Expression of resistance to Leptosphaeria maculans in Brassica napus double haploid lines in France and Australia is influenced by location

Blackleg, caused by Leptosphaeria maculans, is a major disease of oilseed rape (Brassica napus), worldwide, including Australia and France. The aims of these studies were first, to determine if higher levels of resistance to L. maculans could be generated in double haploid (DH) lines derived from spring‐type B. napus cv. Grouse, which has a good level of field resistance to blackleg; and second, to determine whether the resistance to blackleg disease of individual DH lines responds differentially to different L. maculans field populations within and between the two countries. DH lines were extracted from cv. Grouse and tested in field experiments carried out in both France and Australia against natural L. maculans populations. Extracting and screening DH lines were an effective means to select individual lines with greatly improved expression of resistance to blackleg crown canker disease in comparison with the original parental population. However, relative disease resistance rankings for DH lines were not always consistent between sites. The higher level of resistance in France was shown to be because of a high expression level of quantitative resistance in the French growing conditions. Big differences were observed for some DH lines between the 2004 and the 2005 field sites in Australia where the L. maculans populations differed by their virulence on single dominant gene‐based resistant lines derived from Brassica rapa ssp. sylvestris. This differential behaviour could not be clearly explained by the specific resistance genes until now identified in these DH lines. This investigation highlights the potential to derive DH lines with superior levels of resistance to L. maculans compared with parental populations. However, in locations with particularly high pathogen diversity, such as in southern Australia, multiyear and multisite evaluations should be performed to screen for the most efficient material in different situations.     

A cryptic microbial community persists within micropropagated Bouteloua eriopoda (Torr.) Torr. cultures

Higher plants are ubiquitously colonized with fungal endophytes that often lack readily detectable structures. This study examines the diverse endophyte population within a single line of micropropagated Bouteloua eriopoda (Torr.) Torr., using microscopy and comparison of internal spacer (ITS) gene sequences obtained from both plant and isolated fungal tissues. Microscopy revealed fungal hyphae and lipid bodies, the majority of which lacked distinguishing characters. Internal transcribed spacer (ITS) sequences amplified from fungal isolates and micropropagated plant tissues were subjected to Bayesian analysis, which clearly distinguished six endophyte taxa.

Results confirm a diverse, cryptic endophyte consortium is retained within this micropropagated plant line. The probability of similar complexity in other plant species is discussed. The development of controlled systems in which to study single plant-fungal interactions within such consortia presents significant technical challenges. However, potential for such systems to reveal species interactions that influence plant growth and development is high.     

天门冬纳米制剂对小鼠抗氧化系统的影响

目的:探讨中药天门冬及其纳米制剂对小鼠心肌线粒体中超氧化物歧化酶(SOD)活性,丙二醛(MDA)含量,肝组织中谷胱甘肽过氧化物酶(GSH-Px)活性的影响,观察纳米制剂能否更有效地改善机体的抗氧化能力.方法:采用D-半乳糖致衰老小鼠分别ig相同剂量的天门冬水提液及其纳米中药15 d,测定衰老小鼠心肌线粒体中SOD活性、MDA含量及肝组织中GSH-Px活性.结果:天门冬水提液及其纳米中药均能显著增强天门冬及其纳米中药均可提高小鼠心肌线粒体中SOD的活性(P<0.01),肝组织GSH-Px活性(P<0.01),降低心肌线粒体中MDA(P<0.05),且纳米中药的药效强于天门冬水提液的药效(P<0.01).结论:天门冬纳米制剂抗氧化能力优于天门冬超声波水提液.     

Phoma sp. FOM-8108, a producer of gentisylquinones, isolated from sea sand

A fungal strain, FOM-8108, that was isolated from sea sand was found to produce gentisylquinone and chlorogentisylquinone, inhibitors of neutral sphingomyelinase. The fungus grew well under normal conditions, in the darkness, or on various agar media, but typical morphological characteristics were not observed to determine its taxonomy. Therefore, culture conditions were studied extensively, resulting in formation of a number of pycnidia by the fungus on the media containing seawater or on natural substrates such as hydrangea leaves, gardenia leaves, and rice straw under natural light or near-ultraviolet radiation exposure. Eventually, from the morphological characteristics of pycnidia, conidiogenous cells, and conidia, strain FOM-8108 was considered to belong to the genus Phoma. Culture studies showed seawater in the fermentation medium was necessary for the strain to produce gentisylquinones. Particularly, a full production of chlorogentisylquinone, which has a chloride ion in the structure, was performed in the medium with higher concentration (75%–100%) of seawater. Received: June 27, 2001 / Accepted: December 14, 2001     

Fungi associated with sorghum grain from Argentina

Sorghum (Sorghum bicolor (L.) Moench) is an important cereal produced in and exported from Argentina. The risk of contamination by mycotoxins is related to the mycoflora associated with the sorghum grain. This paper reports on the identification of internal mycoflora of sorghum grain harvested in Argentina in 1991, 1992 and 1993, years with different total rainfall levels. A mycological survey was carried out on sorghum samples, from a location at the humid Argentinian pampa, using a Fusarium/dematiaceous fungi selective medium. The relative density of the prevalent fungal genera were statistically compared. Genus Fusarium was the most prevalent component of the internal seedborne mycoflora in the three harvest seasons. Genera Alternaria, Phoma, Penicillium and Aspergillus were also isolated. The predominant Fusarium was F. moniliforme and the most frequently isolated species of Alternaria, Phoma, Penicillium and Aspergillus were Alt. alternata, Pho. sorghima, Pen. funiculosum and Asp. flavus, respectively. This is the first report of the isolation of Fusarium napiforme in sorghum grain in Argentina. This revised version was published online in June 2006 with corrections to the Cover Date.     

Inheritance of resistance derived from the B-genome of Brassica against Phoma lingam in rapeseed and the development of molecular markers

 Genes of the B genome of Brassica conditioning Phoma resistance at the epicotyle were transferred into Brassica napus by interspecific hybridization. The recombinant lines expressed high resistance similar to that of the donor parents. Unlike the oligo- or poly-genically inherited resistance of B. napus known so far, the B-genome resistance genes of the recombinant lines behaved monogenically dominant. No significant differences in the level of resistance or in the phenotype of the resistance mechanisms were observed among homozygous resistant plants when the different B-genome origins investigated, i.e. B. nigra, B. juncea and B. carinata, were compared. Therefore it was assumed that the resistance genes of each B-genome species and the resistance mechanisms of the species are identical. Temperature increased the expression of internal lesions caused by Phoma lingam. High summer temperatures in the greenhouse led to faster development of tissue damage at the epicotyle of plants, resulting in significant deviations in segregation ratios, when fixed scores were used for disease classification. Independent of origin, the three B-genome resistance genes were introgressed at the same location of the rapeseed genome. The arrangement and distances of closely linked RFLP markers on linkage-groups were similar to those of the same markers on linkage group six of the rapeseed map. It is concluded that the B-genome resistance genes were introgressed by homoeologous recombination after allosyndetical pairing of B-genome chromosomes with the A- or C-genome chromosomes. Received: 3 April 1998/Accepted: 22 April 1998     

Use of high resolution melting analysis to genotype the avirulence AvrLm4‐7 gene of Leptosphaeria maculans,a fungal pathogen of Brassica napus

The oilseed rape (Brassica napus) stem canker disease, due to the fungal pathogen Leptosphaeria maculans, is mainly controlled by host genetic resistance. Since 2004, the specific resistance gene Rlm7 is widely used in France. Specific resistance is effective when fungal populations are mainly composed of avirulent isolates. The development of molecular tools for the identification of virulent isolates towards Rlm7 was needed to undertake large‐scale surveys and to monitor the emergence of virulent populations in fields. Previous studies have described a large diversity of molecular events leading to virulence towards Rlm7, rendering conventional polymerase chain reaction (PCR) methods inapplicable to identify virulent isolates. Interestingly, a very limited nucleotide polymorphism was observed for avirulent, AvrLm7, alleles. Such characteristics were exploited here to develop a diagnostic method based on high resolution melting (HRM) analysis of the AvrLm4‐7 gene. High resolution melting analysis of a collection of 206 reference isolates revealed only four different profiles within 100 avirulent isolates and 87% of virulent isolates showed either no amplification or HRM curves distinct from those of avirulent isolates. The reliability of the method was confirmed using a second set of 119 unknown isolates, for which biological phenotyping and HRM genotyping were in agreement for 93% of the isolates. HRM combined with the PCR amplification of a larger fragment encompassing AvrLm4‐7 led to a correct diagnostic for 97.5% of the isolates.     

Annual Medicago: from a model crop challenged by a spectrum of necrotrophic pathogens to a model plant to explore the nature of disease resistance

BACKGROUND: Annual Medicago spp., including M. truncatula, play an important agronomic role in dryland farming regions of the world where they are often an integral component of cropping systems, particularly in regions with a Mediterranean or Mediterranean-type climate where they grow as winter annuals that provide both nitrogen and disease breaks for rotational crops. Necrotrophic foliar and soil-borne pathogens dominate these regions and challenge the productivity of annual Medicago and crop legume species. SCOPE: This review outlines some of the major and/or widespread diseases these necrotrophic pathogens cause on Medicago spp. It then explores the potential for using the spectrum of necrotrophic pathogen-host interactions, with annual Medicago as the host plant, to better understand and model pathosystems within the diseases caused by nectrotrophic pathogens across forage and grain legume crops. CONCLUSIONS: Host resistance clearly offers the best strategy for cost-effective, long-term control of necrotrophic foliar and soil-borne pathogens, particularly as useful resistance to a number of these diseases has been identified. Recently and initially, the annual M. truncatula has emerged as a more appropriate and agronomically relevant substitute to Arabidopsis thaliana as a model plant for legumes, and is proving an excellent model to understand the mechanisms of resistance both to individual pathogens and more generally to most forage and grain legume necrotrophic pathogens.     

Effects of culture media, temperature, pH, and light on growth, sporulation, germination, and bioherbicidal efficacy of Phoma exigua, a potential biological control agent for salal (Gaultheria shallon)

In order to evaluate the potential use of Phoma exigua isolate PFC 2705 (PFC2705) as a biological control agent for salal (Gaultheria shallon), effect of cultural and environmental parameters on growth, conidia production, and pathogenicity of P. exigua were characterized in studies conducted under laboratory and greenhouse conditions. Within a range of 5-30°C, the optimum growth and germination temperature range was 20-25°C. The effect of pH on mycelial growth and conidial germination was not significant from pH 5 to 10. Fluorescent light significantly enhanced sporulation of the fungus on most agar media tested, yet was not necessary for growth. The type of culture media significantly affected mycelium growth, sporulation, and conidia germination. Age of mycelia used as inoculum affected the disease severity on salal. PFC2705 suppressed the growth of mature salal plant by inciting lesions on leaves, branch tips, and axillary buds and caused 56% death of the total biomass above ground. Characteristics such as easy inoculum production, wide range of growth environments, and high infectivity on salal increased the potential of P. exigua as a biocontrol agent for management of salal.