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Early blight, caused by Alternaria solani and A. grandis, severely affects potato crops around the world, and few management options apart from intensive fungicide use are available. In this work, we tested whether biocontrol treatments with different species of the mycoparasitic fungus Clonostachys could reduce early blight severity on the foliage of pot‐grown potatoes of cultivar Ágata, and affect the survival and sporulation of the causal pathogen A. grandis. Twenty isolates from five Clonostachys species were screened in a preliminary biocontrol trial, and nine of them were selected and tested further in two confirmation trials. Treatments with three isolates from three species (C. chloroleuca, C. pseudochroleuca, C. rhizophaga) resulted in a significant reduction in disease severity in both confirmation trials, with control efficacy ranging from 88.7% to 92.9% in the first trial, and from 83.1% to 84.7% in the second trial. All Clonostachys isolates used in the confirmation trials survived on potato leaf tissues for at least 15 days, and resumed growth when subjected to high humidity, resulting in mycoparasitic overgrowth and significant reduction of the pathogen sporulation. Our results provide evidence that different species of Clonostachys, not only the ubiquitous C. rosea, are sources of useful candidates for the biocontrol of potato early blight and possibly other plant diseases caused by fungal pathogens.

Studies addressing the biological control of Botrytis cinerea have been unsuccessful because of fails in inoculating tomato plants with the pathogen. With the aim of establishing a methodology for inoculation into stems, experiments were designed to assess: i. the aggressiveness of pathogen isolates; ii. the age at which tomato plants should be inoculated; iii. the susceptibility of tissues at different stem heights; iv. the need for a moist chamber after inoculation; and v. the effectiveness of gelatin regarding inoculum adhesion. Infection with an isolate from tomato plants that was previously inoculated into petioles and then re-isolated was successful. An isolate from strawberry plants was also aggressive, although less than that from tomato plants. Tomato plants close to flowering, at 65 days after sowing, and younger, middle and apical stem portions were more susceptible. There was positive correlation between lesion length and sporulation and between lesion length and broken stems. Lesion length and the percentage of sporulation sites were reduced by using a moist chamber and were not affected by adding gelatin to the inoculum suspension. This methodology has been adopted in studies of B. cinerea in tomato plants showing reproducible results. The obtained results may assist researchers who study the gray mold.

Bacillus strains used as biocontrol agents (BCAs) for plant diseases produce antimicrobial metabolites, especially cyclic lipopeptides (LPs), that protect aerial plant parts against pathogens. The Bacillus strain B157 was previously isolated from coffee and shown to reduce coffee leaf rust severity in the field. The biocontrol mechanism of B157 was attributed to antibiosis, but the nature of the antifungal metabolites and the correct identity of this BCA remained unclarified. We investigated the diversity of LPs of B157 and evaluated their antifungal activity against the tomato pathogen Alternaria linariae. The efficacy of the crude organic extract of B157 in controlling tomato early blight in the greenhouse was also tested. Multilocus phylogenetic analyses (16S rDNA, gyrA, rpoB) identified B157 as Bacillus velezensis. Twenty-seven LPs were detected in the extract of B157 and identified as iturins (n=5), fengycins (n=13) and surfactins (n=9). A well-diffusion assay with chromatographic fractions of the bioactive extract showed that all fractions having antifungal activity contained mixtures of fengycins or the combination of fengycins and iturins. In two independent assays, preventive treatments of tomato plants with the crude extract of B157 (1 g/L) significantly reduced the severity of early blight. The disease control efficacy (>90%) was similar to the fungicide treatment (chlorothalonil). Our results suggest that biochemical fungicides enriched in LPs may be used for protecting aerial plant parts against phytopathogens. This approach may complement the common use of Bacillus cell suspensions containing diluted and variable amounts of LPs that can give inconsistent control results in the field.

O uso de métodos de controle de doenças de plantas mais sustentáveis é uma necessidade na agricultura atual. Nessa perspectiva, o controle biológico de doenças de plantas surge como uma alternativa eficaz e viável no contexto de manejo integrado. Dentre os vários agentes de biocontrole estudados, ênfase vem sendo dada ao fungo Clonostachys rosea por seu potencial de uso na agricultura. O fungo pode ser encontrado em diferentes regiões, colonizando todas as partes de diferentes espécies vegetais e, ainda, possui a capacidade de permanecer endofiticamente em algumas plantas. No que diz respeito ao controle biológico, C. rosea é comprovadamente eficiente no controle de diversos patógenos em uma ampla gama de hospedeiro. Além disso, há relatos do antagonista como promotor de crescimento e indutor de resistência em algumas espécies vegetais, e como fungo entomopatogênico. Pela eficiência e versatilidade do antagonista C. rosea, buscamos nessa revisão fornecer uma visão global sobre as perspectivas de uso do antagonista no contexto do controle biológico.

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