S‐locus diversity and cross‐compatibility of wild Prunus avium for timber breeding

Prunus avium is primarily cultivated for its fruit, sweet cherries. However, it is also used to produce high‐quality timber. In a P. avium seed orchard, gametophytic self‐incompatibility is a restriction for free pollen flow and should be considered when establishing basic forest materials. In this study, S‐locus diversity and cross‐incompatibility of wild cherry individuals in clonal banks established for breeding for timber production were investigated. Wild cherry trees (140) with outstanding forest growth habit, collected in northern Spain, grafted and planted in two clonal banks, were genotyped at the S‐locus. The self‐incompatibility S‐locus genes, S‐RNase and SFB, were analysed by PCR. Twenty‐two S‐haplotypes, resulting in 72 different S‐genotypes, were identified. The genotypes were grouped into 33 incompatibility groups and 39 unique genotypes. This initial S‐locus analysis revealed large genetic diversity of wild cherry trees from the Spanish northern deciduous forest, and provides useful information for seed orchard design. Wild P. avium displays significantly more genetic diversity than what is detected in local cultivars, revealing a narrowing of genetic diversity during local domestication.     

Improved <Emphasis Type="Italic">S</Emphasis>-genotyping and new incompatibility groups in Japanese plum

The selection of cross-compatible cultivars is essential to ensure fruit set in self-incompatible species like Japanese plum and thus the S-genotype must be determined in order to establish incompatibility groups. In this study an improved Japanese plum S-genotyping method, based in polymerase chain reaction and capillary electrophoresis detection of intron polymorphisms of S-locus genes, S-RNase and SFB, has been assayed and validated in a wide sample of cultivars. This method allows a more precise determination of amplified fragment sizes and therefore a better differentiation of self-incompatibility alleles. The assayed methodology was proven effective in the detection of 13 different S-alleles of S-RNases and SFBs and was used to S-genotype 105 Japanese plum cultivars, 32 of which are described by first time in this work. Analysed cultivars were assigned into 11 incompatibility groups and two new incompatibility groups (XX and XXI) were identified, increasing to 21 the number of incompatibility groups described in this crop.     

Breaking breeding barriers in Lycopersicon. 5. The inheritance of the unilateral incompatibility between L. peruvianum (L.) Mill. and L. esculentum Mill. and the genetics of its breakdown

Summary The validity of the current hypotheses on the inheritance of unilateral incompatibility is disputed and the importance of intrapopulational research on the inheritance of unilateral incompatibility is emphasized.Such research has been carried out on the unilateral incompatibility between L. peruvianum and L. esculentum with inbred material of L. peruvianum. The results indicate that in this species the inhibition of L. esculentum pollen tube growth, built up of distinct processes, is based on independent dominant genes, and that the breakdown of the phenomenon is a consequence of segregation of recessive alleles, the expressivity of at least some of these being influenced by environmental factors.Research demonstrating differences between self-incompatibility and interspecific pollen tube growth inhibition is reviewed and it is concluded from this and own research that the two phenomena are distinct.     

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.     

Molecular mechanism of the S-RNase-based gametophytic self-incompatibility in fruit trees of Rosaceae

Self-incompatibility (SI) is a major obstacle for stable fruit production in fruit trees of Rosaceae. SI of Rosaceae is controlled by the S locus on which at least two genes, pistil S and pollen S, are located. The product of the pistil S gene is a polymorphic and extracellular ribonuclease, called S-RNase, while that of the pollen S gene is a protein containing the F-box motif, SFB (S haplotype-specific F-box protein)/SFBB (S locus F-box brothers). Recent studies suggested that SI of Rosaceae includes two different systems, i.e., Prunus of tribe Amygdaleae exhibits a self-recognition system in which its SFB recognizes self-S-RNase, while tribe Pyreae (Pyrus and Malus) shows a non-self-recognition system in which many SFBB proteins are involved in SI, each recognizing subset of non-self-S-RNases. Further biochemical and biological characterization of the S locus genes, as well as other genes required for SI not located at the S locus, will help our understanding of the molecular mechanisms, origin, and evolution of SI of Rosaceae, and may provide the basis for breeding of self-compatible fruit tree cultivars.     

Genetic analysis of four self-incompatible lines in Brassica napus

Reciprocal hybridization between four self-incompatible lines of Brassica napus: 271, 181, 184 and ‘White Flower’, revealed incompatibility. The reciprocal F₁s obtained by bud pollination showed self-incompatible reactions, and no segregation for self-incompatibility was observed in all the reciprocal F₂ populations, indicating that lines 271, 181, 184 and ‘White Flower’ were genetically identical with regard to self-incompatibility. Observations of self-incompatibility in 17 hybrids from crosses between line 271 and 17 varieties of B. napus showed 10 of the F₁ hybrids to be self-compatible, while four were partially self-compatible and three were self-incompatible. Genetic analysis based on F₂ and BC₁ populations from five self-compatible F₁ hybrids and two self-incompatible F₁ hybrids suggested the existence of at least two loci controlling the self-incompatibility of line 271: one is the S locus, with dominant and recessive relationships between the S alleles, and the other is the suppressor (sp) of the S locus. The sp locus is genetically different from the S locus, and also shows dominant and recessive relationships between the sp alleles.     

果梅自交不亲和相关基因型(S、SFB/SLF)研究进展

果梅(Prunus mume Sieb. et Zucc.)原产于中国,为蔷薇科典型的配子体自交不亲和(GSI)品种。GSI至少由S位点的花柱S(S-RNase)基因和花粉S(SFB/SLF)基因决定。主要介绍了果梅GSI决定基因S基因和SFB/SLF基因的研究现状,并对基因型的鉴定技术AS-PCR的理论基础进行了介绍,对目前国内外已经鉴定出基因型的果梅品种进行了总结,这些将对果梅品种授粉树的合理配置和杂交育种的亲本选择具有重要的意义。     

Breaking breeding barriers in Lycopersicon. 2. Breakdown of self-incompatibility in L. peruvianum (L.) Mill.

Summary Attempts were made to break the self-incompatibility in L. peruvianum by selection of mutated S-alleles through large-scale self-pollination on clones with pollen which was mutagenically treated in different stages of development. Besides self-compatibility was searched for in inbred lines.The self-incompatibility in L. peruvianum was found to be very strict indeed. From more than 22,000 self-pollinations on 5 clones 1527 seeds were obtained, seed set being very erratic. The possible causes of this seed set are discussed. From 1527 seeds 1036 plants were raised and tested for self-compatibility.In the progenies of 4 clones from 823 plants tested, 7 were more or less self-compatible. It is concluded that this self-compatibility was spontaneous and not the result of the mutagenic treatment.In the progeny of the fifth clone plants were found which reacted as self-compatible at a temperature of about 40°C and as self-incompatible at lower temperatures. It is suggested that this character—a high temperature sensitive incompatibility reaction—is governed by one recessive gene.In inbred lines plants were found with a stable form of self-compatibility and also plants with a high temperature sensitive incompatibility reaction.The problems of an incompatibility research on inbred material are discussed. A brief survey is given of some of the characters found in inbred L. peruvianum.     

A two-loci system of gametophytic incompatibility in Solanum phureja and S. stenotomum

Summary A two-loci gametophytic incompatibility system is indicated in our experiments involving hybrids between S. phureja accessions and between S. stenotomum and S. phureja. The S locus is epistatic to the R locus. An allele R _fi at the latter locus when present in homozygous condition, leads to female incompatibility, independent of the genotype of the pollen. The two-loci system is assumed to have evolved from doubling the chromosome number of ancestral species with one locus for incompatibility. The irregularities observed in the studies are tentatively ascribed to recombining modifier complexes. These modifiers may be maintained in cultivated species owing to their preponderantly vegetative propagation.     

Breakdown of a hybridization barrier between Solanum pinnatisectum Dunal and potato using the S locus inhibitor gene (Sli)

Several attempts have been undertaken to exploit the resistance to late blight [Phytophthora infestans (Mont.) de Bary] of the Mexican diploid Solanum pinnatisectum Dunal (2n = 2x = 24). However, sexual hybridization between S. pinnatisectum and cultivated potatoes is almost impossible because of strict reproductive barriers. In this study, we first induced chromosome doubling of S. pinnatisectum for matching of the species-specific endosperm balance number (EBN), which is a genetic phenomenon responsible for normal endosperm development. We pollinated 4x (2EBN) S. pinnatisectum flowers with pollen from 2x (2EBN) clones carrying the S locus inhibitor gene (Sli), which originally was identified as an inhibitor of S-locus-controlled self-incompatibility in pollen of diploid potatoes. Nine putative hybrid plants were obtained from 613 pollinations, of which two plants were characterized. Both individuals were triploid hybrids with extreme resistance to P. infestans derived from S. pinnatisectum and showed an acceptable level of female fertility for backcrossing. Thus, utilization of the Sli gene, combined with chromosome-doubling for matching of the EBN, is proposed as a technique to overcome barriers to interspecific hybridization between Mexican 2x (1EBN) Solanum species and cultivated diploid potatoes.     

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.     

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.     

Progress on characterization of self-incompatibility in <Emphasis Type="Italic">Brassica napus</Emphasis> L.

Self-incompatibility (SI) is a widespread mechanism in flowering plants that promotes outbreeding and thereby increases genetic diversity. Recognition specificity in Brassica is achieved by the interaction of the female determinant S-receptor kinase (SRK) and its ligand, the male determinant S-locus protein 11 (SP11). The interaction between SP11 and SRK triggers the signaling cascade in an S-haplotype-specific manner and results in the rejection of self-pollen, but the signal components involved are still not well characterized. S haplotypes are widespread in self-compatible amphidiploid B. napus, and the interaction of heterozygous S haplotypes causes the loss of SI. This review highlights the recent advances made towards understanding the genetic analysis, distribution, and evolution of S haplotypes, the signal factors, and the potential of SI in B. napus hybrid breeding program.     

Polyacrylamide gel electrophoresis of S-RNase fragments for identification of S-genotypes of Japanese pear (Pyrus pyrifolia)

Japanese pear (Pyrus pyrifolia) exhibits gametophytic self-incompatibility (GSI) controlled by a complex and multiallelic S locus. The pistil-part product of the S locus is the polymorphic ribonuclease, S-RNase. Information on S-genotypes is important for the production and breeding of Japanese pears. Molecular analyses of S-genotypes of Japanese pear have been conducted with the CAPS (cleaved amplified polymorphic sequence) system; PCR amplification of S-RNase fragments by a common primer pair followed by digestion with restriction enzymes each of which cleaves a specific S haplotype. Here, we show that the separation of S-RNase fragments by polyacrylamide gel electrophoresis (PAGE) distinguishes four out of nine S haplotypes of Japanese pear without restriction digestion. S³-, S⁵-, S⁶- and S⁸-RNases were identified as distinct bands by PAGE. S³- and S⁵-RNases were separated by PAGE despite their identical fragment sizes. Using this system, three Japanese pear lines with unknown S-genotypes were analyzed. The newly determined S-genotypes of the lines were confirmed by CAPS analysis.     

A genetic analysis of self-incompatibility and double flowers in Potentilla fruticosa L.

Summary The self-incompatibility system in Potentilla fruticosa was investigated by examining pollen cytology, and by analysing intercrosses between two self-incompatible, cross-compatible cultivars of the species. The pollen was found to be binucleate, which is consistent with a single locus self-incompatibility system acting gametophytically in the pollen. This was confirmed by the results of the intercrosses. A proposed model for the inheritance of extra petals was tested by backcrossing selected F₁ hybrid plants to both of their parents. Non-random segregation of the double modifier (Dm) locus suggested linkage to the self-incompatibility locus (S). The model was accordingly modified to include this linkage.     

Location of the self-incompatibility gene on the almond linkage map

A progeny obtained from the almond cross ‘Ferragnès’בTuono’ (Prunus amygdalus Batsch) was used to study the self-incompatibility trait in three different ways: fruit set, pollen tube growth and stylar ribonuclease activity. As expected from the genotypes of the parents, all progeny appeared phenotypically as self-compatible. However, the progeny could be scored for the segregation of stylar ribonuclease isozymes and thus allowed the incompatibility locus to be placed on the almond linkage map.     

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.     

Identification of S-alleles using polymerase chain reaction-cleaved amplified polymorphic sequence of the S-locus receptor kinase in inbreeding lines of Brassica oleracea

Identification and DNA polymorphism of the S‐locus receptor kinasegene (SRK) was analysed by pollen tube tests, polymerase chain reaction‐cleaved amplified polymorphic sequence (PCR‐CAPS) and nucleotide sequencing. SRK‐specific primers that can distinguish class and class II S haplotypes amplified single DNA fragments of 900‐1050 bp. The DNA fragments of 22 inbred lines amplified with a class SRK‐specific primer pair determined seven types with HinfI and EcoRII. In addition, the DNA fragments of 17 inbred lines amplified with a class II SRK‐specific primer pair determined three types with Hinf1. Nucleotide sequencing of the DNA fragments amplified from 10S haplotypes showed that exons of the 3′‐end in SRK are highly conserved, and that there is much variation of the introns, which produced polymorphism of the band pattern in PCR‐CAPS profiles. The S haplotypes of the plants were determined by restriction analysis of PCR products and agreed with results based on pollen tube growth tests. The PCR‐CAPS analysis using specific primer pairs of SRK is considered to be useful for S allele identification in breeding programmes.     

Effect of humidity on intergeneric pollinations of iap (Inhibition of Alien Pollen) sorghum [Sorghum bicolor (L.) Moench]

The production of interspecific or intergeneric progeny involving Sorghum spp. is greatly enhanced by the presence of the iap (Inhibition of Alien Pollen) allele in sorghum [Sorghum bicolor (L.) Moench]. Variation in the expressivity of the iap phenotype has been observed in previous studies, leading to the hypothesis that the humidity during pollination is affecting the degree of alien pollen adhesion and pollen tube growth. The objective of this study was to determine the optimum humidity for maximum maize pollen tube growth on sorghum florets homozygous for iap. Growth chambers were used to create environments of 45, 65, and 85 % humidity with reciprocal crosses made between the 65 and 85 % humidity chambers. Maize pollen was dusted onto the stigmas of Tx3361 (iap iap) and ATx623 (Iap Iap). Pollen adhesion and germination were higher for pollinations with Tx3361 at all humidity levels but the greatest adhesion and germination was observed at 45 % humidity for Tx3361. Under this humidity, pollen tube growth to the style and ovary was observed. The results indicate that lower humidity maximizes maize pollen adhesion and germination on the stigmas of Tx3361. Analysis of the differences in adhesion between Tx3361 and ATx623 indicate that Iap affects pollen adhesion at the stigma surface and may be controlling pollen–pistil incompatibility in interspecific crosses in sorghum.     

Breaking breeding barriers in Lycopersicon. 3. Inheritance of self-compatibility in L. peruvianum (L.) Mill.

Summary A brief survey is given of the genetics of self-compatibilith in species with a one-locus gametophytic system of incompatibility.A study has been made of the genetics of the self-compatibility found in L. peruvianum.From the results of various test crosses and selfings and of cytological research it is concluded that self-compatibility in L. peruvianum can be based on different types of S-allele mutations, on addition of an S-allele bearing chromosome fragment, or on genes modifying the S-allele expressivity.The results further indicate that generation of new S-alleles is a frequently occurring phenomenon in inbred material of L. peruvianum and that pollen with an S-allele mutation or an extra chromosome fragment is less vital than normal pollen.A short notation for incompatibility genotypes is given.