Allelism and resistance loci of powdery mildew and leaf rust in Egyptian hexaploid bread wheat

To incorporate resistance genes of powdery mildew (Pm) and leaf rust (Lr) effectively in breeding programs allelic interaction should be explored. The response and molecular patterns of three Pm genes, Pm3, Pm8, Pm17, and three Lr genes, Lr10, Lr24, and Lr26 were investigated in 15 Egyptian wheat cultivars. Postulation of different Pm and Lr resistance genes in Egyptian wheat cultivars was carried out according to seedling phenotyping data that resulted from inoculation with a set of five pathotypes of Blumeria graminis f. sp. tritici and twelve pathotypes of Puccinia triticina. Responses and molecular patterns revealed the presence of resistance genes Pm3 and Lr10 in the cultivar Misr-1, Pm17, and Lr24 in the cultivar Giza-171, and Pm8 and Lr26 in a further ten cultivars. Molecular markers confirmed the presence of Pm8 and Lr26 in six wheat cultivars, Sakha-94, Sakha-95, Gemmeiza-10, Gemmeiza-11, Sids-13, and Shandweel-1. The presence of Pm17 in Giza-171 was confirmed by the STS marker iag95. A comparison of phenotypic and genotypic data between cultivars Giza-171 and Amigo demonstrated that Pm17 in cv Giza-171 is allelic to Pm8. The existence of Lr24 in Giza-171 was confirmed by using STS marker J09. Based on these results, Pm17 and Lr24 in Giza-171 may be located on translocated chromosomes. In cv Misr-1, the presence of Pm3 and Lr10 on the same region of 1AS chromosome could represent a rare recombination event. Field responses revealed specific resistance of Misr-1 and Giza-171, which may be attributed to the presence of Pm3 and Lr10 in Misr-1 and Pm17 and Lr24+ additional genes in Giza-171

Marker assisted transfer of two powdery mildew resistance genes PmTb7A.1 and PmTb7A.2 from Triticum boeoticum (Boiss.) to Triticum aestivum (L.)

Powdery mildew (PM), caused by Blumeria graminis f. sp. tritici, is one of the important wheat diseases, worldwide. Two PM resistance genes, designated as PmTb7A.1 and PmTb7A.2, were identified in T. boeoticum acc. pau5088 and mapped on chromosome 7AL approximately 48cM apart. Two resistance gene analogue (RGA)-STS markers Ta7AL-4556232 and 7AL-4426363 were identified to be linked to the PmTb7A.1 and PmTb7A.2, at a distance of 0.6cM and 6.0cM, respectively. In the present study, following marker assisted selection (MAS), the two genes were transferred to T. aestivum using T. durum as bridging species. As many as 12,317 florets of F1 of the cross T. durum /T. boeoticum were pollinated with T. aestivum lines PBW343-IL and PBW621 to produce 61 and 65 seeds, respectively, of three-way F1. The resulting F1s of the cross T. durum/T. boeoticum//T. aestivum were screened with marker flanking both the PM resistance genes PmTb7A.1 and PmTb7A.2 (foreground selection) and the selected plants were backcrossed to generate BC1F1. Marker assisted selection was carried both in BC1F1 and the BC2F1 generations. Introgression of alien chromatin in BC2F1 plants varied from 15.4-62.9 percent. Out of more than 110 BC2F1 plants showing introgression for markers linked to the two PM resistance genes, 40 agronomically desirable plants were selected for background selection for the carrier chromosome to identify the plants with minimum of the alien introgression. Cytological analysis showed that most plants have chromosome number ranging from 40-42. The BC2F2 plants homozygous for the two genes have been identified. These will be crossed to generate lines combining both the PM resistance genes but with minimal of the alien introgression. The PM resistance gene PmTb7A.1 maps in a region very close to Sr22, a stem rust resistance gene effective against the race Ug99. Analysis of selected plants with markers linked to Sr22 showed introgression of Sr22 from T. boeoticum in several BC2F1 plants. Thus, in addition to PM resistance, these progeny might also carry resistance to stem rust race Ug99

Introgression profile of selected BC₂F₁ plants for chromosome 7AL using SSR markers and gene based marker.

<p>Black area indicates <i>T</i>. <i>boeoticum</i> specific introgression and grey areas indicate recurrent parent genome. The chromosomal locations of various markers are as per Chhuneja et al. [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0128297#pone.0128297.ref034" target="_blank">34</a>].</p

Powdery mildew reaction of the parents and introgression lines developed from the cross a) <i>T</i>. <i>durum</i> cv. PBW114<i>/ T</i>. <i>boeoticum</i> pau5088 //3*PBW343-IL, b) <i>T</i>. <i>durum</i> cv. PBW114<i>/ T</i>. <i>boeoticum</i> pau5088 //3*PBW621 at the adult plant stage under field conditions.

<p>Powdery mildew reaction of the parents and introgression lines developed from the cross a) <i>T</i>. <i>durum</i> cv. PBW114<i>/ T</i>. <i>boeoticum</i> pau5088 //3*PBW343-IL, b) <i>T</i>. <i>durum</i> cv. PBW114<i>/ T</i>. <i>boeoticum</i> pau5088 //3*PBW621 at the adult plant stage under field conditions.</p

Schematic representation of the crossing strategy adopted for transferring powdery mildew resistance genes from <i>T</i>. <i>boeoticum</i> to hexaploid wheat <i>T</i>. <i>aestivum</i> cv. PBW343-IL and PBW621 using durum wheat as bridging species.

<p>Schematic representation of the crossing strategy adopted for transferring powdery mildew resistance genes from <i>T</i>. <i>boeoticum</i> to hexaploid wheat <i>T</i>. <i>aestivum</i> cv. PBW343-IL and PBW621 using durum wheat as bridging species.</p

Meiotic analysis in selected BC₂F₁ plants a) PBW114/<i>T</i>. <i>boeoticum</i> pau5088 //3*PBW343-IL with 2n = 40 (18''+4'), b) PBW114/<i>T</i>. <i>boeoticum</i> pau5088//3*PBW621 with 2n = 42 (19''+4').

<p>Meiotic analysis in selected BC₂F₁ plants a) PBW114/<i>T</i>. <i>boeoticum</i> pau5088 //3*PBW343-IL with 2n = 40 (18''+4'), b) PBW114/<i>T</i>. <i>boeoticum</i> pau5088//3*PBW621 with 2n = 42 (19''+4').</p

<i>In vitro</i> amplification profile of RGA-STS markers linked to <i>PmTb7A</i>.1and <i>PmTb7A</i>.<i>2</i> a) <i>7AL-4556232_rga</i>, b) <i>7AL-4426363_rga</i>. Numbers 1–12 represent different BC₂F₁ plants with either one or both the genes.

<p><i>In vitro</i> amplification profile of RGA-STS markers linked to <i>PmTb7A</i>.1and <i>PmTb7A</i>.<i>2</i> a) <i>7AL-4556232_rga</i>, b) <i>7AL-4426363_rga</i>. Numbers 1–12 represent different BC₂F₁ plants with either one or both the genes.</p