PEAR psylla is one of the most important pests of pome and stone fruit trees. PEAR trees were damaged more than any other hosts of this insect. Several researches in the biology field of this insect have been conducted during the past two decades. Therefore, assessment of ASIAN PEAR trees resistance, considering the value of this new product in the country, is required. For this purpose, this project was conducted in 2008 growing season in order to explore and monitor the resistance of some ASIAN PEAR (Pyrus serotina Rehd.) cultivars including ‘KS6’, ‘KS7’, ‘KS’8, ‘KS9’, ‘KS10’, ‘KS11’, ‘KS12’, ‘KS13’ and ‘KS14’ to PEAR psylla (Cacopsylla pyricola L.). Evaluation of insect resistance were determined based on the number of insects on leaves, the final product, the amount of fruit loss, leaf area, sugar content and leaf chlorophyll content. Among tested plant materials, ‘KS13’ with a few number of the PEAR psylla, ‘KS8’ and ‘KS14’ with lower fruit drop, were found to be moderately resistant to this pest of the antixenosis and tolerance types, respectively. Assessed correlation of sugar content and resistance, indicated that the cultivars with lower sugar content were resistant to the PEAR psylla. Leaf area did not show any significant correlation in respect to resistant to PEAR psylla.

Experiments were conducted to study the in vitro propagation of nine improved ASIAN PEAR cultivars namely "KS6", "KS7", "KS8", "KS9", "KS10", "KS11", "KS12", "KS13" and "KS14"; and the effects o("culture media and plant growth regulators on the micropropagation. Single-node explants, harvested from current season"s growth shoots, were disinfected and cultured on three basal media, murashige and Skoog (MS), halfstrength MS salts (1/2 MS) and woody plant medium (WPM)," supplemented with 1 mg 1-1 benzylaminopurine (BAP). Growth and proliferation of ASIAN PEAR explants at the stablishment phase were obtained only in five cultivars ("KS7", "KS8", "KS12", "KS13" and "KS14"), and WPM was the best medium for their growth. In the multiplication phase, shoots obtained from in vitro conditions were subcultured four times, each with one-month interval, on the fresh media, supplemented with various concentrations of BAP (0, 1 and 2 mg 1-1 The highest shoot proliferation rate was obtained at 2 mg 1-1 BAP. Meanwhile, with increase of BAP concentration in this stage, proliferated shoots height was decreased and vitrified shoots percentage, increased. The best medium for proliferation of "KS7" shoots was WPM, but there was not any significant difference among the various media for the other cultivars (excepting "KS14", proliferated in WPM better than 1/2 MS). Moreover, with increase of subculture number, proliferation rate was increased, too. For rooting, 1/2 MS medium with different concentrations of indolebutyric acid (IBA) were used. Shoots were transferred on mentioned medium for different durations before transfering on the hormone-free MS medium. Micro propagated shoots failed to produce roots in all cultivars, after two months.

In order to determine the self and cross- (in) -compatibility of nine ASIAN PEAR and two European PEAR cultivars native to Iran, two experiments were conducted based on complete randomized block design in two consecutive years (2012-2013). This study was performed in the experimental PEAR orchard in the Tarbiat Modares University, Tehran. Controlled pollination method was used in orchard and then pollen tube growth analysis by fluorescence microscopy was studied. Fruit set percentage was calculated 15, 35 and 75 days after full bloom. Pollinated flowers were picked 48, 72, 96 and 120 hours after pollination, fixed in FAA solution and stored at 4 ˚C until microscopic studies. Results showed that ‘KS9’ had the highest and ‘Sebri’ the lowest fruit set (7.85 and 0 % respectively). Results of controlled pollinations showed that the cultivars ‘Shahmiveh’, ‘Sebri’, ‘KS13’ and ‘KS7’ were self-incompatible and others were self-compatible. It can be concluded that cultivars ‘KS6’, ‘KS12’ and ‘KS13’ are cross-compatible, because their pollen tubes reached the ovaries 96h after pollination and the final fruit set was more than 8.98%.

Fire blight caused by Erwinia amylovora, is one of the most catastrophic diseases of plants in the Rosaceae subfamily Pomoideae. The objective of this study was to determine the resistance of thirty PEAR cultivars to a mixture of four E. amylovora strains. Disease development was assessed according to severity index (I.V.S.) based on the progression of necrosis rate through shoots, from the inoculation point at 3, 6, 9, 12 and 18 days after inoculation. Analysis of variance showed significant differences among cultivars, indicating a wide range of relative resistance to the fire blight pathogen. PEAR cultivars showed considerable variations in resistance to fire blight with the severity of infection ranging from 0.4% to 100%. Cultivars were divided into four groups including very resistant (0-10%), moderately resistant (11%-50%), susceptible (51%-80%) and very susceptible (81%-100%) according to the percentage of the length of necrosis to the total shoot length. Three cultivars ‘Dargazi’, ‘Harrow Sweet’ and ‘Natanzi’ were very resistant, 14 cultivars were moderately resistant, 10 cultivars were susceptible and three cultivars ‘Mohamad Ali’, ‘Duchesse’ and ‘KS6’ were very susceptible. Results obtained from specific primers link to fire blight showed that RLG1 and CH02c02b primers produced resistance allele in Dargazi and some of other cultivars.

Incompatibility is one of the important genetic factors that affect PEAR fruit set. This experiment was carried out to survey incompatibility alleles in some ASIAN PEAR genotypes. PCR with specific primer designed for incompatibility alleles were used. Genomic DNA of nine ASIAN PEAR cultivars (KS6, KS7, KS8, KS9, KS10, KS11, KS12, KS13 and KS14) and two hybrids from their crosses was extracted and incompatibility alleles were amplified by specific primers designed for S alleles. Incompatibility alleles in ASIAN PEAR cultivars KS6, KS7, KS8, KS9, KS10, KS11 and KS12 were a couple of SI or S3-S7 alleles. One the incompatibility alleles of KS13, KS14, hybrid 1 and hybrid 2 was S2 and the other allele probably was S1 or S3-S7. PCR technique is an easy way for S allele identification and is not affected by pollination factors.

To study the flowering time and period, as well as the self- and cross-compatibility, some ASIAN PEAR cultivars, namely KS6, KS8, KS9, KS11, KS13 and KS14, were employed. Two branches on each of four trees in each cultivar were selected for controlled pollination. To prevent either undesired pollen contamination or pollination by insects, selected shoots were protected using cotton tissue bags. For controlled cross- pollination, flowers were emasculated and protected before anthesis, hand pollination being carried out two days after anthesis. In order to monitor pollen tube growth in the style, samples were taken 44, 72 and 96'hours after pollination, and fixed in FAA solution. The percentages of initial and final fruit set after self and cross-pollination were recorded and monitored 15, 35 and 75 days after full bloom (OAFS). A study of flowering time showed that there were some differences in the flowering period and time of bloom in the studied cultivars, the best coincidence being observed between KS11 and KS13. Microscopic examination of pollen tube growth showed that pollen grains were alive after pollination and the pollen tube grew within the style following germination. Results from self pollinated trees (75 OAFS) indicated that KSg had the lowest fruit set, with 2.92%, while the other cultivars KS13, KS6, KS8, KS14, and KS11 showed 4.16, 5.44, 7.03, 10.33, and 14.65% fruit set respectively. In addition, results from cross- pollination revealed that the highest fruit set (34.34%) was obtained from cross-pollination of KS11 (seed parent = ♀) with KS8 (pollen parent = ♂) while KS13 (♀) pollinated with KS8(♂) ended up with the lowest fruit set (4.15%).

Growth in plants is defined as irreversible increase in volume and size. These changes are varied depending on stage of growth and physiological activity of the fruit tree. This research was conducted to determine the duration period of fruit growth and development and to come up with a mathematical model representing the relationship between fruit diameter, volume, and fruit fresh and dry weight. Two experiments were carried out using four mid- (KS13, KS14) and late season (KS8, KS12) maturing fruits of ASIAN PEAR (Pyrus serotina Rehd.) genotypes grown in Research Orchard, Department of Horticultural Sciences at Tarbiat Modarres University (TMU), Iran. In the first experiment, 24 fruits from the middle canopy zone of trees were tagged and fruit diameter measured in time intervals up to fruit harvest. In the second experiment, 3-5 fruits were destructively harvested from each genotype. These fruits were randomly sampled at 15 day intervals from 35 days after full bloom until fruit harvest (ripening). Fruit diameter, length, volume, fresh and dry weights were measured on destructively harvested fruits. Results indicated that simple and complete fruit sigmoid curves were existent for all four genotypes, even though the period of each phase of fruit growth was different for the studied genotypes. Slow growth phase of the curves for mid season genotypes between 120 – 180 days after full bloom (DAFB)while for late season maturing fruit genotypes between 150 – 200 DAFB. In addition, mathematical models were presented based on the correlation existing between fruit diameter, volume and weight. These models are important and can be used in such orchard management systems as irrigation, applying fertilizers and estimation of fruit harvest and yield.

Phenolic compounds are very considerable due to their important role in plant physiology and nutrition (antioxidant role). The amount of phenolic compounds are influenced by genotype and environmental conditions. In the present research, total phenol, antioxidant activity and some phenolic compounds including chlorogenic acid, catechin and pheloredzin of three ASIAN PEAR cultivars (KS6, KS9 and KS13) were studied. Investigated cultivars were 11 years old and had been budded on seedling of European PEAR (Pyrus communis L.) rootstocks with a density of 5000 trees per hectare based on randomized complete block design. Results showed that all studied cultivars differed significantly for all measured phenolic compounds except for pheloredzin content. Cultivar KS6 had the highest amount of chlorogenic acid and catechin. The regression analysis of total phenol and IC50 showed a positive correlation between the amount of total phenol and IC50. The highest amount of IC50 and total phenol was observed in KS13 and KS9, respectively.

Improving the fruit tree germplasm is an important task in Iran in order to use them in the fruit tree breeding program, because Iran is one of the arid and semi-arid regions in the world. However, cultivar introduction and study of stress resistance source in the fruit tree is essential in fruit tree breeding program. This research was carried out on nine ASIAN PEAR genotypes (Pyrus serotina Rehd.) that was introduced to Iran by Dept. of Horticulture, Tarbiat Modarres University from Belgium in 1998. The ASIAN PEAR genotypes are named KS6, KS7, KS8, KS9, KS10, KS11, KS12, KS13 and KS14. Also a native PEAR cv. Shah Miveh was used. Three irrigation treatments were applied: control, mild stress and severe stress. The control was irrigated to provide non-stress conditions. In mild drought stress, Plants irrigated when soil water potential reached - 0.5 MPa and in severe drought stress, plants irrigated when soil water potential reached - 1 MPa.Proline content during two years (three times a year) and soluble sugar (four times a year) were measured. Proline content was affected by drought stress and genotype. In all cases proline content under drought stress was highest and in control was lowest. Also the differences between proline content in the mild and severe drought treatment was significant. In these treatment proline content in KS6, KS7, KS9 was lower than the other genotypes. Soluble sugar increased significantly in the mild and severe drought stress treatment in early stage of the experiment, but this treatment doesn't show any differences significantly.