A Study on Some Physiological and Anatomical Aspects of Rooting 'Nabali' and 'Raseei' Olive Semi-Hardwood Stem Cuttings

Abstract

This research was conducted to study the anatomy of adventitious root formation in semi-hardwood stem cuttings of 'Nabali' and 'Raseei' olive cultivars. Semi-hardwood stem cuttings of 'Nabali' and 'Raseei' olive cultivars were prepared and rooted in a greenhouse at various sampling dates. Stem segments from the basal portion of the cuttings were taken before rooting and at 2-week intervals during the rooting period to investigate anatomical structure and adventitious root formation on the cuttings. The results indicated that anatomical structure of the stem cutting cross sections for both olive cultivars was basically similar. Origin of root initials in 'Nabali' and 'Raseei' olive cuttings is the cambial zone. In both olive cultivars, sclerenchyma tissue was found to form a continuous ring of 3-6 layers of cells, and did not form a mechanical barrier for adventitious root formation. Noticeable increase in the thickness of the cortex during rooting was observed in 'Nabali' cuttings as compared to 'Raseei', which might act as a barrier for development of the root primordia. Difficulty in rooting 'Nabali' cuttings could be attributed to changes in anatomical structure of the cutting during the rooting period.

Reviewing current knowledge on olive (Olea europaea L.) adventitious root formation

“…'Nabali' than in the easy-to-root cv. 'Raseei' (Ayoub and Qrunfleh, 2008). It is, however, worth mentioning that in this study the levels of growth regulators were measured in buds and leaves and not in the base of the cuttings where root formation occurs.…”

“…In semi-hardwood olive cuttings, stem cross sections of easy and difficult-to-root cultivars were already compared and no anatomical differences were found between the studied genotypes. A continuous sclerenchyma ring between the phloem and the cortex was observed (Ayoub and Qrunfleh, 2008;Peixe et al, 2007b). This is considered to be a characteristic feature of the Olea genus (Ayoub and Qrunfleh, 2006) and has been previously pointed out as a possible mechanical barrier to root emergence in recalcitrant cultivars (Ciampi and Gellini, 1963;Qrunfleh and Rushdi, 1994;Salama et al, 1987).…”

“…A continuous sclerenchyma ring between the phloem and the cortex was observed (Ayoub and Qrunfleh, 2008;Peixe et al, 2007b). This is considered to be a characteristic feature of the Olea genus (Ayoub and Qrunfleh, 2006) and has been previously pointed out as a possible mechanical barrier to root emergence in recalcitrant cultivars (Ciampi and Gellini, 1963;Qrunfleh and Rushdi, 1994;Salama et al, 1987). However, the most recent data on this subject show that such a ring, even with 3-6 cell layers, can't be a restricting factor for rooting as it crumbles during the rooting process, even in cultivars where only callus formation occurs and root formation isn't achieved Qrunfleh, 2006, 2008).…”

“…In Olea europaea, most authors have observed adventitious roots arising from the cambial region of the stem [Bakr et al (1977) on cultivar 'Wetaken', Salama et al (1987) on 'Manzanillo', 'Mission', 'Kalamata', or 'Hamed' andQrunfleh (2006) on 'Nabali' and 'Raseei'].…”

“…Moreover, unlike auxin-related genes which show a phase-specific pattern, the expression of ethylene-related genes indicates that ethylene is important to stimulate adventitious rooting but not to regulate the process (Druege et al, 2014). Although the genotype appears to have a stronger influence, changes in auxin concentration have been associated both with the interdependent phases of the process and with the rooting capacity of a species or cultivar (Ayoub and Qrunfleh, 2008;Heloir et al, 1996;Krisantini et al, 2006;Nag et al, 2001;Sagee et al, 1992). According to De Klerk et al (1995), the high auxin levels…”