Although HI is considered as an important trait closely related to yield in high-yielding rice breeding (Khush, 1995; Yuan, 2001), its genetics is poorly studied compared to other yield-related traits.
Although it has been demonstrated that HI is significantly related to yield and is considered as one of the most important traits in high-yielding rice breeding, HI-based high-yielding rice breeding is difficult due to its polygenic nature and insufficient knowledge on the genetic basis of HI.
Plant breeders identified this problem in the 1970s, while trying to increase production in the low-lying areas by introducing submergence tolerance traits to high-yielding varieties which are popular to local farmer [ 4].
The ability to produce fully mature seed is also an important trait for high-yielding rice because immature seeds reduce not only total grain weight, but also grain quality.
Therefore, the impact of population growth in Asia, on both rice production and rice improvement programs, is that new high-yielding rice varieties must contain the quality traits that increasingly-discriminatory consumers in different Asian markets require (Calingacion et al. 2014).
Crosses can be made to combine the tolerance traits of these landraces in the high-yielding backgrounds of modern varieties to improve adaptability and enhance grain yield and quality.
Thus, it is likely that the introgression of genomic regions from indica cultivars has contributed to the improvement of yield and other traits such as disease resistance in current Japanese high-yielding rice cultivars.
The study was, therefore, conducted to identify high-yielding and early storage root bulking cassava genotypes as well as traits associated with early storage root bulking and estimate yield loss if any due to early harvesting.
A long-term, multidisciplinary research program was started to produce high-yielding adaptive cultivars for limited water conditions which exploited the drought-tolerant traits of DT2008.
Reciprocal CSSLs between Koshihikari and the indica-type high-yielding variety Takanari have been developed to precisely identify QTLs for important agronomic traits (Takai et al. 2014).
Previously, high-Zn donors have been crossed with popular high-yielding but low-Zn rice varieties and selection was carried out for agronomic traits in the segregating generations, with final fixed lines tested for grain Zn and yield in replicated large scale plots.
