In each cropping season, five rice genotypes each from
three high-yielding groups of rice cultivars, namely indica
inbred, indica/indica F1 hybrid, and the second-generation
NPT from a cross between tropical japonica and indica, were
used in the study. The genotypes were not exactly the same
across the four seasons. For breeding lines, the selection was
based on the improved grain yield in replicated yield trials done
in a breeding nursery, thus a few newly developed lines replaced
old ones in 2004. For hybrid cultivars, the replacement was due
to the availability of F
1
hybrid seeds. In addition, some cultivars
such as IR8 and SL-8H could not be grown in the WS due to
disease susceptibility. All genotypes were developed by IRRI
except SL-8H and SL-11H, which were developed by a private
seed company in the Philippines.