Vergara - 1976 - Physiological and morphological adaptability of ri

90 crux-rim; AND RICE
produce a variable yet dependable grain yield when. following a period of
adverse weather. the environmental conditions turn favorable for grain production.
The trend in the evolution and domestication processes of the rice plant was
toivard a gradual loss of the strength of photoperitid sensitivity and an increase
in the BVP (Oka and Chang. 1964; Katayama. 1965; Chang. 1976). Disruptive
selection in different crop seasons, as exemplified by the breeding of the ponlai
varieties in 'l'ai\y'an and of the semidwarf varieties at IRRI, has. resulted in
completely or essentially’ insensitive genotypes (Oka. 1966; Chang and Vergara.
1971).
The genetic control of strong photoperiod sensitivity has been investigated by
several rice researchers under natural photoperitid. Inheritance of this discrete
trait was postulated to be controlled by either one dominant gene (Chandraratna.
1955'. Yu and Yao. 1957'. Kuriyrama. I965) or two duplicate genes
(Sampath and Seshu, 1961). In several crosses involving distantly related parents.
sensitivity appeared to be a recessive trait (Sampath and Seshu. 1961'. Kuriyrama.
1965). When controlled photoperiods were used. strong sensitivity was ShOWH
to be governed by either one dominant gene (.522) or two duplicate genes (Se, and
Se, ), along with the absence of a recessive inhibitor to the dominant gene (ii-Se)
(Chang et al. 1969). A short critical photoperiod appeared to be controlled
by a completely (Li, 1970) or partially dominant gene (Kudo. 1968), while a
short optimum photoperiod ‘N215 also a monogenic dominant trait (Li, 1970).
Inheritance of the weakly sensitive response appears to be rather complex.
The F‘ performance indicated the partial dominance of the weak response in
one cross and the reverse in the other two crosses. The F; distributions of the
PSP were continuous. containing a larger proportion of the short-PSP plants
than of long-PSP plants. Transgressive segregation for long-PSP plants was
indicated in all the crosses studied (Fig. 2) and a few strongly sensitive progenies
were obtained i11 one cross (IRRI. 1972; Lin. F. 1-1.. 1972).
In a cross between a strongly sensitive variety} and a weakly} sensitive variety‘
of related descent. strong photoperiod response behaved as a monogenic dominant
trait to the weak response (Fig. 3). However. a few insensitive F, plants
were recovered in the F: population (Chang and Ilung. unpublished). The
appearance of insensitive plants in this cross. along with the finding of stronglyr
sensitive plants in the weakly sensitive x insensitive crosses. indicates the rather
complex nature of the tveak photoperiod response.
Photoperiodic response alone cannot account for all of the variation i11 growth
duration found in rice cultivars. The basic vegetative phase (BVP) is the other
major determinant of growth duration and it is not affected by photoperiod. By
dividing vegetative tillers from the parents as well as hybrid progenies and subjecting
the replicated tillers to different photoperiods. the BVP component can
be separated from the PSP phase on an individual plant basis. Studies at IRRI
have clearly indicated that a short BVP is controlled by several anisorncrie genes
(Efl. Efl. etc.) which are cumulative but unequal in effect (Chang et al.. 1969).