Variation in tillering and geographical distribution of foxtail millet (Setaria italica P. Beauv.)

Abstract

Detailed analysis of tillering in foxtail millet (Setaria italica P. Beauv.) was carried out. The tiller development in 16 strains was observed throughout the growing season. Strains were classified into four tillering types, Type I, Type II, Type III and Type IV. Type I strains had the largest number of tillers with many primary tillers on the main culm, and further secondary and tertiary tillers. This tillering pattern is very similar to that of green foxtail (S. viridis P. Beauv.) the probable ancestor of foxtail millet. Strains of Type II produced only one or two primary tillers and no secondary tillers. Type III strains were non-tillering and produced only one panicle on the main culm. It is supposed that Type I, which having high tillering capacity, was the first type domesticated from green foxtail. Types II and III subsequently differentiated from Type I by obtaining strong apical dominance. Type IV had characteristics intermediate between Types I and II. Only one strain collected from Kochi Prefecture, Japan, was Type IV. After defining the four tillering types as above, 76 strains of foxtail millet from Eurasia were grouped into types as follows; 37 starins were Type I, II were Type II, 27 were Type III, and one was Type IV. Strains of Types I, II and III were not evenly distributed across Eurasia. Almost all the strains from Europe, Central Asia and Southwest Asia were Type I, with the exception of one Type III strain from Georgia. Types II and III were frequent in eastern Eurasia from Southeast Asia to East Asia, while Type I was rarely found. Types I, II and III were all present in South Asia. A high diversity of tillering types is thus apparent in South Asia. The geographical distributions of the above three types suggests the following geographical origin and dispersal routes for foxtail millet: foxtail millet of Type I was domesticated in South Asia and neighboring areas; from there, Type I strains were dispersed through Southwest Asia to Europe. Strains of Types II and III differentiated from Type I, then spread over Southeast Asia and East Asia.