Bacterial brown spot (BBS), caused by Pseudomonas syringae pv. syringae (Pss), Van Hall, is one of the important bacterial diseases of common bean (Phaseolus vulgaris L.) globally including South Africa. The disease is seed-borne and is widely prevalent in dry bean producing areas of South Africa. It mainly infects foliage and to a lesser extent pods. Use of resistant dry bean cultivars is considered the most durable means of managing the disease. This study aimed at updating the incidences of BBS and severities, characterisation of BBS isolates, determining reaction of South African dry bean cultivars and germplasm, and investigating heritability to project possibilities of improving resistance in the local cultivars.
Thirty one locations in five provinces were surveyed for BBS incidences. BBS was observed in 87% of locations. BBS incidence ranged between 40-100% during the 2008/09 season and between 0-100% during the 2010/11 season in all the farming systems surveyed. BBS was more severe in the strip and National Cultivar Trials (NCTs) during the 2008/09 season and in the commercial and NCT during the 2010/11 season. Findings of this study signal the importance of developing BBS resistant dry bean cultivars for South Africa.
The biochemical and genetic variability of 140 Pss isolates collected from dry bean producing areas in South Africa was assessed. Pure isolates were subjected to LOPAT tests and SyrB gene assessment. Biolog GN Microplates were used to assess carbon substrate utilisation. The SyrB gene was present in 42% of isolates. The Biolog GN Microplates showed biochemical variation among isolates. Variable genomic patterns were observed in 48.5% by the BOX A1R primer and in 37.1% of isolates by the ERIC 2 primer. Thus, variability exists in Pss populations of dry beans.
Thirty six dry bean cultivars were assessed at three locations and replicated for three seasons to determine reaction to BBS. Teebus, Teebus-RR1 and Kranskop-HR1 had high BBS mean ratings of 4.7, 4.5 and 4.2, respectively. A similar trend was evident in AUDPC with values of 103.83 (Teebus) and 97.67 (Teebus-RR1) and 96.85 (RS 6). Improvement of BBS resistance in South African cultivars is necessary.
Twenty-eight common bean accessions were assessed over three seasons and locations for resistance to BBS. Hystyle and VAX 4 had lowest disease ratings of 2 and 1.7 and AUDPC values of 29.2 and 39.0, respectively, and are therefore, potential resistance sources.
Crosses between BBS resistant selected sources (Hystyle and BBSR 17) and susceptible local cultivars (Kranskop-HR1, Sederberg and Teebus-RCR2) were made. The parental lines, as well as the F1, F2, BC1F1 and BC1F2 progenies were planted in a commercial greenhouse and the F3 in the field. The Teebus/BBSR 28 population (F5:6) and the Kranskop/VAX 4 population (F6:8) and (F6:9) were received from the Agricultural Research Council รข Grain Crops Institute and planted in the field. All F1 plants were resistant to BBS, the F2 populations showed 3:1 (resistant:susceptible) segregation ratio while the F3 families showed a 1:2:1 segregation ratio. Resistance in both Hystyle and BBSR 17 is conditioned by a single dominant gene. This suggests that resistance may be easily overcome and it is essential that more BBS resistance genes be identified if efficient and long lasting resistance is to be ensured. Furthermore, the BBS resistance gene and yield traits in Hystyle and BBSR 17 are moderately to highly heritable.
These findings highlight the increasing threat of BBS in farming systems and experimental trials, thereby increasing risk of food security and lower profits. The current BBS epidemics, incidences and severities signify the importance and urgency for development of BBS resistant dry bean cultivars.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:ufs/oai:etd.uovs.ac.za:etd-07182013-115451 |
| Date | 18 July 2013 |
| Creators | Muedi, Hangwani Tshisevhe Hamilton |
| Contributors | Dr D Fourie, Prof NW McLaren |
| Publisher | University of the Free State |
| Source Sets | South African National ETD Portal |
| Language | en-uk |
| Detected Language | English |
| Type | text |
| Format | application/pdf |
| Source | http://etd.uovs.ac.za//theses/available/etd-07182013-115451/restricted/ |
| Rights | unrestricted, I hereby certify that, if appropriate, I have obtained and attached hereto a written permission statement from the owner(s) of each third party copyrighted matter to be included in my thesis, dissertation, or project report, allowing distribution as specified below. I certify that the version I submitted is the same as that approved by my advisory committee. I hereby grant to University Free State or its agents the non-exclusive license to archive and make accessible, under the conditions specified below, my thesis, dissertation, or project report in whole or in part in all forms of media, now or hereafter known. I retain all other ownership rights to the copyright of the thesis, dissertation or project report. I also retain the right to use in future works (such as articles or books) all or part of this thesis, dissertation, or project report. |
Page generated in 0.0023 seconds