Asian and European pear scion-rootstock interactions and pyrodwarf rootstock root growth and distribution

In recent years some 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 interactions, root growth and root length density (RLD), and distribution of two Asian (Pyrus serotina Rehd.) and one European pear (Pyrus communis L.) cultivars on vegetatively propagated Pyrodwarf rootstock. Tow Asian pear ‘KS₆’ and ‘KS₁₀’ cultivars with a European pear ‘Shahmiveh’ cultivar budded on Pyrodwarf rootstock in late August 2012. The scions’ vegetative and rootstock root growth and distribution were recorded under Tarbiat Modares University (TMU), Asian pear orchard’s conditions during 2013 and 2014 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 obtained results showed that the vegetative growth of the studied cultivars on Pyrodwarf rootstock was significantly different, although the amount of two years growth on ‘KS₁₀’ cultivar was lower than ‘KS₆’ and ‘Shahmiveh’ cultivars. In addition, the amount of starch content was significantly different among the studied cultivars, so ‘Shahmiveh’ had lower starch than the other two studied cultivars. Isozymes study showed A and B bands in the Pyrodwarf rootstock and ‘Shahmiveh’, although the only B band was observed in the ‘KS₆’ and ‘KS₁₀’ Asian pear cultivars. According to the results, it seems that ‘Shahmiveh’ as a European pear cultivar showed good compatibility on Pyrodwarf rootstock, although ‘KS₆’ and ‘KS₁₀’ as Asian pear cultivars showed semi-incompatibility on Pyrodwarf rootstock. Note that the evaluation on the Pyrodwarf root system showed that the main roots grew most horizontally near the top layer of the soil, so roots were not penetrated and grew well within the deeper layer of the soil. We conclude that because of the root system and structure, Pyrodwarf rootstock may not be suitable in arid and semi-arid areas and will not be suggested to pear fruit orchards facing shortage of irrigation water or drying conditions. Future research using suitable and compatible rootstocks with optimum root growth under drought conditions will warrant suitable fruit production for Asian and European pear orchards in Iran.