New self-incompatibility alleles in apricot (Prunus armeniaca L.) revealed by stylar ribonuclease assay and S-PCR analysis

Apricot (Prunus armeniaca L.) shows gametophytic self-incompatibility controlled by a single locus with several allelic variants. An allele for self-compatibility (S_C) and seven alleles for self-incompatibility (S₁–S₇) were described previously. Our experiments were carried out to ascertain whether the number of allelic variants of apricot S-locus was indeed so small. Twenty-seven apricot accessions were analysed for stylar ribonucleases by non-equilibrium pH gradient electrofocusing (NEpHGE) to determine their S-genotype. To validate the results of electrofocusing, the applicability of the S-gene-specific consensus PCR primers designed from sweet cherry sequences was tested. NEpHGE revealed 12 bands associated with distinct S-alleles in newly genotyped cultivars. Cherry consensus primers amplified 11 alleles out from 16 ones, which indicated that these primers could also recognize most of the S-RNase sequences in apricot, and provided an efficient tool to confirm or reject NEpHGE results. By combining the protein and DNA-based methods, complete or partial S-genotyping was achieved for 23 apricot accessions and nine putatively new alleles (provisionally labelled S₈–S₁₆) were found. Their identity needs to be confirmed by pollination tests or S-allele sequencing. This study provides evidence that similarly to other Prunus species, the S-locus of apricot is more variable than previously believed.     

Description of a new trans-generic <Emphasis Type="Italic">S</Emphasis>kb-RNase allele in apple

Polish apple cvs: ‘Ligol’, ‘Odra’ and ‘Primula’ served for studies of self-incompatibility. Basing on available sequence data, a new set of primers upstream and downstream of the hypervariable (HV) region of apple S-RNases were designed. Using the RT-PCR method, cDNA was amplified on RNA isolated from styles. PCR products were cloned and sequenced. A new trans-generic S-RNase allele, designated as Skb (GenBank accession no. EU443101), was discovered in cvs ‘Odra’ and ‘Primula’. Nucleotide sequence alignment revealed that Skb-RNase shows 98% identity to SaucS19-RNase from Sorbus aucuparia and 97% identity to CmonS17-RNase from Crataegus monogyna. The occurrence of extensive intergeneric hybridization among extant Pyrinae is considered since the deduced amino acid sequence of Skb-RNase from M. × domestica showed higher similarity to CmonS17 from C. monogyna, SaucS19-RNase from S. aucuparia, St from Malus transitoria, S5-RNase and S3-RNase from Pyrus pyrifolia, and S40-RNase from P. ussuriensis than to S-alleles from Malus × domestica and all of them are grouped in the same cluster of phylogenetic tree. In respect to extremely high similarities between aforementioned S-RNases it could be possible that these alleles existed before the separation of Malus, Pyrus, Sorbus and Crataegus genera. Within Malus, the Skb-RNase from M. × domestica and St-RNase from M. transitoria show 100% identity of the HV region at the deduced amino acid level, suggesting that these S-RNases diverged more recently than the other Malus S-RNases. In ‘Ligol’, the agronomically most important cultivar in Poland, the S2 and S9 were identified.     

Sequence of the S 9-RNase cDNA and PCR-RFLP system for discriminating S 1- to S 9-allele in Japanese pear

A new S ₉-allele was discovered in 6 Japanese pear cultivars, ‘Shinkou’, ‘Shinsei’, ‘Niitaka’, ‘Amanogawa’, ‘Nangetsu’ and ‘Nansui’. cDNA encoding S ₉-RNase, a stylar product of S ₉-allele, was cloned from pistils of ‘Shinkou’ and ‘Shinsei’ by 3' and 5' RACE. The S ₉-RNase gene had an open reading frame of 684 nucleotides encoding 228 amino acid residues. S ₉-RNase had a hypervariable (HV) region different from S ₁- to S ₈-RNase and shared higher similarity (95.2%) with apple S ₃-RNase than with 8 Japanese pear S-RNases (from 61.0% to 70.7%). Genomic PCR with primers ‘FTQQYQ’ and ‘anti-(I/T) IWPNV’ provided S ₁- to S ₉-amplicon (product), but could not discriminate the S ₂ from the S ₉ of ca. 1.3 kb. The S ₂ and S ₉ were distinguished by digestion with AflII and BstBI, respectively. The digestion with nine S-allele-specific restriction endonucleases, SfcI, AflII, PpuMI, NdeI,AlwNI, HincII, AccII, NruI and BstBI, distinguished S ₁ to S ₉, establishing that this PCR-RFLP system is useful for S-genotype assignments in Japanese pear harboring S ₁- to S ₉-allele. ‘Shinkou’, ‘Shinsei’, ‘Nangetsu’ and ‘Nansui’ assigned as S ₄ S ₉ were determined to be cross incompatible. This revised version was published online in July 2006 with corrections to the Cover Date.     

Primers amplifying a range of Prunus S-alleles

Although various consensus polymerase chain reaction (PCR) primers have been reported for identifying Prunus S‐alleles, they have been developed from and optimized on a limited set of alleles, which may limit their applicability to a broader allele range. To develop a primer set for use across the genus, degenerate consensus primers were designed from conserved regions of 27 S‐RNase sequences available from five Prunus species. The primers were tested in 15 previously genotyped cultivars of cherry, almond and apricot, representing alleles S₁ to S₆ in each crop and also S_c in apricot. Comparisons were made with previously published primers tested in the same 15 cultivars under reported reaction conditions. The new primers generated an amplification product for each of the 19 S‐alleles whereas those previously available amplified no more than 14. The primers will be useful for genotyping and genetic studies in cultivars and wild populations.     

Identification of self-incompatibility (S) alleles in Latvian and Swedish sweet cherry genetic resources collections by PCR based typing

The Latvian and the Swedish sweet cherry (Prunus avium L.) genetic resources collections comprise valuable material for breeding. The collections represent local Latvian and Scandinavian genetic resources: semi-wild samples, landraces, and cultivars developed in local breeding programmes, as well as diverse germplasm from the northern temperate zone. The objective of this investigation was to determine which S ₁ –S ₆ alleles are most important in the sweet cherry genetic resources collections and to compare the identified allelic and genotypic frequencies in material of different origin. Accessions in the two collections were screened for the presence of the self-incompatibility (S) S ₁ to S ₆ alleles, using PCR based typing. Significant differences (P < 0.05) between screened collections were found in frequencies of S ₄ and S ₅ alleles. Analysis of allele combinations identified the high occurrence of selections with the S-genotype S ₃ S ₆ in both collections. Compared to the S-allele frequencies published for over 250 sweet cherry cultivars from Western and Southern Europe, the Latvian and Swedish germplasm appeared to have a high frequency of the S ₆ allele in both collections, and a relatively high frequency of the S ₅ allele in Latvian germplasm. This study represents the first comprehensive S-allele screening for the sweet cherry genetic resources collections in Latvia and Sweden. Both sweet cherry collections contain high proportion of accessions adapted to north central European growing conditions, not typical for the majority of the documented sweet cherry genetic resources, which explains differences in certain S-allele occurrence.     

Correlation of stylar ribonuclease zymograms with incompatibility alleles in sweet cherry

Summary Protein stylar extracts of 16 cultivars of sweet cherry (Prunus avium), from the 10 different incompatibility groups to which incompatibility alleles have been assigned, were separated on acrylamide gels using isoelectric focusing (IEF) and were stained for ribonuclease activity. When two cultivars from the same incompatibility group were analyzed they gave identical zymograms and the cultivars of the 10 different incompatibility groups gave in all eight distinct zymograms. The ribonuclease polymorphism could be correlated with the reported S allele constitutions of the cultivars. Three ribonuclease bands were identified that each consistently corresponded to one of the six known incompatibility alleles (S ₁, S₂ and S ₆), a fourth band apparently corresponded to S ₃ and to the combination of S ₄ and S ₅, and a fifth band to S ₄ and S ₅ in other combinations. Thus, it seems that S alleles of cherry have ribonuclease activity and that IEF is useful for distinguishing S allele constitutions. The ribonuclease pattern of Summit, a cultivar of unknown incompatibility group, indicated its incompatibility genotype to be S ₁S₂, and this was confirmed by controlled pollination. The same band corresponded to S ₄ and S ₄', the mutant allele in self-compatible cultivars. IEF and ribonuclease staining promise to be useful tools for exploring the incompatibility relationships of cherry cultivars and perhaps of other self-incompatible Prunus crops.     

Genetic diversity evaluation of a loquat (<Emphasis Type="Italic">Eriobotrya japonica</Emphasis> (Thunb) Lindl) germplasm collection by SSRs and <Emphasis Type="Italic">S</Emphasis>-allele fragments

Loquat (Eriobotrya japonica (Thunb.) Lindl.) is a minor Rosaceae fruit of growing interest as an alternative to the main fruit crops. In this context, the selection of new cultivars to satisfy the market demand will request the suitable characterization of the available germplasm. In this work, genetic relationships among 83 loquat accessions from different countries belonging to the European loquat germplasm collection, held at the Instituto Valenciano de Investigaciones Agrarias (IVIA) in Moncada (Spain) were evaluated using microsatellites and S-allele fragments. A total of nine single sequence repeats (SSRs) from Malus and Eriobotrya genera revealed 53 informative alleles and the S-RNases consensus primers detected 11 self-incompatibility putative alleles. The combined data allow to distinguish unambiguously 80 out of the 83 accessions studied. Unweighted pair-group method (UPGMA) cluster and principal coordinates analysis (PCoA), based on Dice’s genetic distance, generally grouped genotypes according to their geographic origins and pedigrees. Discrepancies and similarities of the results obtained with other variability analysis, based on pomological traits or molecular markers, on the same loquat collection are discussed.     

Identification of S-alleles in almond using multiplex PCR

The S-genotypes of eight almond (Prunus dulcis Miller (D.A. Webb)) cultivars from different geographical origins and of nine new selections from the CEBAS-CSIC (Murcia, Spain) breeding program were determined using single and multiplex PCR with different sets of specific oligonucleotide primers. The results of PCR using the AS1II- and AmyC5R-specific primers showed amplification in a single reaction of 10 different self-incompatibility alleles and of the self-compatibility allele S _f. However, the amplified fragments of the S _f allele were of similar sizes to those amplified from the S ₃ self-incompatibility allele. For this reason, a specific PCR primer CEBASf was designed from the intron sequence of S _f. A multiplex-PCR reaction using the AS1II, CEBASf and AmyC5R primers permitted unequivocal identification of the 10 self-incompatibility alleles and of the self-compatibility allele. Multiplex PCR opens the possibility to identify new S-alleles using different sets of primers. The applications of these PCR markers in the almond-breeding programs are discussed.     

The myrobalan (<Emphasis Type="Italic">Prunus cerasifera</Emphasis> L.): a useful diploid model for studying the molecular genetics of self-incompatibility in plums

A series of PCR methods were used to detect S-RNase alleles and SFB alleles and to determine S-genotypes in 25 accessions of myrobalan (Prunus cerasifera L.). Firstly, primers flanking the polymorphic second intron were used to identify S-RNases in agarose gels. These primers amplified one or two bands per accession in 25 accessions. Then consensus primers were designed for amplifying the polymorphic first intron, unique to Prunus S-RNases, for automated fluorescent detection. Each accession produced one or two peaks. New primers were then developed to amplify the intron in the SFB gene, for detection by fluorescence. Cross-referencing PCR bands and peaks indicated 15 S-alleles were present in the 25 accessions. Cloning, sequencing and comparison with published data indicated that the amplified products were S-RNase alleles. Sequence information was used to design primers specific for each S-RNase. Full and consistent S-genotypes were obtained by cross-comparing PCR data for 23 of the 25 accessions, and two accessions appeared to have a single allele. Pollen-tube microscopy indicated function of some but not all of the S-alleles sequenced.     

Identification and characterization of new S‐alleles associated with self‐incompatibility in almond

Almond is a highly heterozygous species with a high number of S‐alleles controlling its gametophytic self‐incompatibility system (GSI). In this work, we have analysed 14 Spanish local almond cultivars for S‐RNase allele diversity. Five new S‐RNase alleles were identified by cloning and sequencing, S₃₁ (804 bp) in ‘Pou de Felanitx’ and ‘Totsol’, S₃₂ (855 bp) in ‘Taiatona’, S₃₃ (1165 bp) in ‘Pou d’Establiments’ and ‘Muel’, S₃₄ (1663 bp) in ‘Pané‐Barquets’ and S₃₅ (1658 bp) in ‘Planeta de les Garrigues’. Additionally, seven already known almond alleles could be recognized in the local cultivars studied. The high number of new alleles identified reveals the wide diversity of almond germplasm still existing and requiring characterization, and points to the possibility of new findings by a wider study focusing on other provenances. The almond S‐RNases have been compared to those of other Prunus species, showing a high identity and confirming that the S‐RNase gene in this genus presents a probable common ancestor.     

S-genotype identification based on allele-specific PCR in Japanese pear

Gametophytic self-incompatibility in Japanese pear (Pyrus pyrifolia Nakai) is controlled by the single, multi-allelic S-locus. Information about the S-genotypes is important for breeding and the selection of pollen donors for fruit production. Rapid and reliable S-genotype identification system is necessary for efficient breeding of new cultivars in Japanese pear. We designed S allele-specific PCR primer pairs for ten previously reported S-RNase alleles (S¹–S⁹ and S^k) as simple and reliable method. Specific nucleotide sequences were chosen to design the primers to amplify fragments of only the corresponding S alleles. The developed primer pairs were evaluated by using homozygous S-genotypes (S¹/S¹–S⁹/S⁹ and S^4sm/S^4sm) and 14 major Japanese pear cultivars, and found that S allele-specific primer pairs can identify S-genotypes effectively. The S allele-specific primer pairs developed in this study will be useful for efficient S-genotyping and for marker-assisted selection in Japanese pear breeding programs.     

Identification of self-incompatibility alleles and pollen incompatibility groups in sweet cherry by PCR based s-allele typing and controlled pollination

A total of 17 pollen incompatibility groups in sweet cherry (Prunusavium L.) were identified among 46 accessions by PCR based S-alleletyping analysis and by controlled test pollinations. Two putativeS-alleles different from S ₁ to S ₆,S _z and S _y were identified. Five S-genotypes, S ₁ S ₅, S ₁ S ₆,S ₂ S ₆, S ₄ S ₆, andS ₅ S ₆, combinations of S ₁ toS ₆ alleles that had not previously been identified from cultivars in NYSAES, were positively confirmed by PCR based S-genotyping analysis. Also, the S-genotypes of cultivars in some pollen incompatibility groups that had previously been incorrectly reported have been clarified. Several popular cultivars, which were previously used as testers for S-allele typing analysis, were found to have been inaccurately genotyped. In addition, the S-genotypes and self-incompatibility groups of some relatively recentlyintroduced cultivars were identified. The molecular typing system ofS-genotypes based on PCR is a useful and rapid method for identifying newS-alleles and incompatibility groups in sweet cherry.     

Genotyping apricot cultivars for self-(in)compatibility by means of RNases associated with S alleles

In previous work the existence of proteins with RNase activity associated with S alleles in apricot was demonstrated. These proteins were inherited as described previously for the inheritance of self‐compatibility in this species. In this study, new cultivars have been genotyped for self‐compatibility using this method and it has been demonstrated that in all self‐compatible cultivars examined, the self‐compatibility allele is the same and is associated with an RNase with high activity. Homozygous self‐compatible individuals have been detected among established cultivars as well as among seedlings following breeding activity. This germplasm is of great value within the breeding programme because only self‐compatible seedlings will be produced. The number of S alleles in apricot appears to be low and only eight different alleles have been found in the large number of different cultivars screened. Furthermore, there are alleles present in the Spanish population that are also found in the genetic pool of North American cultivars. The screening of a progeny from the cross between the American cultivar ‘Goldrich’ and the Spanish cultivar ‘Pepito’ demonstrated the existence of the common allele S₂ (detected previously by examining RNases), which was confirmed by the segregation of self‐compatibility in the progeny.     

甘蓝型油菜Cu/ZnSOD和FeSOD基因的克隆及菌核病菌诱导表达

依据拟南芥、芥菜型油菜和白菜已知超氧化物歧化酶(SOD)保守序列设计引物,用同源序列法和RT-RACE技术克隆甘蓝型油菜Cu/ZnSOD和FeSOD基因,经序列分析和基因片段拼接,得到Cu/ZnSOD和FeSOD基因的全长cDNA,分别为756 bp (GenBank登录号AY970822)和1 037 bp (GenBank登录号EF634058)。以cDNA序列设计引物,获得1 322 bp的Cu/ZnSOD基因组DNA (GenBank登录号DQ431853)和1 659 bp的FeSOD基因组DNA (GenBank登录号EF634057)。生物信息学分析表明,Cu/ZnSOD基因ORF框长459 bp,编码152个氨基酸残基的蛋白质,在基因组序列结构上具有7个外显子和6个内含子。而FeSOD基因ORF框长792 bp,编码263个氨基酸残基的蛋白质,在基因组序列结构上具有8个外显子和7个内含子。二者外显子和内含子交接处完全符合GT/AG规则。利用获得的Cu/ZnSOD的cDNA片段作探针,对菌核病菌诱导甘蓝型油菜叶片的mRNA进行Northern blotting分析,结果显示在同一品种(系)中菌核病菌诱导后Cu/ZnSOD mRNA表达量比诱导前升高,抗(耐)型油菜Cu/ZnSOD mRNA表达量明显高于感病型。油菜叶片SOD酶活性分析结果也获得了完全一致的结果。以上结果表明,甘蓝型油菜SOD基因与菌核病抗性相关。     

Quantitative and molecular characterization of heat tolerance in hexaploid wheat

Understanding the genetic basis of tolerance to high temperature is important for improving the productivity of wheat (Triticum aestivum L.) in regions where the stress occurs. The objective of this study was to estimate inheritance of heat tolerance and the minimum number of genes for the trait in bread wheat by combining quantitative genetic estimates and molecular marker analyses. Two cultivars, Ventnor (heat-tolerant) and Karl92 (heat-susceptible), were crossed to produce F₁, F₂, and F₃populations, and their grain-filling duration (GFD) at 30/25 ^°C 16/8 h day/night was determined as a measure of heat tolerance. Distribution of GFD in the F₁ and F₂ populations followed the normal model (χ², p > 0.10). A minimum of 1.4 genes with both additive and dominance effects, broad-sense heritability of 80%, and realized heritability of 96%for GFD were determined from F₂ and F₃ populations. Products from 59primer pairs among 232 simple sequence repeat (SSR) pairs were polymorphic between the parents. Two markers, Xgwm11 andXgwm293, were linked to GFD by quantitative trait loci (QTL) analysis of the F₂ population. The Xgwm11-linked QTL had only additive gene action and contributed 11% to the total phenotypic variation in GFD in the F₂population, whereas the Xgwm293-linked QTL had both additive and dominance action and contributed 12% to the total variation in GFD. The results demonstrated that heat tolerance of common wheat is controlled by multiple genes and suggested that marker-assisted selection with microsatellite primers might be useful for developing improved cultivars. This revised version was published online in August 2006 with corrections to the Cover Date.     

Distribution of S haplotypes in commercial cultivars of Brassica rapa

Self‐incompatibility in Brassicaceae plants is sporophytically controlled by a single multi‐allelic locus (S locus), which contains at least three highly polymorphic genes expressed in the stigma (SLG and SRK) and in the pollen (SCR/SP11). Using polymerase chain reaction‐restriction fragment length polymorphism (PCR‐RFLP) analysis with SXG‐specific primer pairs, the S haplotypes of F₁ hybrid and open‐pollinated commercial cultivars of Brassica rapa were identified. The number of S haplotypes detected in the F₁ hybrid cultivars of Chinese cabbage, komatsuna, pak‐choi, turnip, open‐pollinated cultivars of Chinese cabbage and turnip were 9, 9, 4, 11, 13 and 12, respectively. Nine of them had different PCR‐RFLP profiles from those of the S‐tester lines that determined the SLG sequences. Four SLG sequences in the F₁ hybrid cultivars were determined and named S⁵³, S⁵⁴, S⁵⁵ and S⁵⁶, respectively. It is demonstrated that the PCR‐RFLP analysis using specific primer pairs of SLG and SRK is useful for identification of the S haplotypes, in both, S homozygous and S heterozygous plants of B. rapa. The possibility of using this method routinely in breeding programmes, and in the evaluation of F₁ hybrid seed purity, is discussed.     

Selection for resistance to Plasmodiophora brassicae Wor. in oriental subspecies of Brassica rapa L.

Summary Selection for resistance to Plasmodiophora brassicae Wor. in oriental groups of Brassica rapa L.Two hundred and sixty-five cultivars of leafy, oriental bassicas were tested for resistance to 18 collections of Plasmodiophora brassicae, the causal agent of clubroot. The tests were conducted in the greenhouse at low and high level inoculum concentrations. Eleven cultivars of B. rapa pe-tsai, five cultivars of B. rapa pak-choy and three cultivars of B. rapa choy-sum consistently segregated for resistance at the lower concentration of inoculum (1000 spores/ml). All 265 cultivars were susceptible at the higher concentration (1 000 000 spores/ml). Three cultivars were used in pedigree and recurrent selection schemes for increased resistance. After three cycles of selfing resistant individuals, significantly more resistant S₃ lines were derived from each cultivar. Lines derived from two cultivars. Chinese White and PI 257236, continued to improve with each cycle of selection and demonstrated increased resistance to higher levels of inoculum (up to 1 000 000 spores/ml) New cultivars based on intercrosses of S₂ resistant individuals also had significantly better resistance than the original cultivar. After two cycles of selection in the third cultivar, PI 419007, resistance did not increase and its S₂ mass did not differ significantly from the original cultivar. Evidence that indicates resistance is pathotype-non-differential and offers an alternative to major gene, pathotype-differential types of resistance currently being introduced to the leafy oriental brassicas from other Brassica rapa groups.     

Genetic relationships of Brassica vegetables determined using database derived simple sequence repeats

Sequence databases were screened to identify simple sequence repeats (SSRs) in Brassica oleracea sequences. A total of 512 B. oleracea DNA sequences were screened and 43 potential SSRs were identified. Thirty-six primer pairs were designed to amplify target sequences. Of the 36 primer pairs, six failed to amplify fragments of expected sizes, and 17 primer pairs failed to generate polymorphisms. Thirteen SSRs were used to assess genetic similarity between 54 B. oleracea cultivars, belonging to 3 variteal groups (cabbage, cauliflower, and broccoli). Pairwise genetic similarities were calculated for cultivars, and a dendrogram of relationships was produced. All cabbage cultivars were distinguished from each other and clustered in two separate groups. Five cauliflower cultivars could not be distinguished with SSR markers used in the study. Three broccoli cultivars clustered with cauliflower cultivars, and two cauliflower cultivars grouped with broccoli cultivars. The varietal group with the narrowest genetic variation in the study was cauliflower (B. oleracea var. botrytis) followed by broccoli (B. oleracea var. italica) and cabbage (B. oleracea var. capitata) groups. Polymorphism information content (PIC) values and number of alleles produced per marker ranged between 0.25 to 0.86 and 1 to 8, respectively, for database derived SSR markers.     

Polymorphism and DNA markers for asparagus cultivars identified by random amplified polymorphic DNA

Summary DNA polymorphism among five Asparagus officinalis L. cultivars-Imperial, Snow, Steline, UC-157 and Larac, as detected by random amplified polymorphic DNA (RAPD), is reported. Thirty one decamer primers were tested. and twenty six of them yielded amplification products. Fourteen primers gave products with at least one polymorphic DNA fragment. Among a total of 119 amplified fragments 33 were polymorphic. These RAPD markers enabled the identification of asparagus cultivars. Unique markers for cultivars were: Snow-bands 475 bp, 772 bp, 412 bp, 935 bp and 820 bp amplified by primers D5, OPA-07, OPA-09, OPA-10 and OPA-18, respectively. Steline-bands 645 bp, 680 bp and 997 bp amplified by primers A32, OPA-03 and OPA-09, respectively. A band 903 bp, amplitied by primer OPA-12, is a marker for Imperial, and a band 420 bp, amplified by primer D52, is a marker for Larac. Cultivar UC-157 could be identified by a combination of shared polymorphic bands. The pairwise marker difference between cultivars ranged from 0.08 to 0.17. A phenogram of the genetic relationship based on RAPD fits with the known origin of the cultivars.     

Evaluation of seedling and adult plant resistance in European wheat cultivars to Australian isolates of <Emphasis Type="Italic">Puccinia striiformis</Emphasis> f. sp. <Emphasis Type="Italic">tritici</Emphasis>

A set of 105 European wheat cultivars was assessed for seedling resistance and adult plant resistance (APR) to stripe (yellow) rust in greenhouse and field tests with selected Australian isolates of Puccinia striiformis f. sp. tritici (Pst). Twelve cultivars were susceptible to all pathotypes, and among the remainder, 11 designated seedling genes (Yr1, Yr3, Yr4, Yr6, Yr7, Yr9, Yr17, Yr27, Yr32, YrHVII and YrSP) and a range of unidentified seedling resistances were detected either singly or in combination. The identity of seedling resistance in 43 cultivars could not be determined with the available Pst pathotypes, and it is considered possible that at least some of these may carry uncharacterised seedling resistance genes. The gene Yr9 occurred with the highest frequency, present in 19 cultivars (18%), followed by Yr17, present in 10 cultivars (10%). Twenty four cultivars lacked seedling resistance that was effective against the pathotype used in field nurseries, and all but two of these displayed very high levels of APR. While the genetic identity of this APR is currently unknown, it is potentially a very useful source of resistance to Pst. Genetic studies are now needed to characterise this resistance to expedite its use in efforts to breed for resistance to stripe rust. Colin R. Wellings seconded from NSW Department of Primary Industries.