Use of Sequence Characterised Amplified Region Markers in Marker Assisted Selection For Common Bacterial Blight Resistance in Breeding Population of Common Bean

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Kalolokesya, Lizzie
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Common bacterial blight is a major seed-borne disease of common bean. Its resistance is complex because of the quantitative nature. The combination of molecular-marker technology (MAS) with traditional phenotypic selection greatly facilitates the selection of resistant lines. The molecular markers mostly used to identify QTL conditioning resistance to CBB are SCARs. SCAR markers BC420, SU91, and SAP6 are linked with three major QTL on B6, B8, and B10 respectively, and are being used for MAS. The overall objective of this study was to select CBB resistant genotypes to be used as donor lines for production of disease free seed in order to increase bean productivity. The specific objectives were (1) Identify parental traits that support conventional breeding and MAS for CBB tolerance (2) Detect the presence of SCAR markers associated with CBB resistance in bean breeding populations (3) Assess the effectiveness of the SCAR markers SAP6, SU91 and BC420 in MAS CBB was negatively correlated with some agronomic traits measured in the parental materials except for flower colour and pod length. There were significant (p<0.001) negative correlations between days to maturity and CBB (r =-0.944) and also between seed yield and CBB (r = -0.917). There were significant differences (p<0.001) among the parental lines in their reaction to Xf260 and Xf410 isolates. The donor parents of Mesoamerican background VAX3 and VAX6 were most resistant with scores of 1 and 2 respectively. The donor parents of Andean origin (RMX lines) had intermediate response to CBB (scores of 4 and 5) and they possessed SAP6 marker. SCAR markers SU91 and SAP6 were present in VAX3 and VAX6 donors. Most of the susceptible parents also possessed SAP6 except RMA 71 (ALS donor parent) that possessed both SAP6 and SU91. None of the parental lines had BC420 marker. Artificial inoculation of Xanthomonas campestris pv. phaseoli using Xf260 and Xf410 isolates showed significant differences among the F4.6 (p<0.001) and F3.5 (p<0.001) populations tested in the greenhouse and field. Correlation analysis for field and greenhouse scores showed that there were no statistically significant relationship (p0.10) between field and greenhouse scores for both F3.5 and F4.6 generations. MAS results indicated that SAP6 marker was detected in most of the progenies with intermediate reaction to CBB. SU91 was associated with phenotypic resistance though it was also detected in some intermediate and susceptible genotypes. Correlation analysis showed highly significant relationship (p<0.001) between phenotypic and marker scores in some of the populations and insignificant (p>0.005) in some populations. Using direct selection, 51 of the F3.5 progenies were resistant and 40 of these had the marker indicating successful transfer of the resistant QTL. In the F4.6 generation, 46 progenies were resistant to the isolates and 44 of these had the marker band.
Bacterial Blight Resistance , Breeding Common Bean