Gibberellin and cytokinin in synergy for a rapid nodal multiplication system of avocado

Conventional clonal avocado rootstock propagation relies on a 40 year old method and derivatives thereof that is labour intensive and does not facilitate cost effective supply of clonal rootstocks for the rapidly developing needs of the industry. This is especially relevant if high density plantings or clonal rootstocks are to be adopted. An alternative tissue-culture-based clonal propagation system could provide efficient, cost effective, high volume and sterile production of clonal rootstocks. Avocado, being a woody plant species, is not highly amenable to tissue culture, with most attempts confined to nodal culture methods. Thus far, nodal cultures of avocado show very slow growth and produce stunted shoots, limiting rapid shoot multiplication. The current study aims to develop a system to multiply nodal avocado shoots using gibberellins and cytokinins to produce taller shoots with a higher number of nodes for continuous culturing. Cytokinins, the most important plant growth regulator in shoot regeneration, and gibberellins, which promote internode elongation, can synergistically improve the quality shoots for rapid nodal multiplication. The effect of different combinations of the natural aromatic cytokinin, Meta-topolin, and the active gibberellin, GA3, on bud breaking time, shoot height, number of open leaves, overall shoot quality, vitrification and callus production in continuous culture of avocado nodes were assessed. The results reveal optimal hormone combinations for improved nodal multiplication for the avocado tissue culture pipeline.