The role of thionins in rice defence against root pathogens

Thionins are antimicrobial peptides that are involved in plant defence. Here, we present an in‐depth analysis of the role of rice thionin genes in defence responses against two root pathogens: the root‐knot nematode Meloidogyne graminicola and the oomycete Pythium graminicola. The expression of rice thionin genes was observed to be differentially regulated by defence‐related hormones, whereas all analysed genes were consistently down‐regulated in M. graminicola‐induced galls, at least until 7 days post‐inoculation (dpi). Transgenic lines of Oryza sativa cv. Nipponbare overproducing OsTHI7 revealed decreased susceptibility to M. graminicola infection and P. graminicola colonization. Taken together, these results demonstrate the role of rice thionin genes in defence against two of the most damaging root pathogens attacking rice.     

An annotated checklist of Pythium species from Iran

The genus Pythium, with slightly over 280 described species has been classified traditionally with other filamentous, coenocytic, sporangia-producing fungi as “Phycomycetes”. However, with recent advances in chemical, ultrastructural and molecular studies Pythium spp. are now considered as “fungus-like organisms” or “pseudo-fungi” and are placed in the kingdom Chromista or kingdom Straminopila, distinct from the true fungi or the kingdom Fungi. Little is known about the biodiversity of Pythium in Iran. This paper attempts to assess the position of the genus Pythium and provides details of the historical development of the study of Pythium in Iran. The survey list contains 33 species, 4 species groups and 1 unknown species of Pythium.     

Alteration of the Unsaturated to Saturated Ratio of Fatty Acids in Bacterial Lipids by Alcohols

Silver-coated cloth (SCC) effectively controlled root rot that was caused by Pythium aphanidermatum in hydroponically grown cucumber plants. The presence of SCC in the hydroponic solution reduced the root rot from 100% to 10% 20 days after inoculation with zoospores of P. aphanidermatum. It was suggested that the inhibition of SCC was caused not only by the silver ion dissolved from SCC, but also by the metallic silver and silver compounds formed on the surface of the root.     

瓜果腐霉菌丝中除草活性物质的初步研究

将瓜果腐霉进行液体发酵,其菌丝用等体积乙酸乙酯和甲醇进行依次萃取,甲醇萃取液旋转蒸发去溶剂后进行硅胶柱层析,以乙酸乙酯和石油醚(V/V=3:1和V/V=2:1)的混合液进行梯度洗脱,每50 mL收集为一个馏分,共收集到40个馏分。生物测定结果表明,以乙酸乙酯和石油醚(V/V=2:1)洗脱得到的馏分21 24对供试杂草马唐表现出了较强的活性,其对马唐的生长抑制作用均为4级。合并馏分21 24,以乙酸乙酯和石油醚(V/V=2:1)的混合液为展开剂进行等度洗脱,每50 mL收集为一个馏分,共收集到20个馏分。生物测定结果表明,馏分3对马唐有较强的抑制活性。HPLC分析发现,该馏分主要含有3个组分,其保留时间分别为12.7、14.0和30.5 min。     

Beauveria bassiana: endophytic colonization and plant disease control

Seed application of Beauveria bassiana 11-98 resulted in endophytic colonization of tomato and cotton seedlings and protection against plant pathogenic Rhizoctonia solani and Pythium myriotylum. Both pathogens cause damping off of seedlings and root rot of older plants. The degree of disease control achieved depended upon the population density of B. bassiana conidia on seed. Using standard plating techniques onto selective medium, endophytic 11-98 was recovered from surface-sterilized roots, stems, and leaves of tomato, cotton, and snap bean seedlings grown from seed treated with B. bassiana 11-98. As the rate of conidia applied to seed increased, the proportion of plant tissues from which B. bassiana 11-98 was recovered increased. For rapid detection of B. bassiana 11-98 in cotton tissues, we developed new ITS primers that produce a PCR product for B. bassiana 11-98, but not for cotton. In cotton samples containing DNA from B. bassiana11-98, the fungus was detected at DNA ratios of 1:1000; B. bassiana 11-98 was detected also in seedlings grown from seed treated with B. bassiana 11-98. Using SEM, hyphae of B. bassiana11-98 were observed penetrating epithelial cells of cotton and ramifying through palisade parenchyma and mesophyll leaf tissues. B. bassiana11-98 induced systemic resistance in cotton against Xanthomonas axonopodis pv. malvacearum (bacterial blight). In parasitism assays, hyphae of B. bassiana 11-98 were observed coiling around hyphae of Pythium myriotylum.     

Intraspecific and within-isolate sequence variation in the ITS rRNA gene region of Pythium mercuriale sp. nov. (Pythiaceae)

Sixteen Pythium isolates from diverse hosts and locations, which showed similarities in their morphology and sequences of the internal transcribed spacer (ITS) region of their rRNA gene, were investigated. As opposed to the generally accepted view, within single isolates ITS sequence variations were consistently found mostly as part of a tract of identical bases (A-T) within ITS1, and of GT or GTTT repeats within the ITS2 sequence. Thirty-one different ITS sequences obtained from 39 cloned ITS products from the 16 isolates showed high sequence and length polymorphisms within and between isolates. However, in a phylogenetic analysis, they formed a cluster distinct from those of other Pythium species. Additional sequencing of two nuclear genes (elongation factor 1 alpha and beta-tubulin) and one mitochondrial gene (nadh1) revealed high levels of heterozygosity as well as polymorphism within and between isolates, with some isolates possessing two or more alleles for each of the nuclear genes. In contrast to the observed variation in the ITS and other gene areas, all isolates were phenotypically similar. Pythium mercuriale sp. nov. (Pythiaceae) is characterized by forming thin-walled chlamydospores, subglobose to obovoid, papillate sporangia proliferating internally and smooth-walled oogonia surrounded by multiple antheridia. Maximum likelihood phylogenetic analyses based on both ITS and beta-tubulin sequence data place P. mercuriale in a clade between Pythium and Phytophthora.     

First records of Pythium aquatile and P. macrosporum isolated from soils in Japan

Pythium aquatile and P. macrosporum were isolated from the soil of a cultivated field in Gunma Prefecture and a forest in Nagano Prefecture for the first time in Japan. Their morphological characteristics are described, and their pathogenicity and taxonomy are discussed.     

Flavonoids in roots of white clover: interaction of arbuscular mycorrhizal fungi and a pathogenic fungus

The effects of two arbuscular mycorrhizal fungi (AMF) (Glomus mosseae and G. claroideum) and a pathogenic fungus (Pythium ultimum) on the production of eight flavonoids in roots of two white clover (Trifolium repens L.) cultivars were evaluated. Quantification of AM and pathogenic fungi in the roots showed that the AM symbiosis significantly reduced P. ultimum biomass and in some cases prevented infection. The flavonoid productions in clover roots varied depending on the presence of beneficial and/or pathogenic fungi, fungal isolate or plant cultivar. Only plants colonized with G. claroideum showed detectable concentrations of either coumestrol or kaempferol (cultivar-dependant). In addition, inoculation with G. claroideum resulted in significantly higher concentrations of coumestrol in cv. Sonja and medicarpin in cv. Milo. A low production of coumestrol and kaempferol in mycorrhizal plants may be G. mosseae-specific. Only the concentrations of formononetin and daidzein increased in clover roots in response to infection with P. ultimum. These flavonoids are supposedly stress metabolites, synthesized or produced from glycosides in response to pathogen infection. However, the presence of one or both AMF significantly lowered the formononetin and daidzein concentrations, and overruled the inductive effect of P. ultimum. Therefore the antagonistic action of AM against the pathogen must take place through another mechanism.     

Serological detection of red rot disease initiation stages of microbial pathogen, Pythium porphyrae (Oomycota) on Porphyra yezoensis

Pythium porphyrae (Oomycota), a pathogen causing red rot diseasein Porphyra spp., can at present only be detected when colonizationof the host thallus has already occurred and so it is often too late to takeappropriate disease control measures. The paper presents an account of an effective methdology for early detection of the disease. Since Py.porphyrae zoospores are the primary means of pathogen dispersal,polyclonal antibodies (Pabs) were raised against the surface components ofzoospores and encysted zoospores. Using these Pabs the disease initiationstages of the Pythium porphyrae were detected on the surface of Porphyra thalli by immunofluorescence assay. The specificity of theseantibodies and the efficacy of immunofluorescence assay in the detectionof red rot disease are discussed.     

Production of potato intraspecific somatic hybrids with improved tolerance to PVY and Pythium aphanidermatum

Somatic hybridization can be an interesting alternative for the selection of heterozygous and vigorous potato plants through combination of dihaploid genomes. The resulting hybrids can harbour interesting characters and thus can be used in agriculture if they are in agreement with agronomic criteria.

In this report, we used an intraspecific somatic hybridization technique for the production of tetraploid potato lines. Two parental combinations were used in protoplast electrofusion procedure: Aminca-Cardinal and Cardinal-Nicola. The selection of somatic hybrids was based on in vitro plant vigour. Therefore, among the 75 regenerated plants obtained from Aminca-Cardinal fusion, 3 putative hybrids were retained and 2 plant lines were selected among the 54 regenerated from the Cardinal-Nicola fusion. Heterosis was observed in the larger hybrid tuber size compared to the parents’. Our results also showed a precocity in the in vitro tuberization for the hybrids. Moreover, all of the regenerated putative hybrids were tetraploid (2n=4x=48 chromosomes). Isocitrate dehydrogenase and malate dehydrogenase isoenzyme analyses confirmed the hybrid nature of these lines. A molecular characterization performed by PCR amplification of simple sequence repeats and inter-simple sequence repeats confirmed that all these lines were somatic hybrids.

The effect of potato virus Y infection on these hybrid lines was tested by mechanical inoculation of plants cultivated in a greenhouse. The majority displayed a reduction of infection rate associated with a delayed appearance of symptoms compared to the parents. Moreover, complete resistance was noted for one hybrid line (CN2). All hybrids also showed improved tolerance to Pythium aphanidermatum infection during tuber storage or after plant inoculation.