Pear Genotypes Research Articles

Pear resistance to Psilla (Cacopsylla pyri L.). A review

Pear psylla, Cacopsylla pyri L., is one of the most important insect pests in European pear production areas. Control measures are directed specifically at controlling pear psylla and require accurate and timely information about insect densities in the orchard. Thus, there is a widespread interest in the search for suitable biological control agents and in breeding for resistance to pear psylla. Modes of host plant resistance to pear psylla damage have been studied extensively by several authors and the susceptibility of many European pear genotypes have been investigated in order to detect cultivars resistant or highly tolerant to this pest useful in breeding programs. This review presents an update of published results and knowledge on psylla life, host finding for feeding and oviposition, type of damages, monitoring and control strategies with renewed and improved efficacies, resistance characterization and breeding, with particular regard to the identified sources of resistance and the screening methods.

Fire blight resistance of pear genotypes from different European countries.

Several old cultivars, and breeding clones of European pear Pyrus communis L. originating from Belgium, England, Sweden, and Switzerland were evaluated for their resistance/susceptibility to fire blight. Studies were carried out during three consecutive years 2007–2009 in the greenhouse of Warsaw University of Life Sciences, Poland. Strain 691 of Erwinia amylovora was used for artificial infection of plants. Genotypes included in this study considerably varied in their resistance to fire blight. The most resistant was the old English cultivar ‘Hessle’. The other two genotypes, i.e., ‘Gränna Rödpäron’ originating from Sweden, and Pyrus communis FG 1606 from Switzerland were included in a group of low susceptible ones. The most susceptible were Cra Py H 18, Cra Py V 22 and Cra Py W 14 from Belgium.

English

In vitro established shoots of nine pear genotypes namely; Khurolli, Bagugosha, Pathar nakh, Desi nakh, Kotharnul, Btangi, Frashishi, Kashmiri nakh, and Raj btung, were preserved by lowering concentration of growth regulators [(0.00, 0.25 or 0.50mg l-1 6-benzyaminopurine (BAP) or adding growth retardants, 10 mg L-1 Alar (diaminazide or B-9), or abscisic acid (ABA)] in the culture medium. The cultures were assessed for their survival and regenerability percentages after 3, 6, 9 and 12 months of storage. The genotypes differed significantly for survival and regeneration percentage. The culture medium supplemented with 0.50 mg L-1 BAP was comparatively more effective and resulted in higher survival rate and re-growth after transferring onto the fresh medium. Storage for short duration (3 months) resulted in significantly higher survival and regeneration rates than other storage periods. As storage period was prolonged, survival and regenerability of shoots progressively decreased. Overall results indicated that the shoots of Desi nakh had the highest survival (73.33 %) and Pathar nakh showed the maximum regenerability (67.66 %) when cultured on the medium supplemented with 0.50 mg L-1 BAP and stored for 3 months. However, no shoots of Kotharnul survived when cultured on the medium without any growth regulator and kept for 12 months.   Key words: Growth retardants, in vitro preservation, pear genotypes, slow growth.

Levels of fire blight (Erwinia amylovora) susceptibility of native apple, pear and quince germplasm from Lake Van Basin, Turkey

Fire blight resistance of apple, pear and quince genetic resources from Lake Van Basin (eastern Turkey) was tested using Erwinia amylovora strain Ea Van. Shoot tips of 92 native accessions (48 accessions for apple, 38 accessions for pear and 6 accessions for quince) were wounded for inoculation, and artificially inoculated with pathogenic bacteria under greenhouse conditions. The levels of resistance of accessions were classified in comparison with control varieties according to the genotype susceptibility index (GSI%) scores based on the lesion length on shoots of each genotype. Fire blight resistance of accessions consisted of five classes: resistant (R), moderately resistant (MR), moderately susceptible (MS), susceptible (S) and highly susceptible (HS). GSI% scores differed significantly among accessions from each fruit species (p < 0.01). GSI values ranged from 12.4% to 64.1% for apple genotypes, from 17.2% to 55.1% for pear genotypes, and from 17.8% to 43.4% for quince genotypes. No resistant genotypes of apple, pear and quince were observed. Seven accessions of apple, two accessions of pear and one accession of quince were MR. 25 accessions of apple, 14 accessions of pear and one accession of quince were MS. These findings indicate a considerable variation in fire blight resistance and could contribute to breeding efforts regarding fire blight resistance in apple, pear and quince.

Adventitious shoot regeneration of pear (Pyrus spp.) genotypes

Adventitious shoot regeneration of twenty-four pear genotypes was compared in a common in vitro shoot induction and development protocol. This study also compared cultures newly established from scionwood with cultures that been in long-term cold storage. In vitro cultures of 13 Pyrus genotypes and budwood from 23 Pyrus genotypes were obtained from the National Clonal Germplasm Repository (NCGR) in Corvallis, Oregon. With the exception of one genotype of P. elaeagrifolia Pall., and ‘Ya Li’ (P. pyrifolia var. sinensis Teng & Tanabe), all were P. communis L. cultivars. The basal shoot induction media consisted of Chevreau and Leblay (CL) basal nutrients, vitamins, and organics (Chevreau and Leblay in Acta Hortic 336: 263–268, 1993). The analysis of variance indicated that differences among genotypes were highly significant and the main effect of culture origin was non-significant. However, there was a significant interaction between genotype and culture origin, with percentage regeneration of ‘Abate Fetel’ from new budwood significantly greater than that from long-term in vitro cultures, while ‘Jesinji Vodenac’ cultures derived from the old NCGR cultures regenerated significantly more adventitious shoots. The ranges of mean regeneration frequency were similar for both in vitro (0–87.7%) and scionwood-derived cultures (0–70.7%). Maximum regeneration was observed for ‘Conference’, followed by ‘Magness’, ‘Dr. Jules Guyot’, and Packham’s Triumph’. The range of number of adventitious shoots was relatively narrow, with the minimum of 1.0 for seven genotypes to 2.2 for ‘Conference’.

Effect of phase of medium, growth regulators and nutrient supplementations on in vitro shoot-tip necrosis in pear

The incidence of shoot-tip necrosis (STN) was observed during the in vitro shoot multiplication and rooting stages of five Pyrus genotypes. During shoot multiplication, there was no incidence of STN in any of the five pear genotypes after 2 weeks of culture. However, after 6 weeks of culturing, necrotic apices were observed in all the pear genotypes, except wild pear. After 8 weeks of culture, 79.31% STN was observed in Punjab Beauty, followed by Patharnakh (49.60%), kainth (24.65%), shiara (17.68%) and wild pear (7.32%). Irrespective of the genotype, STN increased with an increase in BA concentration only in 8-week-old cultures. During in vitro rooting, the incidence of STN also varied with the genotype. In all five pear genotypes, the use of liquid media for in vitro rhizogenesis was useful in reducing the incidence of necrotic apices. The auxin type and level also influenced the occurrence of STN significantly. In wild pear, the incidence of necrotic apices increased with an increase in the concentration of auxins. A combination of Naphthalene acetic acid (NAA)+Indole-3-butyric acid (IBA) resulted in a higher incidence of STN than IBA or NAA alone at higher concentrations. Lower concentrations of IBA (0.62 to 2.46 µM L−1) resulted in a higher incidence of STN compared with the lower levels of NAA (0.67 and 1.34 µM L−1). In kainth, there was no significant difference in the incidence of STN at higher concentrations of IBA (5.37 and 10.74 µM L−1) and NAA (4.92 and 9.84 µM L−1). 2, 4-D resulted in a higher incidence of STN in comparison with IBA, NAA or NAA+IBA in the rooting medium. In Punjab Beauty, the percentage of necrotic apices at 0.67 and 1.34 µM L−1 NAA (40.46% and 40.04%, respectively) was on a par with the control (37.92%), but it was significantly less than the STN observed at 0.62 and 1.23 µM L−1 of IBA. In Patharnakh, IBA resulted in a significantly higher incidence of STN than NAA at all tested concentrations. In shiara, all the auxin treatments significantly increased STN. At lower levels (0.62 and 1.23 µM L−1), IBA resulted in a higher incidence of STN than the lower concentration of NAA (0.67 and 1.34 µM L−1), whereas at higher levels (2.46 to 9.84 µM L−1) IBA was on a par with NAA (2.69 to 10.74 µM L−1). Supplementation with calcium and boron significantly affected the percentage of necrotic apices in wild pear, Punjab Beauty and Patharnakh. In wild pear, raising the calcium level to 3 mM reduced the STN to 2.60%. In Punjab Beauty and Patharnakh, STN increased with an increase in calcium levels. Boron supplementations eliminated the incidence of STN in wild pear. Similarly, in Patharnakh, boron (500 µM and 1000 µM) significantly reduced the STN. Callus development was also observed at the base of pear shoots showing STN symptoms during rooting phase, but it did not show any significant trend. Higher levels of IBA, NAA+IBA and 2, 4-D resulted in the formation of large-sized calluses and STN in wild pear shoots on solid medium. There was a high incidence of STN in Punjab Beauty, Patharnakh and shiara but, the basal callus development in these genotypes was much less.

Development of a novel and efficient strategy for practical identification of Pyrus spp (Rosaceae) cultivars using RAPD fingerprints

Accurate and reliable cultivar identification of crop species is essential to guarantee plant material identity for purposes of registration, cultivar protection and production. To facilitate identification of plant cultivars, we developed a novel strategy for efficient recording of DNA molecular fingerprints in genotyped plant individuals. These fingerprints can be used as efficient referential information for quick plant identification. We made a random amplified polymorphic DNA (RAPD) marker analysis of 68 pear cultivars. All pear genotypes could be distinguished by a combination of eight 11-mer primers. The efficiency of the method was further verified by correct identification of four cultivars randomly chosen from the initial 68. The advantages of this identification include use of fewer primers and ease of cultivar separation by the corresponding primers marked on the cultivar identification diagram. The cultivar identification diagram can efficiently serve for pear cultivar identification by readily providing the information needed to separate cultivars. To the best of our knowledge, this is the most efficient strategy for identification of plant varieties using DNA markers; it could be employed for the development of the pear industry and for the utilization of DNA markers to identify other plant species.

Genetic diversity of European pear cultivars (Pyrus communis L.) and wild pear (Pyrus pyraster (L.) Burgsd.) inferred from microsatellite markers analysis

The aim of this study was to identify the group of highly polymorphic microsatellite markers for the identification of six pear cultivars (P. communis) and two individuals of wild pear (P. pyraster). From among 40 tested SSR markers, 19 were selected to profile genetic diversity in pear genotypes due to high polymorphisms. These markers showed high heterozygosity levels (0.5–1) and, on average, 6.4 alleles per marker were found. The set of microsatellite markers employed in this study demonstrated usefulness of microsatellite markers for the identification of pear genotypes. The examined wild forms were represented in this study by only two individuals of P. pyraster. It can be assumed that these forms were distinctly different from the cultivated pear cultivars.

Susceptibility of European pear genotypes in a gene bank to pear psylla damage and possible exploitation of resistant varieties in organic farming

We evaluated 285 pear genotypes (commercial cultivars, ancient local varieties, unnamed local strains, seedlings, wild seedlings) in the largest gene bank of pear in Hungary from the point of view of psylla resistance to explore their possible exploitation in organic farming. We have found some 10 new resistant types (Bókoló körte, Bôtermô Kálmán, Füge alakú körte, Nagyasszony körte, Nyári Kálmán, Rozs nyári körte, Viki körte, Pb-242, Pb-299, 0-632) and 7 highly tolerant ones (Cure-6, Kései Kálmán, Kieffer, Kieffer Éd, Steiner, Téli Kálmán, II. B-3- 6/4, 96-16/5) (Table 1). These made up 3.5 + 2.8 per cent of the investigated genotypes, while 93.7 per cent of them were susceptible to pear psylla damage. Taking earlier and present results into account we can list more than 30 European pear cultivars being resistant or highly tolerant to pear psylla infestation and damage. In fact, the list of resistant and highly tolerant cultivars may serve as a basis selecting pear cultivars fitting to the specific requirements of the organic farming. By the end we can conclude that there is some real hope to exploit some resistant or highly tolerant ancient or local cultivars in organic farming but further investigations are needed to estimate their yield capacity and fruit quality.

In vitro storage of some pear genotypes with the minimal growth technique

Shoot cultures of 9 pear genotypes collected from different areas of Azad Jammu and Kashmir (northern Pakistan) were maintained on MS medium supplemented with 30 g L^{-1} of sucrose + 7 g L^{-1} of agar + 1 mg L^{-1} of BAP. For in vitro preservation shoot tips were excised from these cultures and transferred onto different media, i.e. full strength, ¼ strength, ½ strength MS medium, and full strength MS medium containing 2.5% or 3.5% (w/v) mannitol. The cultures were assessed for their survival after storage periods of 3, 6, 9, and 12 months. To test the regenerability of the cultures they were transferred onto fresh culture medium. The genotypes differed significantly in their survival; however, they were statistically similar in terms of regenerability when transferred onto fresh medium. Shoots of the Khurolli and Bagugosha genotypes remained quite healthy, with relatively high survival rates (53.25% and 50.50%, respectively), whereas those of the Desi nakh genotype had the lowest survival rate (41.02%). Full strength MS medium containing 2.5% (w/v) mannitol gave the highest survival and regenerability rates (55.82% and 52.31%, respectively) in cultured shoots. Preservation for the shortest period (3 months) resulted in the highest survival (63.41%) and regeneration (58.81%). Genotypes and storage period interaction showed maximum shoot survival in Kashmiri nakh stored for 3 months, while Raj btung cultures stored for 12 months responded poorly, with the minimum survival rate. Addition of mannitol at the lower concentration of 2.5% (w/v) was an effective technique to lengthen subculture duration, possibly because of a gradual increase in osmotic pressure in the medium, which resulted in reduced availability of water to the growing cultures.

Genetic Relationships among Slovenian Pears Assessed by Molecular Markers

A sample of 94 pear (Pyrus L.) genotypes, traditionally present in the Slovenian landscape, was analyzed by amplified fragment length polymorphism (AFLP) and SSR (SSR), focusing on the assessment of genetic relationships. The analyzed samples involved germplasm of Pyrus communis L., P. nivalis Jacq., and P. pyraster L. The AFLP technique, using five EcoRI and MseI primer combinations, revealed molecular polymorphism at a level of 65.95%, representing 93 polymorphic bands among the total of 141 scored. With SSR analysis, 64 polymorphic alleles were found at seven microsatellite loci, with an average of 9.14 alleles per locus. Genetic distances among the individuals being studied were calculated using the Dice coefficient of similarity, and a dendrogram supported by AFLP and SSR data was constructed using the neighbor-joining method. The clustering method grouped the analyzed genotypes into three main clusters. The first cluster included the P. communis germplasm. The genotypes resembling P. nivalis were grouped in the second largest cluster, which could be divided in to four subclusters. The germplasm of P. pyraster, in this cluster, was found to be much less distinct than we had assumed. The most typical cultivar group in the third cluster was ‘Vinska Mostnica’. The study indicated that P. nivalis germplasm is frequently present in Slovenia, but not as a pure species.

WORLD PYRUS COLLECTION AT USDA GENEBANK IN CORVALLIS, OREGON

In 1980 the U.S. Department of Agriculture (USDA), Agricultural Research Service (ARS), established a genebank, the National Clonal Germplasm Repository (NCGR) in Corvallis, Oregon. This facility is devoted to conservation of temperate fruit and nut crops. A globally diverse collection of Pyrus germplasm has been assembled and expanded over the subsequent 27 years. Unique pear genotypes are maintained as growing plants, evaluated for phenotypic and genotypic traits, tested for virus contamination, documented in a national public germplasm database, and freely distributed to international researchers. Seed collections represent wild Pyrus populations. The Corvallis genebank now maintains 2031 clonal Pyrus accessions and 327 seedlots representing 36 taxa from 53 countries. About 10% of clonal accessions are backed up either in vitro or as cryopreserved meristems. A DNA microsatellite fingerprint database has been initiated. About 75% of the clonal collection has tested negative for common latent viruses. During the past 3 years, on average 775 accessions were distributed annually to researchers around the world. While originally conceived as a working collection for crop improvement, this genebank also provides the raw materials for basic genetic research, and preserves rare species, vulnerable landraces and historic cultivars. The NCGR collection serves as a laboratory and a classroom to promote the preservation of pear genetic diversity for future generations.

Genotypic difference for the susceptibility of Japanese, Chinese and European pears to Venturia nashicola, the cause of scab on Asian pears

Abstract Venturia nashicola, the cause of scab on Asian pears, is distinct from Venturia pirina, a causal fungus of European pear scab. Although scab caused by V. nashicola is one of the most serious diseases in the Japanese pear (Pyrus pyrifolia Nakai var. culta Nakai), information available regarding resistant breeding against V. nashicola is limited. In this study, 12 genotypes of Japanese pear, seven genotypes of Chinese pear (Pyrus ussuriensis Maxim.) and four genotypes of European pear (Pyrus communis L. var. sativa DC.) and/or their offspring were evaluated for susceptibility to V. nashicola with leaf and fruit inoculation tests. At 30–40 days after full bloom in their developmental stage, unfolded young leaves and fruit were inoculated with conidial suspensions of V. nashicola for each genotype, and the responses were rated at 30 days postinoculation for the inoculated leaves and at 42 days postinoculation for the inoculated fruits. No visible symptoms were found in European pear ‘Bartlett’ and ‘La France’ and their respective offspring ‘290‐36’ and ‘282‐12’, in the Japanese pear ‘Kinchaku’ and in the Chinese pears ‘Cangxili’ and ‘Hongli’; these genotypes were evaluated as highly resistant to V. nashicola. Necrotic lesions without sporulation were observed in the Chinese pears ‘Qiubaili’, ‘Manyuanxiang’, ‘Yuanbali’ and ‘Xiangyali’, which were regarded as resistant. Sporulating lesions were formed on the other genotypes, such as the major Japanese pear cultivars ‘Kosui’ and ‘Nijisseiki’, which were regarded as susceptible. The response of inoculated leaves coincided well with that of inoculated fruit for each genotype. When the severity of scab symptoms on scab‐susceptible genotypes was further rated with disease severity (DS) values, a genotypic difference was observed for overall DS values in a successive 2‐year measurement among the susceptible genotypes. Based on the DS values of leaf and fruit scabs, the Japanese pears ‘Niitaka’, ‘Shinko’, ‘Nijisseiki’, ‘Gold Nijisseiki’, ‘Osa Nijisseiki’ and ‘Shinsui’ were considered to be less susceptible to V. nashicola than the typical susceptible cultivar ‘Kosui’.

The Differences among Pear Genotypes to Fire Blight (Erwinia amylovora) Attack, Based on Observations of Natural Infection

Fire blight, caused by the bacterium Erwinia amylovora, is one of the most damaging diseases of pear in the world. In Cluj-Napoca area, situated in central Transylvania, Romania, fire blight was observed first in 1994, very late comparative with the other countries from occidental Europe. The response of the pear cultivars and species from National Pear Collection from Cluj-Napoca to fire blight attack, assessed in natural conditions of infection, range on a large scale of variability, which denotes a strong influence of the genotype in expression of resistance or sensitivity to disease. From all genotypes, about 20.5% have not presented symptoms of attack, among them being the following: 'Blanquet precoce', 'Klementinka', 'Severianka', 'Beurre Bachelier', 'Kieffer Seedling', 'Er Shi Shinge', 'Beurre Amanlis', 'Bristol Cross', 'Beurre Liegel', 'Beurre Lucon', 'Grand Champion', 'Magness', 'Mericourt' etc. and several ancient autochthonous cultivars ('Pere malaiete', 'De zahar de Bihor', 'Cu miez rosu', 'Clopotele', 'Garoafa mare', 'Craiese', 'Para de apa'). Also, there were identified several species of Pyrus with no attack, as P. pollveria, P. common pear, P. lindlezi, P. malifolia, P. persica, P. ussuriensis, P. variolosa. The remarked genotypes could be potential sources for further breeding programmes and increase the number of genotypes available for breeding new pear cultivars resistant to Erwinia attack.

Genetic diversity in local Tunisian pears ( Pyrus communis L.) studied with SSR markers

Few records are available about local Tunisian pear cultivars characterized by low chilling requirements and adaptation to dry conditions. In this work, seven SSRs derived from apple were successfully transferred to 25 local Tunisian pear genotypes and 6 common varieties of Pyrus communis cultivated in Europe. The 7 SSRs used amplified a total of 36 fragments. All the microsatellites except one seem to amplify more than one locus in some of the genotypes studied. Only 12 different fingerprinting patterns could be distinguished among the 25 Tunisian cultivars studied indicating a high number of synonymies. The mean expected and observed heterozygosities in the 25 Tunisian cultivars analyzed averaged 0.71 indicating a high level of genetic diversity among the local Tunisian pear germplasm. These markers will be useful to optimize the conservation of this highly threatened germplasm.

Polymorphism of SFBB −γ and its use for S genotyping in Japanese pear (Pyrus pyrifolia)

Japanese pear (Pyrus pyrifolia) exhibits the S-RNase-based gametophytic self-incompatibility where the pollen-part determinant, pollen S, had long remained elusive. Recent identification of S locus F-box brothers (SFBB) in Japanese pear and apple suggested that the multiple F-box genes are the pollen S candidates as they exhibited pollen specific expression, S haplotype-specific polymorphisms and linkage to the S locus. In Japanese pear, three SFBBs were identified from a single S haplotype, and they were more homologous to other haplotype genes of the same group (i.e., alpha-, beta- and gamma-groups). In this study, we isolated new seven PpSFBB(-gamma) genes from different S genotypes of Japanese pear. These genes showed S haplotype-specific polymorphisms, however, sequence similarities among them were very high. Based on the sequence polymorphisms of the PpSFBB(-gamma) genes, we developed a CAPS/dCAPS system for S genotyping of the Japanese pear cultivars. This new S genotyping system was found to not only be able to discriminate the S(1)-S(9), but also be suitable for identification of the mutant S(4sm) haplotype for the breeding of self-compatible cultivars, and detection of new S haplotypes such as S(k).

(274) Genetic Diversity of Wild Pyrus communis L.

Edible European pears (Pyrus communis sp. communis L.) are thought to be derived from wild relatives native to the Caucasus Mountain region and eastern Europe. We collected genotype, phenotype, and geographic origin data for 145 P. communis individuals derived from seeds collected from wild relatives. These individuals are currently maintained in the USDA–ARS National Plant Germplasm System (NPGS) in Corvallis, Ore. Pear genotypes were obtained using 13 microsatellite markers. A Bayesian clustering method grouped the individual pear genotypes into 12 clusters. The subspecies of pears native to the Caucasus Mountains of Russia, Crimea, and Armenia could be genetically differentiated from the subspecies native to eastern European countries. Pears with large fruit clustered closely together and are most closely related to a group of genotypes that are intermediate to the other groups. Based on the high number of unique alleles and heterozygosity in each of the 12 clusters, we conclude that the genetic diversity of wild P. communis is not fully represented in the NPGS

Microsatellites are Used to Examine Apple and Pear Identities and Genetic Relationships

Simple Sequence Repeat (SSR) markers developed in apple and pear were used to determine genetic relationships among heritage apple and pear cultivars from Portugal's Azore Islands, and to develop identity fingerprints for European and Asian pear accessions at the USDA–ARS National Clonal Germplasm Repository (NCGR). We used 11 SSR markers (six from apple and five from pear) to examine 18 heritage apple and 9 heritage pear cultivars from the Azores. Eight additional Portuguese and economically important cultivars of apple and eight of pear were used as standards. Cluster analysis separated the apple and pear accessions into two distinct groups. Among apple genotypes, 12 unique accessions and five groups of synonyms were identified, while, in pear, seven unique genotypes and three pairs of synonyms were found. None of the accessions obtained from the Azores corresponded to widely grown standard Portuguese apple or pear cultivars. To examine 144 NCGR pear accessions, we used nine polymorphic SSR loci that were developed from GenBank sequences. Cluster analysis identified five sets of synonyms (four in P. communis L. and one in P. ussuriensis Maxim.) and four pairs of homonyms (three in P. communis and one in P. pyrifolia Burm. f. Nakai), and confirmed three clonal sets. Morphological evaluations and additional SSR markers will be used to confirm these results, and to genetically document the identities of pear genotypes. SSR markers will greatly assist the management of ex situ pome fruit germplasm collections by helping to eliminate duplicate accessions and expanding the genetic diversity represented.

Diversity of Wild Pyrus communis Based on Microsatellite Analyses

Edible european pears (Pyrus communis L. ssp. communis) are derived from wild relatives native to the Caucasus Mountain region and eastern Europe. Microsatellite markers (13 loci) were used to determine the relationships among 145 wild and cultivated individuals of P. communis maintained in the National Plant Germplasm System (NPGS). A Bayesian clustering method grouped the individual pear genotypes into 12 clusters. Pyrus communis ssp. caucasica (Fed.) Browicz, native to the Caucasus Mountains of Russia, Crimea, and Armenia, can be genetically differentiated from P. communis ssp. pyraster L. native to eastern European countries. The domesticated pears cluster closely together and are most closely related to a group of genotypes that are intermediate to the P. communis ssp. pyraster and the P. communis ssp. caucasica groups. Based on the high number of unique alleles and heterozygosity in each of the 12 clusters, we conclude that genetic diversity of wild P. communis is not fully represented at the NPGS. Additional diversity may be present in seed accessions stored in the NPGS and more pear diversity could be captured through supplementary collection trips to eastern Europe, the Caucasus Mountains, and the surrounding countries.

Pear ( Pyrus communis) and quince ( Cydonia oblonga) roots exhibit different ability to prevent sodium and chloride uptake when irrigated with saline water

Soil salinity is a major constraint to the cultivation of horticultural crops. In the present study, potted trees of the pear variety Abbé Fetel, either with their own roots or grafted on different rootstocks, received irrigation water at two levels of salinity to: (i) evaluate the effect of the rootstock genotype on the vegetative growth; (ii) assess their differential ability to take up and partition sodium (Na +) and chloride (Cl −); (iii) verify the effect of salinity on the uptake of major cations (potassium, calcium and magnesium). Irrigation water at 5.0 dS m −1 only slightly reduced vegetative growth regardless the genotype used as rootstock, suggesting a relative degree tolerance of pear ( Pyrus communis) to soil salinity, at least in the short term. Quince ( Cydonia oblonga) and pear rootstock genotypes had a contrasting effect on the uptake of chloride and sodium and differed regarding their ability to exclude these ions from the foliage. Quinces significantly increased their uptake of sodium and chloride when irrigated with saline water, while pear roots adopted an ion exclusion strategy to avoid accumulation of Na + and Cl −. Trees grafted on quinces accumulated a significant amount of Cl − in the leaves, but were able to store most absorbed Na + in their roots, a mechanism that prevented xylem loading and transport to the leaves. No effect of salinity on the uptake of potassium (K +), calcium (Ca 2+) and magnesium (Mg 2+) was recorded; however, leaf potassium concentration was markedly lower when roots belonged to quince than to pear. The ability of pear genotypes to take up K + occurred in control trees and was unaffected by saline treatment and might be related to the strategy adopted by pears to exclude Na + due to a high selectivity K +/Na +.