Genetic characterisation of novel resistance alleles to stem rust and stripe rust in wheat-alien introgression lines
Abstract: Bread wheat (Triticum aestivum L., 2n = 6x = 42, AABBDD) is one of the most important food crops world-wide, but is attacked by many diseases and pests that cause significant yield losses. Globally, stem rust (Sr) (Puccinia graminis f. sp. tritici Erikss & E. Henning), stripe rust (Yr) (Puccinia striiformis Westend. f. sp. tritici Eriks) and leaf rust (Lr) (Puccinia triticina Eriks) are a great threat to wheat production. The majority of the Sr, Yr and Lr resistance genes are already defeated by numerous virulent races, so enhanced genetic resistance against these devastating diseases are essential. Wheat-alien introgressions from derivatives of Secale cereale L. (2n = 2x = 14, RR), Leymus mollis (2n = 4x = 28, NsNsXmXm), Leymus racemosus (2n = 4x = 28, NsXm) and Thinopyrum junceiforme (2n = 4x = 28; J1J1J2J2) are important genetic resources for new sources of resistance genes. To identify new sources of resistance, this thesis evaluated seedling and adult plant resistance to a wide array of stem rust and stripe rust races. Three wheat-rye disomic substitution lines 2R (2D) were found to carry new resistance gene/s to stem rust races and six multiple wheat-rye introgression lines with 5RS·5AL+4R+6R carried new resistance gene/s to stripe rust races. At adult plant stage, the wheat-rye translocation line with 1BL·1RS and 2RL·2BS exhibited low susceptibility to race TTKSK under field conditions. The wheat-rye T2DS·2RL Robertsonian translocation line (TA5094) with a new stem rust resistance gene was developed through the breakage-fusion mechanism and verified using seedling resistance assays and molecular and cytogenetic analyses. Three kompetitive allele-specific PCR (KASP) markers located on rye chromosome 2RL were identified as being closely associated with the new stem rust resistance gene. Fluorescence in situ hybridisation (FISH) analysis confirmed the resistance gene in F3:4 homozygous lines. The stem rust resistance gene in TA5094 line on chromosome 2RL arm was designated Sr59. Wheat cultivars, advanced lines and landraces from Tajikistan were assessed at seedling and adult plant stages against Sr, Yr and Lr races. Based on multipathotype assessment and molecular markers, the presence of Sr6, Sr31/Yr9/Lr26, Sr38/Yr17/Lr37, Yr2 and Yr27 and pleiotropic resistance genes Sr57/Lr34/Yr18/ and Sr2/Yr30/Lr27 was postulated. Overall, this thesis identified novel genetic resistance resources against stem rust, stripe rust and leaf rust in Tajik wheat and in wheat-alien introgressions. This resistance gene/s will be useful in diversifying the current set of resistance genes deployed to control these devastating diseases.
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