Vergara - 1976 - Physiological and morphological adaptability of ri

GENETIC \';-\RIOL='S1\'lESS IN CLIMATIC ADAPTATION 101
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Meat yield trnl/nol
5. Scatter diagram indicating the relationship between
regression coefficient on site means and mean yield of I9
rice varieties (l.R..-\.E Phase A experiments, 44 environments).
The 5 ponlai varieties bred in 'l'aiwan showed both
high stability and high mean yield.
controlled character. Photoperiod-sensitive varieties are more variable in yield
than insensitive ones when tested at different sites. When only insensitive and
weakly sensitive varieties were tested, however, yield stability significantly"
differed according to yiarietal genotypes (JIBP, unpublished). When measured
on a logarithmic scale, yield stability appeared in many cases tn be weakl_v positively
correlated with mean yield (Fig. 5) (Oka, 1975).
It is known that phenotypic plasticity plays an important role in the adaptation
of plants t0 changing environment, (Bradshaw. 1965). This also appears to
be a genotjppically controlled character. Wild rice strains of the O. perennis
complex were generally more plastic than cultivars of O. sativa in the size of
organs (Table l). Ten tester varieties in the IBPIUV experiments (phase B.
1971-72) varied greatly in the plasticity‘ indexes of panicle number and panicle
length, and in other characters due to location, yjear, and other environmental
conditions (Morishirna and Oka, 1975).
Among the l0 varieties, the stability of panicle length was strongly correlated
with yield stability (r = 0.90). On the other hand. the stability of particle number
(per m=) showed a weaker negative relationship with those of panicle length and
grain yield (Table 2). This suggests that a certain degree of plasticity at the
tillcring stagc and stability during panicle development result in yicld stability
Negative associations. between other stability: estimates vyerc also found. For
instance. the standard deviation of grovt-th rate at heading time (glday/ m1) and
that ofthe seeding-to-heading period were significantly and negatively; correlated
(r = ~0.72). It tnay be inferred that stability’ in one phase of development is