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

Abstract

Despite a "ploidy barrier," interspecific crosses to wild and/or cultivated sorghum (<i>Sorghum bicolor</i>, 2n = 2x = 20) may have aided the spread across six continents of <i>Sorghum halepense</i>, also exemplifying risks of "transgene escape" from crops that could make weeds more difficult to control. Genetic maps of two BC₁F₁ populations derived from crosses of <i>S. bicolor</i> (sorghum) and <i>S. halepense</i> 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 <i>S. halepense</i> homologs. Segregation distortion favored <i>S. halepense</i> 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 <i>S. bicolor</i> alleles on chromosome 6 (0-40 Mb), which contains both a large heterochromatin block and the <i>Ma1</i> gene. Regions of the <i>S. halepense</i> 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 <i>S. bicolor</i> and <i>Sorghum propinquum</i> have extensively recombined in <i>S. halepense</i>. 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 <i>S. halepense</i>.