Regeneration and characterization of plants derived from leaf in vitro culture of two sweet orange (Citrus sinensis (L.) Osbeck) cultivars

In the current work attempts were made to investigate culture of leaf explants derived from in vitro seedlings of two sweet orange (Citrus sinensis (L.) Osbeck) cultivars, Bingtangcheng and Valencia. Effects of several factors, including culture medium, lighting condition, explant age and genotype on regeneration response were examined based on three parameters, percentage of explants producing shoots, mean number of shoots per explant and shoot forming capacity. Culture of the explants on shoot-inducing media (SIM) composed of MT salts supplemented with different growth regulators gave rise to disparate shoot regeneration, in which SIM₁ (MT + 0.5 mg L⁻¹ BA + 0.5 mg L⁻¹ Kinetin + 0.1 mg L⁻¹ NAA + 3% sucrose + 0.8% agar, pH 5.8) was shown to be the most effective medium for direct induction of shoots from leaf explants. Highly significant difference in the response of shoot bud regeneration was noted between the two cultivars, with Bingtangcheng being more responsive than Valencia. Culture of explants from fully developed leaves led to better shoot regeneration capacity in comparison to undeveloped ones. However, the two lighting conditions used herein did not cause significant difference in shoot regeneration. Phenotypic observation and randomly amplified polymorphic DNA (RAPD) analysis confirmed that all the regenerated plants from both genotypes were genetically identical to their donor plants, suggesting absence of detectable genetic variation in the regenerated plants. The data presented here demonstrated that direct initiation of plants from leaf explants has been successfully accomplished. To our knowledge, this is the first report on direct regeneration of shoots from leaf explants in Citrus, which will provide an alternative source for citrus genetic manipulation in the future.