一般认为，玉米青枯病病原主要是从根部侵染而后向地上部扩展，继而导致发病。但作者在研究中发现一些没有发病的植株茎节也可分离到病原菌。为进一步证实这一现象，作者通过对不同的发病时期和部位进行了观察。发病时期分为发病前、正发病和已发病（l周左右）3期；分离部位分 It is generally believed that the pathogen of corn bacterial wilt mainly spreads from the roots to the shoots and then causes the disease. However, in the study, the authors found that some uninjured plant stem nodes can also be isolated from pathogens. To further confirm this phenomenon, the author through different stages of disease and site were observed. Incidence period is divided into before onset, is the incidence and has been the incidence (l weeks) 3; part of the separation