Vergara - 1976 - Physiological and morphological adaptability of ri

RICE GROWTH l.\l DII~'FERE.\IT' ENVIRONIVIEN'I‘S 435
Type III: A slow growth at early stages followed by a high growth rate until
grovrth ceases; frequently observed in high-latitude areas where the temperature
is low in spring; generally‘ the total dry-matter production is small, and sometimes
the grain yield is moderate due to a reasonable grain-straw ratio but
frequently the grain yield is low due to a small grain-straw ratio.
Type IV: Continuous slow growth; caused by insufficient nutritional supplies.
adverse soil conditions, ete.; very low grain yields; this tyjpe is not discussed
in this paper because climatic environment is not the growth-limiting
factor.
Type V (V'): A moderate (or high) growth rate followed by a high growth rate
during later stages; possible only’ with abundant solar radiation during ripening
(or throughout the growth) with good plant type varieties; an extremely high
grain yield due to large values of the total dry-matter production as well as the
grain-straw ratio.
In a varietal comparison of grow-th. Oka et al. (1970) described early and
sustained vigor types. These correspond to Type I and Type II. respectively‘.
lf we look at various types of growth patterns from the standpoint of phasal
development the following three types can be classified (Fig. 3) (Tanaka et al._
1964).
Type A (vegetative phase—rcproduetive phase): The paniele-primordia are
initiated soon after the maximum tiller number stage; considered to be normal;
the growth curve is generally Ty-"pe II or Type V; uniform flowering; generally
the grain yield is high.
'l"_vpe B (vegetative phase—reproductive phase overlapped with vegetative
phase) : Tillering continues after the paniele-primordia initiation stage‘, generally‘
caused by a continuous active nitrogen uptake which is induced by a slow nitrogen
uptake at early growth stages due to low temperatures, excess nitrogen application.
untimely nitrogen top-dressing. excessively’ wide spacing‘ use of unduly
short-duration varieties etex. the growth curve is irften Type lll; flowering is
irregular due to a wide age variation among tillers; the number of spikelets per
panicle is small because the photosynlhale after the panicle-primordia initiation
stage is consumed not only by the panicle-primordia but also by the new-"lf;
developing tillers; frequently associated with low grain yields.
Type C (vegetative phase—vegetative-lag phase—reproductive phase) :
Tillering
diseontinues long before the panicle-primordia initiation stage; occurs when
the vegetative phase is extremely long; associated with high temperatures from
transplanting. and exhaustion of nitrogen supply in the soil from an early growth
stage; the growth curve is generally Type l; the number of panicles per unit field
area tends to be small due to a high percentage of ineffective tillers; the number
of spikelets is frequently small due to insufficient supply of nitrogen during the
reproductive phase; the grain yield is often low. As the dry-matter production is
slow during the period between the maximum tiller number stage and the panicle-primordia
initiation stage, this period is called the vegetative-lag phase.
During this phase the internodes at the base start to elongate before the paniele-