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When Rht1 Rht2 (Rht1 Rht1
Rht2 Rht2) NILs were compared to rht1 rht2 NILs, this
genotype significantly enhanced grain yield (22%) and harvest index
(27%) but was neutral for kernels/ spike and spike number, while
reducing test weight and kernel weight. These results were in
agreement with the earlier study for test weight and kernel weight.
In the earlier test, the Rht1 Rht2 genotype generally enhanced
spike number and kernels/spike but caused inconsistent effects on
grain yield (Allan 1989).
Lodging was inversely related to plant height (Table
1). Higher yields
of the three semidwarf genotypes over the nonsemidwarf genotype were
only partly due to their superior lodging resistance. The percentage
yield increase of semidwarf NILs compared to nonsemidwarf NILs in
tests sustaining significant versus minor lodging were: Rht1
NILs (45 versus 30%), Rht2 NILs (33 versus 24%) and
Rht1 Rht2 NILs (24 versus 21%), respectively.
These results may explain the exceptional performance of Nugaines in
the PNW of USA. Background genes of Nugaines appear to be especially
compatible with Rht1 or Rht2 genes allowing for
maximum grain yield increase. Furthermore, the Rht2 gene does
not reduce test weight in the Nugaines background whereas it has
consistently reduced test weights in all other genetic backgrounds.
Nugaines was a sib of Gaines and was released to replace Gaines
because it had higher test weight and flour yield.
The grain yield superiority of Rht1 compared to Rht2
was unexpected since Nugaines contributed the Rht2 allele
while Chugoku 81 contributed the Rht1 allele. One explanation
could be that favorable yield genes of Chugoku 81 remained linked to
Rht1 when backcrossed to Nugaines. That Rht1 Rht2 NILs
had unusually high mean grain yields which were comparable
(P>0.05) to Rht2 NILs supports this possibility. O.A. Vogel
selected Nugaines from a cross of Sel 14/50-3 and Burt. Sel 14/50-3
had the Rht2 gene while Burt had neither semidwarf gene. Hence
there was no possibility of obtaining selections with Rht1
from the cross that produced Nugaines.
References
Allan RE (1989) Agronomic comparisons between Rht1 and
Rht2 semidwarf genes in winter wheat. Crop Sci
29:1103-1108.
Dalrymple DG(1980) Development and spread of semi-dwaf varieties of
wheat and rice in the United States.
USDA-0ICD in Coop. with U.S. Agency for Int. Devel. Agric. Economic
Rpt. No 455. US Gov. Print. Office, Washington, DC.
Patterson FL and Allan RE (1981) Soft wheat breeding in the United
States. In: Yamazaki WT and Greenwood CT (eds) Soft Wheat:
Production, breeding, milling and uses. Am Assoc Cereal Chemists Inc,
St. Paul, MN 33-98.
Vogel OA (1964) Registration of Gaines wheat. Crop Sci 4:
116-117.
Vogel OA and Peterson CJ Jr. (1974) Registration of Nugaines wheat.
Crop Sci 14: 609.
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