Abstract
The authors have carried out taxonomic investigations of the causal fungus of Japanese pear scab for several years. The results are summarized in this paper as follows.
1. The overwintered spots of Japanese pear scab on the twigs are somewhat sunken and show distinct cracks surrounding the lesions, while those of European pears are more or less swollen, producing the stroma under the periderm in the spots.
2. The stroma of Japanese pear fungus develop well and conidiophores abundantly grow in cluster, causing dark sooty appearance of the spots. Conidia are 7∼23×5.0∼7.5μ in size, smaller than those of European pear fungus.
3. The perithecia of Japanese pear fungus are depressed conic globoid in shape and 50.0∼150.0μ in height, while those of European pear fungus are globoid and 77.5∼200.0μ in height, much taller than the former.
4. The ascospores of Japanese pear fungus are unequally 2-celled and measure 10.0∼15.0× 3.8∼6.3μ. They are smaller than those of the European pear fungus, especialy the lower cells are much shorter than those of the latter.
5. According to the inoculation experiments, Japanese pear fungus showed distinct pathogenicity to the leading varieties of Japanese pear, but was unable to attack the European pear varieties such as Flemish Beauty and Bartlett. On the other hand the European pear fungus infected only Flemish Beauty but no Japanese varieties.
6. Based on the data reported in the present as well as the previous papers (23) by the authors, the causal fungus of Japanese pear scab is considered to be a distinct species from European pear scab fungus, Venturia pirina Aderhold. The authors propose the name Venturia nashicola to the present fungus.“Nashi”represents pear in Japanese. The diagnosis of the fungus is as follows.
Venturia nashicola n. sp.
Perithecia gregarious or scattered under the epidermis of the affected leaves, depressed conic globoid, the wall dark colored, membranous, hard, and consist of two or three layers of brownish cells, 50∼150μ in height and 53∼138μ in diameter; ostiole very long.
Asci hyaline, clavate or long ovate, 35∼60×5∼10μ; eight-spored. Ascospores hyaline or light brown, two celled, shoesole-shaped, 10∼15×3.8∼6.3μ.
Conidia dark brown, long oval or fusiform, 7.5∼22.5×5.0∼7.5μ, and 14.4×6.0μ on the average. Conidiophores clustered, erect, and simple, 10∼20μ in length. Conidia borne singly on the warty tips of conidiophores.
Habitat: On the leaves, twigs, and fruits of Pirus serotina Rehder and Pirus ussuriensis var. sinensis Kikuchi, producing scabby spots.
Locality: Throughout Japan
