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Occurrence and host range of soft rot enterobacteria
Soft rot Pectobacteria are pathogens with a worldwide distribution, but with divergent host ranges and host specificities. These characteristics are shown by their serological reactions and temperature requirements (Pérombelon and Kelman, 1980). Pa is a pathogen that mainly affects potato grown in cool climatic conditions, but strains similar to Pa have been identified on other crops (Dickey, 1979). Most Pa strains irrespective of origin form a serologically homogenous group (De Boer et al ., 1979) and do not grow at temperatures above 30˚C. Pcc and Dd on the other hand, prefer higher temperatures and have wide host ranges. Pcc strains cause soft rots in many crops in the temperate and tropical regions and cause diseases in many plant species than Dd (Graham, 1964). Pectobacterium and Dickeya species have been reported as pathogens in one half of the angiosperm plant orders and these host ranges overlap but are not identical (Ma et al ., 2007). Pectobacterium spp. were reported as pathogens of 16 dicot families in 6 orders. Dickeya spp. were reported to cause disease in 11 dicot families in 10 plant orders and in 10 monocot families in 5 orders. In many cases, only one report of one species per family and order could be found. Although Pectobacterium and Dickeya spp. cause disease in many identical host species, their reported host ranges do not completely overlap. Of all these reported plant family hosts of Pectobacterium and Dickeya spp., only 6 dicot and 4 monocot families have been reported as hosts for both genera (Ma et al ., 2007). This lack of host overlap extends to higher levels of classification, for example, Pectobacterium has been reported on avocado ( Persea americana Miller) (Volcani, 1957) which is in the magnolis clade, but there are no reports on Dickeya spp. causing disease on any species in the same clade. Ma et al . (2007) found no reports of soft rot enterobacteria causing disease under natural conditions in nonangiosperms, the basal angiosperm orders, or the eudicots clade in their review.
Fluorescent amplified fragment length polymorphism
The restriction enzymes Eco RI and MseI together with selective primers E00 and MSeI-C generated between 40 and 60 distinguishable bands within a range of 40 – 550bp for each isolate tested (Fig. 4). Following numerical analysis of the AFLP banding profiles by UPGMA, the isolates clustered according to identity as determined by rep-PCR and gyrB – and recA -gene sequencing.
D. dadantii subsp. dadantii , P. c. subsp. brasiliensis and P. c. subsp. carotovorum isolates clustered separately in different clades. Within the P. c. brasiliensis clade, isolates grouped into 12 distinct clusters, several according to geographical origin, at a similarity level of 70 %. The reference strain ATCC BAA419 grouped with the isolates in cluster 1. In clusters 1, 2, 3, 6 and 7 isolates from South Africa clustered with those from Zimbabwe. Clusters 4 and 10 contained isolates from Limpopo and Mpumalanga provinces respectively (South Africa), while clusters 11 and 12 were exclusively made up of isolates from the Sandveld region, also in South Africa. Isolates from Zimbabwe (Marondera and Harare) grouped together in cluster 5, while clusters 6 and 9 contained isolates from Zimbabwe and China. Cluster 8 included isolates from South Africa, Zimbabwe and China. Pcc isolates clustered at a similarity level of 75%, while Dd isolates clustered at a relatively low similarity level of 30%.
Chapter 1 General introduction
1.1 Background and motivation of study
1.2 Fundamental objective
1.3 Specific objectives
1.4 Chapter outline
1.5 References
Chapter 2 Review of literature
2.1 Introduction
2.2 The pathogens
2.3 Disease process
2.4 Diagnostics and DNA fingerprinting
2.5 Defense systems in plants
2.6 Control
2.7 Conclusion
2.8 References
Chapter 3 Pectolytic pathogens associated with potato soft rots in zimbabwe
3.1 Introduction
3.2 Materials and methods
3.3 Results
3.4 Discussion
3.5 References
Chapter 4 Role of polyphenol oxidase, peroxidise, phenylalanine ammonia lyase, Chlorogenic acid and total soluble phenols in the resistance of potatoes to soft rot
4.1 Introduction
4.2 Materials and Methods
4.3 Results
4.4 Discussion
4.5 References
Chapter 5 Effect of calcium soil amendment in increasing resistance of potato to soft rot pathogens
5.1 Introduction
5.2 Materials and method
5.3.2Disease severity
5.4 Results
5.5 Discussion
5.6 References
Chapter 6 Survey: to assess the distribution and impact of potato blackleg and soft rot diseases in zimbabwe
6.1 Introduction
6.2 Materials and method
6.3 Results
6.4 Discussion
6.5 Acknowledgements
6.6 References 149 Summary
