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.

PEAR (Pyrus communis L.) such as many members of Rosaceae is self-incompatible and for adequate bearing needs suitable pollinizer CULTIVARS. This research was carried out to determine suitable pollinizer (s) for some important native PEAR CULTIVARS. Reciprocal crosses were made between Shah Miveh, Shekari, Natanzi, Sebri, Dar Gazi and Bartlett CULTIVARS. Fruitset (%) and number of viable seeds per fruit were considered as indices of pollen compatability. In addition to above combinations, these indices were also evaluated in natural and artificial self pollinated as well as open pollinated trees. Artificial selfing showed advantage to the natural selfing for overcoming the incompatibility barrier in Sebri and Bartlett CULTIVARS. Moreover, pattern of fruitsets in open pollinated trees were in accordance with commercial bearing potential of the CULTIVARS. In cross pollinated combinations Dar Gazi led to highest fruitset with 10.2%, 5.1% and 0.86% as pollinizer for Sebri, Shekari and Natanzi CULTIVARS. This cultivar also demonstrated 90% of blooming overlap with Sebri, and 50% with two other CULTIVARS. Apparently, high compatability of Dar Gazi as a pollinizer for other PEAR CULTIVARS stems from its genetic distance that leads to existence of different self incompatibility alleles in this cultivar.

PEAR psylla [(Cacopsylla pyricola (Foerster)] is one of the most important pests affecting PEAR production. The main purpose of this research was to investigate the resistance of PEAR CULTIVARS to PEAR psylla for recommendation in integrated pest management and national PEAR breeding programs. This research was carried out using randomized complete block design with foure replications in Kamalshahr research station in Karaj, Iran, in four growing seasons from 2019 to 2023. Nine PEAR CULTIVARS; Boheme, Shah Mieveh, Natanzi, Sebri, Dargazi, Louis Bonne, Harvest Queen, Potomac and Coscia. Data about psyllids population at different stages; eggs, nymphs, and dult, was collected and recorded at the peak of its activity, i.e., from early February to November, every seven days. Antixenosis resistance indices included; attraction index, mean crowding intensity, relative abundance establishment rate, non-preference index and prevalence index of eggs, nymphs and adults were calculated. Tree characteristics; form, one year old branches growth, leaves, flowers and fruits were examined. The results showed that the most resistant CULTIVARS to PEAR psylla were; Cosia, Boheme, Sabri, Natanzi and Potomac. Atteraction index was 0.99, 0.99 and 0.95, crowding intensity index was 58.30, 149.14 and 16.13, relative establishment rate was 3.68, 3.65 and 3.40 for egg, nymph and adult stages, respectively. Non-perference index was 98.04, 98.06 and 19.98 and the prevalence index was 49.66, 49.47 and 47.50 for egg, nymph and adult stages, respectively. Keywords: PEAR, Psylla, Host finding, Host acceptance, Cultivar sensitivity. IntroductionCurrent management practices are sufficient to effectively control PEAR psylla (Murray et al., 2021). In many countries, collections of PEAR CULTIVARS have been established in some important PEAR-growing areas with a wide range of CULTIVARS of national, local and foreign origin to evaluate resistance to diseases and pests (Braniste and Militaru, 2007). Antixenosis resistance of PEAR CULTIVARS to PEAR psylla has been described with non-preferential egg laying. It has also been found that this type of resistance mechanism affects the size of the initial nymph population (Bell and Puterka, 2003). The main goal of this research was to investigate the details of the host preference and resistance mechanism of nine PEAR CULTIVARS to PEAR psylla for recommendation in integrated pest management and national PEAR breeding programs. Materials and MethodsThis research was carried out using randomized complete block design with foure replications in Kamalshahr research station in Karaj, Iran, in four growing seasons from 2019 to 2023. Nine PEAR CULTIVARS; Boheme, Shah Mieveh, Natanzi, Sebri, Dargazi, Beiruti (Louis Bonne), Harvest Queen, Potomac and Coscia. Data about psyllids population at different stages; eggs, nymphs, and dult, was collected and recorded at the peak of its activity, i.e., from early February to November, every 7 days. Antixenosis resistance indices included; attraction index, mean crowding intensity, relative abundance establishment rate, non-preference index and prevalence index of eggs, nymphs and adults were calculated. Tree characteristics; form, one year old branches growth, leaves, flowers and fruits were examined. After testing normality of the data Kolmogorov-Smirnov test, analysis of variance was performed based on priciples of random complete block design using IBM SPSS Statistics 27.0.1.0 software. For grouping PEAR CULTIVARS based on the level of sensitivity to PEAR psylla, cluster analysis was employed. The relationship between characteristics of PEAR CULTIVARS and antixenosis resistance indices was studied using correlation analysis. Factor analysis was performed to identify unobservable effective combined factors on resistance mechanism based on sets of observable indices. The accuracy of cluster analysis method was examined using linear discriminant analysis (LDA), normal discriminant analysis (NDA), or discriminant function analysis and Fisher's linear discriminant analysis. Results and DiscussionShah Miveh PEAR cultivar was the most sensitive cultivar to PEAR psylla. The most resistant CULTIVARS to PEAR psylla were; Coscia, Boheme, Sebri, Natanzi and Potomac. Increase in host antixenosis properties based on reduction of attraction index led to increase in the time spent in egg-laying activities, decrease in the egg-laying rate, and as its consequences, decrease in attractiveness of the host for egg-laying in resistant PEAR CULTIVARS. In host-finding stage, adult psylla must randomly search in a habitat until it finds one of the important stimuli for selection of PEAR CULTIVARS.Morphological stimuli of PEAR CULTIVARS for host-finding include different growth characteristics of the tree, flower, leaves and availability of host. PEAR CULTIVARS resistant to PEAR psylla can be good alternatives to chemical control and manage the pest. It has been reported that the genetic control of resistance to PEAR psylla is polygenic trait (Dondini et al., 2015). This genetic mechanism reduces the possibility of the emergence of resistant biotypes of the pest, and rewards investing in development and use of resistant PEAR CULTIVARS to psylla in integrated pest management and control. This approach is very important and eco-friendly. ReferencesBell, R.L. and Puterka, G.L. 2003. Modes of host plant resistance to PEAR psylla: a review. Proceedings of the XI Eucarpia Symposium on Fruit Breeding and Genetics 663 (pp. 183-188). DOI: 10.17660/ActaHortic.2004.663.26Branişte, N. and Militaru, M. 2007. Germplasm fund of Pyrus sp. presently in ex situ Romanian collections. In X International PEAR Symposium 800 (pp. 497-502). DOI: 10.17660/ActaHortic.2008.800.63Dondini, L., De Franceschi, P., Ancarani, V., Civolani, S., Fano, E.A. and Musacchi, S. 2015. Identification of a QTL for psylla resistance in PEAR via genome scanning approach. Scientia Horticulturae, 197, pp.568-572. DOI: 10.1016/j.scienta.2015.10.018Murray, K., Jepson, P.C. and Hedstrom, C. 2021. Integrated pest management strategic plan for Oregon and Washington PEARs: Summary of a Workshop Held on March 5, 2020 in Hood River, Oregon. Oregon State University Extension Service. 80 pp.

We studied the effect of polyethylene glycol (PEG)-induced osmotic stress on PEAR CULTIVARS (Harrow Sweet and Bartlett) under in-vitro culture conditions. Explants were cultured in QL medium containing 4% and 8% PEG6000 using a factorial experiment based on completely randomized design. The medium without PEG was considered as control. Drought injury index, which was calculated based on morphological disorders, increased at 8% PEG nearly to 2. 00 and 1. 50 units in CVs. Bartlett and Harrow Sweet, respectively. Owing to osmotic stress, the increase of malondialdehyde was accompanied with the reduction of cell membrane stability index in both CULTIVARS. Total phenolic components and antioxidant activity in leaves increased significantly in response to application of 4% and 8% PEG. However, the severity of increase was higher in CV. Harrow Sweet. It was revealed that CV. Harrow Sweet had higher tolerance to osmotic stress than Bartlett. Moreover, the parameters related to oxidative damages and ROS scavenging capacity were more descriminant against osmotic stress under in vitro system.

PEAR psylla [Cacopsylla pyricola (Foerster)] is one of the important pest of PEAR trees. Understanding of effective factors on population structure and stability of the pest is the first step in selection and development of resistant PEAR CULTIVARS. This research was conducted from 2020 to 2023. Nine PEARs CULTIVARS including: Boheme, Shah Miveh, Natanzi, Sebri, Dargazi, Louis Bonne, Harvest Queen, Potomac, and Coscia were studied. The PEAR psylla populations were sampled from early March to November. Leaf traits were also studied. The results showed that the highest and the lowest population stability of in the egg in cv. Shah Miveh and cv. Natanzi were 470.4 and 33.7 in October and May, respectively. The highest cross-correlation coefficient (0.91-0.92) of color indices including R (red), G (green), and B (blue and yellow) observed in May, and for the leaf surface are was 0.74 in June. The lint density had significant effect on the population stability from the beginning of the season until August.These traits can be used to screen resistance PEAR cultivar against PEAR psylla. Keywords: PEAR, adult insect, leaf surface area, lint density, esistance. IntroductionThe PEAR psylla [(Cacopsylla pyricola (Foerster)] is an important pest of PEAR trees and has a worldwide distribution (Luo et al., 2012). In the climatic conditions of Iran, where spring and summer are dry and rainfall is low, the indirect damage caused by honeydew is more than the damage caused by sucking plant sap (Behdad, 1991). Researches that have been conducted on different pests have shown that leaf morphological characteristics, such as leaf size, leaf thickness, presence of villi, thickness of cuticle, presence of waxy material on the epidermis, color, chlorophyll content, water content, overall shape, and other traits are effective on pest population changes during growing season (Khalil et al., 2017; Rutledge et al., 2003). Understanding the effective factors that drive changes in population structure and stability is the initial step in selection and development resistant PEAR CULTIVARS. The characteristics of the host plant affect the abundance, structure, stability and diversity of the pest population (Steffan-Dewenter et al., 2001). Therefore, this research was conducted to determine the effect of morphological characteristics of leaf of nine PEAR CULTIVARS on population structure and stability of PEAR psylla and their relationship in different growth stages of PEAR psylla. Materials and MethodsNine PEAR CULTIVARS including: Boheme, Shah Miveh, Natanzi, Sebri, Dargazi, Louise Bonne, Harvest Queen, Potomac, and Coscia were used in this study. This research was conducted from 2020 to 2023. Data of the population of different stages of development of psylla PEAR was scored at the peak of its activity, i.e. from the beginning of April to November, every seven days. From each cultivar, 10 leaves were randomly selected from the crown’s lower, middle, and upper parts. The monthly average of the effective population at different growth stages and the percentage of each stage relative to the total population density were calculated. The population stability index for the active PEAR psylla population on each PEAR CULTIVARS was estimated. The leaf color index including R (red), G (green), and B (blue and yellow) were determined using the mobile phone software called Color Grab 3.9.2 with constant light and at a distance of 15 cm from the leaf surface. A relatively accurate leaf surface area was estimated using the mobile phone software Easy Leaf Area. The leaf chlorophyll content was evaluated using the OPTi-Sciences CCM-200 chlorophyll meter. Results and DiscussionThe maximum population density in the first and second activity periods was 242.3 and 359.3, respectively. The minimum density in the first and second activity periods was 73.2 and 175.5, respectively. The lowest and highest percentage of egg density in the population structure was recorded at 16% and 18 %, respectively, in May and September. The highest and lowest population stability, in different growth stage, of PEAR psylla eggs were in cv. Shah Miveh (470.4 eggs) and cv. Natanzi (33.7eggs), in October and May respectively. The highest and the lowest population stability index of nymphs and beloged to cv. Shah Miveh (2.2 nymphs) and cv. Dargazi (8.6 nymphs), in October and May respectively. The highest and lowest population stability index of adult insects recorded in cv. Shah Miveh (126.5 adult insects) and cv. Darghazi (3.3 adult insect), respectively.Leaf color indices (R, G, and B) with correlation coefficients of more than 0.9, leaf surface area index and lint density with correlation coefficients of -0.84 and 0.63, respectively, had significant relationship with the population stability index of PEAR psylla. Considering the resuts of this study, it was found that different leaf characteristics, especially color and lint density, were highly effective on population density and stability indices of PEAR psyll. These characteristics can be used in PEAR breeding programs for selction and development of new resistant cutivars to PEAR psylla. ReferencesBehdad, E. 1991. Iran pests of fruit trees (2nd edition), Bahman Nashr Press, Esfahan, Iran, 826 pp. (in Persian).Khalil, H., Raza, A. B. M., Afzal, M., Aqueel, M. A., Khalil, M. S. and Mansoor, M. M. 2017. Effects of plant morphology on the incidence of sucking insect pests complex in few genotypes of cotton. Journal of the Saudi Society of Agricultural Sciences, 16(4), pp.344-349. DOI: 10.1016/j.jssas.2015.11.003Luo, X., Li, F., Ma, Y. and Cai, W. 2012. A revision of Chinese PEAR psyllids (Hemiptera: Psylloidea) associated with Pyrus ussuriensis. Zootaxa, 3489(1), pp.58-80. DOI: 10.11646/ZOOTAXA.3489.1.4Rutledge, C. E., Robinson, A. P. and Eigenbrode, S. D. 2003. Effects of a simple plant morphological mutation on the arthropod community and the impacts of predators on a principal insect herbivore. Oecologia, 135, pp.39-50. DOI: 10.1007/s00442-002-1114-2Steffan-Dewenter, I., Münzenberg, U. and Tscharntke, T. 2001. Pollination, seed set and seed predation on a landscape scale. Proceedings of the Royal Society of London. Series B: Biological Sciences, 268(1477), pp.1685-1690. DOI: 10.1098/rspb.2001.1737

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%.

Many PEAR genotypes and CULTIVARS exist in the west part of Iran. Some of these CULTIVARS have has unique nutritional or storage ability traits. The current study was carried out to study biophysical and biochemical changes of PEAR fruit during storage and ripening. Seven local PEARs and ‘Shah Miveh’ were harvested and stored at 1 ˚C up to 90 days. Sampling was carried out at harvest time and 30 days interval from the cold storage. Some factors such as fruit weight loss, firmness, fruit density, dry matter percent, vitamin C and total phenolic content, titratable acidity (TA), total soluble solids (TSS) and pH were measured in each sampling time. The results showed that TSS increased from 13.2 to 15.98 percent in all CULTIVARS during the storage time while the overall TA decreased. The vitamin C content decreased during the storage time and both the average value for CULTIVARS and the rate of decrease were different in the studied CULTIVARS. Fruit weight loss increased during study the and reached 10.1 percent by 90 days cold storage. The correlation among ascorbic acid, density and fruit firmness was observed so that the fruits with higher density value were firmer and the ascorbic acid content was higher in fruit with higher firmness. The correlation was observed between dry matter and fruit weight loss, so that dry matter increased in the high level of fruit weight loss.

Such different factors as days following full bloom till harvest, exterior change of fruit color and percentage of soluble solids have been suggested for determining the suitable harvest time. These factors are on the other hand greatly dependent on yearly climatic factors, type of fruit, and position of fruit on the tree as well as on orchard management. In this research, some of the above mentioned factors along with some other supplementary factors as change in firmness, percentage of dry material, percentage of acidity, fruit juice pH and changes of starch were comparatively investigated in a four months period during the growth season and as well during 2 months following the storage of the fruits. Nine CULTIVARS of foreign and local PEAR including Spadona, Barttlet, Beyrouti, Dargazi, Dutchesse, Shah Miveh, Felestini, Coscia and Louise Bonne were studied. Percentage of soluble solids and pH of fruit juice increased while acidity of the fruits decreased in the same process. Dry material percentage of Intuits was approximately stable. Therefore, the use of this index in determining the suitable fruit harvest time was impossible. The firmness of the fruits decreased and followed the same behavioral pattern in the fruits on different parts of the tree. Since starch test did not reveal significant changes, it was not considered as an effective and practical test to determine the maturity in different PEAR CULTIVARS.Results showed that fruit firmness can be considered as one of the effective indices to determine commercial fruit maturity of different PEAR CULTIVARS.

Despite adaptability of Pyrodwarf semi-dwarf PEAR rootstock in Iran, the final yield and yield efficiency of different commercial PEAR CULTIVARS on this rootstock have not been studied and analyzed in detail. Therefore, in recent study, the yield, yield potential and yield efficiency of four commercial PEAR CULTIVARS including Louis Bonne, Spadona, Dargazi and Beyrut CULTIVARS were evaluated on Pyrodwarf rootstock during four years (2017 to 2020) in commercial bearing phase. Growth traits according to high vigor of Dargazi and Spadona CULTIVARS were higher than Louise Bonne cultivar and all CULTIVARS in 2020 (8 years old) had a height between 294. 4 to 352. 7 cm, which indicates semi-dwarf habit of this rootstock. The highest yield per tree was in Dargazi cultivar and then at a lower level in two CULTIVARS Spadona and Louise Bonne. In spite of increase in tree yields with increasing age of the trees, the yield per trunk cross-sectional area (TCSA) decreased consistently, so this index in 2017 was more than 0. 2 in most CULTIVARS and decreased to about 0. 05 kg per cm2 TCSA in two years 2019 and 2020. A similar situation was observed in terms of fruit number and yield per unit volume of canopy and the highest efficiency of canopy volume unit was observed in Louise Bonne cultivar. It can be concluded that for higher yield efficiency of PEAR CULTIVARS on Pyrodwarf rootstock, evaluation of training forms that decrease the canopy shading in the internal parts of canopy is essential.