Comparison of the Infection Characteristics of Tobacco-infecting Cyst Nematode among Three Soil Moisture Conditions

The purpose of this study was to investigate the effects of soil moisture on the infection of tobacco-infecting cyst nematode (Heterodera glycines, HGT). In the study, quantitative inoculation and cup experiment were conducted, and population densities and dynamics of different HGT developmental stages under three soil moisture treatments, the low one with the moisture volume percentage (MVP) of 3%-9%, the middle one with the MVP of 15%-25% and the high one with the MVP of 30%-40%, were ascertained through periodical sampling and microscopic examination of the juveniles, white females and newly-formed cysts extracted from soil and the juveniles stained in tobacco roots. The results showed that the emergence in soil and penetration to root of HGT 2nd stage juveniles were both inhibited, and the developmental quantities and processes of the 3rd and 4th stage juveniles were obviously decreased and delayed under the low moisture treatment as compared with the middle one. The penetration to root of the 2nd stage juveniles were speeded up and the development of the 3rd and 4th stage juveniles occurred ahead of time under the high moisture treatment as compared with the middle one. The reproduction factors (R_f) of HGT were 0.7, 1.0 and 0.4 under the low, middle and high moisture treatments, respectively. It could be concluded that both too low and excessive soil moistures were unfavorable for the normal infection of HGT, and excessive moisture inhibited the reproduction of HGT more obviously.