Vergara - 1976 - Physiological and morphological adaptability of ri

98 CLINLXIE imp RICE
Himeno. 1973) supports our postulate that several genes with unequal and
cumulative effect control dormancy-i Contrary to earlier reports, grain dormancy
and growth duration are not gcnotypically correlated (Chang and Yen. 1969'.
Chang and Taguinpay‘, 1973).
Lodging of rice plants is more serious in the rainy‘ season than in the dry
season. The impact of raindrops, compounded by strong winds, aggravate the
lodging susceptibility‘ of tall and weak-culmed tropical cultivars. The long and
droopy leaves of these cultivars enhance the accumulation of raindrops on the
leaf surface and lcad to overloading (Chang, 1964; IRRI. [Undatcd]b). Short
plant height, large culm area, short basal internodes. and tight sheath wrapping
of the lower internodes have been shown to be important to lodging resistance
(Chang, 1967b).
Although resistance to lodging is essential to high yields and wide adaptive
range (Chang, 19672:), stiffculms are not required for the adaptation of eultivars
to ill-drained or deep-\vater conditions. Many tropical varieties possess the
“kneeing" characteristic which enables a lodged plant to have the panicles and
the upper internodes assume a fairly erect position at heading. The histological
and physiological bases ofthis characteristic have not been fully elucidated.
Strong winds cause leaf damage by breakage of blades or shredding of leaf
tips. Cultivars differ markedly in their resistance to wind damage (IRRI. 1967,
1970', Alluri et a1, 1973). The probable relation of wind resistance to leaf thickness
or histological structure needs to be investigated.
It has been observed at IRRI that rice cultivars shatter more in the dry season
than in the wet season. Shattering is more serious in an upland planting than in
a flooded crop. Perhaps a combination of relative humidity and air movement
is involved. Varietal differences in the shattering characteristic have been recognized
by several workers (Bhatcrao. 1930; Jones. 1933; Nagamatsu and
Ishikan-"a, 1954). The bulu varieties of Indonesia. japonica varieties of the temperate
regions. and many upland varieties shatter less than the tropical indicas.
The wild taxa ofthe genus (Jryza are generally highly shattering. Genetic control
of the shattering habit has been ascribed to one or more dominant genes (Onodera.
1929; Kadam, 1936", Ramiah and Rao. 1936). a single recessive gene
(Jones. 1933). or polygenes (IIu et al.. 1964'. Ouang, 1967). 1t appears necessary"
to study the quantitative nature of shattering from plants grown under controlled
environments.
RESPONSE TO WATER REGIMES
Aside from irrigated areas, rice is grown over a larger acreage in either rainfedlowland,
upland, deep water, or shallovtt-utater and ill-drained conditions. In
any ltnv-ly-ing area, rice is subject to the hazards of being submerged under flood
water. O11 higher grounds, drought occurs frequently. 1n rainfed cultures, rice
production often faces the threat of flood or drought, or one following the
other.