This review gives a presentation of the gametophytic self-incompatibility system in the roscaeous fruit trees. Studies to discover the pistil (S-ribonucleases) and pollen-part components (F-box molecules) are summarized and models for the self-incompatibility reactions as well as their molecular background are discussed. We describe how mutatio...ns within the S-RNase or F-box genes can contribute to the transition from self-incompatibility to the self-compatible phenotype in many fruit tree crops. The current state of the arts is compared to the information obtained in other plant species possessing similar incompatibility system.
Apple (Malus x domestica Borkh.) is one of the most important fruit crops showing ribonuclease-mediated self-incompatibility, and no self-compatible apple cultivars are known. Twenty-nine S-alleles were identified in apple and many more incompatibility groups are present compared to sweet cherry. Results from a Belgian, Englis...h and a Japanese research group are combined and the S-genotypes of the most important world cultivars are collected. Two different allele labelling system are reconciled and detection methods used in case of the specific alleles are shown. Effects of the resistance breeding programmes are discussed; and scientific efforts involving transgenic technology to create self-compatible genotypes are shown. This review covers the most interesting issues regarding self-incompatibility in apple.
This review endeavours to collect all recent and substantial contributions to the quickly deepening fields of tree fruit self-incompatibility studies and hence updating previously published reviews. Studies carried out to discover the molecular basis of gametophytic self-incompatibility are summarized and a newly described model for the solanac...eous plants is also outlined. We describe recent findings in all economically important fruit tree crops involving apple, European pear, sweet and sour cherries, almond, Japanese plum, sloe, Japanese apricot, European apricot and peach. Additional DNA sequences are now available for both the pistil and pollen component genes in several species and their molecular, evolutionary or economic implications are discussed in the light of the fruit setting behaviour.
Self-incompatibility (SI) in flowering plants is a widespread genetic system that promotes out-crossing. In Prunus species the SI is a gametophytic trait, which is controlled by a single multiallelic locus, termed S-locus. S-alleles codify stylar glycoproteins with ribonuclease activity (S-RNases). Our objective was to assess the S-genotype of...some Hungarian apricot varieties by isoelectric focusing of stylar RNases as well as by PCR analysis using cherry consensus primers. Consensus primers amplified one or two bands of various sizes. Primers amplifying the 1st intron gained fragments the size of which ranged from 250 to 500 bp; while those amplifying the 2nd intron resulted in fragments of 800-2000 by length. Our data demonstrated that the first intron of the apricot S-RNase gene is shorter than the second one, which coincides with the structure of cherry S-RNase alleles. `Hargrand' (S1S2) and `Harcoe (S1S4) possessed one common S-RNase isoenzyme. Hungarian 'Orias' apricot cultivars showed different bands compared to the previous cultivars, but they shared completely identical patterns confirming that they possess the same S-genotype. 'Bergeron', `Harmat' and 'Korai zamatos' are characterised by an evidently distinct S-RNase pattern. The self-compatible cultivar (`Bergeron') had one allele, which suggests its correspondence to the Sc. Primers for the 2nd intron was unsuccessful in gaining fragments, which indicates that the 2nd intron in the Sc allele is too long to get any amplification. On the basis of our data, identities and differences were revealed in the S-allele constitution of some economically important Hungarian apricot cultivars at protein and DNA levels.
Japanese plums (P salicina) and cherry plums (P cerasifera) are diploid species, while European plum (P. domestica) cultivars are hexaploids. Most diploid species are self-incompatible while fertility relations of the hexaploid European plums are variable between self-incompatibility and self-compatibility. A...bout twenty S-alleles and six inter-incompatibility groups and one S-haplotype responsible for the self-fruitful phenotype were described in Japanese plum cultivars, but studies on cherry plums and even on the European plum cultivars are severely restricted. This review is focused on the available information obtained from myrobalans and European plums; and discusses recent hypotheses regarding the putative origin of the hexaploid plums, and thereby indicates the possibility of allele flow between different plum species.
Sour cherry (Prunus cerasus L.) is an allotetraploid species derived from hybridisation of the diploid sweet cherry (P avium L.) and the tetraploid ground cherry (P. fruticosa Pall.). Although numerous self-incompatible cultivars exist, the most sour cherry cultivars are self-compatible, which might be due to their te...traploid nature. This review is dedicated to show the limited information on the genetics of self-incompatibility in sour cherry accumulated during the last five years. Two different hypotheses (genomic arrangement of the alleles or the accumulation of non-functional S-haplotypes) are discussed. Heteroallelic sour cherry pollen was shown to be self-incompatible, which is counter to the Solanaceae where heteroallelic pollen frequently self-compatible due to a kind of competitive interaction between the two different alleles. This review highlights some inconsistencies in the hope that clarification will be achieved in the near future.
Self-incompatibility system and allele pool of three different pear species, European pear (Pyrus communis), Japanese pear (P. serotina) and Chinese pear (P ussuriensis) are displayed. Several inconsistencies and the absence of the harmonization of three different allele series are revealed i...n the European pears. By collecting data from several reports eight incompatibility groups of Japanese pear cultivars could be established. A self-compatible genotype is analysed in details and shown to be a stylar-part mutant. As Japanese pear was the first fruit tree species from which S-ribonucleases were identified, the history of S-genotyping from the beginning to the latest achievements and technical developments can be also monitored from the experiments enumerated. In Chinese pears, seven S-alleles and one incompatibility group could be identified.
European plum is an important fruit crop with complex, hexaploid genome of unknown origin. The characterization of the selfincompatibility (S) locus of 16 European plum cultivars was carried out using the PaConsI-F primer in combination with the EM-PC1consRD primer for the first intron and the EM-PC2consFD and EM-PC3consRD primers for the secon...d intron amplification. Altogether, 18 different alleles were scored indicating high genetic diversity. These alleles were labelled using alphabetical codes from SA to SS. We identified 5 different alleles in 9 cultivars, 4 alleles in 5 cultivars, while 3 alleles were shown in two of the assayed cultivars. A total of 16 different S-genotypes were assigned, and discrimination of all plum cultivars was successful based on their unique S-genotypes. However, further research is required to reliably identify the S-alleles based on their DNA sequence and clarify complete S-genotypes.
Almond [Prunus dulcis (Mill.) D. A. Webb.] as one of the oldest domesticated plants is thought to have originated in central Asia. Gametophytic self-incompatibility of almond is controlled by the highly polymorphic S-locus. The S-locus encodes for an S-ribonuclease (S-RNase) protein in the pistils, which degrades RNA in self-pollen tubes and he...nce stops their growing. This study was carried out to detect S-RNase allelic variants in Hungarian and Eastern European almond cultivars and Turkish wild growing seedlings, and characterize their S-allele pool. Five new alleles were identifi ed, S31H, S36-S39 in Eastern European local cultivars. The village Bademli and Akdamar island are two distinct places of almond natural occurrence in Turkey. Trees growing wild around Bademli city showed greater genetic diversity than those originated on Akdamar island. Many of the previously described 45 S-RNase alleles have been also detected in these regions. Homology searches revealed that Turkish almonds carried some P. webbii alleles indicating hybridization between the two cultivars and massive introgression events. Our results supply long-awaited information on almond S-allele diversity from regions between the main cultivation centres and the centre of origin of this species; and are discussed from the aspect of methodological developments and evolution of the cultivated almond.
Some traditional sweet cherry cultivars of Ukrainian origin may represent perspective material for Hungarian cherry breeding. A total of eight cultivars analysed represent great diversity in several phenotypic traits including fruit ripening time or fruit flesh colour. Considerable differences in the anthocyanin content may result in different...antioxidant capacity of fruits. In the present study, we used ferric reducing antioxidant power (FRAP) and total phenolic content (TPC) assays to characterize fruits’ nutraceutical properties. These values were compared with the respective values measured for eight commercial cultivars grown in Hungary. The average of FRAP and TPC values was higher for the Ukrainian cherries compared with commercial cultivars suggesting they might be included in functional breeding programs. Since, cherry is a self-incompatible species, the determination of S-genotype is required for both breeding and successful cultivar association in commercial orchards. Complete or partial S-genotypes were determined for 5 and 3 cultivars, respectively.
Fruit setting behaviour of fruit trees remains to be in the focus of plant breeders and growers. Realizing that most species (cherry, apple, pear etc.) are self-incompatible and certain cultivars are cross-incompatible, mutual fertility properties and their reliable determination are of great interest. This review gives a comprehensive descript...ion of all known S-genotyping procedures, i.e. the classical fruit set analysis after open field test crosses; pollen tube growth monitoring with fluorescent microscopy; stylar ribonuclease electrophoresis (using different types of isoelectric focusing and 2-dimension polyacrilamide gel electrophoresis); as well as the most recent polymerase chain reaction based DNA-level analyses and DNA sequencing. The review presented not only gives a compilation of the bases of the methods described but also provides a critical evaluation and a comparative characterization of their applicability.
Pollen-limited fruit set has long been suspected in some relatively low-yielding orchards with the Swedish pear cultivar 'Carola'. Fruit was therefore harvested on 23 'Carola' trees in a commercial pear orchard. The seeds were germinated and five seedlings from each tree were sampled to determine which of the surrounding cultivars had been the...most successful pollinators. Leaves of 'Carola', the 7 putative pollinating cultivars and the 115 seedlings were analysed with 6 RAPD primers. By comparison of the band patterns, paternity could be ascertained for 74 seedlings. The by far most successful pollinator was 'Clara Frijs' which had sired approx. half of the seedlings, followed by 'Herzogin Elsa', `Skanskt Sockerpiiron', 'Alexandre Lucas', 'Coloree de Juillet' and 'Doyenne du Cornice'. The latter is the maternal parent of 'Carola', and these two cultivars must therefore share one S-allele and hence can only be semi-compatible. In addition, 6% of the seedlings were in all likelihood derived from selling_ since they showed no bands that did not occur also in 'Carola'. Maximum distance between 'Carola' trees and suitable pollinators should not exceed 15-20 tn. Longer distances may produce a serious dearth of compatible pollen as evidenced by the large percentage of seedlings derived either from selling. (25%) or from long-distance (> 40 m) pollen transfer (25%) when 'Carola' trees were surrounded by non-preferred pollinators.
Central Europe can be taken as a geographical and historical connection zone between the western growing countries and Asian gene centres of Prunus tree fruits. The determination of the S-genotype of stone fruit (mainly almond, plum, cherries and apricot) cultivars and landraces has both practical and theoretical significance. Our group has all...ocated complete S-genotypes for more than 200 cultivars and selections of almond, Japanese plum, sweet cherry and apricot. Among Eastern European almond cultivars, two novel cross-incompatibility groups (CIGs) were identified. S-alleles of a related species were also shown in P. dulcis accessions; a fact seems to be indicative of introgressive hybridization. Our results with Japanese plum clarified and harmonized two different allele nomenclatures and formed a basis for intensive international studies. In apricot, a total of 13 new S-alleles were identified from Eastern European and Asian accessions. Many Turkish and North African cultivars were classified into new CIGs, III–XVII. Results suggest that the mutation rendering apricot self-compatible might have occurred somewhere in south-east of Turkey and we were successful to confirm the presumed Irano-Caucasian origin of North African apricots based on the geographical distribution of S-alleles. In sweet cherry, new alleles have been identified and characterized from Turkish cultivars and selections. In addition, wild sweet cherry and sour cherry S-alleles were also shown indicating a a broader gene pool in Turkey as compared with international cultivars. We also used S-genotype information of Ukrainian sweet cherry cultivars to design crosses in a functional breeding program. Our results exhibit an increased number of S-alleles in tree fruit accessions native to the regions from Eastern Europe to Central Asia, which can be used to develop S-genotyping methods, to assist cultivation and draw inferences for crop evolution.
The low productivity in the Japanese plum (Prunus salicina Lindl) is related with self-incompatibility characteristics, so other species or varieties that act as pollinators need to be present to improve fruit production. The objective of this work was to study the efficiency of pollination in different genotypes of P. salicina ...m>using treatments of natural self-pollination, cross-pollination with P. armeniaca cv. Giada and open pollination. These treatments were evaluated through viability techniques and in vitro and in vivo germination of pollen grains; the growth of pollen tubes along the pistil was also observed. Genotypes used in this study showed differences for each one of the pollination treatments. Some genotypes showed signs of self-sterility and interincompatibility with P. armeniaca cv. Giada, while others showed partial self-fertility characteristics or pseudocompatibility. Moreover, some genotypes showed a higher affinity coefficient with cv. Giada and these will be indicating a possible intercompatibility. These studies will be an important contribution breeding and selection of intra and intercompatible genotypes to be used in commercial orchards.
Experiments were conducted during the period between 1972 and 2002 at three sites in Hungary. At Érd 97, Helvetia 10, and Újfehértó, 3 cultivars were studied in variety collections. Observations were made on the blooming phenology (start, main time, end and length of the bloom period), on the blooming dynamics (the rate of the open flowers...counted every day), on the receptivity of sexual organs, on the fruit set following self- and open-pollination and on the effect of association of varieties in the orchards (choice, rate and placement of pollinisers).
Based on the results the rate of the overlap of the blooming times were calculated and varieties were assigned into five bloom time groups according to their main bloom. Self-fertility conditioned by natural self pollination was studied and good pollinisers were chosen (sweet, sour and duke cherry varieties) for the self-sterile and partially self-fertile varieties.
The necessity of bee pollination was proved by different pollination methods: natural self-pollination, artificial self-pollination, open pollination. Summary: Experiments were conducted during the period between 1972 and 2002 at three sites in Hungary. At Érd 97, Helvetia 10, and Újfehértó, 3 cultivars were studied in variety collections. Observations were made on the flowering phenology (start, main time, end and length of the bloom period), on the flowering dynamics (the rate of the open flowers counted every day), on the receptivity of sexual organs, on the fruit set following self- and open-pollination and on the effect of association of varieties in the orchards (choice, rate and placement of pollinisers).
Quince (Cydonia oblongaMill.) is a minor fruit crop, which is primarily used for marmalade, jam and sauce.Very few quince cultivars are known all over the world and in many cases similar names are used for presumably different cultivars. The aim of the present study was to evaluate and characterize the genetic diversity of 36 quince cultivars a...nd selections with SSR markers. Seven out of 8 SSR markers designed from apple sequences could successfully yield amplification also in quince cultivars. Number of alleles per locus ranged from 2 to 3 alleles. These allele numbers are quite low when compared to apple. It is supposed to be the consequence of a genetic bottleneck. In spite of the low allele number per locus, the 36 quince cultivars formed 30 different genotypes. The ratio of homozygosity was low, which might be coupled with the self-(in)compatibility phenotype of quinces. SSR markers proved unable to differentiate putatively closely related cultivars (e.g. ‘Bereczki’ and ‘Bereczki bôtermő’). In general, the level of polymorphism among the tested quince genotypes was much restricted due to the low allele number detected. However, it must be considered that the number of analysed SSR loci is not enough high to estimate the overall heterozygosity of the quince genome. Further experiments are needed and the SSR markers proved to be a reliable and useful tool for such analyses.
The morphology of the stigma has been studied in 50 varieties belonging to 6 stone fruit species. The majority of samples had elliptical stigmata with some exceptions with circular form (Duane, Tuleu gras). The surface of the stigma is papillary, flattened in side view (sweet cherry) or bulging (apricot, peach). The suture of the stigm...a is clearly visible as a depression and the varieties may differ in this respect.
The size of the stigma depends highly from the season, although the varietal differences are maintained. The dimension of stigmatic surface is characteristic for the species expressed in square millimetres: sweet cherry 0.92 to 2.91; sour cherry 1.64 to 2.48; plum 0.83 to 1.80; oriental plum 0.53 to 1.15; apricot 0.57 to 1.69 mm2.
The size and morphology of the stigma changes according to varieties too, and it may used in description and identification of varieties. No correlation has been found between the size of stigma and the fertility relations (self-fertility or self-incompatibility) of the respective varieties.
In commercial fruit tree orchards, consistently high yields are necessary for a durable economy. The Swedish pear cultivar 'Carola' has been noted for low setting in some orchards, possibly due to insufficient pollination. In this study, fruit set was evaluated in a research orchard where `Carola' had been planted together with four potential p...ollinators. Total yield and number of fruits was noted during three and four years, respectively. In 2003, seeds were germinated from the harvested `Carola' fruits, and the paternity of three seedlings from 50 trees was determined with RAPD analysis. 'Clapp's Favourite' had sired 39.6% of the seedlings, closely followed by `Seigneur d'Esperen' (30.7%) and 'Clara Frijs' (26.7%) whereas 'Skanskt sockerparon' only sired 1.1% of the seedlings. The remaining 2.3% appeared to have been derived by selfing. Pollen-limited seed set was indicated at surprisingly short distances; accumulated number of fruits on the `Carola' trees was significantly higher when separated by only 2 m from one of the two most efficient pollinators, 'Clapp's Favourite' or 'Seigneur d'Esperen‘, compared to trees 4—l0 in away in the same row. Number of viable seeds per fruit was also higher in fruits from trees immediately adjacent to the pollinators, suggesting an effect of improved pollination success. The importance of very short inter-cultivar distances for efficient pollen transfer became even more clear when comparisons involved the true pollination distances as determined by RAPD; the accumulated yields decreased linearly from 55 kg at a 2 in distance to only 17 kg at 13 m.
In the majority of Hungarian orchards of stone fruits, the planting distance is 6-7 m x 4-5 m. As many of the current varieties are self-incompatible, planting designs are applied to provide for adequate pollinisers. As long as differences in blooming time are small, i.e. 3-5 days at most, overlaps of blooming of the associated varieties are su...fficient for fruit set.
In sour cherry, one leading variety, Pándy, is self-incompatible and requires two polliniser varieties at least (Ciganyneggy or some sweet cherry varieties). Pándy is, moreover, cross-incompatible with the varieties Debreceni bőtermő, Kántorjánosi and Újfehértói fürtös being all of them self-fertile as most of new varieties recommended, by the way, for being planted to monovarietal blocks.
Among European plums there are varieties registered as male sterile, self-incompatible, parially self-fertile and self-fertile, respectively. For the purpose of cross pollination, the choice of two varieties, at least, to be associated to any variety belonging to the first three groups, is recommended. The number of rows in blocks planted to self incompatible or male-sterile varieties should not be higher than 2-(4). Inter-incompatibility has been observed within the currently recommended assortment, between the varieties Cacanska najbolja and Stanley, only. Chinese-Japanese plums are scarcely represented in Hungarian plantations. Variation of blooming time in varieties is somewhat more pronounced, i.e. 5-8 days. There is but a weak tendency to self-fertility, thus practically, all varieties are considered as self-incompatible, thus the planting of two-row blocks for each of three varieties, at least, are recommended to be associated.
Self-incompatibility and partially self-fertile apricot varieties are recommended to be combined with two polliniser varieties, at least, each planted to two-row blocks. The varieties Ceglédi óriás, Ligeti óriás, Nagykőrösi óriás and Szegedi Mammut are mutually inter-incompatible. Most of the peach varieties grown in Hungary are self-fertile, thus they are planted to large blocks, each. On sites threatened by late spring frost, it is recommended to plant (monovarietal) blocks of 4-6 rows at most. Cross-pollination may increase fruit set even in self-fertile varieties.