Scion/Rootstock Interaction in Some European (Pyrus communis L.) and Asian (Pyrus serotina Rehd.) Pear Cultivars on Vegetatively Propagated “Pyrodwarf” Rootstock

In recent years some of pear nurseries have been suggested using vegetative propagated European pear (Pyrus communis L.) `Pyrodwarf’ rootstock for pear orchards in Iran. This research was carried out to explore the scion/rootstock interaction, root growth and root length and distribution of two Asian and one European pear cultivars on vegetatively propagated “Pyrodwarf” rootstock. Two Asian pear; cv. `KS6ˊ and cv. `KS10ˊ with one European pear; `Shahmiveh’ cultivar, budded on `Pyrodawrf' rootstock in late August 2012. The scion’s vegetative and rootstock root growth and distribution were recorded under Tehran environmental conditions in 2014 and 2015 growing seasons. In addition, to study the scion/rootstock compatibility, the amount of starch in the above and below of the graft union was determined using isozyme study by polyacrylamide gel electrophoresis. The results showed that the vegetative growth of cultivars on “Pyrodwarf” rootstock was significantly different. The growth of `KS10ˊ cultivar was lower than `KS6ˊ and `Shahmivehˊ cultivars. Starch content was significantly different among the cultivars. `Shahmiveh’ had the lower starch content than the other two cultivars. Isozymes study showed A and B bands in the `Pyrodwarf' rootstock and `Shahmiveh’ cultivar, however, only B band was observed in the `KS6ˊ and `KS10ˊ cultivars. `Shahmiveh’ as an European pear cultivar showed good compatibility on `Pyrodwarf' rootstock, but `KS6ˊ and `KS10ˊ as Asian pear cultivars showed semi-incompatibility on `Pyrodwarf'. The evaluation of the `Pyrodwarf' root system in comparison with `Dargazy’ seedling rootstock showed that the main roots of this rootstock grew horizontally near to the top layer of the soil. Roots did not penetrate and grew well in the deeper layers of the soil. It was conclude that due to the root system and structure, `Pyrodwarf' rootstock may not be suitable for the arid and semi-arid areas and should not be recommended to pear fruit orchards which facing shortage of irrigation water. Further research using suitable and compatible rootstocks with optimum root growth under drought conditions would warrant suitable fruit production of Asian and European pear orchards in Iran.