Anatomical features of the bark as a factor of resistance of fir species to infestation by the four-eyed fir bark beetle

Abstract

To elucidate the reasons for the differences Fir species (Abies. Mill.) damage by four-eyed fir bark beetle (Polygraphus proximus Blandford), we studied the structure of fir bark in sections Balsamea, Momi, Abies, Grandis from the collections of the Tsitsin Main botanical garden of the Russian Academy of Sciences. In the bark, the features of the structure of the outer bark tissues (periderm and rhytidome) and the inner bark, which consisted of the cortex and secondary phloem, were studied. Species of fir, the outer bark of which are formed by periderms including layers of spongy and stony (lignified) phellem (phellem of Manchurian fir (Abies holophylla Maxim.), Nikko fir (A. homolepis Siebold & Zucc.), Nordmann fir (A. nordmanniana (Steven) Spach)), as well as species that early formed a rhytidome (Nordmann fir), are practically not colonized by the P. proximus. The cork of fir species, the phellem of which is represented by the same type of suberinized cells, and having a small thickness (species from section Balsamea), is more attractive for invasion by the P. proximus. The relationship between damage by the P. proximus and the structural features and the ratio of the components of the outer and middle layers of the inner bark, where the degree of sclerification is the main factor, is noted. The least attractive for P. proximus are the fir species that have a high degree of sclerification of the outer and middle layers of the inner bark. The degree of constitutional resistance to P. proximus increases with an increase in the degree of accretion and size of sclereid groups, the uniformity and density of their distribution. The most vulnerable are firs with a low degree of sclerification of the outer and middle layers and/or an uneven and loose distribution of sclereid groups, and firs with an increased and high content of mucilage cells (Siberian fir (A. sibirica Ledeb.)). An inverse relationship was noted between the degree of sclerification and the content of mucilage cells. A clear relationship between P. proximus and the content of calcium oxalate crystals, as well as the characteristics of the resinous system, has not been established.

Keywords

• polygraphus proximus blandford
• abies
• rhytidome
• periderm
• phellem
• cortex
• secondary phloem
• sclereid groups
• mucilage cells