Search

S.G., J.C., C.H.M. and P.J.G.M.d.W. were financially supported by a grant from the Royal Netherlands Academy of Sciences.; Fungal biotrophy is associated with a reduced capacity to produce potentially toxic secondary metabolites (SMs). Yet, the genome of the biotrophic plant pathogen Cladosporium fulvum contains many SM biosynthetic gene clusters, with several related to toxin production. These gene clusters are, however, poorly expressed during the colonization of tomato. The sole detectable SM produced by C. fulvum during in vitro growth is the anthraquinone cladofulvin. Although this pigment is not detected in infected leaves, cladofulvin biosynthetic genes are expressed throughout the pre-penetration phase and during conidiation at the end of the infection cycle, but are repressed during the biotrophic phase of tomato colonization. It has been suggested that the tight regulation of SM gene clusters is required for C. fulvum to behave as a biotrophic pathogen, whilst retaining potential fitness determinants for growth and survival outside its host. To address this hypothesis, we analysed the disease symptoms caused by mutant C. fulvum strains that do not produce or over-produce cladofulvin during the biotrophic growth phase. Non-producers infected tomato in a similar manner to the wild-type, suggesting that cladofulvin is not a virulence factor. In contrast, the cladofulvin over-producers caused strong necrosis and desiccation of tomato leaves, which, in turn, arrested conidiation. Consistent with the role of pigments in survival against abiotic stresses, cladofulvin protects conidia against UV light and low-temperature stress. Overall, this study demonstrates that the repression of cladofulvin production is required for C. fulvum to sustain its biotrophic lifestyle in tomato, whereas its production is important for survival outside its host.

Fulvia fulva (syn. Cladosporium fulvum, Mycosphaerellaceae) is a dematiaceous fungus that causes tomato leaf mould. It is characterized by its biotrophic lifestyle and the synthesis of the bianthraquinone secondary metabolite, cladofulvin. The aim of the study was to characterize the dark pigment photochemically synthesized by F. fulva and to elucidate its biochemical pathway. We isolated a black pigment from in vitro cultures of the fungus. We determined the pigment to be 1,8-dihydroxynaphthalene (DHN)-melanin based on its chemical and photochemical characteristics, as well as the presence of flaviolin, when fungal reductases were inhibited by tricyclazole. Furthermore, the pks1 gene involved in pigment synthesis has a KS domain already associated with DHN-melanin. Our findings support the relevance of studying melanization in F. fulva., Centro de Investigaciones de Fitopatología, Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas, Instituto de Fisiología Vegetal, Instituto de Botánica "Dr. Carlos Spegazzini"

Races ofCladosporium fulvum, which can overcome the resistance of the genes Cf2, Cf4, Cf5, Cf8, Cf9 and Cf11 have appeared in the Netherlands, France and Poland. Known isolates from the Netherlands and France and three new isolates from Poland have been investigated for the presence of virulence genes using a set of genotypes carrying resistance genes Cf2 to Cf11.Several Dutch isolates of races, earlier designated as 2.4, 2.4.5 and 2.4.5.9, were found to break down the resistance gene Cf11. These races must therefore be designated as 2.4.11, 2.4.5.11 and 2.4.5.9.11 respectively. In the new Polish isolates virulence genes, overcoming the resistance genes Cf2, Cf4, Cf8, Cf9 and Cf11 were found. Since all races able to grow on genotypes with Cf4, could also grow on genotypes carrying Cf8, it was impossible to discriminate between the genes Cf4 and Cf8. These Polish isolates were designated as races 4.11, 2.4.11 and 2.4.9.11. The consequences of the occurrence of these races for tomato breeding are discussed. Fysio's vanCladosporium fulvum, die de resistentie-genen Cf2, Cf4, Cf5, Cf8, Cf9 en Cf11 kunnen doorbreken, zijn in Nederland, Frankrijk en Polen opgetreden. Met behulp van een groep genotypen, die de resistentie genen Cf2 tot en met Cf11 dragen, zijn Nederlandse, Franse en enkele nieuwe Poolse isolaten onderzocht op de aanwezigheid van virulentiegenen. Enkele Nederlandse isolaten, eerder aangeduid met 2.4, 2.4.5. en 2.4.5.9, bleken het resistentie-gen Cf11 te kunnen doorbreken. Deze moeten daarom aangeduid worden als respectievelijk 2.4.11, 2.4.5.11 en 2.4.5.9.11. In de nieuwe Poolse isolaten werd virulentie gevonden voor Cf2, Cf4, Cf8, Cf9 en Cf11. Alle fysio's die op genotypen met Cf4 konden groeien, groeiden ook op genotypen met Cf8. Daarom kon geen ondersheid gemaakt worden tussen Cf4 en Cf8. De Poolse isolaten behoren tot de fysio's 4.11, 2.4.11 en 2.4.9.11. De gevolgen van het voorkomen van deze fysio's voor de tomateveredeling worden besproken.

In an allelic test it was proven that the genes Cf4 and Cf8 for resistance toC. fulvum in tomato are undistinguishable, confirming a recent suggestion that Cf8 does nott provide a novel source for resistance toC. fulvum.

Leaf mould of tomato caused by Cladosporium fulvum (syn. Fulvia fulva) has proved to be a useful system for studying mechanisms of host specificity. There are several important advantages to this host-pathogen combination. First, it is a gene-for-gene interaction for which there is available a good collection of C. fulvum races and tomato cultivars with one or a combination of genes for resistance. Some cultivars are near-isogenic, and as well, several races can be considered near-isogenic because of their origin [1,2]. Second, resistance occurs just after stomatal penetration and is rapid and localized [3]. Third, the fungus grows as a biotroph in a strictly intercellular manner [4], a feature which permits the use of intercellular wash fluids in some studies [2,5,6,7] and which also allows for direct contact between races in a doubly inoculated plant. This latter feature was important in this study.

VanCladosporium fulvum, de veroorzaker van bladvlekkenziekte van tomaat, zijn talrijke fysio's bekend. Van tomaterassen met resistentiegen Cf5 werd, zowel bij materiaal uit Bulgarije als uit Frankrijk, een nieuw fysio, 2.5, geisoleerd. Dit bezit naast het noodzakelijke virulentiegen 5 ook het overbodige gen 2. Dit is weer een voorbeeld van afwezigheid van ‘stabilising selection’.

Cladosporium fulvum staat bekend om zijn vermogen zich snel aan te passen aan nieuw geintroduceerde resistentiegenen. Die laatste jaren bleven tomaterassen met ‘C5 resistentie’ in de praktijk resistent. Deze rassen zijn zelfs resistent tegen het complexe fysio 2.4.5 door het bezit van Cf9 of een ander resistentie-gen. Een fysio 2.4.5.9 trad weliswaar op bij proeven op het IVT (Wageningen), maar werd nooit in de praktijk gevonden. In 1985 werd in Frankrijk het ras Rianto F1 in een praktijkteelt aangetast. Een isolaat vanC. fulvum van dit C5-resistente ras bleek fysio 2.5.9 te zijn. Een deel van de thans bij onderzoek gebruikte resistentiebronnen, zoals Bulgaria no. 1, Japan 74S en Japan 76S, is resistent voor dit nieuwe fysio. Het optreden van dit nieuwe fysio onderstreept de wenselijkheid ten minste twee ‘nieuwe’ resistentiegenen in nieuwe rassen te gebruiken ter verbetering van de duurzaamheid van de resistentie.