The principle of its identification

5 .8, 18 and 28 SrRNA genes on rDNA are highly conserved, that is, they have extensive heterologous homology. However, because the mature ribosome is not added to its region, there is little pressure on natural selection of its fragments during evolution, so it can tolerate more variation. There is a wide range of sequence polymorphism in most eukaryotes. Even if two species are closely related, their ITS sequences will be different, showing the characteristics of recent evolution. The research shows that the evolution rate of its fragment is 10 times that of 18 S rDNA. This is the theoretical basis of ITS sequence in microbial species identification and community analysis. ITS 1 and ITS2 are moderately conserved areas, and their conservativeness is basically characterized by relative consistency within species and obvious differences among species. This feature makes it suitable for molecular identification of fungal species and phylogenetic analysis of flora with obvious intraspecific or interspecific differences. Because ITS sequence analysis can substantially reflect the difference of base pairs among genera, species and plants, and its sequence fragments are small and easy to analyze, it is widely used in the phylogenetic study of different species or similar genera in fungi. ITS sequence analysis can also effectively solve the controversy caused by the classification of black seed beans, black seed beans, tuber beans, black seed beans and oil tree beans by morphological characteristics, and make up for some shortcomings in traditional classification.