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item Miklas, Phillip - Phil

Submitted to: Southern African Society of Plant Pathology
Publication Type: Abstract Only
Publication Acceptance Date: 12/1/2005
Publication Date: 1/14/2006
Citation: Fourie, D., Miklas, P.N. 2006. Bacterial resistance improvement in dry beans. Southern African Society of Plant Pathology, January 14-16, p. 15.

Interpretive Summary:

Technical Abstract: Common bacterial blight (CBB) (Xanthomonas axonopodis pv. phaseoli) and halo blight (HB) (Pseudomonas savastanoi pv. phaseolicola) are serious seedborne diseases of dry beans. These diseases are widely distributed throughout the bean producing areas in South Africa and can cause severe yield and seed quality loss. The use of resistant cultivars is the most effective and economical control strategy for bacterial diseases. Backcross breeding was used to improve resistance in two major seed types (red speckled sugar- and small white canning beans) using resistance from XAN 159 and Vax 4 for common blight and race non-specific resistance in Edmund for halo blight. High resistance levels in near-isogenic lines, developed in the two independent breeding programmes, indicated successful transfer of resistance from sources used. Results obtained from artificially inoculated CBB field trials conducted over three seasons indicated a significant improvement in disease resistance in improved Teebus breeding lines (rating 2.1 on a 1-9 scale, 8.0% leaf area loss and 11.7% disease incidence) when compared to Teebus (rating of 7.3, 53.3% leaf area loss and 56.1% disease incidence). CBB resistance in improved Teebus lines was confirmed by presence of SCAR-markers (BC420, SU91 and SAP6). Halo blight inoculated seedlings in greenhouse studies indicated a significant improvement in halo blight resistance in improved Kranskop breeding lines (mean HB rating of 2.0 on a 1-5 scale) against all prevailing races when compared to the original Kranskop (mean rating of 4.0). Two cultivars, Kranskop-HR1 (halo blight resistant) and Teebus RCR2 (common blight resistant) have been released from this programme. Results from the National Cultivar Trials indicated a yield increase of 17.8% in Kranskop-HR1 compared to Kranskop and an increase of 21.8% in Teebus RCR2 compared to Teebus.