Abstract
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.
Highlights
Bread wheat, Triticum aestivum, is the second most important staple food crop, providing ~20% of the calories and the protein requirements of the world population
Triticum boeoticum pau5088 is resistant to powdery mildew (PM) and the resistance is conferred by two genes, a novel gene and a new allele of Pm1, both tentatively designated as PmTb7A.1 and PmTb7A.2, respectively [33], [34]
Only 78 pentaploid F1 seeds germinated and survived in the field, which were later backcrossed to the respective recurrent parent (Table 2)
Summary
Triticum aestivum, is the second most important staple food crop, providing ~20% of the calories and the protein requirements of the world population. The world average wheat yield is projected to rise from 3.2 tonnes/ha in the year 2013 to 3.4 tonnes/ha in 2025 but it must reach to 4.5 tonnes/ha to meet the global demand of 998 million tonnes or with the current growth rate of 0.9% per year an additional 46 million ha land needs to be added to meet the demand [1]. Among the several production constraints, diseases are the most important stress which can cause significant yield losses. Among the various foliar diseases, powdery mildew (PM) caused by the fungus Blumeria graminis f. Damage caused by PM ranges from 13–34% when infection is low to moderate but under severe infection it could be more than 50% [2]—[5]. The use of resistant cultivars is an efficient, economical and environmentally safe approach to control PM and reduce yield losses
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
