| Stem blight of Eleocharis dulcis is a novel fungal disease in Tuanfeng County, Hubei province, China. Since2010, this disease has been becoming more destructive for tuber quality and production throughout Tuanfeng County. In the paper, the causal agent of E. dulcis stem blight was identified based on morphological characteristics, color response, and analysis of ITS sequences. And then, other research contents of aetiology, such as biological characteristics, host range and cultivar resistance, and physical and chemical properties of phytotoxin produced by the pathogen were also studied. The final objectives were to know well about this disease and to provide more information for disease control. The results were demonstrated as follows:Typical diseased stems were collected from E. dulcis fields in Fanggaoping Town, Tuanfeng County, Hubei province. Phoma sp. isolates with the highest isolation rate of24%were obtained using regular pathogen-isolation method. After inoculated with fungal plugs or conidial suspensions, red-brown symptom was seen obviously on all inoculated stems of E. dulcis for isolates CTF-3, CTF-10and CTF-11. The three isolates were transferred onto OA or MA plates which shared similar culture and morphology characteristics, and then identified as Phoma bellidis Neerg. based on descriptions of colonies, NaOH testing, pycnidia and conidia from Phoma identification manual. The ITS sequences of the above three isolates were obtained, and comparison with sequences in GenBank showed99.4%similarity with Phoma sp., P. macrostoma and P. herbarum. The phylogenetic tree of the ITS sequences was then constructed with neighbor-joining method, and Phoma sp.(HQ631000) and the three isolates were clustered together.Isolate CTF-3was used for testing biological characteristics of P. bellidis. Mycelia of isolate CTF-3could grow in the temperature from5to35℃and in the pH from4to10. Temperature of25℃and pH of6were the most suibable conditions. For testing utilization of nitrogen and carbon sources, peptone and starch were the best ones for mycelial growth. The lethal temperature of mycelia was50℃,10minutes. Nine fungicides were choosed to test inhibition effect for P. bellidis in vitro. Hexaconazole showed the highest inhibitory effect with EC50at0.2171μg ml-1. Host range and cultivar resistance were tested by inoculating mycelial plugs of P. bellidis on detached plants in lab. Among11different crops, inoculated crops including E. dulcis, Lactuca saliva var. aspargina, Zea mays, Glycine max, Brassica chinensis, Gossypium hirsutum and Spinacia oleracea had disease symptoms with100%disease incidence while L. sativa var. longifolia gave80%disease incidence. No symptom was observed on Allium tuberosum, A. fistulosum and Apium graveolens plants. And then,38E. dulcis cultivars were used for resistance testing, and results showed that cultivars Yangjiaqi, Sanjiangqi (98), Lushanbiqi, Yichangdangyangqi and Xiangtanqi were the most resistant with lesion measuring less than90mm2in size.To determine the chemical and psychical properties of phytotoxins produced by P. bellidis, the culture filtrates were treated in various ways. Culture filtrate from ME cultures was significantly more toxic to stems than filtrates from other media, OB、PDB and PSB. The toxic activity of culture filtrates was reduced obviousely after treated at70-100℃, and totally lost at121℃. After treatment of proteinase K or pepsin, the activity of culture filtrates was not changed. No toxin could be detected in the absorbed fractions after treated with active carbon. The most toxins were found in solvent fraction of ethyl acetate. Hence, ethyl acetate could be used for isolating phytotoxins of P. bellidis from culture filtrates. |
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