Transmission Genetics of a Sorghum bicolor × S. halepense Backcross Populations

Abstract

Despite a "ploidy barrier," interspecific crosses to wild and/or cultivated sorghum (Sorghum bicolor, 2n = 2x = 20) may have aided the spread across six continents of Sorghum halepense, also exemplifying risks of "transgene escape" from crops that could make weeds more difficult to control. Genetic maps of two BC 1 F 1 populations derived from crosses of S. bicolor (sorghum) and S. halepense with totals of 722 and 795 single nucleotide polymorphism (SNP) markers span 37 and 35 linkage groups, with 2-6 for each of the 10 basic sorghum chromosomes due to fragments covering different chromosomal portions or independent segregation from different S. halepense homologs. Segregation distortion favored S. halepense alleles on chromosomes 2 (1.06-4.68 Mb, near a fertility restoration gene), 7 (1.20-6.16 Mb), 8 (1.81-5.33 Mb, associated with gene conversion), and 9 (47.5-50.1 Mb); and S. bicolor alleles on chromosome 6 (0-40 Mb), which contains both a large heterochromatin block and the Ma1 gene. Regions of the S. halepense genome that are recalcitrant to gene flow from sorghum might be exploited as part a multi-component system to reduce the likelihood of spread of transgenes or other modified genes. Its SNP profile suggests that chromosome segments from its respective progenitors S. bicolor and Sorghum propinquum have extensively recombined in S. halepense. This study reveals genomic regions that might discourage crop-to-weed gene escape, and provides a foundation for marker-trait association analysis to determine the genetic control of traits contributing to weediness, invasiveness, and perenniality of S. halepense.

Comparative evolution of vegetative branching in sorghum

“…These maps respectively span 37 and 35 linkage groups, with 2-6 for each of the 10 basic sorghum chromosomes due to fragments covering different chromosomal portions or independent segregation from different S. halepense homologs. Details of population development, genotyping methods and methods for QTL analysis were discussed in Kong, Nabukalu [29] and [30].…”

“…To fully utilize the available data while protecting against false-positive results, genetic analysis employed two approaches. Using genetic maps that were constructed as described [29] from selected well-groomed SNP segregation data for each of the two SBSH-BC 1 F 2 populations, interval mapping was conducted [33]. Permutation tests (with α = 0.10) suggested LOD scores of 2.9 and 3.1 for H4 and H6 populations, respectively.…”

“…Here, we describe a quantitative trait study of two important components of plant architecture, tillering and vegetative branching, in two half-sib tetraploid BC 1 F 2 populations derived from crossing Sorghum bicolor BTx623 and Sorghum halepense Gypsum 9E. A two-year, twoenvironment phenotypic evaluation in Bogart, GA and Salina, KS permitted us to identify major effect and environment specific QTLs [29,30]. Quantitative trait loci (QTLs) discovered in these two populations are compared to those from two diploid sorghum recombinant inbred line (RIL) populations sharing BTx623 as a common parent but sampling the breadth of the Sorghum genus, one a cross to S. bicolor IS3620C [31], and the other to S. propinquum [32].…”

Detection of quantitative trait loci regulating seed yield potential in two interspecific S. bicolor2 × S. halepense subpopulations

“…Genotyping and linkage map construction were reported previously (Kong et al 2020). Briefly, genotypes were determined by single nucleotide polymorphism (SNP) 'calling' based on the reference genome of S. bicolor BTx623 v1.4 (Paterson et al 2009), using Tassel-GBS 5 (Glaubitz et al 2014).…”

Cytogenetics and fertility of an induced tetraploid Sorghum bicolor x S. propinquum hybrid

“…While Paterson et al (1995) reported that S. halepense contained restriction fragment length polymorphisms (RFLPs) specific to S. propinquum and S. bicolor, they also identified S. halepense specific alleles. More recent studies have shown introgression of S. halepense alleles to S. bicolor in crop : weed hybridization events (Kong et al, 2020;Morrell et al, 2005), confounding the determination of S. halepense evolutionary origins from genomic data alone. Collectively, these molecular findings suggest that S. halepense is either a derivative from hybridization between S. bicolor and S. propinquum or an unknown, but closely related Sorghum species with increased homology due to cumulative introgression events over evolutionary time periods.…”