An efficient protocol for micropropagation of lemon (Citrus limon) from mature nodal segments

Abstract

The influence of the basal medium and different plant growth regulators on micropropagation of nodal explants from mature trees of lemon cultivars was investigated. Although the basal medium did not affect any of the variables, explants on DKW medium were greener. Several combinations of 6-benzyladenine (BA) and gibberellic acid (GA) were used to optimise the proliferation phase. The number of shoots was dependent on the BA and GA concentrations and the best results were obtained with 2 mg l−1 BA and 1 or 2 mg l−1 GA. Explants length was shorter with the higher BA concentrations and, in all genotypes, shoot length was greater with 2 mg l−1 GA. The best results for productivity (number of shoots × the average shoot length) were obtained with 2 mg l−1 BA and 2 mg l−1 GA, although explants with chlorosis and narrow leaves were observed. The presence of BA and GA in the proliferation medium was essential for the explant multiplication but GA had a greater influence. The transfer of in vitro shoots to rooting media, containing different concentrations of indole butyric acid (IBA) and indole acetic acid (IAA) produced complete plantlets. Lemon shoots rooted well in all rooting combinations. The highest rooting percentages were obtained on media containing 3 mg l−1 IBA alone or IBA in combination with 1 mg l−1 IAA and on these media the highest numbers of roots were produced. The average root length was affected significantly by the IBA and IAA concentrations. Root length was greater when only 3 mg l−1 IBA was used, and in this rooting medium explants had a better appearance, with greener and larger leaves. The success during the acclimatisation was close to 100% and the plantlets exhibited normal growth in soil under greenhouse conditions.