Impaginato 311 Adv. Hort. Sci., 2017 31(4): 311-317 DOI: 10.13128/ahs-21031 Investigation on rooting ability of twenty olive cultivars from Southern Italy C. Cirillo 1, R. Russo 1, F. Famiani 2, C. Di Vaio 1 (*) 1 Università degli Studi di Napoli Federico II, Dipartimento di Agraria, Via Università, 100, 80055 Portici (NA), Italy. 2 Università degli Studi di Perugia, Dipartimento di Scienze Agrarie Alimentari ed Ambientali, 06121 Perugia, Italy. Key words: cuttings, germplasm, NAA, NAD, Olea europaea L., propagation. Abstract: The effects of two different types of auxins (660 ppm alpha-naph- thaleneacetic acid - NAA - in liquid solution or 750 ppm alpha-naphthaleneac- etamide - NAD - dispersed in a talcum powder) and cuttings from three differ- ent portions of the shoots (basal, middle and apical) on the rooting ability of twenty autochthonous olive cultivars were investigated in two growing seasons (spring and autumn). The results showed that the autochthonous olive cultivars of the Campania Region are characterized by a wide variability in the potential rhizogenic ability. The two periods of cutting collection (March and September) significantly affected the rooting aptitude of the cultivars, indicating that in some cultivars the cuttings collected in autumn had a higher rooting rate than those collected in spring. The effects of NAA and NAD on rooting strongly depended on interaction with the cultivar, time of collection (autumn or spring) and type of cuttings (basal, medium or apical). Among the twenty cultivars test- ed, we found only eight cultivars with a satisfactory rooting ability after hor- monal applications (Ortolana, Racioppella, Tenacella, Tonda, Biancolilla, Carpellese, Cornia and Pisciottana). In general, the apical and the median por- tions of the shoots gave the best rooting results. 1. Introduction Among the vegetative propagation methods of olive cultivars (Olea europaea L.) the use of semi-hardwood cuttings is the most common, since rootings are easy to prepare and the requirement in special equip- ment is negligible and cheap (Cimato, 1999; Ismaili et al., 2011). This is why in the Mediterranean basin olive is mainly propagated by cuttings, a propagation method that relies on the ability of the cuttings to form adventitious roots (Fabbri et al., 2004). While some cultivars are easily propagated by this technique, others are difficult-to-root and this poses a challenge for their preservation and commercialization (Hartmann and Kester, 1975; Hartmann et al., 1990; Carfi et al., 1994; Porfírio et al., 2016). Rooting aptitude of the different olive cuttings depends on both intrinsic and extrinsic factors (Wiesman and Lavee, 1994; Hechmi et al., (*) Corresponding author: divaio@unina.it Citation: CIRILLO C., RUSSO R., FAMIANI F., DI VAIO C., 2017 - Investigation on rooting ability of twenty olive cultivars from Southern Italy. - Adv. Hort. Sci., 31(4): 311-317 Copyright: © 2017 Cirillo C., Russo R., Famiani F., Di Vaio C. This is an open access, peer reviewed article published by Firenze University Press (http://www.fupress.net/index.php/ahs/) and distribuited under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. Data Availability Statement: All relevant data are within the paper and its Supporting Information files. Competing Interests: The authors declare no competing interests. Received for publication 30 July 2017 Accepted for publication 26 October 2017 AHS Advances in Horticultural Science Adv. Hort. Sci., 2017 31(4): 311-317 312 2013), such as the genotype (Avidan and Lavee, 1978; Fabbri et al., 2004; Chiancone et al., 2011), the age of the mother tree, the timing of cutting collec- tion as well as the type of cuttings (Fontanazza and Jacoboni, 1975; Del Rio et al., 1991; Khabou and Trigui, 1999). Taking this background into considera- tion, the main aim of this study was to assess the rooting ability of olive cuttings obtained from twenty autochthonous olive cultivars of the Campania Region, by using different combinations of auxin treatments (NAA and NAD), times of collection of cuttings (spring and autumn) and portions of shoots to prepare the cuttings (basal, middle or apical). The cultivars considered in this study have been previous- ly evaluated in terms of vegetative-productive char- acteristics and oil quality, and some of them present agronomical behaviors and quality of the oils which make them interesting for the use in new olive orchards, also for the production of oils with a strong yet greatly diverse typicality (Di Vaio et al., 2013). This makes very important to know their intrinsic ability to root and the best combination of factors (hormones, time of cutting collection and portion of shoots to use) to utilize in order to obtain the best rooting results from each cultivar. 2. Materials and Methods Experimental site and plant material The trial was carried out in 2014/2015 at the Experimental Station “Improsta” of the Campania Region, located in Battipaglia (40°37′ 00’’ N lat, 15°03′ 23’’ E long, 72 m above sea level) Sele Plain (Salerno, South Italy). The average annual rainfall and the average minimum and maximum temperature of the area were 988 mm, 10.9°C and 21.0°C, respec- tively. The experimental station hosts a germplasm col- lection orchard, established in 2001, which includes all the main autochthonous olive cultivars of the Region. Trees were trained at central leader and spaced 6 × 3 m. Among the available germplasm, 20 cultivars were selected for their economic importance and potential to be used in new orchards considering their good agronomical characteristics (productivity and resis- t a n c e t o b i o t i c a n d a b i o t i c s t r e s s e s ) a n d h i g h quality/typicality of the oils, since some of them also allow the production of certified oils under the Protected Designation of Origin. The cultivars were grouped according to their origin (main province of cultivation). Therefore, the selected olive cultivars were four from the province of Avellino (‘Ogliarola campana’, ‘Ravece’, ‘Ritonnella’ and ‘Ruveia’), five from the province of Benevento (‘Femminella’, ‘Ortice’, ‘Ortolana’, ‘Pampagliosa’ and ‘Racioppella’), f o u r f r o m t h e p r o v i n c e o f C a s e r t a ( ‘ A s p r i n i a ’ , ‘Caiazzana’, ‘Tonda’ and ‘Tenacella’) and seven from the province of Salerno (‘Biancolilla’, ‘Carpellese’, ‘Cornia’, ‘Oliva Bianca’, ‘Pisciottana’, ‘Rotondella’ and ‘Salella’) (Di Vaio et al., 2013). Cutting collection and preparation The cuttings were collectioned in the autumn (end of September) and in the next spring (second decade of March). For each cultivar, three trees were select- ed by following homogeneity criteria for develop- mental stage and productivity. The semi-hardwood cuttings were obtained in autumn (A) and spring (S) from 30 cm long one-year shoots/season. Each shoot was divided in three different portions (basal, middle and apical) (180 cuttings/cultivar/season). Cuttings were 10 cm long and presented 4 nodes and 2 pairs of terminal leaves. Rhizogenic treatments For each combination of cultivar, collection time, portion of shoot and hormonal treatment three groups of ten cuttings each were used. The trial was conducted under mist system in cold greenhouse conditions. Two different commercial formulations of auxins, alpha-naphthaleneacetic acid (NAA) in liquid formulation (hydroalcoholic solution at 30% alcohol) at the concentration of 660 ppm (T1) and alpha- naphthaleneacetamide (NAD) at the concentration of 7 5 0 p p m ( T 2 ) i n t a l c u m p o w d e r f o r m u l a t i o n (0.075/100 w.w.) were compared to untreated con- trol (T0). These concentrations were used consider- ing the good results obtained with NAA 500-1000 ppm in other cultivars (Denaxa et al., 2011). The T1 treatment was performed by dipping 2 cm basal part of cuttings in the hydroalcoholic solution for 5 sec- onds, whereas the T2 treatment by dipping 2 cm basal part of cuttings in distilled water first and then in the powder. The T0 (control) was obtained by dip- ping 2 cm basal part of cuttings in distilled water for 5 seconds. Cuttings were then placed in perlite filled rooting benches provided with basal heating (sub- strate temperature 22-24°C) and with mist system to get periodically wet the cuttings avoiding their dehy- dration (air humidity about 90-95%). Rooting sampling and score Semi-hardwood cuttings were evaluated 70 days after the rooting treatments and each cutting was Cirillo et al. - Rooting ability of twenty olive cultivars from Southern Italy 313 scored for the rooting rate, the number of roots/cut- ting (primary and secondary roots), and the length of roots/cutting (the length of the different roots of each cutting was summed). The percentage of root- ing was calculated as the number of rooted cuttings with respect to the total number of cuttings per treatment. Statistical analysis All data were statistically analyzed by three-way analysis of variance (ANOVA) using the SPSS 13 soft- ware package (SPSS 13.0 for Windows; SPSS Inc., Chicago, IL). Whenever the two-way interaction was significant, a one-way ANOVA was performed. To separate treatment means for each measured para- meter, Duncan’s multiple range test was performed at a significance level of P≤0.05. 3. Results and Discussion Adventitious rooting process in cuttings is still to be unraveled under the genetic point of view, how- ever, as referred in studies on Italian and internation- al olive cultivars (Fontanazza and Baldoni, 1989; Chiancone et al., 2011), the capability of cuttings of forming adventitious roots is mainly affected by the cultivar. Among the wide number of local and world- wide grown cultivars, the main part of them displays a poor aptitude for rooting of cuttings, whereas few cultivars are known to be well rooting cultivars. A dataset of the International Olive Council (IOC, 2005) reported the results of a screening on rooting rate of 426 cultivars: 59 cultivars showed an average rooting rate of 1.5%, 213 cultivars reached an average rate of 21.3%, whereas the rooting rate recorded in 86 culti- vars was approximately 54% and only 68 (=16% of the total) showed a rate of rooting higher than 70%. In the present study, rooting rate of the cuttings was significantly affected by the cultivar (C), by the interaction between the cultivar and the time of sam- pling (C × TS) and by the interaction between the hor- monal treatment and the time of sampling (T × TS) (Table 1). The highest percentage of rooted cuttings, over the rooting treatment and the time of sampling, was recorded in cv. Ortolana (66%), followed by cv. Racioppella (54.6%) and cv. Biancolilla (51%) (Fig. 1). On the contrary, cv. Ogliarola campana, cv. Ortice and cv. Salella showed the lowest rooting rate (14.9%, 15.8% and 11.2%, respectively). Timing of cutting collection, according to the liter- ature, is the second pivotal element, following the cultivar, to be concerned about, since very relevant differences in the success of rooting process may depend on this factor (Hartmann and Loreti, 1965). Thus, the definition of the most suitable season for cutting collection from mother plants has been a crit- ical item for researchers dealing with fruit trees species, although the fine tuning of protocols ready to use in the nurseries is still lacking, especially if sin- gle cultivars are considered. The C × TS interaction highlighted that the cultivars considered in this study responded differentially to the time of cutting sam- pling (Fig. 2). For instance, among the three cultivars that showed the highest rooting rate, cv. Ortolana and cv. Raciopella reached higher percentages of rooting when the cuttings were collected during spring season, whereas the rooting rate of cv. Biancolilla was significantly increased by using the cuttings collected in autumn (Fig. 2). On the contrary, the cultivars that showed the lowest rooting rate (cvs. Ogliarola campana, Ortice and Salella) did not NS= Non significant; *, **; ***= significant at P≤ 0.05, ≤ 0.01, 0.001, respectively. Fig. 1 - Average rooting rate (mean ± standard error) of semi- hardwood cuttings of the olive cultivars of the Campania Region. Bars with the same colour correspond to culti- vars of the same province. Abbreviations of the names of the cultivars: OGL = Ogliarola campana, RAV = Ravece, RIT = Ritonnella, RUV = Ruveia, FEM = Femminella, ORTI = Ortice, ORTO = Ortolana, PAM = Pampagliosa, RAC = Racioppella, ASP = Asprinia, CAI = Caiazzana, TEN = T e n a c e l l a , T O N = T o n d a , B I A = B i a n c o l i l l a , C A R = Carpellese, COR = Cornia, OB = Oliva Bianca, PIS = Pisciottana, ROT = Rotondella, SAL = Salella. Means fol- lowed by different letters are significantly different for P ≤ 0.001. Source of variance Rooting rate (%) Cultivar (C) *** Hormonal treatment (T) NS Time of sampling (TS) NS C × T NS C × TS *** T × TS * C × T × TS NS Table 1 - Analysis of variance for cultivars, hormonal rooting treatments, time of sampling and their interactions on rooting rate of olive cuttings Adv. Hort. Sci., 2017 31(4): 311-317 314 perform differently comparing the two times of sam- pling (Fig. 2). The overall influence of hormonal treatments (NAA or NAD) and time of sampling (T × TS) on cut- ting rooting rate indicated that the effect of treat- ments was significantly different on the cuttings col- lected in spring (Fig. 3). In particular, the lowest root- ing rate was observed on T0 cuttings collected in spring (Fig. 3). O n t h e b a s e o f c u t t i n g r o o t i n g r a t e , t h e International Olive Council classified the cultivars in four ranks: 0-5%; 5-40%; 40-70% and 70-100% (IOC, 2005). According to this classification, the twenty cul- tivars tested in the present experiment resulted to be distributed in three different groups: twelve between 5 and 40% (‘Ogliarola campana’, ‘Ravece’, ‘Ritonnella’, ‘Ruveia’, ‘Femminella’, ‘Ortice’, ‘Pampagliosa’, ‘Asprinia’, ‘Caiazzana’, ‘Oliva Bianca’, ‘Rotondella’, ‘Salella’); seven between 40 and 70% (‘Racioppella’, ‘Tenacella’, ‘Tonda’, ‘Biancolilla’, ‘Carpellese’, ‘Cornia’ a n d ‘ P i s c i o t t a n a ’ ) ; o n e b e t w e e n 7 0 a n d 1 0 0 % (‘Ortolana’). As far as root number and length are concerned, the effects of cultivar, hormonal treatments and por- tion of the shoot and their first level interactions were all significant (Table 2). The twenty cultivars of olive exhibited a high variability in the number and length of roots produced both in autumn and spring experiments. The root number and length were increased by the rhizogenic treatments. Generally, both the liquid and powdery formulations used for the rooting stimulation of the cuttings were effective in improving rooting emission and growth. With regard to the number of roots, our findings indicated that the liquid treatment with 660 ppm NAA was the most effective, showing, with respect to the control, an average increase of about 266% in cuttings from the basal, median and apical portions of the shoots. The same treatment was particularly effective in stimulating the length growth of the roots, with an average increase of 236% compared to the control. Furthermore, the root number and length of cuttings collected in autumn and spring were significantly affected by the interaction between the cultivar (C) and hormonal rooting treatment (T) (Table 2). For instance, the average root number in autumn cut- tings was 2.7 roots per cutting, and the application of t h e r h i z o g e n i c t r e a t m e n t T 2 , c o m p a r e d t o T 0 , induced a significant increase of the number of roots in nine cultivars: Ortolana (+245%), Cornia (+169%), Tonda (+160%), Ruveia (+165%), Tenacella (+192%), Asprinia (+312%), Biancolilla (+320%), Pisciottana Fig. 3 - Average rooting rate (mean ± standard error) of semi- h a r d w o o d c u t t i n g s a s a f f e c t e d b y t h e i n t e r a c t i o n between the hormonal rhizogenic treatments (T0= con- trol - no hormonal treatments; T1= NAA treatment; T2= NAD treatment) and the time of sampling. A= autumn; S= spring. Means followed by different letters are signifi- cantly different for P ≤ 0.05. Fig. 2 - Average rooting rate (mean ± standard error) of semi- h a r d w o o d c u t t i n g s a s a f f e c t e d b y t h e i n t e r a c t i o n between the cultivar and the time of sampling. A= autumn; S= spring. Abbreviations of the names of the cultivars: OGL = Ogliarola campana, RAV = Ravece, RIT = Ritonnella, RUV = Ruveia, FEM = Femminella, ORTI = Ortice, ORTO = Ortolana, PAM = Pampagliosa, RAC = Racioppella, ASP = Asprinia, CAI = Caiazzana, TEN = T e n a c e l l a , T O N = T o n d a , B I A = B i a n c o l i l l a , C A R = Carpellese, COR = Cornia, OB = Oliva Bianca, PIS = Pisciottana, ROT = Rotondella, SAL = Salella. Means fol- lowed by different letters are significantly different for P≤0.001. Source of variance Root number Root length (cm/cutting) Autumn Spring Autumn Spring Cultivar (C) *** *** *** *** Hormonal treatment (T) *** *** *** *** Portion (P) *** ** *** *** C × T ** *** *** ** C × P * *** * *** T × P * NS NS * C × T × P NS *** NS * NS= Non significant; *, **; ***= significant at P≤ 0.05, ≤ 0.01, 0.001, respectively. Table 2 - Analysis of variance for cultivars, hormonal rooting treatments, shoot portion and their interactions on number and length of roots of olive cuttings obtained in autumn or spring Cirillo et al. - Rooting ability of twenty olive cultivars from Southern Italy 315 (+610 %) and Carpellese (+236 %) (Fig. 4A). The average root length in autumn cuttings was 4.2 cm per cutting, and, similarly to the root number, it was also increased by the rhizogenic treatment T2 in ten cultivars: Ortolana, Ravece, Cornia, Tonda, R u v e i a , T e n a c e l l a , A s p r i n i a , B i a n c o l i l l a a n d Pisciottana (Fig. 4 B). A similar pattern was observed in the spring cuttings (Fig. 5 A, B), even though the Fig. 4 - Effects of the interaction of the cultivars and the hormonal rhi- zogenic treatment (T0= Control - no hormonal treatments; T1= NAA treatment; T2= NAD treat- ment) on root number/cutting (A) and root length/cutting (B) of semi-hardwood cuttings collect- ed in autumn. The dotted line shows the average value of all c u l t i v a r s u n d e r o b s e r v a t i o n . Abbreviations of the names of the cultivars: OGL = Ogliarola campana, RAV = Ravece, RIT = Ritonnella, RUV = Ruveia, FEM = F e m m i n e l l a , O R T I = O r t i c e , O R T O = O r t o l a n a , P A M = Pampagliosa, RAC = Racioppella, ASP = Asprinia, CAI = Caiazzana, TEN = Tenacella, TON = Tonda, B I A = B i a n c o l i l l a , C A R = Carpellese, COR = Cornia, OB = Oliva Bianca, PIS = Pisciottana, ROT = Rotondella, SAL = Salella. Fig. 5 - Effects of the interaction of the cultivars and the hormonal rhi- zogenic treatment (T0= Control - no hormonal treatments; T1= NAA treatment; T2= NAD treat- ment) on root number/cutting (A) and root length/cutting (B) of semi-hardwood cuttings col- lected in spring. The dotted line shows the average value of all cultivars under observation. Abbreviations of the names of the cultivars: OGL = Ogliarola campana, RAV = Ravece, RIT = Ritonnella, RUV = Ruveia, FEM = Femminella, ORTI = Ortice, O R T O = O r t o l a n a , P A M = Pampagliosa, RAC = Raciop- p e l l a , A S P = A s p r i n i a , C A I = Caiazzana, TEN = Tenacella, TON = Tonda, BIA = Biancolilla, CAR = Carpellese, COR = Cornia, O B = O l i v a B i a n c a , P I S = Pisciottana, ROT = Rotondella, SAL = Salella. Adv. Hort. Sci., 2017 31(4): 311-317 316 values of both the average number and length of roots were higher than those recorded in autumn. The root number of autumn cuttings was also affected by the interaction between the hormonal treatment (T) and the shoot portion (P). Indeed, the number of roots per cutting increased from the bot- tom (B), to the middle (M), and then to the apical (A) portion of collected shoots with the highest value recorded in the apical cuttings treated with T1 (4.5 roots/cutting) followed by T2 treated apical and mid- dle cuttings (3.9 and 3.4 roots/cutting, respectively) (Fig. 6 A), whereas the lowest number of roots was observed in the basal cuttings of untreated control (T0) and T1 (1.5 roots/cuttings) (Fig. 6 A). With respect to the control and T1, a significant increase of the root number was observed in the basal cutting treated with T2 (2.8 roots/cuttings). The capability of olive cuttings on forming adventitious roots is known to be related to the portion (basal, middle or apical) of the shoots, even though different cultivars can respond differentially. A general hypothesis has been formulated on the higher aptitude for rooting of sub- apical cuttings that seems to be related to a possible h i g h e r c o n t e n t i n a u x i n i c c o m p o u n d s d r i v e n basipetally from the young leaves of cuttings (Fabbri et al., 2004). On the other hand, only the root length of spring cuttings was significantly affected by the interaction between the hormonal treatment (T) and the shoot portion (P) (Table 2, Fig. 6 B), with the high- est values (11.4 cm) recorded in the apical cuttings treated with NAA in liquid formulation (T1) and in basal, middle and apical cuttings (10.3, 10.9, and 12.2 cm, respectively) treated with NAD in powdery for- mulation (T2). 4. Conclusions This study highlighted that the olive cultivars belonging to autochthonous germplasm of the Campania Region are characterized by a wide vari- ability in the potential rhizogenic activity. Overall the two sampling periods of cutting collection (March and September) significantly affected the rooting aptitude of several cultivars, indicating that in some cultivars the cuttings collected in autumn may have a higher rooting rate than the spring collected ones. Moreover, it was possible to evaluate the rhizogenic aptitude of the cultivars belonging to the olive Campanian germplasm under the influence of rhizo- genic treatments. The results showed that the effects of NAA and NAD on rooting strongly depended on interaction with the cultivar, time of collection (autumn or spring) and type of cuttings (basal, medi- um or apical). In general, the apical and the median portions of shoots were confirmed to be the most suitable for improving the rooting of cuttings. References AVIDAN B., LAVEE S., 1978 - Physiological aspects of the rooting ability of olive cultivars. - Acta Horticulturae, 79: 93-101. CARFI C.H., BEN HADJ SALAH H., MSALLEM M., HADDAR T., HELLALI R., 1994 - Effet des doses d’AIB et des dates de prélévement sur la rhizogenése des boutures de 6 var- iétés d’olivier (Olea europaea L.) “Chetoui”, “Meski”, “Picholine”, “Besbessi”, “Chemlali”, “Arbequina”. - Revue INAT, vol. 9, no. 1-2. CHIANCONE B., MACALUSO L., GERMANà M.A., 2011 - Prove sulla radicazione di talee di cultivar siciliane di Olea europaea L. - Acta Italus Hortus, 1: 370-375. CIMATO A., 1999 - L’élevage des plants d’olivier en pèpiniè- re. Innovations technologiques et leur application en oléiculture et oléotechnie. - Séminaire international, Firenze (Italia). DEL RIO C., RALLO R., CABALLERO J.M., 1991 - Effect of car- bohydrate content on the seasonal rooting of vegeta- tive and reproductive cuttings of olive. - J. Hortic. Sci., Fig. 6 - Effects of the interaction of the hormonal rhizogenic treat- ment (T0= Control - no hormonal treatments; T1= NAA treatment; T2= NAD treatment) and shoot portion used to make the cuttings (B= Basal; M= Medium; A= Apical) on root number/cutting (A) of semi-hardwood cuttings collected in autumn and on root length/cutting (B) of semi-hardwood cuttings collected in spring. Means followed by different let- ters are significantly different for P≤0.05 (root number) and P≤0.05 (root length). Cirillo et al. - Rooting ability of twenty olive cultivars from Southern Italy 317 66(3): 301-309. DENAxA N.K., VEMMOS S.N., ROUSSOS P.A., KOSTELENOS G., 2011 - The effect of IBA, NAA and carbohydrates on rooting capacity of leafy cuttings in three olive cultivars (Olea europaea L.). - Acta Horticulturae, 924: 101-109. DI VAIO C., NOCERINO S., PADUANO A., SACCHI R., 2013 - Characterization and evaluation of olive germplasm in southern Italy. - J. Sci. Food Agric., 93(10): 2458-2462. FABBRI A., BARTOLINI G., LOMBARDI M., KAILIS S.G., 2004 - Olive propagation manual, pp. 2-7. - In: FABBRI A., G. BARTOLINI, M. LOMBARDI, and S.G. KAILIS. Olive prop- agation manual. CSIRO Publishing, Landlinks Press, Collingwood VIC, Australia, pp. 145. FONTANAzzA G., BALDONI L., 1989 - Innovazioni tecnologi- che in olivicoltura. Olivicoltura: innovazioni tecnologi- che e valutazione dei risultati economici in alcune r e a l t à a z i e n d a l i . - F o r m e z , A r c h i v i o d e i C o r s i d i Formazione, pp. 41-54. FONTANAzzA G., JACOBONI N., 1975 - Indagine sugli effet- ti della defogliazione e della degemmazione di talee di olivo sulla rizogenesi in camera di nebulizzazione. - Frutticoltura, 9: 25-30. HARTMANN H.T., KESTER D.E., 1975 - Plant propagation: principles and practices. - Prentice-Hall Inc., Englewood Cliffs, NJ, USA, pp. 662. HARTMANN H.T., KESTER D.E., DAVIES F.T., 1990 - Plant propagation principles and practices. - Prentice-Hall Inc., Englewood Cliffs, NJ, USA, pp. 547. HARTMANN H.T., LORETI F., 1965 - Seasonal variation in rooting leafy olive cuttings under mist. - Proc. Amer. Soc. Hort. Sci., 87: 194-198. HECHMI M., KHALED M., ABED S., EL-HASSEN A., FAIEz R., M’HAMED A., 2013 - Performance of olive cuttings (Olea europaea L.) of different cultivars growing in the agro-climatic conditions of Al-Jouf (Saudi Arabia). - Am. J. Plant Physiol., 8(1): 41-49. IOC, 2005 - Olive nursery production and plant production techniques. - International Olive Council http://www. internationaloliveoil.org/projects/paginas/Section- b.htm. ISMAILI H., IANNI G., DERVISHI A., 2011 - Study of main factors influencing olive propagation. - J. Int. Environ. Appl. & Sci., 6(4): 623-629. KHABOU W., TRIGUI A., 1999 - Optimisation of the hard- wood cutting as a method of olive tree multiplication. - Acta Horticulturae, 474: 55-58. PORFíRIO S., SONON R., GOMES DA SILVA M.D.R., PEIxE A., CABRITA M.J., AzADI P., 2016 - Quantification of free auxins in semi-hardwood plant cuttings and micro- shoots by dispersive liquid-liquid microextraction/ microwave derivatization and GC/MS analysis. - Anal. Methods, 8: 6089-6098. WIESMAN z., LAVEE S., 1994 - Vegetative growth retarda- tion, improved rooting and variability of olive cuttings in response to application of growth retardants. - Plant Growth Regul., 14: 83-90.