Vergara - 1976 - Physiological and morphological adaptability of ri

198 CLIh-LATE AND RICE
Both of these methods have disadvantages, hoyvever, because there are sometimes
negative correlations between the ripening index and spikelet number.
Ripening index needs to represent only the ripening ability, which removes the
effect of sink size 0n grain yield. That the grain yield is divided by spikelet
number means elimination of the effect of sink size. It is not desirable for analysis
to have negative correlation between ripening index and spikelet number. Such
correlation is brought about by assuming that the relation between grain yield
and sink size might be linear.
Munakata et al. (1967) found that the relation between grain yield and
spikelet numbers was ShOWfl by the non-linear formula:
Y3 = Cl Yz/(b +
where l}: the kernel yield per square meter. Y2: the number of spikelets, a:
the index of ripening grade, and b: a constant with 5 >< 104.
From the above formula, ripening index is as follows:
a = Ur, X (a + 2;).
In this report, “kernel yield per total number of spikelets" is used as a ripening
index for the following reasons:
l. Much information on spikelet numbers is available for growth analysis in
Japan.
2. When the data were analyzed by both the method of kernel yield per total
number of spikelets and by Munakatzfs method. the results obtained indicated
no significant differences. This seemed to be due to the fact that no significant
correlation was found between the ripening index and spikelel number (see
Table l).
The stage most sensitive to elim atie factors for the ripening grade
In an attempt to clarify the stage most sensitive to climatic factors for ripening
grade, the multiple correlations in different stages were calculated. Several
models were tried. considering the complex interactions of light and temperature.
As a result, the following model of modified type Ill was used.
(l: i",)0= = b,/r~~is»= + ease/r“ + b,r»==/.s'-= + saris“
+ bJT + bJS + b_./r= + bJT’ + c (2)
where Y4: ripening grade (l'3/ Y3). T; and S}: equivalent to eq. (1), and j: stage
number.
The above equation is effective for analyzing the combined effect of light and
temperature, although individual effects are not determined.
From Fig. 9, two maxima in multiple correlation coefficients were found in
[-20] stage and [+20] stage. The first peak includes the meiosis stage in which
physiological activity‘ of pollen and ovary is determined as well as number and
size of spikelets. The first peak of ripening grade means that the physiological
activity of the reproductive organ is definitely governed by the climate in [-20]
stage. The second peak is equal to the most active ripening stage when the
increasing rate of dry weight ofkernels reaches its highest.