Abstract
Viability, one of the major components of fitness, has been studied in natural populations of T. kamtschaticum. The main points discussed are as follows.
1. The f value computed for chromosome E was chosen as an estimate of inbreeding coefficient for each population. This was on the assumption that this chromosome was relatively neutral in viability.
2. With this f value, a method was proposed to measure the viabilities of genotypes when the only available data are from natural populations.
3. The method was applied to actual data obtained from natural populations of T. kamtschaticum and it was concluded that the heterotic viability is a general phenomenon in natural populations of this plant.
