Pyricularia oryzae pathotype Triticum (PoT) causes Wheat Blast, a devastating crop disease present in many wheat-producing countries. With the aim to contribute with the understanding of the mechanisms underlying pathogenesis of the fungus on wheat (Triticum aestivum), cytological and molecular studies were performed here. Susceptible and resistant interactions of wheat-PoT in cultivars of different levels of resistance were investigated by cellular changes and the molecular responses of wheat leaves according PR-1 expression. There was significant difference between susceptible (Apogee-PY15-PY34, Buck, MSINTA-PY15) and resistant (Buck-PY34, MSINTA-PY34) interactions in the responses tested. The two isolates of PoT analysed showed different ability to infect wheat plants at the cellular level during early tissue penetration analysed and documented by epifluorescence microscopy, patterns of PR-1 genes, and wheat plant defense reaction. Microscopic time-course analysis (24, 48, 72 and 96 h after inoculation) of individual interaction sites per leaf revealed different leaf invasion strategies of the more and less aggressive PoT isolates during the first stages of the course of pathogenesis. The results and conclusions of the present study provides the first evidence that different PR-1 spatial and temporal expression patterns occur in the early infective process of wheat-PoT, underlying two different defence mechanisms in plants according susceptible or resistant interactions. Thus, the results here laid a theoretical foundation for the future control of wheat blast using the different pattern of PR-1 gene as markers for disease resistance during the first stages of infection providing a significant contribution to a more efficient selection of wheat genotypes in breeding studies.

Grapevine (Vitis vinifera) is a key crop in Mediterranean agriculture, now increasingly threatened by Xylella fastidiosa subsp. Fastidiosa (Xff), the causal agent of Pierce’s disease. This study investigated: (1) the diversity of culturable fungal endophytes in the xylem sap of naturally Xff-infected grapevines, and (2) the interaction between Xff and the pathogenic fungus Sclerotinia sclerotiorum identified in the sap. The xylem sap was collected from Cabernet Sauvignon vines in Mallorca, Spain, and fungal communities were characterized using culture-dependent methods. Both beneficial fungi (e.g., Aureobasidium pullulans, Rhodotorula mucilaginosa) and pathogenic species (e.g., S. sclerotiorum, Cladosporium sp., Alternaria alternata, and the Phoma complex) were isolated from both Xff-positive and Xff-negative plants, indicating similar community profiles. Although limited by small sample size, these findings offer preliminary evidence of complex ecological interactions between Xff and the xylem-associated mycobiota, with potential implications for grapevine health and disease development under varying environmental and management conditions. Further experiments under controlled conditions revealed that grapevines co-inoculated with Xff and S. sclerotiorum showed increased disease severity, suggesting a synergistic interaction. These preliminary results highlight the complex interplay between Xff and the fungal endophytic microbiome, which may modulate grapevine susceptibility depending on environmental and management conditions.

In 2021, grapevines (Vitis vinifera L.) cv. Callet growing in a commercial vineyard located at Pollença (northeast of the island of Majorca, Spain) showed severe symptoms of shoot blight during spring and early summer, with an incidence of 70%. Symptoms consisted of elongated cankered-like lesions, surrounded by water-soaked darker tissues, that developed at the base or around the middle nodes of the shoot. For fungal isolation, shoot samples with lesions were collected, surface disinfected with 2% NaCl for 90s, rinsed twice with deionized water and placed in Petri plates containing potato dextrose agar (PDA). The plates were incubated at 25°C under 12 h light-darkness for 6 days. Isolations consistently yielded on kind of fungal colonies that produced white mycelium and black spherical to elongated sclerotia (2 to 10 mm in diameter). Morphological characterization was consistent with the description of Sclerotinia sclerotiorum (Lib.) de Bary (Bolton et al. 2006). Three isolates (UIB 118-1, UIB 118-26, and UIB 129-41) were preserved and deposited in the Culture Collection of Microbiology-Faculty of Sciences, University of Balearic Islands, Spain. Genomic DNA was extracted from isolates UIB 118-26 and UIB 129-41 using the EZNA Miniprep Kit (Omega Bio-Tek, Norcross, GA). The internal transcribed spacer (ITS) region of ribosomal DNA, β-tubulin (BTUB) and calmodulin (CAL) gene regions were amplified using ITS1F-ITS4 (Gardes and Bruns, 1996; White et al. 1990), Bt-2a/Bt-2b (Glass and Donaldson 1995) and CAL228F/CAL737R (Carbone and Kohn 1999) primer sets, respectively. Amplicons were sequenced and deposited in GenBank with accession numbers MZ604647 and MZ604648 for ITS, OK634402 and OK634403 for BTUB and OK634404 and OK634405 for CAL. BLASTn search showed that isolates were >99 % (ITS, BTUB and CAL) identical to S. sclerotiorum GenBank accession no. KF859933, CP017815 and KF871381, respectively. Pathogenicity tests were conducted using eight one-year old grapevines cv. Cabernet Sauvignon. Old and new green shoots were inoculated by inserting a 6-mm plug of mycelium taken from actively growing cultures on PDA into cuts made at the base and at the distal part of each shoot with a sterile scalpel with a total of eight inoculation points per plant. Inoculated wounds were sealed with Parafilm tape to avoid rapid dehydration. Inoculated plants and an equal number of wounded but non-inoculated plants (negative controls) were maintained at 25 ± 1°C for 48 h in plastic containers to ensure a high relative humidity (>90%). After 5 days, the infection girdled and rotted the green new shoots, whereas the older partially lignified shoots developed a localized long brown lesion that reached 16 cm in length. Due to the rotting of the basal part of the petiole, leaves turned gray, wilted, and died, easily detaching from the stem. In advanced stages of the disease, 7 days after infection, branches died and fell with the leaves remained attached (Fig 1 A, B). Reisolations from diseased shoots were successfully performed on PDA to fulfill Koch's postulates. S. slerotiorum was previously reported on grapevine causing shoot blight in Chile (Latorre and Guerrero, 2001), Korea (Jong-Han et al. 2009), California-USA (Boland and Hall, 1994) and Australia (Hall et al. 2002). AlsoS. sclerotiorum was reported among the endophytic mycobiota associated with Vitis vinifera in the Iberian Peninsula (Gonzalez and Tello, 2011) but not as a pathogen causing visible symptoms on that crop. So, this is the first report of the occurrence of S. slerotiorum as a pathogen of grapevines in Spain causing symptoms of canker and shoot blight. This finding highlights a potential risk of this fungal disease for the wine industry in the Mediterranean region and specially for Spain, the country with the largest acreage devoted to grapevines. Although chemical and biological are suitable control strategies, disease management is difficult as sclerotia of Sclerotinia can remain in the soil for up to eight years (Adams and Ayears, 1979), and preventive surveys are greatly recommended as an important epidemiological tool to monitor the epidemiology of disease and identify potential outbreaks of this new pathogen on grapevine in Spain.

Charcoal rot, caused by Macrophomina phaseolina (Tassi) Goid., is one of the world's most serious diseases because it reduces yield and seed quality. Nowadays, biological control is an environment-friendly option for controlling plant diseases. The goals of this study were to (i) test eight endophytic Trichoderma spp. strains as biocontrol agents against M. phaseolina and (ii) further investigate two selected strains showing good behaviour against the pathogen. Pathogen-antagonist interactions were studied in dual culture, and the morphological alterations of M. phaseolina mycelia in the interaction zone were examined by light microscopy. Trichoderma strains were applied to soya bean seeds by a seed coating technique. Their bioprotective effects were assessed by in vitro and in vivo assays to evaluate radicle length, the germination percentage and the presence of typical charcoal rot symptoms in seedlings. Two Trichoderma strains were selected and they were molecularly identified as T. harzianum species complex. Their antagonistic ability against M. phaseolina was evaluated under different water availability conditions. The mechanisms used by these two endophytic strains against the pathogen were evaluated by cryo-scanning electron microscopy. The results showed that all eight Trichoderma strains successfully performed biocontrol activity against M. phaseolina by reducing colony growth and causing morphological alterations in the mycelia of M. phaseolina. All endophytes improved seed germination and radicle length, and reduced typical symptoms and disease progression on seedlings. Water availability in the medium impacted on fungal growth. At 0.995 ɑw, all the fungi grew more and faster. At 0.95 ɑw M. phaseolina grew more than the Trichoderma strains, while the pathogen grew slightly more at 0.98 ɑw than the Trichoderma strains. However, both selected Trichoderma strains grew larger and faster than the pathogen at 0.995 ɑw. The mechanisms involved in pathogen control revealed by the light and cryo-scanning microscopy studies included competition for nutrients or space and direct mycoparasitism. All the endophytic Trichoderma strains were antagonistic against M. phaseolina, however our study allowed us to select two Trichoderma strains with good potential to be included for charcoal rot management.

Los hongos xilófagos atacan frecuentemente ejemplares del arbolado urbano descomponiendo su madera. Esto afecta negativamente la estabilidad y resistencia al quiebre, poniendo en riesgo a la población y sus bienes. Durante un relevamiento de las pudriciones presentes en el arbolado de la ciudad de La Plata, fueron observados ejemplares de Melia azedarach (Meliaceae) con evidencias de pudrición blanca en duramen expuesto. El objetivo del trabajo fue identificar al hongo responsable de esta pudrición y analizar las alteraciones anatómicas y químicas que causa en el leño. Se examinaron muestras de duramen con evidencias de pudrición blanca en estadios intermedio y avanzado extraídas de fuste y rama, respectivamente. Los aislamientos fúngicos fueron obtenidos de secciones de madera sembradas en agar malta con antibiótico y fungicida. La identificación fue llevada a cabo a partir de las características de las colonias y confirmada mediante técnicas moleculares. Los estudios anatómicos fueron realizados con microscopios estereoscópico, óptico y electrónico de barrido, y los análisis químicos mediante química húmeda y espectroscopía infrarroja transformada de Fourier (FT-IR). Phlebia brevispora (Basidiomycota, Polyporales) fue la única especie xilófaga aislada del material. Las alteraciones anatómicas registradas permitieron diagnosticar pudrición blanca simultánea en fuste y coexistencia de pudrición blanca simultánea y selectiva en rama. Mediante química húmeda fueron determinados incrementos relativos en el tenor de lignina y extraíbles lipofílicos, y disminuciones en el porcentaje de los extraíbles hidrofílicos en las muestras de ambos estadios de degradación (rama y fuste); la disminución del tenor de celulosa sólo fue identificada en rama. El FT-IR reveló el ataque a la celulosa y la lignina. Si bien existe información previa de la presencia P. brevispora en árboles en pie, el presente hallazgo constituye el primer registro para la Argentina, mientras que la interacción P. brevispora - Melia azedarach es reportada por primera vez en esta contribución.

Wheat blast caused by Magnaporthe oryzae pathotype Triticum (MoT), initially restricted to South America, is a global threat for wheat after spreading to Asia in 2016 by the introduction of contaminated seeds, raising the question about transmission of the pathogen from seeds to seedlings, a process so far not well understood. We therefore studied the relationship between seed infection and disease symptoms on seedlings and adult plants. To accomplish this objective, we inoculated spikes of wheat cv. Apogee with a transgenic isolate (MoT-DsRed, with the addition of being resistant to hygromycin). We identified MoT-DsRed in experiments using hygromycin resistance for selection or by observation of DsRed fluorescence. The seeds from infected plants looked either apparently healthy or shrivelled. To evaluate the transmission, two experimental designs were chosen (blotter test and greenhouse) and MoT-DsRed was recovered from both. This revealed that MoT is able to colonize wheat seedlings from infected seeds under the ground. The favourable conditions of temperature and humidity allowed a high recovery rate of MoT from wheat shoots when grown in artificial media. Around 42 days after germination of infected seeds, MoT-DsRed could not be reisolated, indicating that fungal progression, at this time point, did not proceed systemically/endophytically. We hypothesize that spike infection might occur via spore dispersal from infected leaves rather than within the plant. Because MoT-DsRed was not only successfully reisolated from seed coats and germinating seeds with symptoms, but also from apparently healthy seeds, urgent attention is needed to minimize the risks of inadvertent dispersal of inoculum.

Fil: Uranga, Juan Pablo. Consejo Nacional de Investigaciones Cientificas y Tecnicas. Centro Cientifico Tecnologico Conicet - La Plata; Argentina. Universidad Nacional de La Plata. Facultad de Ciencias Agrarias y Forestales. Catedra de Cerealicultura; Argentina

An endophytic fungus isolated from healthy wheat seeds cultivar Klein Yarara in Buenos Aires Province, Argentina, was initially identified as belonging to the Fusarium fujikuroi species complex based on morphological and cultural characteristics. The fungus role in pathogenicity was investigated by artificial inoculation of wheat seeds. Symptoms evaluated 7 and 14 days after inoculation showed that the fungus was pathogenic on seed and seedlings causing symptoms as seed decay, seedling blight and seed rot. The fungus was re-isolated to fulfill Koch's Postulates and was identified as F. sudanense (strain LBEA 3100), a new species recorded in Argentina. The fungal identity was corroborated using molecular techniques by sequencing the ITS region, D1/D2 domains of the LSU gene and TEF-1 alpha region and by comparison with international databases. Ecophysiological studies of F. sudanense (LBEA 3100) performed at different water activities and temperatures showed faster growth rate at the highest water activity and 25 degrees C. This is the first report of F. sudanense, isolated from healthy wheat seeds, causing typical symptoms of seedling blight and seed rot on wheat. (C) 2018 The Authors. Production and hosting by Elsevier B.V. on behalf of King Saud University.

Fusarium sudanense is a novel fungus recently isolated from asymptomatic samples of wheat grains in Argentina. The fungus caused symptoms of seedling blight and seed rot on wheat after artificial inoculations. It is known that the production of mycotoxins by pathogens belonging to the Fusarium genus is harmful to human and animal health. Moreover, the warm and humid conditions that are favorable for growth and mycotoxin production of these species put the Argentinian wheat production area at a high risk of mycotoxin contamination with this novel pathogen. The aim of this work was to evaluate the antagonistic effect of Trichoderma harzianum against F. sudanense under in vitro tests at different environmental conditions. Fungi were screened in dual culture at different water activities (αw) (0.995, 0.98, 0.95, and 0.90) and temperatures (25 and 15 °C). The growth rate of the fungi, interaction types, and dominance index were evaluated. Also, the interaction between T. harzianum and F. sudanense was examined by light and cryo-scanning microscopy. T. harzianum suppressed the growth of F. sudanense at 0.995, 0.98, and 0.95 αw at 25 °C and 0.995 and 0.98 αw at 15 °C. Macroscopic study revealed different interaction types between F. sudanense and T. harzianum on dual culture. Dominance on contact where the colonies of T. harzianum overgrew the pathogen was the most common interaction type determined. The competitive capacity of T. harzianum was diminished by decreasing the temperature and αw. At 0.95 αw and 15 °C, both fungi grew slowly, and interaction type "A" was assigned. Microscopic analysis from the interaction zone of dual cultures revealed an attachment of T. harzianum to the F. sudanense hyphae, penetration with or without formation of appressorium-like structures, coiling, plasmolysis, and a veil formation. According to our results, T. harzianum demonstrated capability to antagonize F. sudanense and could be a promising biocontrol agent.

Wheat blast, caused by the fungal pathogen Magnaporthe oryzae pathotype Triticum, is a serious threat to wheat production, causing losses that can vary from meagre to almost 100%. The disease can attack all aboveground parts of the plant; however, severe spike infection can be observed with very little infection on the leaves or culms. The blast pathogen attacks the base or upper part of the rachis affecting spike formation that makes the spike partial or completely bleached or sterile resulting in shrivelled or no grains. Potential sources of primary inoculum for disease development are the infected wheat seeds, crop residues and infected wheat stubble, and conidia from grass species other than wheat where the fungus overwinters. Other steps in the disease cycle are still not very well known. Moreover, limited data are available on the environmental determinants for optimal wheat blast infection. Nowadays, it is known that the intensity of the damage caused by wheat blast is directly proportional to the level of rainfall during the heading stage of wheat. A combination of high temperatures, excessive rain and long and frequent leaf wetness has favoured the occurrence of this disease. These factors must be taken into account when establishing a system to predict the intensity of the disease in a certain area of cultivation.

The fungus Pyrenophora teres causing disease symptoms similar to P. tritici-repentis was recently detected on wheat in Argentina. After confirmation by molecular studies the pathogen was identified as P. teres f. maculata , part of a complex of leaf spots that affect wheat and other cereal crops. The objective of this work was to characterize the virulence and identify QTL conferring resistance to two isolates of P. teres f. maculata ( Ptm ) in a collection of 110 spring wheat genotypes previously assembled for association mapping and genotyped with 2836 DArT markers. Two isolates of Ptm (PT2047 and PT2050) were used in field experiments. To find marker-trait associations (MTAs) a mixed linear model implemented in TASSEL 5.1 software was used. Considerable phenotypic variation in disease severity was observed at the seedling and adult stages, and some accessions were resistant to both isolates over 2 years. Twelve MTAs identified with nine markers were significantly associated with resistance. The nine markers were distributed over seven chromosomal regions on 6 of the 21 wheat chromosomes. These QTL were novel since this is the first study to identify genomic regions associated with resistance to Ptm in wheat. Wheat genotypes with moderate to high levels of resistance to P. teres f. maculata were identified and will be useful in breeding programs.

La mancha amarilla producida por Pyrenophora tritici-repentis es una de las enfermedades mas importantes que afectan al trigo (Carmona et al., 1999). El hongo Pyrenophora teres causa la mancha en red de la cebada, pero algunos trabajos concluyen que tambien puede atacar trigo causando sintomas similares a los producidos por P. tritici-repentis (Mikhailova et al., 2010; Toth et al. 2007). El objetivo de este trabajo fue determinar variabilidad genetica para resistencia a ambos patogenos y localizar molecularmente los factores geneticos determinantes de la resistencia frente a estos patogenos. En 2014 y 2015 en la EEJH, FCAyF (UNLP) se inocularon con aislados novedosos, dos de P. tritici-repentis (LH y G) y dos aislados de P. teres (Pt1 y Pt2) a una poblacion de 110 genotipos de trigos. Se evaluo severidad en plantula (EC 14) y en estado adulto (EC 49). Se realizo un ANVA y test LSD (P=0,05). La poblacion de trigos fue genotipada utilizando 2132 marcadores DArT. Se realizo un mapeo asociativo utilizando el modelo linear general (GLM) y el modelo linear mixto (MLM). Se consideraron como significativos solo aquellos marcadores con valores de P≤0.05 en los dos modelos y ambientes ensayados. La severidad en plantula en el 2014 oscilo entre 6,5% y 64,8% y en 2015 entre 4,1% y 29,6%. En 2014 la severidad en adulto oscilo entre 19,2% y 100%, y en 2015 entre 27,1% y 100%. Se encontraron 187 asociaciones marcador-caracter, que involucraron 110 marcadores. Los marcadores asociados con resistencia en plantula fueron diferentes a los de resistencia en adulto, indicando una diferente expresion de la resistencia en ambos estadios. En plantula se identificaron 36 asociaciones involucrando 34 marcadores. Se detectaron 23 marcadores asociados con resistencia a P. tritici-repentis en plantula, dos asociados al aislado LH, 19 al G y dos a ambos. Se encontraron 11 marcadores asociados con resistencia en plantula a P. teres, tres a Pt1 y ocho a Pt2. Los 34 marcadores se corresponden con 29 regiones genomicas en los cromosomas 1A (un marcador), 1B (dos), 1D (dos), 2A (dos), 2B (dos), 2D (tres), 3A (cuatro), 3B (cuatro), 5A (cinco), 6A (tres), 6B (uno), 6D (cuatro), 7A (cuatro) and 7D (uno). En el estado adulto se identificaron 151 asociaciones que involucraron 78 marcadores. Se detectaron 50 marcadores asociados con resistencia a P. tritici-repentis, 20 a LH, 12 a G y 18 a ambos. Ademas, 62 marcadores se asociaron con resistencia en estado adulto frente a P. teres, 21 al aislado Pt1, 20 al Pt2 y 21 a ambos. Los 78 marcadores se correspondieron con 64 regiones genomicas diferentes en los cromosomas 1A (cuatro), 1B (tres), 1D (uno), 2A (cinco), 2B (cinco), 2D (seis), 3A (cinco), 3B (ocho), 3D (dos), 4A (uno), 4B (cuatro), 5B (dos), 6A (cuatro), 6B (tres), 6D (uno), 7A (doce) and 7D (cinco). Se observo una importante variabilidad de la resistencia a ambos patogenos en los genotipos utilizados. Se identifico una importante cantidad de marcadores asociados a la resistencia que fueron diferentes para ambos patogenos y estadios de evaluacion.

1 Santa Catalina Phytotechnical Institute, Faculty of Agricultural and Forestry Sciences UNLP Calle 60 y 119 (1900) La Plata, Buenos Aires, Argentina 2 Morphologic Botany, Faculty of Agricultural Sciences National University Lomas de Zamora. Ruta N° 4, km 2 (1836) Llavallol, Buenos Aires, Argentina 3 Phytopathology, CIDEFI, FCAyF-UNLP, CONICET. Calle 60 y 119 (1900) La Plata, Buenos Aires, Argentina

Four wheat cultivars commonly used in Argentina displayed different pattern of reaction depending of the Pyricularia oryzae isolate inoculated, according to the observed lesions and type of reaction both on seedlings and spikes of the plants tested grown under greenhouse conditions. At seedling stage, Buck Meteoro showed a susceptible reaction with seven of the eight isolates tested (phenotypic reaction 3 and 4). On the contrary, Baguette 11 showed a resistant reaction with most of the isolates tested (phenotypic reaction 1 and 2). At heading stage, cultivars Klein Proteo and Baguette 11 showed the greatest susceptibility to P. oryzae (more than 95% severity with isolates ArW22 and ArR1). On the contrary, low disease severity was shown in ACA 303 particularly in combination with isolates ArR3, ArR4, BrW27 and BolW8 with mean values of 2.18%-11.50%. The results indicate variation in aggressiveness among P. oryzae isolates evaluated. A low negative correlation between seedling disease severity and spike disease severity was found. The 1000-grain weight was negatively correlated with spike blast severity. Reduction values induced by each isolates ranged from 18.53% to 74.94%. ACA 303 showed the highest reduction in 1000-grain weight. The lower weight registered, in the most affected genotype ACA 303 infected with ArR2, was of 9.32 g. Protein extractability was higher in Wheat blast (WB) infected grains compared to the control healthy wheat. Protein values increased with the increasing severity of WB infection demonstrating P. oryzae interfered with the grain protein profile, thereby altering the grain protein content and quality. (C) 2018 The Authors. Production and hosting by Elsevier B.V. on behalf of King Saud University.

Pyrenophora tritici-repentis, causal agent of tan spot, is the species commonly associated with leaf spotting symptoms on wheat (Triticum aestivum L.) worldwide and in Argentina. On the other hand, P. teres is a major constraint on barley (Hordeum vulgare L.) production, however the pathogen has not been reported in association with wheat crop in Argentina. In 2018, following a routine survey of wheat fields, leaves showing symptoms compatible with those caused by Pyrenophora spp. were observed in the principal wheat production areas in Buenos Aires and Entre Rios Provinces of Argentina. The disease incidence varied from 30% to 80%. Symptomatic wheat plants were collected from production fields and spotted foliar tissue with symptoms was plated onto PDA 2% growth medium. The isolates were tentatively identified as putative Pyrenophora spp. based on its colonies and conidia characteristics. Given the possibility of confusion by similar characteristics between some Pyrenophora species that infect wheat plants, the aim of this work was to clarify the identity of the fungus infecting this crop. In this study, we were able to confirm field observations in greenhouse assays on wheat plants using the fungal isolates. The seedling symptoms rate under artificial inoculation of five commercial wheat varieties was 100%. Pathogenicity tests and morphological studies as well as analyses indicated that the disease was caused by Pyrenophora teres. Molecular identification of the two isolates was doubled checked by PCR. First, the internal transcribed spacer (ITS) amplification and sequencing and specific PCR assay using PTT and PTM primers allowed to confirm that two monosporic isolates were P. teres f. maculata. This is a novel disease on wheat in Argentina caused by this pathogen. This finding is of great importance from the epidemiological point of view of the biodiversity of the fungus and also to contribute with the future management of the disease.

Plants exposed to combined abiotic and biotic stress conditions may show enhanced pathogen resistance. Biocontrol agents (BCAs) can further contribute to ameliorate plant responses to these complex situations. In recent years, wheat production has been challenged by the expansion of salt-affected soils as well as by severe outbreaks of emerging diseases such as wheat blast. Here, the role of two BCAs, Pseudomonas stutzeri AN10 and Trichoderma harzianum Th56, was examined in salt-stressed seedlings infected with two Pyricularia oryzae isolates of contrasting aggressiveness. BCAs did not enhance plant tolerance to high salt stress. However, BCAs improved performance of salt-stressed wheat plants infected with the less aggressive Pyricularia isolate. The lower infection in salt-stressed BCAs-treated plants could be due to a salt-induced priming state required to trigger an early expression of plant defence genes.

The abundance of Zymoseptoria tritici ascospores and conidia in a field was examined throughout two one-year periods (1998-1999 and 1999-2000) establishing the relationship between spore release and weather variables. Radiation, temperature, intensity of rainfall, and relative humidity significantly affected the dispersal of ascospores and pycnidiospores of this pathogen. Spore traps collected both types of spores, at weekly intervals, at two different stages of the wheat crop (vegetative and wheat stubble stages) and different distances from the sources. Ascospores were the predominant sources of inoculum in the field. The numbers of ascospores and pycnidiospores declined with the increase of distance from the sources. The release of pycnidiospores was associated with the increase in rainfall intensity 7 days before the released event and the increase in radiation 60 days before the same event. Relative humidity 3 and 15 days before the release event was positively correlated with ascospores release and negatively correlated with radiation and temperature in all the sampling interval. Also for the first time, a positive correlation between radiation and pycnidiospores dispersal is reported. Understanding the relationship between environment conditions and spores dispersal event could improve the control strategies of the disease.

Th e eff ect of loose kernel smut fungus Sporisorium cruentum on Sorghum halepense (Johnson grass) was investigated in vitro and in greenhouse experiments. Smut infection induced a decrease in the dry matter of rhizomes and aerial vegetative parts of the plants evaluated. Moreover, the diseased plants showed a lower height than controls. Th e infection resulted in multiple smutted buds that caused small panicles infected with the fungus. In addition, changes were observed in the structural morphology of the host. Leaf tissue sections showed hyphae degrading chloroplasts and vascular bundles colonized by the fungus. Subsequently, cells collapsed and widespread necrosis was observed as a symptom of the disease. Th e pathogen did not colonize the gynoecium of Sorghum plants until the tassel was fully developed. Th e sporulation process of the fungus led to a total disintegration of anthers and tissues. When panicles were inspected before emergence, fungal hyphae were observed on fl oral primord. Histological sections of panicles showed fungal hyphae located in the parenchyma tissue and the nodal area. Infection occurred in the fl oral primordium before the tassel had fully developed and emerged from the fl ag leaf. Grains were replaced by sori surrounded by a thin membrane that usually was broken before or aft er the emergence of the panicle. Th e results, together with the signifi cant decrease of the dry matter of rhizomes and seeds of S. halepense, suggest that S. cruentum could be considered as a potential biocontrol agent in the integrated management of this weed.

Argentina is one of the top 10 world producers and exporters of wheat. In routine surveys of wheat (Triticum aestivum L.) in Buenos Aires Province, Argentina, a new disease was observed in 2012 on seeds of wheat cv. Buck Meteoro. Symptomatic grains (black points) and leaves (chlorosis and spots) were collected during the spring of that year. The objectives of the present study were to identify the causal agent, to investigate its pathogenicity in relation to nine wheat cultivars and to identify the secondary metabolites produced by fungus. Symptomatic grains were plated on potato dextrose agar (PDA). Morphological characterization of colonies and sequencing of the ITS region after DNA extraction identified it as Pseudopithomyces chartarum. For pathogenicity tests, two different isolates, P221 and P224, were inoculated on seedlings of nine wheat cultivars, which showed different disease symptoms, % of grain germination (GG), % of grain discoloration (GD) and % of weak seedlings (WS), suggesting different levels of response against Pseudopithomyces chartarum. Particularly B. Meteoro, Buck Guapo and Klein Proteo cultivars demonstrated major infection tolerance for GD and WS. In contrast, Sy 100 and Klein Pantera were most affected showing weakness, chlorosis, or reduced length of coleoptile, and 50% of necrotic symptoms. Pseudopithomyces chartarum isolates produced secondary metabolites including alternariol, alternariol mono-methyl ether, altertoxin I and altertoxine II. The fungus is a new pathogen of wheat in Argentina that can cause diseases on different cultivars as well as produce mycotoxins.