Optimization of In Vitro Embryo Rescue for Mandarins Triploids (Citrus reticulata) Obtained from Diploids Crosses

Abstract

Triploidy represents a promising method for developing new citrus varieties with seedless fruits. Thus, the objective of this study was to investigate the influence of seed shape size and female parent genotypes factors on the efficiency of embryo rescue technique for the regeneration of triploids seedless hybrids from mandarin’s diploids crosses. The culture of immature embryos was initiated from the excised embryos of the four varieties of mandarin (Murcott honney, Nadorcott, variant of Murcott M104 and Ortanique). Seeds extracted from ripe fruits and immature embryos derived from abnormal seeds (small and flat) were cultured in vitro on Murachige and Tucker (MT) culture medium, supplemented with 1mg/L of acid gibberellic (GA3). The triploid seedlings were identified by the flow cytometry technique. The variance analysis showed that there are significant differences between the varieties studied for all the criteria except for the germination interval having an average value of 3 days. The germination percentage of immature embryos varied from 77% (Ortanique) to 92% (Nadorcott). Similarly, the aerial growth rate of vitroplants oscillated from 1 mm/day (Murcott Honney) to 3.70 mm/day (Ortanique) while the root growth rate evolved from 1.90 mm/day (variant of Murcott M104) to 3.80 mm /day (Ortanique). In addition, the triploidy rate evolved from 2.70% (Murcott Honney) to 13.51% (Ortanique). Flow cytometry Analysis revealed that the majority of triploids come from abnormally developed seeds (flat and small), specifically small seeds. This gave a high number of triploid seedlings, and from this the variety Ortanique showed the highest rate of regeneration of the triploid seedlings (15.38%) in comparison with the other varieties. The variation in germination rate, seedling growth and triploidy of the citrus varieties studied depends on the genotype and seed shape factors. The development and mastery of this method of preferential selection of triploids opens the way to the creation of populations of varieties of mandarin trees with seedless and easy-to-peel fruits.