Integrated species recognition of the genus Alternaria

• Material Type: 博士論文
• Title: Integrated species recognition of the genus Alternaria
• Author/Editor: Nishikawa, Junji
• Author Heading: Nishikawa, Junji
• Publication, Distribution, etc.: 三重大学
• Publication Date: 2019-03-25
• Publication Date (W3CDTF): 2019-03-25
• Alternative Title: 統合的概念によるAlternaria 属菌の種の類別
• Degree grantor/type: 三重大学
• Date Granted: 2019-03-25
• Date Granted (W3CDTF): 2019-03-25
• Dissertation Number: 乙学術第1033号
• Degree Type: 博士(学術)
• Text Language Code: eng
• Alias of Author: ニシカワ, ジュンジ; 西川, 盾士
• Target Audience: 一般
• Note (General): application/pdf; Alternaria is well known as one of the most ubiquitous fungus genera, inhabiting every environmental substrate, but actually consists of mostly plant parasitic species. Especially for vegetables and ornamental flowers, these fungi are often regarded as seed-borne pathogens that cause large economic losses; therefore, they are very important for agriculture and seed production. In previous taxonomies of Alternaria, morphological features especially conidial shapes and sporulation patterns were the focus of species keys. However, this made species recognition complicated and confusing because of their morphological variation and fundamental pleomorphism. Moreover, the use of host plants as an additional taxonomic key made matters worse and resulted in the genus being split into more than 400 species. The latest molecular phylogenies have drastically reconstructed Alternaria and allied genera, and reconsidered several species, but the relationships between taxonomy and plant parasitism remain unclear. In addition, comprehensive studies on the distribution and biodiversity of Japanese species of the genus Alternaria have been inconclusive. Therefore, 85 alternarioid isolates obtained through field surveys by the author and from several collaborators or public culture collections were used for morphological and cultural comparisons, and molecular phylogenetic analyses using multi-locus DNA sequences (ITS, actin, Alt-a 1, endoPG, gapdh, rpb2, and tef1). This thesis proposed integrated species criteria for the taxonomy of the genus Alternaria based on morphology, molecular phylogeny, and pathogenicity. To make species boundaries clearer, systematic pathological phenotyping, namely determining the experimental host ranges of each species, was conducted. To reveal morphological variability and pleomorphism within an Alternaria species, detailed morphological comparisons of three isolates of A. cinerariae with different source host plants were performed. The results suggest that A. cinerariae has considerable morphological variation with respect to sporulation patterns, conidial swelling, and chlamydospore formation, and provide an example of the high variability within Alternaria species. Phylogenetic analysis using gapdh, rpb2, and tef1 sequences clustered the isolates together in a single clade and supported the above conclusion. In addition, inoculation tests on 17 species produced etiologically interesting results indicating that the experimental host range of A. cinerariae is mostly selective to one tribe, Senecioneae. The strawberry black leaf spot pathogen is one of the most host-selective pathogens in the genus Alternaria. This pathogen, which is known to be host variety-selective, has been identified as A. alternata, which is also known to be a highly confusable morphological taxon. Based on morphological observations and phylogenetic analysis of a combined dataset of ITS, gapdh, rpb2, tef1, Alta1, and endoPG sequences, the examined isolates were identified as A. gaisen rather than A. alternata together with isolates of Japanese pear pathotypes of A. alternata. Furthermore, A. gaisen was taxonomically re-examined and re-described as A. gaisen Nagano ex Bokura, which includes two formae speciales, A. gaisen f. sp. Fragariae producing AF-toxin and f. sp. Pyri producing AK-toxin. To phenotype four species new to Japan, A. alstroemeriae, A. celosiicola, A. crassa, and A. petroselini, an integrated species recognition method based on morphology, phylogenetic analysis using ITS sequences, and experimental host range was tested. Inoculation tests on different species revealed that these species had selective host ranges limited to one genus (A. alstroemeriae), two related tribes (A. crassa) or two subfamilies (A. celosiicola), or were widely pathogenic within one family (A. petroselini. The results also suggested that integrated species criteria are helpful to find potential susceptible hosts to individual Alternaria species and to recognize species boundaries between related species, especially for plant pathologists. Furthermore, the integrated species recognition method was extended to some known species distributed in Japan to clarify their species boundaries, focusing on phylogenetically, morphologically, or pathologically closely related species. The experimental host range results suggested that species in sect. Alternantherae, which includes A. celosiicola, A. gomphrenae, and a novel species named A. paragomphrenae, could be clearly differentiated by pathogenicity to Amaranthaceae plants, reflecting their morphological and phylogenetic differences. Conversely, the experimental host ranges of three morphologically and phylogenetically distinct species pathogenic on Brassicaceae, A. brassicae, A. brassicicola, and A. japonica, interestingly showed almost no differences in host selectivity. For the other obtained species including A. iridicola pathogenic to Iris spp. (Iridaceae) and A. cumini pathogenic to Cuminum(Apiaceae), species boundaries were determined based on integrated species recognition to discuss the validity of the concept. During this study, 85 isolates were obtained and described as 26 species, which included three novel species and five new records to Japan, with several taxonomic treatments. Comprehensive inoculation tests revealed distinctive host selectivities along with the systematic ranks of the host plants, including not only genus but also tribe, subfamily, and variety, for most plant-pathogenic species of Alternaria. Therefore, phenotyping using experimental host ranges can reflect species boundaries. It was concluded that integrated species recognition based on morphology, phylogeny, and pathogenicity can make species boundaries clearer and will provide a practical way to re-define the species concept in the genus Alternaria.; Graduate School of Bioresources Mie University; 275p
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• Date Accepted (W3CDTF): 2023-12-15T22:13:26+09:00
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