In Vitro Development and Germination of Immature Embryos of Sweet Oranges Parson Brown and Pineapple (Citrus sinensis)

Abstract

Oranges are classified as the most traded fruit variety worldwide. The diversification of the varietal profile of this group is among the objectives of the Citrus breeding program. So, the creation of new triploid hybrids via immature embryos rescue, can lead to an increase in gene pool and produce seedless varieties. In addition, flow cytometry was successfully used for analyzing ploidy levels and genetic origin of triploid plants. The present study was aimed at optimizing immature embryos in vitro germination and plantlet development based on medium chemical composition of the two orange varieties, Pineapple and Parson Brown. When the fruit gets matured, they are harvested and the seeds extracted are classified according to their size. Only those which are small are cultured in a sterile Murashige and Tucker (MT) basal medium. The different concentrations of growth regulators are put to the test in order to gain the best medium for seeds development. M1 (MT + 1 mg/L gibberellic acid (GA3)), M2 (MT + 1 mg/L kenitin + 0.5 mg/L 6-benzylaminopurine (BAP) + 0.1 naphthalene acetic acid (NAA)), M3 (MT + 25 mg/L adenine sulfate (ADS)), M4 (MT + 0.5 mg/L kenitin + 0.5 mg/L BAP + 1 mg/L GA3). Percentage of germinated embryos (PGE) is the highest in M3 with 100% and 90% for both Pineapple and Parson Brown varieties, respectively. In addition, the germination interval average (GIA) is shorter in M1 for both varieties, which takes 6 d and 7 d, respectively. As regard to speed seedling growth (mm/week), both varieties undergo significant change in all four mediums. Similarly, the highest rate of acclimatization for the Pineapple and Parson Brown varieties is 80% and 90% in M1. In general, the smaller the embryos are, the more sensitive they are to culture medium composition. It is therefore essential to optimize the medium components in order to stimulate their in vitro development. Therefore, M1 (MT + 1 mg/L GA3) remains the best to promote short term good germination and produce a better rate of acclimatization.