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The influence of distance between host trees and leaf litter removal on population density of Cameraria ohridella have been for the first time examined in an isolated population of horse chestnut (Aesculus hippocastanum L.) trees. The observation was performed in the small town (area 13,58 km²) in Wielkopolska region (West Poland) on the total number of 49 trees: 31 (11 clumps) of them with autumnal leaves removal (controlled sites), and 18 (5 clumps) without this procedure (uncontrolled sites). The main factors determining the extent of the leaf destruction by larvae were the leaf litter removal and the number of subsequent generations on a given tree. The effect of mean distance between trees on the infestation level was statistically significant only for the third generation larvae, when analyzing all sites. There was no significant correlation when checking the impact of mean and short distance on the leaves infestation between controlled and uncontrolled sites. The abundance of the first generation of the larvae of raked sites is possibly a result of low number of in situ overwintering individuals and the number of immigrants from uncontrolled areas. Assuming the random choice of direction of the migration, the effect of the immigrants on the trees which leaves have been disposed of is not as high as it should be expected. Additionally, the moths can be blown away by the wind in a random direction. Consequently, the noted increase in the leaves infestation by the third generation larvae can be result of the rate of population increase innate for the species and only partly a result of immigration from refuge areas.
Caspian forests (in the region it is called – Hyrcanian Forests) with an area of about 1.9 million ha are located in north of Iran, in southern coast of Caspian Sea. It is exclusive site for some valuable species like Populus caspica Bornm., Gleditsia caspica Desf., Parrotia persica Meyer. and Pterocaria fraxinifolia (Lam.) Spach., and the forests are dominated by Fagus orientalis Lipsky, Quercus castanifolia C. A. M., and Alnus glutinosa Gaertn. The mistletoe (Viscum album L.) effects on the area and weight of leaves of the two host tree species ( hornbeam Carpinus betulus L. and ironwood Parrotia persica Meyer.) were studied on a number of severely infected individuals and control trees in selected parts of Hyrcanian Forests. Almost 100 leaves from infested and non-infested branches of two host species were sampled in order to compare with control trees (non-infested trees growing near each host). Results showed, that area and weight of leaves taken from infested branches of ironwood were significantly lower (at 95% confidence level) than leaf area and weight in non-infested branches and control trees. The amount of K, Mn and Zn was higher in infested branches of both species compared to control trees. However, the amount of nitrogen in infected branches of ironwood was lower. The results suggest that V. album may have detrimental effect on leaf structure, physiology and chemical composition of strongly infested host trees.
The study aims at investigating the impact of ivy (Hedera helix L.) on the growth and on some wood anatomical characteristics of black alder trees. Ivy-hosting and non-hosting black alder have a similar wood anatomy in terms of qualitative properties. However, in ivy-hosting trees tangential and radial diameter of vessels are narrower (p <0.001), and inter-vessel pits are smaller (p <0.01), whereas vessel frequency is higher (p<0.05) than those of non-hosting ones. The average maximum ray height is greater (p<0.05), and ray number mm-1 is lower (p < 0.001) than those of non-hosting individuals. In addition, the last ten years’ average radial growth has decreased 39.5% compared to that of non-hosting black alder.
Two field inoculation experiments were conducted to study intraspecific variation in vertical spread of the P-, S- andF-IS-group isolates of Heterobasidion annosum in stems of Pinus sylvestris, Picea abies and Abies alba. Host-plants were inoculated with four isolates of each IS group after 10 mm long wounds made with a sterile knife (experiment 1) or 3 mm diameter radial holes made with a drill (experiment 2). On pine, the P-group isolates were more virulent than S andF isolates in terms of infection frequency, mortality rate andvertical spread in sapwood. The S isolates had higher incidence of infection and extensive growth on spruce than on pine. The F isolates were significantly less virulent on pine andspruce than on fir. Vertical spreadof all IS groups on fir was similar. In spite of between-strain-within-IS group variation in vertical spreadon each host, the study provided strong evidence for the occurrence of intraspecific differences in the host preference. In the interspecific analysis with three hosts, the isolates, IS groups andhost × strain andhost × IS group interactions accountedfor most of the explainedvariation, while host-plants accountedfor the smallest portion of the variance.
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