Estimation of the Process Invaded by Accidentally Introduced Strains of Abutilon theophrasti into Japan: Temporal Change of Chloroplast DNA Haplotype Frequencies across a Century

Thirty-nine herbarium specimens of Abutilon theophrasti collected between 1883 and 2000 were examined for chloroplast DNA (cpDNA) analysis in order to examine the invasion process by cpDNA haplotype B, which was mixed in imported grain and accidentally introduced into Japan. By using nested PCR, all of the 39 specimen materials prepared were determined to be either of two haplotypes (the total numbers of haplotype A and B were 21 and 18, respectively). The first specimen of haplotype A was the oldest of all the samples; it had been collected in Yamagata in 1883. The collection times of the haplotype A specimens ranged evenly over the surveyed period. The first specimen of haplotype B was also old; it had been collected in Tokyo in 1893. Compared to haplotype A, the collection times of haplotype B concentrated on the 1960s and 1970s. The frequency of haplotype B has significantly increased after 1946 (before 1945: 27.8%; after 1946: 61.9%). These results may suggest that the accidental introduction of haplotype B has been increasing after World War II, reflecting the increase in the amount of grain imports.