Leaf Pathogen Research Articles

Variation Within and Between Vitis spp. for Foliar Resistance to the Downy Mildew Pathogen Plasmopara viticola.

To complement existing control strategies, grape growers in humid climates desire cultivars with resistance to downy mildew caused by Plasmopara viticola. Numerous disease resistance screens of diverse Vitis germplasm have been conducted previously to identify downy mildew resistance; however, ratings of named cultivars were inconsistent and identities of resistant individuals in wild species were not typically provided. Inconsistencies among previous studies could be due to race-specific resistance. In the current study, controlled inoculations of two single isolates onto two leaf ages of 883 Vitis accessions were used and these results compared with natural infection in a fivefold replicated vineyard of 80 Vitis accessions in 2006 and 2007. Of the accessions rated in both assays, 16.2% were resistant to a single isolate but susceptible in the vineyard. Otherwise, there was good correlation of ratings between the field assay and the rating of older leaves (r = 0.62 to 0.71). Five accessions from Vitis cinerea, V. labrusca, and Vitis × champinii averaged zero severity in both vineyard years, yet some individuals of V. cinerea and V. labrusca were moderately or highly susceptible in the field. Similarly, although significant differences in mean severity separated V. vinifera, Vitis hybrid, V. riparia, and V. labrusca for single-isolate inoculations (from susceptible to resistant), notable intraspecies variation was identified for all well-represented species. Resistant individuals were identified in most species with the prominent exceptions of V. vinifera and V. acerifolia. Single-isolate, detached-leaf resistance ratings in 2006 corresponded well (94.6%) to 2007 ratings using a separate isolate collected from the same vineyard. Categorizing the ratings for this and previous studies, ratings infrequently corresponded among previous studies (31.9%) as well as between previous studies and the current single-isolate (34.9%) or vineyard (46.4%) ratings. These results highlight important factors for downy mildew resistance screens: leaf age, pathogen genotype, and host species and accession. The results further underscore the importance to breeders of uniform testing in multiple environments.

Species of Botryosphaeriaceae occurring on Proteaceae

The Botryosphaeriaceae includes several species that are serious canker and leaf pathogens of Proteaceae. In the present study, sequence data for the ITS nrDNA region were used in conjunction with morphological observations to resolve the taxonomy of species of Botryosphaeriaceae associated with Proteaceae. Neofusicoccum luteum was confirmed from Buckinghamia and Banksia in Australia, and on Protea cynaroides in South Africa. A major pathogen of Banksia coccinea in Australia was shown to be N. australe and not N. luteum as previously reported. Neofusicoccum protearum was previously reported on Proteaceae from Australia, Madeira, Portugal and South Africa, and is shown here to also occur in Hawaii and Tenerife (Canary Islands). Furthermore, several previous records of N. ribis on Proteaceae were shown to be N. parvum. Saccharata capensis is described as a new species that is morphologically similar to S.proteae. There is no information currently available regarding its potential importance as plant pathogen and pathogenicity tests should be conducted with it in the future.

Constitutively activated barley ROPs modulate epidermal cell size, defense reactions and interactions with fungal leaf pathogens

RHO-like monomeric G-proteins of plants (ROPs, also called RACs), are involved in plant development and interaction with the environment. The barley (Hordeum vulgare) ROP protein HvRACB has been shown to be required for entry of the biotrophic powdery mildew fungus Blumeria graminis f.sp. hordei (Bgh) into living host cells. To get a deeper insight into evolutionarily conserved functions of ROPs in cell polarity and pathogen responses, we stably expressed constitutively activated (CA) mutant variants of different barley ROPs (HvRACB, HvRAC1, HvRAC3) in barley. CA HvROPs induced epidermal cell expansion and/or abolished polarity in tip growing root hairs. All three CA HvROPs enhanced susceptibility of barley to penetration by Bgh whereas only CA HvRAC1 supported whole cell H(2)O(2) production in non-penetrated cells. Despite increasing penetration by Bgh, CA HvRAC1 promoted callose deposition at sites of fungal attack and resistance to penetration by Magnaporthe oryzae. The data show an involvement of ROPs in polar growth processes of the monocot barley and in responses to fungal pathogens with different life style.

Pathogen attack and spatial patterns of juvenile mortality and growth in a temperate tree, Prunus grayana

To examine whether the Janzen–Connell hypothesis is valid in temperate forests, we investigated the density, growth, mortality, and agents of mortality of seedlings and the density, size, and age of saplings of Prunus grayana Maxim. at three distances (0–3, 6–10, and 16–26 m) from conspecific adults in a temperate forest in Japan. An inoculation experiment was also conducted to test the host range of a leaf pathogen. The probability of mortality was highest at 0–3 m during the first 2 years of growth. Mortality mainly resulted from distance-dependent attack by two types of pathogen that caused damping-off epidemics and spot symptoms on leaves. The leaf pathogen was identified as Phaeoisariopsis pruni-grayanae Sawada, which infected many more seedlings of Prunus grayana than of the two other tree species tested in an inoculation experiment. The vertical and diameter growth was lowest at 0–3 m and highest at 16–26 m in both seedlings and saplings. As a result, the greatest number of large and older saplings was observed at 16–26 m. Our results demonstrate that the Janzen–Connell mechanism operates in a beech-dominated forest in the temperate region of Japan.

Identification of plant defence genes in canola using Arabidopsis cDNA microarrays

We report the identification of novel defence genes in canola by using a cDNA microarray from Arabidopsis. We examined changes that occur in the abundance of transcripts corresponding to 2375 Arabidopsis expressed sequence tags (selected for defence gene identification) following inoculation of canola plants with the fungal necrotrophic leaf pathogen, Alternaria brassicicola. Microarray data obtained from this cross-hybridisation experiment were compared to expression profiles previously obtained from the equivalent Arabidopsis experiment. Homology searches using a canola expressed sequence tag database with approximately 6000 unique clones led to identification of canola defence genes. Pathogen-responsive transcripts included those associated to known defence genes, reactive oxygen species metabolism, disease resistance and regulatory genes, and cell maintenance/metabolism genes. Using specific primers for quantitative real-time reverse transcriptase PCR, gene expression profiles in canola were obtained that demonstrated coordinated defence responses, including systemic responses in distal tissue and salicylic acid- and methyl jasmonate-mediated signalling against A. brassicicola.

A new host for Nigrospora sphaerica causing leaf spots on Glycyrrhiza glabra

Glycyrrhiza glabra is a perennial medicinal plant. Commercially, it is known as liquorice or mulathi consisting of dried roots and rhizomes of the plant. It is used for the preparation of expectorant, and anti-inflammatory drugs as well as demulscent to improve the flavour of various bitter medicinal preparations. Glycyrrhizi is one of the important active constituents of the drug. During survey, a leaf spot disease was noticed in G. glabra plants growing in Udaipur, India. Symptoms of the disease appear in the form of small (2–5 mm), circular to irregular, red coloured spots on leaflets, covering major area of the leaf. Occasionally, the spots are seen delineated by the midrib. In advanced stages of the disease, some spots cracked at the centre. Eventually, leaves dry and the plant defoliates. Isolations from infected leaves were made on potato dextrose agar (PDA). The fungus on PDA was identified as Nigrospora sphaerica, on the basis of culture and morphological characters. The fully developed colonies were flat and grey coloured, having dark brown, septate, branched mycelium. Conidia were black, single celled, globose (12·4–18·5 µm), borne on a hyaline vesicle at the tip of the conidiophore. The culture was deposited with the Agharkar Research Institute, Pune, India (Accession No. ARIFCC-1085). Koch's postulates were satisfied by spraying a conidial suspension (105 conidia mL−1), obtained from 10-day-old culture plates, onto the healthy leaves of G. glabra. Inoculated leaves and water-sprayed controls were covered with polythene bags for 48 h and kept under natural environmental conditions. Disease symptoms started developing on the inoculated leaves after 8–10 days. The fungus was reisolated from the infected plants. Review of the pertinent literature revealed that Nigrospora sphaerica is known as leaf pathogen for several hosts (Pavgi et al., 1966; Chowdhry, 1969; Mazumdar et al., 2006). However, G. glabra constitutes a new host record for this pathogen in India and worldwide.

Dimerization Controls the Activity of Fungal Elicitors That Trigger Systemic Resistance in Plants

The soilborne fungus Trichoderma virens secretes a small protein (Sm1) that induces local and systemic defenses in plants. This protein belongs to the ceratoplatanin protein family and is mainly present as a monomer in culture filtrates. However, Hypocrea atroviride (the telomorph form of Trichoderma atroviride) secretes an Sm1-homologous protein, Epl1, with high levels of dimerization. Nonetheless, the molecular mechanisms involved in recognition and the signaling pathways involved in the induction of systemic resistance in plants are still unclear. In this report, we demonstrate that Sm1 and Epl1 are mainly produced as monomer and a dimer, respectively, in the presence of maize seedlings. The results presented show that the ability to induce plant defenses reside only in the monomeric form of both Sm1 and Epl1, and we demonstrate for the first time that the monomeric form of Epl1, likewise Sm1, induces defenses in maize plants. Biochemical analyses indicate that monomeric Sm1 is produced as a glycoprotein, but the glycosyl moiety is missing from its dimeric form, and Epl1 is produced as a nonglycosylated protein. Moreover, for Sm1 homologues in various fungal strains, there is a negative correlation between the presence of the glycosylation site and their ability to aggregate. We propose a subdivision in the ceratoplatanin protein family according to the presence of the glycosylation site and the ability of the proteins to aggregate. The data presented suggest that the elicitor's aggregation may control the Trichoderma-plant molecular dialogue and block the activation of induced systemic resistance in plants.

Emergence of Tan Spot Disease Caused by Toxigenic Pyrenophora tritici-repentis in Australia Is Not Associated with Increased Deployment of Toxin-Sensitive Cultivars

The wheat disease tan (or yellow leaf) spot, caused by Pyrenophora tritici-repentis, was first described in the period 1934 to 1941 in Canada, India, and the United States. It was first noted in Australia in 1953 and only became a serious disease in the 1970s. The emergence of this disease has recently been linked to the acquisition by P. tritici-repentis of the ToxA gene from the wheat leaf and glume blotch pathogen, Stagonospora nodorum. ToxA encodes a host-specific toxin that interacts with the product of the wheat gene Tsn1. Interaction of ToxA with the dominant allele of Tsn1 causes host necrosis. P. tritici-repentis races lacking ToxA give minor indistinct lesions on wheat lines, whereas wheat lines expressing the recessive tsn1 are significantly less susceptible to the disease. Although the emergence and spread of tan spot had been attributed to the adoption of minimum tillage practices, we wished to test the alternative idea that the planting of Tsn1 wheat lines may have contributed to the establishment of the pathogen in Australia. To do this, wheat cultivars released in Australia from 1911 to 1986 were tested for their sensitivity to ToxA. Prior to 1941, 16% of wheat cultivars were ToxA-insensitive and hence, all other factors being equal, would be more resistant to the disease. Surprisingly, only one of the cultivars released since 1940 was ToxA insensitive, and the area planted to ToxA-insensitive cultivars varied from 0 to a maximum of only 14% in New South Wales. Thus, the majority of the cultivars were ToxA-sensitive both before and during the period of emergence and spread of the disease. We therefore conclude that the spread of P. tritici-repentis in Australia cannot be causally linked to the deployment of ToxA-sensitive cultivars.

Agricultural Land Use and Biodiversity in the Alps

Alpine grasslands are ecosystems with a great diversity of plant species. However, little is known about other levels of biodiversity, such as landscape diversity, diversity of biological interactions of plants with herbivores or fungal pathogens, and genetic diversity. We therefore explored natural and anthropogenic determinants of grassland biodiversity at several levels of biological integration, from the genetic to the landscape level in the Swiss Alps. Differences between cultural traditions (Romanic, Germanic, and Walser) turned out to still affect land use diversity and thus landscape diversity. Increasing land use diversity, in turn, increased plant species diversity per village. However, recent land use changes have reduced this diversity. Within grassland parcels, plant species diversity was higher on unfertilized mown grasslands than on fertilized or grazed ones. Most individual plants were affected by herbivores and fungal leaf pathogens, reflecting that parcels harbored a great diversity of herbivores and pathogens. However, as plant damage by herbivores and pathogens was not severe, conserving these biological interactions among plants is hardly compromising agricultural goals. A common-garden experiment revealed genetic differentiation of the important fodder grass Poa alpina between mown and grazed sites, suggesting adaptation. Pervillage genetic diversity of Poa alpina was greater in villages with higher land use diversity, analogous to the higher plant species diversity there. Overall, landscape diversity and biodiversity within grassland parcels are currently declining. As this contradicts the intention of Swiss law and international agreements, financial incentives need to be re-allocated and should focus on promoting high biodiversity at the local and the landscape level. At the same time, this will benefit landscape attractiveness for tourists and help preserve a precious cultural heritage in the Swiss Alps.

Pepper pectin methylesterase inhibitor protein CaPMEI1 is required for antifungal activity, basal disease resistance and abiotic stress tolerance

Pectin is one of the main components of the plant cell wall that functions as the primary barrier against pathogens. Among the extracellular pectinolytic enzymes, pectin methylesterase (PME) demethylesterifies pectin, which is secreted into the cell wall in a highly methylesterified form. Here, we isolated and functionally characterized the pepper (Capsicum annuum L.) gene CaPMEI1, which encodes a pectin methylesterase inhibitor protein (PMEI), in pepper leaves infected by Xanthomonascampestris pv. vesicatoria (Xcv). CaPMEI1 transcripts are localized in the xylem of vascular bundles in leaf tissues, and pathogens and abiotic stresses can induce differential expression of this gene. Purified recombinant CaPMEI1 protein not only inhibits PME, but also exhibits antifungal activity against some plant pathogenic fungi. Virus-induced gene silencing of CaPMEI1 in pepper confers enhanced susceptibility to Xcv, accompanied by suppressed expression of some defense-related genes. Transgenic ArabidopsisCaPMEI1-overexpression lines exhibit enhanced resistance to Pseudomonas syringae pv. tomato, mannitol and methyl viologen, but not to the biotrophic pathogen Hyaloperonospora parasitica. Together, these results suggest that CaPMEI1, an antifungal protein, may be involved in basal disease resistance, as well as in drought and oxidative stress tolerance in plants.Electronic supplementary materialThe online version of this article (doi:10.1007/s00425-008-0719-z) contains supplementary material, which is available to authorized users.

Detection of Plant-Modulated Alterations in Antifungal Gene Expression in Pseudomonas fluorescens CHA0 on Roots by Flow Cytometry

The biocontrol activity of the root-colonizing Pseudomonas fluorescens strain CHA0 is largely determined by the production of antifungal metabolites, especially 2,4-diacetylphloroglucinol. The expression of these metabolites depends on abiotic and biotic environmental factors, in particular, elements present in the rhizosphere. In this study, we have developed a new method for the in situ analysis of antifungal gene expression using flow cytometry combined with green fluorescent protein (GFP)-based reporter fusions to the phlA and prnA genes essential for the production of the antifungal compounds 2,4-diacetylphloroglucinol and pyrrolnitrin, respectively, in strain CHA0. Expression of phlA-gfp and prnA-gfp in CHA0 cells harvested from the rhizosphere of a set of plant species as well as from the roots of healthy, leaf pathogen-attacked, and physically stressed plants were analyzed using a FACSCalibur. After subtraction of background fluorescence emitted by plant-derived particles and CHA0 cells not carrying the gfp reporters, the average gene expression per bacterial cell could be calculated. Levels of phlA and prnA expression varied significantly in the rhizospheres of different plant species. Physical stress and leaf pathogen infection lowered phlA expression levels in the rhizosphere of cucumber. Our results demonstrate that the newly developed approach is suitable to monitor differences in levels of antifungal gene expression in response to various plant-derived factors. An advantage of the method is that it allows quantification of bacterial gene expression in rhizosphere populations at a single-cell level. To our best knowledge, this is the first study using flow cytometry for the in situ analysis of biocontrol gene expression in a plant-beneficial bacterium in the rhizosphere.

Quambalaria species, including Q. coyrecup sp. nov., implicated in canker and shoot blight diseases causing decline of Corymbia species in the southwest of Western Australia

A severe canker disease has been causing decline and death of Corymbia calophylla in the southwest of Western Australia (WA) for some years, but the causal agent has never been investigated. However, there have been historical reports dating back to the 1920s of a canker disease of amenity planted C. ficifolia caused by ‘ Sporotrichum destructor’, though the description and Latin diagnosis were never published. It has been suggested that there may be links between this species and the genus Quambalaria, a group containing leaf and shoot pathogens of species of Eucalyptus and Corymbia. The aim of this study was to investigate the identity of the pathogen historically attributed to canker disease of C. ficifolia, determine whether this pathogen is responsible for the current epidemic of C. calophylla canker, and whether it is synonymous with Quambalaria. Surveys examined the range of Quambalaria spp. on Corymbia spp. endemic to southwest WA. Their phylogenetic relationship to Q. cyanescens, Q. eucalypti, and Q. pitereka was examined using rLSU and ITS sequence data. Morphological characters were also compared. Sequences confirmed that Q. cyanescens and Q. pitereka are present in southwest WA, with the latter associated with leaf and shoot disease. A third group isolated from cankers represent a new species of Quambalaria. Comparisons of disease symptoms and conidiogenesis indicate this species is synonymous with ‘ S. destructor’. The species is formally described here as Q. coyrecup sp. nov.

The 18mer peptaibols from Trichoderma virens elicit plant defence responses

SUMMARY Peptaibols, the products of non-ribosomal peptide synthetases (NRPS), are linear peptide antibiotics produced by Trichoderma and other fungal genera. Trichoderma virens strain Gv29-8, a well-known biocontrol agent and inducer of plant defence responses, produces three lengths of peptaibols, 11, 14 and 18 residues long, with several isoforms of each. Disruption of the NRPS gene, tex1, encoded by a 62.8-kb uninterrupted open reading frame, results in the loss of production of all forms of 18-residue peptaibols. Tex1 is expressed during all Trichoderma developmental stages (germinating conidia, sporulating and non-sporulating mycelia) examined on solid media. Expression analysis by reverse transcriptase PCR shows that in Gv29-8 wild-type the abundance of tex1 transcript is greater during co-cultivation with cucumber seedling roots than when grown alone. Cucumber plants co-cultivated with T. virens strains disrupted in tex1 show a significantly reduced systemic resistance response against the leaf pathogen Pseudomonas syringae pv. lachrymans, and reduced ability to produce phenolic compounds with inhibitory activity to the bacteria as compared with plants grown in the presence of wild-type. Two synthetic 18-amino-acid peptaibol isoforms (TvBI and TvBII) from Gv29-8 when applied to cucumber seedlings through the transpiration stream can alone induce systemic protection to the leaf pathogenic bacteria, induce antimicrobial compounds in cucumber cotyledons and up-regulate hydroxyperoxide lyase (hpl), phenylalanine ammonia lyase (pal1) and peroxidase (prx) gene expression. These data strongly suggest that the 18mer peptaibols are critical in the chemical communication between Trichoderma and plants as triggers of non-cultivar-specific defence responses.

ISSR fingerprinting for the assessment of the bindweed biocontrol agent Stagonospora convolvuli LA39 after field release

To develop a molecular identification method based on ISSR fingerprints to monitor the fungal leaf pathogen Stagonospora convolvuli LA39 used to biologically control bindweeds after a field release. The developed method proved to be suitable to clearly distinguish LA39 from resident Stagonospora spp. and was applied in two field experiments. First, the environmental persistence of LA39 was assessed in an overwintering experiment. LA39 could be re-isolated from infected bindweed 1 year after field application, but with very low frequency of occurrence. Secondly, LA39 was applied in an area with natural bindweed infestation and re-isolated from infected bindweed. The dispersal of LA39 during one season was poor (4-5 m). ISSR fingerprinting has been shown to be a valuable tool to monitor the environmental fate of S. convolvuli in the field. It is concluded that an LA39-based mycoherbicide will have minimal environmental impact caused by the restricted mobility, poor proliferation and poor persistence over seasons of LA39. Studies about the dispersal and survival of biocontrol agents after field release as well as the development of methods needed for this purpose are indispensable for a comprehensive risk assessment for biocontrol agents.

The origin and colonization history of the barley scald pathogen Rhynchosporium secalis

The origins of pathogens and their past and present migration patterns are often unknown. We used phylogenetic haplotype clustering in conjunction with model-based coalescent approaches to reconstruct the genetic history of the barley leaf pathogen Rhynchosporium secalis using the avirulence gene NIP1 and its flanking regions. Our results falsify the hypothesis that R. secalis emerged in association with its host during the domestication of barley 10,000 to 15,000 years ago in the Fertile Crescent and was introduced into Europe through the migration of Neolithic farmers. Estimates of time since most recent common ancestor (2500-5000 BP) placed the emergence of R. secalis clearly after the domestication of barley. We propose that modern populations of R. secalis originated in northern Europe following a host switch, most probably from a wild grass onto cultivated barley shortly after barley was introduced into northern Europe. R. secalis subsequently spread southwards into already established European barley-growing areas.

Performance of the Biocontrol Fungus Piriformospora indica on Wheat Under Greenhouse and Field Conditions

ABSTRACT The endophyte Piriformospora indica colonizes roots of a range of host plants and increases biomass production and resistance to fungal pathogens and, thus has been considered a biocontrol fungus. However, the field performance of this fungus has not yet been tested in temperate climates. Therefore, we evaluated the performance of this fungus in different substrata under greenhouse and practical field conditions. Roots of winter wheat were colonized efficiently, and biomass was particularly increased on poor substrata. In greenhouse experiments, symptom severity of a typical leaf (Blumeria graminis f. sp. tritici), stem base (Pseudocercosporella herpotrichoides), and root (Fusarium culmorum) pathogen was reduced significantly. However, in field experiments, symptoms caused by the leaf pathogen did not differ in Piriformospora indica-colonized compared with control plants. In the field, Pseudocercosporella herpotrichoides disease severity was significantly reduced in plants colonized by the endophyte. Increased numbers of sheath layers and hydrogen peroxide concentrations after B. graminis attack were detected in Piriformospora indica-colonized plants, suggesting that root colonization causes induction of systemic resistance or priming of the host plant. Although the endophyte is not well suited for growth at Central European temperature conditions, it remains to be shown whether P. indica is more suitable for tropical or subtropical farming.

Anatomy and cytology of Taphrina entomospora during infection of Nothofagus

Taphrina entomospora is one of the few species of the genus described on native plants of the Southern Hemisphere and also one of the few leaf pathogens known on Nothofagus species. The anatomical changes it produces on N. pumilio leaves, and its morphology, cytology, and sporogenesis were studied. The fungus is a perennial species that overwinters as mycelium in the foliar buds and infects the developing leaves, so the whole blade develops the disease symptoms. Interveinal areas of the leaves become chlorotic, thickened and rounded. Palisade parenchyma fails to develop, with spongy parenchyma developing as packed, rounded, isodiametric cells with little intercellular space. The mycelium is subcuticular, dikaryotic, and produces ascogenous hyphae, asci, and ascospores as described for other species in the genus. Before ascus discharge, ascospores bud in a regular, unique way. The life-cycle of T. entomospora is compared with other representative taxa in the genus and the distribution of this pathogen is discussed.

Kirramyces viscidussp. nov., a new eucalypt pathogen from tropical Australia closely related to the serious leaf pathogen,Kirramyces destructans

Kirramyces destructans is a serious pathogen causing a leaf, bud and shoot blight disease of Eucalyptus plantations in the subtropics and tropics of South-East Asia. During surveillance of eucalypt taxa trials in northern Queensland, symptoms resembling those of K. destructans were observed on Eucalyptus grandis and E. grandis × E. camaldulensis. Phylogenetic and morphological studies revealed that the Kirramyces sp. associated with these symptoms represents a new taxon described here as K. viscidus sp. nov., which is closely related to K. destructans. Plantation assessments revealed that while E. grandis from the Copperload provenance, collected in northern Queensland, recovered from disease, E. grandis × E. camaldulensis hybrids from South America were highly susceptible to infection by K. viscidus and are not recommended for planting in northern Queensland. Preliminary results suggest the fungus probably originates from Australia. K. viscidus is closely related to K. destructans and causes a disease with similar symptoms, suggesting that it could seriously damage Australian eucalypt plantations, especially those planted off-site.

Genetic variability of maize pathogens in Serbia

Variability of some maize pathogens was identified in the last 50 years of research in Serbia, mostly by their cultural characteristics and susceptibility of test genotypes and only in some cases by determination of mating types, vegetative compatibility or biochemical methods. Although more advanced methods that can determine within population variability at the molecular level were developed, they are still not applied in research in Serbia. The highest variability was determined for maize leaf pathogens - Exserohilum turcicum (Pass.) Leonard & Suggs (2 races) and Bipolaris zeicola (Stout) Shoemaker (2 races), although this variability is significantly lower than the variability of the same pathogens found in the world. Researches conducted with the aim to determine mating types and vegetative compatibility of the Fusarium species, a maize root and stalk pathogen, indicated their high variability in Serbia. Considering the pathogen ability to adapt easily and quickly to new genotypes, agro-ecological conditions and crop practice, a constant surveillance of parasite divergence and epidemiology is necessary in order to avoid detrimental consequences on maize yield and quality.

Characterization of a Mitogen-Activated Protein Kinase Gene from Cucumber Required for Trichoderma-Conferred Plant Resistance

The fungal biocontrol agent Trichoderma asperellum has been recently shown to induce systemic resistance in plants through a mechanism that employs jasmonic acid and ethylene signal transduction pathways. Mitogen-activated protein kinase (MAPK) proteins have been implicated in the signal transduction of a wide variety of plant stress responses. Here we report the identification and characterization of a Trichoderma-induced MAPK (TIPK) gene function in cucumber (Cucumis sativus). Similar to its homologs, wound-induced protein kinase, MPK3, and MPK3a, TIPK is also induced by wounding. Normally, preinoculation of roots with Trichoderma activates plant defense mechanisms, which result in resistance to the leaf pathogen Pseudomonas syringae pv lachrymans. We used a unique attenuated virus vector, Zucchini yellow mosaic virus (ZYMV-AGII), to overexpress TIPK protein and antisense (AS) RNA. Plants overexpressing TIPK were more resistant to pathogenic bacterial attack than control plants, even in the absence of Trichoderma preinoculation. On the other hand, plants expressing TIPK-AS revealed increased sensitivity to pathogen attack. Moreover, Trichoderma preinoculation could not protect these AS plants against subsequent pathogen attack. We therefore demonstrate that Trichoderma exerts its protective effect on plants through activation of the TIPK gene, a MAPK that is involved in signal transduction pathways of defense responses.