Development and validation of molecular markers linked with stem rust resistance gene Sr13 in durum wheat

Stem rust resistance gene Sr13, found frequently in tetraploid wheats, was tested effective against Puccinia graminis f. sp. tritici pathotype Ug99 (TTKSK) and its derivatives. It remains a candidate for developing new cultivars with diverse combinations of stem rust resistance genes. To combine Sr13 with other genes that produce a similar phenotype, linked markers would be required. We used the AFLP approach to identify markers linked closely with Sr13. The STS marker AFSr13, derived from an AFLP fragment, mapped at 3.4-6.0 cM proximal to Sr13 across three mapping populations. Marker dupw167, previously reported to be linked with Sr13, mapped 2.3-5.7 cM distal to Sr13 in four F-3 populations. Marker gwm427 mapped proximal to AFSr13 in two populations, and these markers were monomorphic on one population each. The map order dupw167-Sr13-AFSr13-gwm427 was deduced from the recombination data. Markers dupw167 and AFSr13 were validated on 21 durum wheat genotypes. Combination of dupw167 and AFSr13 would facilitate marker-assisted selection of Sr13 in segregating populations. At the hexaploid level, only gwm427 showed polymorphism and differentiated the presence of Sr13 in 10 of the 15 backcross derivatives carrying Sr13 from their Sr13-lacking recurrent parents

Detection of puroindoline (Pina-D1 and Pinb-D1) allelic variation in wheat landraces

Allelic variation at the grain texture-controlling linked loci Pina-D1 and Pinb-D1 was studied among wheat landraces from the Watkins collection (pre-green revolution) using gene specific PCR based approaches. Of the 803 landraces, 593 carried the wild type alleles at these loci and were classified as soft textured. The remaining 210 genotypes were classified as hard-textured based on the presence of mutant Pin alleles known to be associated with grain hardness. Five allelic variants of Pinb-D1 were observed. Four allelic classes Pinb-D1a, Pinb-D1b, Pinb-D1c and Pinb-D1e resulted from separate single nucleotide substitutions leading to mis-sense changes, while a single base deletion at position 213 resulted in the Pinb-D1p allele exhibiting a frame shift and consequently stop codons. These five alleles occurred in six different allelic combinations with two Pina-D1 alleles (wild type and null), i.e. Pina-D1a/Pinb-D1a, Pina-D1b/Pinb-D1a, Pina-D1a/Pinb-D1b, Pina-D1a/Pina-D1c, Pina-D1a/Pinb-D1e and Pina-D1a/Pina-D1p. The alleles identified in this study provide additional resources for breeding programs for grain texture manipulations and may also have implications in microbial pathogen defence. Near-isogenic lines carrying different alleles are currently being produced to study the effect of this genetic variation on flour processing properties