Abstract
Diploid japanese plum (Prunus salicina Lindl.) cultivars are commonly self-incompatible. To date, 14 incompatibility alleles (S-alleles) have been identified and labeled with alphabetical (S a-S n) and 5 with numeric codes (S 1, S 3-S 6). We applied polymerase chain reaction amplification of the S-RNase alleles with degenerate and allele-specific primers in 10 japanese plum cultivars and two pluots of unknown incompatibility alleles. Besides DNA sequencing, an additional method for the exact length determination of the first intron region was used for the first time for S-genotype japanese plums. The S 3-allele was shown to correspond to S k in the alphabetic nomenclature, S 4 to S c, S 5 to S e, and S 6 to S f. The S 5-allele-specific primer can be used as a reliable marker for self-compatibility in japanese plum. ‘Black Amber’, ‘October Sun’, ‘TC Sun’, and ‘Super Giant’ share the S b S c genotype, which was confirmed by test crosses. These cultivars belong to the widest incompatibility group currently known in japanese plum. An additional incompatibility group (S c S h) was established, including ‘Green Sun’ and ‘Queen Rosa’, a cultivar formerly known as a universal donor. By incorporating all previous and recent results, a table was assembled including 49 cultivars assigned to I–VII incompatibility groups, to the self-compatible group and to the group O of unique genotypes. These data may considerably contribute to further growing and breeding activities.
Self-incompatibility in the Rosaceae L. family is of the gametophytic type based on pistil S-ribonucleases (S-RNases) controlled by the highly polymorphic S-locus (de Nettancourt, 2001). If two different cultivars share identical S-genotypes, it presents an incompatible combination in each direction, i.e., pollen tubes are arrested in the middle part of the stylar tissue.
Because Prunus L. species are unable to bear fruit parthenocarpically and adequate fertilization is crucial to fruit set, the self-incompatibility genotypes of self-incompatible (SI) tree crops have been studied intensively. Several S-alleles and incompatibility groups were described on the basis of molecular studies in sweet cherry (Prunus avium L.) (Boškovic and Tobutt, 2001; Sonneveld et al., 2003; Tao et al., 1999), almond [P. dulcis (Mill.) D.A. Webb.] (Boškovic et al., 2003; Sánchez-Pérez et al., 2004; Tamura et al., 2000), apricots (P. armeniaca L. and P. mume Sieb. et Zucc.) (Halász et al., 2005; Yaegaki et al., 2001), and plums (Sutherland et al., 2004a).
Most commercial cultivars of japanese plum (Prunus salicina) are self-incompatible (Nyéki and Szabó, 1995; Ontivero et al., 2006; Sansavini et al., 1981). The first S-genotype (S a S b) of a japanese plum cultivar (‘Sordum’) was described by Yamane et al. (1999). Later, Beppu et al. (2002, 2003) demonstrated the diversity of S-haplotypes in japanese plum by molecular cloning of genomic DNAs and cDNAs with primers designed from the conserved sequences of rosaceous S-RNases (Tao et al., 1999; Yamane et al., 2001). They identified 14 different S-alleles (S a-S n) and found that S-RNase genes of japanese plum also contained two introns at the same sites as those of other Prunus species (Igic and Kohn, 2001). Both introns varied in size in an S-haplotype-specific manner.
Sapir et al. (2004) cloned five additional S-alleles from three commercially important japanese plum cultivars and labeled them with numeric codes (S 1, S 3–S 6). Four of the five clones were described as new alleles (S 3–S 6) and S 1 from ‘Red Beaut’ was shown to correspond to the S a-allele identified by Yamane et al. (1999). Allele-specific primers were designed and used to analyze compatibility relationships among five cultivars.
The aim of this study was to identify self-incompatibility alleles in commercially significant plum and pluot cultivars with unknown incompatibility genotypes using polymerase chain reaction (PCR), DNA sequencing, or precise length determination of the PCR amplification products as well as to establish new and to clarify previously described incompatibility groups in this species.
Materials and Methods
Plant materials.
Ten cultivars of japanese plum were analyzed (‘Black Amber’, ‘Friar’, ‘Green Sun’, ‘October Sun, ‘Santa Rosa’, ‘Shiro’, ‘Angeleno’, ‘Sweet Autumn’, ‘TC Sun’ and ‘Super Giant’) from the orchard at Derecske, Hungary and two pluots—interspecific hybrids between Prunus salicina Lindl. and P. armeniaca L.—(‘Flavor Grenade’ and ‘Flavor King’) from an orchard at Siófok, Hungary.
DNA extraction.
Genomic DNA was extracted from fully expanded young leaves using the DNeasy Plant Mini Kit (Qiagen, Hilden, Germany). DNA concentrations were measured using a spectrophotometer GeneQuant II RNA/DNA Calculator (Pharmacia Biotech., Budapest, Hungary).
S-Polymerase chain reaction analyses.
PCR was conducted using the degenerate primers EM-PC2consFD and EM-PC3consRD for the amplification of the second intron region according to Sutherland et al. (2004b). To amplify the first intron, the fluorescently labeled forward primer PaConsI-F (Ortega et al., 2005; Sonneveld et al., 2003) was used in combination with the reverse primer EM-PC1consRD (Ortega et al., 2005). Allele-specific PCR primers were used to selectively detect the S 1-(IB2 and A6), S 3-(IW5 and A5), S 4-(IZ1 and IZ4), S 5-(IZ2 and IZ5), and S 6-alleles (PruC2 and IW2) (Sapir et al., 2004; Tao et al., 2000; Yamane et al., 1999). PCR was carried out in a PTC 200 thermocycler (MJ Research, Budapest, Hungary) using the programs described for the consensus (Ortega et al., 2005; Sutherland et al., 2004b) and allele-specific primers (Sapir et al., 2004). Approximately 20 to 80 ng of genomic DNA was used for PCR amplification in a 25 μL reaction volume containing 1 × PCR buffer (Sigma, Budapest, Hungary) with the final concentrations of 10 mm Tris-HCl (pH 8.3), 50 mm KCl, 1.5 mm MgCl2, 0.2 mm of dNTPs, 0.4 μm of the adequate primers, and 0.625 U of Taq DNA polymerase (Sigma). PCR products were separated by electrophoresis in 2% TAE agarose gels for 2 h at 100 V and DNA bands were visualized by ethidium bromide staining. Fragment lengths were estimated by comparison with the 1-kb DNA ladder (Promega, Madison, Wis.). To determine the exact size of the first intron region products under 500 bp, fluorescently labeled amplicons were run in an automated sequencer ABI PRISM 3100 Genetic Analyzer (Applied Biosystems, Budapest, Hungary).
Cloning, sequencing, and analyses of DNA sequences.
Some PCR products were cloned into a pGEM-T Easy vector (Promega) and sequenced with the previously described sequencer. For each allele, the nucleotide sequences of three clones were determined in both directions. DNA sequences were submitted to the GenBank/EMBL/DDBJ database under accession numbers DQ790372 (second intron region of S k-RNase from ‘Friar’), DQ790373 (second intron region of S h-RNase from ‘Green Sun’), DQ790374 (second intron region of S h-RNase from ‘Friar’), DQ790375 (first intron region of S b-RNase from ‘Black Amber’), and DQ790376 (first intron region of S c-RNase from ‘Black Amber’). Homology searches were performed using the BLASTN program at NCBI (Altschul et al., 1990), and partial S h- and S c-RNase sequences were aligned manually.
Crosspollination test.
Crosses between cultivars with the putatively same S-genotype (‘Black Amber’ × ‘TC Sun’, ‘Black Amber’ × ‘Super Giant’, ‘Super Giant’ × ‘TC Sun’, ‘October Sun’ × ‘Super Giant’) were carried out in an orchard at Derecske, Hungary, in 2006. Flowers were emasculated just before anthesis and then the previously collected and dried pollens were transferred to the stigmas. Open flowers and late buds were removed to prevent self- and crosspollination. After 6 weeks, percentage of fruit set was determined.
Results
All analyzed cultivars showed two different fragments on agarose gels except ‘Shiro’ after the amplification with consensus primers for the second intron (Fig. 1). Six fragments of different lengths were obtained from 12 cultivars; fragment lengths could be determined by comparing them with the 1-kb DNA ladder (Table 1). Two different fragment lengths exactly sized with an automated sequencer could also be obtained in each tested plum accession. Seven different fragment sizes were described (Table 1).
S-RNase gene-specific polymerase chain reaction for 12 cultivars using the EM-PC2consFD and EM-PC3consRD consensus primers to amplify the second intron region of the gene. M: 1-kb ladder, BA: ‘Black Amber’ (proposed genotype: S b S c), FG: ‘Flavor Grenade’ (S b S c), OS: ‘October Sun’ (S b S c), TC: ‘TC Sun’ (S b S c), SG: ‘Super Giant’ (S b S c), SR: ‘Santa Rosa’ (S c S e), SAu: ‘Sweet Autumn’ (S c S e), GS: ‘Green Sun’ (S c S h), An: ‘Angeleno’ (S c S h), F: ‘Friar’ (S h S k), Sh: ‘Shiro’ (S f–), FK: ‘Flavor King’ (S b S e). *Combined bands.
Citation: HortScience horts 42, 1; 10.21273/HORTSCI.42.1.46
Sizes of the polymerase chain reaction amplification products for the first and second intron regions (bp) and correspondences between the two previously established allele nomenclatures.
Five SI cultivars (‘Black Amber’, ‘October Sun’, ‘TC Sun’, ‘Super Giant’, and ‘Flavor Grenade’) had identical fragment sizes for the second (≈1550 and ≈1200 bp) and the first (343 and 367 bp) intron regions. Therefore, fruit set evaluation was carried out after controlled pollinations between some of those cultivars. Crosspollination among the tested cultivars has not resulted in fruit set or the percentage of the fruit set was negligible (Table 2). Two other SI cultivars, ‘Green Sun’ and ‘Angeleno’, possessed equally sized fragments for the first (343 and 388 bp) and second (≈1200 and ≈550 bp) intron regions. Two self-compatible (SC) cultivars, ‘Santa Rosa’ and ‘Sweet Autumn’, also shared an identical pattern with 343- and 372-bp-long fragments for the first intron region and ≈1200- and ≈1450-bp-long fragments for the second intron.
Test crosses made at Derecske, Hungary, in 2006 to confirm cross-incompatible genotypes.
Allele-specific primers designed by Sapir et al. (2004) for the S 4-allele amplified a fragment of the relevant size in 7 SI and 2 SC cultivars (Fig. 2A). Primers specific for the S 5-allele resulted in successful amplification only in three SC cultivars (‘Santa Rosa’, ‘Sweet Autumn’, and ‘Flavor King’) (Fig. 2B). We could not detect any PCR product with primers for the S 1-allele; however, primers for S 3 worked in the cultivar Friar and primers for the S 6 in ‘Shiro’ (data not shown). This cultivar showed only one thick band in the agarose gel when the fragments PCR amplified with consensus primers were detected (Fig. 1), although first intron amplification resulted in two differently sized fragments (295 and 327 bp).
S-polymerase chain reaction analysis using allele-specific primers. (A) IZ1 + IZ4 for amplifying S 4- and (B) IZ2 + IZ5 for detecting S 5-allele. Codes for samples are the same as in Figure 1.
Citation: HortScience horts 42, 1; 10.21273/HORTSCI.42.1.46
Genomic DNA fragments amplified by the EM-PC2consFD and EM-PC3consRD primers (Sutherland et al., 2004b) from ‘Green Sun’ and ‘Friar’ as well as fragments amplified by the PaConsI-F (Sonneveld et al., 2003) and EM-PC1consRD (Ortega et al., 2005) primer set from ‘Black Amber’ were cloned and sequenced. BLAST homology searches revealed that ‘Green Sun’ and ‘Friar’ carried the S h-allele (Fig. 3A). The other allele cloned from the cultivar ‘Friar’ was clarified to be identical with the S k-allele (data not shown). Sequence analysis of ‘Black Amber’ confirmed that this cultivar carried the S b- (data not shown) and S c-alleles (Fig. 3B) following the nomenclature established by Beppu et al. (2002, 2003). Alignments revealed that the identity was 100% between the partial sequence of the S k-allele cloned from ‘Friar’ and that retrieved from the GenBank database (sequenced from ‘Stark Gold’) or between the S b cloned from ‘Black Amber’ and that found in the GenBank database (‘Sordum’) (data not shown). In ‘Friar’ S h- and ‘Black Amber’ S c-alleles, single nucleotide polymorphisms (SNP) were detected; however, all SNPs occurred within the intron regions (Fig. 3A, B).
Alignment of nucleotide sequences of the second intron region from P. salicina ‘Kelsey’ (PsK-S h, accession no. AB084148), ‘Friar’ (PsF-S h, DQ790374), and ‘Green Sun’ (PsG-S h, DQ790373) S h-alleles (A) as well as the first intron region from P. salicina ‘Oishiwasesumomo’ (PsO-S c, AB084144) and ‘Black Amber’ (PsB-S c, DQ790376) S c-alleles (B). Black boxes indicate different residues between the aligned sequences. The conserved regions (C1, C2, and C3) and the hypervariable region (RHV) are boxed as indicated by Ushijima et al. (1998) and dashed box shows the predicted signal peptide sequence (SP) as determined by Tao et al. (1999). Speckle and diamond denote the starting and ending borders of the deduced intron sequences, respectively.
Citation: HortScience horts 42, 1; 10.21273/HORTSCI.42.1.46
The genotypes proposed for all 12 cultivars analyzed in this study and the 37 analyzed previously are arranged in Table 3 following the practice in sweet cherry. Cultivars could be assigned to seven incompatibility groups, each of them containing two to eight cultivars. Nine self-compatible cultivars and 12 cultivars in the group O of unique genotypes can be widely used as universal pollen donors.
S-genotypes and predicted incompatibility groups of Japanese plum cultivars assembled by the incorporation of former and recent results.
Discussion
Consensus and allele-specific PCR amplification of the S-RNase gene fragments has already proved to be an effective and rapid method for identifying S-genotypes in cherry (Sonneveld et al., 2003), almond (Ortega et al., 2005; Tamura et al., 2000), japanese apricot (Tao et al., 2002; Yaegaki et al., 2001), apricot (Halász et al., 2005), peach [P. persica (L.) Batsch] (Hegedűs et al., in press), and japanese plum (Beppu et al., 2002, 2003; Sapir et al., 2004). In this study, we could identify five different S-genotypes in japanese plum and pluot cultivars not studied earlier and possessing high economic value both in the U.S. and in the Mediterranean region (Bassi and Pirazzoli, 1998; Faust and Surányi, 1999). This is the first study in which detecting S-alleles with a degenerate primer set amplifying the second intron region of the Prunus S-RNase gene (Sutherland et al., 2004b) was successful in S-genotyping japanese plum cultivars, and also the precise fragment length determination method elaborated by Ortega et al. (2005) was adopted to improve discrimination between the first intron amplification products, which are characterized by restricted size variability.
Because the degenerate consensus primer sets amplified both S-alleles carried by the tested cultivars, they can be proposed for further S-genotyping studies not only in cherry, almond, and apricot, but also in japanese plum. The success of these robust primers may partly be because two P. salicina alleles were also used for primer designing (Sutherland et al., 2004b).
The S e-haplotype was shown to be responsible for the self-compatibility trait (Beppu et al., 2002, 2005). We can hypothesize that the fragments of 372 (first intron) and ≈1450 bp (second intron) lengths correspond to the S e-allele because they are present in all SC cultivars, whereas the allele indicated by the 343-bp- and ≈1200-bp-long fragments of ‘Santa Rosa’ also appears in seven SI cultivars. Because S-genotype of ‘Santa Rosa’ was determined as S c S e by Beppu et al. (2002), this fragment putatively corresponds to the S c-allele.
Besides the 14 alphabetically labeled S-alleles (Beppu et al., 2002, 2003; Yamane et al., 1999), five additional alleles were isolated and labeled with numeric codes and four of them were considered to be new alleles (Sapir et al., 2004). Allele-specific primers for all five alleles were designed (Sapir et al., 2004), which were also applied in this study to reveal correspondences between the two nomenclatures. Allele-specific primers confirmed that the S 4-allele corresponded to S c and S 5 to S e. Because both primers worked in ‘Santa Rosa’, its previously identified S c S e genotype should be translated into S 4 S 5 in the numeric label system. Furthermore, the S 5-allele-specific primer can be used as a reliable marker for determining self-compatibility in japanese plum accessions.
The only band detected after the second intron amplification of ‘Shiro’ may be the result of alleles with very similar intron sizes. The presence of two different alleles as expected under gametophytic self-incompatibility was clarified by the first intron amplification results. One of these alleles is the S 6, as confirmed by the relevant allele-specific primer. BLAST searches revealed that partial sequence of the S 6-allele was identical to S f. By DNA sequencing and BLAST searches, the S-genotype for ‘Friar’ was determined to be S h S k, a haplotype combination, which has not been detected in any other cultivar, thereby ‘Friar’ may be considered as a universal pollen donor because their pollen should be fully or semicompatible on all cultivars of currently known genotypes. Allele S k was clarified to be identical with S 3 (Table 1) using allele-specific primers (Sapir et al., 2004) and DNA sequence alignment. Alignments of the partial sequences of S h- and S c-RNase alleles have revealed one and three SNPs, respectively, in the intron regions, which may be the result of the more rapid mutation rate of introns (Sutherland et al., 2004a). However, these changes will not influence the function of the coding regions, because it was evident from the failure in fruit set after crosspollination (Table 2) between some of the group II cultivars carrying the S c-allele with three SNPs in their first intron (Fig. 3B).
We have found two incompatible groups among the analyzed cultivars; one of them consists of ‘Black Amber’, ‘October Sun’, ‘TC Sun’, and ‘Super Giant’. Their mutual incompatibility was confirmed by test crosses. DNA sequencing of their first intron region and BLAST searches allowed us to determine their genotype as S b S c similarly to ‘Laroda’, ‘Oishinakata’, and ‘Taiyo’ genotyped by Beppu et al. (2003). These seven cultivars form the widest incompatibility group presently known in japanese plum. Furthermore, PCR results (Fig. 1; Table 1) suggest that ‘Flavor Grenade’, a pluot cultivar also belongs to this group, but it requires confirmation. This would be interesting as pluots with interspecific origin have more complex genetic background, although with predominantly plum parentage (Ahmad et al., 2004).
The second incompatibility group identified in the present study contains ‘Green Sun’ and ‘Queen Rosa’ (S c S h), which was previously considered as a unique genotype (Beppu et al., 2003). The second intron region of the S h-RNase allele containing the hypervariable region was sequenced from the cultivar ‘Green Sun,’ which together with the use of allele-specific primers clarified that this cultivar also had the S c S h genotype. The inclusion of ‘Angeleno’ to this incompatibility group seems possible on the basis of its PCR analysis with consensus primers (Fig. 1; Table 1); however, for there to be no doubts, clarification from test crosses or sequence analyses are required. Because the S c-allele is shared between the two identified incompatibility groups, cultivars belonging to these groups are semicompatible with each other. Semicompatibility is also of major horticultural significance, because cultivars may be low-potency pollinizers for each other as was described in the case of apple (Goldway et al., 1999).
All five numerically labeled alleles were shown to be identical with some of the alleles initially described and labeled with alphabetic codes; hence, until now, only 14 alleles could have been identified in japanese plum cultivars indicating a quite restricted allele pool as compared with apple, almond, sweet cherry, or even apricot (Hegedűs et al., in press). It suggests that further alleles are expected to be identified as putatively as the one in ‘Shiro’ other than the S f.
Table 3 shows the genotypes not only of cultivars analyzed in this article, but also of those genotyped by Beppu et al. (2002, 2003), Sapir et al. (2004), and Yamane et al. (1999). This is the first study to assign these cultivars to incompatibility groups presenting a table similar to those available in an updated form for cherry (Boškovic and Tobutt, 2001) and almond cultivars (Boškovic et al., 2003). By incorporating all known data, Table 3 consists of 49 cultivars arranged to I–VII incompatibility groups to the group O encompassing cultivars of unique genotypes, which can be considered as “universal pollen donors,” and an additional group accumulating all SC cultivars. This information may provide valuable guidelines for horticulturists to design successful combinations for breeding programs and to aid cultivar association in plum orchards all over the world.
Literature Cited
Ahmad, R. , Potter, D. & Southwick, S.M. 2004 Identification and characterization of plum and pluot cultivars by microsatellite markers J. Hortic. Sci. Biotechnol. 79 164 169
Altschul, S.F. , Gish, W. , Miller, W. , Myers, E.W. & Lipman, D.J. 1990 Basic local alignment search tool J. Mol. Biol. 215 403 410
Bassi, D. & Pirazzoli, C. 1998 The stone fruit industry in the Mediterranean region: Agronomic and commercial overview Options Méditerr. CIHEAM/IAMB. 19 4 38
Beppu, K. , Komatsu, N. , Yamane, H. , Yaegaki, H. , Yamaguchi, M. , Tao, R. & Kataoka, I. 2005 Se-haplotype confers self-compatibility in japanese plum (Prunus salicina Lindl.) J. Hort. Sci. Biotechnol. 80 760 764
Beppu, K. , Takemoto, Y. , Yamane, H. , Yaegaki, H. , Yamaguchi, M. , Kataoka, I. & Tao, R. 2003 Determination of S-haplotypes of japanese plum (Prunus salicina Lindl.) cultivars by PCR and cross-pollination tests J. Hort. Sci. Biotechnol. 78 315 318
Beppu, K. , Yamane, H. , Yaegaki, H. , Yamaguchi, M. , Kataoka, I. & Tao, R. 2002 Diversity of S-RNase genes and S-haplotypes in japanese plum (Prunus salicina Lindl.) J. Hort. Sci. Biotechnol. 77 658 664
Boškovic, R. & Tobutt, K.R. 2001 Genotyping cherry cultivars assigned to incompatibility groups, by analysing stylar ribonucleases Theor. Appl. Genet. 103 475 485
Boškovic, R. , Tobutt, K.R. , Batlle, I. , Duval, H. , Martínez-Gomez, P. & Gradziel, T.M. 2003 Stylar ribonucleases in almond: Correlation with and prediction of incompatibility genotypes Plant Breed. 122 70 76
de Nettancourt, D. 2001 Incompatibility and incongruity in wild and cultivated plants 2nd ed. Springer-Verlag Berlin
Faust, M. & Surányi, D. 1999 Origin and dissemination of plums Hort. Rev. Amer. Soc. Hort. Sci. 23 179 231
Goldway, M. , Shai, O. , Yehuda, H. , Matityahu, A. & Stern, R.A. 1999 ‘Jonathan’ apple is a lower potency pollenizer of ‘Topred’ than ‘Golden Delicious’ due to partial S-allele incompatibility J. Hort. Sci. Biotechnol. 74 381 385
Halász, J. , Hegedűs, A. , Hermán, R. , Stefanovits-Bányai, E. & Pedryc, A. 2005 New self-incompatibility alleles in apricot (Prunus armeniaca L.) revealed by stylar ribonuclease assay and S-PCR analysis Euphytica 145 57 66
Hegedűs, A. , Halász, J. & Pedryc, A. The pistil component: A ribonuclease enzyme Nyéki J. , Soltész M. & Szabó Z. Morphology of flowers, floral biology, regularities of fertilisation and fertility in fruit species Akadémiai Kiadó Budapest (in press).
Hegedűs, A. , Szabó, Z. , Nyéki, J. , Halász, J. & Pedryc, A. 2006 Molecular analysis of S-haplotypes in peach, a self-compatible Prunus species J. Amer. Soc. Hort. Sci. 131 (in press)
Igic, B. & Kohn, J.R. 2001 Evolutionary relationships among self-incompatibility RNases Proc. Natl. Acad. Sci. USA 98 13167 13171
Nyéki, J. & Szabó, Z. 1995 Cross-incompatibility in stone fruits Intl. J. Hort. Sci. (Hungary) 28 23 31
Ontivero, M. , Radice, S. , Giordani, E. & Bellini, E. 2006 Effects of different pollination treatments in genotypes of Prunus salicina Lindl Intl. J. Hort. Sci. (Hungary) 12 141 146
Ortega, E. , Sutherland, B.G. , Dicenta, F. , Boškovic, R. & Tobutt, K.R. 2005 Determination of incompatibility genotypes in almond using first and second intron consensus primers: Detection of new S-alleles and correlation of reported S genotypes Plant Breed. 124 188 196
Sánchez-Pérez, R. , Dicenta, F. & Martínez-Gómez, P. 2004 Identification of S-alleles in almond using multiplex PCR Euphytica 138 263 269
Sansavini, S. , Zambrini, M. , Costa, G. & Cavicchi, C. 1981 Indagine su nuove e vecchie cultivar di susino; poche le cultivar pienamente ‘affidabili’ per la Valle Padana. Scelte varietali in frutticoltura Ferrara 95 102
Sapir, G. , Stern, R.A. , Eisikowitch, D. & Goldway, M. 2004 Cloning of four new japanese plum S-alleles and determination of the compatibility between cultivars by PCR analysis J. Hort. Sci. Biotechnol. 79 223 227
Sonneveld, T. , Tobutt, K.R. & Robbins, T.P. 2003 Allele-specific PCR detection of sweet cherry self-incompatibility (S) alleles S1 to S16 using consensus and allele-specific primers Theor. Appl. Genet. 107 1059 1070
Sutherland, B.G. , Robbins, T.P. & Tobutt, K.R. 2004b Primers amplifying a range of Prunus S-alleles Plant Breed. 123 582 584
Sutherland, B.G. , Tobutt, K.R. & Robbins, T.P. 2004a Molecular genetics of self-incompatibility in plums Acta Hort. 663 557 562
Tamura, M. , Ushijima, K. , Sassa, H. , Hirano, H. , Tao, R. , Gradziel, T.M. & Dandekar, A.M. 2000 Identification of self-incompatibility genotypes of almond by allele-specific PCR analysis Theor. Appl. Genet. 101 344 349
Tao, R. , Habu, T. , Namba, A. , Yamane, H. , Fuyuhiro, F. , Iwamoto, K. & Sugiura, A. 2002 Inheritance of Sf-RNase in japanese apricot (Prunus mume) and its relation to self-compatibility Theor. Appl. Genet. 105 222 228
Tao, R. , Habu, T. , Yamane, H. , Sugiura, A. & Iwamoto, K. 2000 Molecular markers for self-compatibility in japanese apricot (Prunus mume) Hort. Sci. 35 1121 1123
Tao, R. , Yamane, H. , Sugiura, A. , Murayama, H. , Sassa, H. & Mori, H. 1999 Molecular typing of S-alleles through identification, characterization and cDNA cloning for S-RNases in sweet cherry J. Amer. Soc. Hort. Sci. 124 224 233
Ushijima, K. , Sassa, H. , Tao, R. , Yamane, H. , Dandekar, A.M. , Gradziel, T.M. & Hirano, H. 1998 Cloning and characterization of cDNAs encoding S-RNases from almond (Prunus dulcis): Primary structural features and sequence diversity of the S-RNases in Rosaceae Mol. Gen. Genet. 260 261 268
Yaegaki, H. , Shimada, T. , Moriguchi, T. , Hayama, H. , Haji, T. & Yamaguchi, M. 2001 Molecular characterization of S-RNase genes and S-genotypes in the japanese apricot (Prunus mume Sieb. et Zucc.) Sex. Plant Reprod. 13 251 257
Yamane, H. , Tao, R. & Sugiura, A. 1999 Identification and cDNA cloning for S-RNases in self-incompatible japanese plum (Prunus salicina Lindl. cv. Sordum) Plant Biotechnol. 16 389 396
Yamane, H. , Tao, R. , Sugiura, A. , Hauck, N.R. & Iezzoni, A.F. 2001 Identification and characterization of S-RNases in tetraploid sour cherry (Prunus cerasus) J. Amer. Soc. Hort. Sci. 126 661 667
