Pyrenophora tritici repentis, the causal agent of tan spot: a review of intraspecific genetic diversity

In some countries where the wheat is cultivated, the biological adversities are led by foliar disease. These diseases have emerged as a serious problem in many areas where the wheat is the principal crop. In the last few years, minimum tillage has been considered advantageous to soil conservation, but it leads to a loss of available nutrients and a potential increase in necrotic pathogens whose saprophytic stage lives in the straw of the crop (Annone, 1985). Establishment of the crop under this management can be affected by pathogens of this type. Leaf spotting diseases can be caused by one or a combination of leaf spotting pathogens (Table 1). Leaf spotting diseases affect wheat grown reduce the photosynthetic area of leaves resulting in reduced grain filling and lower yields; particularly when the top two leaves (penultimate and flag leaves) are severely infected. The most of these diseases are similar in host symptomatology, disease cycle, life cycles of pathogens and types of damage induced. Whitin of these pathogens the Ascomycota fungus, Pyrenophora tritici-repentis (Ptr) (Died.) Drechs. It is a facultative pathogen whose asexual stage is Drechslera tritici-repentis (Dtr) (Died.). This pathogen is the causal agent of tan spot of wheat

First report of virulence and effects of Magnaporthe oryzae isolates causing wheat blast in Argentina

Our results indicate that M. oryzae has established itself in the principle wheat agroecological region of Buenos Aires, Argentina, and may pose a significant threat to wheat production, and therefore poses a significant threat to wheat production in Argentina.Facultad de Ciencias Agrarias y Forestale

First report of virulence and effects of Magnaporthe oryzae isolates causing wheat blast in Argentina

Our results indicate that M. oryzae has established itself in the principle wheat agroecological region of Buenos Aires, Argentina, and may pose a significant threat to wheat production, and therefore poses a significant threat to wheat production in Argentina.Facultad de Ciencias Agrarias y Forestale

Características morfológícas y patogénicas de aislamientos de Septoria tritici Rob ex Desm

Se analizó el comportamiento cultural y patogénicos de 8 aislamientos de Septoria tritici obtenidos a partir de hojas de trigo colectadas en el campo e infectadas naturalmente. Los diversos aislamientos monospóricos pueden diferenciarse en cultivo artificial por su aspecto, la producción de esporas, la presencia o ausencia de micelio, y el color y la frecuencia de saltaciones observadas en las colonias. Las cepas varían tanto en la abundancia como en el tipo de las esporas producidas bajo condiciones similares. Además de las picnidiosporas de forma y tamaños típicos de la especie, algunas cepas produjeron sólo esporas libres muy pequeñas (microsporas), y otras, macro y mícrosporas dentro des picnidios. Los tipos culturales predominantes de los aislamientos fueron 5: - estromático (mayor frecuencia), - albino pulverulento, - levaduroide, - mixto y - miceliar. Estos tipos culturales, en algunos casos no se mantuvieron estables a través de 3 generaciones de subcultivos. Las inoculaciones efectuadas sobre plantas de trigo en invernáculo, revelaron diferencias altamente significativas en la patogenicidad de ciertas cepas. Se encontró una relacíón entre las características culturales de los aislamientos y la severidad de la enfermedad: los aislamientos de tipo albino y levaduroide fueron los menos virulentos, tanto sobre variedades resistentes como susceptibles. La presente, constitutuye la primer cita de la presencia de esta clase de microsporas de S tritici.This study analyzed the cultural and pathogenic behavior of S tritici isolates from wheat leaves infected and collected in the field. When cultured artificially, monosporic isolates were differenciated in aspect, spore production, presence or absence of mycelium, and in color and frequency of saltation observed in the colonies as shown in table I. The characteristics noted led to the classification of the cultures as mycelial (M), typical (stromatic-pycnidial) (T) (the most frequent), powdery albino (A), yeast-like (Y) and mixed (Mx) (figs 1 and 2). In some cases these cultural types, though pure, did not remain stable after three subculture generations. The variants from the parental type appeared patches or sectorings of the yeast-like and/or the mycelial type. Sometimes these appeared in the first generation, some others in the third generation, with a low frequency of appearance with respect to the parental type. In the greenhouse, inoculation in the form of wheat plants revealed highly significant differences in the pathogenicity of some strains. Correlation of the mean percentages of pycnidial coverage showed a significant difference in isolate pathogenicity levels in the same cultivar and within cultivars (table II). Thus, the existence of physiologic specialization in S tritici is again confirmed. A relationship was found between the isolates’ cultural characteristics and the disease severity: the albino and yeast-like isolates were the least virulent for both the resistant and susceptible cultivars. Under similar conditions the strains varied in spore abundance as in the spore type produced (fig 4). Besides pycnidiospores with shape and size characteristics of the species, some strains produced only very small free spores (microspores), and some others macro and microspores within pycnidia (table III). Microspores produced in vivo were much smaller than those obtained artificially. This is the first report regarding this type of microspore in S tritici

Alternaria infectoria species-group associated with black point of wheat in Argentina

Regional surveys are being conducted in Argentina to assess the presence of wheat (Triticum aestivum) pathogens on grains across the main cropping area. During 2001 and 2002, grain samples with a dark brown or blackish discoloration around the embryo end, known as black point, were observed on several cultivars across the wheat region of Buenos Aires Province.Centro de Investigaciones de Fitopatologí

In vitro efficacy of garlic extract to control fungal pathogens of wheat

In vitro studies were carried out to investigate the inhibitory effect of allicin in garlic juice on hyphal growth and spore germination of Drechslera tritici-repetis, Bipolaris sorokiniana and Septoria tritici. The purpose was to investigate the possibility of developing an organic agriculture compatible garlic/allicin-based management strategy for the wheat fungal spotting complex. Allicin in garlic juice inhibited radial colony growth of all three pathogens on agar plates. Spore germination of all three pathogens was inhibited by allicin in garlic juice in seeded agar plates and in conidial suspensions. At high concentrations of allicin (>80 µg/ml) in garlic juice and pure (synthetic) allicin, conidia lysed. The minimum inhibitory amount of pure synthetic allicin which inhibited spore germination completely ranged between 80-120 µg/ml depending on fungal species. At 10 µg/ml Allicin caused morphological abnormalities in hyphae and conidia of D. tritici-repentis and B. sorokiniana. Allicin-treated hyphae were either collapsed, damaged or thinner when compared with the control. These results suggest that use of garlic juice is a promising, effective and environmentally friendly management measure against fungal pathogens that could be used in the production of an organically grown wheat crop.Facultad de Ciencias Agrarias y Forestale

Alternaria infectoria species-group associated with black point of wheat in Argentina

Regional surveys are being conducted in Argentina to assess the presence of wheat (Triticum aestivum) pathogens on grains across the main cropping area. During 2001 and 2002, grain samples with a dark brown or blackish discoloration around the embryo end, known as black point, were observed on several cultivars across the wheat region of Buenos Aires Province.Centro de Investigaciones de Fitopatologí

Effect of garlic extract on seed germination, seedling health, and vigour of pathogen-infested wheat

The effect of garlic extract containing bioactive allicin on the germination and subsequent seedling vigour of pathogeninfested wheat seeds, was tested. The first aim was to characterize the antifungal activities of garlic extract and pure allicin, on the most frequently occurring wheat pathogens of the Helminthosporium genus (sensu lato) in Argentina. The second aim was to characterize the antifungal activities of garlic extract and pure allicin on moulds belonging to the natural endogenous microflora. Garlic extract showed fungicidal activity on the endogenous fungal contamination of the wheat seeds and particularly reduced the degree of disease caused by Bipolaris sorokiniana and Drechslera tritici-repentis. Allicin in garlic juice corrected the poor germination of wheat seeds caused by natural mycoflora of grain. Growth promoting activities of garlic juice on wheat seedling vigour was reported. Interestingly, the inoculum on naturally infected wheat seeds could be reduced with garlic juice as a seed dressing biofungicide, before sowing. In this study, we demonstrated the efficacy and the high control potential of garlic extract against seed-borne wheat fungi. Such results suggest that using garlic extract can minimise the risk of infection as well as minimise the risk of chemical fungicide exposure. On the basis of these results, scale-up to field trials using garlic extract and allicin as the dressing biofungicide before sowing for disinfection of wheat seeds, seems justified as a sustainable alternative to the use of chemical fungicides.Facultad de Ciencias Agrarias y ForestalesCentro de Investigaciones de Fitopatologí

Effect of garlic extract on seed germination, seedling health, and vigour of pathogen-infested wheat

The effect of garlic extract containing bioactive allicin on the germination and subsequent seedling vigour of pathogeninfested wheat seeds, was tested. The first aim was to characterize the antifungal activities of garlic extract and pure allicin, on the most frequently occurring wheat pathogens of the Helminthosporium genus (sensu lato) in Argentina. The second aim was to characterize the antifungal activities of garlic extract and pure allicin on moulds belonging to the natural endogenous microflora. Garlic extract showed fungicidal activity on the endogenous fungal contamination of the wheat seeds and particularly reduced the degree of disease caused by Bipolaris sorokiniana and Drechslera tritici-repentis. Allicin in garlic juice corrected the poor germination of wheat seeds caused by natural mycoflora of grain. Growth promoting activities of garlic juice on wheat seedling vigour was reported. Interestingly, the inoculum on naturally infected wheat seeds could be reduced with garlic juice as a seed dressing biofungicide, before sowing. In this study, we demonstrated the efficacy and the high control potential of garlic extract against seed-borne wheat fungi. Such results suggest that using garlic extract can minimise the risk of infection as well as minimise the risk of chemical fungicide exposure. On the basis of these results, scale-up to field trials using garlic extract and allicin as the dressing biofungicide before sowing for disinfection of wheat seeds, seems justified as a sustainable alternative to the use of chemical fungicides.Facultad de Ciencias Agrarias y ForestalesCentro de Investigaciones de Fitopatologí

Potenciales agentes de biocontrol de las principales enfermedades de poscosecha del Kiwi en Argentina

El objetivo de este trabajo fue identificar enfermedades del fruto de Kiwi en poscosecha, conocer sus agentes causales y disponer de métodos de control alternativos que minimicen el uso de agroquímicos. El uso de microorganismos antagonistas ofrece una alternativa complementaria de escasos antecedentes y no explorada en Argentina. Se identificaron enfermedades fúngicas a partir de frutos enfermos y se seleccionaron potenciales antagonistas desde la micoflora asociada al filoplano, fruto y suelo del cultivo de kiwi. La capacidad antagónica se evaluó in vitro. Se identificaron como agentes causales de podredumbres a Botrytis cinerea, Alternaria alternata y Pestalotiopsis sp. Los antagonistas seleccionados fueron Epicoccum nigrum y Trichoderma harzianum. Las cepas de T. harzianum presentaron efecto antagónico reduciendo significativamente la expresión de la enfermedad. Existen hongos saprobios que pueden utilizarse en el manejo integrado de enfermedades del kiwi.There is little information about diseases of Kiwi fruit in postharvest. It is necessary to know their causal agents and alternative control methods to minimize the use of agrochemicals. Antagonistic microorganisms offer a complementary alternative to analyze. The objectives of this study were to identify postharvest diseases and select antagonists to be used as biocontrol agents. Microorganisms were isolated from diseased fruits and pathogenicity tests were performed. Potential antagonists were selected from micoflora associated to phyloplane, fruit and soil cultivation. The antagonistic capability was assessed in vitro. Botrytis cinerea, Alternaria alternata, and Pestalotiopsis sp. were identified as causal agents of kiwi rot. Epicoccum nigrum and three strains of Trichoderma harzianum were selected as antagonists to perform biocontrol bioassays under in vitro conditions. T. harzianum strains tested showed antagonistic effect when compared with the controls. This saprophytes fungi could be used into an integrated kiwi diseases management.Eje A1 Sistemas de producción de base agroecológica (Trabajos científicos