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Evaluating grain yield as influenced by biological yield and harvest index in four winter wheat (Triticum aestivum) crosses involving near-isogenic lines
Crosses between four near isogenic lines for height reducing genes
Rhtâ and Rhtâ and one agronomically superior dwarf line, including
generations through Fâ with reciprocal backcrosses constituted the
experimental materials. Mean, range and standard deviation values for
eleven traits pertaining to the different generations were obtained.
Heterosis and inbreeding depression along with broad and narrow sense
heritability estimates for the traits provided information regarding
nature of gene action. Possible relationship between selected traits
were also determined.
The amount of genetic diversity between crosses depended upon the
number and specific dwarfing genes involved. A limited number of traits
were different in crosses involving either Rhtâ or Rhtâ isolines. This
may have resulted since 'Yamhill Dwarf also carries the Rhtâ allele.
For generations, differences were detected for all eleven traits measured. The cross involving the standard height isoline (rhtârhtâ)
and Yamhill Dwarf registered the highest mean values for plant height,
grain yield, 300-kernel weight and biological yield; but had the lowest
value for harvest index. Increased grain yield was more a function of
higher "biological yield" than "harvest index" in all crosses and
populations examined.
Consistent and positive associations were also found between grain
yield and biological yield; however the same was not true for grain
yield with harvest index where little or no associations were detected
for any of the crosses.
Heterosis estimates were high for most traits in rhtâRhtâ/Yamhill
Dwarf cross and low in the cross Rhtârhtâ/Yamhill Dwarf.
Inconsistent broad and narrow sense heritability estimates were
observed in several crosses for most traits measured. The one exception
was for 300-kernel weight, being relatively high and consistent in all
crosses except RhtâRhtâ/Yamhill Dwarf. In some instances, negative
narrow sense heritability estimates were realized. This was
particularly true for the cross between the standard height isoline
(rhtârhtâ) and Yamhill Dwarf. Also, depending on the cross and trait
measured, larger narrow sense heritability estimates were obtained when
compared to the broad sense estimates. This could reflect some sampling
error or a large genotype X environmental interaction which was
observed