虽然植物病理学有较长期的发展,但直到目前仍有许多植物病害的病原还未被查明。其原因在于研究方法的不完善和许多国家在这方面的工作进行得很不广泛。直到1967年方止,一般认为多数黄化病的病原是病毒;它们可以由嫁接或传毒昆虫传布,但在任何时候几乎不由汁液,也就是机械的方式传布,因而它的真正的病原并没有被研究者们加以肯定。 1967年道伊等研究这类病害时在被侵染植株的韧皮部发现了形态既不象细菌,更不象病毒的细胞含物。研究者们推测,这些细胞含物是有生命的有机体,其组成结构 Although plant pathology has longer-term development, the pathogen of many plant diseases has not been identified until now. The reason for this is the imperfectness of the research methodology and the very poor work done by many countries in this area. Until the end of 1967, the majority of the etiological agents of yellowing were thought to be viruses; they could be spread by grafting or poisoning insects, but at any time they were rarely spread by juice, that is, mechanically, so that their true pathogen did not Be affirmed by researchers. In 1967, when studying such diseases, Dow et al. Found that the morphology of the phloem in the infected plants was not like that of bacteria but rather of the cellular contents of viruses. Researchers speculate that these cellular contents are living organisms, the composition of the structure