Silvina Larrán

Isolation and analysis of endophytic microorganisms in wheat (Triticum aestivum L.) leaves

The present investigation was undertaken in order to select the surface-sterilization technique most efficient for eliminating epiphytes, to document the spectrum of endophytes of healthy leaves from three wheat cultivars in Buenos Aires Province (Argentina) and to determine their infection frequencies at three growth stages. Surface-sterilization with undiluted commercial solution of sodium hypochlorite was reaffirmed as adequate for removing epiphytes on wheat leaves. From the 450 wheat leaf segments incubated, three bacterial isolates and 130 fungal isolates were obtained. From all the isolates, 19 fungal species were identified. Bacterial isolates were characterized as Bacillus sp. There were significant differences between microorganisms, stages of growth, and stages × microorganisms interaction. Differences between cultivars, stages × cultivars, microorganisms × cultivars and for the triple interaction were not significant. Frequency of microorganisms isolated increased with crop age, but it was statistically similar for the three wheat cultivars tested (Klein Centauro, Klein Dragón and Buck Ombú). Rhodotorula rubra, Alternaria alternata, Cladosporium herbarum and Epicoccum nigrum were isolated in the highest frequency. The other microorganisms were present at intermediate or low values. The species isolated may be assigned to three groups: (a) well-known and economically important pathogens of wheat, (b) commonly abundant phylloplane fungi considered to be primary saprobic and minor pathogens and (c) species occasionally present in wheat.

In Vitro Fungistatic Effect of Essential Oils Against Ascosphaera apis

Abstract Different essential oils were tested against the fungus Ascosphaera apis, the causal agent of Chalkbrood Disease of honey bees. Essential oils from lavandin (Lavandula x intermedia Emeric ex Loiseleur), coriander (Coriandrum sativum L.), laurel leaf (Laurus nobilis L.), false camphor (Cinnamomum glandulifera Nees), basil (Ocimum basilicum L.), tagetes (Tagetes minuta L.), rosemary (Rosmarinus officinalis L.) and eucalyptus (Eucalyptus globulus Labill.) were assayed to prove their fungistatic activity at different concentrations: 700, 800 and 900 μ.L/L. Strains of Ascosphaera apis were collected from apiaries of different places of Buenos Aires province (Argentina). At all concentrations tested, coriander oil was the most effective fungistatic control while basil and tagetes oils were effective only at 800 μL/L. No differences in effectiveness of oils were observed against the different strains of Ascosphaera apis.

Biological control of Botrytis cinerea on tomato using naturally occurring fungal antagonists

Abstract In order to evaluate the potential of naturally occurring filamentous fungi having potential as biocontrol agents effective against grey mould and post-harvest fruit rot caused by Botrytis cinerea on tomato, fungal saprophytes were isolated. They were obtained from leaves, fruits and flowers belonging to different species of cultivated and spontaneous Solanaceous plants collected at the horticultural area of La Plata, Argentina. Of 300 isolates screened for inhibition of B. cinerea using the dual culture technique on agar plate, 12 strains inhibited strongly mycelial growth of the pathogen. Among the antagonists one isolate of Epicoccun nigrum (126), four of Trichoderma harzianum (110, 118, 248 and 252) and four isolates of Fusarium spp. decreased the spore germination of B. cinerea between 30 and 70%. These isolates were probed on tomato fruits to evaluate their biocontrol activity against post-harvest grey mould. In growth chamber tests, E. nigrum (27), F. equiseti (22, 105) and T. harzianum (118, 252) reduced the diameter of fruit lesions by 50 – 90% and were selected for further biocontrol assays of tomato plants in the greenhouse. Although there were not significant differences between the treatments and the control, F. equiseti (105), E. nigrum (27) and T. harzianum (118) reduced by 20, 22 and 22 respectively the disease on whole plants. The targeted application of isolates of E. nigrum, T. harzianum and F. equiseti provides a promising alternative to the use of fungicide spray to control B. cinerea on tomatoes.

First report of Peronospora parasitica on rocket (Eruca sativa) in Argentina.

In the autumn and winter of 2005 severe attacks by a foliar disease were observed on rocket (Eruca sativa) in a commercial greenhouse in La Plata, Buenos Aires, Argentina. The disease affected newly expanded leaves of plants 15–20 days old. The etiology of the disease was investigated. The disease was identified as downy mildew caused by Peronospora parasitica. Pathogenicity was confirmed by pressing one adaxial infected leaf with abundant sporulation onto one adaxial healthy leaf. Downy mildew developed on inoculated plants after 8 days and the pathogen morphology matched that of the originally identified pathogen. In the same field, symptoms of downy mildew caused by P. farinosa were observed on swiss chard (Beta vulgaris var. cicla). The pathogenicity of this fungus on rocket was confirmed. This is the first report of downy mildew on rocket caused by Peronospora parasitica in Argentina.

Biological control of leaf grey mould of greenhouse tomatoes caused by Botrytis cinerea

Botrytis cinerea (grey mould) is one of the most common diseases of glasshouse crops and is a major cause of plant death in long-season tomato production. A disease management field trial was conducted in a commercial tomato production greenhouse for comparison of seven fungal antagonists which had previously exhibited potential as biological control agents with respect to Botrytis cinerea incidence and severity. Isolates of Trichoderma harzianum, Candida pelliculosa, Rhodotorula rubra, and Fusarium semitectum were recovered from leaves, fruits and flowers of different solanaceous plants. The fungal antagonists were tested for their control of leaf grey mould on tomato under greenhouse conditions during 2008 and 2009. In both years, foliar spray with strains of Trichoderma harzianum and Fusarium semitectum suppressed the foliar infection of B. cinerea. The suspensions of T. harzianum 118 and 252 and F. semitectum 25 significantly reduced disease incidence (65–95%) and severity (50–77%) in inoculated plants compared to untreated controls (P ≤ 0.05). Our results suggest that formulations of saprophytic fungi selected from the naturally occurring mycoflora could be an effective tool in the biological control of tomato grey mould.

First report of Colletotrichum gloeosporioides causing anthracnose on Blepharocalyx salicifolius in Argentina

Anthracnose symptoms were observed on Blepharocalyx salicifolius from Entre Ríos and Buenos Aires provinces, Eastern Argentina. Colletotrichum gloeosporioides sensu lato (teleomorph Glomerella cingulata) was identified as the causal agent based on disease symptoms, the morphological characteristics of the isolated fungus and pathogenicity tests. To our knowledge, this is the first report of C. gloeosporioides causing leaf spot on Blepharocalyx salicifolius.

Grey mould of the globe artichoke in Argentina

During the growing season 2000–2001, symptoms of rot and brown to black mummified buds were observed on artichoke plants cultivated in Arana, Buenos Aires, Argentina, an area of intensive horticulture production. The present study was undertaken in order to determine the aetiology of the disease. The fungus isolated was identified as Botrytis cinerea. Pathogenicity was confirmed by inoculating buds of globe artichoke plants and cut buds with a spore suspension. Inoculated plants and cut buds developed symptoms and spores characteristic of grey mould. B. cinerea was re-isolated from inoculated buds. This work confirms the presence the grey mould, caused by Botrytis cinerea, on artichoke in Argentina.

Weather Conditions Associated with the Release and Dispersal of Zymoseptoria tritici Spores in the Argentine Pampas Region

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.

First report of Alternaria alternata causing black spot on pink lapacho (Handroanthus impetiginosus)

A severe leaf spot disease was observed on pink lapacho trees, Handroanthus impetiginosus for the first time in Buenos Aires province, Argentina during the autumn of 2013. The pathogen was identified as Alternaria alternata based on the morphological characteristics and sequence data from the internal transcribed spacer region of ribosomal DNA, and partial β-tubulin sequence. A pathogenicity test was performed and Koch’s postulates were confirmed by re-isolating the fungus from artificially inoculated leaves. This is the first report of Alternaria black spot of Handroanthus impetiginosus trees.