Studies On The Origin Of Broomcorn Millet(Panicum Miliaceum L.)Inferred From Ribosomal DNA ITS And ETS Sequences

Broomcorn millet(Panicum miliaceum L.),one of the most ancient crops,has the characteristics of salt resitance,alkali resistance,drought resistance and barren resistance,and shorter growth period.It is suitable for planting in the backwoods and wilderness.It has long been an important staple food in the semiarid regions of Eurasia,and it also has a certain nutritional value and medicinal value.Around the world,in addition to China,India,Russia,Iran,Mongolia,Poland,and Ukraine are the main cultivated coutries of Broomcorn millet.In China,Inner Mongolia,Shaanxi,Ningxia,Gansu,Shanxi,Northeast China and Northern Hebei are the main producing areas of Broomcorn millet.However,the geographical origin of this crop remains a controversial issue.Archeological evidence and previous genetic study both support the possibilities of a single China origin and independent multiple China/Europe origins.In this study,ribosomal DNA(rDNA)internal transcribed spacer(ITS)and external transcribed spacer(ETS)of 190 broomcorn millet landraces from China and other countries were sequenced to trace the origin center of this cereal.Eighteen rDNA types were classified and further categorized into five groups,A total of 13 variants were detected by cloning sequencing of one to three samples of each type.Among them,variant 1 was found in every types and was placed at the center of the star-like network tree of ITS variants.So it was suggested to be the most ancestral sequence.Accordingly,as the only homozygous type and with single ancestral variant 1 in ITS region,Type I was considered to be the most ancestral type.The limited distribution of Type I in China and India supported China as the origin center of broomcorn millet because India is short of early aechaeological sites and it is not regarded as one of origin areas.On the other hand,types in group D and E almost exclusively distributed outside China.They were supposed to have arisen much recently following the Chinese broomcorn millet spread westward because their unique ITS variants derived from variant 1 and half of them had one more mutation step than other variants.Eastern Europe or other regions on the route of broomcorn millet spreading from Chinese origin area to Eastern Europe were probably a secondary domestication area for types in group D and/or E.The results of the study will provide valuable genetic evidences for the origin and spread of the Broomcorn millet,and even the origins of the Northern dry farming.