The Rootstock and Scion Interaction Effects on Growth and Bearing Characteristics of Young Pear Trees

 Pear (Pyrus communis L.) is one of the major fruit trees in the world which grown in temperate zones. In pear breeding program the bigger fruit size with better quality as well as market acceptability are usually in interest. In fruit trees, the size and yield of fruit are closely depended on cultivar and rootstocks. The variations of nutrient uptake, water use efficiency, photosynthesis performance, and resistance to biotic and abiotic stresses have been reported among different combinations of cultivars and rootstocks. Therefore there is a close relation between cultivar and rootstock with yield and quality of produced fruits. In recent years the semi dwarf clonal rootstocks of pear including OH×F, Pyro and FOX series have received more attention. However the performance of these rootstocks varies depending on scion cultivar, climatic condition, soil type, and planting system.

 This experiment was conducted to assay the growth characters and fruit yield of Dargazi and Louise Bonne (Beyrouti) grafted onto PyroDwarf and OH×F69 rootstocks at the Orchard of Astan Quds Razavi, Mashhad, Iran (36°17' N, 59°36' E; altitude. 985 m) during 2018-2019 and 2019-2020. The experiment in both consecutive years was done as a factorial in the base of randomized complete blocks with four replications. The studied cultivars were grafted onto PyroDwarf and OH×F69 rootstocks in late spring 2016. The used water was pit water with 695 µSiemens/cm EC and pH 7.17. Evaluation of plant growth was carried out at the end of the season. The studied traits were included tree height, internode length, vertical and horizontal growth of shoots in the current season, trunk diameter above, below and in the grafting line, leaf area, shoots angel and the number of sucker per tree. These characters were assayed in three trees per each replication. The trunk diameter at the below and above the grafting line was calculated according to trunk circumference that was measured at 10 cm above and below the grafting point. Leaf area in each tree was assayed with area measuring device. Flowering characteristics (start blooming and end of bloom) were determined. Fruit ripening season was also recorded. Yield of trees was assayed by weighting of produced fruits in each tree with a digital scale. The combined analysis of obtain data was conducted by SPSS and differences among means of data were determined by Duncan's multiple ranges test at P≤0.05. The reported data was the mean of two studied years.

 The obtained results showed the variation in growth and bearing properties of different combinations of Beyrouti and Dargazi cultivars with PyroDwarf and OH×F69 rootstocks throughout the studied years. The analysis variance showed the significant effect of year, cultivar and rootstock on growth characteristics of pear tree. Also the interaction effects of cultivar and rootstock were significant on tree growth response with exception of internode length. The most studied parameters showed a significant increasing during the two consecutive years. During the studied years the height and width of pear trees were increased up to 10.44 and 14.54%, respectively and the trunk diameter was increased by 10%. According to obtained results the growth of Dargazi cultivar was higher than the Beyrouti cultivar. The effect of OH×F69 rootstock on growth increasing of studied cultivars was prominent than PyroDwarf regards to tree height, shoot length and internode length. However the highest trunk diameter and leaf area density of both cultivars was found in PyroDwarf rootstock. Although the time of blooming and fruit ripening of each cultivar was not influenced by the rootstock but the bearing characters were varied between the Dargazi and Beyrouti cultivars. The highest yield of pear fruit was obtained in Dargazi cultivar and grafting onto PyroDwarf rootstock significantly enhanced the fruit yield in both cultivars.

 The rootstocks have a key role on growth and yield of pear trees as well as their responses to abiotic stress. Rootstocks through influencing the physiological characteristics of grafted scions regulate the quantity and quality of produced fruits. The results of present study showed the variation in growth and bearing properties of different combinations of Beyrouti and Dargazi cultivars with PyroDwarf and OH×F69 rootstocks throughout the studied years. The PyroDwarf rootstock greatly reduced the tree growth and enhanced fruit yield of both Dargazi and Beyrouti cultivars. According to the obtained results the PyroDwarf rootstock is recommended for Dargazi cultivar to reach the highest pear fruit yield under similar environmental condition of present study.