This is the first study to rigorously com-pare the second-generation NPT lines with
indica inbred and hybrid cultivars. Overall,
NPT has not shown yield superiority over
hybrids and indica inbreds for the following
reasons: (i) NPTs did not show higher bio-mass production or harvest index than hybrids and indica
inbreds; (ii) the panicle size of NPT was not greater than
that of hybrids; and (iii) the grain-filling percentage of
NPT has not reached the same level as that of indica
inbreds. To improve the grain yield of NPT, large panicle
size is necessary to assure the increase in sink size. We may
look for genes of large panicle size from donor parents
other than tropical japonicas. Spikelet production efficiency and grain filling percentage should be increased in
NPTs. These traits plus lodging resistance are also impor-tant to further increase the grain yield of indica inbred and
hybrid cultivars.