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Techn. Hochsch., Diss., 2004--Aachen.

Techn. Hochsch., Diss., 2004--Aachen.

N/A / Thesis / Master of Science (MS)

Certain problems relating to the formation of ascospores by baker's yeast were investigated. The effect of acetate concentration and cell population density on ascospore formation and optima were determined. An effort was made to determine factors responsible for some unpredictable variation in ascospore abundance. Certain chemicals were evaluated as sporulation stimulants with results that may be of value in yeast taxonomy. The effect of adding sporulation stimulants to both presporulation and sporulation media was also studied. / Thesis / Bachelor of Arts (BA)

Bryophilous Pezizales represent a species-rich group of fungi closely associated with bryophytes. Their ascospore morphology is highly variable and they strongly differ also in the genome size and ecology. They could thus represent an interesting model system for the research of evolution of ascospore morphology and their dispersal. The aims of my thesis were to test whether their genome size, number of nuclei in ascospores and ecology of host bryophyte influence their ascospore morphology and to experimentally test the effect of ascospore morphology on their active dispersal. I studied 52 species of bryophilous Pezizales. I reconstructed their phylogeny based on the sequences of three DNA regions, which I then used for the testing of relationships between individual variables using the phylogenetic generalized least squares. For the majority of species, I obtained measurements from morphometric analysis, genome size measurements using flow cytometry, and determined the number of nuclei in their ascospores using the fluorescent microscopy. I localised the infection apparatus and included also the ecological characteristics of the host bryophytes into the analyses. Using the experiments with horizontal ascospore discharge, I measured the distance of active ascospore ejection and recorded whether...

Leptosphaeria maculans and L. biglobosa co-infect winter oilseed rape plants to cause phoma stem canker disease. The sexual spores of both species are produced in pseudothecia on infected winter oilseed rape stem debris after harvest and this is the most important source of inoculum for infection of newly-emerged plants in autumn. Field experiments investigated the effects of host resistance on proportions of pathogens Leptosphaeria maculans and L. biglobosa in most leaf and stem tissues during 2011/2012, 2012/2013 and 2013/2014 growing seasons and on the pseudothecial development on crop debris on nine winter oilseed rape cultivars; cvs Adriana (Rlm4 + quantitative resistance (QR)), Bilbao (Rlm4), Capitol (Rlm1), Drakkar (no R gene against L. maculans), DK Cabernet (Rlm1 + (QR), Es-Astrid (QR), Excel (Rlm7), Roxet (Rlm7) and NK Grandia (QR). Cultivars with a combination of R-gene resistance and QR [Adriana (Rlm4 + QR), DK Cabernet (Rlm1 + QR)] or cultivars with only QR [(Es-Astrid and NK Grandia)] had more numbers of L. maculans leaf spots than other cultivars in autumn but less stem canker damage. There was greater number of L. biglobosa leaf spots on leaves of cvs Roxet and Excel with resistance gene Rlm7 than those of other cultivars and later more L. biglobosa DNA was detected in their stems than in those of other cultivars. In all cultivars in the three growing seasons, there was a greater amount of L. biglobosa DNA than L. maculans DNA in basal stem canker and upper stem lesions. The cv. Drakkar (no R gene against L. maculans) was susceptible in all three growing seasons, with a great number of L. maculans and L. biglobosa leaf spots and severe stem cankers. There were four cultivars (Adriana, Bilbao, Drakkar and NK Grandia) selected for the study of pseudothecial development under natural conditions with different times of exposure and in controlled environment conditions (20oC, continuous wetness). The fastest development was on the susceptible cv. Drakkar (no R gene against L. maculans), followed by Bilbao (Rlm4), Adriana (Rlm4 + QR) and NK Grandia (QR) for stem base cankers and upper stem lesions in controlled conditions. Results for pseudothecial development on stems of the nine winter oilseed rape cultivars that were exposed in natural conditions at Bayfordbury support the controlled environment results, with pseudothecia on stems of cultivars with a combination R-gene and QR consistently maturing later than those on other cultivars, regardless of the weather conditions in three growing seasons. Ascospores produced in pseudothecia are the primary inoculum that initiate phoma stem canker epidemics in autumn. Ascospore release was later in autumn 2011 than in autumn/winter 2012/2013 or 2013/2014 because of dry weather. The pattern of ascospore release had a peak, or maximum in autumn/winter 2011/2012 (4958 spores/m-3 on 22 Jan 2012) and several maxima in autumn/winter 2012/2013 (1307 spores/m-3 on 5 Nov 2012, 1291 spores/m-3 on 15 Nov 2012, 1306 spores/m-3 on 25 Dec 2012) and 2013/2014 (4575 spores/m-3 on 27 Oct 2013, 4619 spores/m-3 on 3 Nov 2013, 3674 spores/m-3 on 9 Nov 2013, 3521 spores/m-3 on 12 Dec 2013). Results from the qPCR showed that ascospores of L. maculans were released earlier than ascospores of L. biglobosa at Bayfordbury in the 2013/2014 growing season. There were differences in phenotype of isolates amongst ninety-five isolates of L. maculans and forty-eight isolates of L. biglobosa obtained from different sources (phoma leaf spots, upper stem lesions or basal stem cankers) on different cultivars. Cotyledon tests showed that the resistance genes Rlm4, Rlm5, Rlm6 and Rlm7 are still effective in England. Most isolates from phoma leaf spots carried avirulent AvrLm4 (39 isolates; 97.5%), AvrLm5 (39 isolates; 97.5%) and AvrLm6 alleles (36 isolates; 90%) and all 40 isolates carried the avirulent allele AvrLm7 (100%). Fewer isolates from basal stem cankers carried avirulent AvrLm4 (4 isolates, 16.7%) or AvrLm6 alleles (16.7%) but all 24 isolates carried the avirulent AvrLm7 (100%). Fewer isolates from upper stem lesions carried the avirulent AvrLm4 allele (5 isolates; 16.1%), but 15 isolates carried avirulent AvrLm5 (48.4%), 21 isolates carried AvrLm6 (67.7%) and all 31 isolates carried AvrLm7 (100%). By contrast, all isolates were virulent against Rlm1, Rlm2, Rlm3 and Rlm9. This knowledge, together with knowledge about R genes present in current winter oilseed rape cultivars, should be useful to provide recommendations on cultivar selection to growers based on regional frequencies of avirulent alleles of Avr allele genes in the L. maculans populations (races) and improved understanding of the race structure of L. maculans. There is a need to further investigate any R genes that operate against L. biglobosa (possibly from wild brassicas) and to study if any R genes or QR can provide resistance against both L. maculans and L. biglobosa.

Blackleg, caused by Leptosphaeria maculans, inflicts greatest canola yield losses when plants are infected before reaching the six-leaf growth stage. Studies were conducted to model pseudothecia maturation and ascospore dispersal to help growers make timely foliar fungicide applications. Pseudothecia maturation occurred mostly during the second half of June or in July in 2017 and 2018 in North Dakota and ascospores concentrations peaked during mid to late June in both years. A logistic regression model developed using temperature and relative humidity predicted the maturation of pseudothecia and ascospore dispersal with approximately 74% and 70% accuracy respectively. In addition, trials to evaluate the efficacy of five seed treatment fungicides were conducted under greenhouse and field conditions. All treatments reduced (P = 0.05) disease severity on seedlings in greenhouse trials, but not in field trials. Seed treatments, while a valuable tool, should not be used as the only means to manage blackleg.

京都大学 / 新制・課程博士 / 博士(農学) / 甲第23961号 / 農博第2510号 / 新制||農||1092(附属図書館) / 学位論文||R4||N5396(農学部図書室) / 京都大学大学院農学研究科地域環境科学専攻 / (主査)教授 田中 千尋, 教授 本田 与一, 教授 日本 典秀 / 学位規則第4条第1項該当 / Doctor of Agricultural Science / Kyoto University / DGAM

L’ascomicete Guignardia bidwellii, agente causale del marciume nero della vite, è un patogeno economicamente importante in alcuni areali viticoli. La conoscenza, disponibile sul marciume nero dell’uva, è stata recuperata dalla letteratura, analizzata e sintetizzata per sviluppare un modello meccanicistico del ciclo di vita del patogeno, guidata dalle variabili meteorologiche e dalla fenologia della vite, e basata sull'analisi dei sistemi. Il modello è stato poi valutato per la sua capacità di rappresentare il sistema reale e la sua utilità per la comprensione di epidemie di marciume nero su foglie e grappoli in un vigneto del Nord Italia, nel 2013 al 2015. Successivamente, le mancanze di conoscenza sono state analizzate, studiate e quindi colmate attraverso specifici esperimenti. In un primo passo, le dinamiche dell’inoculo primario e dei modelli di dispersione (di entrambi ascospore e conidi) da mummie svernate sono state studiate in un vigneto sperimentale per tre anni. In un secondo passo, l'effetto della temperatura e dell'umidità sulla formazione di picnidi di G. bidwellii e la successiva estrusione di cirri, nelle lesioni su foglia, la produzione e la germinazione dei conidi (inoculo secondario), e la lunghezza del periodo di latenza sono stati studiati sia in condizioni di campo che in ambiente controllato. In un terzo passo, sono stati condotti studi in ambiente controllato per studiare la produzione di conidi di G. bidwellii sulle lesioni di foglie, influenzata da lavaggi ripetuti e alternando periodi di secco ed umido. Il modello epidemiologico sviluppato in questa tesi può essere utilizzata da viticoltori come strumento predittivo per la pianificazione di trattamenti fungicidi nei vigneti. / The ascomycete Guignardia bidwellii, causal agent of black-rot on grapevines, is an economically important pathogen in some viticultural areas. The available knowledge on black-rot of grape was retrieved from literature, analyzed, and synthesized to develop a mechanistic model of the life cycle of the pathogen, driven by weather and vine phenology, and based on the systems analysis. The model was then evaluated for its ability to represent the real system and its usefulness for understanding black-rot epidemics on leaves and bunches in a vineyard of north Italy, in 2013 to 2015. Thereafter, weaknesses in our knowledge were analysed and studied through specific experiments. In a first step, dynamics of primary inoculum and dispersal patterns (both ascospores and conidia) from overwintered grape mummies were investigated in an experimental vineyard during three years. In a second step, the effect of temperature and humidity on the formation of G. bidwellii pycnidia and the extrusion of cirri in grape leaf lesions, production and germination of conidia (secondary inoculum), and the length of the latency period were studied under both environmental and controlled conditions. In a third step, environmental-controlled studies were conducted to investigate the production course of G. bidwellii conidia on grape leaf lesions as influenced by repeated washing events and alternate dry and wet periods. The model developed in this thesis can be used by vinegrowers as a predictive tool for scheduling fungicide sprays in the vineyards.