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Materials and methods

Seventeen bread wheat cultivars homozygous for chromosome 1B or T1BL.1RS, the germplasms utilized in this study:

a) Parental wheats homozygous for chromosome 1B
Ten cultivars (Yecora, Agatha/6*Yecora, Yaco, Ciano T79, Mrl/Buc, Pfau, Opata, Ocoroni, Esmeralda, Buc//Maya/Mon) were crossed with either Glennson M81 or Seri M82 (T1BL.1RS homozygous) to generate 1B,T1BL.1RS heterozygote F1 hybrids (Table 1). Each F1 was backcrossed by its 1B parental cultivar to obtain 1B/1B or 1B, T1BL.1RS seed progeny. Endosperm halves of BC1 of each cross were subjected to A-Page analysis and 1B homozygous progeny was discarded since they lacked the rye secalin bands which were present only in the 1B, T1BL.1RS heterozygotes. BC1 heterozygote seeds were germinated and cytologically tested for the presence of one T1BL.1RS chromosome. Two seedlings were advanced/combination and used to generate the BC2 generation as done for BC1 production. The A-Page and cytological diagnostic protocols (Bushuk and Zillman 1978; Mujeeb-Kazi et al. 1996) were followed up to BC7. Selfing the BC7 heterozygote plants yielded a mixture of seed that were: (i) homozygous 1B and called "extracted", (ii) homozygous T1BL. 1RS and (iii) the, 1B,T1BL. 1RS heterozygote, which were all identified by biochemical procedures. Endosperm halves from the BC7 selfed seed were subjected to glucose phosphate isomerase (GPI) analyses (Chojecki and Gale 1982) which separated the T1BL.1RS homozygotes. The remaining endosperm. halves after the GPI assay were subjected to A-Page analyses which separated the 1B homozygotes (were saved), and 1B,T1BL. 1RS heterozygotes that were discarded. Embryo portions corresponding to endosperm data for T1BL.1RS or 1B homozygotes were germinated and served for increasing seed of each combination

b) Parental cultivars homozygous for chromosome T1BL.1RS.
Seven cultivars (Glennson M81, Spinebill, Bagula, Fink, Kauz, Bobwhite, Veery 10) were crossed with either Ciano T79 or Pavon 76 (1B homozygous) to produce heterozygote T1BL.1RS, 1B F1's. The protocols for the advance up to BC7, selfing, identifying T1BL.1RS homozygotes (extracted), 1B homozygotes, and T1BL.1RS, 1B heterozygotes to be discarded were similar to those described for the germplasm in (a).

After the seed increase, one plant per combination was analyzed by fluorescent in situ hybridization (Islam-Faridi and Mujeeb-Kazi 1995), seed increased if validated and serve as the cultivars genetic stock. For each of the seventeen cultivars, three groups of germplasm form a tester set. Each cultivar set will comprise of:
1) The original breeders line,
2) The line selected after BC7 selfing possessing the same chromosomal 1B or T1BL.1RS composition as present in the breeders line and designated as "extracted" (Table 1), and
3) The line resembling the original breeders line but differing in having that cultivars 1B or T1BL.1RS chromosome replaced (substituted) by T1BL.1RS or 1B.

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