Genetic variation within populations of Cercospora beticola
Marizeth Groenewald and Pedro W. Crous, Centraalbureau voor Schimmelcultures, Fungal Biodiversity Centre, Uppsalalaan 8, 3584 CT Utrecht, Netherlands
The genus Cercospora was first described by Fuckel in 1863. It is one of the largest and most heterogeneous genera of hyphomycetes. The evolutionary relationships among recognized species of Cercospora are unknown, and the morphological similarity among species in this genus makes it quite difficult to identify isolates to species level. Cercospora apii represents the oldest name for a large complex of morphologically indistinguishable Cercospora taxa that occur on a very wide host range, and have a wide geographical distribution. Cercospora beticola belongs to the morphological complex C. apii s. lat., and causes Cercospora leaf spot of sugar beet (Beta vulgaris). Several conflicting reports pertaining to the genetic diversity present among isolates of C. beticola have been found in literature. The aim of this study, therefore, was to develop microsatellite markers to determine the genetic diversity present within and between populations of C. beticola from different countries. Many properties of microsatellite markers such as their co-dominance and multi-allelic nature favour their use in population studies, and make them ideal molecular markers to study genetic variation at the population level. The repeat motifs of the markers developed in this study, however, were not polymorphic and could therefore not be used to determine the genetic diversity within populations. Sequencing of the amplicons revealed single nucleotide polymorphisms (SNP’s) in the areas that flank the microsatellite regions. Restriction Fragment Length Polymorphisms (RFLP’s) and internal primers were developed from the SNP’s to screen populations for polymorphisms. These new markers revealed genetic variation within as well as between the different populations. However, based on the limited number of clones observed, it is unlikely that the mechanism of variation is sexual, though further research would be required to determine the nature of the exact mechanism involved.
Experimental evolution of fungicide resistance in Mycosphaerella graminicola
Francesca L Stefanato, Bruce McDonald
Institute of Plant Sciences, ETH Zentrum / LFW Universitätstrasse 2 CH-8092 Zürich (Switzerland)
Mycosphaerella graminicola is part of the Septoria disease complex, this is an important cause of crop yield loss in cereal growing, with up to 30% losses in the most affected areas. In Europe the main form of control is chemical. In vitro evolution experiments have been performed in the past with bacteria and yeasts, this is, as far as we know, the first example of this kind of study on a filamentous fungus of agricultural importance. We have chosen M. graminicola as a model for our evolutionary study since it has a yeast growth phase and it grows relatively fast in vitro. This allowed us to design a passage experiment using liquid cultures. The aim of the study was to explore the ability of the M. graminicola to develop fungicide resistance under controlled laboratory conditions simulating the pressure that the pathogen could encounter in a treated field. We designed a passage experiment using 3 Swiss isolates of the fungus and 2 fungicides belonging to different classes: a strobilurin (Azoxystrobin) and an azol fungicide (Cyproconazole). An untreated control was included to verify the effect of the growth conditions on the fungus. An aliquot of each culture was transferred to a new flask of medium amended with a sub lethal concentration of fungicide every 3 day to obtain a new generation. For each passage aliquots of the cultures were stored at -80°C. Passaging was stopped after 30 generations, there is evidence of lowered sensitivity for some of the fungicide evolved strains and we are at the moment analyzing the mechanisms behind this lowered sensitivity. We are assessing the fitness of the end point strains in planta: pathogenicity on untreated plants seems not to be affected by the prolonged in vitro growth, pathogenicity on fungicide treated plants tests are in progress.
A CORIANDER CONUNDRUM – WHAT IS THE CAUSE OF OEDEMA?
Nathalie King*, Jeremy Pritchard*, Emma Garrodo
*University of Birmingham, UK. oHorticultural Development Council, UK.Contact: N. King, University of Birmingham, School of Biosciences, Edgbaston, Birmingham, B15 2TT, UK.
Over the last decade, the increased popularity of Asian cuisine has lead to the steady rise in demand for fresh-cut coriander (Coriandrum sativum L.) in the UK, which now exceeds 2000 tonnes per year. Three quarters of this is grown in the UK as a field crop, in poly-tunnels or under glass and has a farmgate value in excess of £1.8 million. Coriander suffers from a condition known in the herb trade as ‘oedema’ (US spelling edema). Unfortunately, this term is used to describe two completely separate sets of symptoms: an angular grey patch with a pin-prick indentation within, which occurs only very early or very late in the season; and a slate-blue, bruised-looking blotch, which develops over a much longer period. This PhD project is charged primarily with identifying the cause of the disease, but also with investigating any links between the two sets of symptoms and, if necessary re-classifying them.The predominant opinion amongst growers is that oedema arises when the air is humid and the ground is wet and cold. Originally it was thought that these conditions cause transpiration to cease and root water pressure to dominate, forcing water through the xylem, into the leaf, causing cells to burst and resulting in the symptoms of the disease. However, a number of experiments have been carried out to test this theory, along with observations of weather data correlating to disease outbreak. The hypothesis has not been supported. A further two theories have also been put forward. The first is that a pathovar of the bacterium Pseudomons syringae is causing previously unrecorded symptoms. Bacterial blight, flowerstand blight and petal blight are known to be caused by P. syringae pv coriandricola (Taylor and Dudley, 1980; Toben & Rudolph, 1996; Dennis & Wilson, 1997; Refshauge and Nyudu, 2001), although most studies have related this to seed, rather than leaf production. These diseases are known to be the cause of large losses