Somatic embryogenesis in non-irradiated and gamma-irradiated embryogenic cultures of avocado (Persea americana Miller)

摘要

The embryogenic culture and somatic embryogenesis induction responses of eight avocado varieties and select seedling trees were established during a four-year (2002-2005) study. Higher embryogenic culture formation was induced from immature zygotic embryos of seven avocado genotypes cultured in SE2 medium (MS + 30 g/L sucrose + 0.1 mg/L picloram) than in SE1 medium (MS + 30 g/L sucrose + 5 mg/L 2,4-D + 0.5 mg/L BAP). Embryogenic cultures developed into somatic embryos after repeated subcultures in SE2, SE3 (MS + 3 0 g/L sucrose + 0.1 mg/L TDZ + 0.5 mg/L GA(3)) and SE4 (MS + 30 g/L sucrose + 2 mg/L BAP + 1 mg/L IBA) media. Plantlet and shoot regeneration from matured somatic embryos of 'Semil' variety were consistently obtained in 3 trials at 16.3, 23.0 and 20.7%. The best medium for germinating somatic embryos was R4 regeneration medium (B5 macro salts + MS minor salts and vitamins + 60 g/L sucrose + 400 g/L glu +2 mg/LBAP+ 4.5g/L Phytagel). Exposure of the embryogenic cultures of 'Semil' to gamma rays (10-30 Gy)resulted in reduced re-growth/proliferation of embryogenic cultures and consequently reduced formation of torpedo/cotyledonary stage somatic embryos. However, plantlet and shoot regeneration from somatic embryos from gamma-irradiated cultures was comparable or even higher (17.8-26.9%) as compared to the control (18.3%). Over 200 somatic embryo-derived putative avocado variant and mutant lines were produced from tissue culture alone and tissue culture-gamma irradiation technologies. Micrografting and in vitro rooting are being done to rescue and ensure greenhouse establishment of the regenerants for mutant confirmation by molecular analysis. This is the first ever successful application of tissue culture and gamma irradiation technologies towards the production of potentially useful mutants or variants in avocado.