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(S-) Genotypes of Apple Cultivars

(S-) Genotypes of Apple Cultivars

REPORTS BREEDING, , ROOTSTOCKS, AND GERMPLASM RESOURCES HORTSCIENCE 39(5):943–947. 2004. determined but their presumed gene products were detected by RNase zymogram analysis (Boškovic and Tobutt, 1999). However, so far Update on and Review of the all of the RNases for which the corresponding

gene sequences are unknown, except S6 and S8, Incompatibility (S-) Genotypes of have been detected only in a single, generally obsolete . For some of them, evidence Cultivars has been reported showing that they correspond to known S-alleles, which, if confi rmed, would Wim Broothaerts1 exclude their existence as distinct S-alleles Better3Fruit N.V., Willem de Croylaan 42, B-3001 Leuven, Belgium (Broothaerts, 2003; Matsumoto et al., 2003). Several other new S-alleles that were proposed Ilse Van Nerum and Johan Keulemans by Tobutt’s group may, therefore, also appear Fruitteeltcentrum K.U.Leuven, Willem de Croylaan 42, B-3001 Leuven, to be false if adequately examined. We have, Belgium therefore, decided to limit our investigations to the 16 S-alleles that are characterized at the

Additional index words. ×domestica, allele-specifi c PCR, S-allele, self-incompatibility, nucleotide sequence level. Additionally, the S6 and S8-allele were included in our study, as these are characterized both phenotypically and Abstract. Apple cultivars display a self-incompatibility system that restricts self-fertilization at the protein level. While S has been found and fertilization between cultivars bearing identical S-alleles. There has been considerable 6 in two uncommon, local Swiss cultivars, S8 progress in identifi cation of S-alleles in apple in recent years and methods are now avail- has been discovered in a few more common able for the accurate S-genotyping of cultivars. Following a recently revised numerical cultivars (Kobel et al, 1939; Boškovi and identifi cation system for apple S-alleles, we present the fi rst extensive compilation of apple Tobutt, 1999). cultivars with their S-genotypes. This list contains data from our own investigations using Broothaerts (2003) validated the revised S-allele-specifi c PCR methodology, including a number of new data, as well as published conditions for S-allele analysis by analysis of data from various other sources. Eighteen different S-alleles are discriminated, which al- a collection of old apple cultivars that were lowed the determination of the S-genotypes for 150 diploid or triploid European, American, genotyped by Kobel et al. (1939) through ex- and Japanese cultivars. Many of these cultivars are cultivated worldwide for their fruit. tensive cross-pollination studies. Here we have Also included are a number of old, obsolete cultivars and a few nondomestic genotypes. applied the same methodology to assay the S- We observed a wide variation in the frequency of S-alleles in the apple germplasm. Three allele genotypes of a number of generally more

S-alleles (S2, S3, and S9) are very common in the cultivars evaluated, presumably as a result common European, American and Japanese of the widespread use of the same breeding parents, and seven alleles are very rare (S4, apple cultivars. Our results were complemented S6, S8, S16, S22, S23, S26). by the inclusion of data from various other sources, resulting in an extensive overview of The production of generally requires Several alleles of the S-gene in apple have the current knowledge of the S-genotypes of that pollen be transferred from one cultivar (the been identifi ed and their nucleotide sequences primarily domestic apple cultivars. pollinizer) to the stigmas of the cultivar to be have been determined (Broothaerts, 2003). pollinated (main fruit-bearing cultivar). There, Based on the diversity of nucleotide sequences Experimental Protocols the pollen grains germinate and produce a tube encoding the S-RNase family members, a that enters the stigmatic tissue and elongates method has been developed using allele-spe- The plant material used was primarily through the style towards the ovules where cifi c PCR primers to selectively amplify and derived from the extensive gene bank of the fertilization takes place. During their growth, identify particular S-alleles (Janssens et al., Fruitteeltcentrum K.U.Leuven, with a few the pollen tubes are attacked by abundant 1995). This method was recently re-examined, cultivars from the Brogdale (UK) collection. cytotoxic proteins that enter their cytoplasm. modifi ed, and extended for the identifi cation Unless otherwise indicated, the methods Lethal attack is avoided through the expression of additional alleles (Broothaerts, 2003). At used in our work were described in Broothaerts of specifi c inhibitors of these proteins, allow- the same time, the annotation of S-alleles was (2003). Genomic DNA was isolated from ing pollen tube growth to proceed (Golz et al., revised because of the occurrence of more than leaves of various cultivars, amplifi ed with al- 2001). This mechanism appears to be the way one symbol for some S-alleles in the literature. lele-specifi c primers by PCR, and the fragments separated by agarose gel electrophoresis. For the gametophytic self-incompatibility system The new numbering introduced S16, S19, S22, the unique identifi cation of a few S-alleles (S , operates. The style-encoded toxic proteins are and S23, as a replacement of the former S27a (in 4 S , S , S ), allele-specifi c restriction enzymes the products of the S-gene, which are the S- ‘Baskatong’), S28/Sd (in ‘Delicious’), S27b (in 16 20 22 were employed to digest the amplifi ed products RNases. The pollen-expressed inhibitors of the ‘’), and the erroneously assigned “S10” pollen-S gene have not been identifi ed. Both (in ‘’), respectively. Following before gel analysis. Of the 18 S-alleles evalu-

genes are part of the polymorphic S-locus. further investigations (S. Matsumoto, personal ated here, only S6 and S8 were not determined by allele-specifi c PCR because their nucleotide If the alleles of the S-gene and of pollen-S communication), it appeared that S19 is a rare, match, i.e. they have the same S-locus speci- but distinct allele, and hence the proposed sequences are unknown. The presence of these two alleles was inferred from the analysis of fi city, an incompatibility reaction is elicited, merger with S28 as suggested by Broothaerts which is manifested by the arrest of pollen (2003) should be corrected. In this paper, we their stylar RNase patterns by Boškovic and Tobutt (1999). Also we did not determine the tube growth somewhere in the style. In such therefore refer to S28 for the S-allele of Deli- presence of the S -allele, which only recently cases, the inhibitors produced in the pollen cious and keep S19 for the S-allele assigned to 25 tube were apparently unable to inactivate the Bohnapfel (Boškovi and Tobutt, 1999) and has been sequenced. stylar S-RNases. sequenced by Matsumoto (unpublished data). Allele-specifi c analysis conditions have been Results described for the detection of 15 S-alleles Received for publication 2 Jan. 2003. Accepted for that operate in the domestic apple germplasm We have assayed a large number of apple publication 23 June 2003. cultivars by allele-specifi c PCR to evaluate (Broothaerts, 2003). An additional allele, S25, 1Current address: Center for the Application of has recently been cloned and sequenced and cross-incompatibility relationships in the Molecular Biology to International Agriculture a PCR/digestion method was suggested for its apple germplasm. Complementing our previ- (CAMBIA), GPO Box 3200, Canberra, ACT 2601, detection (Kitahara and Matsumoto, 2002). The ous report on the S-genotypes of a collection ; email [email protected]. sequences of a few other alleles have not been of old cultivars with known incompatibility

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77648-Breed.indd648-Breed.indd 994343 66/22/04/22/04 99:41:23:41:23 AAMM Table 1. S-allele genotypes of apple cultivars. Cultivar S-genotype Referencez Parentage (if known)

Adam’s S1S3S10 16 Ahrista (scab resistant) S3S10 17 x TSR15T3 S7S24 10, 11, 13 x Akita Gold S2S9 11 Alkmene S5S22 8, 14 Geh. Dr. Oldenburg x Cox O.P. Amanishiki S1S7 11, 13 x Ambitious S2S9 13 Toko x ? American Summer Pearmain S1S20 11 Arlet S2S7 8, 17 x Baskatong S16S26 7, 16 y Beni No Mai S7S24 13 x ? Berner Rosen S1S2 1, 8, 16 Boskoop (=) (3n) S2S3S5 1, 8, 16 , Braeburn Hillwell S9S24 7, 8 ? Lady Hamilton x ? Brünnerling S5S7S10 1, 8, 16 S2S28 13 Charlotte S5S10 8 McIntosh Wijcik x Greensleeves Champagner S2S4 1, 8, 16 S5S9 17 Cox Pippin, Queen Cox S5S9 4, 8, 10, 11 x ? Danziger Kantapfel S2S7 1, 8, 16 Delbard Jubilé S2S22 14 Golden Delicious x Lunbytrop , Delcorf S3S10 17 Golden Del. x Stark Jongrimes Delicious, Topred, Starking Delicious S9S28 11, 12, 16 S10S24 17 Worc Pearmain x Ecolette (scab resistant) S3S10 17 Elstar x Prima Elstar, Red Elstar, Elshof S3S5 4, 8 Golden Delicious x S10S28 15 McIntosh x Delicious Falstaff S2S5 8 x Golden Delicious (=Red Pippin) S3S5 4, 8 Cox O.P. x Idared (scab resistant) S3S9 17 Jonathan x 612-1 Fuhong S9S20 11 Fuji S1S9 2, 5, 8, 11, 12, 17 Ralls Janet x Delicious Fukutami S2S9 11 (Galaxy, Regal, Royal) S2S5 4, 6, 8 Kidd’s Orange Red x Golden Del S3S28 13 Ginrei S3S7 11 Gloster S4S28 16 Glockenapfel x Richared Del. Golden Delicious (Reynders, Smoothee, B) S2S3 2, 3, 6, 8, 11 x ? Golden Melon S2S7 11 Golden Supreme S3S28 13 Goldrush (scab resistant) S2S28 13, 17 Golden Delicious x Co-op 17 Granny Smith S3S23 16 French crab seedling Greensleeves S2S5 8 James Grieve x Golden Delicious Hacnine (3n) S1S3S9 13 Fuji x Tsugaru Hatsuaki S3S9 11 Himekami S7S9 6, 11 Fuji x Jonathan 3 Hokuto (3n) S1S7S9 2, 13 Fuji x ? Holly S9S28 11, 12 Jonathan x Delicious Holsteiner Cox S5S9 17 Cox O.P. x ? y S2S24 13 Macoun x Horei S2S3 11 Idared S3S7 4, 7, 8 Jonathan x Wagener Indo S7S20 9, 11, 14 ? x ? Ingrid Marie S5S? 17 Cox O.P. x ? Iwakami S1S7 11 James Grieve S5S8 8 Cox O.P. (or Potts Seedling) x ? Jester S2S3 8 Worc. Pearmain x Golden Del. S9S28 11, 12 Jonathan x Delicious , Jonagored (3n) S2S3S9 2, 4, 8 Jonathan x Golden Delicious Jonathan S7S9 2, 4, 6, 8, 11 ? x ? Joseph Musch S1S3 17 Kagayaki S2S9 11 Kanada Reinette S1S2S3 1, 8, 16 (3n) S5S7S9 17 Cox O.P. x Jonathan KaroFumei S1S3 11 3 Kent S3S9 4, 8, 13 Cox O.P. x ?Jonathan Kidd’s Orange Red S5S9 17 Delicious x Cox O.P. Kinsei S2S9 6, 11 Golden Delicious x ? Kitarou S3S9 11 Kitekami S9S25 15 Tohoku2 x Redgold Kogetsu S3S7 6 Golden Delicious x Jonathan y Korei S3S28 13 Golden Delicious x ? Indo Kuifua S3S9 11 La Paix S3S9 17 1 (scab resistant) S3S5S10 17 Macoun x PRI 54-12 Lobo S10S22 17 Malus fl oribunda 821 (scab resistant) S26S? 16 Maypole S10S16 14, 17 Wijcik x Baskatong McIntosh S10S25 8, 11, 15, 16 ?Fameuse or Saint Lawrence x ? Megumi S2S9 6, 11 Ralls Janet x Jonathan Meku 10 S3S20 11, 12 S9S28 11, 12, 13 Jonathan x Delicious Merlijn S3S22 14 Alkmene x Idared Murasaki S9S28 13 Jonathan x Delicious Mutsu (3n) S2S3S20 2, 8, 9, 11, 14 Golden Delicious x Indo

944 HORTSCIENCE VOL. 39(5) AUGUST 2004 phenotypes, we report here on the analysis of S-alleles in apple. On the basis of our current discrimination by gel electrophoresis or on the another group of apple cultivars, comprising knowledge on the S-alleles operating in apple, basis of pollination studies have been compiled diploid and triploid cultivars of various origin we have reviewed the results of other S-allele as well, unless the results were different from (Table 1). Of the 39 new entries examined, 28 genotyping initiatives in apple using previous those obtained by allele-specifi c PCR. In represent cultivars that have not been shown or similar versions of our allele-specifi c PCR every case, the corresponding references are before. For the remaining eleven entries, our method (Sakurai et al., 1997, 2000; Matsumoto indicated. The numbering used to identify results confi rmed those reported earlier. et al., 1999). These data were included in the S-alleles follows the revised annotation Over the time period 1995–2003, our Table 1 whenever they reported the complete (Broothaerts, 2003) and may, therefore, differ lab has reported the S-genotypes of a total S-genotype of the cultivars assayed, i.e., both from that in earlier publications. of 73 cultivars using various versions of the S-alleles for a diploid cultivar and all three In Table 1, a total of 150 apple cultivars S-allele-specifi c PCR methodology that is alleles for a triploid cultivar. Moreover, the are listed with their S-genotype. This includes now commonly used for the detection of the S-genotypes proposed on the basis of S-RNase most cultivars commonly cultivated in various

Table 1 (continued). S-allele genotypes of apple cultivars. Cultivar S-genotype Referencez Parentage (if known)

Natsumidori S3S9 11 Narihokou S1S2 11 Nebuta S3S9 13 Kitakami x Tsugaru S1S3 11, 13, 17 North Queen S1S3 13 Fuji x Tsugaru Oberrieder Glanzreinette S3S6 1, 8 Oetwiler S3S6 1, 8, 17 Ontario S1S8 1, 8 Wagener x Northern Spy Orei S2S28 11, 12, 13 Golden Delicious x Delicious Orin S2S7 6, 11 Golden Delicious x Indo Qingguan S2S20 11 Pink Lady S2S23 17 Golden Del. x Prima (scab resistant) S2S10 8, 17 PRI 14-510 x N.J. 123249 Princess S3S7 11 Priscilla (scab resistant) S3S9 17 Starking Delicious x PRI 610-2 Radoux S1928S? 17 Ralls Janet S1S2 11, 13, 15, 17 Redfree (scab resistant) S3S7 13 Raritan x PRI 1018-101 Redgold S2S9 6 Reine de Reinettes (=) S1S3 1, 8, 16 ? x Ribston Pip. Rewena (scab resistant) S3S9 17 Rome Beauty (=Morgenduft, Imperatore) S20S24 17 Rubin S2S3 17 Rubinette, Rafzubin S3S5 17 Golden Delicious x Cox O.P. Sampion S3S5 17 Golden Delicious x Cox O.P. Sansa S5S7 6 Gala x Akane Sauergrauech, Rote Sauergrauech S1S3 1, 8, 16 Sayaka S3S9 6 Jonathan x Sekai-ichi Sekai-ichi S3S9 6, 11 Delicious x Golden Delicious Sekihikari S20S2 11 Toko x Fuji Senshu S1S7 9, 11, 13 Shinkou S1S9 11 Shinsei S3S5 13 Golden Del. x Early McIntosh Shinano Red S3S10 15 Tsugaru x Vista Bella Shizuka S2S3S20 11 S9S10 17 McIntosh x ? Spencer S2S10 15 McIntosh x Golden Delicious Spigold (3n) S1S2S3 13 Red Spy x Golden Delicious Spijon S3S7 13 Red Spy x Monroe Stäfner Rosen S3S7S8 1, 8 Summerred S2S9 4, 8 (McIntosh x Golden Del.) x ? Telamon S3S10 14, 17 Wijcik x Golden Delicious Tohoku2 S24S25 15 McIntosh x Worcester Pearmain Tohoku4 S9S24 13 Tohoku5 S2S7 11 Tohoku6 S2S9 11 Tohoku10 S2S9 11 (scab resistant) S2S5 17 Rubin x Vanda Toyo S5S28 13 Delicious x ? Trajan S2S25 8 Transparent von Croncels S2S3 1, 8, 16 Trezeke Meyers S7S20 17 Tsugaru S3S7 11, 15 Golden Delicious x ? Tuscan S5S10 8 Wijcik x Greensleeves Tydeman’s Early Worcester S24S25 8, 17 McIntosh x Worcester Pearmain Umezawa S1S3 11 Vanda S5S7 17 Jolana x Vista Bella S10S24 15 S1S5 1, 8, 16 Wellington Reinette (Dumelow’s Seedl.) S8S9 1, 8 Wijcik S10S25 17 Mutant of McIntosh S3S5 17 Worcester Pearmain S2S24 11, 12, 17 ?Devonshire Quarrenden x ? Yingqiu S1S7 11 zReferences: 1. Kobel et al., 1939; 2. Sassa et al., 1994; 3. Broothaerts et al., 1995; 4. Janssens et al., 1995; 5. Sassa et al., 1996; 6. Sakurai et al., 1997; 7. Verdoodt et al., 1998; 8. Boškovi and Tobutt, 1999; 9. Matsumoto et al., 1999; 10. Kitahara et al., 2000; 11. Komori et al., 2000; 12. Matsumoto and Kitahara, 2000; 13. Sakurai et al., 2000; 14. Van Nerum et al., 2001; 15. Kitahara and Matsumoto, 2002; 16. Broothaerts, 2003; 17. Broothaerts, this work and previous unpublished work. References are shown according to the reported evidence for S-allele assignment, i.e. based on DNA analysis (in normal text), protein analysis (in italics), or pollination studies (in bold). yReported parentage confl icts with the S-allele genotype of the cultivar, which probably indicates that the male parent was different from the one suggested. x In our own analysis, we detected 3 alleles in Liberty (S3S5S10), while Sakurai et al. (2000) reported only S3 and S5 (see discussion).

HORTSCIENCE VOL. 39(5) AUGUST 2004 945 at the DNA and protein level, as well as by functional assessments through . The S-genotype listing presented in this paper should provide valuable information for the planning of apple breeding programs prevent- ing incompatible crossings. Furthermore, the selection of suitable pollinizers may now more accurately include the correct compatibility relationships in addition to other factors that need to be considered, such as the overlapping of the blooming periods. ‘Liberty’ presents a special case, for we

detected three S-alleles (S3S5S10) for this dip- loid cultivar. A similar observation was earlier reported for ‘Adam’s Pearmain’ (Broothaerts, 2003). On the basis of fl uorescence microscopy evaluation of a limited number of reciprocal pollinations, ‘Liberty’ was found to be cross-

incompatible with ‘Delbarestivale’ (S3S10), but ‘Liberty’ x ‘Elstar’ (S S ) revealed plenty of Fig. 1. Frequency of S-alleles in the 150 apple cultivars evaluated 3 5 pollen tubes near the stylar base. While these results suggest the S-genotype of ‘Liberty’ parts of the world, as well as a number of older several other alleles (S4, S6, S8, S16, S22, S23 and to be S3S10, Sakurai et al. (2000) reported it cultivars that were studied for their incompat- S26) were extremely rare and appeared in only to be S3S5. In our pollination study, ‘Liberty’ ibility phenotype and cultivars that have been four or fewer cultivars. produced many nonviable pollen grains used in breeding programs. All entries reveal and irregular pollen tubes when applied to both alleles of the cultivar, or all three alleles in Discussion various pistil genotypes, which suggest ploidy the case of a triploid cultivar, except for three distortions. Moreover, several seedlings of cultivars in which we found only one of the Due to the inconsistent labeling of S-alleles ‘Liberty’ unexpectedly are triploids, in which S-alleles. These cultivars are ‘Ingrid Marie’, and some erroneous data in the literature, there ‘Liberty’ contributed the unreduced gamete ‘Radoux’, and Malus fl oribunda 821. The is confusion on the S-allele genotypes in apple. (Sakurai et al., 2000 and S. Brown, personal remaining allele is specifi ed with a question We present the fi rst comprehensive overview communication). It is clear that our detection mark (S?) in Table 1, which could refer to S6, of common apple cultivars with their S-allele of three S-alleles in ‘Liberty’ (and ‘Adam’s S8, S25 (not determined) or one of the alleles genotype, based on the most recent evidence on Pearmain’) is intriguing in light of these other that is not discriminated here. the unique identifi cation of the apple S-alleles. observations and merits further examination As the S-allele inheritance may be used to Most of the 20 cultivars based upon their in additional studies. confi rm the presumed origin of a cultivar, the share of world production (The World Apple In total, 18 S-alleles have been discrimi- parentage of the cultivars, if known, is included Report, Jan. 2002, Belrose Inc.), and many nated in this study. Two of them, S16 and S22, in Table 1. In all but fi ve cases, the deduced more local cultivars grown in North America, express the same functional specifi city, while S-genotype of the cultivars corresponded Europe, and Japan were included in the evalu- differing only slightly at the DNA level (Van with the inheritance of the S-alleles from the ation. The majority of the entries in Table 1 are Nerum et al., 2001). With these 18 S-alleles, presumed parents of known S-genotype. The domestic cultivars, along with two crabapple the S-genotype of all 2n and 3n apple cultivars doubtful parentage of four cultivars for which cultivars (‘Maypole’ and ‘Baskatong’) and M. investigated could be assigned, except for three the S-alleles differed from that conferred by the fl oribunda. Sports of common cultivars are not cultivars that were only partly genotyped. If parents has already been reported (Boškovi listed separately, except for ‘Wijcik’, which is a these three cultivars each bore a different and Tobutt, 1999; Sakurai et al., 2000). For columnar sport of ‘McIntosh’. The list contains unknown S-allele, then the total number of

‘Korei’ (S3S28), the male parent should have data on 137 diploid and 14 triploid cultivars, of S-alleles in the apple germplasm studied would been different from ‘Indo’, because ‘Indo’ which the S-genotypes are composed of vari- be 21. Sixty diploid incompatibility groups are does not have the S28-allele. ous combinations of the 18 S-alleles that have represented in Table 1. While theoretically Many common cultivars are derived from been unequivocally discriminated. Cultivars it is possible to form 306 incompatibility a small group of successful cultivars, such that have been proposed to bear one or more groups out of 18 alleles, the actual number as ‘Golden Delicious’ (S2S3), ‘Delicious’ S-alleles differing from these 18 alleles were of cross-incompatible groups is already large (S9S28), ‘Jonathan’ (S7S9) and ‘Cox Orange excluded. These excluded S-alleles, S11 to S15, enough to expect few incompatibility problems Pippin’ (S5S9). It is, therefore, predicted that S17 to S19 and S21were originally introduced by in natural settings or in breeding practices. the S-alleles of these donor cultivars have Boškovi and Tobutt (1999). The evidence for There are, however, large differences in the been preferentially introgressed in the pool of their discrimination is controversial (except frequency of occurrence of the S-alleles in cultivars that are the result of planned breed- for S19, see introduction), as only their gene apple cultivars. For instance, there is almost ing programs. Many new apple cultivars have products have been visualized on protein gels a 30-fold difference in frequency between the resulted from chance hybridizations, however, and they were only reported from a single most frevalent allele (S3) and the four most rare making it diffi cult to distinguish between those cultivar (Broothaerts, 2003 and Matsumoto alleles. Furthermore, 131 of the 150 entries that have one of the common parental donors et al., 2003). The S-genotypes of the excluded (87%) are fully genotyped with only 11 of the in their breeding history and those that have cultivars have, however, been reported and 18 S-alleles. The remaining seven alleles were not. Therefore, we decided to calculate the discussed in a separate paper (Broothaerts, found in less than 5 of the 150 cultivars, and frequency of different S-alleles among the 150 2003). Also a number of cultivars that were fi ve of them, S4, S6, S16, S23 and S26, occurred cultivars examined. The frequency distribution only partly examined in the past were omit- only twice. Some of these rare alleles have revealed the strong prevalence of the S3-allele, ted from this compilation, except for three been detected in other old or noncommercial and to a slightly lesser extent that of S2 and S9 cultivars which were the only three cultivars cultivars (Broothaerts, 2003). (Fig. 1). In fact, 19% of the cultivars (28/150) from our own recent work in which the second Although it has not been our objective to had an S-genotype composed of these three allele was not detected. For most cultivars, the provide an unbiased or random sample of cul-

S-alleles, and at least one of these was pres- evidence for the correct S-allele assignment tivars, the wide distribution of the S3-allele in ent in 116 cultivars (77%). On the other hand, seems strong and is often supported by studies particular is striking. The high frequency of the

946 HORTSCIENCE VOL. 39(5) AUGUST 2004 Broekaert. 1995. cDNA cloning and molecular HortScience 34:708–710. S3-allele is attributed mainly to the widespread analysis of two self-incompatibility alleles from Matsumoto, S. and K. Kitahara. 2000. Discovery use of ‘Golden Delicious’ (S2S3) and its deriva- tives in many breeding programs in the past and apple. Plant Mol. Biol. 27:499–511. of a new self-incompatibility allele in apple. present. However, among the cultivars in Table Broothaerts, W. 2003. New fi ndings in apple S- HortScience 35:1329–1332. 1 that are derived from ‘Golden Delicious’, genotype analysis resolve previous confusion Matsumoto, S., K. Kitahara, Y. Furusawa, H. Kom- and request the re-numbering of some S-alleles. atsu, J. Soejima, and H. Fukui. 2003. S-allele the inheritance of the S2-allele was similar Theor. Appl. Genet. 106:703–714. genotype of apple cultivars and selections. Acta to that of the S3-allele (14 and 13 cultivars, Golz, J.F., H.-Y. Oh, V. Su, M. Kusaba, and E. Hort. (in press). respectively). The dominance of the ‘Golden Newbigin. 2001. Genetic analysis of Nicotiana Sakurai, K., S.K. Brown, and N.F. Weeden. 1997. Delicious’ S-alleles in breeding programs is pollen-part mutants is consistent with the pres- Determining the self-incompatibility alleles further exemplifi ed by the presence of either ence of an S-ribonuclease inhibitor at the S-locus. of Japanese apple cultivars. HortScience of its S-alleles in all of the scab-resistant cul- Proc. Natl. Acad. Sci. USA 98:15372–15376. 32:1258–1259. tivars evaluated (Table 1). M. fl oribunda 821 Janssens, G.A., I.J. Goderis, W.F. Broekaert, and W. Sakurai, K., S.K. Brown, and N.F. Weeden. 2000. has been widely employed as a source of scab Broothaerts. 1995. A molecular method for S-al- Self-incompatibility alleles of apple cultivars and resistance (Vf gene) in the breeding of such lele identifi cation in apple based on allele-specifi c advanced selections. HortScience 35:116–119. PCR. Theor. Appl. Genet. 91:691–698. Sassa, H., N. Mase, H. Hirano, and H. Ikehashi. 1994. cultivars. It is striking that none of the ten scab Kitahara, K., J. Soejima, H. Komatsu, H. Fukui, and Identifi cation of self-incompatibility-related gly- resistant cultivars studied introgressed either S. Matsumoto. 2000. Complete sequences of the coproteins in styles of apple (Malus ×domestica). of the S-alleles from its scab resistant parent. S-genes ‘Sd-’ and ‘Sh-RNase’ cDNA in apple. Theor. Appl. Genet. 89:201–205. As the introgression of the resistance from M. HortScience 35:712–715. Sassa, H., T. Nishio, Y. Kowyama, T. Hirano, T. fl oribunda into a commercial cultivar requires Kitahara, K. and S. Matsumoto. 2002. Sequence Koba, and H. Ikehashi. 1996. Self-incompatibil- several generations, we can assume that a large of the S10 cDNA from ‘McIntosh’ apple and a ity (S) alleles of the Rosaceae encode members of PCR-digestion identifi cation method. HortSci- a distinct class of the T /S ribonuclease superfam- part of the crabapple background, including 2 its S-locus, was removed through breeding. ence 37:187–190. ily. Mol. Gen. Genet. 250:547–557. It would be interesting to investigate more Kobel, F., P. Steinegger, and J. Anliker. 1939. Van Nerum, I., M. Geerts, A. Van Haute, J. Keule- Weitere Untersuchungen über die Befruchtungs- mans, and W. Broothaerts. 2001. Re-examination carefully whether the widespread presence of verhältnisse der Apfel- und Birnsorten. Landw. of the self-incompatibility genotype of apple some of the S-haplotypes has affected some of Jb. Schweiz 53:160–191. cultivars containing putative ‘new’ S-alleles. the attributes of modern apple cultivars. Komori, S., J. Soejima, K. Abe, N. Kotoda, and Theor. Appl. Genet. 103:584–591. H. Kato. 2000. Analysis of S-allele genotypes Verdoodt, L., A. Van Haute, I.J. Goderis, K. De Witte, Literature Cited and genetic diversity in the apple. Acta Hort. J. Keulemans, and W. Broothaerts. 1998. Use 538:83–86. of the multi-allelic self-incompatibility gene in Boškovi , R. and K.R. Tobutt. 1999. Correlation of Matsumoto, S., K. Kitahara, S. Komori, and J. apple to assess homozygocity in shoots obtained stylar ribonuclease isoenzymes with incompat- Soejima. 1999. A new S-allele in apple, ‘Sg’, through haploid induction. Theor. Appl. Genet. ibility alleles in apple. Euphytica 107:29–43. and its similarity to the ‘Sf’ allele from ‘Fuji’. 96:294–300. Broothaerts, W., G.A. Janssens, P. Proost, and W.F.

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