Agriculture Reference
In-Depth Information
SF and those of panicle exsertion (PE) also reached signifi cant
level with the correlation coeffi cients ranged from 0.161 to
0.975. The range of coeffi cient of variation varied with the
traits, and that of PE were maximum compared with other three
traits. Hence, PE was also a valuable trait in evaluation of cold
tolerance. As for to PE and DH, their broad sense heritabilities
were 59.6% and 81.4% respectively, the biggest compared with
other effect values for heritability. DH was mainly controlled
by genetic effects, with the least infl uence by environmental
conditions. The low temperature stress should be one of the
essential conditions to breed varieties with cold tolerance (Fu-
rong et al. 2009).
Results also showed a large spatial variability in terms of
spikelet sterility within the fi eld which related to water and air
temperatures as well as their differences (Ortega et al. 2009).
Grain fi lling starts from apical part of a panicle and moves
downwards in the main panicle and then in the branches
gradually following the same process. In this way the green
spikelets accumulate the translocated reserve assimilates from
leaf sheath and culms.
To increase the yield further and to break the yield ceiling,
breeding efforts have expanded the yield sink capacity mainly
by increasing the number of spikelets per panicle. As a result,
cultivars with large panicle have become available, such as the
New Plant Type of the IRRI, and hybrid rice and 'super' rice or
'super' hybrid rice in China. These cultivars, however, do not
frequently exhibit their high yield potential due to their poor
grain-fi lling, as in a slow grain-fi lling rate and many unfi lled
grains (Ao et al. 2008).
