Cultivated Sorghum Research Articles

Adaptive values of wild × cultivated sorghum (Sorghum bicolor (L.) Moench) hybrids in generations F1, F2, and F3

Gene flow between cultivated and their wild relatives is one of the main ecological concerns associated with the introduction genetically modified (GM) cultivars. GM sorghum cultivar has been developed and its commercial production may be possible in the near future. The rate of gene flow depends on the fitness of wild × cultivated sorghum hybrids. The study aimed at estimating adaptive values of wild × cultivated sorghum hybrids in generations F1, F2, and F3 compared to their parents. Artificial crosses of four wild sorghums, five cultivated sorghums, and two male sterile lines were made to produce the F1 generation, which were advanced to F2 and F3. Each hybrid generation and their respective parents were evaluated for their adaptive value at two sites in a randomised complete block design with seven replicates. The resulting progenies did not show serious fitness penalties. Some hybrids were as fit as their respective wild parents and no consistent differences exist between the three generations studied. Thus, the resultant wild × cultivated hybrids may act as avenue for introgression.

Genetic structure and relationships within and between cultivated and wild sorghum (Sorghum bicolor (L.) Moench) in Kenya as revealed by microsatellite markers

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

Investigation of pollen competition between wild and cultivated sorghums (Sorghum bicolor (L.) Moench) using simple sequence repeats markers

In self-compatible plant species stigmata receive a mixture of self and outcrossed pollen and competition between them is expected to play a major role in determining the pollen-mediated gene flow. The use of male sterile bait plants in field trials to demonstrate the rate of gene flow is questionable due to lack of pollination competition. However, little direct evidence has been published. A field experiment of male sterile and male fertile sorghum pollen recipient bait plants was conducted to evaluate pollen competition between wild and cultivated sorghums and the effects of pollen competition on gene flow assessment. Pollen competition between wild and cultivated sorghums was estimated from two-component pollen mixtures of wild and cultivated sorghum (1:1 ratio) applied to wild, cultivated and male-sterile maternal bait plants. Paternity was determined in the progeny using two diagnostic Simple Sequence Repeat markers. The study found that self pollen has higher seed-siring success. Maternal genotype influences the siring ability of the pollen donor components which significantly deviated from the 1:1 pollen loads. The study showed that published estimates of gene flow derived from studies using male-sterile bait plants seriously overestimate gene flow and that pollen competition may be a significant factor influencing outcrossing rates. The results suggest that the predominant direction of gene flow is from cultivated to wild sorghum, potentially leading to introgression of crop genes into wild sorghum. Pollen competition should be taken into account in gene flow estimation, since presence of self-pollen can account for over half of seed produced irrespective of maternal genotype.

Growth and fitness components of wild × cultivated Sorghum bicolor (Poaceae) hybrids in Nebraska

Gene flow from crops to wild relatives has received considerable attention since the advent of genetically modified crops. Numerous researchers have found wild-crop hybrids to be nearly as fit as their wild parents, which suggests that crop genes may persist in wild populations. Components of the ecological fitness of cultivated sorghum, its wild relative, shattercane, and their hybrids have not been studied. • To assess the potential for gene introgression into shattercane, we crossed cultivated sorghum to a single inbred shattercane line to produce F(1) hybrids and measured growth and several components of ecological fitness in relation to both parents in Nebraska, USA. • Germination of F(1) seeds was similar to that of its shattercane parent except at high temperatures, where it was as sensitive as the sorghum parent. The F(1) grew taller and produced more biomass than either parent, but the F(1) leaf area index was intermediate. Fecundity of the F(1) plant was similar to that of shattercane and much greater than that of cultivated sorghum. • Considering all data, the ecological fitness of shattercane × cultivated sorghum F(1) hybrids may be equivalent to the wild shattercane parent, which suggests that crop genes that are either neutral or beneficial to shattercane would persist in populations within agroecosystems.

Allelic variation of the β-, γ- and δ-kafirin genes in diverse Sorghum genotypes

The β-, γ- and δ-kafirin genes were sequenced from 35 Sorghum genotypes to investigate the allelic diversity of seed storage proteins. A range of grain sorghums, including inbred parents from internationally diverse breeding programs and landraces, and three wild Sorghum relatives were selected to encompass an extensive array of improved and unimproved germplasm in the Eusorghum. A single locus exists for each of the expressed kafirin-encoding genes, unlike the multigenic α-kafirins. Significant diversity was found for each locus, with the cysteine-rich β-kafirin having four alleles, including the first natural null mutant reported for this prolamin subfamily. This allele contains a frame shift insertion at +206 resulting in a premature stop codon. SDS-PAGE revealed that lines with this allele do not produce β-kafirin. An analysis of flour viscosity reveals that these β-kafirin null lines have a difference in grain quality, with significantly lower viscosity observed over the entire Rapid ViscoAnalyser time course. There was less diversity at the protein level within the cysteine-rich γ-kafirin, with only two alleles in the cultivated sorghums. There were only two alleles for the δ-kafirin locus among the S. bicolor germplasm, with one allele encoding ten extra amino acids, of which five were methionine residues, with an additional methionine resulting from a nucleotide substitution. This longer allele encodes a protein with 19.1% methionine. The Asian species, S. propinquum, had distinct alleles for all three kafirin genes. We found no evidence for selection on the three kafirin genes during sorghum domestication even though the δ-kafirin locus displayed comparatively low genetic variation. This study has identified genetic diversity in all single copy seed storage protein genes, including a null mutant for β-kafirin in Sorghum.

Phylogenetic analysis of the genus Sorghum based on combined sequence data from cpDNA regions and ITS generate well-supported trees with two major lineages

Wild Sorghum species provide novel traits for both biotic and abiotic stress resistance and yield for the improvement of cultivated sorghum. A better understanding of the phylogeny in the genus Sorghum will enhance use of the valuable agronomic traits found in wild sorghum. METHODS Four regions of chloroplast DNA (cpDNA; psbZ-trnG, trnY-trnD, trnY-psbM and trnT-trnL) and the internal transcribed spacer (ITS) of nuclear ribosomal DNA were used to analyse the phylogeny of sorghum based on maximum-parsimony analyses. Parsimony analyses of the ITS and cpDNA regions as separate or combined sequence datasets formed trees with strong bootstrap support with two lineages: the Eu-sorghum species S. laxiflorum and S. macrospermum in one and Stiposorghum and Para-sorghum in the other. Within Eu-sorghum, S. bicolor-3, -11 and -14 originating from southern Africa form a distinct clade. S. bicolor-2, originally from Yemen, is distantly related to other S. bicolor accessions. Eu-sorghum species are more closely related to S. macrospermum and S. laxiflorum than to any other Australian wild Sorghum species. S. macrospermum and S. laxiflorum are so closely related that it is inappropriate to classify them in separate sections. S. almum is closely associated with S. bicolor, suggesting that the latter is the maternal parent of the former given that cpDNA is maternally inherited in angiosperms. S. bicolor-3, -11 and -14, from southern Africa, are closely related to each other but distantly related to S. bicolor-2.

Ecogeographical distribution of wild, weedy and cultivated Sorghum bicolor (L.) Moench in Kenya: implications for conservation and crop-to-wild gene flow

The potential gene flow between a crop and its wild relatives is largely determined by the overlaps in their ecological and geographical distributions. Ecogeographical databases are therefore indispensable tools for the sustainable management of genetic resources. In order to expand our knowledge of Sorghum bicolor distribution in Kenya, we conducted in situ collections of wild, weedy and cultivated sorghum. Qualitative and quantitative morphological traits were measured for each sampled wild sorghum plant. Farmers’ knowledge relating to the management of sorghum varieties and autecology of wild sorghum was also obtained. Cluster analysis supports the existence of several wild sorghum morphotypes that might correspond to at least three of the five ecotypes recognized in Africa. Intermediate forms between wild and cultivated sorghum belonging to the S. bicolor ssp. drummondii are frequently found in predominantly sorghum growing areas. Crop-wild gene flow in sorghum is likely to occur in many agroecosystems of Kenya.

Genetic diversity in Chinese sorghum landraces revealed by chloroplast simple sequence repeats

A collection of sorghum, including more than 12,000 Chinese landraces, has been constructed and maintained in China. However, the genetic diversity of Chinese sorghum landraces has not been fully investigated, and the origin of Chinese sorghum is still in dispute. In this study, the complete chloroplast genome sequence of sorghum line Tx623B was searched for simple sequence repeats (SSRs). 31 SSR loci with at least 10 mononucleotide repeats or five dinucleotide repeats were identified, and primer pairs for 27 loci were designed. Chloroplast DNA variation in cultivated sorghum was investigated by using these primer pairs on 185 Chinese sorghum landraces and 70 cultivated sorghum accessions from other countries. Among the 27 loci, 14 were polymorphic. The number of alleles per polymorphic locus ranged from 2 to 5 with an average of 2.79. Allelic data at 14 polymorphic loci were combined to give 12 haplotypes. The average allelic diversity index across the 14 polymorphic loci and corresponding haplotype diversity were markedly lower for Chinese sorghum landraces than were those for accessions from other countries. However, Chinese sorghum landraces shared a predominant allele at each polymorphic locus and a predominant haplotype with foreign accessions. Our results indicate that Chinese landraces experienced a severe maternal bottleneck during the introduction process with a predominant haplotype being present in 171 of 185 accessions analyzed. Except for one rare exception, haplotypes found in Chinese landraces were either identical or closely related to those found in foreign accessions and could not be separated clearly from them by cluster analysis. Our results are consistent with the hypothesis of African origin of Chinese sorghum.

The Potential for Crop‐to‐Wild Gene Flow in Sorghum in Ethiopia and Niger: A Geographic Survey

Information about the potential for crop–wild hybridization is needed to understand how crop genes, including transgenes, affect the population genetics and ecology of sexually compatible relatives. Transgenic sorghum is under development for use by traditional farmers in Africa, the center of origin for sorghum [Sorghum bicolor (L.) Moench], but systematic surveys of the current extent of contact with wild and weedy relatives are lacking. We studied wild and weedy sorghums that are interfertile with the crop and constitute a crop–wild–weed complex. The survey was conducted in 2005 in areas of traditional sorghum cultivation in three regions of Ethiopia and two regions of Niger. Within each region, we examined eight representative sorghum fields at each of 10 locations during peak flowering of the crop. In all regions, wild and weedy sorghum occurred intermixed with and adjacent to cultivated sorghum. Wild and weedy sorghums were detected at 56, 44, and 13% of the Ethiopian sites (Amhara, Tigray, and Hararghe regions, respectively), and 74 and 63% of sites in Niger (Maradi‐Tahoua and Tillabery‐Dosso regions, respectively). Flowering periods of wild and weedy sorghum populations overlapped with those of cultivated sorghum at most sites where the two co‐occurred, especially in Ethiopia, and many putative crop–wild hybrids were observed. Therefore, current gene transfer from cultivated sorghum to wild and weedy sorghum populations in Ethiopia and Niger is likely to be widespread.

Assessment of genetic diversity and relationship among a collection of US sweet sorghum germplasm by SSR markers

Sweet sorghum (Sorghum bicolor L.) is a type of cultivated sorghums and has been recognized widely as potential alternative source of bio-fuel because of its high fermentable sugar content in the stalk. A substantial variation of sugar content and related traits is known to exist in US sweet sorghum. The objectives of the study were to assess the genetic diversity and relationship among the US sweet sorghum cultivars and lines using SSR markers and to examine the genetic variability within sweet sorghum accessions for sugar content. Sixty-eight sweet sorghum and four grain sorghum cultivars and lines were genotyped with 41 SSR markers that generated 132 alleles with an average of 3.22 alleles per locus. Polymorphism information content (PIC) value, a measure of gene diversity, was 0.40 with a range of 0.03-0.87. The genetic similarity co- efficient was estimated based on the segregation of the 132 SSR alleles. Clustering analysis based on the genetic similarity (GS) grouped the 72 sorghum accessions into 10 distinct clusters. Grouping based on clustering analysis was in good agreement with available pedigree and genetic background informa- tion. The study has revealed the genetic relationship of cultivars with unknown parentage to those with known parentage. A number of diverse pairs of sweet sorghum accessions were identified which were polymorphic at many SSR loci and significantly different for sugar content as well. Information generated from this study can be used to select parents for hybrid development to maximize the sugar content and total biomass, and development of segregating populations to map genes controlling sugar content in sweet sorghum.

Location, acceptance and suitability of lepidopteran stemborers feeding on a cultivated and wild host-plant to the endoparasitoid Cotesia flavipes Cameron (Hymenoptera: Braconidae)

Maize fields in Africa are usually surrounded by land occupied by wild plants many of which harbor lepidopteran stemborer species not found on crops. It is not known if the exotic braconid parasitoid Cotesia flavipes, which was released in Kenya in 1993 against the invasive crambid Chilo partellus, searches for and attacks these borers in their natural habitats and whether they are suitable for parasitoid development. The objective of this study was to assess the relationship between acceptance and suitability of six stemborer species attacking cultivated sorghum (C. partellus, Busseola fusca, Sesamia calamistis, and S. nonagrioides) or Napier grass (Busseola phaia and Sciomesa piscator) to C. flavipes. Although all stemborer species were equally accepted for ovipositor probing by C. flavipes, only C. partellus and S. calamistis were suitable and produced parasitoids. In olfactometric bioassays, C. flavipes females were more attracted to stemborer-infested than uninfested plants. Analyses of the volatile compounds showed that they produced richer volatile profiles, mainly comprising C5–C6 alcohols, terpenoids, aromatic and aliphatic compounds, than uninfested plants. It can be concluded that stemborer species, that were accepted for oviposition but were unsuitable for parasitoid development, form a reproductive sink and that the exotic parasitoid would not establish in areas where these are the predominant species.

Development of NIR Equations for Food Grain Quality Traits through Exploitation of a Core Collection of Cultivated Sorghum

A sorghum core collection representing a wide range of genetic diversity and used in the framework of a sorghum breeding and genetics program was evaluated by near-infrared reflectance spectroscopy (NIRS) to predict food grain quality traits: amylose content (AM), protein content (PR), lipid content (LI), endosperm texture (ET), and hardness (HD). A total of 278 sorghum samples were scanned as whole and ground grain to develop calibration equations. Laboratory analyses were performed on NIRS sample subsets that preserved the core collection racial distribution. Principal component analysis performed on NIRS spectra evidenced a level of structure following known sorghum races, which underlined the importance of using a wide range of genetic diversity. Performances of calibration equations were evaluated by the coefficient of determination, bias, standard error of laboratory (SEL), and ratio of performance deviation (RPD). Ground grain spectra gave better calibration equations than whole grain. PR equation...

Sorghum resolved as a distinct genus based on combined ITS1, ndhF and Adh1 analyses

Recent studies on Sorghum have attempted to determine the genetic relationships between the 17 Australian native Sorghum species and the cultivated species, with several studies contradictory in their findings. To resolve these issues within Sorghum, a detailed investigation of the phylogenetic relationships was made. The alcohol dehydrogenase 1 gene (Adh1) from 25 Sorghum species and Cleistachne sorghoides was sequenced. Independent analyses of the Adh1 data, and combined analyses of the Adh1, ITS1 and ndhF data were carried out. All Sorghum species were resolved to a distinct clade with 100% support. Within Sorghum, the Eu-sorghum species were resolved to a strongly supported lineage that included the Australian native species S. macrospermum and S. laxiflorum. All other Australian species were resolved to a second strongly supported lineage. Sorghum laxiflorum and S. macrospermum have again been identified as the Australian species most closely related to cultivated sorghum. Analysis based on three genes has shown that the 25 Sorghum species form a distinct monophyletic group, and that there is little evidence to support the recent taxonomic revision of these species into three separate genera.

Genetic diversity of sorghum in greenbug resistance

Resistance of the sorghum gene pool to the Krasnodar greenbug population is investigated. A high level of resistance is established in accessions of cultivated sorghum species. Genetic uniformity of resistance donors widely used in Russian and US breeding programs is shown. Fifteen greenbug resistance genes are identified.

Evidence for a Selective Sweep on Chromosome 1 of Cultivated Sorghum

Recently, a simple sequence repeat (SSR)‐based genome‐wide diversity scan of Sorghum bicolor (L.) Moench identified several candidate loci with patterns of variation consistent with directional selection in cultivated lines. Data were insufficient, however, to determine if selection had actually occurred at or near candidate SSR loci or if the unusual diversity patterns observed were due to the effects of demographic factors such as population bottlenecks or mating system. In the present study, we collected DNA sequences from 10 segments within a 99 kb region flanking one of the previously identified candidates, SSR locus Xcup15, located near the distal end of chromosome 1. We performed statistical tests both to address alternative hypotheses to selection and to aid in localizing the selection target. Analyses of genomic DNA sequences from a panel of 17 cultivated and 13 wild accessions indicated that cultivated lines had reduced diversity in this region (about one‐third of the diversity present in wild sorghums) and a moderate degree of differentiation was observed between cultivated and wild groups (Fst = 0.15). Several features of the data support the hypothesis that recent directional selection shaped diversity patterns around Xcup15, including overall low levels of variation and extensive haplotype structure (a predominant haplotype occurred over the 99 kb region) in cultivated sorghum, and a derived fixed difference at the 5′ untranslated region (UTR) of a protein phosphatase 2C (PP2C) gene between cultivated and wild sorghums. Moreover, two of the four tests employed to detect deviations from the neutral, equilibrium model, the Hudson Kreitman Aguadé (HKA), and the composite likelihood ratio (CLR) tests indicated that patterns of diversity in the Xcup15 region were consistent with a selective sweep. Although we were unable to rule out demography as a possible explanation for the diversity patterns observed along this region, this study supported previous findings based on SSR diversity and identified candidates for the target of selection; the confirmation of which will require functional and association studies.

Development of NIRS Equations for Food Grain Quality Traits through Exploitation of a Core Collection of Cultivated Sorghum

A sorghum core collection representing a wide range of genetic diversity and used in the framework of a sorghum breeding and genetics program was evaluated by near-infrared reflectance spectroscopy (NIRS) to predict food grain quality traits: amylose content (AM), protein content (PR), lipid content (LI), endosperm texture (ET), and hardness (HD). A total of 278 sorghum samples were scanned as whole and ground grain to develop calibration equations. Laboratory analyses were performed on NIRS sample subsets that preserved the core collection racial distribution. Principal component analysis performed on NIRS spectra evidenced a level of structure following known sorghum races, which underlined the importance of using a wide range of genetic diversity. Performances of calibration equations were evaluated by the coefficient of determination, bias, standard error of laboratory (SEL), and ratio of performance deviation (RPD). Ground grain spectra gave better calibration equations than whole grain. PR equation (RPD of 5.7) can be used for quality control. ET, LI, and HD equations (RPD of 2.9, 2.6, and 2.6, respectively) can be used for screening steps. Even with a small SEL in whole sample analysis, a RPD of 1.8 for AM confirmed that this variable is not easy to predict with NIRS.

Genetic and epigenetic regulation of male fertility restoration in the 9E, A4 and M35 CMS-inducing cytoplasms of sorghum

The use of new CMS-inducing cytoplasms significantly increases the genetic variability of cultivated sorghum hybrids. The aim of the research was to study the inheritance of fertility restoration in new types of male-sterile cytoplasms (A4, 9E, M35) and to explore the reasons for its instability. Genetic analysis revealed that the restoration of male fertility was controlled by dominant genes, whose expression was strongly dependent on a sufficient level of water availability to plants during anther and pollen formation. An epigenetic mechanism for “switching on” fertility-restoring gene expression in F1 hybrids is proposed, which is regulated by water availability to plants. This “active” state of fertility-restoring genes is stably expressed in self-pollinated progenies of restored hybrids, irrespective of their water availability conditions, but is not transmitted to testcross hybrids grown under arid conditions.

Alignment of genetic maps and QTLs between inter- and intra-specific sorghum populations

To increase the value of associated molecular tools and also to begin to explore the degree to which interspecific and intraspecific genetic variation in Sorghum is attributable to corresponding genetic loci, we have aligned genetic maps derived from two sorghum populations that share one common parent (Sorghum bicolor L. Moench accession BTx623) but differ in morphological and evolutionarily distant alternate parents (S. propinquum or S. bicolor accession IS3620C). A total of 106 well-distributed DNA markers provide for map alignment, revealing only six nominal differences in marker order that are readily explained by sampling variation or mapping of paralogous loci. We also report a total of 61 new QTLs detected from 17 traits in these crosses. Among eight corresponding traits (some new, some previously published) that could be directly compared between the two maps, QTLs for two (tiller height and tiller number) were found to correspond in a non-random manner (P<0.05). For several other traits, correspondence of subsets of QTLs narrowly missed statistical significance. In particular, several QTLs for leaf senescence were near loci previously mapped for 'stay-green' that have been implicated by others in drought tolerance. These data provide strong validation for the value of molecular tools developed in the interspecific cross for utilization in cultivated sorghum, and begin to separate QTLs that distinguish among Sorghum species from those that are informative within the cultigen (S. bicolor).

A global view of genetic diversity in cultivated sorghums using a core collection

We report here an analysis of the structure of genetic diversity in cultivated sorghums. A core collection of 210 landraces representative of race, latitude of origin, response to day length, and production system was analysed with 74 RFLP probes dispersed throughout the genome. Multivariate analyses showed the specificity of the subrace guinea margaritiferum, as well as the geographical and racial pattern of genetic diversity. Neighbour-joining analysis revealed a clear differentiation between northern and southern equatorial African accessions. The presence of Asian accessions in these 2 major geographical poles for sorghum evolution indicated two introductions of sorghum into Asia. Morphological race also influenced the pattern of sorghum genetic diversity. A single predominant race was identified in 8 of 10 clusters of accessions, i.e., 1 kafir, 1 durra, 4 guinea, and 2 caudatum clusters. Guinea sorghums, with the exception of accessions in the margaritiferum subrace, clustered in 3 geographical groups, i.e., western African, southern African, and Asian guinea clusters; the latter two appeared more closely related. Caudatum were mainly distributed in 2 clusters, the African Great Lakes caudatum cluster and those African caudatum originating from other African regions. This last differentiation appears related to contrasting photoperiod responses. These results aid in the optimization of sampling accessions for introgression in breeding programs.

A Diploid, Interspecific, Fertile Hybrid from Cultivated Sorghum, Sorghum Bicolor, and the Common Johnsongrass Weed Sorghum Halepense

Valuable agronomic traits are often present but inaccessible in the wild relatives of cultivated crop species. Utilization of wild germplasm depends on the production of fertile interspecific hybrids. Several unsuccessful attempts have been made to hybridize cultivated sorghum with its wild relatives to broaden its genetic base and enhance agronomic value. The successful approach used in this study employed the nuclear male sterility gene ms3 to generate a diploid fertile hybrid between the diploid cultivated sorghum (Sorghum bicolor (L) Pers.) and its weedy tetraploid wild relative Johnsongrass (Sorghum halepense (L.) Pers.). Eight sorghum plants were selected from a Nebraska stiff stalk collection that contains the male sterility gene ms3 and were used as the female parent. About 36,000 florets of male sterile sorghum were pollinated with Johnsongrass pollen to produce an average of one well-developed and 180 severely shriveled seed/18,000 crosses. The well-developed seed gave rise to a self-fertile diploid, while none of the shriveled seed were able to germinate. The F1 hybrid was confirmed by using cultivated sorghum SSR markers and was selfed to produce an F2 population. A sub-sample of 96 segregating F2 plants was examined with 36 sorghum polymorphic SSR markers. Thirty-four markers showed a normal 1:2:1 segregation ratio, evidence of normal recombination across the genome. Preliminary results showed that several desirable traits from Johnsongrass, including resistance to greenbug and chinch bug and adaptability to cold temperatures, were expressed in the resulting progenies. These observations suggest that speciation within the genus Sorghum, giving rise to widely divergent phenotypes, is effected largely by ploidy-maintained crossing barriers but apparently not by extensive genomic divergence.