Abstract
To investigate whether or not basic vegetative phase
(bvp) and photoperiod sensitive phase (PSP) interact, the
relation between these two characters was studied. It was
found to be linear but the regression coefficient varied
with the nature of sensitivity of the parents and crosses
involved. A significant relation existed between PSP and
bvp for photoperiod-sensitive parents whereas no such
relation existed for photoperiod-insensitive parents. For
F2 data, all crosses showed significant interaclion with
the highest slope within a set of crosses being associated
with photoperiod-sensitive plants only. The greater
separation in the bvp means occurred as the bv mean for
photoperiod sensitive plants increased with the increased
PSP and intermediate bvp in each cross.
The mean broad sense heritability for PSP and bvp was
found to be 84.88% and 77.87%, respectively and the genetic
advance for PSP and BVP was also 13.99% and 2.14%, respectively. This indicate that these characters were complexly
inherited.
1/ Post-doctoral Fellow and Plant Breeder (Former), respectively.
The International Rice Research Institute, Los Baños, Laguna,
Philippines.
It is of vital interest for rice breeders to estimate the
recovery ratio of photoperiod sensitive plants in the hybrid populations resulting from the crosses of photoperiod sensitive varieties
with photoperiod insensitive varieties. And it is assumed that such
hybrid populations are able to be harvested in a shorter period in
the rapid generation advance. Theoretically, there should be fairly
high frequency of photoperiod-sensitive genes in such crosses
regardless of tne degree of basic vegetative growth, but the recovery
of the photoperiod sensitive plants seems sometimes scarce and
complicated (Ahnad, 1978). Therefore, a question arises whether
there is any interaction between the length of basic vegetative
growth and photoperiod sensitivity in the expression of the total
growth duration. This point was looked into in detail by evaluating
the recovery of photcperiod sensitive plants in hybrid populations
which covers various combinations of photoperiod-sensitive rices of
different origin and varying length of the basic vegetative growth.
MATERIALS AND METHODS
Three phctoperiod-sensitive cultivars namely, Lemo, Leb Muе
Nahng 111 (IMN 1ll) and FTB 33 £rom Indonesia, Thailand and South
India, respectively, were crossed to three photoperiod-insensitive
varieties, IR32, IR34, and IR36 with varying length of basic vegetative
phase, and one photoperiod-sensitive cultivar, Sulai from Sri Lanka.
Thus a set of 12 cross-combinations were studied.
F1 and F2 seeds of 12 crosses along with their respective parents
were grown both under short daylength (8 hours) and natural daylength
during the period from May 13 through November 1978. The materials
were grown under natural daylength were the first tillers of each
individual plant grown under short daylength in Phytotron under same
temperature regime (day/night temperature 29/21°C). Plastic cups
filled with soil and placed on shallow iron boxes was the medium for
growing. The cups on each iron boxes were surrounded and supported
by soil. The soil of each cup was taken from soil stock fertilized
with each of solophos and muriate of potash at the rate of 2 g/4 kg
soil. Then after 7 days of germination 0.1 g of ammonium sulphate was
applied/cup/week till booting stage. The procedure followed for
planting the materials of each cross under study were 4 for each male,
female and Fl plants plus 60 F2 plants per cart. For each ciuss?
carts were assigned for each treatment, that is, 2 carts under short
daylength and 2 carts under natural daylength.
of the
The major records were taken on the growth duration plants
from seeding to flowering. The basic vegetative phase was estimated
by the number of days required by the main culm from seeding to
panicle initiation under 8 hours photoperiod. The date of panicle
initiation was obtained by subtracting 35 days from the date of
panicle emergence (Vergara et al., 1966). The photoperiod sensitive
phase (PSP) was calculated by subtracting the number of days required for flowering under short day of 8 hours from the number of days
required for flowering under natural daylength.
Heritability in broad sense (h2B) was estimated both for bvp and
PSP by the method of Mahmud and Kramer (1951), in which the F2 was
used as the phenotypic variance and the square root of the product
of the parental variances (geometric mean) was taken as the environmental variance, was also used. The calculations may be represented
symbolically as follows:
Heritability (h2B) VF,VP. Vp2
VF2
Vp VE VG
Vp Vp
The symbols Vp, VG and VE mean phenotypic, genotypic and environ
mental variance, respectively.
The genetic advance ( G) in percent of the mean(s) was calculated
both for bvp and PSP using the formula of Empig et al. (1970) as shown
below:
G=KF2( $2) . H
Σ
where K= 2.06 (5% selection intensity)
X= mean of the F2 population
VF2 = variance of F2
H= heritability (broad sense)