The fungal pathogen Botrytis cinerea causes severe rots on tomato fruit during storage and shelf life. Biological control of postharvest diseases of fruit may be an effective alternative to chemical control. Yeasts are particularly suitable for postharvest use, proving to be highly effective in reducing the incidence of fungal pathogens. Yeast fungi isolated from the surface of solanaceous plants were evaluated for their activity in reducing the postharvest decay of tomato caused by B. cinerea. Of 300 isolates, 14 strains of Rhodotorula rubra and Candida pelliculosa were found to be strongly antagonistic to the pathogen in vitro and were selected for further storage experiment. The antagonists were evaluated for their effect on the biological control of postharvest grey mould. Artificially wounded fruits were treated by means of a novel technique: small sterile discs of filter paper imbibed separately in suspensions of each yeast and the pathogen were superposed onto each wound. After 1-week, 11 isolates were significantly effective in reducing the diameter of lesions by more than 60% compared to the control treated with B. cinerea alone. Total protection was obtained with the strain 231 of R. rubra on fruits challenged with pathogen spores. To our knowledge, R. rubra and C. pelliculosa have not been described as biocontrol agents against grey mould caused by B. cinerea. Our data demonstrate that the application of antagonistic yeasts represents a promising and environmentally friendly alternative to fungicide treatments to control postharvest grey mould of tomato.

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Species of the genus Trichoderma are economically important as biocontrol agents, serving as a potential alternative to chemical control. The applicability of Trichoderma isolates to different ecozones will depend on the behavior of the strains selected from each zone. The present study was undertaken to isolate biocontrol populations of Trichoderma spp. from the Argentine wheat regions and to select and characterize the best strains of Trichoderma harzianum by means of molecular techniques. A total of 84 out of the 240 strains of Trichoderma were able to reduce the disease severity of the leaf blotch of wheat. Thirty-seven strains were selected for the reduction equal to or greater than 50% of the severity, compared with the control. The percentage values of reduction of the pycnidial coverage ranged between 45 and 80%. The same last strains were confirmed as T. harzianum by polymerase chain reaction amplification of internal transcribed spacers, followed by sequencing. Inter-simple sequence repeat was used to examine the genetic variability among isolates. This resulted in a total of 132 bands. Further numerical analysis revealed 19 haplotypes, grouped in three clusters (I, II, III). Shared strains, with different geographical origins and isolated in different years, were observed within each cluster. The origin of the isolates and the genetic group were partially related. All isolates from Paraná were in cluster I, all isolates from Lobería were in cluster II, and all isolates from Pergamino and Santa Fe were in cluster III. Our results suggest that the 37 native strains of T. harzianum are important in biocontrol programs and could be advantageous for the preparation of biopesticides adapted to the agroecological conditions of wheat culture.

Alternaria spp. are among the major fungal contaminants of wheat grain under postharvest and storage conditions, where A. arborescens was recently detected as a new member of this complex in Argentina causing black point. The aim of this study was to assess the potential of some biorational agents to control A. arborescens and their plant growth promoting of wheat. Seed treatments with spore suspensions of Trichoderma harzianum and Eppicoccum nigrum, extracts from Lippia alba and garlic, sodium bicarbonate, salicylic acid (SA), potassium chloride and dibasic sodium phosphate (SP) were applied to grains of wheat cultivar BIOINTA 1004 before their inoculation with the pathogen. After 7 days, seed germination and infection, necrotic symptoms on emerged seedlings and fresh weight were evaluated. Remarkable results were obtained with L. alba, SA and SP treatments that reduced symptoms markedly compared with the control. Interestingly, necrosis of radicles was significantly reduced by the application of all treatments tested. Moreover, fresh weight of seedlings was significantly increased with the application of the two antagonists, diluted garlic juice and the three tested salts in comparison with controls. Therefore, a positive role as growth promoters can be elucidated. It is concluded that compounds here tested have potential as ecofriendly alternatives to control seed-borne Alternaria fungi of wheat.

Una alternativa al uso indiscriminado de fitosanitarios es la incorporación de microorganismos antagónicos competitivos para la protección de los cultivos de los patógenos habitantes del suelo. En este trabajo se evaluó la potencialidad del establecimiento de Trichoderma harzianum Rifai (cepa Th5cc) en el suelo bajo diferentes formulaciones, con el objeto de conocer cuál es la más efectiva en mantener la población del antagonista a niveles moderados. La población se cuantificó mediante la técnica del suelo diluido en placa utilizando un medio selectivo para Trichoderma. Los resultados muestran que tanto en el formulado líquido como en las semillas recubiertas aumenta la población de Th5cc hasta los 90 días desde que se incorporó el formulado al suelo (1,4 x 104 unidades formadoras de colonia/g de suelo). En contraste, con la aplicación de formulado sólido la población del antagonista comienza a disminuir a los 90 días. En el caso de la incorporación en la semilla, la población de T. harzianum al inicio fue menor a la del testigo, pero a los 60 y 90 días alcanzaron valores mayores a la población original del suelo (testigo). La eficiencia de la aplicación de T. harzianum como antagonista en plantas está estrechamente relacionada con su formulación, la cual tiene una clara influencia en la supervivencia en el suelo.