Characterization and cross‐species amplification of microsatellite loci in the plant pathogenic fungus Leptosphaeria maculans

Seven polymorphic microsatellite markers suitable for population genetic studies and genetic mapping were developed for Leptosphaeria maculans, a fungal pathogen of canola (Brassica napus). Polymorphism was evaluated using 14 isolates from diverse geographical locations. Each locus had either two or three alleles. Cross‐species amplification was observed for almost all loci in L. biglobosa ‘brassicae’ and L. maculans ‘lepidii’.     

Tn<Emphasis Type="Italic">5</Emphasis> transposase-assisted high-efficiency transformation of filamentous fungus <Emphasis Type="Italic">Phoma herbarum</Emphasis> YS4108

Conventionally, filamentous fungi are transformed by using conidia or protoplasts as recipients. However, induction of sporulation is difficult in some fungi, and protoplasting is an awing, frequently frustrating, and batch-dependent work. In this study, we established a simple and convenient method to prepare single cells from mycelia without enzymatic protoplasting. As a case study on the pathogenic fungus Phoma herbarum YS4108, the single cells could be directly and highly efficiently transformed with the aid of Tn5 transposase. The optimal electric pulse delivery parameters were 25 muF in capacitance, 0.75 kV (0.2-cm cuvette) in voltage, and 400 Omega in resistance, under which the efficiency of transposase-assisted transformation (TNAT) was enhanced to two to threefold compared to that of non-TNAT method, resulting in >230 transformants/cuvette (10(6) recipients). Further cell wall weakening of the single cells by lytic enzymes and linearization of the plasmid were found to have no effects on transformation efficiency, but vector linearization apparently lowered the background growth. The present study for the first time explained that Tn5 transposase could be used to increase transformation efficiency in filamentous fungi, and the method presented here may be of wide applicability in different studies and may be the first choice when transformation efficiency and convenience are priorities and mycelia have to be used as transformation recipients.     

Structure and biological activity of maculansin A, a phytotoxin from the phytopathogenic fungus Leptosphaeria maculans

During a search for elicitors and phytotoxins produced by virulent isolates of the phytopathogenic fungus Leptosphaeria maculans (Desm.) Ces. et de Not. [asexual stage Phomalingam (Tode ex Fr.) Desm.], the selective phytotoxin maculansin A was isolated and its structure determined by analysis of spectroscopic data and chemical degradation. Maculansin A, a unique derivative of mannitol containing the unusual chromophore 2-isocyano-3-methyl-2-butenoyl, was isolated from potato dextrose cultures of L. maculans virulent on canola (Brassica napus L. cv. Westar). Surprisingly, maculansin A was more toxic to resistant plants (B. juncea L. cv. Cutlass, brown mustard) than to susceptible plants (canola). Maculansin A, however, did not elicit the production of phytoalexins either in resistant or susceptible plants. In addition, other maculansin type structures and the metabolite 2,4-dihydroxy-3,6-dimethylbenzaldehyde were isolated and the latter was found to be a strong inhibitor of root growth of both brown mustard and canola. Considering that L. maculans seems to be expanding its host range to infect brown mustard as well, maculansins could assist in chemotaxonomic studies to group the diverse isolates.     

Relationship between quantum efficiency of PSII and cold-induced plant resistance to fungal pathogens

The aim of the presented work was to study whether the efficiency of photosynthesis may influence resistance of hardened plants to disease. Seedlings of spring barley, meadow fescue and winter oilseed rape were chilled at 5 °C for 2, 4 or 6 weeks and at these deadlines the changes in cell membrane permeability (expressed as electrolyte leakage), chlorophyll fluorescence (initial fluorescence - F₀, maximal fluorescence - F_m, quantum yield of PSII - F_v/F_m) and net photosynthesis rate (F_N) were measured. Also, the influence of cold on the degree of plant resistance to economically important pathogens -Bipolaris sorokiniana or Phoma lingam was estimated. Two, four or six week-hardened plants were artificially infected: barley and fescue by B. sorokiniana, and oilseed rape by P. lingam. Hardening at 5 °C stimulated resistance of barley, fecue and rape to their specific pathogens. Six-week long acclimation was the most effective for plant resistance. Cold significantly changed cell membrane permeability and decreased chlorophyll fluorescence (F₀, F_m and F_v/F_m) of all studied plant species, while net photosynthesis rate was found to decrease only in barley. The results indicate that cold-induced resistance of plants to pathogens was correlated with a decrease in cell membrane permeability. In the case of fescue and barley a significant connection between the quantum yield of PSII and their resistance to B. sorokiniana was shown. Additionally, the resistance of barley to fungus was depended on net photosynthesis rate. In general this research shows that the efficiency of photosynthesis may be used as an indicator of plant resistance to disease.     

First report of <Emphasis Type="Italic">Phoma sorghina</Emphasis> (Sacc.) Boerema Dorenbosch &; van Kest on wheat leaves (<Emphasis Type="Italic">Triticum aestivum L</Emphasis>.) in Argentina

A new disease caused by Phoma sorghina has been detected for the first time on wheat plants in the Province of Buenos Aires, Argentina. The pathogen was isolated from wheat leaves growing under field conditions, cultured on PDA and identified by its morphobiometric and cultural characters. The disease symptoms and morphological characters of the pathogen are described. Pathogenicity of the isolate was confirmed by inoculating 10 wheat cultivars under greenhouse conditions.     

Recurring challenges from a necrotrophic fungal plant pathogen: a case study with Leptosphaeria maculans (causal agent of blackleg disease in brassicas) in Western Australia

BACKGROUND: Blackleg disease of Brassica napus, caused by the necrotrophic fungus Leptosphaeria maculans, causes severe yield losses in Australia, Europe and Canada. In Western Australia, it nearly destroyed the oilseed rape industry in 1972 when host genotypes and conducive environmental conditions favoured severe epidemics. The introduction of cultivars with polygenic resistance and the adoption of sound cultural practices two decades later helped to manage the disease. These were abandoned by many farmers in recent years in favour of the effective but ephemeral resistance conferred by the single dominant gene-based resistance derived from B. rapa ssp. sylvestris. Recently, several cultivars carrying this gene have collapsed widely within a period of 3 years after their commercial release. An environment conducive to the disease and the association of the pathogen with susceptible hosts in Western Australia for over 80 years together have led to the proliferation of L. maculans races, amounting to half of all races delineated to date from Europe, including the United Kingdom, Canada and Australia. SCOPE: This review demonstrates the problems that emerge when traditional cultural practices employed, along with cultivars containing polygenic resistance to a serious necrotrophic pathogen, are discarded in preference to the exclusive deployment of effective but ephemeral single dominant gene-based resistance to the disease across Southern Australia. CONCLUSIONS: Single dominant gene-based resistance currently available, on its own, will not confer durable resistance to blackleg disease in oilseed rape. Return to earlier management practices, including reliance upon polygenic resistance and induced resistance, may be the best currently available options to maintain production in regions across Southern Australia predisposed to severe epidemics.     

Transfer of resistance against Phoma lingam to Brassica napus by asymmetric somatic hybridization combined with toxin selection

Summary Irradiated mesophyll protoplasts from nine different accessions of B. juncea, B. nigra and B. carinata, all resistant to Phoma lingam, were used as gene donors in fusion experiments with hypocotyl protoplasts isolated from B. napus as the recipient. A toxin, sirodesmin PL, was used to select those fusion products in which the resistant gene(s) was present. In the fusion experiments different gene donors, various irradiation dosages and toxin treatments were combined. Symmetric and asymmetric hybrid plants were obtained from the cell cultures with and without toxin selection. Isozymes were used to verify hybrid characters in the symmetric hybrids, whereas two DNA probes were used to identify donor-DNA in the asymmetric hybrids. Resistance to P. lingam was expressed in all symmetric hybrids, and in 19 of 24 toxin-selected asymmetric hybrids, while all the unselected asymmetric hybrids were susceptible.     

Brassica naponigra,a somatic hybrid resistant to Phoma lingam

Summary Brassica napus and B. nigra were combined via protoplast fusion into the novel hybrid Brassica naponigra. The heterokaryons were identified by fluorescent markers and selected by flow sorting. Thirty hybrid plants were confirmed by isozyme analysis to contain both B. nigra and B. napus chromosomes; of these, 20 plants had the sum of the parental chromosome numbers. A non-random segregation of the chloroplasts was found in the hybrids. Of 14 hybrid plants investigated, all had the B. napus type of chloroplast. The resistance to Phoma lingam found in the B. nigra cultivar used in the fusion experiments was expressed in 26 of the hybrid plants. The hybrids obtained in this study contain all of the three Brassica genomes (A, B and C) and have thus created unique possibilities for genetic exchanges between the genomes. Since most of the plants were fertile as well as resistant to P. lingam, they have been incorporated into conventional rapeseed breeding programs.     

First Report of Leaf Spot Disease in Angelica dahurica Caused by Phoma bellidis in China

Angelica dahurica is a perennial herb belonging to the Umbelliferae family that has been used as a valuable traditional Chinese medicine. In August 2013, leaf spot disease in A. dahurica was first observed at the Medicinal Herb Garden in Shenyang Agricultural University, Shenyang, Liaoning, China. Morphological assessment, evaluation of culture characteristics, internal transcribed spacer and beta‐tubulin sequence analysis and pathogenicity identified the causal agent as Phoma bellidis. To our knowledge, this is the first report of leaf spot disease in A. dahurica that was caused by P. bellidis.     

茎点霉和叶点霉两属的新种及国内新记录种

本文对采自东北地区的115份茎点霉(Phoma)和叶点霉(Phyllosticta)的标本进行分类研究,有新种2个和国内新记录种9个。新种是木瓜生叶点霉(Phyllosticta chaenomelesicola L.Yu et Bai)和草玉铃生叶点霉(Phyllosticta convallaricola L.Yu et Bai)。新种有拉丁文和汉文描述及图。对新记录种作了简要介绍。模式标本保存于沈阳农业大学植保系真菌标本室(HMSAU)。