The development of the number of the panicles in response to the growing
environment is considered as an important factor for seed yield (Morishima
and Oka 1975). In plant development, the number of panicles is determined
depending on the developmental fates of tiller buds formed at the each
node. Although the number of tillers rapidly increases at the early stage
of development, the development of tillers tends to cease at the later
stage, resulting in production of non-productive tillers (Matsushima 1957,
Nemoto et al. 1995). The changes in the developmental fate of the
tiller buds along the developmental axis are regarded as a mechanism related
to the reproductive success. However, the genetic regulation is poorly
understood at present. Among various dwarf mutants in rice, five tillering
dwarf types were distinguished based on the increment in the tiller number
(Shinbashi 1982). Here we discuss the change in the developmental pattern
of tillers in relation to the seed yield affected by the d17 causing
a marked increment in the tiller number.
The materials used were a cultivar, Shiokari (Japonica type) and ID-17
which was a NIL of the Shiokari carrying the tillering dwarf gene, d17
(Shinbashi 1982, Kinoshita and Shinbashi 1982). Pregerminated seeds were
individually sown in the plastic pots (17 cm diameter) with fertilizers
of 0.8-0.8-0.5 g NPK/pot. Four plants per line were examined regarding
the tiller development and yield components. The nodal position was numerically
counted from the uppermost node (the flag leaf axil = 0) on the heading
tillers and the emergence position of tillers was taken as the nodal position
on the mother stem.
Five yield components were compared between Shiokari and ID-17 (Table
1). The number of panicles in ID-17 was about five times as many as in
Shiokari. The increment in the panicle number caused a higher number of
spikelets per plant in ID-17 than in
Shiokari. Although the panicle formed
in the main stem was highly fertile (more than 90% fertility in the both
lines), the seed fertility per plant was lower in ID-17 than in Shiokari
and the number of seeds produced was not significantly different between
them. As a result, the seed yield of the ID-17 was lower than that of
Shiokari in spite of larger sink size in ID-17.
To examine the change in the developmental patterns of yield components,
the nodal position was taken as a measurement of the developmental time.
In Shiokari, the tiller emergence was not observed at the upper 2nd node
and non-productive tillers were produced at the 3rd and 4th nodes. On
the other hand, ID-17 produced productive tillers at the 2nd node, suggesting
that the growth of tillers or tiller buds might be suppressed in the later
stage of development in Shiokari.
Taking the value in the main stem as 100, the pattern of change along
the developmental axis was examined among three yield components (Fig.
1). In Shiokari, % of productive tillers markedly reduced above the 5th
node, while the seed fertility was high in all the panicles formed. On
the other hands, in ID-17, the seed fertility reduced above the 5th node,
without producing non-productive tillers. The number of spikelets per
panicle reduced in tillers from the upper nodes of the both lines. The
present results suggest that the wild type allele of the d17 contributes
to the suppression in tiller development, resulting in a high seed setting
in the remaining tillers.
Kinoshita, T. and N. Shinbashi, 1982. Identification of dwarf genes and
their character expression in the isogenic background. Jpn. J. Breed.
Matsushima, S., 1957. Analysis of developmental factors determining yield
and yield prediction in lowland rice. Bull. Natl. Inst. Agric. Sci. A5:
1-271. (in Japanese)
Morishima, H and H.-I. Oka, 1975. Phenotypic plasticity, growth pattern
and yield stability. In Adaptability in plants - With special reference
to crop yield, T. Matsuo (ed.), Univ. Tokyo Press, Tokyo, p.133-140.
K., S. Morita and T. Baba, 1995. Shoot and root development in rice related
to the phyllochron. Crop Sci. 35: 24-29.
Shinbashi, N., 1982. Genetical studies on morphogenesis in rice plant
- With special reference to dwarfness. Hokkaido Pref. Agric. Exp. Stn.,
Rep. 38: 1-55. (in Japanese)