Tetraploid Sorghum Research Articles

Sorghum bicolor x S. halepense interspecific hybridization is influenced by the frequency of 2n gametes in S. bicolor

Tetraploid johnsongrass [Sorghum halepense (L.) Pers.] is a sexually-compatible weedy relative of diploid sorghum [Sorghum bicolor (L.) Moench]. To determine the extent of interspecific hybridization between male sterile grain sorghum and johnsongrass and the ploidy of their progeny, cytoplasmic (CMS), genetic (GMS) and chemically induced male sterile lines of Tx623 and Tx631 were pollinated with johnsongrass pollen. At maturity 1% and 0.07% of the developing seeds of Tx623 and Tx631 respectively were recovered. Ninety-one percent of recovered hybrids were tetraploid and two percent were triploid, the tetraploids resulting from 2n gametes present in the sorghum female parent. Their formation appears to be genotype dependent as more tetraploids were recovered from Tx623 than Tx631. Because a tetraploid sorghum x johnsongrass hybrid has a balanced genome, they are male and female fertile providing opportunities for gene flow between the two species. Given the differences in 2n gamete formation among Tx623 and Tx631, seed parent selection may be one way of reducing the likelihood of gene flow. These studies were conducted in controlled and optimum conditions; the actual outcrossing rate in natural conditions is expected to be much lower. More studies are needed to assess the rates of hybridization, fitness, and fertility of the progeny under field conditions.

High proportion of diploid hybrids produced by interspecific diploid × tetraploid Sorghum hybridization

A perennial version of grain sorghum [S. bicolor (L.) Moench] would create opportunities for greatly reducing tillage and preventing soil degradation. Efforts to select for perenniality and grain production among progeny of hybrids between S. bicolor (2n = 20) and the weedy tetraploid perennial S. halepense (L.) Pers. (2n = 40) are complicated in that F1 hybrids produced by diploid × tetraploid sorghum crosses are usually tetraploid. In 2013, a set of random pollinations between 19 diploid cytoplasmic male-sterile inbred lines and 43 tetraploid perennial plants produced 165 F1 hybrid plants, more than 75% of which had highly atypical plant, panicle, and seed phenotypes. Phenotypic segregation in F2 populations derived from atypical hybrids was also anomalous. Examination of mitotic metaphase cells in F1 or F2 root tips revealed that 129 of the 165 hybrids were diploid. Parentage of the diploid progenies was confirmed using simple-sequence repeat analysis. The mechanism by which diploid hybrids arise from diploid × tetraploid crosses is unknown, but it may involve either production of monohaploid (n = 10) pollen by the tetraploid parent or chromosome elimination during early cell divisions following formation of the triploid zygote. The ability to produce diploid germplasm segregating for S. bicolor and S. halepense alleles could have great utility, both for the development of perennial sorghum and for the improvement of conventional grain sorghum.

Molecular Characterization of Non-flowering Perennial Sorghum spp. Hybrids

Aims: The goal of this study was to characterize recently identified, non-flowering, putative tetraploid Sorghum spp. hybrids utilizing bulked segregant analysis with SSRs and compare them to S. bicolor, S. halepense, and triploid putative Sorghum spp. hybrids. Confirmed species hybrids between S. bicolor and S. halepense would provide resources for investigating risks of invasiveness and transgene escape alongside potential for identifying novel perennial Sorghum feedstocks of value. Study design: Bulked segregant analysis of Sorghum species and S. species hybrids. Place and Duration of Study: Department of Soil & Crop Sciences; Texas AM College Station, TX, USA; 2009 2011 Methodology: A bulked segregant analysis approach was conducted using SSRs mined from the S. bicolor genome sequence. Bulked samples of S. bicolor, typical flowering S. halepense, non-flowering tetraploid putative Sorghum spp. hybrids, and triploid putative Sorghum spp. hybrids were surveyed to identify both unique markers specific to each bulk and markers indicative of S. bicolor genetic material introgressed into the Sorghum spp. hybrids. Results: Thirty-nine and 23 markers were found to be unique to the S. bicolor and typical flowering S. halepense bulks, respectively. These unique markers could be utilized in breeding programs to identify interspecific hybrids. A subset of 23 unique SSRs were found in the non-flowering tetraploid putative Sorghum spp. hybrid, and they may be useful in the characterization of the non-flowering phenotype. Conclusion: Markers identified in this study provide: 1) species-specific tools for confirmation of interspecific Sorghum spp. hybrids and quantification of gene flow between Sorghum spp., 2) candidate gene and genomic region resources for dissection of the nonResearch Article American Journal of Experimental Agriculture, 2(1): 9-20, 2012 10 flowering phenotype, and 3) Sorghum spp. hybrid-specific markers suitable towards development of perennial biofuel and forage sorghum feedstocks.

Seed yield and biomass allocation in Sorghum bicolor and F1 and backcross generations of S. bicolor × S. halepense hybrids

The Land Institute is developing perennial grains to be grown in prairie-like mixtures. One approach involves the development of a perennial grain sorghum by crossing tetraploid Sorghum bicolor with wild S. halepense to combine high seed yield with overwintering ability via rhizome production. We grew tetraploid S. bicolor, F1 hybrid (BC0), and two backcross generations (BC1 and BC2) in a randomized block design to examine total biomass, seed yield, and allocation to plant parts within and across generations. Root, rhizome, stem and leaf, and total biomass decreased from the BC0 to BC2 to S. bicolor generations, whereas panicle mass, seed mass, and reproductive allocation were lowest in the BC0 generation (p < 0.05, ANOVA). Mean seed mass (g ∙ plant−1) was 39.1 in the BC0, 107.3 in the BC1, 84.1 in the BC2, and 92.7 for the S. bicolor parent, which translated into yields of 171.9, 471.6, 396.7, and 407.5 g ∙ m−2, respectively. Reproductive allocation varied from 14.7% in BC0 to 28.9% in BC2 compared with 33.5% in S. bicolor. Mean allocation to rhizomes was 2.71% in BC0 but negligible in BC1 and BC2. There was no relationship between rhizome mass and seed mass within any generation, but there was a positive correlation between total plant mass and rhizome mass in BC0. We divided the BC0 population into four groups with respect to rhizome production and found no significant differences among the groups in plant size or seed yield. Within each generation, reproductive allocation was inversely related to culm mass. The lack of an apparent trade-off between allocation to rhizome versus allocation to seed within any generation supports the possibility of combining within a population high seed yield and production of perennating belowground organs. Key words: backcross, hybrid, perennial grains, reproductive allocation, rhizome, seed mass, Sorghum bicolor, Sorghum halepense.

Crytology and Morphology of a Tetraploid Sorghum Population Recovered from a Saccharum ✕ Sorghum Hybrid1

Sugarcane (Saccharum sp.) with 2n = ca. 112 chromosomes was crossed with diploid (2n = 20) sorghum (Sorghum bicolor (L.) Moench), and their hybrids were backcrossed twice with diploid and twice with tetraploid (2n = 40) sorghum. The BC4 individuals, so obtained, were selfed twice to produce a recovered tetraploid sorghum population (BC4F3). Fifty‐one BC4F3 individuals, sugarcane and the sorghum parents, were studied cytologically and morphologically. Irregular cytological behavior of recovered sorghum plants, characterized by an increase in bivalent formation and decrease in tetravalent formation at diakinesis (in comparison to their tetraploid ‘Rio’ sorghum parent) indicated that the sorghum chromosomes may be contaminated with sugarcane genetic material. Morphological data were analyzed by cluster analysis, principal component analysis, univariate analysis of variance, F‐test, and t‐test to study the variability in the hybrid populations and to test the significance of morphological differences among groups. Modified recovered tetraploid sorghums had various combinations of Saccharum characteristics superimposed on a basic Sorghum morphology. Sixteen of 26 plant characters studied were influenced by sugarcane genetic material to varying degrees and frequencies. The presence of these sugarcane characters in recovered sorghums indicated intergenomic genetic exchange.

Cytogenetics of Introgression from Saccharum into Sorghum1

Grain sorghum [Sorghum bicolor (L.) Moench] crosses with sugarcane (Saccharum officinarum L.) when the latter species is the female parent. These hybrids are male sterile but produce offspring when pollinated with either parent. Four backcrosses, the first and second with diploid (2n=20) and then with tetraploid sorghum (2n=40), produced plants that are male and female fertile even though they combine 40 Sorghum + 4–10 Saccharum chromosomes. Selfing or further backcrossing with sorghum for one or more generations, results in complete elimination of Saccharum chromosomes, and essentially pure or morphologically modified sorghums are recovered. Modified sorghums have various combinations of Saccharum characteristics superimposed on a basic Sorghum morphology. The study was initiated in an attempt to transfer shoot fly resistance from sugarcane to grain sorghum. Whether this aim was achieved is now being investigated.

Effects of Autoploidy on Grain Sorghum

Artificially induced sorghum tetraploids have been reported by numerous workers including Chin (19461, Casady and Anderson (19521, Schertz (1962) and Washington ct a/. (1998). Reported attempts to develop a tetraploid sorghum crop are few, and only...

COLCHICINE-INDUCED SOMATIC CHROMOSOME REDUCTION IN SORGHUM VI. NUCLEAR VOLUME CHANGES WITHIN DIPLOID STEM APICES AFTER COLCHICINE APPLICATION

The induction of diploid plants by colchicine treatnlent of tetraploid sorghum seedlings (Sanders and Framlte, 1962, and Chen and Ross, 1963) indicated that a somatic chronlosome reduction had occurred. Chen and Ross (1965) followed the growth of diploid cells from close to the time of origin, at 2 days after colchicine application, until they had overgro\vn the polyploid cells to form diploid apical domes at tlie 5th to 9th day. The true-breeding nature of some mutants obtained after colchicine treatnlent of diploid seedlings has been sIio\\ln to result from sonlatic chromosome reduction by Siniantel et nl . ( 1963) and Simantel and Ross ( 1963). They used s t ruc tura l l~ marlted chron~oson~es to denlonstrate separation of hon~ologues of t\\lo and four pairs of ch ro~noso~~~es . This study is concerned with nuclear behavior in diploid seedlings after colchicine application.

Somatic Reduction of Tetraploid Sorghum to Diploid Mutants following Colchicine Treatment

COLCHICINE treatment of seedlings of certain sorghum lines has resulted not only in the expected polyploids, but also in diploid plants which are mutant for many characters. Some of these diploid mutants breed true immediately while others give segregating progenies1–3. The original hypothesis to explain their appearance suggested that a somatic reduction of the chromosomes (similar to that observed by Huskins4) occurred and was followed by duplication. These mechanisms could result in the concentration of chromatin from ancestors of a putative allopolyploid. However, investigations have produced either no or little cytological evidence for duplication or relocation of chromatin5,6. In addition, mutant characters which have been studied have shown Mendelian inheritance7–10. The alternative hypothesis was then proposed that, in addition to a balanced somatic reduction of the chromosomes after application of colchicine, mutations at many loci also occurred prior to duplication back to the diploid number.