Preliminary Selection of Different Species of Genus Pear (Pyrus) for Dwarfing and Nutrients Uptake

Dwarfing and nutrient uptake ability are among the important traits in pear rootstocks breeding programs. In this research, growth characteristics and macronutrients and iron uptake ability was compared in seedlings of 13 native and introduced species of genus pear (Pyrus), one commercial interspecies hybrid and three common clonal rootstocks of Pyrodwarf, Quince EMA and Quince BA29 from the species of genus Cynodonia (Cydonia oblonga Mill.). Evaluation was carried-out under controlled conditions using completely randomized design with 10 replicates in 2022. Growth characteristics and chlorophyll index in 70, 120, and 160 days after establishment were evaluated and measured. Nitrogen, phosphorus, potassium and iron uptake was evaluated and compared in Pyrus and Cydonia rootstocks 160 days after seedlings establishment. The results showed that the highest dwarfing rate belonged to P. syriaca followed by the clonal rootstocks, and the highest growth rate was measured in seedling rootstocks of P. communis derived from cv. Dargazi followed by P. bretschneideri. In P. syriaca, the lowest internode length was observed after 160 days with an average of 1.61 cm, which indicated the effect of dwarfing on slowing the growth of this species. Regarding the uptake of nutrient, P. hyrcana, P. nivalis, and P. pashia had the highest nitrogen uptake, P. amygdaliformis and P. nivalis had the highest phosphorus uptake and P. syriaca had the highest leaf potassium content. Considering the results of this research, future researches should focus on e evaluation of using P. syriaca as a dwarf rootstock for in establishment of intensive/ highly intensive pear orchards, or as the parent for dwarfing traits in pear breeding programs.
 
Keywords: Pear, iron, quince rootstock, germplasm, vegetative growth, chlorophyll index.
 
Introduction
Pear (Pyrus spp.) is one of the oldest cultivated fruits in the world and some evidence show the cultivation of pear trees in the Neolithic era (Simionca Mărcășan et al., 2023). About 22 different species of the genus Pyrus have been identified in the world, of which about 12 species have been reported in Iran. The existence of different species of this genus in the plateau of Iran has contributed to the country as one of the main centers of diversity of pear species in the world (Abdollahi, 2010). Currently, the cultivated areas of pear orchards in the world is estimated to be about 1.5 million hectares, from which about 24 million tons of fruits are harvested annually. According to the World Food and Agriculture Organization, China, USA, and Italy were the most important pear-producing countries in 2021 and Iran ranks 15th in the world (FAO, 2022).
The rootstock of fruit trees plays a very important role in determining the efficiency and sustainability of orchards of different horticultural crops. In a standard and modern pear orchard, the trees should have uniform canopy, which facilitates husbandry operations and harvest as well as producing uniform and high-quality fruits (Roberto et al., 2022). One of the problems in the cultivation of pears in Iran is the lack of access to suitable and adapted rootstocks to Iran's different climatic conditions. European pear seedling rootstocks obtained from cv. Dargazi are used in the nurseries (Abdollahi, 2010). Considering the existence of germplasm of different pear species in Iran and the existence of different growth rates among different species, it is necessary to evaluate this germplasm for use in rootstock breeding programs. Also, the availability of different introduced species of the genus Pyrus from Southeast Asia in Iran facilitates evaluation and comparison of the growth vigor and characteristics of these species for further use in the national pear breeding programs.
Vegetative growth and nutrients uptake potential has not been evaluated between seedlings obtained from many native and introduced species of the genus Pyrus and pear clonal rootstocks in Iran, Therefore, the present research aimed to evaluate and compare the vegetative growth and nutrient uptake in the seedlings obtained from different species of the genus Pyrus and commercial clonal rootstocks.
 
Materials and Methods
Growth characteristics and macronutrients and iron uptake ability was compared in seedlings of 13 native and introduced species of genus pear (Pyrus), one commercial interspecies hybrid and three common clonal rootstocks of Pyrodwarf, Quince EMA and Quince BA29 from the species of genus Cynodonia (Cydonia oblonga Mill.). Evaluation was carried-out under controlled conditions using completely randomized design with 10 replicates in 2022. Growth characteristics and chlorophyll index in 70, 120, and 160 days were evaluated and measured. Nitrogen, phosphorus, potassium and iron uptakes was also measured in the two genera of Pyrus and Cydonia rootstocks, 160 days after establishment. Phosphorus, potassium, and total iron contents were measured using an inductively coupled plasma device (model Agilent Technologies, Varian 700-es ICP-OES, USA), and nitrogen content was determined using the Kjeldal and via the digestion method. Analysis of variance for data was performed using SAS 9.2 software. Duncan’s Multiple Range Test was employed for means comparison at the 5% probability level.
Results and Discussion
Analysis of the variance showed significant difference between rootstocks for all vegetative traits. These significant differences were observed in all three developmental stages; 70, 120, and 160 days after seedlings establishment. Pear species originated from Southeast Asia including; P. calleryana, P. betulifolia, and P. bretschneideri had the most vigorous vegetative growth as they reached 107.20, 98.80, and 132.0 cm, respectively, after 120 days after establishment. On 160 days after establishment, Dargezi seedlings with 145.6 cm had the tallest plant height and P. syriaca seedlings with 56.10 cm had the shortest height, respectively.
The results also showed that in 120 and 160 days after seedling establishment, chlorophyll index increased in most of rootstocks. In 70 days after establishment, chlorophyll index varied from 25.66 to 62.66. According to the reports, different pear cultivars have demonstrated good compatibility with P. syriaca species. P. syriaca is known as an excellent tolerant genotype to drought stress as well as calcareous soils. Therefore, this species has great potential for breeding of new dwarfing pear rootstocks in Iran. Regarding nutrient uptake ability, P. hyrcana, P. nivalis, and P. pashia had the highest nitrogen content, P. amygdaliformis and P. nivalis had the highest phosphorus and P. syriaca had the highest leaf potassium contents. Also, all species of the genus Pyrus had higher total iron content when compared to the rootstocks belonging to
C. oblonga.
 
References
Abdollahi, H. 2010. Pear: botany, cultivars and rootstocks. Nashr-e-Amoozesh, Agricultural Education and Extension Institute, Karaj, Iran. 210 pp. (in Persian).
FAO. 2022. World food and agriculture-statistical yearbook. Food and Agriculture Organization Publication. Rome, Italy. 380 pp.
Roberto, S.R., Novello, V. and Fazio, G. 2022. New rootstocks for fruit crops: breeding programs, current use, potential, challenges and alternative strategies. Frontiers in Plant Science, 13, 878863. DOI: 10.3389/fpls.2022.878863
Simionca Mărcășan, L.I., Pop, R., Somsai, P.A., Oltean, I., Popa, S., Sestras, A.F., Militaru, M., Botu, M. and Sestras, R.E. 2023. Comparative evaluation of Pyrus species to identify possible resources of interest in pear breeding. Agronomy, 13(5), 1264. DOI: 10.3390/agronomy13051264