Study on inheritance of huge root in radish 'Sakurajima Daikon'

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'Sakurajima Daikon' is the biggest radish in the world. It is maintained only by 11 local farmers around Mt. Sakurajima, Kagoshima. Each of them maintains this cultivar in his small field, producing his own seeds. The gene pool of this cultivar is considered to be very small. On the other hand, radish has strong inbreeding depression which produces very small, feeble plants only by 3 successive selfings. The purpose of this research was to clarify the mechanism of hugeness maintaining in this cultivar which has only a small gene pool.Each farmer has his own growing and seeding method. They select "Female(F)" , "Male(M)" and their intermediate type from their population, and these plants are open-pollinated for seeding. The seeds collected from F and the intermediate type were used and planted here, and the "sex" type of the seedlings were judged for pollination later. In 1999 and 2000 they were self- and cross-pollinated, and then the plants were harvested in the following years.In the first generation, selfed population showed lower yield than the controlof the farmer's original population, while crossed population showed higher yield. However, in the second generation, the selfed population of F type reduced the yield to a half, and that of M type did not reduce the yield, while crossed one of the both increased it.Selfed populations of both F and M type produced a variation of "sex type".'Sakurajima Daikon' is considered to be a heterogeneous population, and M type might be a factor of vigor in the population. DNA markers related to the "sex" type will be searched to clarify the machanism of hughness maintaining.