FRIABLE CALLUS INDUCTION AND ORGANOGENESIS CONDITIONS IN A FEW STRAINS OF Poncirus trifoliata

Citrus species are the most widely produced fruit crops in the world. Citrus rootstock Poncirus trifoliata, is characterized by cold hardiness and resistance to Phytophthora, nematodes and Tristeza virus. These characteristics can be exploited in somatic hybridization using protoplast fusion, which enabled to produce promising somatic hybrids. Nevertheless, the Poncirus trifoliata genotypes are highly recalcitrant to friable callus formation, hence the need to optimize the conditions and improve the efficiency of tissue culture. The objective of this study is to evaluate the effect of hormonal composition of the medium on friable callus induction, rate of growth, and regeneration of plants by organogenesis from Poncirus trifoliata calluses. Mature embryos of two Poncirus trifoliata genotypes were isolated from the seeds of ripe fruits, then cultured on MS medium supplemented with 30 g/l of sucrose and plant growth regulators (2,4-dichlorophenoxyacetic acid [2,4-D] and 6-benzylaminopurine [Bap]) at different concentrations. Comparison of the two genotypes was reported with regard to the efficiency of callus induction from mature embryos. In all media, both genotypes of Poncirus responded by forming friable callus. Some media have resulted in the plant neoformation depending on their composition. Furthermore, the study has revealed that callogenesis is conditioned by the nature of the plant regulator used and its interaction with the genotype. The protocol used in this research will pave the way for the development of an in vitro regeneration system for these cultivars and will therefore favor the application of plant tissue culture in the resistance improvement programs.