Abstract: 【Objective】 The objective of this study is to observe and analyze the characteristics of population dynamics and generation cycle of Heterodera glycines (SCN) on soybean and tobacco in the same growing season of 2013, and explore the host suitability of the two host crops and the possible influences of temperature/humidity conditions on occurrence of H. glycines.【Method】 H【Result】 In soybean and tobacco soil, the 2nd stage juvenile of H. glycines emerged both from April 7to September 15, and the maximum PD occurred both in late July, but before which there were two and one unconspicuous occurrence climax, respectively. The white female first appeared in both soil on June 3, the PD of which obviously peaked two times in soybean soil in middle July and middle August, respectively, and only had one climax period of lower level in tobacco soil in June. The cyst PD peaked in both soil in middle July, afterwards it constantly maintained a relatively high level in soybean soil but declined gradually to a very low level in tobacco soil. In soybean and tobacco root, the 2nd stage juvenile first appeared both on May 19, the PD of which had three obvious peaks in soybean root occurring in late May, late June and middle July, but had only two peaks in tobacco root in middle May and late June with the former one being not obvious. The 3rd-4th stage juvenile first occurred in soybean and tobacco root on May 26and May 19, respectively, the maximum PD occurred both in late June, but there were two extra and less obvious PD climaxes on soybean in late May and middle-late July. The white female first appeared in both root on May 26. In the growing season, the nematode reproduction factors (Rf=Pf/Pi) were 5.0 and 0.5 on soybean and tobacco, respectively. Entering July afterwards, a secondary infection of H. glycines occurred on soybean, but penetration almost no longer occurred on tobacco, on the root of which a large number of empty, shrunken or small brown cysts half-embededly emerged instead.【Conclusion】In the same growing season, H. glycines occurred three generations on soybean, but only two generations on tobacco. H. glycines reproduced much better on soybean, which was much higher than tobacco in the host suitability for H. glycines. It was indicated that there was a correlation between the non-root penetrating of the 2nd stage juvenile in tobacco soil and the prolonged high soil humidity in July, and the generation progress of H. glycines seemed to be inhibited by the high temperature in July and August on soybean.. glycines samples were simultaneously and periodically collected with “Zig-Zag” sampling method and at a time interval of 6-8 d from the two crop fields in the same and fixed location. The nematodes were extracted from soil with elutriation-sieving and Baermann funnel techniques, were stained in root with sodium hypochlorite-acid fuchsin staining technique, and examined and counted under microscope. The number of each H. glycines stage in 100 g of soil or 10 g of root, population density (PD), was calculated for every ten days period in the growing season.

Key words: Heterodera glycines, Glycine max, Nicotiana tobacum, population dynamics, generation cycles, host suitability