Impaginato 77 Adv. Hort. Sci., 2019 33(1): 77-85 DOi: 10.13128/ahs-23298 Apple seed stocks affected scion tree vigor and performance based on maternal self(in)compatibility H. Hajnajari Temperate and Cold Fruits Research Institute (Karaj), Horticulture Sciences Research Institute, Ag. Research Education and Extension Organization (AREEO), Karaj, Iran. Key words: breeding, dwarfness, genetic purity, inductive effect, Malus × domes- tica Borkh., seed rootstock. Abstract: In a breeding program to increase uniformity of apple saplings size, shape and vigor the genetic improvement of seed rootstocks was considered as a key point. The Half-Sib seeds of two selected native crab parents, self-com- patible “Morabbaei” and self-incompatible “Azayesh”, both dwarf, were con- sidered as the main sources of variances into the six grafted scions. The induc- tive effects of the two seed masses were assessed on vegetative traits of 6 and 7-year-old scion trees. According to the results, shoot length, shoot thickness and internode length as main components of tree vigor showed significant dif- ferences at 1% level in all the six scions. The shoot length mean of the grafted scions on “Azayesh” seed progeny was higher than “Morabbaei” seed stock. The grafted scions on self-compatible “Morabbaei” seed stock gave place to the shoots with higher thickness than the same grafted on “Azayesh” seed source. Combinations of “Red Delicious”-“Morabbaei” and “Braeburn”-“Azayesh” demonstrated max and min values of internodes length during two consecutive years. Both rootstock and scion trunk diameters on self-incompatible “Azayesh” seeds resulted higher than seed progeny of self-compatible “Morabbaei”. Shoot number was not affected by rootstock type, whereas the effect of rootstock × scion, scion and year resulted significant. 1. Introduction Malus genus is characterized by great phenotypic and genetic diversi- ty. High heterozygosity is reinforced by dominant self-incompatibility besides inbreeding depression (Korban and Skirvin, 1984). Among 6000 documented apple cultivars, a large part of commercial production still relies on few cultivars including “Golden Delicious”, “Granny Smith”, “Fuji”, “Gala” and Delicious group (O’rourke, 2003). rootstocks can influ- ence vigor, habit and cropping of the scion cultivar as well as tolerance to unfavorable climatic or edaphic conditions (Webster, 2005). rootstock performance is highly correlated with the genetic potential of rootstock to provide anchorage, adaptaion to pedo-climatic conditions and resist to abiotic stress efficiently (Fazio, 2014). Trees with limited height are requested due to facilitate orchard management. Smaller trees are also (*) Corresponding author: hassanhajnajari@yahoo.com Citation: HAjnAjAri H., 2019 - Apple seed stocks affected scion tree vigor and performance based on maternal self(in)compatibility. - Adv. Hort. Sci., 33(1): 77-85 Copyright: © 2019 Hajnajari H. This is an open access, peer reviewed article published by Firenze University Press (http://www.fupress.net/index.php/ahs/) and distributed 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 28 May 2018 Accepted for publication 12 December 2018 AHS Advances in Horticultural Science http://creativecommons.org/licenses/by/4.0/ http://creativecommons.org/licenses/by/4.0/ Adv. Hort. Sci., 2019 33(1): 77-85 78 easier to target with sprays, reducing undesirable spray drift and increasing efficiency of usage (jobir, 2016). Good performance, dwarfness, precocious- ness, scion compatibility, free from suckers and bur- rknots are some of the attributes of an ideal root- stock (Wertheim and Webster, 2005). Clonal root- stocks are being developed rapidly while seed root- stocks have gradually decreased. Still today, many nurseries in Canada, Belarus and Finland use apple seed rootstocks. “Antonovka” was selected as a seed source due to the freeze resistance and its cytoplas- mic heritability (Żurawicz and Lewandowski, 2014), the system for which some traits are transmitted to the next generation by maternal parent (Lorenzetti and Ceccarelli, 1980). Seed rootstocks improvement is applied for dwarfing effect, and tolerance to dry soil conditions (Brown and Maloney, 2005). in iran seed rootstocks are used because of the alkaline and dry soils and also due to bad topography and exag- gerated fragmentations. in absence of a specialized sector for pure seed production, the mixture of recy- cled seeds of processing industry characterized by high genetic diversity are used in saplings production (Hajnajari and Tarrahi, 2009; Hajnajari, 2010). increasing genetic purity of seed rootstocks will enhance scion tree size and uniformity by taking advantage of their neglected aspects (Hajnajari and Mizani, 2015). Similarly, almond trees are raised on wild peach and bitter almond rootstock (Sharma et a l . , 2 0 0 4 ) . “ M a z z a r d ” s e e d l i n g s f o l l o w e d b y “Mahaleb” are the most widely used rootstocks for cherry tree production (Demirsoy et al., 2017). Each open pollinated seed has its specific hormonal status due to the different genetic provenience different from the rest which will cause a gradient of tree growth habits and vigor within the same scion culti- var. While tree vigor is provoked by hybrid heterosis (Lorenzetti et al., 2011), the mandatory inbreeding ruling the self-compatible cultivars as maternal seed source may cause vigor decline of scion trees. it was suggested that the inbred F1 seed stocks could weak- en the vigor of scion. Vigorous trees with higher canopy size need increased planting distance (Kosina, 2010). Selection of proper parents as seed source was the unique pass to way out from the emblematic situation (Hajnajari, 2018). Cultivar evaluation pro- gram led to selection of few native dwarf crabs “Morabbaei”, “Zinati” and “Azayesh” as seed source parents (Hajnajari, 2010). Contemporaneous field screening program for determination of self-compati- bility level of the 92 cultivars followed by fluorescent microscope studies showed complete self-compati- bility of “Morabbaei”, “Zinati” and “Azayesh” as self- incompatible (Forughikia et al., 2014; Hajnajari and Moradi, 2014). Using such maternal parents that profit high level of self-compatibility accompanied with dwarfness can minimize seed genetic variability leading to production of the F1 seed progeny marked by high genetic purity. Both traits of dwarfism and low vigor within the seedlings can be used for pro- duction of uniform saplings. The same parents were used for production of clonal rootstocks resistant to the crown rot disease (Hajnajari et al., 2012). The e f f e c t s o f t w o s e e d m a s s e s , a s F 1 p r o g e n y o f “Azayesh” (self-incompatible) and “Morabbaei” (self- compatible) on growth characteristics of six apple scion cultivars were investigated. Practically, the two open pollinated seed masses derived from two differ- ent maternal parents are assumed as two family’s genetically, diverse within the lots and among them, however two various sister masses belonging to dif- ferent families. nevertheless, both parents as crab apples carry jointly dwarfness trait and are native to iranian habitat. Here is shown that the seed root- stocks bred by self- compatible parent incur more morphological uniformity and control of tree vigor in scion trees compared with the rival sister seeds pro- duced by heterozygote parent “Azayesh” which afford more vigorous and less homogenous tree architecture due to the need of self-incompatible parent for foreign pollen. 2. Materials and Methods T h e m a t u r e a p p l e t r e e s , 6 a n d 7 - y e a r - o l d ( “ G o l d e n D e l i c i o u s ” , “ r e d D e l i c i o u s ” , “ G r a n n y Smith”, “Braeburn”, “Gala” and native “Golab-e Kohanz”) pruned in spindle form, grafted on two selected seed masses were studied to understand the effects of seed sources on vegetative characteris- tics of the scion cultivars. Genetically, the two seed lots were identified as F1 Half-Sib progenies derived from two different maternal parents including the self-compatible cultivar “Morabbaei” and the other self-incompatible “Azayesh”, revealed as homozy- gote and heterozygote, correspondingly. The two seed lots were obtained from the maternal parents exposed equally to open pollination, so forming two genetically diverse seed masses as two families con- sidered as the main treatments. The investigated traits included annual diametric growth of scion Hajnajari - Seed rootstocks improvement in apple 79 trunk, graft point and rootstock. For each tree, 4 annual shoots were selected and labelled, and internodes number, internodes length, shoot length, shoot thickness and lenticels number were assessed. Also, shoot numbers per tree and crotch angle were studied. The entire comparative inter and intra vari- etal measurements were achieved to distinguish the influences of the two seed rootstocks as the main treatments. interaction of scion per rootstock was recorded to study also the role of scion tree vigor against dwarfing effect of the seed source. Six trees, 3 × 3 m, were assigned for each combination of “Scion cv-Seed progeny” within six replications, large enough to explain seed source inductive effects. Growth traits of grafted scions were measured in two successive vegetative seasons (2014 and 2015). T h e e x p e r i m e n t a l o r c h a r d w a s e s t a b l i s h e d i n Meshkin-Abad Station under Temperate and Cold F r u i t r e s e a r c h C e n t e r l o c a t e d i n K a r a j , A l b o r z Province (iran). The experiment was set as according to a Completely randomized Blocks Design (rCBD) with six replications for statistical analysis. AnOVA was performed by combining the analysis of the col- lected data regarding all growth traits in exam, both seed rootstocks and cultivars. All statistical analyses were carried out using the general linear model (GLM) procedure of the SAS version 9.0. The Duncan’ multiple range test (P≤0.01) was used to evaluate dif- ferences between treatments. 3. Results Shoot length and thickness Shoot length and shoot thickness were affected significantly by rootstock, scion and year interactions (Table 1). All variables are measured at annual shoots. Shoot length in 2014, “red Delicious”-”Azayesh” combinations showed the longest shot lenght, while “Golden Delicious” on “Morabbaei” had the lowest value, in 2015. Comparing the treatments, no significant dif- ferences were observed for effects of the two seed progenies “Azayesh” and “Morabbaei” on the single cultivars, at the end of the first growing season. in t h e s e c o n d y e a r , s i g n i f i c a n t d i f f e r e n c e s w e r e observed by different sources of seed rootstocks for grafted cultivars (Table 2). in 2014, it was found that shoot length value for all scions of “Golab-e Kohanz”, “Gala”, “Granny Smith” and “Braeburn” combined with “Morabbaei” seed rootstocks showed lower val- ues than “Azayesh” F1 progeny; albeit “Braeburn” d e m o n s t r a t e d s i g n i f i c a n t d i f f e r e n c e , “ G o l d e n Delicious” and “red Delicious” showed no significant differences on the 2 seed sources for shoot length. These results indicate that the maternal self-incom- patible “Azayesh” gave place to more vigorous seed progeny. Whereas in 2015, the entire scions had low- ered values of Shoot length showing significant dif- f e r e n c e a f f e c t e d b y s e e d s o u r c e ( T a b l e 2 ) . Considering the prevailing traits of dwarfness associ- ated with homozygosis carried by “Morabbaei” it becomes clear how these are transmitted to the rela- tive F1 seed progeny whom could control the vigor of the combined scion trees. Though both parents may produce seeds which reinforced vigor control of scion trees but the “Morabbaei” seed progeny showed the capability both to induce dwarfism and uniformity in size and shape into the scion cultivars (Table 2). Parallel researches of artificial self-pollination fol- lowed by florescent microscopy studies put in evi- dence how the pollen tubes of “Morabbaei” could penetrate to its own ovary confirming the total self- c o m p a t i b i l i t y o f s e l e c t e d m a t e r n a l p a r e n t (Forughikia, et al., 2014). Future investigations are Source DF Mean Square Shoot length Shoot thickness internode number internode length rootstock diameter Graft diameter Trunk diameter Shoot number Branch angle Lenticels number Year (Y) 1 44376.9 ** 3.92 ** 7.65 ** 1.14 ** 1912.11 ** 4460.61 ** 0.22 ** 0.25 * 67.79 nS 0.007 nS Block (year) 10 4982.37 ** 0.04 ** 0.17 ** 0.07 ** 223.66 nS 108.48 nS 0.01 nS 0.03 nS 420.71 ** 0.07 * rootstock (r) 1 39402.37 ** 0.67 ** 0.04 nS 0.56 ** 1005.01 * 911.83 * 0.03 nS 0.03 nS 3679.76 ** 1.29 ** Scion (S) 5 10396.58 ** 0.063 ** 0.24 ** 0.12 ** 28.27 nS 111.47 nS 0.02 nS 0.14 * 833.27 ** 0.24 ** r × S 5 6614.24 ** 0.067 ** 0.06 nS 0.23 ** 409.78 * 143.15 nS 0.02 nS 0.17 ** 1749.75 ** 0.76 ** Y × r 1 17580.61 ** 0.003 nS 0.05 nS 0.56 ** 56.99 nS 31.91 nS 0.03 nS 0.006 nS 667.52 * 0.10 nS Y × S 5 7960.64 ** 0.06 ** 0.12 ** 0.08 ** 82.02 nS 79.06 nS 0.02 nS 0.10 nS 440.02 * 0.20 ** Y × r× S 5 11061.31 ** 0.07 ** 0.12 ** 0.06 ** 52.05 nS 46.51 nS 0.01 nS 0.01 nS 668.91 ** 0.37 ** CV (%) 25.62 12.16 16.52 10.74 24.007 23.11 7.63 22.32 16.80 14.83 Table 1 - Analysis of variance regarding the effects of year, rootstock and scion on vegetative traits **= Significant differences at 1% level, *= Significant differences at 5% level, nS= not significant. Adv. Hort. Sci., 2019 33(1): 77-85 80 required to elucidate the mechanisms and biochemi- cal pathways by which a self-compatible cultivar can accept insider pollen leading to fertilization, within a self-incompatible species. Shoot thickness Combination of “red Delicious”-”Morabbaei”, in the first year, showed the highest shoot thickness, while both combinations of “Golden Delicious” and “red Delicious” on “Azayesh”, in the second year, showed the lowest rates. it could be inferred that low vigor of “Morabbaei” F1 progeny inhibited Shoot length growth rising inversely shoot thickness. in 2014, Converse growth rhythm was registered in “Golden Delicious” and “Braeburn” on heterozygote seeds of “Azayesh” inducing significant differences, while “Golden Delicious”, “red Delicious” and “Gala” were affected significantly by “Azayesh” F1 progeny for the measured variables in 2015. Moreover, in 2014 “Morabbaei” seeds induced significant differ- ences between “Golden Delicious” and “Granny Smith”. Similar differences were observed among “Golden Delicious”, “red Delicious” and “Gala”, in 2015 (Table 2). Such differences in successive years within the combinations are attributed to the normal annual growth. Internode number Year and scion main effects and year × scion and year × rootstock × scion interaction significantly affected internode number (Table 1). The highest number of internode was found in 2014 in combina- tion of “Golden Delicious”-“Morabbaei” confirming the role of homozygosity on lowering vegetative growth, changes in metabolic pathways and relative hormonal modifications at intra-cellular level. However, the lowest expression of the genes for internode number was found in “Gala”-“Azayesh” combination, in 2015. As a reason, the latter low vigor of “Gala” occurred in “On” year could influence such result. in 2014, there were no significant differ- ences among the cultivars for internode number on “Azayesh” seeds, while in the second year significant differences were observed caused by annual growth. Contrarily, “Morabbaei” seed stocks induced signifi- cant differences in “Gala”, “Golden Delicious” and “Granny Smith”, in 2014, which confirms relatively lower vigor of “Gala”, whilst in 2015 significant differ- ences was observed among the grafted cultivars (Table 2). in 2014, there were no significant differ- ences between rootstocks for each scion combina- tion, but in 2015, “Golden Delicious” and “red Table 2 - The interaction effects of year × scion × rootstock on some vegetative traits of the apple scion cultivars Year Seed stock Scion Shoot length mm Shoot thickness mm internodes number internodes length mm rootstock diameter mm Graft diameter mm Trunk diameter mm Shoot number Crotch angle Lenticels number 2014 Azayesh 'Golden Delicious' 179.24 b-g 5.70 ef 21.06 ab 14.66 b-e 45 a 43 a 30.2 a 7.75 a 61.67 cd 16.25 ij 'red Delicious' 208.22 a 6.43 de 19.26 a-d 17.20 bc 43.6 a 47.2 a 38.5 a 10.2 a 68.33 bcd 24.23 cde 'Granny Smith' 177.39 b-h 6.87 bcd 20.17 abc 17.19 bc 57.5 a 58.25 a 52.25 a 17.66 a 73.75 a-d 33.12 a 'Braeburn' 175.25 b-h 5.10 ghi 18.08 b-e 15.54 b-e 49.4 a 56 a 40.5 a 11.16 a 83.33 a-d 14.53 j 'Golab-e Kohanz' 168.75 b-h 6.80 cd 19.40 a-d 14.66 cde 47.33 a 51.66 a 50.83 a 8.5 a 87.50 ab 10.22 k 'Gala' 178.45 b-g 6.86 bcd 18.16 b-e 17.83 b 62.83 a 60.83 a 47.66 a 10.5 a 85.00 abc 18.16 e-i Morabbaei 'Golden Delicious' 193.63 abc 6.18 de 22.86 a 16.83 bcd 47 a 43.66 a 35.83 a 14.5 a 82.17 a-d 21.21 c-f 'red Delicious' 195.06 ab 8.00 a 19.46 a-d 20.33 a 56 a 41 a 51 a 17.16 a 95.00 a 21.94 c-g 'Granny Smith' 174.61 b-h 6.36 de 20.20 abc 13.73 b-e 40.25 a 49.6 a 41.8 a 13 a 90.00 ab 21.40 c-h 'Braeburn' 159.70 e-i 7.63 ab 19.58 a-d 15.75 b-e 43.4 a 49.6 a 43.4 a 9.33 a 60.00 d 23.80 bcd 'Golab-e Kohanz' 165.74 c-h 7.41 abc 19.56 a-d 15.30 b-e 44.6 a 54.5 a 43.16 a 6.33 a 82.50 a-d 29.27 ab 'Gala' 171.44 b-h 7.86 ab 15.57 d-g 15.03 b-e 41.2 a 44.5 a 36 a 8.00 a 73.33 a-d 15.50 hij 2015 Azayesh 'Golden Delicious' 176.64 b-h 3.94 k 13.39 fgh 13.24 ef 69.33 a 70.33 a 58.66 a 6.33 a 68.33 bcd 14.18 ij 'red Delicious' 149.59 hi 4.03 k 9.52 hi 11.36 fg 51 a 62 a 52.33 a 10.16 a 70.00 bcd 22.65 c-g 'Granny Smith' 164.23 d-h 4.47 h-k 14.17 efg 14.89 b-e 63.2 a 70.2 a 58.8 a 10.66 a 69.00 bcd 19.34 c-h 'Braeburn' 181.71 a-f 4.31 jk 11.32 ghi 9.97 g 62.16 a 69.16 a 61 a 9.4 a 59.00 d 16.30 hij 'Golab-e Kohanz' 187.42 a-e 4.30 ijk 14.11 efg 10.23 g 60.33 a 68.66 a 58 a 7.5 a 76.67 a-d 18.22 d-i 'Gala' 185.61 a-e 4.63 g-j 8.25i 10.36 g 68.33 a 68.5 a 57.5 a 9.16 a 83.33 a-d 17.28 ghi Morabbaei 'Golden Delicious' 143.23i 6.10 de 9.11i 14.67 cde 53 a 58.33 a 45.83 a 10.00 a 90.00 ab 21.08 c-g 'red Delicious' 191.06 a-d 4.33 h-k 16.10 c-f 21.24 a 60 a 62 a 53 a 17.16 a 95.00 a 22.56 bc 'Granny Smith' 116.40 j 4.63 g-j 14.70 efg 13.79 ef 44.6 a 57.5 a 44.66 a 7.33 a 85.00 abc 17.26 hij 'Braeburn' 151.71 ghi 4.68 g-j 11.31 ghi 16.79 bc 51.66 a 64 a 50 a 6.66 a 76.67 a-d 23.19 bc 'Golab-e Kohanz' 156.16 f-i 4.97 gh 14.43 efg 15.61 b-e 58.25 a 65.75 a 53 a 7.83 a 73.33 a-d 19.94 c-h 'Gala' 150.88 ghi 5.24 fg 11.82 f-i 11.50 fg 44 a 57.66 a 44 a 9.33 a 83.33 a-d 17.50 f-i in each column, means with similar letters are not significantly different at the 1% probably level using Duncan multiple range test. Hajnajari - Seed rootstocks improvement in apple 81 D e l i c i o u s ” s h o w e d s i g n i f i c a n t d i f f e r e n c e s o n “Morabbaei” and “Azayesh” seed sources (Table 2). Internode length internode length was affected by year, scion culti- var and rootstock main effects and their interactions (Table 1). The longest internode was found in “red Delicious” on “Morabbaei” rootstocks in both years and the lowest value was registered in combination of “Braeburn”-“Azayesh”, in 2015 (Table 2). in the first year, among all the scions combined with “Azayesh” rootstocks, there was significant differ- ence between “Golab-e Kohanz” and “Gala” and among the grafted cultivars on “Morabbaei” sole “red Delicious” showed significant difference. “Golab-e Kohanz” is the most vigorous iranian culti- var early and “Gala” with moderate tree vigor. Tree vigor, denoted as potential of vegetative growth, is measured based on height and spread of adult trees self-rooted, or relative to reference cultivars on the same rootstock in apple descriptors (Watkins and Smith, 1997). “Golden Delicious” and “red Delicious” were used as reference cultivars to assess rootstocks efficiency for tree vigor, the trait that encompasses other components as shoot length, shoot thickness, internode number, internode length, shoot number, and crotch angel by which the tree overall size, shape and architecture will be reflected. Fazio (2014), assumed that rootstock performance is highly corre- lated with the genetic potential to impart positive architectural properties to the scion like vigor con- trol. Considering the ruling genetic purity carried by “Morabbaei” seed rootstocks, it imparted uniformity in the size of internode length in all the scion culti- vars. in the second year, “Golden Delicious” and “Granny Smith” showed significant differences against other scions grafted on “Azayash”, while “red Delicious” and “Gala” had significant difference rela- tive to the other scions on “Morabbaei” (Table 2). Such differences are attributed to the different genetic vigor of scion materials. Rootstock, graft point and scion diameter According to the Table 1, the effect of year was significant for rootstock, graft union and scion trunk diameters. Overall, rootstock diameter, graft and trunk were higher in the second year. rootstock and graft point were affected equally by rootstock factor. interaction of rootstock × scion was significant for rootstock (Table 1). interaction effect of scion × root- stock on rootstock demonstrated that combination of “Granny Smith” on “Azayesh” and “Morabbaei” rootstocks endured modifications on the trait, for example 60.66 mm to 42.66 mm, respectively. There w a s o n l y s i g n i f i c a n t d i f f e r e n c e b e t w e e n “ r e d Delicious” (47.30 mm) and “Gala” (65.58 mm) for rootstock limiting factor to “Azayesh” rootstock. Similar comparison within seed lots of “Morabbaei” revealed significant difference in combination with “Granny Smith” (42.66 mm) and “Gala” (60.22 mm). Surprisingly, both seed rootstocks influenced “Gala” increasing rootstock to the highest values of 65.58 mm and 60.22 mm (Table 3). Moreover, significant difference was observed between the combinations of “Granny Smith”-“Azayesh” and “Granny Smith”- “Morabbaei” for the effect of rootstock type on each scion for rootstock, while no difference was observed between seed rootstocks for other combinations (Table 3). This result is assumed positive for uniform apple tree saplings production on the improved seed rootstock. Shoot number Shoot number was not affected by rootstock type, while the effects of year, scion and rootstock × scion were significant (Table 1). in 2014, more lateral branches were grown than 2015. Among scions- s t o c k s c o m b i n a t i o n s , “ M o r a b b a e i ” s e e d s t o c k showed both max. and min. shoot number, on “red Delicious” (17.16) and on “Golab-e Kohanz” (7.08), respectively (Table 3). no significant difference was found among the six scion cultivars for shoot number on “Azayesh”, whilst “Morabbaei” rootstock induced significant differences of shoot number on “Golden Delicious” and “red Delicious”. Crotch angle in this study crotch angle was affected by year, rootstock Scion rootstock diameter (mm) Shoot number 'Azayesh' 'Golden Delicious' 55.43 abc 7.14 c 'red Delicious' 47.30 bc 10.18 bc 'Granny Smith' 60.66 ab 13.00 bc 'Braeburn' 56.36 abc 10.36 bc 'Golab-e Kohanz' 53.83 abc 8.00 bc 'Gala' 65.58 a 9.83 bc 'Morabbaei' 'Golden Delicious' 50.27 abc 12.25 ab 'red Delicious' 58.00 abc 17.16 a 'Granny Smith' 42.66 c 10.16 bc 'Braeburn' 46.50 bc 8.00 bc 'Golab-e Kohanz' 50.67 abc 7.08 c 'Gala' 60.22 ab 9.25 bc Table 3 - The interaction effect of scion × rootstock on rootstock diameter and shoot number in each column, means with similar letters are not significantly different at the 1% probably level using Duncan multiple range test. 82 Adv. Hort. Sci., 2019 33(1): 77-85 rootstock and scion interaction (Table 1). The combi- nation of “red Delicious”-“Morabbaei” showed the widest value of crotch angle probably as a result of heavy cropping, while light bearing trees in the com- bination of “Braeburn”-“Azayesh” had the lowest crotch angle rates, in both years. in general, the scion cultivars grafted on “Morabbaei” had wider crotch angle than on “Azayash” progeny (Table 2). Except partial genetic role of the scions regarding growth habit, this effect might be result of higher tree vigor control by self-compatible parent “Morabbaei” root- stocks and subsequent decrement of woody parts in favor of flower bud initiation and fruit set (Wertheim and Webster, 2005). Clearly, bearing shoots under higher fruit weight were bent downward increasing crotch angle. Lenticels number Lenticels number was affected by year × rootstock × scion interaction (Table 1). The max and min values of lenticels number were found in “Granny Smith” and “Golab-e Kohanz” both on Half-Sib seed stocks of “Azayesh”, in the first year. it can be deduced that the increased leaf lenticels number of the “Golab-e Kohanz” as the most vigorous scion is a normal physi- ological trend appeared trough interaction of the grafting with as much vigorous seed stock “Azayesh” in the year. More vegetative growth induced by vig- orous seeds demands higher respiration rate for which a higher lenticels number equilibrate the defined biological status. in both years, significant difference was observed among the fruit scions on “Azayesh” and “Morabbaei”. This confirms significant effect of rootstock seed masses for lenticels number. in 2014, comparisons of rootstocks for each cultivar showed that “Golden Delicious”, “Granny Smith”, “Braeburn” and “Golab-e Kohanz” were affected by seed stocks for lenticels number. Also in 2015, “Golden Delicious” and “Braeburn” were affected for this trait (Table 2). The comparison between two seed sources put in evidence of high dominant uni- formity of lenticels number trait for scions grafted on the seed stocks and originated from self-compatible “Morabbaei”. 4. Discussion and Conclusions According to the results, shoot length, shoot thickness and internode length as 3 main compo- nents of tree vigor showed significant difference in all t h e s i x c u l t i v a r s g r a f t e d o n t w o s e e d m a s s e s . Dominant homozygosity carried out by self-compati- ble “Morabbaei” and relative progeny overcame het- erosis effects which induced by “Azayesh” seeds and tree vigor interaction. Our results regarding control of tree vigor “Morabbaei” seed stocks demonstrated that it could reduce shoot length; infact this trait decreased in all the cultivars except for “Golden Delicious”, in 2014. This cultivar showed the same opposite rhythm for all growth traits like crotch angle, internode thickness, internode number, roost- ock, and scion diameter on “Morabbaei” seed stock. Also, other four scion cvs. decreased shoot length value and were affected by dwarfing seeds in the range of 13 to 3 mm for “red Delicious” and “Golab-e Kohanz”, 7 and 3 mm for “Gala” and “Granny Smith”, respectively. These results confirm the reciprocal influences of two genomes, scion and seed rootstock within the same genus, each one specialized differ- ently for which were selected in the selection proce- dure. There is no clear reason for reaction of “Golden Delicious” for measured trait when compared with five scion cultivars grafted on the same seed pure line progeny. This may not be related to the distant geographical origin of two genomes, iran-USA. With studying scion tree vigor was suggested that j-TE-E as an acceptable rootstock for “rubin” among 14 root- s t o c k s ( K o s i n a , 2 0 1 0 ) . T h e s c i o n c u l t i v a r s o n “Morabbaei” seeds showed higher shoot thickness than the same scions on “Azayesh” seed progeny. increased shoot thickness as the diametric growth of annual shoots on “Morabbaei” seeds indicated accu- mulation of carbohydrates for productive functions. However the final canopy size is determined geneti- cally by scion-rootstock interaction. Higher dwarfing efficiency raised in “Morabbaei” than “Azayesh” progeny is in agreement with Tworkoski and Miller (2007 a), who indicated that Malling rootstocks have different size-controlling effects on different apple scions. The lowest interned number (8.25) was found in “Gala”-“Azayesh” combination, in 2014, while the highest (22.86) was found in combination of “Golden Delicious”-“Azayesh”, in 2015. The biennial compar- isons evidenced that the higher mean of internode number was induced by “Morabbaei” in both years, 22.86 and 9.11, related to “Azayesh” equal to 21.06 and 8.25. These finding confirmed stronger dwarfing effects of the self-compatible parent. Dwarfing mech- anism acted through an increase of internode length and contrarily shortening internode length. Highest v a l u e o f i n t e r n e d l e n g t h w a s f o u n d i n “ r e d Hajnajari - Seed rootstocks improvement in apple 83 Delicious”-“Morabbaei” combination for 2014 and 2015 and the lowest in “Braeburn” on “Azayesh” in 2015 (Table 2). Others reported that wild peach root- stocks influenced shoot growth and leaf area for the scions only during the first year (Sharma et al., 2004). in general, in the first year, the internode number and internode length were higher than the second year. it can be attributed also to the difference between orchard management during two years. interesting results were obtained in 2015 comparing effects of two seed stocks on major part of the scions. Dwarfing property of “Morabbaei” seed stocks overcame in the next season which caused shoot length shortening in appropriate growth rhythm and shoot thickness increasing and internode number and decreasing rootstock and scion diame- t e r . A p a r t o f l e s s e x p e c t e d b e h a v i o r o f “ r e d Delicious” on “Morabbeai” stock which shoot length and internode length was both increased, but other traits like shoot thickness, internode numbe , and scion diameter followed normal dwarfing trend. All the other growth traits assessed in the rest of four scion cultivars were highly affected by dwarfing effect of “Morabbeai” seed progeny, without excep- tion (Table 2). Weibel et al. (2003) indicated that dif- ferences in peach shoot length were related primarily to the internode length rather than the node num- ber, whereas Seleznyova et al. (2003) attributed the differences in apple branch size to the reduction in neoformed internode length and node number. Mean of internode length depended on node num- ber. it means that shorter internodes are caused by lower node number (Costes and Garcia-Villanueva, 2007). Measured diametric values of graft union and scions on self-incompatible “Azayesh” seed stocks s h o w e d h i g h e r t h a n t h o s e o n s e l f - c o m p a t i b l e “Morabbaei” F1 seed progeny. Scion-rootstock dis- continuity may lead to Burrknot formation and high diametric difference between rootstock and trunk that may be a site where xylem may be affected by modified cell diameters or cell disorganization between different scions and rootstocks (Atkinson et al., 2003; Tworkoski and Fazio, 2011). Such morpho- logical differences may in turn affect hydraulic con- ductivity, root hormones production, or nutrient transport and explain the differences in growth. Tworkoski and Fazio (2015) reported that the scion cultivars “Gala”, “SM.9”, and “SM.27” reduced root- stock of “G.41” and “G.11” compared with “Fuji” scion. in the second year, the most of fruit scions on “ M o r a b b a e i ” s e e d h a d s m a l l e r d i a m e t e r t h a n “Azayesh” without significant difference, except for “red Delicious” (Table 2). This implies that rootstocks may affect scion. So, shoot number was not affected b y r o o t s t o c k t y p e , w h e r e a s t h e e f f e c t o f rootstock×scion, scion and year resulted significant. “red Delicious” and vigorous “Golab-e Kohanz” on “Morabbaei” seed rootstock had the highest and lowest Brn, respectively (Table 3). “Morabbaei” F1 seeds induced more new shoots than “Azayesh” seed stocks. Generally, the mandatory cut back of leader in Spindle pruning method activates the latent buds, forming new lateral shoots due to removal of apical dominance. This practice however was performed equally on the leader of all combinations. Thus, it may be concluded that while, on one side, homozy- gosis affects canopy size and decreases shoot length, on the other side, the reserved carbohydrates might be used in activation of latent buds in absence of api- cal dominance. Obviously, winter pruning obliges crossing out of adventitious shoots for flower initia- tion purposes. Across all scions, the dwarfing M.9, and seedling rootstock induced the lowest and the highest tree height and scion diameter, respectively. Significant interactions indicated that effects of size- controlling rootstock on components of shoot growth vary with apple tree growth habit (Tworkoski and Miller, 2007 a). in this study all the six scions carried the spread habit, for which crotch angle was investi- gated. Meantime, it might be attributed to the hor- monal factor due to the genetic factor derived from seed stocks, scions and relative interaction. Seedling rootstock might affect growth habits by increasing the Auxin/Cytokinin ratio. Changing in hormonal ratio might be a factor regulating the development of growth habit in apple scions, and rootstock might modify the hormone concentrations in shoot tips (Tworkoski and Miller, 2007 b). As prerequisite, crotch angle is mentioned as a stable trait and used in cultivar differentiation and cultivar/progeny evalu- ation (Watkins and Smith, 1997), and less affected by external factors which is agreed with our results of crotch angle among five scions on two diffrent stocks, except for “red Delicious”. in general, the grafted scions on “Morabbaei” seeds showed wider crotch angle than “Azayash” progeny, probably for higher fruit weight as a result of higher set. The sig- nificant differences of crotch angle between “Golden Delicious” and “Granny Smith” on “Azayesh” seed rootstocks, in the first year, can be attributed to the stability of this trait, whereas lack of differences in the second year would be justified by pruning effect. it is however very important that the single cultivars on “Azayesh” didn’t show significant differences in Adv. Hort. Sci., 2019 33(1): 77-85 84 terms of crotch angle with the same cultivar on “Morabbaei”, except for “red Delicious” (Table 2). However, endogenous growth regulators mainly aux- ins and cytokinins play a major role in the control of lateral bud development (Sachs and Thimann, 1967). There are numerous reports of growth-regulating chemicals affecting branch crotch angle (Verner, 1938; Williams and Billingsley, 1970; Elfving and Forshey, 1977). Warner (1991) reported that root- stock affects primary scaffold branch crotch angle of apple trees, which is consistent with our results. Also lenticels number of annual shoots unit, defined as stable trait like crotch angle, was affected by root- stocks and year, and interaction of rootstock × scion × year. Comparisons of rootstocks for each cultivar, in 2014, showed that “Golden Delicious”, “Granny Smith”, “Braeburn” and “Golab-e Kohanz” were affected by seed stocks for lenticels number, and in 2015, “Golden Delicious” and “Braeburn” were affected for this trait (Table 2). 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