Herbarium collections in molecular genetic studies

There are more than 3400 scientific herbaria in the world, with about 390 million specimens collected over the past 400 years, which document the Earth’s plant diversity. Information stored in the herbarium collections is not out of date over time and creates the basis for conducting and developing biodiversity research. The real breakthrough in the methodology of studying herbarium specimens over the past two decades has been the use of DNA technology, which has become possible due to the development of more advanced methods of DNA extraction, PCR analysis and sequencing. More often, herbarium specimens are becoming the object of comprehensive studies on systematics and phylogeny, changes in the genetic structure of populations in different historical periods and on the analysis of the gene pool and in studying the history of the introduction of plant species, using both classical botanical methods and involving modern methods of molecular genetics. At the same time, parallel studies of herbarium plants and pathogenic organisms preserved on them are carried out to study historical epiphytoties and the joint evolution of the pathogen-host system. Present review summarizes the recent results of molecular genetic studies of the herbarium collections. Molecular genetic studies of herbarium specimens are associated with a number of methodological difficulties. Analysis of the literature indicates that DNA changes can be caused by various reasons and factors associated with both plant herbarization and with long-term storage of herbarium specimens. In a number of studies, the dependence of the quality of isolated DNA on the age of the herbarium specimen, as well as on the state of the stored plants, has been demonstrated. Moreover, the rate of fragmentation of nuclear and plastid DNA in herbarium plants may vary. The use of modified techniques aimed at the removal of oxidized polyphenols and the extraction of even small fragments allows to overcome the problems of drug contamination and the loss of significant fractions of the degraded DNA during isolation. The prospects for studies of herbarium collections using NGS analysis, which removes many methodological limitations, are considered.