Fongs patògens i mortalitat forestal induïda per sequera

Si bé encara es desconeixen amb precisió els mecanismes pels quals les plantes es moren quan els manca l'aigua, se sap que quan hi ha sequera, els seus sistemes de transport i emmagatzematge d'aigua i carboni es veuen afectats. D'aquesta manera, els arbres queden debilitats, situació que aprofiten plagues i patògens forestals, com és el cas d'alguns fongs, el paper dels quals és poc conegut. Aquest estudi ha descrit els efectes que els fongs tenen sobre els arbres en funció del tipus d'interacció tròfica entre ells.Si bien aún se desconocen con precisión los mecanismos por los que las plantas se mueren cuando les falta el agua, se sabe que cuando hay sequía, sus sistemas de transporte y almacenamiento de agua y carbono se ven afectados. De esta manera, los árboles quedan debilitados, situación que aprovechan plagas y patógenos forestales, como es el caso de algunos hongos, cuyo papel es poco conocido. Este estudio ha descrito los efectos que los hongos tienen sobre los árboles en función del tipo de interacción trófica entre ellos

Hot water treatment causes lasting alteration to the grapevine (Vitis vinifera L.) mycobiome and reduces pathogenic species causing grapevine trunk diseases

The effective management of grapevine trunk diseases (GTDs) is an ongoing challenge. Hot water treatment (HWT) is an environmentally friendly and economically viable option; however, the short-term effects of HWT on grapevine (Vitis vinifera L.) health and production are not fully understood. The aim of this study was to compare the effects of HWT on plant growth and fungal community structure in nursery stock until plants were completely established in the field. We assessed eleven graft and three rootstock varieties from four local nurseries in a region of Catalonia (NE Spain) where GTDs are a serious threat. After treatment, the plants were left to grow under field conditions for two growing seasons. Metabarcoding of the ITS region was used to study the mycobiomes of plant graft unions and root collars. We also assessed the influence of plant physiological indicators in community composition. Hot water treatment caused lasting changes in GTD communities in both the root collar and graft union that were not always characterized as a reduction of GTD-related fungi. However, HWT reduced the relative abundance of some serious GTD-associated pathogens such as Cadophora luteo-olivacea in graft tissues, and Phaeomoniella chlamydospora and Neofusicoccum parvum in the root collar. Treatment had the greatest influence on the total and GTD-related fungal communities of Chardonnay and Xarel center dot lo, respectively. Total community variation was driven by treatment and nursery in rootstocks, whereas HWT most significantly affected the GTD community composition in R-110 rootstock. In conclusion, changes in fungal abundance were species-specific and mostly dependent on the plant tissue type; however, HWT did reduce plant biomass accumulation in the short-term.This research was partially funded by the Generalitat of Catalonia Department of Agriculture (S.B.L.). J.O. was supported by the "Ramon y Cajal" fellowship RYC-2015-17459 through the Spanish Ministry of Science and Education. D.S. was supported by the European Union's H2020 research and innovation program, under Marie Sklodowska-Curie grant agreement No 801586

Drought and Phytophthora Are Associated With the Decline of Oak Species in Southern Italy

Forest decline induced by climate change is a global phenomenon that affects many tree species, mainly in drought-prone areas as the Mediterranean region. In southern Italy, several oak species have shown decline symptoms and elevated mortality since the 2000s due to drought stress. However, it remains to be answered whether decline occurred alone or whether a pathogen was also involved. To this aim, we compared two coexisting oak species in a forest located in southern Italy which are assumed to be less (Quercus cerris) and more tolerant to drought (Quercus pubescens). We sampled fifteen couples of neighboring declining (D) and non-declining (ND) trees of both species. Wood cores were taken from all trees to perform dendrochronological analyses to detect the decline onset and link it to potential climatic drivers. Carbon isotope ratios (d13C) were analyzed in wood of the two vigor classes to compare their water-use efficiency. Phytophthora presence was also assessed in soil samples from ten D-ND couples of trees per species. The oak species most affected by drought-induced decline in terms of leaf shedding and mortality was Q. cerris, i.e., the least tolerant to drought. In both species, the D trees showed a reduced growth rate compared with ND trees from 2000 onward when drought and warming intensified. Q. pubescens showed higher growth sensitivity to precipitation, temperature and drought than Q. cerris. This sensitivity to climate was magnified in D trees whose growth decreased in response to warm and dry conditions during the prior winter and the late summer. The Q. pubescens D trees were more efficient in their water use than ND trees before the growth divergence between D and ND trees amplified. In the studied area, Phytophthora quercina was isolated from 40% of the sampled trees, and tended to be more frequent amongst ND than amongst D trees. Our data suggests that droughts and warm summer conditions triggered oak decline. The high prevalence of P. quercina in the studied area warrants further study as a potential predisposing factor