Alloplasmic male-sterile <Emphasis Type="Italic">Brassica juncea</Emphasis> with <Emphasis Type="Italic">Enarthrocarpus lyratus</Emphasis> cytoplasm and the introgression of gene(s) for fertility restoration from cytoplasm donor species

A new cytoplasmic male sterility (CMS) source in Brassica juncea (2n = 36; AABB) was developed by substituting its nucleus into the cytoplasm of Enarthrocarpus lyratus (2n = 20; E(l)E(l)). Male sterility was complete, stable and manifested in either petaloid- or rudimentary-anthers which were devoid of fertile pollen grains. Male sterile plants resembled the euplasmic B. juncea except for slight leaf yellowing and delayed maturity. Leaf yellowing was due mainly to higher level of carotenoids rather than a reduction in chlorophyll pigments. Female fertility in male-sterile plants varied; it was normal in lines having rudimentary anthers but poor in those with petaloid anthers. Each of the 62 evaluated germplasm lines of B. juncea was a functional maintainer of male sterility. The gene(s) for male-fertility restoration ( Rf) were introgressed from the cytoplasm donor species through homoeologous pairing between A and E(l) chromosomes in monosomic addition plants (2n = 18II+1E(l)). The percent pollen fertility of restored F(1) ( lyr CMS x putative restorer) plants ranged from 60 to 80%. This, however, was sufficient to ensure complete seed set upon by bag selfing. The CMS ( lyr) B. juncea compared favourably with the existing CMS systems for various productivity related characteristics. However, the reduced transmission frequency of the Rf gene(s) through pollen grains, which was evident from the sporadic occurrence of male-sterile plants in restored F(1) hybrids, remains a limitation.     

Organelle DNA variation in parental<Emphasis Type="Italic"> Solanum</Emphasis> spp. genotypes and nuclear-cytoplasmic interactions in<Emphasis Type="Italic"> Solanum tuberosum</Emphasis> (+)<Emphasis Type="Italic"> S. commersonii</Emphasis> somatic hybrid-backcross progeny

Nuclear-cytoplasmic interactions can influence fertility and agronomic performance of interspecific hybrids in potato as well as other species. With the aim of assessing the potential value of a novel recombinant cytoplasm derived by interspecific somatic hybridization, backcross progeny were produced by crossing a somatic hybrid between Solanum tuberosum (tbr) and the wild incongruous species S. commersonii (cmm) with various potato clones. BC₁ clones were evaluated for male fertility and other agronomic traits. Male fertility clearly depended on the cross direction and the cytoplasm source. Genotypes with cytoplasms sensitive to nuclear genes derived from Solanum commersonii and inducing male sterility showed identical mtDNA composition, as based on mtDNA analyses with various PCR-based and RFLP markers. On the other hand, genotypes with cytoplasms not inducing male sterility in the presence of the cmm nuclear genes showed a different mtDNA organisation. Analysis of cpDNA confirmed similarity of cytoplasmic composition in CMS-inducing genotypes and clear differences with the others. Genotypes with recombinant cytoplasm induced by somatic hybridization generally showed similar agronomic performances in reciprocal hybrids with tbr cytoplasm, suggesting that the novel cytoplasm can be used in potato breeding.Contribution no. 24 from the Institute of Plant Genetics, Research Division of Portici     

Simple sequence repeat analyses of interspecific hybrids and MAALs of <Emphasis Type="Italic">Oryza </Emphasis><Emphasis Type="Italic">officinalis</Emphasis> and <Emphasis Type="Italic">Oryza sativa</Emphasis>

Wild rice is a valuable resource for the genetic improvement of cultivated rice (Oryza sativa L., AA genome). Molecular markers are important tools for monitoring gene introgression from wild rice into cultivated rice. In this study, Simple sequence repeat (SSR) markers were used to analyze interspecific hybrids of O. sativa-O. officinalis (CC genome), the backcrossing progenies and the parent plants. Results showed that most of the SSR primers (335 out of 396, 84.6%) developed in cultivated rice successfully amplified products from DNA samples of wild rice O. officinalis. The polymorphism ratio of SSR bands between O. sativa and O. officinalis was as high as 93.9%, indicating differences between the two species with respect to SSRs. When the SSR markers were applied in the interspecific hybrids, only a portion of SSR primers amplified O. officinalis-specific bands in the F(1) hybrid (52.5%), BC(1) (52.5%), and MAALs (37.0%); a number of the bands disappeared. Of the 124 SSR loci that detected officinalis-specific bands in MAAL plants, 96 (77.4%) showed synteny between the A and C-genomes, and 20 (16.1%) showed duplication in the C-genome. Sequencing analysis revealed that indels, substitution and duplication contribute to the diversity of SSR loci between the genomes of O. sativa and O. officinalis.     

Identification and fine mapping of <Emphasis Type="Italic">S-d</Emphasis>, a new locus conferring the partial pollen sterility of intersubspecific F<Subscript>1</Subscript> hybrids in rice (<Emphasis Type="Italic">Oryza sativa</Emphasis> L.)

The partial pollen abortion of hybrids between the indica and japonica subspecies of Asian cultivated rice is one of the major barriers in utilizing intersubspecific heterosis in hybrid rice breeding. Although a single hybrid pollen sterility locus may have little impact on spikelet fertility, the cumulative effect of several loci usually leads to a serious decrease in spikelet fertility. Isolating of the genes conferring hybrid pollen sterility is necessary to understand this phenomenon and to overcome the resulting genetic barrier. In this study, a new locus for F₁ pollen sterility, S-d, was identified on the short arm of chromosome 1 by analyzing the genetic effect of substituted segments of the near-isogenic line E11-5 derived from the japonica variety Taichung 65 (recurrent parent) and the indica variety Dee-geo-woo-gen (donor parent). The S-d locus was first mapped to a 0.8 cM interval between SSR markers PSM46 and PSM80 using a F₂ population of 125 individuals. The flanking markers were then used to identify recombinants from a population of 2,160 plants derived from heterozygotes of the primary F₂ population. Simultaneously, additional markers were developed from genomic sequence divergence in this region. Analysis of the recombinants in the region resulted in the successful mapping of the S-d locus to a 67-kb fragment, containing 17 predicted genes. Positional cloning of this gene will contribute to our understanding of the molecular basis for partial pollen sterility of intersubspecific F₁ hybrids in rice.     

Asynchronous meiosis in an interspecific hybrid of <Emphasis Type="Italic">Brachiaria ruziziensis</Emphasis> and <Emphasis Type="Italic">B. brizantha</Emphasis>

Male meiosis is generally synchronous in higher plants. The regulation of the cell cycle is still not well understood, and a powerful tool for gaining an understanding of this regulation is the development of mutations that affect cell-cycle synchrony. We report here asynchronous microsporogenesis in an interspecific hybrid between two important tropical grasses. In young spikelets of the interspecific hybrid 49.10% of anther meiocytes entered meiosis, exhibiting typical phases of the first and second divisions, while the other 50.90% showed distinctive features of early prophase. In older spikelets, anthers containing mature pollen grains also displayed meiocytes still undergoing meiosis. At this time, the latter cells were enclosed by the exine wall. Despite asynchrony, all cells completed meiosis. Old anthers contained only pollen grains that appeared to be in the same stage of development. Pollen fertility was estimated to be 52.76% in dehiscent anthers. An independent genetic control for meiosis synchrony and meiotic stages is suggested.     

Genetic characterization of a new cytoplasmic male sterility system (<Emphasis Type="Italic">hau</Emphasis>) in <Emphasis Type="Italic">Brassica </Emphasis><Emphasis Type="Italic">juncea</Emphasis> and its transfer to <Emphasis Type="Italic">B. napus</Emphasis>

A novel cytoplasmic male sterility (CMS) was identified in Brassica juncea, named as hau CMS (00-6-102A). Subsequently, the male sterility was transferred to B. napus by interspecific hybridization. The hau CMS has stable male sterility. Flowers on the A line are absolutely male sterile, and seeds harvested from the line following pollinations with the maintainer gave rise to 100% sterile progeny. The anthers in CMS plants are replaced by thickened petal-like structures and pollen grains were not detected. In contrast, in other CMS systems viz. pol, nap, tour, and ogu, anthers are formed but do not produce viable pollen. The sterility of hau CMS initiates at the stage of stamen primordium polarization, which is much earlier compared with the other four CMS systems. We have successfully transferred hau CMS from B. juncea to B. napus. Restorer lines for pol, ogu, nap, and tour CMS systems were found to be ineffective to restore fertility in hau CMS. Sixteen out of 40 combinations of mitochondrial probe/enzyme used for RFLP analysis distinguished the hau CMS system from the other four systems. Among these sixteen combinations, five ones alone could distinguish the five CMS systems from each other. The evidence from genetic, morphological, cytological and molecular studies confirmed that the hau CMS system is a novel CMS system. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Mapping of yield-related QTLs in pepper in an interspecific cross of <Emphasis Type="Italic">Capsicum annuum</Emphasis> and <Emphasis Type="Italic">C. frutescens</Emphasis>

An advanced backcross QTL study was performed in pepper using a cross between the cultivated species Capsicum annuum cv. Maor and the wild C. frutescens BG 2816 accession. A genetic map from this cross was constructed, based on 248 BC(2) plants and 92 restriction fragment length polymorphism (RFLP) markers distributed throughout the genome. Ten yield-related traits were analyzed in the BC(2) and BC(2)S(1) generations, and a total of 58 quantitative trait loci (QTLs) were detected; the number of QTLs per trait ranged from two to ten. Most of the QTLs were found in 11 clusters, in which similar QTL positions were identified for multiple traits. Unlike the high percentage of favorable QTL alleles discovered in wild species of tomato and rice, only a few such QTL alleles were detected in BG 2816. For six QTLs (10%), alleles with effects opposite to those expected from the phenotype were detected in the wild species. The use of common RFLP markers in the pepper and tomato maps enabled possible orthologous QTLs in the two species to be determined. The degree of putative QTL orthology for the two main fruit morphology traits-weight and shape-varied considerably. While all eight QTLs identified for fruit weight in this study could be orthologous to tomato fruit weight QTLs, only one out of six fruit shape QTLs found in this study could be orthologous to tomato fruit shape QTLs.     

<Emphasis Type="Italic">Brassica napus</Emphasis> lines with rearranged <Emphasis Type="Italic">Arabidopsis</Emphasis> mitochondria display CMS and a range of developmental aberrations

Numerous Brassica napus (+) Arabidopsis thaliana somatic hybrids were screened for male sterility and aberrant flower phenotypes. Nine hybrids were selected and backcrossed recurrently to B. napus. The resulting lines displayed stable maternal inheritance of flower phenotypes. Nuclear and organellar genomes were characterized molecularly using RFLP analysis. No DNA from A. thaliana was found in the nuclear genome after six back-crosses, whilst the mitochondrial genomes contained rearranged DNA from both A. thaliana and B. napus. Each line tested had a unique RFLP pattern of the mitochondrial DNA (mtDNA) that remained unchanged between the BC(3) and BC(6) generation. The plastid genomes consisted of B. napus DNA. Five lines of the BC(5) generation were subjected to more comprehensive investigations of growth, morphology and fertility. On the basis of these investigations, the five CMS lines could be assigned to two groups, one represented by three lines displaying reduced vegetative development, complete male sterility, and homeotic conversions of stamens into feminized structures. The second group, represented by the other two lines, were not completely male-sterile but still displayed severely affected flower morphologies. These two lines did not display any reduction in vegetative development. For both groups only stamens and petals suffered from the morphological and functional aberrations, while the sepals and pistils displayed normal morphology. All plants were fully female-fertile. Different rearrangements of the mitochondrial genome disturbed nuclear-mitochondrial interactions and led to various types of aberrant growth and flower development. The existence of numerous CMS lines with different mitochondrial patterns involving a species with a sequenced genome offers new opportunities to investigate the genetic regulation of CMS and its associated developmental perturbations.     

A genetic linkage map of grape,utilizing <Emphasis Type="Italic">Vitis rupestris</Emphasis> and <Emphasis Type="Italic">Vitis arizonica</Emphasis>

A genetic linkage map of grape was constructed, utilizing 116 progeny derived from a cross of two Vitis rupestris x V. arizonica interspecific hybrids, using the pseudo-testcross strategy. A total of 475 DNA markers-410 amplified fragment length polymorphism, 24 inter-simple sequence repeat, 32 random amplified polymorphic DNA, and nine simple sequence repeat markers-were used to construct the parental maps. Markers segregating 1:1 were used to construct parental framework maps with confidence levels >90% with the Plant Genome Research Initiative mapping program. In the maternal (D8909-15) map, 105 framework markers and 55 accessory markers were ordered in 17 linkage groups (756 cM). The paternal (F8909-17) map had 111 framework markers and 33 accessory markers ordered in 19 linkage groups (1,082 cM). One hundred eighty-one markers segregating 3:1 were used to connect the two parental maps' parents. This moderately dense map will be useful for the initial mapping of genes and/or QTL for resistance to the dagger nematode, Xiphinema index, and Xylella fastidiosa, the bacterial causal agent of Pierce's disease.     

Molecular mapping and inheritance of restoration of fertility (<Emphasis Type="Italic">Rf</Emphasis>) in A4 hybrid system in pigeonpea (<Emphasis Type="Italic">Cajanus cajan</Emphasis> (L.) Millsp.)

Key message

We report molecular mapping and inheritance of restoration of fertility (Rf) in A4 hybrid system in pigeonpea. We have also developed PCR-based markers amenable to low-cost genotyping to identify fertility restorer lines.

Abstract

Commercial hybrids in pigeonpea are based on A4 cytoplasmic male sterility (CMS) system, and their fertility restoration is one of the key prerequisites for breeding. In this context, an effort has been made to understand the genetics and identify quantitative trait loci (QTL) associated with restoration of fertility (Rf). One F₂ population was developed by crossing CMS line (ICPA 2039) with fertility restorer line (ICPL 87119). Genetic analysis has shown involvement of two dominant genes in regulation of restoration of fertility. In parallel, the genotyping-by-sequencing (GBS) approach has generated ~?33 Gb data on the F₂ population. GBS data have provided 2457 single nucleotide polymorphism (SNPs) segregating across the mapping population. Based on these genotyping data, a genetic map has been developed with 306 SNPs covering a total length 981.9 cM. Further QTL analysis has provided the region flanked by S8_7664779 and S8_6474381 on CcLG08 harboured major QTL explained up to 28.5% phenotypic variation. Subsequently, sequence information within the major QTLs was compared between the maintainer and the restorer lines. From this sequence information, we have developed two PCR-based markers for identification of restorer lines from non-restorer lines and validated them on parental lines of hybrids as well as on another F₂ mapping population. The results obtained in this study are expected to enhance the efficiency of selection for the identification of restorer lines in hybrid breeding and may reduce traditional time-consuming phenotyping activities.

     

A Diploid,Interspecific, Fertile Hybrid from Cultivated Sorghum, <Emphasis Type="Italic">Sorghum Bicolor</Emphasis>, and the Common Johnsongrass Weed <Emphasis Type="Italic">Sorghum Halepense</Emphasis>

Valuable agronomic traits are often present but inaccessible in the wild relatives of cultivated crop species. Utilization of wild germplasm depends on the production of fertile interspecific hybrids. Several unsuccessful attempts have been made to hybridize cultivated sorghum with its wild relatives to broaden its genetic base and enhance agronomic value. The successful approach used in this study employed the nuclear male sterility gene ms3 to generate a diploid fertile hybrid between the diploid cultivated sorghum (Sorghum bicolor (L) Pers.) and its weedy tetraploid wild relative Johnsongrass (Sorghum halepense (L.) Pers.). Eight sorghum plants were selected from a Nebraska stiff stalk collection that contains the male sterility gene ms3 and were used as the female parent. About 36,000 florets of male sterile sorghum were pollinated with Johnsongrass pollen to produce an average of one well-developed and 180 severely shriveled seed/18,000 crosses. The well-developed seed gave rise to a self-fertile diploid, while none of the shriveled seed were able to germinate. The F₁ hybrid was confirmed by using cultivated sorghum SSR markers and was selfed to produce an F₂ population. A sub-sample of 96 segregating F₂ plants was examined with 36 sorghum polymorphic SSR markers. Thirty-four markers showed a normal 1:2:1 segregation ratio, evidence of normal recombination across the genome. Preliminary results showed that several desirable traits from Johnsongrass, including resistance to greenbug and chinch bug and adaptability to cold temperatures, were expressed in the resulting progenies. These observations suggest that speciation within the genus Sorghum, giving rise to widely divergent phenotypes, is effected largely by ploidy-maintained crossing barriers but apparently not by extensive genomic divergence.     

Detection of hybridization between two loach species (<Emphasis Type="Italic">Paramisgurnus dabryanus</Emphasis> and <Emphasis Type="Italic">Misgurnus anguillicaudatus</Emphasis>) in wild populations

Artificial interspecific hybrids between large scale loach P. dabryanus and tetraploid pond loach M. anguillicaudatus (Cobitidae, Cypriniformes) are viable. To detect the occurrence of possible natural hybridization, genetic analyses by using microsatellite markers were performed for natural populations of large scale loach and pond loach, the reciprocal laboratory hybrids, and “supposed hybrids” with ambiguous morphology. The fertility of the artificial hybrids was also tested. At one diagnostic microsatellite (Mac50), one out of 20 “supposed hybrids” was identified to be F₁ hybrid between the two loach species because it had the same genotype as that of the laboratory hybrids. The triploid hybrids between the two species were confirmed to be female-sterile. The results show that rare hybridization has occurred between diploid large scale loach and tetraploid pond loach in nature although it may have little effect in genetic introgression. This study is helpful for fish conservation and encourages further investigation on natural hybridization and introgression of loaches.     

Genetic analysis of loci associated with partial resistance to <Emphasis Type="Italic">Sclerotinia sclerotiorum</Emphasis> in rapeseed (<Emphasis Type="Italic">Brassica napus</Emphasis> L.)

Sclerotinia stem rot is the most devastating disease of rapeseed (Brassica napus L.) in China. Quantitative trait loci (QTLs) involved in resistance to Sclerotinia sclerotiorum were detected in a rapeseed population of 128-F(2:3) families derived from a cross between the male sterility restorer line H5200 and a partial resistant line Ning RS-1. A total of 107 molecular markers including 72 RFLPs, 30 AFLPs, 3 SSRs and 2 RAPDs were employed to construct a genetic linkage map with 23 linkage groups covering 1,625.7 cM with an average space of 15.2 cM. Resistance was assessed empirically at two developmental stages: with a detached leaf inoculation at the seedling stage and in vivo stem inoculation at the mature plant stage. The observed resistance was scored for each plant as leaf resistance at the seedling stage (LRS) and stem resistance at the mature plant stage (SRM). A total of 13 loci were identified by one-way ANOVA and six QTLs were detected with MapMaker-QTL. We found that three of the six QTLs were associated with leaf resistance at the seedling stage and collectively accounted for 40.7% of the total phenotypic variation, each accounting for 23.2%, 16.6% and 13.6% respectively. Three QTLs were found corresponding to the disease resistance at the mature plant stage, explaining 49.0% of the phenotypic variation. Epistasis was observed for the resistance and the additive by additive interactions were the predominant type of epistasis. It was concluded that both single-locus QTLs and epistatic interactions played important roles in Sclerotinia resistance in rapeseed.     

Genetic mapping of local adaptation along the altitudinal gradient in <Emphasis Type="Italic">Abies sachalinensis</Emphasis>

Understanding the genetic bases of local adaptation in dominant conifer species is critical in predicting the impacts of rapid climate change on forest ecosystems. However, the genetic basis of adaptation is not yet fully understood due to the huge and complex genomes of conifers and the unavailability to date of suitable crossing material. In this study, we constructed a linkage map for Abies sachalinensis (2n = 24) and investigated quantitative trait loci (QTLs) associated with local adaptation along an altitudinal gradient. A segregating population of 239 seedlings was produced from a cross between two F₁ hybrids (high-altitude × low-altitude genotypes). QTL mapping of phenological and growth traits was performed using a pseudo-testcross strategy with linkage maps based on 1251 single-nucleotide polymorphism (SNP) and three simple sequence repeat (SSR) markers. Two maps consisting of 12 linkage groups with an average marker interval of ca. 3 cM were constructed for each parent. The total lengths of the maps were 1861 and 1949 cM. A permutation test identified four significant QTLs and 11 additional suggestive QTLs, with high logarithm of odds (LOD) scores (> 3.0). This is the first highly saturated linkage map produced for Abies taxa. Our results suggest that spring bud phenology is controlled by several QTLs with moderate effects. The use of the mapping population created by crossing two hybrids (high × low altitude genotypes) and numerous SNP markers enabled us to investigate the genetic basis of adaptive traits in conifer species.     

Genetic architecture of male fertility restoration of <Emphasis Type="Italic">Triticum timopheevii</Emphasis> cytoplasm and fine-mapping of the major restorer locus <Emphasis Type="Italic">Rf3</Emphasis> on chromosome 1B

Key message

Restoration of fertility in the cytoplasmic male sterility-inducing Triticum timopheevii cytoplasm can be achieved with the major restorer locus Rf3 located on chromosome 1B, but is also dependent on modifier loci.

Abstract

Hybrid breeding relies on a hybrid mechanism enabling a cost-efficient hybrid seed production. In wheat and triticale, cytoplasmic male sterility based on the T. timopheevii cytoplasm is commonly used, and the aim of this study was to dissect the genetic architecture underlying fertility restoration. Our study was based on two segregating F₂ triticale populations with 313 and 188 individuals that share a common female parent and have two different lines with high fertility restoration ability as male parents. The plants were cloned to enable replicated assessments of their phenotype and fertility restoration was evaluated based on seed set or staining for pollen fertility. The traits showed high heritabilities but their distributions differed between the two populations. In one population, a quarter of the lines were sterile, conforming to a 3:1 segregation ratio. QTL mapping identified two and three QTL in these populations, with the major QTL being detected on chromosome 1B. This QTL was collinear in both populations and likely corresponds to Rf3. We found that Rf3 explained approximately 30 and 50% of the genotypic variance, has a dominant mode of inheritance, and that the female parent lacks this locus, probably due to a 1B.1R translocation. Taken together, Rf3 is a major restorer locus that enables fertility restoration of the T. timopheevii cytoplasm, but additional modifier loci are needed for full restoration of male fertility. Consequently, Rf3 holds great potential for hybrid wheat and triticale breeding, but other loci must also be considered, either through marker-assisted or phenotypic selection.

     

Interspecific hybridization of <Emphasis Type="Italic">Prunus persica</Emphasis> with <Emphasis Type="Italic">P. armeniaca</Emphasis> and <Emphasis Type="Italic">P. salicina</Emphasis> using embryo rescue

Embryo rescue technique was used successfully to produce interspecific hybrids by crossing peach (P. persica) as a female parent with apricot (P. armeniaca) and plum (P. salicica). In those crosses that had ‘Yuhualu’ or ‘Zhonghuashoutao’ as female parents, hybrid embryos aborted from the 7th or 8th week after pollination mainly due to post-pollination incompatibility. An embryo rescue protocol was established to rescue such embryos and recover hybrid plants. Modified half-strength MS medium containing 4 mg l⁻¹ 6-BA and 0.5 mg l⁻¹ IBA produced up to 90% germination in the embryos. Modified MS medium with 1.0 mg l⁻¹ 6-BA and 1.0 mg l⁻¹ IBA gave the highest bud induction and multiplication whereas modified MS medium containing 0.5 mg l⁻¹ IAA and 0.2 mg l⁻¹ NAA gave the best rooting percentage. All the hybrids obtained using this embryo rescue technique were verified using simple sequence repeat (SSR) markers. A series of pollen treatments were carried out to partially overcome pre-pollination incompatibility, and it was found accidentally that pollen treatment with electrostatic field not only improved pollen germination but also increased the multiplication coefficient of embryo-induced shoots.     

Diploid hybrids between allotetraploid wild potato species <Emphasis Type="Italic">Solanum acaule</Emphasis> Bitt., <Emphasis Type="Italic">S. stoloniferum</Emphasis> Schltdl. and dihaploids of <Emphasis Type="Italic">S. tuberosum</Emphasis> L.

The possibility to obtain diploid hybrids by pollination of allotetraploid wild potato species Solanum acaule and S. stoloniferum plants with fertile pollen of S. tuberosum dihaploids was demonstrated for the first time. Dihaploid hybrids have arisen with comparatively high frequency (from 12.5 to 33.3%). They were characterized by high regularity of meiosis and high fertility. They easily crossed with S. tuberosum dihaploids, forming viable progeny. This seems prospective for effective introgression of valuable genetic gene pool of wild allotetraploid potato species in breeding material of S. tuberosum on the diploid level.     

<Emphasis Type="Italic">Rf5</Emphasis> is able to partially restore fertility to Honglian-type cytoplasmic male sterile <Emphasis Type="Italic">japonica</Emphasis> rice (<Emphasis Type="Italic">Oryza sativa</Emphasis>) lines

Three-line japonica hybrids have been developed mainly on Chinsurah Boro II (BT)-type cytoplasmic male sterile (CMS) lines of Oryza sativa L., but the unstable sterility of some BT-type CMS lines, and the threat of genetic vulnerability when using a single cytoplasm source, have inhibited their use in rice cultivation. Previously, the sterility of Honglian (HL)-type japonica CMS lines derived from common red-awned wild rice (Oryza rufipogon) has been proven to be more stable than that of BT-type japonica CMS lines. Here, we genetically characterized HL-type japonica CMS lines and the restorer-of-fertility (Rf) gene for breeding HL-type japonica hybrids. HL-type japonica CMS lines displayed stained abortive pollen grains, unlike HL-type indica CMS lines. The BT-type japonica restorer lines, which contain Rf, had different capabilities to restore HL-LiuqianxinA (HL-LqxA), an HL-type japonica CMS line, and the restorers for the HL-type japonica CMS lines could be selected from the preexisting BT-type japonica restorers in rice production. A genetic analysis showed that the restoration of normal fertility to HL-LqxA was controlled by a major gene and was affected by minor effector genes and/or modifiers. The major Rf in SiR2982, a BT-type japonica restorer, was mapped to a ~100-kb physical region on chromosome 10, and was demonstrated to be Rf5 (Rf1a) by sequencing. Furthermore, Rf5 partially restored fertility and had a dosage effect on HL-type japonica CMS lines. These results will be helpful for the development of HL-type japonica hybrids.     

Post-pollination hybridization barriers in <Emphasis Type="Italic">Nicotiana</Emphasis> section <Emphasis Type="Italic">Alatae</Emphasis>

Nicotiana section Alatae contains eight species with variable flower sizes and morphologies. Section members readily hybridize in the glasshouse, but no hybrids have been observed in natural sympatric and parapatric populations. To investigate interspecific crossing relationships with respect to mechanisms preventing hybridization, all members of section Alatae were intercrossed in a complete diallel. We found positive correlation between the pistil length of the pollen donor and interspecific seed set relative to the conspecific cross. Pollen tube growth rate and pollen donor pistil length were positively correlated as well. Furthermore, pollen from short-pistil members of section Alatae could only grow a maximum distance proportional to, but greater than, their own pistil lengths. Our results show that pollen tube growth capacity (i.e., rate and distance), provides a hybridization barrier in long-pistil species × short-pistil species crosses. We also found another hybridization barrier not specifically related to pollen tube growth capacity in short-pistil species × long-pistil species. Taken together, these barriers can generally be described by a ‘pistil-length mismatch’ rule; in section Alatae, pollen has the most success fertilizing ovules from species with pistil lengths similar to their own. This rule could contribute to hybridization barriers in Section Alatae because the species display dramatically different pistil lengths. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.