Investigation of improved seed rootstocks efficiency on vegetative growth control in some apple cultivars

Background and objectives: In a 5-Year-trial in the experimental orchard located in Samirom-Isfahan, in order to improve seed rootstocks used for production of uniform trees, 7 scion cultivars were grafted on 4 preselected seed masses obtained from dwarf maternal parents, beside controls as 2 impure seed populations current in Iranian nurseries. The effect of improved Half-Sib seed masses was examined on the trend of scion tree vegetative growth through a group of traits as vigor components of scion trees compared to the 2 controls. Distinction of the best seed masses with highest genetic purity will permit the control of scion tree vigor as well as production of trees with uniform size and shape.
Materials and Methods: In the first 2 years, 2010-2012, the inductive effect of the preselected seed masses on the height of 2-Year-old of 7 scion trees were studied compared to the 2 impure populations as control characterized with high genetic variability in Dastgerd Hort. Research Station (Isfahan). The root length of the all treatments was recorded before transfer of the plant material in Samirom Research Station. In the next 3 years, 2013-2015, more vegetative traits of 5-Year-old trees including tree height, number of lateral branches; crown shading area, annual branch growth, rootstock and scion diameter and length of scion trunk were recorded within 42 scion-rootstock combinations (42 :2+4×7)
A factorial design within completely randomized block with two replications was conducted. The first factor as seed stocks in 4 levels contained Gami almasi, Zinati, Morabbaei and Azayesh and 2 levels of controls; the second factor including 7 levels of fruit scions as Red Delicious, Golden Delicious, Golab kohanz, Braeburn, Granny Smith, Fuji and Gala.
Results: No significant difference was found for root length between the 4 improved rootstocks and control despite of less developed tap root of the 2 controls. The scions tree height with moderate growth showed no significant differences on seed sources of Azayesh and Zinati compared to the Control. "Red Delicious" and "Golden Delicious" showed both the highest rates of scion height as 107.2 Cm and 105.3 cm, related to the other combinations. Vice verse, the shortest scion length was registered in "Fuji" and " Gala" on Gami almasi seed rootstocks, 70.2 cm and 68.5 cm, respectively. Both of the rootstock, scion diameters and the annual shoot growth showed increased values on the improved seed rootstocks than control. The "Fuji-"Zinati seeds combination had the largest rootstock diameter (6.1cm). The highest growth rate of annual shoots (74.66 Cm) was noted in" Red Delicious" on Zinati seeds. The Morabbaei seed mass induced the highest shading area in "Fuji" (165 Cm2). "Granny Smith-"Gami Almasi combination presented the highest scion tree height (350 Cm). The control seeds – "Red Delicious" combination formed‎ the max rate of rootstock length (18 Cm). The highest number of lateral branches (8.33 and 9.33) was found in "Braeburn" on the two control seeds rootstock.
Conclusion: Use of the improved seed rootstocks affected significantly the growth of vegetative traits decreasing the tree heights, length of the rootstocks and consequently increased the rootstocks diameter causing a reduced canopy size. Contrarily, the controls induced significantly the scion tree size by production of more lateral branches. Gami almasi seed mass induced higher control of scions tree vigor and so smaller crown size and higher rootstocks diameter in "Red Delicious". Azayesh, Zinati and Morabbaei seed sources showed a vast dwarfing effect on whole studied cultivars, probably for the influence of their crab parents. Low vigor cultivars on such dwarfing seed rootstocks may be used for intensive fruit growing.