The following websites show that many cereal remains such as Setaria italica Beauv. and Panicum miliaceum) in the Early Yayoi period (about 2500 years ago) were excavated from the Sho-Kuramoto site in Tokushima-shi, Tokushima Prefecture. Those photos can be seen on both of links.
Sankei News (JAPANESE)
Yayoi zenki no awa, kibi nado zakkoku shushi ga shutsudo Tokushima-dai konai no iseki (Seed remains such as Setaria italica Beauv, and Panicum miliaceum were found from the campus site in Tokushima University)
Tokushima Shimbun (JAPANESE)
Yayoi-ki kara awa saibai Tokushima-shi no Sho-Kuramoto iseki no shushi bunseki (Analysing results of seed remains found from the Sho-Kuramoto site in Tokushima-shi can show millet cultivation in the Yayoi period)