S. Peng et al., Yield potential trends of tropical rice since the release of IR8 and the challenge of increasing rice yield potential, CROP SCI, 39(6), 1999, pp. 1552-1559
Since the release of IR8 in 1966, 42 additional indica rice (Oryza sativa L
,) cultivars developed by the International Rice Research Institute (IRRI)
for the irrigated and favorable rainfed lowlands have been released in the
Philippines. The maximum yield of IR8 has been reduced by about 2 Mg ha(-1)
during the past 30 yr. Empirical breeding for population improvement withi
n the indica germplasm has resulted in the maintenance of rice yield potent
ial in the tropics of about 10 Mg ha(-1). To break the yield barrier, sever
al approaches are being explored. These include development of a new plant
type (NPT) with low tillering capacity and large panicles from tropical jap
onica germplasm and exploitation of heterosis through intervarietal and int
ersubspecific hybrids. Hybrid rice between indicas increased yield potentia
l by about 9% under the tropical conditions. The higher yield potential of
indica/indica hybrids compared with indica inbred cultivars was attributed
to the greater biomass production rather than harvest index. New plant type
breeding has not Set improved yield potential due to poor grain filling an
d low biomass production. Factors that cause poor grain filling and low bio
mass production of the NPT lines have been identified. Selecting parents wi
th good grain filling traits, introduction of indica genes into NPT's tropi
cal japonica background, and a refinement of the original NPT design are ex
pected to improve the performance of the NPT lines. Further enhancement in
yield potential may be possible from use of intersubspecific heterosis betw
een indica and NPT lines.