Mycoflora and mycotoxins natural occurrence in corn from entre rios province, Argentina

Corn samples were collected in 1999 from three departments of Entre Réos province, Argentina, and were surveyed for mould contamination and natural occurrence ofFusarium mycotoxins, ochratoxin A and aflatoxins.Fusarium verticillioides was the most prevalent fungal species recorded at all departments. Zearalenone, deoxynivalenol and ochratoxin A were not found in any samples. Only one of the 52 corn samples analysed was contaminated with aflatoxin B₁ (17 μg/kg). Fumonisin B₁ was found in 58 % of samples (range of positive samples: 47– 3,347 μg/kg), fumonisin B₂ in 33.0 % (range of positive samples: 23–537 μg/kg) and fumonisin B₃ in 25.0 % (range of positive samples: 24–287 μg/kg) of them. This is the first report on the natural occurrence of mycotoxins in corn from Entre Ríos province, Argentina. Levels of fumonisins were lower than detected in other Argentinian provinces.     

Fungi associated with sorghum grain from Argentina

Sorghum (Sorghum bicolor (L.) Moench) is an important cereal produced in and exported from Argentina. The risk of contamination by mycotoxins is related to the mycoflora associated with the sorghum grain. This paper reports on the identification of internal mycoflora of sorghum grain harvested in Argentina in 1991, 1992 and 1993, years with different total rainfall levels. A mycological survey was carried out on sorghum samples, from a location at the humid Argentinian pampa, using a Fusarium/dematiaceous fungi selective medium. The relative density of the prevalent fungal genera were statistically compared. Genus Fusarium was the most prevalent component of the internal seedborne mycoflora in the three harvest seasons. Genera Alternaria, Phoma, Penicillium and Aspergillus were also isolated. The predominant Fusarium was F. moniliforme and the most frequently isolated species of Alternaria, Phoma, Penicillium and Aspergillus were Alt. alternata, Pho. sorghima, Pen. funiculosum and Asp. flavus, respectively. This is the first report of the isolation of Fusarium napiforme in sorghum grain in Argentina. This revised version was published online in June 2006 with corrections to the Cover Date.     

Potential schistosome-vector snails and associated trematodes in ricefields of Corrients province, Argentina. Preliminary results

Considering the possibility of introduction of schistosomiasis mansoni into Argentina as a consequence of dam construction on the Rio De La Plata basin, preliminary studies have been carried out on agrosystems such as ricefields in Corrientes province with the following purposes: 1) to survey and estimate the relative abundance of planorbids and identify potential vector species; 2) to identify environmental factors capable of influencing Biomphalaria population dynamics; and 3) to find out snail-parasite associations and estimate snail infection rates in order to detect possible competitive interactions between larval stages of native trematodes that could be used in biological control of Schistosoma mansoni. Three potential schistosome vectors were detected in ricefields, namely Biomphalaria straminea, B. tenagophila and B. peregrina, although B. orbignyi, a species refractory to infection with S. mansoni, proved the most frequent and abundant. Positive correlations (P less than 0.05) were found between Biomphalaria abundance and some environmental parameters: conductivity, hardness, calcium, nitrites plus nitrates, ammonium and bicarbonates. Water temperature correlation was negative (P less than 0.05). No correlation (P less than 0.05) was found in total iron, phosphates (SRP), pH and soil granulometry.     

Simple method for isolation of 4-deoxynivalenol from rice inoculated with Fusarium graminearum.

A new method for preparative isolation of 4-deoxynivalenol (DON) is presented. This method avoids the loss of material during purification on silica gel by column chromatography. DON and 3-acetyldeoxynivalenol in crude extracts of rice inoculated with Fusarium graminearum were converted to triacetyldeoxynivalenol; the acetylated product was easier to purify by silica gel chromatography than DON is. After hydrolysis and further purification on a charcoal-alumina column, the 71% pure DON was recovered in yields as high as 450 mg of DON per kg of rice. Subsequent separation on a Sephadex LH20 column yielded DON that was greater than 90% pure.     

Fungi associated with the seedling roots ofAllium porrum L.

Summary Data is provided on the fungi isolated from the roots ofAllium porrum which have been grown in three soils. These data show that the roots support a typical root-surface mycoflora, although this is more sparse than that recorded for several other Angiosperm roots.The results indicate that, as suggested by Peterson³, soil pH influences the association of saprophytic fungi with plant roots. Species of Cylindrocarpon, Fusarium, Mortierella and Gliocladium are fungi which seem to be most affected in this respect.The need for detailed studies on the biology of individual species, which frequently occur in close association with plant roots, is emphasized.     

Assessing non-specificity of resistance in wheat to head blight caused by inoculation with European strains of Fusarium culmorum,F. graminearum and F. nivale using a multiplicative model for interaction

To determine whether resistance to Fusarium head blight in winter wheat is horizontal and non-species specific, 25 genotypes from five European countries were tested at six locations across Europe in the years 1990, 1991, and 1992. The five genotypes from each country had to cover the range from resistant to susceptible. The locations involved were Wageningen, Vienna, Rennes, Hohenheim, Oberer Lindenhof, and Szeged. In total, 17 local strains of Fusarium culmorum, F. graminearum, and F. nivale were used for experimental inoculation. One strain, F. culmorum IPO 39-01, was used at all locations. Best linear unbiased predictions (BLUPs) for the head blight ratings of the genotypes were formed within each particular location for each combination of year and strain. The BLUPs over all locations were collected in a genotype-by environment table in which the genotypic dimension consisted of the 25 genotypes, while the environmental dimension was made up of 59 year-by-strain-by-location combinations. A multiplicative model was fitted to the genotype by-environment interaction in this table. The inverses of the variances of the genotype-by-environment BLUPs were used as weights. Interactions between genotypes and environments were written as sums of products between genotypic scores and environmental scores. After correction for year-by-location influence very little variation in environmental scores could be ascribed to differences between strains. This provided the basis for the conclusion that the resistance to Fusarium head blight in winter wheat was of the horizontal and non-species specific type. There was no indication for any geographical pattern in virulence genes. Any reasonable aggressive strain, a F. culmorum strain for the cool climates and a F. graminearum strain for the warmer humid areas, should be satisfactory for screening purposes.     

Fungi associated with terrestrial orchid mycorrhizas,seeds and protocorms

The identity and ecological role of fungi in the mycorrhizal roots of 25 species of mature terrestrial orchids and in 17 species of field incubated orchid seedlings were examined. Isolates of symbiotic fungi from mature orchid mycorrhizas were basidiomycetes primarily in the generaCeratorhiza, Epulorhiza andMoniliopsis; a few unidentified taxa with clamped hyphae were also recovered. More than one taxon of peloton-forming fungus was often observed in the cleared and stained mycorrhizas. AlthoughCeratorhiza andEpulorhiza strains were isolated from the developing protocorms, pelotons of clamped hyphae were often presents in the cleared protocorms of several orchid species. These basidiomycetes are difficult to isolate and may be symbionts of ectotrophic plants. The higher proportion of endophytes bearing clamp connections in developing seeds than in the mycorrhizas is attributed to differences in the nutritional requirements of the fully mycotrophic protocorms and partially autotrophic plants. Most isolates ofCeratorhiza differed enzymatically fromEpulorhiza in producing polyphenol oxidases. Dual cultures with thirteen orchid isolates and five non-orchid hosts showed that some taxa can form harmless associations with non-orchid hosts. It is suggested that most terrestrial orchid mycorrhizas are relatively non-specific and that the mycobionts can be saprophytes, parasites or mycorrhizal associates of other plants.     

FgVELB is associated with vegetative differentiation, secondary metabolism and virulence in Fusarium graminearum

The velvet complex containing VeA, VelB and LaeA has been showed to play critical roles in the regulation of secondary metabolism and diverse cellular processes in Aspergillus spp. In this study, we identified FgVelB, a homolog of Aspergillus nidulans VelB, from Fusarium graminearum using the BLASTP program. Disruption of FgVELB gene led to several phenotypic defects, including suppression of aerial hyphae formation, reduced hyphal hydrophobicity and highly increased conidiation. The mutant showed increased resistance to osmotic stress and cell wall-damaging agents, which may be related to a high level of glycerol accumulation in the mutant. Additionally, the mutant exhibited increased sensitivity to the phenylpyrrole fungicide fludioxonil. Ultrastructural and histochemical analyses revealed that conidia of FgVELB deletion mutant contained numerous lipid droplets. Pathogenicity assays showed FgVELB deletion mutant was impaired in virulence on flowering wheat head, which is consistent with the observation that FgVelB is involved in the regulation of deoxynivalenol biosynthesis in F. graminearum. All of the defects were restored by genetic complementation of the mutant with wild-type FgVELB gene. Yeast two hybrid assays showed that FgVelB does not interact with FgVeA. Taken together, results of this study indicated that FgVelB plays a critical role in the regulation of various cellular processes in F. graminearum.     

Rodent control at different spatial scales on poultry farms in the province of Buenos Aires,Argentina

In poultry farms of central Argentina rodents cause economic losses by the consumption and contamination of chicken food, and also pose a serious sanitary risk as transmitters of several diseases to human and domestic animals, such as leptospirosis, salmonellosis, trichinosis, hantavirus pulmonary syndrome, hantavirus renal syndrome, and Argentine hemorrhagic fever. Because one of the problems in controlling rodents is recolonization from the surroundings, we wanted to assess the effect of control measures applied at different spatial scales on rodent abundance in farm sheds. The treatments applied were the following: anticoagulant application in farms and their surroundings (F + S), anticoagulant application only within farms (F), and standard management (C). Rodent abundance was assessed previous to treatments (t₀), at the moment of bait removal (t₁), and after 15 (t₂), 30 (t₃), and 60 days (t₄). Differences in rodent abundance between t₀ and t₁, t₂, t_3, and t₄ were compared among treatments by means of a Kruskal Wallis test. We only found significant differences among treatments between t₀ and t₂, where F and F + S treatments showed differences with respect to the C treatment. This result suggests that the effect of control measures was due to the control of the perimeter, and not of farther areas. Also, reproduction of remaining individuals may have contributed to the population recovery in sheds of experimental farms. We conclude that more effective control must include the perimeter of the farm, but the effect of control of more distant areas may depend on the characteristics of the particular farm, its surroundings, and the ecology of the species involved.     

Fungi associated with stored unprocessed cowpea and groundnut varieties available in Borno State, Nigeria.

Five stored unprocessed cowpea (Vigna spp) and four groundnut (Arachis hypogeae) varieties available in Borno State were examined for the mould flora. The degree of infestation of the grains ranged from 31% to 100% and 68% to 86% for surface sterilized cowpea and groundnut respectively. The mould flora commonly encountered were species of the genera Aspergillus. Penicillium species, Scopulariopsis species and Trichoderma species were also found. The flora of the cowpea was dominated by Aspergillus niger while Aspergillus flavus was the dominant mould on groundnut.     

Quantitative trait loci associated with drought tolerance at reproductive stage in rice

Drought is a major constraint to rice (Oryza sativa) yield and its stability in rainfed and poorly irrigated environments. Identifying genomic regions influencing the response of yield and its components to water deficits will aid in our understanding of the genetics of drought tolerance and development of more drought tolerant cultivars. Quantitative trait loci (QTL) for grain yield and its components and other agronomic traits were identified using a subset of 154 doubled haploid lines derived from a cross between two rice cultivars, CT9993-510 to 1-M and IR62266-42 to 6-2. Drought stress treatments were managed by use of a line source sprinkler irrigation system, which provided a linearly decreasing level of irrigation coinciding with the sensitive reproductive growth stages. The research was conducted at the Ubon Rice Research Center, Ubon, Thailand. A total of 77 QTL were identified for grain yield and its components under varying levels of water stress. Out of the total of 77 QTL, the number of QTL per trait were: 7-grain yield (GY); 8-biological yield (BY); 6-harvest index (HI); 5-d to flowering after initiation of irrigation gradient (DFAIG); 10-total spikelet number (TSN); 7-percent spikelet sterility (PSS); 23-panicle number (PN); and 11-plant height (PH). The phenotypic variation explained by individual QTL ranged from 7.5% to 55.7%. Under well-watered conditions, we observed a high genetic association for BY, HI, DFAIG, PSS, TSN, PH, and GY. However, only BY and HI were found to be significantly associated with GY under drought treatments. QTL flanked by markers RG104 to RM231, EMP2_2 to RM127, and G2132 to RZ598 on chromosomes 3, 4, and 8 were associated with GY, HI, DFAIG, BY, PSS, and PN under drought treatments. The aggregate effects of these QTL on chromosomes 3, 4, and 8 resulted in higher grain yield. These QTL will be useful for rainfed rice improvement, and will also contribute to our understanding of the genetic control of GY under drought conditions at the sensitive reproductive stage. Close linkage or pleiotropy may be responsible for the coincidence of QTL detected in this experiment. Digenic interactions between QTL main effects for GY, BY, HI, and PSS were observed under irrigation treatments. Most (but not all) DH lines have the same response in measure of productivity when the intensity of water deficit was increased, but no QTL by irrigation treatment interaction was detected. The identification of genomic regions associated with GY and its components under drought stress will be useful for marker-based approaches to improve GY and its stability for farmers in drought-prone rice environments.     

Fusarium spp. associated with rice Bakanae: ecology,genetic diversity,pathogenicity and toxigenicity

African and Asian populations of Fusarium spp. (Gibberella fujikuroi species complex) associated with Bakanae of rice (Oryzae sativa L.) were isolated from seeds and characterized with respect to ecology, phylogenetics, pathogenicity and mycotoxin production. Independent of the origin, Fusarium spp. were detected in the different rice seed samples with infection rate ranges that varied from 0.25% to 9%. Four Fusaria (F. andiyazi, F. fujikuroi, F. proliferatum and F. verticillioides) were found associated with Bakanae of rice. While three of the Fusaria were found in both African and Asian seed samples, F. fujikuroi was only detected in seed samples from Asia. Phylogenetic studies showed a broad genetic variation among the strains that were distributed into four different genetic clades. Pathogenicity tests showed that all strains reduced seed germination and possessed varying ability to cause symptoms of Bakanae on rice, some species (i.e. F. fujikuroi) being more pathogenic than others. The ability to produce fumonisins (FB₁ and FB₂) and gibberellin A3 in vitro also differed according to the Fusarium species. While fumonisins were produced by most of the strains of F. verticillioides and F. proliferatum, gibberellin A3 was only produced by F. fujikuroi. Neither fumonisin nor gibberellin was synthesized by most of the strains of F. andiyazi. These findings provide new information on the variation within the G. fujikuroi species complex associated with rice seed and Bakanae disease.     

Water deficit and aluminum tolerance are associated with a high antioxidative enzyme capacity in Indica rice seedlings

Plant growth and productivity are greatly affected due to changes in the environmental conditions. In the present investigation, the interactive effects of two important abiotic stresses, i.e., water deficit and Al toxicity, were examined in the seedlings of two rice (Oryza sativa L.) cvs. Malviya-36 (water deficit/Al sensitive) and Vandana (water deficit/Al tolerant). When 15 days grown seedlings were exposed to water deficit (created with 15 % polyethylene glycol 6000) or Al (1 mM AlCl₃) treatment or both the treatments together for 48 h, the lengths of root/shoot, relative water content, and chlorophyll greatly declined in the seedlings of the sensitive cultivar, whereas in the tolerant seedlings, either little or insignificant decline in these parameters was observed due to the treatments. Seedlings subjected to water deficit or Al treatment alone or in combination showed increased intensity of the isoenzyme activity bands of superoxide dismutase (SOD), guaiacol peroxidase (GPX), and ascorbate peroxidase (APX) in in-gel activity staining studies. Water deficit caused decrease in intensity of catalase (CAT) activity bands; however, when seedlings were exposed to AlCl₃ alone or in combination with water deficit, the intensity of the CAT isoforms increased in both the rice cultivars. The level of expression of the activity bands of SOD, CAT, GPX, and APX was always higher in the seedlings of tolerant cv. Vandana compared to the sensitive cv. Malviya-36 under both controls as well as stress treatments. Higher intensity of isozymes representing higher activity levels of antioxidative enzymes in the rice seedlings and their further increase under water deficit, Al exposure, or in combination of both the stresses appears to serve as useful marker for specifying a combination of water deficit and Al tolerance in rice.     

Trajectories associated to regional and extra-regional pollen transport in the southeast of Buenos Aires province, Mar del Plata (Argentina)

Long range transport of airborne pollen has been seldom studied in South America. Backward trajectories of Celtis and Nothofagus pollen grains trapped over a meteorological station outside Mar del Plata City were calculated in one-hour steps using the regional hybrid model developed by the NOAA (HYSPLIT 4.5) and the data of the NCEP filed in the NOAA server. Results showed that the observed trajectories agree with the location of vegetation sources of the collected tree species. In the case of Celtis, the transport was associated to anticyclones located east of the city, generating winds with a N-NE component, which produce pollen cloud advection from the Celtis forests located some tens of kilometers to the N and NE of the city. The sources of Nothofagus pollen correspond to a narrow strip on the Andes slopes between 39° and 55°S, at least 1100 km to the SW of Mar del Plata. The transport was associated to eastward displacement of the troughs corresponding to the Westerlies circulation and the presence of an anticyclone system that brings back Nothofagus pollen towards Mar del Plata area.     

Fungi associated with black pepper plants in Quang Tri province (Vietnam), and interaction between Meloidogyne incognita and Fusarium solani

During a survey of nurseries and plantations of black pepper plants in Quang Tri province in Vietnam during the rainy season of 2007, nine fungal taxa were isolated from the roots of the black pepper plants. Fusarium solani was found in about one out of four black pepper root samples examined but not in the nurseries and also not from black pepper plants younger than five years growing in plantations. Since in these nurseries about one out of two black pepper plants examined had yellow leaves, this observation suggests that another pathogen must be the initial cause of the yellowing of the leaves. A likely pathogenic candidate is M. incognita which was extracted from every single black pepper plant examined in the nurseries. During the same survey, we also observed that F. solani was not isolated from the roots of black pepper plants that did not had yellow leaves and that the percentage of black pepper plants with yellow leaves increased with increased frequency of occurrence of F. solani. This observation indicates that F. solani plays a role in the yellowing of the leaves of black pepper plants in a later stage of the development of the plants. The results of a greenhouse experiment showed the negative effects inoculation with M. incognita alone or in combination with F. solani may have on the percentage of black pepper plants with yellow leaves and on plant growth. No effect of inoculation with F. solani before, at the same time, or two weeks after inoculation with M. incognita on root galling and nematode reproduction was observed.     

ROP18 and ROP5 alleles combinations are related with virulence of T. gondii isolates from Argentina

The allelic combination of ROP18/ROP5 genes of Toxoplasma gondii has been shown to be highly predictive of mouse virulence in canonical isolates and strains. The aims of this study were to analyze the alleles present in the ROP18/ROP5 genes from T. gondii isolates obtained in Argentina, to associate the results with the virulence registered in mouse model, and to compare with other isolates and reference strains using a phylogenetic network. Fourteen T. gondii isolates from Argentina were analyzed by nPCR-RFLP for ROP18/ROP5. Phylogenetic network analysis was inferred using the ToxoDB genotypes and the ROPs molecular markers. All isolates and reference strains were categorized as lethal or non-lethal. As results, combinations 2/2, 3/3 and 4/3 for ROP18/ROP5 were detected in 12 isolates, whereas only alleles 1 and 2 of ROP5 were detected in 2 isolates. The majority of the isolates had a mouse virulence matching to that predicted by the ROP18/ROP5 allele combination. The 3 isolates that differed from the expected virulence presented non-clonal genotypes. ROPs incorporation increased the accuracy of the phylogenetic network relations among the T. gondii samples, prevailing the clustering according to regions. Our results indicate a predominance of type 3 allele in both ROP18 and ROP5 markers and an association of allelic profiles 3/3 and 4/3 of non-clonal genotypes from Argentina, both with virulent and avirulent profiles in mice.     

Mites (Acari: Laelapidae) associated with sigmodontinae rodents in Entre Ríos Province, Argentina.

The richness, diversity, abundance and prevalence of mite species associated with sigmodontine rodents of different species in Entre Ríos province, Argentina are studied. Five of the six species of mites were reported for the first time in the study area. The richness and diversity of mites was higher on Oligoryzomys flavescens and O. delticola than on Akodon azarae. Androlaelaps rotundus was dominant and exhibited higher values of mean abundance and prevalence on A. azarae, Mysolaelaps microspinosus on O. flavescens and Gigantolaelaps mattogrossensis on O. delticola.     

Polymorphism at the esterase isozyme locus Est10 associated with phylogenetic differentiation in rice

A new esterase isozyme locus, Est10, with 6 alleles including the null form, has been found in rice by using polyacrylamide gel electrophoresis. Thirty F(2) populations of all possible combinations between 5 different band morphs were studied. The segregation pattern indicated that bands 1, 2, 3, 4, and the null form (0) were allelic with each other. The alleles of Est10 were distributed at different frequencies among different varietal groups of rice and also between cultivated rice and its wild relatives (Oryza rufipogon Griff.). Alleles 1 and 2 were frequently found in Japonica and Indica types, respectively. Allele 3 showed a high frequency in Aus and Boro, both Indica types cultivated in South Asia. Allele 4 was frequent in wild rice O. rufipogon. Judging from the linkage between Est10 and RFLP marker RG220 and isozyme marker Est5, Est10 is located on chromosome 1. The importance of this locus in evolutionary studies of rice is discussed.