Vergara - 1976 - Physiological and morphological adaptability of ri

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2. Day length changes in Bangkok, Thailand; Rangoon, Burma; and Habigani. Bangladesh.
this case is exactly the OppOSllC of the traditional varieties. i.e. removing the
sensitivity to day length.
A majority of the improved rice varieties are insensitive to photoperiod.
However, specific adaptability is still needed in the millions of hectares planted
to deep-water rice. 3t) to 500 cm u=ater depth. where long growth-duration
varieties are necessary.
ln the floating-rice areas of Thailand, Bangladesh, Vietnam, and Burma, the
planting season begins in April to May and harvesting is from November to
December. Flowering occurs only after the water level has reached its peak, a
necessity for survival. Panicle initiation occurs in September t0 October in these
areas. Since the latitudes differ, the day length at this time of panicle initiation
also differs, so varieties developed at one latitude may not necessarily flower at
the desired time at other latitudes. Varieties developed at Bangkok. Thailand.
with a critical photoperiod of l2 hours and l5 minutes may flower earlier in
Rangoon, Burma, and very early at l-Iabiganj, Bangladesh. if sown during their
regular planting season (Fig. 2). General adaptability for a floating-rice variety
would be very difficult to attain
lnsetisitibitv to day length is a requisite for adaptability in one case and a
liability in another.