Abstract
Key message: Lack of function of a D-genome adult plant resistance gene upon introgression into durum wheat. The wheat Lr34/Yr18/Sr57/Pm38/Ltn1 adult plant resistance gene (Lr34), located on chromosome arm 7DS, provides broad spectrum, partial, adult plant resistance to leaf rust, stripe rust, stem rust and powdery mildew. It has been used extensively in hexaploid bread wheat (AABBDD) and conferred durable resistance for many decades. These same diseases also occur on cultivated tetraploid durum wheat and emmer wheat but transfer of D genome sequences to those subspecies is restricted due to very limited intergenomic recombination. Herein we have introgressed the Lr34 gene into chromosome 7A of durum wheat. Durum chromosome substitution line Langdon 7D(7A) was crossed to Cappelli ph1c, a mutant derivative of durum cultivar Cappelli homozygous for a deletion of the chromosome pairing locus Ph1. Screening of BC1F2 plants and their progeny by KASP and PCR markers, 90 K SNP genotyping and cytology identified 7A chromosomes containing small chromosome 7D fragments encoding Lr34. However, in contrast to previous transgenesis experiments in durum wheat, resistance to wheat stripe rust was not observed in either Cappelli/Langdon 7D(7A) or Bansi durum plants carrying this Lr34 encoding segment due to low levels of Lr34 gene expression.