Effect of Huntiella decorticans and drought on Nothofagus dombeyi seedlings.

In the temperate forests of Patagonia, Argentina, Nothofagus dombeyi, commonly known as Coihue, has shown sensitivity to intense drought events, leading to mortality. Studies have been conducted on Coihue decline and mortality using a variety of approaches, including the role of extreme heat waves and drought, pests and pathogens, particularly the fungus Huntiella decorticans. This work aimed to evaluate survival, vitality, necrosis extension and growth response of inoculated and non-inoculated Coihue seedlings from different provenances exposed to different soil moisture levels. To achieve this goal, 96 Coihue seedlings from 2 different provenances were assigned to 8 different experimental treatments. Treatments were composed of the presence or absence of H. decorticans and different soil moisture content conditions, dry, wet and the exposure to dry condition at different times of the experiment. Both dry conditions and H. decorticans had negative effects on the survival and growth rate of Coihue. The combination of both factors resulted in 100 % mortality, regardless of the plants' geographical provenances. Mortality began to be observed 3 months after pathogen inoculation, during the warmest month. Necrosis extension produced by the pathogen was similar for most of the inoculated treatments. The treatment under wet condition during the experiment but subjected to dry condition in the previous growing season presented lower necrosis extension (8.4 ± 3.2 %), than the other treatments. The radial increase was also affected by the treatments and geographical provenance, being those plants exposed to dry conditions which grew less (0.19 ± 0.21 mm). This study enhances our understanding of the plant-pathogen interaction. According to our results, Coihue may become more susceptible to mortality, when H. decorticans and water deficit conditions act synergistically.