ECOPHYSIOLOGICAL CHARACTERISTICS OF LEAVES ON TWIG OF PRUNUS YEDOENSIS SUFFERING FROM WITCHES' BROOM DISEASE CAUSED BY TAPHRINA WIESNERI
Kansai Research Center, Forestry and Forest Products Research Institute, Ministry of Agriculture, Forestry and Fisheries, Momoyama, Fushimi, Kyoto 612, Japan
Background and objectives
Witches' broom of cherry trees, caused by Taphrina wiesneri (Rath.) Mix, is an epidemic disease on various species of Prunus. This disease particularly affects Prunus yedoensis Matsum., which is one of the most famous ornamental trees in Japan. The symptom of disease is characterized by the Witches'-broom formation of leafy twigs with small leaves, with no flower buds forming on infected twigs, only leaf buds . When the cherry flowers are in bloom, the leaf buds break. For this disease mycological studies and studies on plant hormonal substances produced by Taphrina wiesnerihave been conducted. Gas exchange and water relations in peach leaves infected by T. deformans, in the same genus as T. wiesneri, have been studied in detail . However, there are no studies on physiology of the cherry tree infected by T. wiesneri. In order to deepen our understanding of effect of Witches'-broom on the cherry tree, the ecophysiological characteristics in sun and shade leaves on twigs of cherry trees grown under field conditions, suffering from Witches'-broom disease, were studied in relation to gas exchange, water relations and photosynthetic pigments.
Results and conclusions
Although the xylem pressure potential in sun leaves of infected twigs did not differ from that in sun leaves of healthy twigs, the photosynthetic rate, transpiration rate and stomatal conductance in sun leaves of infected twigs were lower than those in sun leaves of healthy twigs. There were no differences in photosynthetic rate, transpiration rate and stomatal conductance between shade leaves of infected and healthy twigs. The xylem pressure potential in shade leaves of infected twigs, however, was lower than that in shade leaves of healthy twigs. These results show that both sun and shade leaves of infected twigs were more water-stressed in comparison with those of healthy twigs. There were no differences in relative area of stomatal pore per leaf area between leaves of infected and healthy twigs under both sun and shade conditions. The amount of water supplied to each leaf of the infected twig might be small in comparison with that in healthy twig. Specific leaf area in sun and shade leaves of infected twig was smaller than that of healthy twigs. Carotenoid, chlorophyll and cc-carotene in leaves of infected twig were larger than those in leaves of healthy twigs under both sun and shade conditions. These results indicate that the leaves of infected twigs are more shade-leaved in comparison with the leaves of healthy twigs.
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