No abstract

Photoperiodic sensitivity in heading of Echinochloa oryzicola Vasing., an obligate weed in flooded rice, was determined with 20 strains originally collected in nine countries from 7S to 44N. Plants of the strains were grown under 12, 14 and 16-hr photoperiods at 25C and the days to heading after sowing were recorded to classify them in photoperiod sensitivity by the duration of the basic vegetative phase (BVP) and photosensitive phase (PSP). The strains originally collected in the temperate region above 30N were classified into those with either weak or strong sensitivity. A geographical cline was apparent among them and the strains from higher latitude exhibited heading earlier under 14-hr photoperiod. All of the seven strains from the subtropical and tropical regions below 30N had a PSP of less than 30 days and were classified among those with photoperiod insensitivity. It is likely that this trait of E. oryzicola is advantageous for its wider adaptability in diverse rice cropping systems in these regions.