Pine pitch canker (PPC) is a serious disease that affects pines worldwide caused by the fungus Fusarium circinatum. As there are no means to eradicate the disease once established, PPC leads to significant economic losses when valuable species like Pinus pinaster are affected. It is known that PPC leads to the appearance of drought-like symptoms in P. pinaster, and recent studies have reported further resemblances between the plant’s response to the fungus and to drought. Nevertheless, a direct comparison between pine response to F. circinatum and to drought has never been conducted. Thus, the aim of this work was to evaluate the similarities and divergences between the mechanisms of response to drought and F. circinatum in P. pinaster in the moment of tip-wilting appearance, through a holistic approach combining morphological, physiological, hormonal, and biochemical data. In this study we found a similar severe drought-like response in both P. pinaster infected with F. circinatum and subjected to drought, evidenced by a decrease in water potential, a non-stomatal photosynthesis impairment and the accumulation of starch in the needles, possibly due to phloem collapse functioning. However, there was a greater accumulation of osmolytes and antioxidants in water-stressed plants while fungus-infected pines presented a greater decrease in water potential and a less prolongated stomatal closure, suggesting that F. circinatum disrupts the water allocation more abruptly than drought. These findings are in accordance with a previous hypothesis that drought similarities found in PPC are due to tissue breakdown caused by the fungus, but it still does not explain the positive correlation between tolerance to both conditions. We anticipate that the knowledge obtained in this thesis will provide some useful insight on P. pinaster response to F. circinatum, thus contributing to more efficient management strategies of PPC in the future.

Tese de mestrado, Biologia dos Recursos Vegetais, 2023, Universidade de Lisboa, Faculdade de Ciências