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Life Science Research and Sustainable Development ISBN: 978-98-84663-33-9

width, and thickness), and the degree of filling(Xing et al.,2010).Rice varieties differ tremendously
in thelevels of grain yield, with immense variabilityin the combinations of component traits
owingto the vast diversity of genetic constitutions.In addition, yield levels of rice varietiesare also
greatly influenced by the environmentalconditions and the field management practices.There are
also remarkable interactionsbetween genotypes and environments such thatvarieties are adapted
to specific environmentalconditions.
Besides these traits the other physiological traits of plant system also contributed to
enhance yield. The traits like Plant height (PHT), Total Number of tillers (NT), Effective number
of tillers (ENT), Flag leaf length (FLL), Flag leaf width(FLW) and Panicle length(PL) also
contributed to increases the grain yield. Many studies show that these traits contributed to yield
indirectly by enhancing the rate of photosynthesis and thus increases the rate of transportation
of photo assimilates from source to sink and thus contributed to enhance yield.
3. Molecular markers and dissection of the molecular bases of rice yield traits
The inheritance of quantitative traits classicallyinvolves multiple genes, each having a
small effectthat is sensitive to environmental changes.These traits are known in general as having
lowheritability and thus have earned the reputationof being difficult to investigate. However,the
development of molecular marker, genome mapping, and QTL analysis technologies hasgreatly
facilitated the investigation of geneticbases of quantitative traits. In rice, researchershave
constructed high-density genetic linkagemaps based on restriction fragment length
polymorphism(RFLP) and simple sequence repeat(SSR) markers (McCouchet al.,1988; Kurataet
al., 1994 and McCouchet al.,2002). With the rapid development of different types of DNA markers,
marker-assisted selection (MAS) has been playing a prominent role in plant breeding. Both
random genomic marker and genic marker could be used in MAS. The random genomic markers
like RFLP have been used to construct high density linkage maps based on restriction fragment
length polymorphism and simple sequence repeat (SSR) markers for genotyping experiments.
However, are limited in MAS application due to their relatively low accuracy in selection caused
by the genetic recombination between the marker and the target gene. The genic or functional
markers, derived from polymorphic loci within genes affecting phenotypic variation, would
overcome the problem of the recombination, and thus are highly predictive of phenotype, and
will facilitate efficient selection of favorable alleles in breeding programs (Andersen and
Lubberstedt, 2003). However, there are still many challenges such as existence of any particular
alleles in a given breeding line and availability of user friendly DNA markers for MAS application
in complex traits (Xuet al., 2005). Identification of agronomically important genes and mining of
the alleles in natural populations are primarily required to develop the genic or functional
markers (Takeda and Matsuoka, 2008).
Fanet al. (2009)has been developed a cleaved amplified polymorphic sequence (CAPS)
marker based on the C-A mutation in GS3 loci, a gene contributed for grain size. This CAPS
marker is highly associated with grain length, thus could be used for selection of rice grain length
in breeding. However, its efficiency in MAS is still limited as the PCR product needs to be
digested by a restriction endonuclease and this procedure is relatively expensive and elaborative
once applied to a largebreeding population. It would be useful to develop somePCR-based
functional markers for grain length improvement.Knowledge of the allelic diversity in GS3 and
their effects would be helpful for genetic manipulation of grain size in rice. Takano-Kai et al.(2009)
also demonstrated that the C-A mutation in GS3 gene played a critical role in seed size differences
among the modern subpopulations of O. sativa.

https://jesjalna.org/Zoology-Publications/index.html 37 Department of Zoology, J. E. S. College, Jalna