Marker Assisted Transfer of Two Powdery Mildew Resistance Genes <i>PmTb7A</i>.<i>1</i> and <i>PmTb7A</i>.<i>2</i> from <i>Triticum boeoticum</i> (Boiss.) to <i>Triticum aestivum</i> (L.)

<div><p>Powdery mildew (PM), caused by <i>Blumeria graminis</i> f. sp. <i>tritici</i>, is one of the important wheat diseases, worldwide. Two PM resistance genes, designated as <i>PmTb7A</i>.<i>1</i> and <i>PmTb7A</i>.<i>2</i>, were identified in <i>T</i>. <i>boeoticum</i> acc. pau5088 and mapped on chromosome 7AL approximately 48cM apart. Two resistance gene analogue (RGA)-STS markers <i>Ta7AL-4556232</i> and <i>7AL-4426363</i> were identified to be linked to the <i>PmTb7A</i>.<i>1</i> and <i>PmTb7A</i>.<i>2</i>, 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 <i>T</i>. <i>aestivum</i> using <i>T</i>. <i>durum</i> as bridging species. As many as 12,317 florets of F₁ of the cross <i>T</i>. <i>durum</i> /<i>T</i>. <i>boeoticum</i> were pollinated with <i>T</i>. <i>aestivum</i> lines PBW343-IL and PBW621 to produce 61 and 65 seeds, respectively, of three-way F₁. The resulting F₁s of the cross <i>T</i>. <i>durum/T</i>. <i>boeoticum//T</i>. <i>aestivum</i> were screened with marker flanking both the PM resistance genes <i>PmTb7A</i>.<i>1</i> and <i>PmTb7A</i>.<i>2</i> (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 <i>PmTb7A</i>.<i>1</i> maps in a region very close to <i>Sr22</i>, a stem rust resistance gene effective against the race Ug99. Analysis of selected plants with markers linked to <i>Sr22</i> showed introgression of <i>Sr22</i> from <i>T</i>. <i>boeoticum</i> in several BC₂F₁plants. Thus, in addition to PM resistance, these progeny might also carry resistance to stem rust race Ug99.</p>