Stock plant etiolation reduces rooting of sub-terminal olive cuttings by reducing total sugars, IAA, indole/phenol ratio, and IAA/GA ratio

Adventitious root formation is the key to successful propagation of olives through cuttings. Etiolation, as an eco-friendly practice, can modulate the plant's endogenous phytohormone, which plays an important role in stimulation of rooting of cuttings. Therefore, this study was aimed to investigate the effect of etiolation on the rooting behavior of both 'Manzanillo' and 'Picual' olive cuttings (terminal and sub-terminal) treated with IBA (0, 4000 ppm). The results indicated that sub-terminal cuttings in both cultivars were more effective in olive propagation than terminal cuttings as they recorded increased leaves number, C/N ratio, total carbohydrates, total indoles, IAA, IAA/GA ratio, and total phenols. Etiolation of both olive cultivars for both terminal and sub-terminal cuttings significantly decreased rooting percent, roots number, IAA, and IAA/GA ratio; while, it increased GA and GA/IAA. Moreover, etiolation decreased total sugars, IAA, IAA/GA ratio, and indole/phenol ratio in both sub-terminal cuttings. Terminal 'Manzanillo' cuttings achieved a higher rooting percent than terminal 'Picual' cuttings by 5.83% and 202.2% as mean of both seasons for untreated and IBA-treated cuttings, which was accompanied by significant increase in vascular bundle%, total phenol, phenol/indole ratio, IAA, and IAA/GA ratio by 21.48%, 49.2%, 44.72%, 12.9%, and 22.9%, respectively. Also, terminal 'Manzanillo' cuttings recorded lower GA by 7.98% and GA/IAA ratio by 18.21% and pith by 6.13% than terminal 'Picual' cuttings. This study proved that olive plants need exposure to full sunlight to propagate easily by cuttings since etiolation had negative effects on IBA-treated cuttings.