Potentiel des Endophytes locaux pour la production de Rhizomes, de Curcumine et la stimulation des activités antioxydantes et antimicrobiennes chez Curcuma longa

Abstract

Turmeric has enormous medicinal properties due to the presence of curcumin, hence its high demand on the international market. However, the production of turmeric and curcumin in Cameroon remains low and not well known. One of the ways to maximise this production is to evaluate the association between turmeric and endophytes. The objective of this work is to determine the effect of local endophytes on the production of rhizomes and curcumin and on the stimulation of the antioxidant and antimicrobial activities of Curcuma longa. For this purpose, turmeric was grown on 8 different substrates. At the 3rd month of culture, endophytes trapped in turmeric roots were isolated on different culture media. Isolation was performed by the fragment method after surface sterilisation. Endophytes were then characterised, and the most efficient ones were applied to another turmeric culture in a non-randomised block design. Endophytes were tested in vitro against 4 major plant pathogens and the curcumin content and oxidation markers of the biofertilised turmeric were determined by spectrophotometry. After 7 months of cultivation in pots on 8 substrates (from 5 agro-ecological zones of Cameroon), the rhizome biomass obtained ranged from 5.0 to 11.44 g/plant for the Douala and Dschang substrates respectively. The most suitable substrates for rhizome production are those with a clayey to silty-sandy texture, moderately to slightly acidic (pH 5.6 - 6.5) and close to neutral (pH 6.6). Biologically, they show medium to high sporulation of arbuscular mycorrhizal fungi (AMF) (28-41 spores/g) and medium to high root colonisation of AMF (55%-78%). About 105 different endophyte isolates were obtained, including 83 types of bacteria and 22 types of fungi. These endophytes are stress tolerant. Based on their ability to tolerate high levels of stress (15% NaCl; 100 mM Al3+ and pH 3) and to contain plant growth promoting properties, 23 endophytes were selected. These improve turmeric growth and rhizome production by shortening the cycle by 12 months. In addition, 74% of the isolates increased curcumin content compared to the control; 84% showed antagonistic effects on 4 major plant pathogens: Fusarium oxysporum, Ralstonia solanacearum, Pythium myriotylum and Phytophthora megakarya. Also, a significant stimulation of the production of sulphur metabolism compounds (glutathione, total thiols by 22% and 26%) and vitamin A precursors (carotenoids by 91%) was observed by these endophytes compared to the control. In general, the endophyte-turmeric association strongly stimulates the antimicrobial and antioxidant activities; and thus the functional properties of this spice.