Cercospora Leaf Spot in Sugar Beet
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Cercospora leaf spot in sugar beet Epidemiology, life cycle components and disease management Jessica Vereijssen Cercospora leaf spot in sugar beet Epidemiology, life cycle components and disease management Jessica Vereijssen Promotor prof. dr. MJ Jeger hoogleraar in de ecologische fytopathologie Co-promotoren dr. ir. JHM Schneider projectleider Stichting IRS, Bergen op Zoom dr. ir. AJ Termorshuizen universitair docent bij de leerstoelgroep Biologische Bedrijfssystemen Wageningen Universiteit Leden van de dr. MJC Asher promotie Broom’s Barn Research Station, Engeland commissie prof. dr. PW Crous Centraalbureau voor Schimmelcultures, Utrecht / Wageningen Universiteit / Stellenbosch University, Zuid Afrika prof. dr. A Stein Wageningen Universiteit / International Institute for Geo-Information Science and Earth Observation (ITC), Enschede prof. dr. ir. PC Struik Wageningen Universiteit The studies described in this thesis were part of the research program of the Graduate School PE&RC (Production Ecology and Resource Conservation). Cercospora leaf spot in sugar beet Epidemiology, life cycle components and disease management Jessica Vereijssen Proefschrift ter verkrijging van de graad van doctor op gezag van de rector magnificus van Wageningen Universiteit, prof. dr. ir. L. Speelman in het openbaar te verdedigen op dinsdag 15 juni 2004 des namiddags te half twee in de Aula Bibliographic data Vereijssen J, 2004 Cercospora leaf spot in sugar beet. Epidemiology, life cycle components and disease management. PhD thesis Wageningen University, Wageningen, The Netherlands. With references – with summary in Dutch – 200 pp. ISBN 90-8504-065-5 The research presented in this thesis was conducted at Stichting IRS (Institute of Sugar Beet Research), Van Konijnenburgweg 24, 4611 HL, Bergen op Zoom, The Netherlands. Photos on cover by Jessica Vereijssen. Cover design by Miep Hazen and Jessica Vereijssen. Front: beet leaf with Cercospora leaf spot symptoms. Back: Cercospora field trial at Wijnandsrade (province of Limburg) in 2003. Figures on the first page of each chapter: individual Agronomica disease index figures (Agronomica, Ferrara and University of Piacenza). Abstract Cercospora beticola, the causal agent of Cercospora leaf spot (CLS) in sugar beet, causes reductions in sugar yield and financial returns. Section I describes the epidemiology of CLS. Two disease severity indices were compared and their relation with sugar yield modelled. A linear curve fitted the Agronomica disease severity index with sugar yield in both severely and mildly infected fields, whereas for a leaf disease severity assessment this relationship was exponential and linear, respectively. The Agronomica disease severity index was less laborious and improved disease assessment. Using spatial and temporal models, the within-row dependencies of CLS disease severities was demonstrated. However, disease increase on a given plant was largely determined by disease on that plant. Similarly when describing the within-plant dynamics of disease, it was concluded that the major determinant of disease increase on a given leaf layer on a plant was from disease on that leaf layer. Spraying a fungicide twice changed the contribution of the lower leaf layers. In one mildly infected field, these leaf layers were more often significant in the model; in the other severely infected field less often. In section II studies on the life cycle of CLS are reported. It was demonstrated that C. beticola is able to infect sugar beet through the root in glasshouse, climate room, and in field experiments. The genetic variability of C. beticola was studied in an international collection of isolates. Between and within geographic regions, genetic variability is high. A C. beticola specific PCR primer was developed, which enabled detection of C. beticola in plant tissue. We showed systemic growth of C. beticola in a sugar beet seedling after root infection. Section III describes the development of a supervised control system. The use of an action threshold involving two early sprays and weather-based treatments resulted in sugar yields and financial returns similar to calendar sprayed treatments, and saved up to two fungicide applications. Sail away with me honey I put my heart in your hands Sail away with me honey Now, now, now Sail away with me What will be will be I wanna hold you now, now, now (David Gray – Sail away) Contents Chapter 1 General Introduction 1 Section I Epidemiology of Cercospora beticola Chapter 2 Comparison of two disease assessment methods for assessing 21 Cercospora leaf spot in sugar beet Chapter 3 Differences in spatial pattern of Cercospora leaf spot of sugar 37 beet in fields high and low in disease severity Chapter 4 The contribution of within-row neighbouring plants to temporal 63 increase of Cercospora leaf spot on individual sugar beet plants Chapter 5 Vertical profiles of Cercospora leaf spot on individual sugar 75 beet plants and the relative contribution of different leaf layers to disease increase Section II The life cycle of Cercospora beticola Chapter 6 Possible root infection of Cercospora beticola in sugar beet 95 Chapter 7 Root infection of sugar beet by Cercospora beticola in a 103 climate room and in the field Chapter 8 Cercospora beticola: genetic variability, identification and detection 121 Section III Disease management Chapter 9 Supervised control of Cercospora leaf spot in sugar beet 149 Chapter 10 General Discussion 175 Samenvatting 189 List of publications 193 Curriculum vitae 195 Nawoord 197 1 General Introduction Chapter 1 The sugar beet The first explicit references to beet were made in two comedies, ‘The Acharneans’ and ‘Peace’, written by the Greek poet Aristophanes and performed in Athens around 420 BC (Winner, 1993). Since the first century BC different varieties of the beet plant were already being cultivated on the shores of the Mediterranean (De Rougemont, 1989). They were grown mainly for their leaves, and probably resembled spinach or Swiss chard. In both the Greek and, later, the Roman civilisations they were highly valued supplements to the ordinary diet. References from the Middle Ages, when beet passed from areas dominated by the Romans into the cultural circles of Northern Europe, do not always differentiate clearly between roots of Brassica and Beta plants, so it is difficult to be certain where beet was known or grown regularly (Winner, 1993). Figure 1.1 Beet plant (here illustrated in its reproductive stage with seed-bearing shoot) as it was cultivated in gardens and for feeding purposes at the end of the sixteenth century in many parts of France. In this variety the upper part of the root is already of considerable thickness, and the base of the stunted shoot is red-coloured (after Dalechamps, 1587 and Winner, 1993). By the end of the fifteenth century beet was probably grown all over Europe (Deerr, 1950) but did not resemble the sugar beet as we know today (Figure 1.1). It was not until the seventeenth century that beet was cultivated regularly in the field, making it a relatively recent crop in the history of European agriculture. The development of beet into an industrial crop grown for sugar did not start until the second half of the eighteenth century (Winner, 1993). In 1747, the pharmacist Marggraf found that the sweet substance in beets 2 General Introduction was sucrose and efforts to extract sugar from beets began. Because of the very low sugar content of the beet he devoted himself to other fields of research. It was his student, Achard, who investigated the beet root in more detail and opened the way towards industrial sugar production from the roots. Sugar beet, Beta vulgaris L. spp. vulgaris (Tranzschel, 1927), is a biennial plant, a member of the Chenopodiaceae, and like many others in the family is a halophyte (able to grow on saline soils) (Elliot and Weston, 1993). It is a highly variable species containing four main groups of agricultural significance: leaf beet (Swiss chard), garden beet (beetroot), fodder beet (including mangolds) and sugar beet (Elliot and Weston, 1993). Since its origin in central Europe in the early part of the nineteenth century, the sugar beet crop has spread around the world, and it is now grown in all of the populated continents except Australia (Figure 1.2). It is essentially a crop of temperate regions, the great majority being grown between 30° and 60°N (e.g. from Cairo to Helsinki) in Europe, Asia, North America and North Africa, with a relatively small amount grown in South America (Chile and Uruguay) (Cooke and Scott, 1993). Figure 1.2 Regional distribution of sugar beet (Beta vulgaris) growing areas (black filled ovals) (after F.O. Licht’s Weltkarte der Zuckerindustrie) and distribution of Cercospora beticola, not only on sugar beet but also on other hosts as mangold, spinach and Beta maritima (black lines) (after Bleiholder and Weltzien, 1972 and Anonymous, 1969). Sugar beet is one of two crops, the other being sugar cane, which constitute the only important sources of sucrose, a product with sweetening and preserving properties that make it a major component of, or additive to, a vast range of foods, beverages and 3 Chapter 1 pharmaceuticals (Cooke and Scott, 1993). However, sucrose is used in the manufacture of a range of potentially high-volume products (e.g. polyurethane foams) and high-value, low- volume products (e.g. high intensity sweeteners, vitamins and antibiotics) (Cooke and Scott, 1993). By-products of the crop (tops, pulp, fibre and molasses) are extensively used as animal feeds and, to a small degree, in human dietary fibre. Molasses are also used for alcohol production and in other forms of fermentation (e.g. penicillin production), which is in great contrast to sugar cane, where the principal by-product (bagasse) is used simply as a fuel in the factory. 12 160 140 10 xx 120 xx 8 100 6 80 ight (ton/ha) e 60 4 40 Acreage (hax1000) Sugar w 2 20 0 0 49 53 57 61 65 69 73 77 81 85 89 93 97 01 9 9 9 19 19 19 1 19 19 19 1 19 19 19 1 19 20 Year Figure 1.3 Development of sugar beet acreage and sugar yield in The Netherlands in the period 1947 – 2003.