CITRUS PENTAPLOIDS FROM SMALL SEEDS OF DIPLOID X DIPLOID CROSSES

Seedlings from some small seeds of diploid x diploid crosses using 'Miyauchi iyokan' (Citrus iyo Hort. ex Tanaka) as the seed parent were found to be pentaploid (2n = 5x = 45). The growth of pentaploid seedlings was extremely weak on their own roots, but was much more vigorous when micrografted on seedlings of tetraploid trifoliate orange [Poncirus trifoliata (L.) Raf.]. Diploid 'Miyauchi iyokan' produced hexaploid seedlings from small seeds in addition to triploid and tetraploid seedlings from normal seeds when crossed with tetraploid 'Funadoko' (C. funadoko Hort. ex Y. Tanaka) and 'Trovita' sweet orange [C. sinensis (L.) Osbeck]. Based on this phenomenon, the origin of pentaploids is discussed.