Thesis (M. Ag. Sc.)--University of Adelaide, Dept. of Horticulture, Viticulture and Oenology, 1997. / Includes bibliographical references (leaves 184-195).

A survey of the quality of brassica seed used for commercial transplant production revealed that overall germination was high but that there was a wide range of seed vigour, as assessed by the controlled deterioration test. These vigour differences were reflected in the performance of seed in modules, the use of low quality seed resulting in problems of a reduced rate of emergence and a lack of seedling uniformity. The improvement of seed quality was considered using three approaches. First, the use of seed soakwater conductivity as a means of predicting germination was investigated for individual seeds. This proved not to be a reliable means of sorting seeds. However, the combination of controlled deterioration followed by assessment of conductivity on bulks of seeds gave a good indication of vigour and was developed as a possible rapid vigour test. Secondly, the relation between seed size and seed performance was examined. No clear relationship was found between seed size and seed quality, although, seed size had a marked effect on seedling growth, the larger seeds consistently producing taller seedlings. Thirdly, a physiological means of seed improvement was considered. Aerated hydration in water columns was successful as an invigoration treatment resulting in increased germination rate, root length of seedlings and seed vigour leading to enhanced performance in modules. These improvements were maintained after drying and storage. The optimum short-term treatment was 8 hours hydration at 25oC. The improvement could be partly attributed to germination advancement and in addition the effect of temperature, aeration and the greater improvement of aged seeds suggested that repair processes were activated during aerated hydration. Also, prolonged hydration for up to 32 hours gave an improvement such that the performance of aged seed was not significantly different to unaged seed. Finally, one possible mechanism by which aerated hydration resulted in such improvements in seed quality was investigated. DNA synthesis began approximately 24 hours earlier in unaged than in aged seed. Hydration reduced this lag phase, indicating that the onset of DNA replication was accelerated. The use of hydroxyurea, an inhibitor of DNA replication, indicated that the repair of accumulated DNA damage may have been occurring between the 16th and 32nd hours of germination.

The focus of my research was on the secondary metabolites produced by crucifer plants under stress and their biological activity against fungi. Both cultivated and wild plants were investigated to isolate phytoalexins and phytoanticipins, and determine their metabolite profiles.<p>The first chapter of this thesis describes cruciferous plants and their most important pathogenic fungi. These plants are divided into three groups: oilseeds, vegetables and wild species. The metabolites isolated from these plants and their biosynthetic studies are reviewed. In addition economically important necrotrophic fungi such as <i>Leptosphaeria maculans</i>, <i>Alternaria brassicae</i>, <i>Sclerotinia sclerotiorum</i> and <i>Rhizoctonia solani</i> are also reviewed along with their phytotoxins. <p>The second chapter of this thesis describes the detection, isolation, structure determination, syntheses of stress metabolites and biological activity of these metabolites against <i>L. maculans</i>, <i>S. sclerotiorum</i> and <i>R. solani</i>. The investigation of cauliflower led to the isolation of seven phytoalexins: 1-methoxybrassitin (55), spirobrassinin (71), isalexin (64), brassicanal C (60), caulilexins A (106), B (107), and C (105). The phytoalexins caulilexins A (106), B (107) and C (105) were reported for the first time. Caulilexin A (106), having a disulfide bridge, showed the highest activity against S. sclerotiorum and R. solani among the known phytoalexins. Similarly four phytoalexins: 1-methoxybrassitin, brussalexins A (121), B (117) and C (118) along with four metabolites: ascorbigen (51), diindolylmethane (50), 1-methoxy-3,3-diindolylmethane (119) and di-(1-methoxy-3-indolyl)methane (120) were isolated from Brussels sprouts. The phytoalexins brussalexins A (121), B (117) and C (118) are new metabolites. Brussalexin A (121) is the only cruciferous phytoalexins having an allyl thiolcarbamate functional group. The metabolite 1-methoxy-3,3-diindolylmethane (119) is reported for the first time.<p>The investigation of brown mustard for polar metabolites led to the isolation of indole-3-acetonitrile (76) and spirobrassinin (71) along with isorhamnetin-3,7-diglucoside (134). Investigation of wild species such as Asian mustard, sand rocket, wallrocket, hedge mustard and Abyssinian mustard for production of stress metabolites led to the isolation of indole-3-acetonitrile (76), arvelexin (84), 1,4-dimethoxyindole-3-acetonitrile (137), rapalexins A (138) and B (142), methyl-1-methoxyindole-3-carboxylate (59) and metabolites bis(4-isothiocyanotobutyl)-disulfide (139), 5-(3-isothiocyanato-propylsulfanyl)-pentylisothiocyanate (136) and 3-(methylsulfinyl)-propylisothiocyanate (135). <p>Two metabolites were also isolated from Brussels sprouts and brown mustard; however, these structures are not yet determined. The metabolites 1,4-dimethoxyindole-3-acetonitrile (137) and 5-(3-isothiocyanato-propylsulfanyl)-pentylisothiocyanate (136) are reported for the first time.

The focus of my research was on the secondary metabolites produced by crucifer plants under stress and their biological activity against fungi. Both cultivated and wild plants were investigated to isolate phytoalexins and phytoanticipins, and determine their metabolite profiles.<p>The first chapter of this thesis describes cruciferous plants and their most important pathogenic fungi. These plants are divided into three groups: oilseeds, vegetables and wild species. The metabolites isolated from these plants and their biosynthetic studies are reviewed. In addition economically important necrotrophic fungi such as <i>Leptosphaeria maculans</i>, <i>Alternaria brassicae</i>, <i>Sclerotinia sclerotiorum</i> and <i>Rhizoctonia solani</i> are also reviewed along with their phytotoxins. <p>The second chapter of this thesis describes the detection, isolation, structure determination, syntheses of stress metabolites and biological activity of these metabolites against <i>L. maculans</i>, <i>S. sclerotiorum</i> and <i>R. solani</i>. The investigation of cauliflower led to the isolation of seven phytoalexins: 1-methoxybrassitin (55), spirobrassinin (71), isalexin (64), brassicanal C (60), caulilexins A (106), B (107), and C (105). The phytoalexins caulilexins A (106), B (107) and C (105) were reported for the first time. Caulilexin A (106), having a disulfide bridge, showed the highest activity against S. sclerotiorum and R. solani among the known phytoalexins. Similarly four phytoalexins: 1-methoxybrassitin, brussalexins A (121), B (117) and C (118) along with four metabolites: ascorbigen (51), diindolylmethane (50), 1-methoxy-3,3-diindolylmethane (119) and di-(1-methoxy-3-indolyl)methane (120) were isolated from Brussels sprouts. The phytoalexins brussalexins A (121), B (117) and C (118) are new metabolites. Brussalexin A (121) is the only cruciferous phytoalexins having an allyl thiolcarbamate functional group. The metabolite 1-methoxy-3,3-diindolylmethane (119) is reported for the first time.<p>The investigation of brown mustard for polar metabolites led to the isolation of indole-3-acetonitrile (76) and spirobrassinin (71) along with isorhamnetin-3,7-diglucoside (134). Investigation of wild species such as Asian mustard, sand rocket, wallrocket, hedge mustard and Abyssinian mustard for production of stress metabolites led to the isolation of indole-3-acetonitrile (76), arvelexin (84), 1,4-dimethoxyindole-3-acetonitrile (137), rapalexins A (138) and B (142), methyl-1-methoxyindole-3-carboxylate (59) and metabolites bis(4-isothiocyanotobutyl)-disulfide (139), 5-(3-isothiocyanato-propylsulfanyl)-pentylisothiocyanate (136) and 3-(methylsulfinyl)-propylisothiocyanate (135). <p>Two metabolites were also isolated from Brussels sprouts and brown mustard; however, these structures are not yet determined. The metabolites 1,4-dimethoxyindole-3-acetonitrile (137) and 5-(3-isothiocyanato-propylsulfanyl)-pentylisothiocyanate (136) are reported for the first time.

This thesis was designed to address three seldom studied aspects of the relationship between herbivores and vegetational diversity. 1. Interactions between vegetational diversity and herbivore mortality due to predation were assessed by experimentally manipulating both the species diversity of plants and the densities of a common generalist predator, the spider Enoplagnatha ovata. 2. The importance of plant size to herbivore densities was examined by quantifying plant size (measured as plant height, width, leaf area and growth rates) and adjusting for it through covariate analysis. 3. Differences in population responses of several species of herbivores to both vegetational diversity and a predator, were compared by concurrently studying four lepidopterans. The main experiment used a two factor design, with two planting treatments and two predator treatments. The planting treatments consisted of plots planted with monocultures of brussels sprouts (Brassica oleraceae) and dicultures of brussels sprouts intercropped with peppermint (Mentha piperita). The natural enemy treatments involved augmentations of E ovata in some plots and untreated controls. Two of the herbivores studied, Plutella xylostella and Pieris rapae are monophagous lepidopterans, specializing on crucifers, while the others, Autographa californica and Mamestra configurata are polyphagous. For two species, P. xylostella and M. configurata responses to augmentations of the spider, E. ovata. were different in monocultures and dicultures. Reduced densities of these two species were found in monoculture plots with added spiders; in dicultures increased densities were found in plots with added spiders. This interaction effect points out that generalist predators can be effective in monocultures. I suggest that the importance of natural enemies in monocultures is often overlooked because only the initial colonization phase is being studied. By augmenting predator populations I was able to simulate densities equivalent to those in more established cropping systems. The increased herbivore densities in dicultures with added spiders might be explained by possible predation by E. ovata on other natural enemies of P. xylostella and M. configurata in dicultures but not in monocultures. Supporting evidence for this interpretation lies in the fact that percent parasitism of P. xylostella by the ichneumonid, Diadegma insulare was lower in plots with added spiders than in control plots. Furthermore, parasitism of P. xylostella by D. insulare increased with host density in diculture plots, but not in monoculture plots. Mamestra configurata was not subject to parasitism in this study, precluding assessment of a similar relationship. No A. californica larvae were found in plots with additional spiders. In contrast, P. rapae larvae were not affected by the experimental treatments. Plant size was a crucial determinant of both herbivore populations and percent parasitism of those herbivores. Most importantly, had plant size not been accounted for, the importance of vegetational diversity to both herbivore densities and percent parasitism would have been overestimated. For example, the incorrect conclusion, that vegetational diversity alone was important in determining the abundance of both of the generalist feeders would have been reached. The greater densities of A. californica in monocultures and M. configurata in dicultures were accounted for by plant size. Without plant size adjustments, percent parasitism of P. xylostella by D. insulare would have been misinterpeted as being greater in monocultures than dicultures. With plant size adjustments, the importance of E. ovata augmentations on lowering percent parasitismwas unmasked. All important interaction effects were discovered only after adjustments for plant size had been made. Despite the low densities of all herbivore species, significant responses to experimental treatments were found in three of the four species studied. Only P.l rapae was unaffected by any of the treatments. However, conclusions based on the feeding ng habits of the herbivores could not be made. The polyphagous feeders were affected by generalist predation as much as the crucifer specialist. Parasitism was found in only two of the species, P. xylostella and A. californica. Of these two species parasitism of the specialist, P. xylostella was affected by both vegetational diversity and generalist predation, whereas parasitism of A. californica was not. My study emphasizes multifaceted interactions between the size and diversity of a primary resource and several trophic levels of consumers. Multifactor models, involving several aspects of a cropping system, are required to uncover the important mechanisms behind variable herbivore responses to vegetational diversity. / Land and Food Systems, Faculty of / Graduate

Thesis (Ph. D.)--West Virginia University, 2004. / Title from document title page. Document formatted into pages; contains xiii, 108 p. : ill. (some col.). Includes abstract. Includes bibliographical references (p. 93-99).

Investigations were carried out on the seasonal changes of aphids, particularly Myzus persicae (Sulz.), on hrussels sprouts and the importance of their natural enemies, from autumn 1968 to spring 1971 in the area around Edinburgh. M. persicae overwintered anholocyclically on weeds, particularly on dock plants, hut rarely on brassica crops. Plants in glasshouses also provided overwintering sites for M. persicae and Macrosiphum euphorbiae (Thomas). These aphids started gradually to infest the brussels sprout plants during the end of June in a constant but irregular movement. Both M. persicae and M.euphorbiae have no fixed patterns of population changes throughout the field nor from year to year. During early July the initially low densities of M. persicae and M. euphorbiae populations increased fast. By early August parasitism and predation increased; condensation of water droplets on the aphids also appeared in August and drowned some of them. Subsequently these mortality factors caused a sharp decline of the first peak of M. persicae abundance, and complete disappearance of H. euphorbiae from the field by mid-September. Favourable weather and reduced activities of natural enemies caused another peak of M. persicae to be reached in September. A slight drop in abundance occurred again, due mainly to parasitism; the third and last peak of a season appeared during late October and early November. The fall of this peak was attributed to the cold weather which reduced the rate of reproduction and hastened the abscission of bottom leaves which carried the aphid population. Eighteen species in eight genera of aphid parasites and at least eight species in five genera of hyperparasites were recorded. All the eleven species of primary parasites and five genera containing at least eight species of hyperparasites noted as parasites of M. persioae; and fifteen species of primary parasites and five genera of at least eight species of the hyperparasites listed tinder M. euphorbias were first records of any such parasites in Scotland. The M. persicae records as aphid host of seven species of primary parasites and two genera of at least three species of hyperparasites; and M. euphorbiae also as an aphid host of seven species of primary parasites and two genera of at least four species of hyperparasites were new records in Britain. Three and four species of primary parasites listed respectively under M, persicae and M. euphorbiae as aphid host were found to he new records in the general literature. Praon volucre (Hal.) was the dominant species of the primary parasites followed by Diaeretiella rapae Mcintosh and Aphidius picipes (Hees) which were about half and one third as numerous as the dominant species. Asaphes vulgaris Walker was the dominant species of the hyperparasites with cynipids about equally abundant. Some aspects of the bionomics of hyperparasites and primary parasites, particularly P. volucre, were given. Factors which limited the effectiveness of the parasites, particularly P. volucre, included 1. the fast developmental rate and the lower threshold of the aphid host (M, persicae) as compared to that of thep parasite (P. volucre). 2. hyperparasitism; - in 1969 and 1970 aphids on brussels sprouts were hyperparasitised respectively to the extent of 39.4% and 46.9% 3. harvesting of brassica crops during autumn which destroyed some of the aphid mummies and the aphid populations which could be parasitised to increase the numbers of the overwintering mummies. 4. overwintering of the parasites which started during late summer and early autumn while the aphid hosts were reproducing.