ABSTRACT
Development of new plant types (NPTs) and
hybrids are two major approaches for improving
the yield potential of irrigated rice (Oryza sativa
L.). This study was conducted (i) to compare
grain yield and yield attributes among three high-yielding groups of rice, namely indica inbred,
indica/indica F
1
hybrid, and second-generation
NPT, and (ii) to identify the morphophysiological
traits responsible for the yield difference among
the three groups. Fifteen genotypes, five from
each of the three groups, were grown in the dry
(DS) and wet seasons (WS) of 2003 and 2004 at
the International Rice Research Institute, Philip-pines. On average, hybrids produced 11 to 14%
greater grain yield than indica inbreds and NPTs
in the DS. In the WS, the difference in grain yield
was relatively small among the three groups. High
grain yield of hybrids in the DS was the result of
high number of spikelets per square meter due
to a large number of spikelets per panicle and
high harvest index rather than biomass produc-tion. The NPTs did not show yield advantage over
the indica inbreds and demonstrated signifi-cantly lower yield than hybrids, mainly because
of fewer spikelets per panicle and per square
meter. Spikelet production efficiency per unit of
N uptake and per unit of aboveground biomass
at physiological maturity was generally higher in
hybrids than indica inbreds or NPTs. Increasing
harvest index and spikelet production efficiency
by developing NPTs with more spikelets per
panicle should be emphasized for improving the
grain yield of NPTs.