QTLs For Resistance To Leaf Rust And Powdery Mildew In Two Wheat Cultivars

wheat (Triticum aestivum L.) is a staple food crop and a major issue pertaining to food security. The fungi Puccinia triticina Eriks.(Pt) and Blumeria graminis DC. f. sp. tritici (Bgt) infect wheat plants and pose a threat on wheat production. These diseases can be controlled by utilization of host resistance, a strategy that can reduce the application of fungicides, decreasing the cost of wheat production and alleviating environmental pollution. Major genes conferring race-specific resistance are vulnerable to Pt and Bgt adaptation, being usually rendered ineffective by new virulent pathotypes within a few years of commercial use. Evidence indicates that certain quantitative trait locus (QTL) conferring quantitative resistance have remained durable. Progress is being made in investigating disease-resistance QTL globally. Our Laboratory (Laboratory of Genetics of Plant resistance to Diseases, China Agricultural University) have found that the wheat cultivars Luke and AQ24788-83(AQ) possess quantitative resistance to Pt and the latter to Bgt as well. The Laboratory constructed a LukexAQ population and a LukexAquileja (AL) population that are consisted of1589and149recombinant inbred lines (RILs) respectively. The author of this paper, in co-operation with the other members in the Laboratory, conducted several experiments and achieved corresponding findings:(1) These RILs were phenotyped for resistance to Pt and Bgt in11environments involving multiple locations (fields in Beijing, Gansu, and Shandong, and greenhouses in Beijing and Inner Mongolia) and five wheat growing seasons during the period from2009to2014.(2) A genetic linkage map for chromosome1A of LukexAL was constructed using149RILs. And, a map for all of the21chromosomes of LukexAQ, covered by605SSR/EST marker loci and207DArT loci, was constructed using307RILs.(3) On the basis of the map and disease phenotypic data of LukexAL, a major QTL for Pt-resistance (QLr.cau-1AS) and its closely linked SSR marker (gpw2246) were identified with the resistant allele being contributed by Luke. QLr.cau-1AS proved to be a novel Pt-resistance QTL. QLr.cau-1AS and gpw2246were validated in a second genetic background, namely, LukexAQ.(4) Additional five Pt-resistance QTLs (including Lr34) were detected in LukexAQ, of which, QLr.cau-4AL, QLr.cau-5AS, and QLr.cau-6DS proved to be novel. These QTLs were consistently effective across all of the test environments.(5) The effect magnitude of QLr.cau-1AS was nearly equal to that of Lr34. Selection for QLr.cau-lAS based on gpw2246was as effective as selection for Lr34based on csffr5(a DNA segment of the cloned gene Lr34and thus diagnostic for Lr34).(6) RILs that accumulated all of the six Pt-resistance QTLs were found via DNA marker-based selection (MBS). Such an accumulation yielded an elevated resistance. The MBS experiments suggested that a DNA marker distant from its represented QTL by less than3cM could result in an effective selection.(7) Seven Bgt-resistance QTLs were detected in Luke×AQ. Linked to each of the seven QTLs, a DNA marker was identified that was distant from its represented QTL by less than3cM. RILs that accumulated all of the seven QTLs were found by MBS, and they exhibited significantly improved resistance. In conclusion, four Pt-resistance QTLs were found to be novel, one of which is comparable to Lr34with respect to effect magnitude. QTLs could be accumulated by MBS provided that a marker is distant from its represented QTL by less than3cM. QTL accumulation via MBS can be a strategy for improving disease-resistance, though influence on QTL expression by genetic backgrounds should be further investigated.