Search

Native Trichoderma spp. were isolated from agricultural fields in several regions of Ecuador. These isolates were characterized via morphological observation as well as molecular phylogenetic analysis based on DNA sequences of the rDNA internal transcribed spacer region, elongation factor-1α gene and RNA polymerase subunit II gene. Fifteen native Trichoderma spp. were identified as T. harzianum, T. asperellum, T. virens and T. reesei. Some of these strains showed strong antagonistic activities against several important pathogens in Ecuador, such as Fusarium oxysporum f. sp. cubense (Panama disease) and Mycosphaerella fijiensis (black Sigatoka) on banana, as well as Moniliophthora roreri (frosty pod rot) and Moniliophthora perniciosa (witches’ broom disease) on cacao. The isolates also showed inhibitory effects on in vitro colony growth tests against Japanese isolates of Fusarium oxysporum f. sp. lycopersici, Alternaria alternata and Rosellinia necatrix. The native Trichoderma strains characterized here are potential biocontrol agents against important pathogens of banana and cacao in Ecuador.

We present a taxonomic study of ‘group Favolus’ and related species in Polyporus. Phylogenetic analyses of nurLSU and ITS regions revealed that the infrageneric ‘group Favolus’ is divided into two main clades. Fungi within the group share laterally stipitate basidiocarps, with non-crustose stipe surfaces, and are distinguishable by the morphology of the pileus surface. One clade is characterized by species with hyaline to brown cutis, composed of hyaline to brown agglutinated generative hyphae. The other clade accommodates species with radially striate pileus, and lacks any distinct cutis of agglutinated hyphae. We propose Neofavolus gen. nov., typified by N. alveolaris, for the former clade, and revise the genus Favolus, typified by F. brasiliensis, for the latter clade. Neofavolus includes N. mikawai and N. cremeoalbidus sp. nov., known only from temperate eastern Asia, in addition to N. alveolaris. Favolus includes members of the Polyporus grammocephalus complex, the P. tenuiculus complex, and P. pseudobetulinus. We reveal that the polypore known as ‘P. grammocephalus’ in Asia includes F. acervatus and F. emerici (= P. grammocephalus), whereas ‘P. tenuiculus’ includes three distinct species; F. brasiliensis from tropical America, and F. spathulatus and F. roseus from tropical Asia. Detailed descriptions and illustrations are provided for the accepted species in Favolus and Neofavolus.

Alternaria alternata tomato pathotypeは，宿主特異的AAL毒素生産によりトマトアルターナリア茎枯病を引き起こす．AAL毒素はマイコトキシン フモニシンの構造類縁体であり，その生物活性も類似する．罹病植物組織内における病原菌の伸長と産生された毒素の確認は，毒素の病理学的重要性とリスクの評価のために重要である．抵抗性植物品種上において，病原菌および毒素は接種部位のみに局在していた．一方，感受性品種上では，毒素の広範な分布と病原菌の伸長が確認された．本研究の結果から，AAL毒素の病理学的重要性が確認されるとともに，罹病トマトにおける毒素による汚染リスクの可能性が示唆された．

The tomato pathotype of Alternaria alternata produces a host-specific AAL-toxin and causes Alternaria stem canker on susceptible tomato cultivars. AAL-toxin is a sphinganine-analog mycotoxin which induces apoptotic cell death in tomato cells and mammalian cells by inhibiting ceramide biosynthesis. Insensitivity to the AAL-toxin in resistant tomatoes and other plants is conferred by the Asc1 gene, a homolog of the yeast ceramide synthase gene Lag1 . The ALT7 gene, a putative acyl-CoA-dependent ceramide synthase, was found to be located in the AAL-toxin biosynthetic ( ALT ) gene cluster of the tomato pathotype of A. alternata . ALT7 and Asc1 have the TLC (TRAM/Lag1/ CLN8) domain characteristic of proteins involved in ceramide biosynthesis and are members of the LASS/Lag family. To test the hypothesis that ALT7 and Asc1 , both of which are Lag1 ceramide synthase gene homologs, might share a common biological function as toxin tolerance genes, we have cloned and characterized ALT7. ALT7 -deleted mutants were generated to investigate the effects of the deletion on vegetative growth, sporulation, toxin-sensitivity, toxin-production and pathogenicity. The deletion of ALT7 has no deleterious effect on the toxin-producing pathogen, indicating that the gene does not act as a resistance/self-tolerance factor against the toxin in the toxin biosynthetic gene cluster.