Molecular marker assisted introgression of loose and covered smut resistance into CDC McGwire hulless barley
CDC McGwire is a high yielding hulless barley cultivar from the Crop Development Centre (CDC), University of Saskatchewan which is susceptible to both true loose and covered smut. Screening for these diseases is time, labour and space consuming and escapes are very frequent making it necessary to screen putative resistant lines several times to confirm resistance. In addition, both the diseases are expressed in the inflorescence, simultaneous screening for them is not possible. Molecular Marker Assisted Selection (MAS) is a good alternative to combine the resistance to both diseases in the same line. Sequence characterized amplified region (SCAR) markers linked to the loose smut resistance gene Run8 (Eckstein et al. 2002) and covered smut resistance gene Ruhq (Ardiel et al. 2002, Grewal et al. 2004) have been developed at the CDC and a program was initiated to introgress loose smut resistance (Run8) and covered smut resistance (Ruhq) into CDC McGwire using MAS. Loose smut resistance was transferred from TR251 (Run8) and covered smut resistance from either Q21861 or TR640 (Ruhq). Two strategies (doubled haploidy and marker-assisted backcrossing) were used to introgress both resistance genes. Screening 35 microspore culture derived doubled haploid (DH) lines against covered and loose smut in the field and greenhouse showed that in most lines, the phenotype defined by disease reactions and genotype defined by the SCAR markers agreed. Screening putative resistant lines three times for covered and loose smut identified 12 DH lines resistant to both smuts and positive to molecular markers of both the diseases. In the marker-assisted backcross program, plants were genotyped in each generation and plants positive for both markers were backcrossed to CDC McGwire. The genotyping of BC1F1, BC2F1 and BC3F1 plants with SCAR markers (UhR450 and Un8700R) showed a 1:2:2:1 segregation indicating the presence of two major genes. Twenty BC3F3 lines (10 lines selected with the covered smut resistance from Q21861 and 10 lines selected with the covered smut resistance from TR640) were evaluated for covered smut reaction in the field in 2004 and in the greenhouse in the fall of 2004. All lines showed resistance to covered smut. BC3F3 lines were inoculated with loose smut in the field in 2004 and evaluated in the greenhouse. Eighteen of 20 lines showed loose smut resistance. These putative double resistant lines will be phenotyped in BC3F5 generations to confirm disease reactions. These results confirm that molecular markers can assist in rapid introgression of simply inherited disease resistance genes into elite lines with considerable savings in time and cost.
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