Abstract
In Diaporthaceae, Diaporthe, Valsa and related genera consist of large species inhabiting many host plants. These large species show usually wide variation in their biologic natures8, 9). On the other hand, it has been recognized that the genus Melanconis consists of small species inhabiting only limited hosts and variation of these species is usually small2). Possibility to combine two or more species of Melanconis into a large one species has been investigated through the morphologic, physiologic and pathogenic studies of the Japanese species of Melanconis. In this paper the results of physiologic study in six species of Melanconis (Table 1, Figure 1) are reported and variation in the size of conidia obtained from various media is described. Growth of mycelial colony and production of conidia on various media consisting of agar media, rice-wheat bran medium and sterilized twigs of certain tree species (Table 2) are presented in Tables 3 to 8 and Figures 3 to 5. Germination of conidia under various temperature conditions is shown in Figures 6 to 8. Variation in the size of conidia produced on various media is given in Figure 9.
As shown in Table 1 and Figure 1, six species of Melanconis found in Japan are divided into three groups, each of which composed of closely related species to each other. The first group contains two species described on Juglandaceae, namely Melanconis juglandis and M. pterocaryae. They are characterized by large, elliptic and olive-brown colored conidia and the absence of B-spores. However, their physiologic characters are quite different from each other. Generally, M. juglandis grew well under various cultural conditions than M. pterocaryae. It was noticed that M. pterocaryae behaved particularly in the growth of mycelial colony and germination of conidia under various temperature and pH conditions. The size of conidia in these two species produced on various media was also separated clearly from each other.
The second group contains three species inhabiting Betulaceae, namely M. stilbostoma, M. marginalis and M. itoana. They are distinguished from the other groups by the presence of hyaline B-spores and ovoid to fusoid and light brown colored conidia. Among them, M. itoana on Betula is recognized to be different from the other two species by its shape and size of conidia and certain characteristic natures in the germination of conidia and the growth of mycelial colony. M. stilbostoma on Betula and M. marginalis on Alnus are usually difficult to distinguish from each other by the size and shape of conidia as shown in Figures 1 and 9. Whether M. stilbostoma and M. marginalis are separated clearly or not would be determined through further investigation on their morphology, physiology and pathogenicity.
Melanconis mcrospora described on Castanea solely constituted the third group. Its behavior on various media quite differed from the other five species and germination of conidia also gave different performance from the others. It is easily distinguished from the other species by its colored ascospores and particular shape of conidia.
