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Results and discussion
For each of the 17 bread wheats chromosome 1B in 10 cultivars
(Yecora, Agatha/6*Yecora, Yaco, Ciano T79, Mrl/Buc, Pfau, Opata,
Ocoroni, Esmeralda, Buc//Mayo/Mon) was substituted by T1BL.1RS, and
chromosome T1BL.1RS in seven cultivars (Glennson M81, Spinebill,
Bagula, Fink, Kauz, Bobwhite, Veery 10) was substituted by 1B
(Table 1). The seven bread wheat cultivars
involved allowed the end products of each cultivar to yield
near-isogenic lines. For each cultivar three sets have been
formulated to stringently evaluate the 1RS contributions in this
diverse set of wheat cultivars. To exemplify further, in the three
sets of each cultivar the first entry is the breeders original
cultivar. If this cultivar was T1BL.1RS, (e.g. Glennson M81,
Table 1) then the second entry would be a
near-isogenic Glennson M81 with the 1B chromosome substitution. The
third entry would be a T1BL.1RS line selected after selfing of the
backcross 7 heterozygotes. This entry is called "extracted". Though
it is a T1BL.1RS type phenotypically like the parent cultivar
(Glennson M81), genetically it may differ from it due to several
allelic variations on 40 chromosomes, and the 1BL arms, but not for
the 1RS arm. These variations occur due to the recombination event
that may happen when Glennson M81 is crossed by Ciano T79 to generate
the F1 heterozygote (T1BL.1RS, 1B). Subsequent backcrosses
to Glennson M81 give a Glennson M81 phenotype. Genetic differences
however, will exist since 20 chromosomes of Glennson M81 and 20 of
Ciano T79 are involved in recombination after the F1 is
produced and advanced up to BC7. Only the 1RS arm remains
similar, since it does not associate at meiosis remaining as the
unpaired arm of the T1BL.1RS/1B rod bivalent.
Each of the cultivars which are T1BL.1RS homozygotes possess biotic
stress resistance genes Lr26, Sr31, Yr9, and Pm8
located on the rye chromosome arm 1RS (McIntosh 1983). Agronomic
differences amongst wheat cultivars have been attributed to the
presence of the T1BL.1RS chromosome. These translocation genotypes
give superior grain yield, aerial biomass, kernel weight, and
spikelet fertility (Moreno-Sevilla et al. 1995; Carver and Rayburn
1994; Schlegel and Meinel 1994). Plant height reduction and delayed
heading was observed by McKendry et al. (1996). T1BL.1RS associated
positive effects for above-ground biomass at maturity, spikes
m-2, 1000-kernel weight, and test weight, were reported by
Villareal et al. (1991, 1994) when diverse spring wheat cultivars
were evaluated. Villareal et al. (1995) further reported a
performance advantage of T1BL.1RS derivatives from random
F2-derived F6 lines of the Nacozari (1B)/Ser!
M82 (T1BL.1RS) cross for higher grain yield, above-ground biomass,
kernels spike-1, 1000-kernel weight, and test weight.
Considering these contributions from the above investigation we feel
that the presently reported germplasm using the backcross protocol
and having the "extracted" entry inclusion will be an asset to
further evaluate the T1BL.1RS contributions more stringently.
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