Comparison of Susceptibility to Racodium therryanum Infection of Seeds and Seedlings of Four Coniferous Species

1990

S. 125-136

5 Abb., 2 Tab., 19 Lit. Ang.

Unselbständiges Werk

200037152

The susceptibility of seeds and seedlings of four coniferous species to dark snow-blight, caused by Racodium therryanum Thuem. was compared by examining the disease development. In a seed inoculation test, the seed viability of Glehn's spruce (Picea glehnii Mast.) decreased much more quickly than that of the Yezo spruce (P. jezoensis Carr.), Sakhalin fir (Abies sachalinensis Mast.) and Japanese larch (Larix kaempferi Carr.) indicating that Glehn's spruce seeds are, of the four species, most susceptible to Racodium therryanum infection. In field testing, both Glehn's spruce seeds and Yezo spruce seeds were found to be markedly susceptible to the complex infections induced by plural pathogens including R. therryanum, more so than the Sakhalin fir and Japanese larch. Temperature-disease relation test showed that at 0C, the tested seeds were completely infected by R. therryanum in all four of the species; however, at 5C and 10C, a portion of Sakhalin fir and Japanese larch seeds germinated without suffering any R. therryanum infection, while none of the Yezo spruce or Glehn's spruce seeds germinated. An explanation of this could be that Sakhalin fir and Japanese larch seeds may possess a partial tolerance to R. therryanum infection under 5C and 10C. On R. therryanum-infested soils, Sakhalin fir seedlings survived much longer than did either the Yezo spruce, Glehn's spruce, or Japanese larch seedlings. This indicates that Sakhalin fir seedlings have a greater tolerance to R. therryanum infection than seedlings of the other tree species. The natural regeneration of Yezo spruce does not occur as often as that of the Sakhalin fir. The remarkable difference in seed-seedling disease- tolerance between these two conifer species, as shown in this study, is likely an important factor responsible for the formation of this phenomenon. Theoccurrence of Glehn's spruce regeneration is, as is well-known extremely restricted to the mineral soil-exposed sites which is usually pathogenic organism-free. Such a restriction of Glehn's spruce regenration may have arisen, at leat partially, from the extreme susceptibility of this species to R. therryanum infestation.