AFLP Variation in <i>Bromus</i> Section <i>Ceratochloa</i> Germplasm of Patagonia

Abstract

Bromus sect. Ceratochloa includes cultivated and native grasses of South and North America. This study examines amplified fragment length polymorphism (AFLP) variation among 30 hexaploid and two octoploid accessions of South American B. catharticus Vahl., B. coloratus Steud., B. lithobius Trin., B. mango Desv., B. stamineus Desv., and B. tunicatus Phil. and one accession representing octoploid North American B. carinatus Hook &amp; Arn. The proportion of shared AFLP fragments among accessions ranged from 0.67 to 0.99. Although 65% of all fragments (including rare phenotypes) were present in hexaploids and octoploids, the South and North American octoploids displayed more fragments per plant and a common set of additional AFLP fragments not present in the hexaploid accessions. The hexaploid B. coloratus , B. lithobius , and B. stamineus accessions form one well‐defined group, evident by the proportion of shared AFLPs, whereas B. mango and B. tunicatus accessions formed another well‐defined hexaploid group. However, taxa within these two hexaploid groups were poorly resolved and subtend the highly diverse group of hexaploid B. catharticus accessions. Excluding octoploids, 94% of the AFLP diversity was partitioned among accessions but only 53% of the variation was distributed among taxa. Moreover, variation within hexaploid B. catharticus alone reflected 97% of the total diversity among hexaploid accessions. The overall correlation between geographical distances and genetic similarities among hexaploid accessions, irrespective of taxa, is low ( r = −0.243) but significant ( P ≤ 0.01). Although recognizable forms of genetic variation certainly exist, it may be difficult practically to identify more than one genetically distinct species in the hexaploid Ceratochloa germplasm of Patagonia.