Five plant families support natural sporulation of <Emphasis Type="Italic">Cronartium ribicola</Emphasis> and <Emphasis Type="Italic">C. flaccidum</Emphasis> in Finland

Fusarium is one of the most destructive fungal genera whose members cause many diseases on plants, animals, and humans. Moreover, many Fusarium species secrete mycotoxins (e.g. trichothecenes and fumonisins) that are toxic to humans and animals. Fusarium isolates from date palm trees showing disease symptoms, e.g. chlorosis, necrosis and whitening, were collected from seven regions across Saudi Arabia. After single-sporing, the fungal strains were morphologically characterized. To confirm the identity of morphologically characterized Fusarium strains, three nuclear loci, two partial genes of translation elongation factor 1 α (tef1α) and β-tubulin (tub2), and the rDNA-ITS region, were amplified and sequenced. Of the 70 Fusarium strains, 70 % were identified as F. proliferatum that were recovered from six regions across Saudi Arabia. Fusarium solani (13 %), as well as one strain each of the following species: F. brachygibbosum, F. oxysporum, and F. verticillioides were also recovered. In addition, five Fusarium-like strains were recognized as Sarocladium kiliense by DNA-based data. The preliminary in vitro pathogenicity results showed that F. proliferatum had the highest colonization abilities on date palm leaflets, followed by F. solani. Although F. oxysporum f. sp. albedinis is the most serious date palm pathogen, F. proliferatum and F. solani are becoming serious pathogens and efforts should be made to restrict and control them. In addition, the potential toxin risks of strains belonging to F. proliferatum should be evaluated.     

<Emphasis Type="Italic">Fusarium ershadii</Emphasis> sp. nov., a Pathogen on <Emphasis Type="Italic">Asparagus officinalis</Emphasis> and <Emphasis Type="Italic">Musa acuminata</Emphasis>

Two Fusarium strains, isolated from Asparagus in Italy and Musa in Vietnam respectively, proved to be members of an undescribed clade within the Fusarium solani species complex based on phylogenetic species recognition on ITS, partial RPB2 and EF-1α gene fragments. Macro- and micro-morphological investigations followed with physiological studies done on this new species: Fusarium ershadii sp. nov can be distinguished by its conidial morphology. Both isolates of Fusarium ershadii were shown to be pathogenic to the monocot Asparagus officinalis when inoculated on roots and induced hollow root symptoms within two weeks in Asparagus officinalis seedlings. In comparison mild disease symptoms were observed by the same strains on Musa acuminata seedlings.     

<Emphasis Type="Italic">Fusarium oxysporum</Emphasis> and <Emphasis Type="Italic">Fusarium avenaceum</Emphasis> associated with yield-decline of pyrethrum in Australia

Fusarium wilt, one of the destructive diseases of cucumber can be effectively controlled by using biocontrol agents such as Trichoderma harzianum. However, the mechanisms controlling T. harzianum-induced enhanced resistance remain largely unknown in cucumber plants. Here we screened the potent T. harzianum isolate TH58 that could effectively control F. oxysporum (FO). Glasshouse efficacy trials also showed that TH58 decreased disease incidence by 69.7 %. FO induced ROS over accumulation, while TH58 inoculation suppressed ROS over accumulation and improved root cell viability under F. oxysporum infection. TH58 inoculation could reverse the FO-induced cell division block and regulate the proportional distribution of nuclear DNA content through inducing 2C fraction. Moreover, the expression levels of cell cycle-related genes such as CDKA, CDKB, CycA, CycB, CycD3;1 and CycD3;2 in TH58 - pre-inoculated seedlings were up-regulated compared with those infected with FO alone. Taken together, these results suggest that T. harzianum improved plant resistance against Fusarium wilt disease via alterations in nuclear DNA content and cell cycle-related genes expression that might maintain a lower ROS accumulation and higher root cell viability in cucumber seedlings.     

Chitinolytic <Emphasis Type="Italic">Streptomyces griseorubens</Emphasis> E44G enhances the biocontrol efficacy against <Emphasis Type="Italic">Fusarium</Emphasis> wilt disease of tomato

Streptomyces griseorubens E44G is a chitinolytic bacterium isolated from cultivated soil in Saudi Arabia (a hot, arid climatic region). In vitro, antifungal potential of S. griseorubens E44G was assessed against the phytopathogenic fungus, Fusarium oxysporum f. sp. lycopersici (the causative agent of the Fusarium wilt disease of tomato). An inhibition zone of 24 mm was recorded. The chitinolytic activity of S. griseorubens E44G was proved when the colloidal chitin agar plate method was used. A thermostable chitinase enzyme of 45 kDa molecular weight was purified using gel filtration chromatography. The optimum activity was obtained at 60 °C and pH 5.5. The purified enzyme has shown a very pronounced activity against the phytopathogenic fungus, F. oxysporum. The molecular characterization of the chitinase gene indicated that it consists of 1218 bp encoding 407 amino acids. The phylogentic analysis based on the nucleotide DNA sequence and the deduced amino acids sequence showed high similarity percentages with other chitinases isolated from different Streptomyces species. In the field evaluation, application of both S. griseorubens E44G treatments significantly increased all tested growth and yield parameters and decreased the disease severity compared with the infected-untreated tomato plants suggesting potential as a biocontrol agent.     

Natural infection of <Emphasis Type="Italic">Nicandra physaloides</Emphasis> by <Emphasis Type="Italic">Tomato severe rugose virus</Emphasis> in Brazil

Nicandra physaloides, a common weed in South America, was found to be infected by an isolate of Tomato severe rugose virus (ToSRV), a bipartite begomovirus. The plants developed severe yellow rugose mosaic and were collected in São Paulo State, Brazil. This isolate of ToSRV was transmitted by Bemisia tabaci B biotype from infected plants of N. physaloides to healthy plants of N. physaloides and tomato in a glasshouse. This is the first report of natural infection of N. physaloides by ToSRV in Brazil.     

Identity and pathogenicity of <Emphasis Type="Italic">Fusarium</Emphasis> species associated with crown rot on wheat (<Emphasis Type="Italic">Triticum</Emphasis> spp.) in Turkey

An extensive survey was carried out to collect Fusarium species colonizing the lower stems (crowns) of bread wheat (Triticum aestivum L.) and durum wheat (T. durum Desf.) from different wheat growing regions of Turkey in summer 2013. Samples were collected from 200 fields representing the major wheat cultivation areas in Turkey, and fungi were isolated from symptomatic crowns. The isolates were identified to species level by sequencing the translation elongation factor 1-alpha (TEF1-α) gene region using primers ef1 and ef2. A total of 339 isolates representing 17 Fusarium species were isolated. The isolates were identified as F. culmorum, F. pseudograminearum, F. graminearum, F. equiseti, F. acuminatum, F. brachygibbosum, F. hostae, F. redolens, F. avenaceum, F. oxysporum, F. torulosum, F. proliferatum, F. flocciferum, F. solani, F. incarnatum, F. tricinctum and F. reticulatum. Fusarium equiseti was the most commonly isolated species, accounting for 36% of the total Fusarium species isolated. Among the damaging species, F. culmorum was the predominant species being isolated from 13.6% of sites surveyed while F. pseudograminearum and F. graminearum were isolated only from 1% and 0.5% of surveyed sites, respectively. Six out of the 17 Fusarium species tested for pathogenicity caused crown rot with different levels of severity. Fusarium culmorum, F. pseudograminearum and F. graminearum caused severe crown rot disease on durum wheat. Fusarium avenaceum and F. hostae were weakly to moderately virulent. Fusarium redolens was weakly virulent. However, F. oxysporum, F. equiseti, F. solani, F. incarnatum, F. reticulatum, F. flocciferum, F. tricinctum, F. brachygibbosum, F. torulosum, F. acuminatum and F. proliferatum were non-pathogenic. The result of this study reveal the existence of a wide range of Fusarium species associated with crown rot of wheat in Turkey.     

Genetic structure of <Emphasis Type="Italic">Pyrenophora teres</Emphasis> f. <Emphasis Type="Italic">teres</Emphasis> and <Emphasis Type="Italic">P. teres</Emphasis> f. <Emphasis Type="Italic">maculata</Emphasis> populations from western Canada

Infection by Pyrenophora teres f. teres (Ptt) or P. teres f. maculata (Ptm), the causal agents of the net and spot forms of net blotch of barley, respectively, can result in significant yield losses. The genetic structure of a collection of 128 Ptt and 92 Ptm isolates from the western Canadian provinces of Alberta (55 Ptt, 27 Ptm), Saskatchewan (58 Ptt, 46 Ptm) and Manitoba (15 Ptt, 19 Ptm) were analyzed by simple sequence repeat (SSR) marker analysis. Thirteen SSR loci were examined and found to be polymorphic within both Ptt and Ptm populations. In total, 110 distinct alleles were identified, with 19 of these shared between Ptt and Ptm, 75 specific to Ptt, and 16 specific to Ptm. Genotypic diversity was relatively high, with a clonal fraction of approximately 10 % within Ptt and Ptm populations. Significant genetic differentiation (PhiPT = 0.230, P = 0.001) was found among all populations; 77 % of genetic variation occurred within populations and 23 % between populations. Lower, but still significant genetic differentiation (PhiPT = 0.038, P = 0.001) was detected in Ptt, with 96 % of genetic variation occurring within populations. No significant genetic differentiation (PhiPT = 0.010, P = 0.177) was observed among Ptm populations. Isolates clustered in two distinct groups conforming to Ptt or Ptm, with no intermediate cluster. The high number of haplotypes observed, combined with an equal mating type ratio for both forms of the fungus, suggests that P. teres goes through regular cycles of sexual recombination in western Canada.     

The chemotaxis regulator <Emphasis Type="Italic">pilG</Emphasis> of <Emphasis Type="Italic">Xylella fastidiosa</Emphasis> is required for virulence in <Emphasis Type="Italic">Vitis vinifera</Emphasis> grapevines

Type IV pili of X. fastidiosa are regulated by pilG, a response regulator protein putatively involved in chemotaxis-like operon sensing stimuli through signal transduction pathways. To elucidate the roles of pilG in pathogenicity of X. fastidiosa, the pilG-deletion mutant XfΔpilG and complemented strain XfΔpilG-C were generated. While all strains had similar growth curves in vitro, XfΔpliG showed significant reduction in cell-matrix adherence and biofilm production compared with wild-type X. fastidiosa and XfΔpilG-C. The genes pilE, pilU, pilT, and pilS were down-regulated in XfΔpliG when compared with its complemented strain and wild-type X. fastidiosa. Finally, no Pierce’s disease symptoms were observed in grapevines inoculated with XfΔpilG, whereas grapevines inoculated with the wild-type X. fastidiosa and complemented strain of XfΔpilG-C developed typical Pierce’s Disease (PD) symptoms. The results indicate that pilG has a role in X. fastidiosa virulence in grapevines.     

First report of phytophthora rot on <Emphasis Type="Italic">Wasabia japonica</Emphasis> caused by <Emphasis Type="Italic">Phytophthora drechsleri</Emphasis> in Japan

In September 2014, Phytophthora rot on wasabi plants [Wasabia japonica (Miq.) Matsum.] was found for the first time in the city of Okutama, Tokyo, Japan. A Phytophthora sp. strain was constantly isolated from brown stem bases and rhizomes of infected plants. The same symptoms as those observed in the field were produced in vitro through inoculation of test plants with the isolated Phytophthora sp. The fungus was identified as Phytophthora drechsleri based on morphological and DNA sequence comparison. Phytophthora rot, “eki-byo” in Japanese, is proposed for this disease common name.     

<Emphasis Type="Italic">Fusarium temperatum</Emphasis> isolated from maize in France

The presence of Fusarium temperatum in France was investigated by analyzing 40 Fusarium strains, previously isolated from infected maize ears in 2011 and formerly identified as Fusarium subglutinans based on morphological characteristics. In this study, 26 strains out of the 40 were identified as F. temperatum and 14 as F. subglutinans based on sequencing of the translation elongation factor 1α gene. The phylogenetic analysis showed that the two species represented two clades strongly supported by bootstrap values. The pathogenicity of F. temperatum strains was confirmed on maize ears. This study provides new information about F. temperatum isolated from maize in France.     

The Eurotiomycete <Emphasis Type="Italic">Apinisia graminicola</Emphasis> as the causal agent of a leaf spot disease on the energy crop <Emphasis Type="Italic">Miscanthus</Emphasis> x <Emphasis Type="Italic">giganteus</Emphasis> in Northern Germany

Miscanthus x giganteus is a fast growing, perennial energy crop for temperate climates. Because of its high annual biomass production rates and its characteristics as a low-input crop, an expansion of field cultivation can be anticipated to cover increasing demands for sustainable biomass production. However, knowledge about pathogens that could have an impact on biomass production is still limited for M. giganteus. Here, we report about the isolation of the filamentous fungus Apinisia graminicola from necrotic leaf lesions of M. giganteus grown on a field trial plot in Northern Germany. Inoculation assays with the isolated A. graminicola strain confirmed its capacity to cause a leaf spot disease on M. giganteus. Additional inoculation assays revealed that A. graminicola also caused necrotic lesions on leaves of the model grass Brachypodium distachyon. Generally, symptoms of A. graminicola-caused leaf spot disease were stronger on B. distachyon compared to M. giganteus. Incubation temperatures above 22 °C during A. graminicola infection resulted in stronger disease symptoms on both, M. giganteus and B. distachyon leaves. Microscopic analysis of cross sectioned, infected leaf tissue revealed an epiphytic mycelium formation on the surface and an endophytic colonization of the mesophyll leave tissue, especially in M. giganteus. Our results revealed that the isolated A. graminicola strain is a causal agent of a leaf spot disease on grass leaves. Its potential on endophytic growth in M. giganteus might open new possibilities in studying this type of plant-fungal interaction on a cellular and molecular level in an energy crop.     

Identification of <Emphasis Type="Italic">Fusarium</Emphasis> species associated with soybean root rot in Sichuan Province,China

Soybean root rot is a worldwide soil-borne fungal disease threatening soybean production, causing large loss in yield and quality of soybean. Fusarium species are well recognized as the important causal agent of Fusarium root rot, which are often distinct with respect to various factors in different soybean-producing regions around the world. Recently, Fusarium root rot has been frequently reported in Sichuan Province of China, where is unique in its climate and diverse cropping patterns, but it is still unclear about the predominant Fusarium species and their pathogenicity on soybean. In this study, diseased soybean roots were collected from three regions of Sichuan Province during 2014–2015. Based on morphological characteristics and phylogenetic analysis of nucleotide sequences of the ribosomal internal transcribed spacer region and the translation elongation factor 1-α gene, 78 isolates of Fusarium were identified as nine distinct species. Pathogenicity tests showed that seven species of Fusarium were able to infect soybean, but differed in pathogenicity. F. oxysporum, F. equiseti and F. graminearum were the most aggressive species to soybean, whereas F. fujikuroi and F. verticillioides were not pathogenic to soybean. There was a strong positive correlation of the pathogenicity of Fusarium species with seedling emergence and fresh root weight. In addition, the diversity of Fusarium species varied among soybean-growing regions. To our knowledge, this report on population and pathogenicity of Fusarium species, in particular, F. graminearum, associated with soybean root rot in Sichuan Province of southwest China, will be helpful to provide effective control strategies for the disease.     

Competence of <Emphasis Type="Italic">Frankliniella occidentalis</Emphasis> and <Emphasis Type="Italic">Frankliniella intonsa</Emphasis> strains as vectors for <Emphasis Type="Italic">Chrysanthemum stem necrosis virus</Emphasis>

The vector competence of Frankliniella occidentalis for Chrysanthemum stem necrosis virus (CSNV) was evaluated. Three vector strains with distinct competences for Tomato spotted wilt virus (TSWV) transmission were investigated, including an artificially selected strain (TsH) that has a particularly high competence (>90 %). Newly hatched larvae of F. occidentalis were given an acquisition access period of 5 days on CSNV-infected D. stramonium leaves, and reared to maturity. Their transmission efficiencies were examined using a leaf disk assay using Petunia x hybrida leaves. Following the leaf disk assay, the virus accumulation in the vectors was examined via a double antibody sandwich enzyme-linked immunosorbent assay (DAS-ELISA) of their bodies. The results showed that the CSNV acquisition and transmission efficiency of the TsH strain did not differ from those of the others, indicating that the competence of F. occidentalis as a vector for CSNV is not related to that for TSWV. The CSNV transmission and acquisition efficiencies of two F. intonsa strains (Hiroshima and Fukuoka) were also evaluated. In Hiroshima strain, 35 % of adults were viruliferous, but only two transmitters (3 %) were observed. In Fukuoka strain, 6 % were viruliferous, and no transmitters were observed. These results indicate that F. intonsa cannot be a major vector for CSNV. The accumulation of CSNV in the adults of F. occidentalis and F. intonsa evaluated using DAS-ELISA showed a significant difference in ELISA values among transmitter, viruliferous non-transmitter, and non-viruliferous individuals. These results clearly demonstrated that only transmitters that accumulated a threshold quantity of virus can transmit CSNV to plants.     

<Emphasis Type="Italic">Fusarium</Emphasis> head blight incidence and detection of <Emphasis Type="Italic">Fusarium</Emphasis> toxins in wheat in relation to agronomic factors

We investigated incidences of Fusarium head blight (FHB) and concentrations of six mycotoxins (deoxynivalenol, nivalenol, 3-acetyldeoxynivalenol, T-2 toxin, HT-2 toxin and zearalenone) in wheat from 2010 to 2013. Field trials were conducted at the Experimental Station of Cultivar Testing in Chrz?stowo, Poland (53^o11’N, 17^o35’E). We examined the effects of four agronomic factors, including pre-crop type (corn, sugar beets and wheat), date of sowing (late autumn: November 8–December 9 or spring: March 29–April 19), fungicidal application (untreated or treated with two applications) and cultivar (Monsun, Cytra), on FHB index (FHBi) and mycotoxin levels in order to minimize the risk of wheat grain contamination by mycotoxins via integrated pest management methods. The dominant Fusarium species observed on wheat heads were F. culmorum, F. avenaceum (Gibberella avenacea) and F. graminearum (Gibberella zeae), at 21.1%, 17.2% and 7.1%, respectively. A monthly rainfall sum of 113.9 mm and a relatively low air temperature (monthly average 15.5 °C) resulted in the highest FHBi in untreated wheat (25.1%). Agronomic factors crucial for the FHB incidence were the pre-crop, fungicidal treatments and cultivar selection. In wheat planted after wheat or corn, the FHBi was higher compared with a pre-crop of sugar beet. A double application of fungicides at BBCH 30–32 with prothioconazole and spiroxamine and at a BBCH 65 with fluoxastrobin and prothioconazole effectively reduced the FHBi and mycotoxin concentrations, respectively, in grain. The cultivar ‘Cytra’ had a greater FHBi (10.4%) than ‘Monsun’ (4.6%), and grain infestations by Fusarium species were also greater in ‘Cytra’, at 16.5%, than in ‘Monsun’, at 11.2%. Untreated cv. Cytra grown after corn in spring produced grains with the highest amounts of the mycotoxins, deoxynivalenol, 3-acetyldeoxynivalenol, zearalenone and HT-2 (605, 103, 17.5 and 5.53 μg/kg, respectively). Total mycotoxin levels in wheat were correlated with five determinants: duration of the period between the end of flowering and the beginning of kernel abscission, FHBi, F. culmorum isolation, G. zeae isolation and Fusarium ratio (FR) as a % of total mould isolations. Although, the mean concentration of mycotoxins in grain did not exceed the maximum permissible values for unprocessed wheat our study suggests necessity to monitor and mitigate FHB risk for susceptible cultivars, when wheat spring sowing follows corn or wheat.     

Overexpression of <Emphasis Type="Italic">SlARG2</Emphasis> or <Emphasis Type="Italic">SlTD2</Emphasis> in Arabidopsis enhances resistance against <Emphasis Type="Italic">Plutella xylostella</Emphasis> L.

Tomato (Solanum lycopersicum L.) ARGINASE2 (ARG2) and THREONINE DEAMINASE2 (TD2) are involved in plant defense. These enzymes act in the midgut of herbivores fed on tomato plants to degrade the essential amino acids Arg and Thr, respectively. Although it has been demonstrated that overexpression of the SlARG2 gene in tomato enhanced its resistance against M. sexta larvae, knock-down the expression of SlTD2 reduced the resistance of tomato to lepidopteran herbivores; it remains unclear whether overexpression of SlTD2 could enhance the resistance of the host plants to herbivores, or whether combined overexpression of SlARG2 and SlTD2 could lead to synergistically enhanced resistance to insects. Here, we generated transgenic Arabidopsis plants overexpressing SlARG2 (SlARG2 OE) and SlTD2 (SlTD2 OE) individually as well as in combination (SlARG2-SlTD2 OE). Overexpression of these genes did not affect Arabidopsis development, seed yield, or Arg and Thr content. Insect-feeding bioassay was performed by feeding diamondback moth (Plutella xylostella L.) larvae on detached leaves of wild-type, SlARG2 OE, SlTD2 OE, and SlARG2-SlTD2 OE plants. Larvae fed on SlARG2 OE leaves showed approximately 31% to 35% reduction in weight and 6% to 10% reduction in survival rate compared to those fed on wild-type leaves. Although larvae fed on SlTD2 OE leaves showed no reduction in survival rate, they gained less weight. Whereas larvae fed on SlARG2-SlTD2 OE leaves showed neither reduction in weight nor reduction in survival rate. We further investigated the arginase enzymatic activity of the SlARG2 OE and SlARG2-SlTD2 OE transgenic plants. The SlARG2 OE line most resistant to diamondback moth larvae displayed the highest arginase activity. Our data indicate that overexpression of SlARG2 or SlTD2 in Arabidopsis can enhance its resistance against diamondback moth, whereas combined overexpression of SlARG2 and SlTD2 did not generate synergistically increased resistance to diamondback moth.     

Antagonistic effects of biofilm-forming bacterial strains co-inoculated with blood disease pathogenic strain, <Emphasis Type="Italic">Ralstonia syzygii</Emphasis> subspecies <Emphasis Type="Italic">celebesensis</Emphasis> in banana plants

A blood disease pathogenic strain, Ralstonia syzygii subspecies celebesensis was used to study the possible association of biofilm-forming bacteria with the development and severity of blood disease in banana plants. Therefore, the objective of this study was to determine the effects of mono-culture and co-culture inoculation of isolated biofilm-forming bacteria with the blood disease pathogen in banana pseudostems in glasshouse conditions. Putative biofilm-forming bacteria were isolated from an infected banana plant and were further identified using 16SrRNA sequencing. Four isolates, identified as Enterobacter hormaechei, Enterobacter cloacae, Kosakonia radicincitans and Klebsiella pneumoniae, were inoculated as a mono- and co-culture with R. syzygii subsp. celebesensis into 2 months old banana plants. The observation after the 8 weeks of post inoculation showed that plants which were co-inoculated with the pathogen and K. radicincitans, a biofilm-forming bacterium, were the most susceptible towards the infection. In contrast, plants under two treatments (which were co-inoculated with the pathogen and E. cloacae and the pathogen with E. hormaechei) were less susceptible towards the infection. This study revealed the antagonistic effects of two biofilm-forming strains which reduced the severity of infection caused by the pathogenic agent. Scanning electron micrographs of the cross section of plant rhizomes indicated the dissimilarity of adhesion and host colonization conditions of the pathogen in each infected plant from different treatments.     

Natural enemies of <Emphasis Type="Italic">Diaspis echinocacti</Emphasis> in Greece and first records of <Emphasis Type="Italic">Aphytis debachi</Emphasis> and <Emphasis Type="Italic">Plagiomerus diaspidis</Emphasis>

Two hymenopteran parasitoids of the cactus scale Diaspis echinocacti (Bouché) (Hemiptera: Diaspididae) on Opuntia ficus-indica (L.) Mill. (Cactaceae) are recorded in Greece. Aphytis debachi Azim, 1963 (Aphelinidae) is first recorded for Europe and Plagiomerus diaspidis Crawford, 1910 (Encyrtidae) is first recorded for Greece. Preliminary data on phenology and natural enemies of the scale D. echinocacti on O. ficus-indica are presented. Parasitism of D. echinocacti by P. diaspidis reached 86% in southern Greece (Kalamata) and parasitism by A. debachi reached 9.3% and 12% in Kalamata and Athens, respectively. Two predators, Cybocephalus fodori Endrödy-Youga (Coleoptera: Nitidulidae) and a mite species (Prostigmata: Bdellidae), were found to be associated with D. echinocacti.     

Rice <Emphasis Type="Italic">OsPBL1</Emphasis> (ORYZA SATIVA ARABIDOPSIS PBS1-LIKE 1) enhanced defense of <Emphasis Type="Italic">Arabidopsis</Emphasis> against <Emphasis Type="Italic">Pseudomonas syringae</Emphasis> DC3000

The receptor-like cytoplasmic kinases (RLCK family VII) are required for plant defense against various pathogens. Previously, OsPBL1 (ORYZA SATIVA ARABIDOPSIS PBS1-LIKE 1) was isolated from rice as a potential RSV (rice stripe virus) resistant factor, but its physiological roles in plant defense are yet to be investigated. In this study, we demonstrated that OsPBL1increased defense against P. syringae in transgenic Arabidopsis. To ascertain the role of OsPBL1 gene in plant defense, OsPBL1 tagged with HA (i.e. Hemagglutinin) was overexpressed in Arabidopsis and examined for the resistance against Pseudomonas syringae pv. tomato DC3000 (i.e. Pst DC3000). At 3 dpi of Pst DC3000, transgenic Arabidopsis lines exhibited the reduced chlorotic lesion and propagation of P. syringae, compared to wild type. Elevated pathogen resistance of transgenic lines was correlated with increased H₂O₂ accumulation and callose deposition on the infected leaves. It was also revealed that expression levels of salicylic acid dependent genes such as PR1, PR2, and PR5, were induced higher in transgenic lines than wild type. Taken together, our data suggested that OsPBL1 exerted the role in defense against pathogen attacks in plant via mainly facilitating salicylic acid dependent pathway.     

Nonhost resistance of <Emphasis Type="Italic">Arabidopsis thaliana</Emphasis> against <Emphasis Type="Italic">Colletotrichum</Emphasis> species

Arabidopsis thaliana exhibits a durable resistance called nonhost resistance against nonadapted fungal pathogens. A. thaliana activates preinvasive resistance and terminates entry attempts by nonadapted fungi belonging to the genus Colletotrichum, which cause anthracnose disease in many plants. In the interaction between A. thaliana and nonadapted C. tropicale, the preinvasive resistance involves the PENETRATION 2-related antifungal secondary metabolite pathway and the ENHANCED DISEASE RESISTANCE 1-dependent antifungal peptide pathway. The development of invasive hyphae by C. tropicale owing to the reduction of preinvasive resistance then triggers the blockage of further hyphal expansion via the activation of the second layer of resistance, i.e., postinvasive resistance, which guarantees the robustness of the nonhost resistance of A. thaliana against Colletotrichum pathogens. Both the tryptophan-derived metabolic pathway and glutathione synthesis play critical roles in the postinvasive resistance against C. tropicale, although the molecular mechanism of postinvasive resistance remains to be elucidated. In this review, we describe the current understanding of the molecular background of the Arabidopsis nonhost resistance against Colletotrichum fungi and discuss perspectives for future research on this durable resistance.