Geographical variation of heading response to daylength in foxtail millet (Setaria italica P. Beauv.).

Abstract

The variations of the heading response to daylength in foxtail millet (Setaria italica P. BEAUV.) were investigated. Twenty strains of foxtail millet collected from various parts of Eurasia including islands of Southeast Asia were cultivated under three daylength conditions : Short-days (10 hrs. light +14 hrs, darkness), natural daylength (14.5 hrs-11.5 hrs. light+9.5hrs. -12.5hrs. darkness) and long-day (16 hrs. light+8hrs. darkness). Based on the variations of the response, three types were identified. Type I : early maturing strains indifferent to daylength condition ; Type II : very long basic vegetative growth period ; Type III : short basic vegetative growth period and high sensitivity to daylength: Type I is represented by strains from areas of a higher latitude such as Europe, Central Asia and northern part of East Asia. Type II is represented by strains from low latitudinal areas such as Halmahera Is., Indonesia and Luzon Is., Philippines. Type III is found in late maturing varieties growing in areas of a latitude of around 30 ??, such as "Shimokatsugi", a landrace of mountainous villages on Shikoku Island, Japan. The other strains were scored as intermediate between these types. These findings suggest that there is a relationship between the types of heading response to daylength and the geographical distribution which determines the planting season in traditional cultivation practices of foxtail millet.