Neem Oil to Reduce Zeatin Use and Optimize the Rooting Phase in Olea europaea L. Micropropagation

Abstract

Micropropagation is an in vitro propagation technique, established in the nursery field sector for numerous species, which offers several advantages compared to traditional agamic propagation techniques. In the case of the olive tree, however, despite the advances made through research, it is still little used, due to the recalcitrance to in vitro proliferation and/or rooting of many olive cultivars and the high cost of zeatin, the only cytokinin that makes it possible to achieve a satisfactory proliferation rate in this species. In this context, numerous attempts have been made to identify alternative cytokinin compounds able to improve the proliferation rate of olive tree explants and thus reduce the unitary production cost. In particular, there is a growing interest in the use of natural substances (called in some cases “complex mixtures”), which, when added to the in vitro cultivation substrates, seem to be able to improve proliferation rates. In the present study, neem oil was added to the propagation substrates (partially/totally replacing zeatin) and in the rooting phase for the olive cultivar Moraiolo. In particular, in the proliferation phase, the effect of neem oil (0.1 mL L−1) in substrates containing different zeatin concentrations (0, 1, 2, and 4 mg L−1) was evaluated. For the rooting phase, agarized substrate and soil were used with shoots derived from a standard proliferation substrate (4 mg L−1 zeatin) and from the substrate that gave the best results in the proliferation phase (2 mg L−1 zeatin and 0.1 mL L−1 neem oil). In the proliferation phase, the addition of neem oil in the substrates with low zeatin concentration (1 and 2 mg L−1) induced an increase in the number of adventitious shoots and shoots length. On the contrary, the addition of neem oil in the rooting substrates did not positively influence the rooting phase, but positive results especially in terms of root number and length were observed in explants derived from a neem oil-enriched proliferation substrate compared to the control substrate. Therefore, the present study demonstrated for the first time the positive role of neem oil in the proliferation of olive in vitro with low zeatin concentrations.

Optimization of the In Vitro Proliferation of an Ancient Pear Tree Cultivar (‘Decana d’inverno’) through the Use of Neem Oil

“…In particular, neem oil, especially at 0.1 mL L −1 improved shoots number and length, and this is very important because it allow to have easy-to-manage shoots in subculturing activity. A similar effect was observed in vitro on olive where neem oil improved shoots length, multiplication rate, and fresh and dry weights of the proliferated explants [19] and was able to replace zeatin partially [20]. To the best of our knowledge the mode of action of neem oil in plants was still not investigated.…”

“…Among the natural substances that can be used in the composition of in vitro growing media there is neem oil. Previous researches [19,20] demonstrated beneficial effects related to the use of neem oil for olive micropropagation, but no studies were conducted on in vitro culture of other plants species. Neem oil is obtained from Azadirachta indica A. Juss seeds and thanks to its composition its widely used in agriculture and for human health [21].…”

Comparative transcriptomic and hormonal analyses reveal potential regulation networks of adventitious root formation in Metasequoia glyptostroboides Hu et Cheng

“…Rooting recalcitrance has been a major limitation in the vegetative propagation of elite plant germplasm [49][50][51]. In general, PGRs can effectively induce or promote AR formation, combined with or without other regulators, and are the dominant factor affecting AR induction in the clonal propagation of many plant species [52][53][54].…”

Micropropagation of autochthonous olive varieties from Türkiye

“…The best results were obtained on OM with the addition of 2.0 mg/l zeatin. Regni et al (2023) used neem oil as an alternative to Zeatin for in vitro micropropagation and rooting of the Moraiolo olive variety. In the experiment they added neem oil to propagation medium.…”