Thesis--University of Wisconsin--Madison. / Typescript. Vita. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references (leaves 127-137).

Braunschweig, Techn. Universiẗat, Diss., 2000.

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A new disease of sugar beet, named Fusarium yellowing decline, was recently found in in the Red River Valley of MN and ND. This disease is caused by a novel pathogen named Fusarium secorum. Pathogens such as F. secorum secrete proteins during infection called ‘effectors’ that help establish disease. Since pathogenicity and disease development may depend on effector proteins produced by F. secorum during infection, effector protein identification furthers our understanding of the biology of this important pathogen. A list of 11 candidate effectors was generated previously. In this study, to characterize putative effectors, we developed a transformation system using polyethylene glycol–mediated transformation. Several mutant lines were created with an effector deleted from the genome using a split-marker knock-out strategy. To explore their role in pathogenicity, mutant strains have been inoculated to sugarbeet and compared to WT F. secorum.

Cercospora leaf spot (CLS), caused by the fungal pathogen Cercospora beticola, is the most important foliar disease of sugar beet worldwide. Control strategies for CLS rely heavily on fungicides including quinone outside inhibitor (QOI) fungicides. We collected 866 C. beticola isolates from sugar beet growing regions in France and Italy and assessed their sensitivity to the QOI fungicide pyraclostrobin. To gain an understanding of the molecular basis of QOI resistance, we cloned the full-length coding region of Cbcytb. All tested QOI-resistant isolates harbored a point mutation in Cbcytb at nucleotide position 428 that conferred an exchange from glycine to alanine at amino acid position 143 (G143A). A PCR assay was developed to discriminate QOI-sensitive and QOI-resistant isolates based on the G143A mutation. Our results indicate that QOI resistance has developed in some European C. beticola populations in Italy and monitoring the G143A mutation is an essential fungicide resistance management strategy.

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La betterave sucrière est la deuxième plante en termes de production de sucre avec 19,6% du sucre produit dans le monde entre 2015 et 2016, derrière la canne à sucre. Cultivée dans les zones tempérées comme le nord de la France et la Belgique, elle est sensible au stress thermique modéré. En effet, une augmentation de 1°C de la température moyenne entraîne une perte de rendement de 29%. Dans le cadre du réchauffement climatique et afin de fournir aux agriculteurs des variétés ayant une meilleure résistance à la chaleur, la compréhension des réponses de la betterave sucrière au stress hyperthermique est nécessaire. Pour cela, une étude des réponses physiologiques et métaboliques a été effectuée avec trois hybrides : un hybride de type sucré avec 18% de sucre dans sa racine, un hybride de type lourd avec un meilleur rendement que la moyenne mais avec seulement 17% de sucre dans sa racine, et un hybride dit « résistant » au stress hyperthermique, ayant le meilleur rendement aux champs avec des températures plus élevées. Alors que la photosynthèse nette n’était pas modifiée en condition de stress, une croissance plus rapide de la rosette a été observée aux stades jeunes pour les trois hybrides. Une approche de modélisation suggère qu’une croissance de la rosette plus rapide contrecarre les effets du stress hyperthermique sur la production racinaire. Cette hypothèse est confirmée par le fait que l’hybride le plus performant a la croissance foliaire la plus rapide. Le stress hyperthermique provoque une forte diminution du stockage transitoire du carbone dans les feuilles matures. Dans les feuilles en cours de développement, le stockage transitoire du carbone, dont la moitié sous forme d’amidon, était seulement maintenu chez l’hybride le plus performant. Un calcul intégrant les besoins en carbone de la croissance foliaire suggère que ce maintien contribue significativement au maintien du rendement chez cet hybride. Par ailleurs, un marqueur putatif de la sensibilité au stress hyperthermique a été identifié lors de cette étude. Au final ce travail a permis de mieux comprendre comment la betterave sucrière répond à l’élévation de la température et ainsi proposer de nouvelles stratégies pour l’amélioration de cette espèce. / Sugar beet is the second largest sugar-producing crop, with 19.6% of the sugar produced in the world between 2015 and 2016, behind sugarcane. Cultivated in temperate zones like the north of France and Belgium, it is sensitive to moderate thermal stress. Indeed, an increase of 1°C in the average temperature leads to a loss of efficiency of 29%. In the context of global warming and in order to provide farmers with varieties with better resistance to heat, an understanding of sugar beet responses to hyperthermic stress is necessary. For this, a study of physiological and metabolic responses was carried out with three hybrids: a sweet-type hybrid with 18% sugar in the root, a heavy-type hybrid with a better yield than average but with only 17% sugar in the root, and a so-called "resistant" hybrid, which has the best yield at higher temperatures. While net photosynthesis was not altered in stress conditions, more rapid growth of the rosette was observed at the young stages for all three hybrids. A modeling approach suggests that faster rosette growth counteracts the effects of hyperthermic stress on root production. This hypothesis was confirmed by the fact that the best performing hybrid had the fastest shoot growth. Hyperthermic stress caused a significant decrease in transient carbon storage in mature leaves. In developing leaves, transient storage of carbon, half as starch, was only maintained in the best performing hybrid. A calculation incorporating the carbon requirement of foliar growth suggests that this maintenance contributes significantly to the maintenance of yield in this hybrid. In addition, a putative marker of hyperthermic stress sensitivity was identified in this study. In the end, this work provides a better understanding of how sugar beet responds to the rise in temperature, thus proposing new strategies for the improvement of this species.

Man has always included some form of sugar in his diet. Only in the past two centuries has sugar been developed as an individual food. During that time vast amounts of money and time have gone into the development and improvement of sugar. In 1747, a German chemist by the name of Andreas Marggraf proved that sugar beets contained sugar. One of his pupils, Franz Karl Achard, in 1799 gave further evidence of this fact by his experiments.