Pathogen attack and spatial patterns of juvenile mortality and growth in a temperate tree, Prunus grayana

To examine whether the Janzen–Connell hypothesis is valid in temperate forests, we investigated the density, growth, mortality, and agents of mortality of seedlings and the density, size, and age of saplings of Prunus grayana Maxim. at three distances (0–3, 6–10, and 16–26 m) from conspecific adults in a temperate forest in Japan. An inoculation experiment was also conducted to test the host range of a leaf pathogen. The probability of mortality was highest at 0–3 m during the first 2 years of growth. Mortality mainly resulted from distance-dependent attack by two types of pathogen that caused damping-off epidemics and spot symptoms on leaves. The leaf pathogen was identified as Phaeoisariopsis pruni-grayanae Sawada, which infected many more seedlings of Prunus grayana than of the two other tree species tested in an inoculation experiment. The vertical and diameter growth was lowest at 0–3 m and highest at 16–26 m in both seedlings and saplings. As a result, the greatest number of large and older saplings was observed at 16–26 m. Our results demonstrate that the Janzen–Connell mechanism operates in a beech-dominated forest in the temperate region of Japan.

Polystigma fulvum. [Descriptions of Fungi and Bacteria].

A description is provided for Polystigma fulvum. Information is included on the disease caused by the organism, its transmission, geographical distribution, and hosts. HOSTS: Prunus padus (syn. Cerasus padus, Padus racemosa), Prunus asiatica (syn. Padus asiatica), Prunus maximowiczii. Records on Prunus grayana (e.g. Anon., 1965) have not been verified. DISEASE: Large brightly coloured spots on leaves. GEOGRAPHICAL DISTRIBUTION: Austria, Belgium [?], China (unverified record cited by Eriksson & Yue, 1988), Czechoslovakia, Finland, France, Germany, Hungary, India, Italy, Japan (46, 1510, unverified), Latvia, Norway, Romania, Russia, Sweden, Switzerland, Ukraine, United Kingdom. TRANSMISSION: Stromata are formed on living leaves in autumn, which do not fall prematurely. Apparently mature ascospores are present by late autumn, but they are probably not released until the following spring, coinciding with the new leaf flush. Ascospores are air-dispersed, and probably germinate on new host tissue to form appressoria and infection pegs.

Tranzschelia asiatica sp.nov. and its taxonomic relationship to Tranzschelia arthurii

Prunus grayana (subg. Padus) was found to serve as the uredinial-telial host of two distinct Tranzschelia species in Japan. Tranzschelia pruni-spinosae has been known to occur on P. grayana, and the other species was previously overlooked. The latter fungus was experimentally proven to form its spermogonial and aecial stages on Hepatica nobilis var. japonica f. variegata and f. magna. The fungus was similar in morphology and host relationships to Tranzschelia arthurii, whose spermogonial and aecial stages occur on H. nobilis var. acuta and uredinial and telial stages on Prunus serotina and Prunus virginiana (subg. Padus) and Prunus americana (subg. Prunophora) in North America. However, the spores at all stages in the life cycle of the Japanese fungus were significantly smaller than those of the North American fungus. Because of this, a new species, Tranzschelia asiatica, was proposed for the geographically separated fungus. This species is expected to occur in East Asia outside of Japan, but this is not yet confirmed. Key words: rust fungus, Uredinales, Rosaceae, Prunus, Ranunculaceae, Hepatica.