuned isoform expressions in domesticated accessions while being highly variable in their wild relatives.

Aggressiveness of Colletotrichum sublineola Strains from Sorghum bicolor and S. halepense to Sweet Sorghum Variety Sugar Drip, and Their Impact on Yield.

Sweet sorghum (Sorghum bicolor) has been grown in the southeastern United States for more than 150 years on a relatively limited scale, primarily for forage and for the production of table syrup. However, interest in the crop has increased recently due to its potential as a feedstock for biofuels. Colletotrichum sublineola is the causal agent of anthracnose on cultivated sorghum and on the wild sorghum relative Johnsongrass (S. halepense). Anthracnose is an important disease of grain sorghum worldwide, but little is known about its impact on sweet sorghum in the U.S. The aggressiveness of four C. sublineola isolates collected from sweet and grain sorghum and from Johnsongrass at various locations across Kentucky was measured as disease incidence and severity on the susceptible heirloom sweet sorghum inbred Sugar Drip in inoculated field trials. The isolate from sweet sorghum was the most aggressive, while the two Johnsongrass isolates caused only minimal disease symptoms. Disease incidences of up to 99%, and severities of up to 16.7% of leaf area affected, had no negative effect on the yield of biomass, grain, juice, or Brix. Removal of sorghum seed heads increased Brix in the stalks and leaves, but did not affect susceptibility to anthracnose. The same group of fungal isolates was evaluated for aggressiveness in greenhouse assays on juvenile plants, and in the laboratory on seedlings and detached leaf sheaths. These protocols will be useful for prescreening sorghum germplasm for new sources of resistance or for characterizing the aggressiveness of new fungal isolates.

Geographical distribution, diversity and gap analysis of East African sorghum collection conserved at the ICRISAT genebank

The aim of the investigation was to assess the geographical distribution, diversity and gaps in sorghum collection from East African countries conserved at the ICRISAT genebank. The collection represents a total of 12,750 accessions including 11,672 landraces, 877 breeding materials, six improved cultivars, and 195 wild accessions. Passport data and FloraMap, a GIS software were used to assess geographical distribution and identify gaps. Range, mean, variance and phenotypic diversity index were estimated using GENSTAT 13.1. to assess the diversity in the collection. Cultivated sorghums classified into races and intermediate races based on spikelet and panicle morphology differed significantly, and races showed more variation than intermediate races for days to 50% flowering in postrainy season, plant height in rainy season, basal tillers per plant, panicle length, seed width and 100 seed weight. A total of 153 districts located in 50 provinces of 10 East African countries were found as the geographical gaps. Probably due to large variation for maturity, timing of collecting mission, and accessibility to the area under sorghum cultivation, both North and South Sudan were found as the major gaps with seven and 50 districts, respectively. The wild sorghum collection from East African countries belongs to S. bicolor, S. halepense, S. lanceolatum, S. macrochaeta, S. purpureosericeum and S. versicolor. Remaining species of genus sorghum were considered as taxonomic gaps. The gaps identified in the present study need to be explored on a priority basis to collect and conserve most diverse sorghum germplasm.

Novel Sources of Witchweed (Striga) Resistance from Wild Sorghum Accessions.

Sorghum is a major food staple in sub-Saharan Africa (SSA), but its production is constrained by the parasitic plant Striga that attaches to the roots of many cereals crops and causes severe stunting and loss of yield. Away from cultivated farmland, wild sorghum accessions grow as weedy plants and have shown remarkable immunity to Striga. We sought to determine the extent of the resistance to Striga in wild sorghum plants. Our screening strategy involved controlled laboratory assays of rhizotrons, where we artificially infected sorghum with Striga, as well as field experiments at three sites, where we grew sorghum with a natural Striga infestation. We tested the resistance response of seven accessions of wild sorghum of the aethiopicum, drummondii, and arundinaceum races against N13, which is a cultivated Striga resistant landrace. The susceptible control was farmer-preferred variety, Ochuti. From the laboratory experiments, we found three wild sorghum accessions (WSA-1, WSE-1, and WSA-2) that had significantly higher resistance than N13. These accessions had the lowest Striga biomass and the fewest and smallest Striga attached to them. Further microscopic and histological analysis of attached Striga haustorium showed that wild sorghum accessions hindered the ingression of Striga haustorium into the host endodermis. In one of the resistant accessions (WSE-1), host and parasite interaction led to the accumulation of large amounts of secondary metabolites that formed a dark coloration at the interphase. Field experiments confirmed the laboratory screening experiments in that these same accessions were found to have resistance against Striga. In the field, wild sorghum had low Area under the Striga Number Progressive curve (AUSNPC), which measures emergence of Striga from a host over time. We concluded that wild sorghum accessions are an important reservoir for Striga resistance that could be used to expand the genetic basis of cultivated sorghum for resistance to the parasite.