Root rot and distortion of ginseng seedling roots caused by Fusarium oxysporum

摘要

Stunted ginseng (Panax quinquefolius) seedlings with distorted roots as a result of girdling of the taproot and rotting of the root tips were observed in British Columbia and Ontario in 2005 in four fields of 1- or 2-year-old plants. Isolation from affected root tissues yielded > 90% recovery of Fusarium oxysporum. Population levels of the fungus were up to 40-fold higher in the rhizosphere of affected plants compared with that of healthy plants. Inoculation of 1-year-old seedlings with four isolates of F. oxysporum under greenhouse conditions resulted in rotting of root tips, brown discolouration and death of lateral roots, followed by distortion of the taproots at a frequency of 52%-70%. DNA of F. oxysporum was detected in flowers, green berries, ripe berries, and seeds of ginseng using a DNA hybridization array. Stratified seeds showed up to an 80% incidence of F oxysporum both in the seed coat and endosperm. Isolates of F. oxysporum from ginseng grew best under laboratory conditions at 25-30 degrees C and PH 5.7-6.8. Mycelial growth was significantly reduced by 10 mu g/mL of the fungicides benomyl, propiconazole, fludioxonil, and thiophanate-methyl. Phylogenetic comparisons of the sequence a portion of the elongation factor-1 alpha gene grouped all 13 isolates of F oxysporum from ginseng with 21 isolates of F. oxysporum from a range of other hosts. Inoculum of F. Oxysporum originating from straw mulch or soil in ginseng gardens, together with seedborne inoculum, may be primary sources for infection of seedling roots.