Analysis of a polyploid complex in Glycine with chloroplast and nuclear DNA

Abstract

Studies of chloroplast DNA and nuclear 18s–25s ribosomal genes have revealed considerable variation in Glycine subgenus Glycine, the perennial relatives of the cultivated annual soybean. We have used these molecular characters to investigate the origins and evolution of G. tabacina, a species that comprises a widespread polyploid complex in Australia and the islands of the southern and west-central Pacific. Two principal groups of accessions were detected in this species using molecular characters. These two types also differ morphologically and have distinct, though overlapping, geographic ranges; comparison with results of artificial hybridisation studies showed that sterility barriers exist between the two groups. Both types are fixed hybrids for nuclear rDNA, and share one rDNA repeat class, presumably derived from a common diploid progenitor. The two types had different maternal progenitors, based on cpDNA variation. One of the two polyploid types is polymorphic for cpDNA, and shares nearly all of its plastome variants with diploid accessions, suggesting multiple, independent origins of the polyploid from a pool of diploid progenitors. Molecular data suggest that polyploids have originated recently, and that dispersal from Australia to the islands of the Pacific has occurred several times.