Phytophthora Disease Monitoring in Alnus Stands

Monitoring activities were conducted during spring 2022 on five natural Alnus glutinosa stands located in the central part of Portugal, the districts of Aveiro and Guarda (Table 1). The altitude of survey sites ranged from 9 to 750 m. a.s.l.
At each site, mature alder trees were visually checked for the presence of typical Phytophthora disease symptoms, including wilting of foliage, shoot and twigs dieback, sudden death, bleeding cankers, and root and collar rot. In Sites 2 and 3, four linear transects of 50 m were randomly established to evaluate disease incidence and mortality rate, expressed as the number of symptomatic trees out of the total number of trees (DI = n/N × 100) and the number of dead trees out of the total number of trees (M = d/N × 100), respectively [19 ].
At each site, representative trees were randomly chosen for sampling (Table 1). Rhizosphere soil samples (about 1 L of soil and fine roots) were collected around the collar of 38 declining alder trees. Among these, eight trees were chosen for the collection of bark tissue samples, taking small fragments from the border of bleeding cankers on the stem. In Sites 2 and 3, the occurrence of Phytophthora species was also monitored in the water streams using nylon mesh bags containing 10 young cork oak (Quercus suber L.) leaves as bait [10 (link),20 ]. The nylon mesh bags were positioned near the root systems of the selected alder trees.