Agriculture Reference
In-Depth Information
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Lowland rice genotypes
FIGURE 1.6
Plant height of 10 lowland rice genotypes. (Adapted from Fageria, N. K. 2007.
J. Plant Nutr
.
30:843-879. With permission.)
the maximum grain-yield-producing genotype CNAs 8993 (at high N level) did not have the maxi-
mum plant height, but this genotype had an intermediate plant height (Fageria et al., 2010).
Although plant height, is influenced by environmental factors, it is a genetically controlled plant
trait and the heritability of dwarfism is high and easy to identify, select, and recombine with other
traits (Jennings et al., 1997). These authors also reported that dwarf segregates have a fairly nar-
row range in height, presumably from minor gene action. Although a few are so short that they are
undesirable, the great majority fall within the useful range from 80 to 100 cm with some reach-
ing 120 cm under certain conditions (Jennings et al., 1997). During the 1960s, rice breeders made
excellent progress in the development of dwarf cultivars that responded to heavy applications of N
(Jennings et al., 1997).
1.2.1.2 Tillering
Tillers are the branches that develop from the leaf axils at each unelongated node of the main shoot
or from other tillers during vegetative growth. The development of tiller buds after differentiation is
greatly affected by environmental conditions, as well as by genotypic characteristics. The environ-
ment must be favorable for tiller development. It is essential that sufficient supplies of water, photosyn-
thate, nutrients, and plant hormones are present, and that stress is minimal (Fageria et al., 2006). The
addition of plant nutrients is particularly important when soils have low fertility. Nutrients required
for the growth of tiller buds of rice must come from the main stem, since tiller buds have neither roots
to absorb inorganic nutrients nor leaves to carry out photosynthesis. Once tillers have emerged from
the subtending leaf sheaths, they can perform photosynthesis and produce carbohydrates. Tillers can
also absorb soil nutrients through their own roots after the third leaf has completely emerged, since
roots appear at the prophyll nodes of tillers at this stage of growth (Handa, 1995).
Tillering is an important trait in cereals in determining yield. It is one of the first development or
growth stage in cereals and mainly depends on sowing density and the availability of water and N
(Simane et al., 1993; Moragues et al., 2006). Tillering has special importance under biotic and abiotic
stresses due to the compensation process. High tillering compensates for missing plants at low densi-
ties, but cultivars with limited tillering capacity lack this plasticity. However, under favorable envi-
ronmental conditions, heavy tillering cultivars have no advantage over low tillering ones in relation to
yield. Heavy tillering is not too advantageous in the direct-seeded rice, which is a common practice
