ABSTRACT Calibrachoa (Calibrachoa hybrida, Solanaceae) is an annual flowering ornamental plant, which is widely used in landscape design. In October 2019, 5% of the plants grown in a greenhouse in Buenos Aires, Argentina, showed a sudden wilt characterized by chlorosis, loss of turgor, and root rot. The objective of this study was to identify the causal agent of the disease. Five morphologically identical isolates developed from the roots of wilting plants. One of the isolates was selected and identified using morphological and molecular markers, while its pathogenicity was confirmed by Koch’s postulates. The obtained results allow concluding that Ceratobasidium sp. AG-A (anamorph Rhizoctonia sp.) is the causal agent of the disease. To the best of the authors’ knowledge, this is the first report of Ceratobasidium sp. as pathogen of calibrachoa in the world.

ABSTRACT The driving forces behind many soil processes are microorganisms and they are able to respond immediately to environmental changes. The soil microbial community impacts on many soil properties. More than one-third of the terrestrial ecosystems are semiarid. However, a limited number of studies have been conducted to characterize soil fungal communities in semiarid grasslands, in particular those of agricultural fields. The aim of this study was to explore changes in the diversity and structure of soil fungal communities in semiarid grasslands, after different doses of glyphosate were applied under field conditions. Changes in soil fungal communities were examined using different approaches including culturing, calcofluor white stain and denaturing gradient gel electrophoresis (DGGE). The different approaches complement each other, revealing different aspects of the effect of glyphosate on soil fungal communities. We demonstrated a negative effect of glyphosate on soil fungal biomass at high doses and an early and transitory stimulatory effect on soil fungal biomass. We also found a negative effect of glyphosate on the species richness of cultivable fungi and changes in the molecular structure of soil fungal communities after double doses or long-term glyphosate application. In summary, our findings demonstrate an overall negative effect of glyphosate on soil fungal communities.

RESUMEN Los microorganismos del suelo son los responsables de llevar a cabo la mayoría de los procesos biológicos que ocurren en el suelo, y son capaces de reaccionar ante el estrés ambiental. Más de un tercio de los ecosistemas terrestres son semiáridos. Sin embargo, son escasos los estudios realizados para caracterizar las comunidades fúngicas en suelos agrícolas en ecosistemas semiáridos. El objetivo del presente trabajo fue estudiar los cambios que se producen en la biomasa, la diversidad y la estructura de las comunidades fúngicas del suelo, luego de la aplicación de distintas dosis de glifosato en condiciones de campo. Se emplearon diferentes técnicas incluidas el cultivo, la tinción directa con blanco de calcoflúor y PCR acoplada a electroforesis en geles de gradiente desnaturalizante (DGGE). Las distintas metodologías empleadas se complementan entre sí al detectar cada una distintos aspectos del efecto del glifosato en las comunidades fúngicas del suelo. Se encontró que el glifosato produce un efecto negativo sobre la biomasa fúngica, también se encontró un efecto transitorio estimulante inmediatamente posterior a la aplicación del herbicida. Además, se vio un efecto negativo sobre la riqueza de hongos cultivables, así como también cambios en la estructura molecular de las comunidades luego de aplicaciones repetidas. En conclusión, se demostró un efecto negativo generalizado sobre las comunidades fúngicas del suelo.

Resumo Calibrachoa hybrida (calibrachoa ou falsa-petúnia) é uma planta ornamental com importância crescente no mercado devido a existência de inúmeras variedades que podem ser cultivadas em vasos, jardins e paisagismo. A característica marcante é sua floração abundante e de cores vibrantes. Em outubro de 2019, foi obtido um isolado de fungo em folhas basais de calibrachoa, com manchas foliares marrons e irregulares, em plantas cultivadas em Buenos Aires, Argentina. O objetivo do presente estudo foi identificar o agente causal das manchas foliares em calibrachoa para expandir o conhecimento sobre as doenças prevalentes nesta importante planta ornamental. O isolado foi identificado por meio de marcadores morfológicos e moleculares, bem como a sua patogenicidade foi comprovada por meio do postulado de Koch. O fungo foi identificado como Nigrospora oryzae, sendo que presente artigo, além de relatar a sua patogenicidade, parece ser o primeiro registro desta doença em calibrachoa no mundo.

Abstract Calibrachoa hybrida (calibrachoa, million bells) is a flowering ornamental with increasing importance due to the existence of many successful cultivars for growing indoors in containers and planting in the garden and landscape. The outstanding characteristic is a profuse flowering and intense colour. In October 2019, a fungal isolate was obtained from basal calibrachoa leaves with irregular brown leaf spots, in plants cultivated in Buenos Aires, Argentina. The aim of the present study was to identify the cause of the disease in this ornamental genus, to expand knowledge about prevalent pathologies. The isolate was identified using morphological and molecular markers, and the pathogenicity tests were fulfilled. This paper reports that Nigrospora oryzae is pathogenic to calibrachoa, which seems to be the first record of this leaf spot disease in the world.