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Abstract
Field-based adult plant resistance assessment at multi-location rust hot spot sites is a crucial job for those plant pathologists screening several wheat lines at a time against the rusts. Rust resistant bread wheat genotypes that have been extracted from previous studies have sustained wheat production in Ethiopia. The objective of this study was to evaluate advanced bread wheat lines extracted from wheat breeding trials against stem rust at adult plat stage under stem rust hot spot sites and at seedling stages in the greenhouse. Eighty three lines were further re-evaluated in consecutive two years. Check varieties were included for comparison. High disease pressure was developed on adult plant in the trial as it has been revealed by high severity on susceptible check varieties. Over years average final rust severity, co-efficient of infection and field reaction have used for differentiating Adult plant resistances. Based on ACI, the 843 genotypes evaluated in initial trial in 2013 were categorized into 10 resistance levels, of which 188 genotypes were in high level resistance category, revealing that various level of adult plant resistance is operating in these test materials. Most of 83 genotypes r-evaluated in consecutive two years after initial stage have sustained low final stem rust severity and coefficient of infection as compared with check varieties. Genotypes were varied by adult plant reaction to stem rust, however, lines ETBW7818, ETBW7819, ETBW7258, ETBW 8008, ETBW 8009, ETBW 8017, ETBW 8027, ETBW 8052, ETBW 8054 and ETBW 8055 concisely showed a reaction of R to R-MR invariably with environments. Of the 83 lines tested at seedling stages against four races, 21 lines exhibited resistance to three races JRCQC, TKTTF, TTKSK and TRTTF whereas 24 lines showed susceptibility to the latter three races. Based on adult reaction, final disease severity and coefficient of infection data, Sixty six bread wheat lines and two cultivars Shorima and Huluka sustained final rust severity <30% and low ACI are acceptable for rust resistance breeding in wheat, However, 52 lines showed comparable resistance to Shorima or Hulluka are the priority materials to be used for developing resistant cultivars potentially combining non-race specific and race specific genes which is more durable than cultivars with major resistance gene effect and more efficient than sole adult plant resistance. Inherent resistance genes of these lines are unknown and warrant further description.