Acclimation ex vitro: How to improve the root system

Acclimation ex vitro is considered one of the most critical stages of the whole micro-propagation cycle. The root system is still weak and root growth and absorption need to be improved to compensate the increasing leaf transpiration and need of nutrients. The experiments presented in this study aimed to improve the aerial and root growth by using different substrates (type and mode of filling of the pots) in combination with specific fertilizers and replacing part of the root absorption with nutrient application to the leaves. The supply of mineral elements and organic compounds to the leaves in synergy with the available reserves in the seedlings can avoid the increasing of the cost of the absorption process for the plantlet. Results confirm the importance of the substrate to affect root growth and establishment. The quality of the growth of root and foliar P, K, Ca, Mg, and humic acids application positively influenced the growth and the plant settlement. Results showed that foliar applications in fertilized growing media are able to enhance vegetative growth, dry matter accumulation and basal steam diameter in all the tested clones. When nonfertilized growing media are used, foliar application is less effective in controlling vegetative growth to obtain the required height and basal stem diameter. This study suggests that is advisable to have a micro-porous substrate and apply moderate fertilizations through the substrate. The supply of the nutrients to the leaves resulted in bigger, but well hardened plants. It is possible to argue that changing concentrations and ratio among the different elements according to the acclimation cycle stage would balance vegetative growth and reduce hidden stresses.