Canola (B. napus L.), one of the most valuable oilseed crops in the world, has been reported with significant crop losses up to 100% due to blackleg disease caused by Leptosphaeria maculans. Genetic resistance is a primary method to control blackleg, and the highest levels of resistance can be introduced from Brassica species containing the B-genome through interspecific hybridization. With successful introgression of resistance, the BC3 recombinant lines, derived between resistant B. juncea UM lines and susceptible B. napus L. cv. Westar, showed high levels of resistance to two L. maculans isolates 03-15-03 and PG4-1M at the seedling stage. In the analysis of blackleg resistance in synthetic hexaploid Brassica lines using susceptible B. juncea UM3086, the resistance against L. maculans isolate 03-15-03 in F2, BC1, BC2 and BC2F2 populations indicated that two genes are inherited in backcross populations and each gene can confer the same level of blackleg resistance. The high number of resistant phenotypes and compatibility of interspecific crosses in hexaploids crossed with tetraploid Brassica imply that synthetic lines are a feasible tool for developing blackleg resistance. / October 2016

Inaug.--diss.--Bern. / "Sonder-abdruck asu dem Archiv f. wissensch. u. prakt. tierheilk." "Literatur": p. 21-22.

Blackleg caused by Leptosphaeria maculans (Desm.) Ces. & De Not. is one of the most serious diseases in canola production. A high level of blackleg resistance has been shown in Brassica carinata A. Braun (BBCC) and new synthetic hexaploid Brassica species (AABBCC) developed from the crosses of B. rapa L. and B. carinata. Blackleg resistance from B. carinata and hexaploid Brassica accessions was transferred into B. napus L. using interspecific hybridization followed by backcrossing to a susceptible B. napus cultivar ‘Westar’ three or four times and selfing one or two times to produce pure lines. Leptosphaeria maculans isolate 03-15-03 was used to select the resistant plants in each generation using cotyledon inoculation, and four L. maculans isolates (03-15-03, 3-42-6, 09stonewall9553, and PG4-1-M) were utilized in advanced generations. In the cross of B. napus ‘Westar’ and B. carinata, all plants in the F1 showed a high level of resistance to L. maculans isolate 03-15-03. According to the chi-square testing for goodness of fit, the segregation of resistant and susceptible plants fit a 1:1 ratio in the BC1, BC3, and BC4. In the BC3F2, two families followed a 3:1 segregation ratio of resistant and susceptible plants. The results suggest that the resistance to L. maculans transferred from B. carinata into canola ‘Westar’ was controlled by a single locus. Embryo rescue tissue culture was used to obtain F1 plants of the crosses of ‘Westar’ and synthetic hexaploid Brassica accessions. In the BC1 and BC2, most families did not fit a 1:1 segregation ratio of resistant and susceptible plants. The segregation of resistant and susceptible plants fit a 3:1 ratio when inoculated with L. maculans isolates in the BC1F2-3.1.1s and BC1F3-3.1.1.1ss families. Meanwhile, the BC2-3.1.1 family also followed a 1:1 segregation of resistant and susceptible plants inoculated with L. maculans isolate 03-15-03. The results suggest that the resistance to L. maculans introgressed from synthetic hexaploid Brassica species into B. napus is most likely controlled by a single locus. / May 2016

Blackleg, caused by the fungus Leptosphaeria maculans, is one of the most important diseases on canola in western Canada. Severe epidemics can cause substantial losses of seed yields and quality. Fungicide application is an important disease management strategy, but little is known about the efficacy of fungicides against blackleg and possible impact on fungicide sensitivity of L. maculans after repeated uses. The results of present study showed that fungicides generally reduced the blackleg incidence and severity on the susceptible canola cultivar, and the QoI fungicides were more effective than the DMI fungicides. Early fungicide application at about 2-4 leaf stage provided a small yield improvement on the susceptible cultivar. Typical point mutation was not found in any of these QoI-insensitive L. maculans field isolates and polymorphism correlating with the QoI-insensitive phenotype was not observed either in the sequence of cytochrome b gene among the L. maculans isolates.

Oilseed rape is largely infected by several phytopathogens and two most economical important diseases are blackleg caused by fungus species complex Leptosphaeria maculans and L. biglobosa and clubroot caused by protist P. brassicae. The sequenced genomes of these phytopathogens provide opportunity to uncover various aspects related to disease infection, host pathogen interactions, plant disease resistance, and evolution of pathogens. Considering these we focused on one of the most conserved family called immunophilins (IMMs) in these genomes. IMMs are comprised of three structurally unrelated sub-families including cyclophilins (CYPs), FK506-binding proteins (FKBPs), and parvulin-like proteins (PARs). We identified putative members of IMMs in each phytopathogen using bioinformatics approaches. We further characterized the IMMs based on domain architecture, subcellular localization, exon-intron organization, transcriptomic expression patterns, gene ontology terms, conserved motifs presents and evolutionary analyses. IMMs are performing several vital roles in plants, animals and fungi. However, in phytopathogens their roles are not well established except for cyclophilin that implicates in pathogenicity in some phytopathogens. Therefore, we exploited the role of cyclophilin in L. maculans and L. biglobosa using expression profiles and in P. brassicae using Magnaporthe oryzae cyclophilin deletion mutant. Overall, we concluded that the cyclophilin acts as a virulence determinant in our studied phytopathogens. However, delineating the precise role of other IMMs would also be imperative. Taken together, our findings for the first time shed light on the highly conserved IMM family in the oilseed rape pathogens.

No description available.

Dessertation describes of the first reported syntheses of the natural products lairdinol A and depsilairdin. The key steps in the synthesis of depsilairdin were N-terminal extension (C←N) of the protected proline fragment, hydrolysis of the tetrapeptide fragment with free secondary alcohol in the proline moiety and esterification of the HOBt ester of tetrapeptide fragment with the bromomagnesium alkoxide of lairdinol A.

Dessertation describes of the first reported syntheses of the natural products lairdinol A and depsilairdin. The key steps in the synthesis of depsilairdin were N-terminal extension (C←N) of the protected proline fragment, hydrolysis of the tetrapeptide fragment with free secondary alcohol in the proline moiety and esterification of the HOBt ester of tetrapeptide fragment with the bromomagnesium alkoxide of lairdinol A.

Phoma stem canker (aka Blackleg) caused by the fungal pathogen Leptosphaeria maculans is a major disease affecting Canola (Brassica napus L.). This study examined 674 L. maculans isolates collected in 2010 and 2011 from western Canada at ten avirulence gene loci. Overall, certain alleles were more prevalent with AvrLm6 and AvrLm7 present in >85% of isolates and AvrLm3, AvrLm9, and AvrLepR2 present in <10% of isolates. This study also examined the genetic diversity of Leptosphaeria maculans populations around the world. Blackleg disease is found in most countries where Brassica spp. are cultivated and there are indications that L. maculans is an expanding species displacing the less aggressive Leptosphaeria biglobosa. Twenty two microsatellite primers were used to screen 96 isolates from 8 countries. A phylogenetic tree to assess the evolutionary relationship between regions was generated and the results indicated that genetic diversity was correlated with geographic location. / October 2015

Pectobacterium carotovorum (Pbc), Dickeya spp., Pectobacterium atrosepticum (Pba), and a new, atypical strain, Pectobacterium carotovorum subsp. brasiliensis (Pbcb) can cause potato blackleg, soft rot and aerial stem rot. To determine the impact and extent of these pathogens on the South African potato industry, samples were collected from 72 potato fields in 10 potato production regions during the 2006/7 production seasons. During these seasons, blackleg outbreaks occurred in commercial production fields causing severe economic losses. Bacteria isolated from diseased material that were Gram-negative, facultative anaerobic with pectolytic ability were identified using a Multiplex PCR targeting the 16S-23S region. Isolates were subjected to partial sequencing of the 16S-23S rDNA and a subsequent PCR-RFLP of the 16S-23S rDNA region. Comparison of RFLP patterns of isolates to reference cultures confirmed the identity of the South African blackleg strains as Pbcb. This is the first report of Pbcb in South Africa. A total of 128 isolates were obtained from 10 production regions. Of these 77% were shown to be Pbcb, 17% Pbc and 6% unkown. Dickeya spp. and Pba were not detected in South Africa. From imported tubers 14 isolates were obtained, 13 of which were identified as Pbcb and one isolate as Pbc. Thus Pbcb was shown to be the most important causal agent of blackleg and soft rot in South Africa and poses a threat to the South African potato industry. Through a questionnaire survey the farmers` knowledge of soft rot / blackleg disease complex and the need for research on these potato diseases in South Africa was determined. A total of 41 questionnaires were collected from potato growers and analysed. Estimates of economic losses experienced by growers due to soft rot / blackleg disease complex, ranged from 1 to 70%. It appears that in South Africa disease symptoms are mainly prevalent at temperate (10 – 20°C) to warm climates with prolonged wet or humid conditions. To reduce disease incidence, low generation seed tubers need to be planted and good crop rotation systems need to be followed. Blackleg is mainly a seed-borne disease and is therefore difficult to control. This prompted the search for a possible management strategy to increase plant / tuber resistance to blackleg and soft rot and to minimise losses. The study also focussed on the effect of a calcium silicate slag soil amendment on phenolic formation in cell walls of potato peels, and subsequent tuber resistance to Pectobacterium carotovorum subsp. brasiliensis (Pbcb) . Pot trials were conducted with the following treatments: Control with and without the pathogen; slag (30% Si) with and without the pathogen; lime treatment (CaCO3) as pH control with and without the pathogen. Results from pot trials show that phenol production in potato stems and tubers increased in both lime and slag treatments, compared to the controls. This suggests that soil pH may play a role in phenol production. This could, however be due to increased silicon absorption by plants at higher pH values. Results also indicate that the best Si source to use is Calmasil, since Si and Ca combined have a synergistic effect in enhancing tuber resistance. This is, however, the first study on the effect of Si on defence responses of potatoes and further research is required to elucidate the modes-of-action of Si in the potato plant. This study has enhanced the understanding of the etiology of soft rot / blackleg diseases in South Africa and opened up new possibilities for the use of Si in commercial production to improve plant health status. However the need for future research on this disease complex has been highlighted in this thesis. / Dissertation (MSc)--University of Pretoria, 2009. / Microbiology and Plant Pathology / unrestricted