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1974年10月, 松戸市に発生したサルスベリの斑点落葉性の新病害について記述した.病徴は葉に初め灰色または淡灰褐色環紋状の輪郭が鮮明な斑点を生じ, やがて1〜2cmの円形病斑となる.病葉はしばしばわん曲し, 脱落しやすい.古い病斑部の裏側には, 長さ1mm足らずの細長いピラミッド状のsporophoresを密生する.本病の病斑部からは種々の方法で容易に菌を分離することができた.分離菌をサルスベリの葉に接種した結果病徴を発現し, 接種病斑からは分離菌が再び得られ, 病原であることを確認した.分離菌はPDA培地では白色ビロード状の菌そうとなり, 直径3〜5mmの扁球形の黒色菌核を数コ形成する.菌そう上にはやがて無数のphialoconidiaを生ずる.本病の病徴と病斑上に生じた典形的なsporophoresの形態, ならびに分離菌の培養所見とくにphialoconidiaの形態, 菌核形成の特徴などを原記載と照合し本病の病原菌をCristulariella pyramidalis WATERMAN and MARSHALLと同定し, 病名としては環紋葉枯病を採用した.本菌は各種天然培地でよく生育し, 生育適温は16〜24℃と幅が広く, 低温性で28℃では生育しない.sporophoresの形成も10〜20℃の低温域で良好であった.培地のpHは酸性側で菌の生育が旺盛であった.

Zonate Leaf Spot Disease of Crapemyrtle Caused by Cristulariella pyramidalis WATERMAN and MARSHALL. K. HIRANO and W. IIDA. Faculty of Horticulture, Chiba University, Matsudo, Japan. Tech. Bull. Fac. Hort. Chiba Univ., No.23: 53-61, 1975. A new leaf spot disease of crapemyrtle (Lagerstroemia indica L.) caused by Cristulariella pyramidalis WATERMAN and MARSHALL was observed in nursery of ornamental trees in Matsudo during October 1974. It constitutes new host record on family Lythraceae of this fungus. The initial symptoms on crapemyrtle leaves are characterized by grayish white or olive-bull color with circular, concentric ring and well-defined margin. Sometimes the naturally infected leaves vary in the shape of curling or distortion and as soon as they fall during the growth period of plant. The cone- or pyramidal-shaped sporophores (fruiting structures) were produced abundantly on the underside of crapemyrtle leaves with large lesion, but these were presented only on necrotic tissue. One or two sclerotia were formed on infected leaves which incubated under the moist condition. The pure cultures of C. pyramidalis were obtained by transferring each specimen of the lesion tissue, single sporophore or sclerotium to potato dextrose agar in petri plates. The colonies of C. pyramidalis on potato dextrose agar showed at first white velvet mycelial mat, then become grayish white partially. Sclerotia and phialoconidia formed on the colony in agar culture, whereas typical pyramidal-shaped sporophores were not found. When the mycelial agar discs or sporophores of C. pyramidalis were inoculated artificially to crapemyrtle leaves, the disease symptoms developed in a few days after inoculation and the lesion discolored to light grayish brown, however, the patterns of leaf spot produced in the moist chamber differed from those of natural infection in the field. The culture experiments to determine the effects of some physiological factors on the development of C. pyramidalis were also investigated.

source:The technical bulletin of Faculty of Horticulture, Chiba University