Assessment of interactions between defoliation and Phytophthora plurivora stem infections of birch seedlings

Silver birch, (Betula pendula), is an important forest tree species in Poland used for afforestation in rural areas and planted in wet forest types to ameliorate excess water. Physiological stress may increase susceptibility of trees to disease and it is hypothesized that insect defoliation can predispose birch to Phytophthora plurivora infection. In order to evaluate the effect of defoliation stress and phytophthora infection, removal of all (100%) or partial (50%) foliage from one-year-old B. pendula seedlings simulating insect damage was carried out in the greenhouse. Inoculation with P. plurivora mycelium at the base of the stem was performed by cutting the bark tissue 5–7 cm above the soil. Stem damage was assessed after 70 days in 2016 and after 365 days (at the end of the next growing season in September 2017) by measuring lesions sizes. We found that B. pendula can serve as a host of the soil-borne pathogen P. plurivora which causes mortality of birch seedlings in Polish nurseries. The results als...