No abstract

One-year-old tree seedlings were incubated in a greenhouse from April to July, under natural daylight conditions, with their root systems at constant temperatures of 5, 10, 15, 20, 25, 30 and 35 ~ and with the above ground parts kept at a constant air temperature of 18-20 ~ The course of height growth, total mass increment, root, shoot and leaf weight as well as leaf areas were measured. The results indicate that clear differences exist in the optimal root zone temperatures for various growth parameters in different tree species. Pinus sylvestris had a maximal height increment at about 5-10 ~ and maximal total mass increment at 15 ~ root temperature. In contrast, the optimum for Quercus robur was at 25 ~ Tilia cordata and Fagus sylvatica had their optima for most growth parameters at 20 ~ The root temperature apparently indirectly influenced photosynthesis (dry weight accumulation) and respiration loss. From the observed symptoms and indications in the literature it seems probable that a change in hormone levels is involved as the main factor in the described effects. Variation of root temperature had only an insignificant effect on bud burst and the time at which the shoots sprouted. Apparently species of northern origin seem to have lower root temperature optima than those of more southern origin. This is to be verified by investigation of other tree species.

With the help of active types of oxygen, extracellular enzymes and mechanical processes, Botrytis cinerea is capable of infecting plant tissue. Whereas no clear correlation was found between the activities of protease, pectolytic or other cell wall degrading enzymes and virulence, a positive correlation between pathogenicity and the intensity of active types of oxygen released was apparent in some isolates. It is assumed that these toxins result from the activity of glucose or xylose oxidases. Antioxidants inhibited the infection. It is concluded from these results, that active types of oxygen play a decisive role in the infection process.

No abstract

No abstract