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     

Evidence for tetrasomic inheritance in a tetraploid Solanum commersonii (+) S. tuberosum somatic hybrid through the use of molecular markers

In order to assess the potential for interspecific recombination between the cultivated Solanum tuberosum (tbr) and the sexually isolated wild species Solanum commersonii (cmm), genetic analysis of a F₂ progeny obtained by selfing one tetraploid cmm (+) tbr somatic hybrid was performed through molecular markers. For this purpose, the extent of disomic and/or tetrasomic inheritance of species-specific RAPD and AFLP markers was determined by following their segregation in a 90-genotype progeny, and testing all the possible segregation ratios in a selfed tetraploid progeny. The RAPD analysis performed using 16 primers revealed that the cmm-specific RAPDs were mainly (93.7%) duplex markers and were equally distributed between loci with a disomic (46.7%) and tetrasomic (53.3%) inheritance. The AFLP analysis led to the identification of 272 (58%) informative AFLPs, which were either cmm- or tbr-specific markers. About 63% of cmm-specific AFLPs were duplex loci, most of which (92.6%) were inherited as tetrasomic loci. As regards the tbr-specific AFLPs, the percentage of simplex loci (52.9%) was higher than that of duplex loci (32.6%), and among the latter most (88.5%) were inherited as tetrasomic loci. Overall, 130 duplex markers were found, of which 53.1% were cmm-specific and 46.9% were tbr-specific. Out of 130 markers, 18 (13.8%) were inherited as disomic, and 112 (86.2%) as tetrasomic, loci. This implies that the majority of duplex markers were located on chromosomes which at meiosis tend to randomly pair as bivalents or to form tetravalents. The total number of simplex loci was 119, and most of them (82.3%) were tbr-specific loci. In some cases the observed segregation ratios even allowed us to clearly determine whether a random chromosome or chromatid segregation was detected. This was the case of three cmm-specific RAPDs, 19 cmm- and 25 tbr-specific AFLPs, which fit a 20.8:1 or 2.5:1 ratio, both cases for which a clear random chromatid segregation can be assumed, since they represent the limit of segregation expected when the distance between the locus and the centromere always leads to a cross-over event. The percentage of ascertained crossing-over events was around 37% out of the tetrasomically inherited loci clearly identified (128 loci), a value indicating that the flow of genes from the sexually isolated S. commersonii to the cultivated potato is possible, for at least a large proportion of genes. Received: 23 July 2001 / Accepted: 9 August 2001     

Molecular marker-assisted introgression of the wild Solanum commersonii genome into the cultivated S. tuberosum gene pool

A breeding scheme involving ploidy and EBN manipulations was set up to overcome the interspecific barriers existing between the cultivated Solanum tuberosum and the wild species S. commersonii. Three backcross generations were obtained that were analyzed by means of molecular markers in order to verify the occurrence of recombination between homeologous chromosomes, the extent of the wild genome carried in each backcross, and the efficiency of introgressing useful genes. Twenty commersonii-specific RFLPs provided evidence for recombination on 5 out of 12 chromoso-mes; for the others no more than 1 commersonii-specific marker was found. Thirty-four commersonii-specific RAPDs and 61 commersonii-specific AFLPs were used to estimate the wild genome content in the BC₁, BC₂, and BC₃ generations. The mean value of commersonii-specific markers was 93% and 91% in the BC₁, 74% and 76% in the BC₂, and 31% and 26% in the BC₃ using RAPDs or AFLPs, respectively. Efficiency of the breeding scheme was evaluated by monitoring across these progenies the introgression of S. commersonii resistance to tuber soft rot caused by Erwinia carotovora. Eleven and five resistant genotypes were found among BC₂ and BC₃ hybrids, respectively. The same progenies were also evaluated for chromosome number and tuber traits. For all analyzed traits except stolon length, all BC₂ and BC₃ hybrids resembled the tuberosum type. In order to choose the best genotypes to obtain the following backcrosses, we performed, in each generation, a negative molecular-assisted selection against the wild genome combined with selection for resistance to Erwinia spp. and other traits. Received: 3 April 2000 / Accepted: 31 August 2000     

Utilization of UPLC/Q‐TOF‐MS‐Based Metabolomics and AFLP‐Based Marker‐Assisted Selection to Facilitate/Assist Conventional Breeding of Polygala tenuifolia

As one of the most important traditional Chinese medicine, the quality of Polygala tenuifolia is difficult to control and a new method must be established to facilitate/assist the breeding of P. tenuifolia. In this study, UPLC/Q‐TOF‐MS‐based metabolomics analysis was performed to determine the chemical composition and screen metabolite biomarkers according to agronomic traits. A total of 29 compounds and 18 metabolite biomarkers were found. AFLP‐based marker‐assisted selection (MAS) was used to identify molecular marker bands and screen characteristic bands associated with specific agronomic traits. 184 bands and 76 characteristic AFLP bands were found. The correlation network between compounds and characteristic AFLP bands was built, so we may directly breed certain P. tenuifolia herbs with special agronomic traits (or characteristic AFLP bands), which exhibit specific pharmacological functions depending on the content of the active compounds. The proposed method of metabolomics coupled with MAS could facilitate/assist the breeding of P. tenuifolia.     

Molecular markers linked to stem rot resistance in rice

Stem rot (Sclerotium oryzae) is an important disease constraint in Californian rice production. Measurement of resistance is laborious, and the low heritability of the trait limits the effectiveness of selection in breeding programs. Molecular markers linked to the trait would therefore provide a superior selection screen to assist in transferring resistance into improved cultivars. The genetics of resistance to stem rot was studied in the germplasm line 87-Y-550 (PI566666), which inherited its resistance from the wild species Oryza rufipogon. Four crosses of 87-Y-550 with susceptible lines were made and recombinant inbred lines of only the most-resistant and most-susceptible progeny within each cross were advanced for late-generation testing. Approximately 900 AFLP (amplified fragment length polymorphism) primer combinations were applied to resistant and susceptible bulks within each cross. One AFLP marker showed significant association with stem rot resistance and accounted for approximately 45.0% of the phenotypic variation in 59 progenies. This marker was mapped on rice chromosome 2 between the RFLP markers RZ166 and RG139 by using F₂-reference population information. The accuracy of AFLP marker mapping was validated by size and sequence comparison of AFLP bands from 87-Y-550 and the reference population. With the strategy of selective genotyping combined with a parental survey, two microsatellite markers, RM232 and RM251, on chromosome 3 were also found associated with stem rot resistance and accounted for 41.1% and 37.9% of the phenotypic variation, respectively. The multiple linear regression model included TAA/GTA167 on chromosome 2 and RM232 on chromosome 3 and cumulatively explained 49.3% of total variation. The molecular markers linked to stem rot resistance should facilitate selection for this recalcitrant trait in rice breeding programs by eliminating the need for early generation screening. Received: 27 March 2000 / Accepted: 4 June 2000     

Interspecific hybridization inBrassica: Application of flow cytometry for analysis of ploidy and genome composition in hybrid plants

Interspecific hybrids from the crosses betweenBrassica campestris, B. carinata, B. juncea andB. napus were obtained throughin vitro ovary and ovule culture. F₁ hybrids were studied morphologically and flow cytometry was used to estimate 2C nuclear DNA content both in parentalBrassica species and their hybrids. It was found that in comparison with the A genome, the B and the C genomes ofBrassica contained 26.9 % and 43.9 % more DNA, respectively. This finding may be used to distinguish interspecific hybrids containing various genome combinations. It was concluded that flow cytometric analysis of nuclear DNA content might be useful tool inBrassica breeding.     

RAPD analysis of the interspecific somatic hybrids: Solanum bulbocastanum (+) S. tuberosum

The diploid Mexican species S. bulbocastanum (blb) was used as a source of late blight resistance in somatic hybridization with the potato (S. tuberosum, tbr) dihaploid H-8105. The produced 2x blb (+) 2x tbr H-8105 somatic hybrids did not retain the blb parent's characteristic high resistance to P. infestans. The revealed aneuploidy of blb (+) tbr H-8105 hybrids indicated a possible loss of individual blb chromosome(s) carrying the resistance genes. Four hybrid clones differing in terms of their ploidy, morphology and growth potential were analysed for the presence of all twelve blb chromosomes (linkage groups). The RAPD markers assigned to particular chromosomes were selected on the basis of the linkage map of S. bulbocastanum constructed by Naess et al., Mol. Gen. Genom. 265 (2001) 694-704. Of the 86 markers analysed, twelve (14%) were common for blb and H-8105, while 34 (40%) and 40 (46%) markers were specific for the blb and H-8105 genome, respectively; this confirms the differences between the nuclear genomes of the two species. Seventeen markers (20%) present in one or the other parent were absent in the hybrids, and only one new marker was found in the hybrids. The poorly growing, aneuploid and chimeric hybrids had the same band profiles as the well growing, morphologically normal hybrids, except for two bands that were present only in normal hybrids. The presence of eleven blb linkage groups in the blb (+) tbr H-8105 hybrids was confirmed. The markers specific for the second linkage group (chromosome 2) of blb were not present in the RAPD patterns of the somatic hybrids analysed, suggesting a loss or rearrangement of this chromosome in the combined nuclear genome of the hybrids.     

Inheritance of frost resistance and winter hardiness in distant hybrids of wheat and amphiploids

The data on inheritance of frost resistance and winter hardiness of bread wheat lines obtained as a result of distant hybridization of wheat-rye and wheat-elymus amphiploids with durum and bread wheat were presented. It was shown that selection of the donors of valuable traits is sensible to make in later progenies of hybrids (F6-F7). So, it is possible to obtain the new initial breeding material for winter bread wheat selection with high frost tolerance, winter hardiness and early maturity. Hypotheses explaining the high frost resistance of hybrids are presented. The crosses of the octoploid amphiploids with durum wheat are more preferable for the alien traits introgression into wheat than the crosses with bread wheat.     

The role of domestication and maternal effects on seed traits of crop–wild sunflower hybrids (Helianthus annuus)

Hybridisation between crops and their wild relatives may promote the evolution of weeds. Seed germination and dormancy are the earliest life‐history traits and are highly influenced by the maternal parent. However, the ecological role of the maternal effect on seed traits in the evolution of crop–wild hybrids has received little attention. In this study, we test the relative importance of maternal and hybridisation effects on seed traits of the first generation of crop–wild sunflower hybrids (Helianthus annuus). Seed germination was tested in two wild populations with contrasting dormancy, two cultivated materials and their reciprocal crosses at four different times after harvest and three different temperatures. Seed germination at each of the four times, after ripening response and secondary dormancy were recorded along with four morphological traits. Additionally, the pericarp anatomy was analysed with light and scanning electron microscopy. We observed strong maternal effects on all seed traits. Seed germination, morphology and pericarp anatomy differed largely between the crop and wild seeds and these traits in the crop–wild hybrids resembled their female parent. Slight but significant hybridisation effects were observed in germination, mainly in seeds produced on wild plants. Crop hybridisation changed seed germination, the after ripening response and secondary dormancy in the crop direction. Morphological and anatomical traits associated with domestication strongly correlated with the observed differences in seed germination and dormancy in crop–wild sunflower hybrids. The large maternal effects along with the evolutionary divergence in seed traits were responsible for the large phenotypic differences observed in crop–wild hybrids with the same genetic composition. Wild‐like seed traits of hybrids suggest that there are no barriers to crop gene introgression at the seed level whereas crop‐like seed traits could be strongly selected against, conditioning the selection of traits expressed later in the life cycle and in the next generations.     

Identification of cytoplasmic ancestor gene-pools of <Emphasis Type="Italic">Musa acuminata</Emphasis> Colla and <Emphasis Type="Italic">Musa balbisiana</Emphasis> Colla and their hybrids by chloroplast and mitochondrial haplotyping

Cytoplasmically inherited characters such as resistance to viral and fungal diseases, determination of starch types, crop yield, resistance to low or high temperature often contribute to the advantageous phenotypic traits of plants. In the present study, our goal was to elucidate the genealogy of cytoplasmic genomes chloroplast and mitochondria in banana. Banana breeding is rather complicated because of the low fertility and mostly unknown origin of the edible cultivars, therefore, knowledge on the putative fertile ancestors of cytoplasmic genomes chloroplast and mitochondria would be beneficial for breeding programmes. Based on the established marker systems distinct species specific gene-pools could be identified for both chloroplast and mitochondrial genomes for Musa acuminata and Musa balbisiana wild types, respectively. Detailed analysis of the species specific chloroplast and mitochondrial gene-pools of M. acuminata and M. balbisiana revealed six chloroplast and seven mitochondrial gene-pools in the analysed accessions. Comparative analysis of the haplotypes revealed the presence of Primary Centers of origin for both chloroplast and mitochondrial genomes of both species supporting the idea of common origin of these genomes. Cytotypes representing combinations of M. acuminata chloroplast and mitochondrial gene-pools were identified in majority of the analysed hybrid cultivars. A single M. acuminata cytotype was present in the majority of the analysed cultivars, which combination was not detected in any of the wild types. On the other part a single balbisiana cytotype was identified participating in the formation of interspecies hybrids. The strong preference for the presence of certain cytoplasmic gene-pools in cultivars may indicate hundreds of years of natural as well as of farmers’ selection supplementing the phenotypic traits provided by the nuclear genome. Based on the present results the present day subspecies classification of M. acuminata is also discussed.     

STS markers linked to Phoma resistance genes of the Brassica B-genome revealed sequence homology between Brassica nigra and Brassica napus

The RFLP and AFLP techniques are laborious and expensive and therefore of limited use for marker-assisted selection, demanding a high throughput of samples in a short time. But marker-assisted selection is most useful for traits which are hard to score on single plants and influenced by environmental factors. Four RFLP and three AFLP markers have been found to be linked to genes of the B-genome of Brassica mediating resistance against Phoma lingam in oilseed rape. One RFLP and one AFLP marker were converted into three PCR-based STS markers: one of dominant, as well as one of codominant inheritance separated in a standard agarose gel and a third one of codominant inheritance to be separated in a polyacrylamide gel on an automated sequencer. As expected, the STS markers mapped at the same position as the original RFLP and AFLP markers. The STS markers are efficient in marker-assisted backcross programs of the resistant B-genome/Brassica napus recombinant lines with most of the tested oilseed rape varieties and breeding lines. More than 90% of the tested oilseed rape varieties and breeding lines exhibited no resistance marker alleles. The mapping results obtained with the markers, as well as comparative sequencing of the marker alleles, indicate synteny and homology between the B-genome resistance gene donors and B. napus in the region of the resistance genes. The location of the resistance genes in the B-genome/B. napus recombinant lines is most likely on the A genome. Thus the transfer of the B-genome resistance genes into Brassica campestris is also possible. Received: 9 December 1999 / Accepted: 21 June 2000     

Freezing tolerance and tuber production in selfed and backcross progenies derived from somatic hybrids between Solanum tuberosum L. and S. commersonii Dun.

 Selfed and backcross progenies developed from tetraploid somatic hybrids between Solanum tuberosum (tbr) and S. commersonii (cmm) were characterized for nonacclimated freezing tolerance (NA) and acclimation capacity (ACC) (two independent genetic components of freezing tolerance) under controlled environments. The segregation covered 28% and 71% of the parental range for NA and ACC, respectively, with the distribution skewed toward the tbr parent. Therefore, ACC appeared to be relatively easier to recover in the segregating generation. Some first backcross progeny had greater freezing tolerance than the cultivated parent primarily through the increase in ACC. When grown in the field, the improved freezing tolerance observed in the selfed progeny under controlled conditions was confirmed. Among NA, ACC, and freezing tolerance after acclimation (AA, which is the cumulative performance of NA and ACC), AA exhibited the highest correlation coefficient with field frost tolerance. In addition to freezing tolerance, vine maturity and tuber traits including tuber yield, tuber number per plant, mean tuber weight, and specific gravity were also segregating. No significant correlation between undesirable tuber traits and freezing tolerance was detected. Vine maturity and freezing tolerance were significantly correlated, so more careful selection for earliness was necessary in incorporating freezing tolerance. Yield comparable or superior to the backcross parent Wis AG 231 and an early Canadian cultivar, ‘Sable’, was found in many backcross progeny and some selfed progeny. The observed high yield can be attributed to the increase in mean tuber weight as well as tuber number. Moreover, a high portion of progeny had a specific gravity higher than 1.085, and some greater than 1.1. The implications derived from this study in breeding for freezing tolerance and further use of these materials are discussed. Received: 22 August 1998 / Accepted: 4 January 1999     

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.     

Production and characterization of somatic hybrids between upland cotton (<Emphasis Type="Italic">Gossypium hirsutum</Emphasis>) and wild cotton (<Emphasis Type="Italic">G. klotzschianum</Emphasis> Anderss) via electrofusion

Symmetric somatic hybrid plants between Gossypium hirsutum Coker 201 and G. klotzschianum were obtained through electrofusion. The fusion products were cultured in KM₈P medium supplemented with 2.685 M -naphthaleneacetic acid and 0.465 M kinetin, and the regenerated plants were morphologically, genetically, and cytologically characterized. Nuclear-DNA flow cytometric analysis revealed that the plants tested (31 of 40) had a relative DNA content close to the total DNA contents of the two parents. Subsequent genome DNA analysis using random amplified polymorphic DNA markers revealed 16 of 18 plants were true somatic hybrids. Cytological investigation of the metaphase root-tip cells of seven hybrids revealed there were 72–81 chromosomes in the hybrids, a value close to the expected 78 chromosomes. The morphology of the hybrids was distinct from that of the parents and from that of the regenerants from protoplasts of Coker 201. Somatic hybridization represents a potent and novel tool for transferring genomes of wild cottons containing economically important traits to cultivars in breeding programs. This is the first report on the regeneration of somatic hybrids via protoplast fusion in cotton.     

Parental genome composition and genetic classifications of derivatives from intergeneric crosses of Festuca mairei and Lolium perenne

Intergeneric hybridization between Festuca and Lolium has been a long-term goal of forage and turfgrass breeders to generate improved cultivars by combining stress tolerance of Festuca and rapid establishment of Lolium. However, wide-distance hybridizations usually result in the wild genome being eliminated from the hybrid due to incomplete chromosome pairing and crossovers. In this study, random amplified polymorphic DNA (RAPD) and simple sequence repeat (SSR) markers were used to detect the parental genome composition of F₁ hybrids and backcross, generated from crosses between Festuca mairei St. Yves (Fm) and Lolium perenne L. (Lp). Each of the hybrids exhibited integration of Fm and Lp genomes with varying levels of Fm/Lp genome ratios. However, cluster and principle component analyses of the progeny consistently revealed four groups depending on the amount of genome introgression from both parents. The parental genome composition and classifications of intergeneric progeny would be useful for breeding material selection. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Overcoming crossing barriers between nontuber-bearing and tuber-bearing Solanum species: towards potato germplasm enhancement with a broad spectrum of solanaceous genetic resources.

The first direct sexual hybrids between diploid nontuber-bearing species and diploid potato breeding lines are reported here. Three nontuberous species of Solanum, S. brevidens, S. etuberosum, and S. fernandezianum, were used for sexual crosses, achieved by a combination of rescue pollinations and embryo rescue. Initial hybrid selection was made using an embryo spot marker, followed by the evaluation of morphological and reproductive traits. Putative hybrids were first tested for resistance to potato leaf roll virus derived from the wild species, and then were tested with molecular markers using species-specific DNA probes. Finally, the tuberization of several 2x hybrids was tested for actual potato germplasm enhancement. These hybrids are unique in terms of their potential to enhance recombination between chromosomes of wild species and those of cultivated potatoes in germplasm utilization, and to exploit the genetic nature of tuber formation. The finding that nontuber-bearing Solanum spp. can be directly crossed with tuber-bearing species also has important implications for the regulatory aspects of the use of genetically modified organisms.     

Introgression of resistance to root-knot nematodes from wild Central American Solanum species into S. tuberosum ssp. tuberosum

 Crossing experiments were conducted to introduce resistance to the root-knot nematodes, Meloidogyne chitwoodi and M. fallax, from various polyploid Central American Solanum spp. into the cultivated potato, S. tuberosum ssp. tuberosum. The most effort was put into producing tetraploid hybrids through inter-EBN (Endosperm Balance Number) crosses. From the crosses of tetraploid S. tuberosum (4 EBN) with tetraploid S. stoloniferum and S. fendleri (both 2 EBN), few seeds were derived that led to viable plants. In vitro culture of immature seeds also yielded several hybrid plants. From crosses of diploid S. tuberosum (2 EBN) with hexaploid S. hougasii (4 EBN) four hybrids were obtained through in vitro culture. Backcrosses were made with selected hybrids and a variable number of seeds was produced depending on the hybrid genotype. The successful introgression of resistance into backcross populations is shown. A scheme is presented for the introgression of traits at a tetraploid level from allotetraploid Solanum species into autotetraploid S. tuberosum through sexual crosses. The relevance of EBN for potato breeding is discussed. Received: 25 November 1996 / Accepted: 14 February 1997     

Genetic analysis of the sugarcane (<Emphasis Type="Italic">Saccharum</Emphasis> spp.) cultivar ‘LCP 85-384’. I. Linkage mapping using AFLP,SSR, and TRAP markers

Tef is a cereal crop of cultural and economic importance in Ethiopia. It is grown primarily for its grain though it is also an important source of fodder. Tef suffers from lodging that reduces both grain yield and quality. As a first step toward executing a marker-assisted breeding program for lodging resistance and grain yield improvement, a linkage map was constructed using 151 F₉ recombinant inbred lines obtained by single-seed-descent from a cross between Eragrostis tef and its wild relative Eragrostis pilosa. The map was primarily based on microsatellite (SSR) markers that were developed from SSR-enriched genomic libraries. The map consisted of 30 linkage groups and spanned a total length of 1,277.4 cM (78.7% of the genome) with an average distance of 5.7 cM between markers. This is the most saturated map for tef to date, and for the first time, all of the markers are PCR-based. Using agronomic data from 11 environments and marker data, it was possible to map quantitative trait loci (QTL) controlling lodging, grain yield and 15 other related traits. The positive effects of the QTL identified from the wild parent were mainly for earliness, reduced culm length and lodging resistance. In this population, it is now possible to combine lodging resistance and grain yield using a marker-assisted selection program targeting the QTL identified for both traits. The newly developed SSR markers will play a key role in germplasm organization, fingerprinting and monitoring the success of the hybridization process in intra-specific crosses lacking distinctive morphological markers.     

Breeding for ”low-gossypol seed and high-gossypol plants” in upland cotton. Analysis of tri-species hybrids and backcross progenies using AFLPs and mapped RFLPs

This work aims at breeding upland cotton [Gossypium hirsutum L., 2(AD)₁ genome] with a reduced level of gossypol in the seeds for optimal food and feed uses, and a high gossypol level in the remaining organs for resistance to pests. Two tri-species Gossypium hybrids, (G. thurberi–G. sturtianum–G. hirsutum and G. hirsutum–G. raimondii–G. sturtianum) including G. sturtianum (2C₁) as a donor, G. thurberi (2D₁) and G. raimondii (2D₅) as a bridge species, were created. Recurrent selection initiated with these tri-species hybrids produced backcross (BC) progenies expressing the ”low-gossypol seed and high-gossypol plant” trait at different levels. We used AFLP markers to assess the genetic similarity among the germplasm and RFLP probes to tag the introgression of specific chomosome segments from the parental species. Five pairs of AFLP primers generated 477 fragments, among which 417 (87.4%) were polymorphic. The genetic similarity between the upland cotton and the wild species ranged from 29.5 to 43.2%, while similarity reached 80% between upland cotton and BC3 plants. Introgression of species-specific AFLPs was evident from all the parental species and confirmed the hybrid origin of the analyzed progenies. Southern-blot analysis based on 49 RFLP probes allowed us to trace the introgression of parental DNA segments in the tri-species hybrids and in three generations of backcross. Introgression was evident from 11, 8 and 7 linkage groups of G. sturtianum, G. raimondii and G. thurberi respectively. The types of introgression revealed by RFLP probes are discussed, and breeding schemes to enhance recombination are proposed. The ability to trace DNA segments of known chromosomal locations from the donor G. sturtianum through segregating generations is a starting point to map the ”low-gossypol seed and high-gossypol plant” traits. Received: 5 January 1999 / Accepted: 17 June 1999     

Genetic diversity and its relationship to hybrid performance and heterosis in rice as revealed by PCR-based markers

Ten elite inbred lines (four japonica, six indica), chosen from those widely used in the hybrid rice breeding program at Human Hybrid Rice Research Center in China, were crossed to produce all possible hybrids excluding reciprocals. The 45 F₁ hybrids along with the ten parents were evaluated for eight traits of agronomic importance, including yield potential, in a replicated field trial. The ten parents were analyzed with 100 arbitrary decamer oligonucleotide primers and 22 microsatellite (simple sequence repeats, SSRs) primer sets via polymerase chain reaction (PCR). Out of the 100 random primers used, 74 were informative and amplified 202 non-redundant bands (variants) with a mean of 2.73 bands per polymorphic primer. All 22 microsatellite primer sets representing 23 loci in the rice genome showed polymorphisms among the ten parents and revealed 90 alleles with an average of 3.91 per SSR locus. Cluster analysis based on Nei's genetic distance calculated from the 291 (202 RAPDs, 89 SSRs) non-redundant variants separated the ten parental lines into two major groups that corresponds to indica and japonica subspecies, which is consistent with the pedigree information. Strong heterosis was observed in hybrids for most of the traits examined. For the 43 diallel crosses (excluding 2 crosses not heading), yield potential, its components (including panicles per plant, spikelets per panicle and 1000-grain weight) and their heterosis in F₁ hybrids showed a significant positive correlation with genetic distance. When separate analyses were performed for the three subsets, yield potential and its heterosis showed significant positive correlations with genetic distance for the 15 indica x indica crosses and the 6 japonica x japonica crosses; however, yield potential and its heterosis were not correlated with genetic distance for the 22 indica x japonica crosses. Results indicated that genetic distance measures based on RAPDs and SSRs may be useful for predicting yield potential and heterosis of intra-subspecific hybrids, but not inter-subspecies hybrids.