Studies on disease cycle and control of celery stunt anthracnose caused by Colletotrichum nymphaeae
Celery seedlings are grown in greenhouse nurseries. Celery producers work to keep pathogen-free conditions to grow healthy seedlings in nurseries by thoroughly removing debris of diseased plants, sterilizing soils and cultivating materials, etc. Although there seems to be a very low possibility that the pathogen remains in the nurseries, seedlings were attacked by the fungus in nursery greenhouses kept warmer than usual. This finding led us to assume that celery seeds may be contaminated with the pathogen. Additional lines of circumstantial evidence suggest that this disease may have spread through seed transmission of the pathogen. Almost all celery producers in the major area in Nagano Prefecture had used celery seeds that were harvested by several farmers producing seeds in the area and storing them for more than 1 year. Around 2006, however, farmers began to use seeds collected in the previous year due to the shortage of stored seeds. Concomitantly, an outbreak of celery stunt anthracnose occurred. In addition, this disease is most prevalent in an area where so-called “home-raised” seeds are used. We therefore hypothesized that C. nymphaeae has spread through seed transmission. To test this hypothesis, we divided the possible infection cycle into the following three steps, and tested each one: (1) primary infection from conidia produced on infected seeds to plant leaves, (2) secondary infection from conidia dispersed from infected leaves to leaves of other plants, and (3) infection of seeds from conidia produced on infected leaves. All results strongly suggested that infested seeds provide the source of the primary Celery [Apium graveolens var. dulce (Mill.) Pers.] is native to high-altitude marshlands of Europe and the Middle East and is also widely cultivated as a vegetable. Cultivars improved and grown in the United States originated from a cultivar grown in Japan in Nagano Prefecture, a major area for celery production in Japan. A new disease causing severe chlorotic spots on leaves, stunting, and dwarfing with leaf curl was found on celery in the prefecture. We found the disease in Nagano, Japan and identified its causal agent. We also elucidated its infection cycle to establish a practical method for controlling the disease.
Molecular re-identification of strains in NIAS Genebank belonging to phylogenetic groups A2 and A4 of the Colletotrichum acutatum species complex
INTRODUCTION An anthracnose pathogen, Colletotrichum acutatum J.H. Simmonds is known as a plurivorous and cosmopolitan fungus. Since it was first described to have fusiform conidia and reddish colonies in Australia (Simmonds, 1965), its distribution, host plants, macroscopic and microscopic morphology have been reported to vary in the extreme (Aa, et al., 1990; Sato, 1997; Sato et al., 1998; Vinnere et al., 2002). A ‘larger spored form’, which Simmonds (1965) described in the first report, appeared to be one of the morphologically distinct groups of C. acutatum. Because some strains of the fungus that are pathogenic to anemone were morphologically similar to Colletotrichum gloeosporioides (Penzig) Penzig & Saccardo, they were misidentified as the latter in Japan (Sato et al., 1996). Recently, several researchers recognized genetic groups A1 to A8 within the species based on sequences of the ribosomal DNA internal transcribed spacer region (rDNA-ITS) (Johnston & Jones, 1997; Lardner et al., 1999; Vinnere et al., 2002; Sreenivasaprasad & Talhinhas, 2005). Group A9 was added based on randomly amplified polymorphic DNA polymerase chain reaction (RAPD-PCR) and b -tubulin-2 (TUB2) gene partial sequences (Whitelaw-Weckert et al., 2007). Some of the researchers proposed dividing the groups into d i s t i n c t s p e c i e s ( G u e r b e r e t a l . , 2 0 0 3 ; Sreenivasaprasad & Talhinhas, 2005; Vinnere et al., 2002), indicating that C. acutatum sensu lato is a typical species complex. Colletotrichum fioriniae (Marcelino & Gouli) R.G. Shivas & Y.P. Tan (=group A3) and Colletotrichum simmondsii R.G. Shivas & Y.P. Tan (=group A2, A9) were separated from the C. acutatum species complex and also defined C. acutatum sensu stricto (=group A5) based on their morphological characteristics in culture and molecular phylogenetic analyses of the ITS region and the b -tubulin-2 gene sequences (Shivas & Tan, 2009). Colletotrichum carthami (Fukui) S. Uematsu, Kageyama, Moriwaki & Toy. Sato was revived as a member of the species complex. This species had distinct b -tubulin-2 gene sequences and specific pathogenicity for asteraceous plants (Uematsu et al., 2012). Although each of the three species except for C. carthami was reported to have characteristic colony color (Shivas & Tan, 2009; Uematsu et al., 2012), differences in microscopic morphology of the four species were still unclear. Quite recently, the species complex was split into 29 species based on phylogenetic studies with the 5.8S nuclear ribosomal gene including the two internal transcribed spacers (ITS), glyceraldehyde-3-phosphate dehydrogenase (GAPDH), chitin synthase 1 (CHS-1), histone 3 (HIS3), actin (ACT) and TUB2 gene sequences of 331 strains (Damm et al., 2012). Twelve of the 29 species were separated from group A2 and Colletotrichum godetiae Neergaard was assigned to the monophyletic group A4. All of the member species including 21 new ones that have been studied in culture were characterized morphologically (Damm et al., 2012). On the other hand, 170 strains deposited as C. acutatum in the NIAS Genebank, Japan were re-identified as C. fioriniae, C. simmondsii, C. carthami, C. acutatum group A2-P, group A4 and other species of the C. acutatum species complex based on phylogenetic analysis with TUB2 (Sato et al., 2013). Morphological differences such as colony color, conidial shape and size of each *Corresponding author E-mail: s1043@affrc.go.jp Molecular re-identification of strains in NIAS Genebank belonging to phylogenetic groups A2 and A4 of the Colletotrichum acutatum species complex
Control of celery leaf curl disease caused by Colletotrichum acutatum
Celery leaf curl disease caused by Colletotrichum acutatum was effectively controlled in the long-stemmed celery cultivar, South Australian Long White, by fortnightly sprays of either copper oxychloride, thiram, mancozeb, or chlorothalonil and in the short-stemmed celery cultivar, Tendercrisp, by either thiram, chlorothalonil or benomyl.