Identification and Biological Characterization of a New Cyst Nematode, Heterodera glycines sbsp.n. tabacum , Parasitizing Tobacco in China.

In an investigation of diseases from plant-parasitizing nematodes in Henan Province, a cyst nematode was found on tobacco roots and in rhizosphere soil. We identified this strain as a new cyst nematode subspecies, Heterodera glycines sbsp.n. tabacum . The cysts and second-stage juveniles (J2s) parasitizing Henan tobacco were larger than those of H. glycines . A single 345-bp fragment was amplified from H. glycines sbsp.n. tabacum , whereas the 345- and 181-bp fragments were amplified from the soybean cyst nematode. Thus, H. glycines sbsp.n. tabacum was distinct from H. glycines . There were base transversions at 504 sites and base transitions at 560, 858, 920, and 921 sites in the rDNA-ITS sequences of H. glycines sbsp.n. tabacum compared with H. glycines , and there were base transitions at 41, 275, 278, and 380 sites in the mtDNA-COI sequences. In the phylogenetic tree based on the rDNA-ITS and mtDNA-COI regions, H. glycines sbsp.n. tabacum was clustered on a single branch. Based on the randomly amplified polymorphic DNA (RAPD) technique, sequence characterized amplified region (SCAR)-PCR primers were designed. A single 1,113-bp fragment was amplified by specific primers (HtF1/HtR1) from H. glycines sbsp.n. tabacum , while no fragments were obtained from H. glycines . The H. glycines sbsp.n. tabacum can infect soybean plants but cannot complete its life cycle on soybean. Eleven tested tobacco cultivars were infected, with an average reproduction factor ( Rf ) of 9.74 and a maximum of 64.2 in 'K326'. The cumulative egg hatching rate of H. glycines sbsp.n. tabacum in the presence of tobacco root exudates was 42.6% at 32 days posthatching, which was significantly greater than that in the presence of soybean root exudates (30.3%) or sterile water (33.1%). In summary, the cyst nematode population parasitizing Henan tobacco was identified as a new subspecies, H. glycines sbsp.n. tabacum .