Abstract
Eighty-three strains of Setaria italica collected from various areas throughout Eurasia were crossed with three tester strains from Japan (tester A), Lan Hsu Island of Taiwan (B) and Belgium(C). The F1 hybrids were obtained in 224 of the 249 cross combinations tried. The pollen fertility of the F1 hybrids ranged widely from almost sterile (8.2%) to highly fertile (99.1%) while there was a little variation among the individual F1 plants of the same cross combination. The 62 strains, which successfully produced F1 hybrids with all of the three testers, could be clearly classified into six types, designated as types A, B, C, AC. BC and X. Pollen fertility of more than 75% was regarded as normal. The strains of types A, B and C were those which produced F1 hybrids having normal pollen fertility when crossed with testers A, B and C, respectively. When both F1 hybrids from the crosses with two testers, A and C, or B and C, showed normal pollen fertility, the strain was classified as type AC or BC. The strains whose F1 hybrids always showed pollen fertility of less than 75% in all three cross combinations were designated as type X. There was no strain whose F1 hybrids always showed normal pollen fertility in the cross combinations with all three testers or both testers A and B. These types classified are thought to reflect the landrace groups phylogenetically differentiated, because hybrid sterility occurs as the results of genetic differentiation between strains. Most type A strains were distributed in East Asia including Japan, Korea and China. Type B strains were narrowly found in Taiwan and in the southwestern part of the Nansei Islands of Japan. Most European strains were found to be type C. Strains of types AC and BC were distributed in Afghanistan and India, respectively. Types AC and BC are thought to be less specialized genetically than A, B or C. The geographical distribution of these landrace groups suggests that S.italica was first domesticated in an area ranging frorn Afghanistan to India, and then dispersed both eastward and westward from there.
