Experiments conducted on seedling age and different water depths revealed that short-duration, 7-day flooding of 3 week-
old seedling was effective in assessing elongation potential in deepwater rice varieties. Water depths of 90-100
cm were sufficient to express elongating ability and 3-week-old seedlings gave better contrast between elongating
modern varieties and non-elongating modern varieties. Maximum internode length was under short-day-length
conditions while shortest internodes were obtained in the long day treatment. Internode elongation may be due only to
the signal effect of day length or the shading effect on assimilation. Further experiments should be conducted to
confirm these findings