Vergara - 1976 - Physiological and morphological adaptability of ri

466 CLIMATE AND RICE
contribution of climatic factors to the whole variation in the total spikelet numbcr
was only about 50%. Thus. it has been found best to use the dry weight at
heading, U} (g/sq m), instead of total spikelet number to represent yield capacity.
Introducing the product of ll], and S‘ (average radiation during the 6
weeks after heading in kcal - sq cm-i-dayi"), he succeeded in explaining 49%
of the total variation in grain yield (in terms of brown rice with 14% moisture,
g/sq m) due to the year, location, and variety by the following regression model:
Y =
382 + 0,627 IVn-S
1t may be considered that W, represents not only yield capacity but also the
average size of photosynthetic organs during the grain-filling period (Mutata and
Togari, 1972} and to some extent, the amount of carbohydrate reserve accumulatcd
before heading. As described earlier. the development of photosynthetic
organs depends mainly on mean temperature combined with the
number of days from transplanting to heading, and this can be well represented
by H}. O11 the other hand, the function of the photosynthetic organ depends
mainly on solar radiation, after the middle stage of growth. Needless to say,
after the heading stage solar radiation plays the most important role in production
of yield content (Soga and Nozakii 1957; Moomaw ct al._ 1967; Wada,
1969; Murata and Togari, 1972; Yoshida, 1972). These may be the reasons for
the superior fitness ofKudos regression model.
On the other hand, the effect of temperature after heading is rather complicated.
At higher lcircls, temperature affects carbohydrate production adversely’
through the acceleration of leaf area decrease and also through the increase of
l,000 qruin weight (q)
24 - 056
6T
68
1m
22 _
1' °72 fies 1o
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2o _
r= - o. s2? *'*
azbfifi 67
i l I I
22 24 26 28 “C
Mean temperature in 3-week period
after heading
7. Relationship between LOGO-grain (brown rice)
weight and mean temperature during the Ii-yveek period
afier heading at Chikugo (Nakamura and Suzuki. impiahiished).
Open and closed circles indicate early season and
nomial season cultures. respectively‘.