In vitro seed culture , germination, shoot regeneration and mutant induction techniques in lansones (Lansium domesticum Correa)

Langsat or Lansones (Lansium domesticum Correa) is a very popular fruit in South-East Asia which ranks among the top ten fruits in Malaysia, Thailand and the Philippines. In this species parthenocarpy is the rule and apomixis as evidenced by multiple seedlings due to polyembryony is quite common. No breeding has been attempted, and propagation is limited to seeds and through grafting to achieve fruiting in half-time (5-7 years). Mutation breeding by ionizing radiation is a potent strategy to induced and select for improved traits particularly early fruiting, dwarfing, improved fruit quality and disease resistance in lansones. This study involve the establishment of in vitro culture requirements for aseptic seed culture, germination and shoot regeneration in lansones 'Paete' followed by gamma-irradiation of cultured seed . The first two replicated experiments involved the culture of 81 seeds in MS basal medium with 30 g/L refined sugar and 2 mg/L BAP) L1 medium). On the average, 86.6 percent germination was achieved in 30 d of culture with 1.5 and 2.1 shoots produced at 30 and 60 d, respectively. The third experiment involved the comparison of germination and shoot regeneration as influenced by four culture media namely LO (MS basal medium with no growth regulator), L2 (B5 basal medium with 1 mg/L each of BAP and GA3, and L3 (WPM medium with 1mg/L each of BAP and GA3) with L1 medium as check. Higher percent germination was achieved using LO (92.2 percent) and L2 (92.6 percent)as compared with L3 (81.3 percent) and L1 (80.4 percent). However, earlier shoot germination was recorded in L2 (24.4 d) and L3 (25.2 d) as compared with L1 (34.6 d) and LO (33.0 d). Highest number of shoots produced after 60 d was obtained in L1 (2.5 shoots) followed by L2, L3 (1.9 shoots) and lowest in LO, (1.5 shoots). Addition of BAP alone or BAP and GA3 had significant effects on days to germination, number of shoots and shoot length. The fourth experiment involved exposure of cultured lansones seeds in L1 medium to gamma rays (_0, 10, 20 and 40 Gy) followed by shoot regeneration. Number of shoots regenerated was significantly reduced from 2.6 (control) to 2.0 (10 Gy), 2.1 (20 Gy) and 1.6 (40 Gy). Shoot tip and nodal explants from irradiated seedlings were successfully advanced through micropropagation.