Abstract
Two species, E. colona and E. crus-galli, belonging to genus Echinochloa from Saudi Arabia were subjected to cytogenetic investigation in this study. These species are common grass belonging to family Poaceae, mostly distributed in wet or damp places throughout agricultural and public gardens in the Arabian Peninsula. Mitotic studies show that E. colona has 36 chromosomes as tetraploid species, whereas E. crus-galli has 54 chromosomes as hexaploid. Both species are based on x=9 as the common basic number in this genus and the majority of genera of family Poaceae. Karyotype structure and mitotic measurements of E. colona show a high degree of homogeneity in chromosome morphology and centromere position, reflecting its autotetraploid nature. Regarding E. crus-galli, the karyotype structure and mitotic measurements show significant variation between chromosome measurements and morphology, insuring the alloploid nature of the species. Meiotic chromosome associations, chiasma frequency, pollen fertility and irregularities for the two species were carried out. E. colona recorded normal association and high ratio of chiasma frequency as well as low irregularities, indicating the genetic stability of the species and giving rise to high pollen viability. In contrast, E. crus-galli shows low frequency of bivalents compared to E.colona, low chiasma frequency and high percentage of meiotic irregularities, reflecting genetic instability and alloploidy structure of the species. The genetic stability of E. colona directly affects seed production, especially at open pollination conditions, in contrast to E. crus-galli, where the heterogenis structure and genetic instability negatively affect seed production at open conditions. Significant low seed set at self-pollination conditions insures that the two species undergo open pollination rather than self-pollination, as common in the grass family.