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Stem canker of crucifers is caused by an ascomycete species complex comprising of two main species. Leptosphaeria maculans and L. biglobosa. These are composed of at least seven distinct subclades based on biochemical data or on sequences of internal transcribed spacer (ITS), the mating type MAT1-2 or fragments of actin or ß-tubulin genes. In the course of a wide-scale characterization of the race structure of L. maculans from Western Australia, a few isolates from two locations failed to amplify specific sequences of L. maculans, i.e., the mating-type or mini-satellite alleles. Based on both pathogenicity tests and ITS size. these isolates were classified as belonging to the L. biglobosa species. Parsimony and distance analyses performed on ITS, actin and ß-tubulin sequences revealed that these isolates formed a new L. biglobosa subclade, more related to the Canadian L. biglobosa 'canadensis' subclade than to the L. biglobosa 'australensis' isolates previously described in Australia (Victoria). They are termed here as L. biglobosa 'occiaustralensis'. These isolates were mainly recovered from resistant oilseed rape cultivars that included the Brassica rapa sp. sylvestris-derived resistance source, but not from the susceptible cv. Westar. The pathogenicity of L. biglobosa 'occiaustralensis' to cotyledons of most oilseed rape genotypes was higher than that of L. biglobosa 'canadensis' or L. biglobosa 'australensis' isolates. [ABSTRACT FROM AUTHOR]

Leptosphaeria maculans, the causal agent of stem canker of oilseed rape, develops gene-for-gene interactions with its hosts. To date, eight L. maculans avirulence (Avr) genes, AvrLm1 to AvrLm8, have been genetically characterized. An additional Avr gene, AvrLm9, that interacts with the resistance gene Rlm9, was genetically characterized here following in vitro crosses of the pathogen. A worldwide collection of 63 isolates, including the International Blackleg of Crucifers Network collection, was genotyped at these nine Avr loci. In a first step, isolates were classified into pathogenicity groups (PGs) using two published differential sets. This analysis revealed geographical disparities as regards the proportion of each PG. Genotyping of isolates at all Avr loci confirmed the disparities between continents, in terms of Avr allele frequencies, particularly for AvrLm2, AvrLm3, AvrLm7, AvrLm8, and AvrLm9, or in terms of race structure, diversity, and complexity. Twenty-six distinct races were identified in the collection. A larger number of races (n = 18) was found in Australia than in Europe (n = 8). Mean number of virulence alleles per isolate was also higher in Australia (5.11 virulence alleles) than in Europe (4.33) and Canada (3.46). Due to the diversity of populations of L. maculans evidenced here at the race level, a new, open terminology is proposed for L. maculans race designation, indicating all Avr loci for which the isolate is avirulent. [ABSTRACT FROM AUTHOR]

Broccoli (Brassica oleracea var. italica), cauliflower (B. oleracea var. botrytis), and cabbage (B. oleracea var. capitata) have been grown in central Mexico since 1970, with 21,000 ha cropped in 2001. In contrast, areas grown with oilseed rape (B. napus) are very limited in Mexico (<8,000 ha). Blackleg, a destructive disease of B. napus in most parts of the world, was first observed in Mexico in Zacatecas and Aguascalientes in 1988 on B. oleracea, causing as much as 70% yield loss. A species complex of two closely related Dothideomycete species, Leptosphaeria maculans and L. biglobosa, is associated with this disease of crucifers (1), but leaf symptoms on susceptible plants are different, with L. maculans typically causing >15-mm pale gray lesions with numerous pycnidia, whereas L. biglobosa causes dark and smaller lesions only containing a few pycnidia. Having a similar epidemiology, both species can be present on the same plants at the same time, and symptom confusion can occur as a function of the physiological condition of the plant or expression of plant resistance responses. A total of 209 isolates from symptomatic B. oleracea leaves were collected from three fields in central states of Mexico (58 to 71 isolates per location). All leaves showed similar symptoms, including a 10- to 15-mm tissue collapse with an occasional dark margin. Cotyledons of seven B. napus differentials were inoculated with conidia of all the isolates as described by Dilmaghani et al. (1). Two hundred isolates caused tissue collapse typical of L. maculans. However, nine obtained from white cabbage in a single location in Aguascalientes caused <5-mm dark lesions. When inoculated onto cotyledons of three B. oleracea genotypes commonly grown in Mexico (cvs. Domador, Monaco, and Iron Man), the nine isolates caused a range of symptoms characterized by tissue collapse (maximum 10 to 15 mm), showing the presence of patches of black necrotic spots within the collapse. The occasional presence of a few pycnidia allowed us to reisolate the fungus for molecular identification. ITS1-5.8S-ITS2, (internal transcribed spacers and 5.8S rDNA), actin, and β-tubulin sequences were obtained as described previously (4). Multiple gene genealogies based on these sequence data showed two subclades of L. biglobosa: L. biglobosa 'occiaustralensis' (one isolate; ITS [AM410082], actin [AM410084], and β-tubulin [AM410083]) and L. biglobosa 'canadensis' (eight isolates; ITS [AJ550868], actin [AY748956], and β-tubulin [AY749004]) (3,4), which were previously described on B. napus in the United States, Canada, and Chile. To our knowledge, this is the first report of L. biglobosa in Mexico. Previously, this species has only been reported once on B. oleracea without discrimination into subclades (2). In the Aguascalientes sampling, 24% of the isolates were L. biglobosa, similar to Canadian locations where this species is still common as compared with L. maculans (1). The large proportion of sampled L. biglobosa 'canadensis', highlights the prevalence of this subclade throughout the American continent (1). References: (1) A. Dilmaghani et al. Plant Pathol. 58:1044, 2009. (2) E. Koch et al. Mol. Plant-Microbe Interact. 4:341, 1991. (3) E. Mendes-Pereira et al. Mycol Res. 107:1287, 2003. (4) L. Vincenot et al. Phytopathology 98:321, 2008.

Bergenia crassifolia (L.) Fritsch (elephant's ears or Siberian tea) (Saxifragaceae) is a perennial rhizomatous plant with pink flowers appearing at the end of winter. Since 1990, large, brown, and necrotic spots have been observed on numerous B. crassifolia plants at the University of Sciences in Nice, France. Spots appeared each year in the spring on newly emerged leaves and enlarged up to 1 to 3 cm in diameter during the summer, sometimes affecting more than half of the leaf surface. Leaves with spots were collected from May to November and placed in a humid atmosphere. Black, sessile, discoid conidiomata developed on the spots and exuded a pink, then brown, spore mass. When a mass was transferred onto a 1% malt agar medium, mycelium grew and then numerous, relatively spherical conidiomata (0.5 to 2.5 mm in diameter) developed and exuded a pink slimy mass, which contained many conidia. The mycelium grown at 24°C in the dark was scarce and pale, pink-beige. Under the light, the fungal culture was much darker with a fluffy mycelium and numerous conidiomata. The base of the conidiomata was dark; conidiophores were hyaline and showed little segmentation. Unicellular, cylindrical, fusiform conidia were hyaline, 5.4 to 8 μm long, and 1.4 to 1.9 μm wide. The morphology and size of conidia were comparable with previous descriptions of Pilidium concavum (Desm.) Höhn. (2,3). The ITS1-5.8S-ITS2 region of two isolates was amplified by PCR with primers PN3 and PN10 according to Mendes-Pereira et al. (1) and sequenced. The 421-nt sequence (GenBank Accession No. FM211810) was 100% identical to that of the P. concavum specimen voucher BPI 1107275 (GenBank Accession No. AY487094). P. concavum was reported to be on stored or rotting leaves or fruits of many dicotyledonous plants (2). To validate Koch's postulates, pieces of mycelium cultures with conidiomata (28 days old) were placed onto the upper surface of leaves of healthy B. crassifolia plants (10 to 12 pieces per plant). The leaf epidermis was previously wounded with a needle and a drop of melted paraffin was poured onto each piece of mycelium to prevent desiccation. Agar plugs without the fungus were placed similarly on wounded leaves of two control plants. Four inoculated and two control plants were incubated in growth chambers at either 24 or 18°C (16 h of light per day, 15,000 lx, 80% humidity). At 24°C, brown spots developed from 90% of the inoculation sites, whereas spots were observed for only 18% of the sites at 18°C. Such spots did not develop on control plants. After 2 months, healthy leaves as well as those with necrotic spots were put in humid chambers. Conidiomata formed after 4 weeks and exuded the same pink mass, which contained numerous conidia and from which the fungus was reisolated. Similar symptoms were also observed in several other locations in France and in botanical gardens in Akureyri (Iceland) and Métis (Canada), from which P. concavum was reisolated. To our knowledge, this is the first report of P. concavum on B. crassifolia. References: (1) E. Mendes-Pereira et al. Mycol. Res. 107:1287, 2003. (2) M. E. Palm. Mycologia 83:787, 1991. (3) A. Y. Rossman et al. Mycol. Prog. 3:275, 2004.