Effect of scion storage and grafting time on graft union of Pistachio minigrafting under in-vivo condition

Micrografting is a relatively new technique for propagation of plants. This technique has been used on woody species to produce viruses-free plants, rejuvenation, and reinvigoration, analysis of grafting compatibility and incompatibility and clone's propagation. Pistachio (Pistacia vera L.) is one of the most important commercial trees grown in arid and semi-arid regions of Iran where it is of vital importance to the permanent farming. Increase of pistachio cultivation areas during last three decades caused a continuous growing demand for pistachio planting materials in Iran. The benefits of applying in vivo and in vitro micrografting to the pistachio are obvious, especially when considering the need to improve the genetic quality of the planting stock of this slow-growing species while increasing crop potential. The objectives of this study were to determine the influence of scion storage and grafting time on clonal propagation of pistachio from elite-mature trees.

In order to evaluate the effect of scion storage and grafting time on grafting success of in-vivo micrografting of Pistachio, an experiment was achieved an factorial based on compeletly randomized design (CRD) during 2017-2018 under greenhouse condition. In the experiment, the success of micrografting in "Ahmad aghaiee " Pistachio on 14-days "Badami-Riz-Zaran" rootstocks were examined. The scion of "Ahmad aghaiee" were prepared from shoot tips of mature trees at three different times (February, march and may) and grafted immediately or after one month storage at 4 °C using inverted cleft grafting method. 21 days after grafting, some traits such as graft union percentage, scion growth, time to graft union, scion leaf number and total soluble sugar were recorded.

The results showed that the highest graft union percentage (100%) was observed on the grafted plants of February, immediately after grafting. Based on the results, soluble sugars were significantly increased in freshly harvested scions in February and March. The results also showed that the maximum time (18 days) for time graft union was obtained in April with the stored scion whereas the lowest time graft union (11 days) was observed in February with scion taken at the same time. In addition, we found that the highest scion growth rate was due to freshly harvested scions and grafts in February.

It was found that February was the best time of micrografting with scion taken at the same time because in this period carbohydrate content of the scions was higher than other months. Also, pistachio contain high amount of phenolic compounds. Exudation of phenolic compounds from the cut surfaces and their oxidation by polyphenoloxidase and peroxidase enzymes cause discoloration of the tissues which results in poor micrografting.