IMPROVEMENT OF TROPICAL AND SUBTROPICAL FRUIT TREES: TANGERINE, PUMMELO IN THAILAND THROUGH INDUCED MUTATION AND BIOTECHNOLOGY

Acute and chronic gamma irradiations for mutation induction in tangerine (C. reliculata) and pummelo (C. grandis) were studied to produce new cultivars with seedless or less seed by using cultured shoot and root from seeds, scions and pot plants. These experiments were conducted at Gamma Irradiation Service and Nuclear Technology Research Center, Horticulture Research Institute, Phichit and Phrae Horticultural Research Center between 2000 and 2006. The results showed that the optimum medium are MS+BA 2 mg L^-1 for shoot induction and MS+BA 2 mg L^-1 (half) for root induction. Irradiation with Chronic 0, 4, 8, 12, 16, 20 and 24 Krad of gamma rays and Acute 0, 4, 6 and 8 Krad of gamma rays were treated and later, they were irradiated one more time. The M₁V₀ were developed to be M₁V₄ in the MS + BA 2 mg L^-1 medium. After that, the plantlets (M₁V₄) were transplanted to pots and will be planted in the field for further selection. The scions which were treated by acute and chronic irradiation were budded on rootstocks and on mature plants and also, the irradiated pot plants were planted in the field at Phichit and Phrae HRC. The cutting back technique was used to develop M₁V₀ to M₁V₄. After that, the fruit quality and seedlessness of these plants were investigated. It was found that 2 M₁V₄ 'Khao Thong Di' pummelo which were treated with gamma rays by chronic irradiation with 9.51 and 32.45 Krad, have fruits with seedless. Also, 6 M₁V₃ and 5 M₁V₄ tangerine plants which were treated with gamma rays by acute irradiation at 4 and 8 Krad, have fruits with less seeds. However, the fruit quality and seedlessness from these plants will be further evaluated for another 1-2 years before release to the farmers.