Studies on the sampling strategy for collecting plant germplasms as genetic resources

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1. Genetic edge effect may occur even with homogeneous environment, when plants operate selfing with a rate proportional to the relative amount of pollen of their own to that coming from other plants. The edge effect occurs in such a way that plants in peripheral region take a higher degree of homozygosity and genetic differentiation than those in central region. Genetic differentiation in mating system may develop in the presence of a stable pattern in plant density. The degree and pattern of this differentiation is influenced by the number of plants composing the population.2. A genetic pattern tracing the pattern of environmental cline or pocket develops under the condition that the standard deviation of gene flow distance is smaller than the width of the environmental cline or pocket. The genetic pattern develops more easily in the cline environment than in the pocket.3. Asian wild rice populations showed a wide range of outcrossing rate, 5-60%. The outcrossing rate is highly associated with life history characters ; populations with low outcrossing rates tended to be annual and have a high reproductive effort (total seed weight/plant weight) and a low pollination effort (anther weight/grain weight), while populations with high outcrossing rates tended to be perennial and have a low reproductive effort and high pollination effort. Genetic differentiation in outcrossing rate was recognized within populations with high outcrossing rates ; plants growing in peripheral region tended to have lower outcrossing rates.