Cytological relationships between some Echinochloa species and Kenyan E. haploclada (Stapf) Stapf.
Previous studies have indicated that (1) the widely distributed hexaploid species E. crus-galli and E. colonum differ from each other in their genomic constitutions [See PBA 34, 5822] and (2) the tetraploid species E. oryzicola is a possible progenitor of E. crus-galli but not of E. colonum. In the present studies, tetraploid E. haploclada was crossed with E. crus-galli, E. colonum and E. oryzicola. E. haploclada is eliminated as a possible tetraploid progenitor of E. colonum but chromosome pairing studies indicate that the two genomes of E. haploclada are partially homologous with those of E. colonum and also with those of E. crus-galli and E. oryzicola. Furthermore, E. haploclada shows a similarity to both E. crus-galli and E. colonum with regard to panicle type and spikelet characteristics. A diploid strain of E. haploclada has been found in Tanzania and a diploid strain of E. pyramidalis has been found in Kenya. No diploid species of the genus have so far been found in any other part of the world and it is suggested that tropical East Africa may be a centre of origin of the genus.