PLANT MATTER OF THE KHAKASIA CATENA

The article presents the material on the species composition and biological productivity of grass ecosystems along the catena to Lake Utichye on the territory of the Iuso-Shirin steppe of Khakasia. Describs pattern of below-ground and above-ground components in stepр ecosystems 30% of the living phytomass is located in the soil and no then 60 % is allocated in below-ground organs. The productivity of the steppes varies depending on the type of ecosystem. In the ecosystem of the desert steppe, the vegetation cover has a minimum number of species, aboveground phytomass, a maximum number of underground organs, and the fraction of dead roots prevails, up to 50%. The richer and more humid ecosystems, the greater the diversity of species in the vegetation cover, the more reserves of aboveground phytomass and living underground organs. Dead root stocks are reduced to 20-35%.

Initial Cellular Interactions Between Thielaviopsis basicola and Tobacco Root Hairs

Cellular events that occur during the initial interactions between Thielaviopsis basicola and root hairs of tobacco (Nicotiana tabacum) were examined microscopically. Time-course documentation of the infection process indicated a dynamic interaction between T. basicola and the living host cell. Upon root hair contact and recognition, the vegetative apex of T. basicola rapidly differentiated to form infection structures, and the host cell responded cytologically. Penetration was achieved by threadlike hyphae that subsequently developed distal swellings, and intracellular hyphae of sickle-shaped morphology advanced from the distal swelling and colonized the cell. Streaming of the host cytoplasm became aggregated near the infection site prior to penetration and accumulated around the infecting hyphae as long as the host cell was viable. Substantial callose deposition, in the form of a bell-shaped collar around infection structures, resulted from the cytological activity at the infection site. Penetration of dead root hairs was common, but did not lead to the development of infection structures or to a sustained association with the host tissue; T. basicola exited dead root hairs and resumed vegetative growth. The establishment of the parasitic relationship by T. basicola was characteristic of hemibiotrophic fungi in that, initially, biotrophic infection led to tissue colonization, and host cell survival was limited under parasitism.

The development of the fungal sheath on Cistus incanus short roots

Sheath development of mycorrhizae of Cistus incanus L. ssp. incanus + Tuber melanosporum Vitt. synthesized under gnotobiotic conditions was studied by anatomical and ultrastructural techniques. Root systems examined at different times after inoculation exhibited short lateral roots which could be categorized as follows: (i) uninfected; (ii) with hyphae in the dead outer root cap cells; (iii) with developed sheaths. In the last case the inner hyphae of the sheath penetrated through remains of dead root cap cells which were trapped in the inner sheath. Remains of root cells were also found in the outer sheath. Growth of hyphae into the dead layers of the root cap leads to formation and development of the sheath.

ROOT WOUNDS AND ASSOCIATED ROOT ROTS OF WHITE SPRUCE

The root systems of 656 trees from 7 to 180 years old at three locations in Manitoba and Saskatchewan were examined for wounding and root rot. Twenty-seven per cent of 1170 diseased roots bore wounds caused by Hylobius spp. larvae which were associated with the entry of root-rotting or staining fungi. The fungi appeared to have entered mainly through insect-girdled roots, one-half inch in diameter or smaller, and to a less extent directly through the decorticated wood of larger roots. In individual trees, root rot and stain was highly correlated (r = 0.5357) with Hylobius wounding. Wounds caused by excessive moisture, root compression, and animal trampling were associated with the entrance of fungi in 7.1, 4.7, and 1.5 per cent, respectively, of the diseased roots. Eight per cent of the diseased roots were infected from established decay in the root crown. Root cankers and dead root ends, both of unknown cause, were associated with the entry of root fungi in 7.3 and 5.7 per cent of the roots respectively.