野生ダイズと栽培ダイズとの自然交雑集団の探索と収集 : 秋田県および広島県における予備的調査

Exploration missions were organized to find hybrid derivatives between cultivated soybean (Glycine max ) and wild soybean (G. soja) in Japan. Presumed hybrid derivatives in NIAS Genebank accessions were screened for seed size and seed coat color in advance. The distribution of 100 seed weight of 439 Japanese wild soybean accessions showed a range from 0.85 to 7.34g with an average 2.20g, whereas 3,531 Japanese cultivars showed a range from 3.5 to 73.9g with an average 27.8g. There was an overlap between cultivated and wild soybean in the range from 3.50 to 7.34g (Fig. 1). Most cultivated accessions in the overlapped range are lines developed from several large seeded wild soybeans for fodder. Japanese wild accessions can be classified into 338 wild (76.9%), 99 semi-wild type I (22.6%) and 2 semi-wild type II (0.5%) from 100 seed weight and these two semi-wild types were collected throughout Japan. Based on an illustrated database of all wild accession seeds, \u27JP68019\u27 from Chiba prefecture, \u27JP90927\u27 from Iwate prefecture, \u27JP201170\u27 and \u27JP201115\u27 from Akita prefecture and \u27JP110756\u27 from Hiroshima prefecture included seeds with an unusual color or larger seeds than typical wild soybean (Photo 2). Although the sample number differs prefecture by prefecture, the semi-wild types or presumed hybrid derivatives between wild and cultivated soybean are distributed throughout Japan. Preliminary exploration at the sites where previous passport data records of them are available was conducted in Hiroshima prefecture at the end of September and the beginning of November (Fig. 2, Fig. 3a), and in Akita prefecture at the end of October, 2003 (Fig. 2, Fig. 3b). During the mission in Hiroshima prefecture, bulk seed samples from 15 wild soybean populations and 2 wild azuki bean populations were collected at 8 sites. In Akita prefecture bulk seed samples from 15 wild soybean populations, 5 soybean cultivars and 1 azuki bean cultivar were collected at 9 sites (Table 2). In Hiroshima prefecture, the distribution of wild soybean populations seems to be restricted due to frequent weeding and cutting around fields and we could not find large-scale soybean cultivation. The site where outcrosses might have occurred between cultivated and wild soybean is a river embankment where the intermediate \u27JP110756\u27 was collected. In Akita prefecture, we visit the sites where \u27JP201170\u27 and \u27JP201115\u27 were collected. In these sites we could not find the same phenotypes but seed without bloom on seed coat was found frequently. This preliminary field survey for wild soybean resulted in identification of an intermediate individual between wild and cultivated soybean in one natural habitat (Photo 2). An intermediate type was found in the wild population on the road side about 15m from soybean field at site 39 in Akita prefecture (Fig. 3). Morphological characteristics of the individual clearly showed its intermediate status between cultivated and wild soybean (Photo 3, Table 1). These indicate that the individual is a hybrid or its derivative and gene introgression is occurring from cultivated into wild soybean. Seeds of the intermediate were retained in the pods whereas wild soybean seeds were already scattered from the pods (Photo 4). We left most of the seeds for future monitoring to determine whether the progenies can survive in the natural environment. This finding leads us to expand exploration throughout Japan next year for wild/cultivated hybrids