Identification of Xiphinema brevicollum detected in Ficus carica from Japan
Xiphinema brevicollum is an important quarantine nematode in China,known to cause damage to its host plants through direct feeding on root tips,typically causing stunted growth and reduced yield.In this study,a Xiphinema species isolated from Japanese fig(Ficus carica)seedlings intercepted at Qingdao Port was morphologically and molecularly identified,providing theoretical support for nematode identification by Chinese plant quarantine services.The intercepted population was identified through morphological observation,morphometric comparison,and phylogenetic analysis based on sequences of the 18S rDNA,ITS1,28S D2/D3 region,and mitochondrial cytochrome c oxidase subunit Ⅰ.The morphological and molecular characteristics of the intercepted Japanese fig nematode population closely resemble those of X.brevicollum.Key morphological features included a medium-sized body forming an open spiral"C"shape when heat-relaxed,tapering gradually towards the ends,with a body length ranging from 1 713.4 to 1 910.2 μm,and a body diameter ranging from 35.8 to 47.1 μm.The lip region appeared rounded in lateral view and was offset from the rest of the body,amphidial fovea funnel-shaped.The odontostyle was 1.5 times longer than the odontophore,with well-developed flanges.The reproductive system was didelphic-amphidelphic,with equally developed branches and reflexed ovaries.The vulva was situated at the midbody,forming a transverse slit,with the vagina occupying 1/3 of the corresponding body diameter.The tail was short and conoid,with a prominent dorsal curvature and straight ventral side,with a length of 24.0-29.5 μm,equal to or slightly longer than the body diameter at the anus.Phylogenetic analyses based on ITS1 region sequences revealed that the intercepted population formed an independent branch with the populations from Brazil,New Zealand,Belgium,and South Africa,with a sequence similarity of 98.5％to 98.7％.Similarly,phylogenetic analyses based on COX Ⅰ sequences revealed that the intercepted population formed an independent branch with five Japanese populations of X.brevicollum,with a sequence similarity of 91.6％-93.6％.The intercepted population was identified as X.brevicollum based on morphological and molecular characteristics,marking the first identification of fig as a natural host for X.brevicollum.To minimize the risk of introduction into China,customs quarantine of such seedlings should strengthen the supervision of X.brevicollum.
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