Inheritance of albinism in grapefruit (Citrus paradisi Macf.; al2+al1-) and ‘Hanayu’ (C. hanaju hort. ex Shirai; al1+al1-).

Albinism seen in very young seedlings from seeds infected with Alternaria fungi and that seen in variegated leaves is known in Citrus. However, genetic control of albinism has not been reported in Citrus accessions probably because of their apomixis, self-incompatibility, long generation time and cross breeding. In the present study, albino seedlings were observed for the first time in the zygotic seedlings obtained from the crosses or backcrosses with grapefruit and Hanayu with the segregation ratio of 1 albino:3 green and 1 albino:7 green. The 1:3 ratio indicated that Hanayu and grapefruit have independent single recessive gene for the albino seedlings. The albino genes detected in Hanayu and grapefruit designated al1 and al2 respectively. On the other hand, the 1:7 ratio indicated that Hanayu or Yuzu has independent single dominant gene designating R2 a green-restorer for restoration of genetic albinism in the crosses with grapefruit. Albinism observed in the seedlings showed the stability in terms of the two albino genes and all the albino seedlings showing slow growth died several months after seed germination. When grapefruit (pummelo×sweet orange?) was crossed to 46 monoembryonic Citrus accessions including 28 pummelo accessions, albino seedlings did not segregate in the progenies of all crosses. The albino seedlings found in this study may be useful as markers in various experiments and contribute to chloroplast research in Citrus.