Comparative studies on the fine root status of healthy and declining spruce and beech trees in the Bavarian Alps and occurrence of Phytophthora and Pythium species

Investigations on root and crown status of spruce and beech were carried ou t on selected trees in the 'Werdenfelser Land' area (Bavarian Alps, Souther n Germany). In addition, the association of fine root pathogens of the gene ra Phytophthora and Pythium with the trees' rhizosphere was studied. In a v ariety of stands representnig various site conditions, soil and root sample s were taken from 12 spruce (Picea abies) pairs and, eight beech (Fagus syl vatica) pairs. Each pair consisted of a healthy and a declining tree as ind icated by crown transparency. The root status was characterized using a set of parameters, and correlations between crown and fine root status were ob served. In spruce, most parameters decreased significantly, with increasing crown transparency, whereas in beech, correlations were less pronounced. T he total number of lateral roots per cm small root (diameter 2-5 mm) was si gnificantly, lower in both species for declining trees compared to healthy trees. Pythium spp. were isolated from 15 of 24 soil samples taken from und er spruce, and from eight of 16 samples from under beech. Phytophthora citr icola was found in two beech stands only. Among the isolated species, Pythi um anandrum, Pythium inflatum and Pythium acrogynum were identified accordi ng to morphological features. After polymerase chain reaction-restriction f ragment length polymorphism analysis, residual Pythium isolates were assign ed to four different groups. No crown transparency-dependent differences in isolation frequency were found. In soil infestation tests, all species tes ted caused root damage on both young spruce and beech plants, with P. citri cola being the most aggressive pathogen. Additionally, Pythium-infected bee ches showed severe leaf chloroses and necroses. Due to their low isolation frequency, Phytophthora spp. are not considered to play a major role in the decline of spruce and beech in the investigated area. Pythium spp., howeve r, were isolated frequently, showed pathogenicity towards the fine roots of spruce and beech, and are therefore considered to be at least contributing factors in the decline of Bavarian mountain forests.