Evaluation of genetic stability in olive callus-induced and meristem-induced shoots using flow cytometry and amplified fragment length polymorphism techniques

BACKGROUND: In vitro culture of olive, as an economically valuable tree, has fundamentally a genotype-dependant low micropropagation rate which needs to be improved in already established and newly released cultivars. Various plant tissue culture media, planting systems and growth factors were evaluated in two promissing Iranian olive cultivars ˈAminˈ and ˈMeshkatˈ and the commercial Spanish cultivar ˈArbequinaˈ. RESULTS: The results showed that cultivars have their specific optimal media, i.e. ˈAminˈ in the MS with 4 mg/L zeatin, ˈArbequinaˈ in the OM with 1 mg/L zeatin, and ˈMeshkatˈ in the OM and MS with 2 mg/L zeatin, which produced significantly a higher number of axillary shoots than other media. The results also indicated a significant improvement in the growth indices of ˈAminˈ (number of axillary shoots) when cultured using periodical mini bioreactor (PMB) in the VS medium. In comparison with VS, OM did not reveal any significant differences when both culturing systems (PMB and semi-solid media (SSM)) were used. Regarding the effect of carbon source and light intensity, mannitol and 2000 cd sr m⁻² greatly enhanced ˈArbequinaˈ growth indices (main shoot length and growth quality). The results of genetic stability of callus induced shoots (CIS) and meristem induced shoots (MIS) revealed that 2C DNA value assessed by partec flow cytometery (FCM) had 0.01, 0.03 and 0.08 pg discrepencies in ˈAminˈ, ˈArbequinaˈ and ˈMeshkatˈ, repectively. The Amplified Fragment Length Polymorphism (AFLP) results also indicated that the cultivars were classified regardless of the micropropagation origin (CIS or MIS), except for ˈArbequinaˈ. The AFLP findings showed that ˈArbequinaˈ had the highest dispersal (7–38%) in CIS and MIS, while the Iranian cultivar of ˈMeshkatˈ (5–9%) had the highest stability. CONCLUSIONS: This study indicated the importance of in vitro growth parameters for improving the micropropagation indices of olive cultivars. It showed that optimized protocols (OM, PMB, zeatin, mannitol and 2000 cd sr m⁻²) co-produced larger calli resulting in indirect organogenesis. Based on FCM and AFLP analysis, it can be concluded that true-to-typeness of micropropagated olive was cultivar-dependent.