Influence of A1 cytoplasmic substitution on the downy-mildew incidence of pearl millet

Large-scale cultivation of pearl millet [Pennisetum glaucum (L.) R. Br. F₁ hybrids in India has led to increased incidence of downy-mildew (Sclerospora graminicola). There is concern that the A₁ male-sterile cytoplasm used in all the hybrids released so far is responsible for this increase. The influence of A₁ malesterile cytoplasm on downy-mildew incidence in pearl millet was studied by comparing the disease reaction of 40 pairs of F₁ hybrids, each pair carrying respectively a₁ male-sterile and normal B cytoplasm. Mean downy-mildew incidence was similar in the hybrids carrying either A₁ male-sterile or B cytoplasm. The general combining ability of lines with and without A₁ cytoplasm was found to be similar for downy-mildew incidence. These results indicated that in pearl millet A₁ cytoplasm is not associated with increased downymildew incidence. The possible danger of using only one source of cytoplasm has been briefly discussed.     

Assessment of cytoplasmic differences of near-isonuclear male-sterile lines in pearl millet

Four near-isonuclear polycytoplasmic versions of 81A and two of Pb 402A male-sterile lines of pearl millet (Pennisetum typhoides) were used in factorial matings with five inbred male testers in different combinations in three sets. The cytoplasmic differences were studied for several agronomic traits using mean values and general combining effects (gca) of male-sterile lines, and specific combining ability effects of hybrids. The fertility/ sterility behaviour of different male-sterile lines in crosses with common male parents was also studied. Significant differences among near-isonuclear polycytoplasmic lines were observed in mean values for a few traits such as plant height, leaf length and peduncle length, but the differences for combining ability were more pronounced. The A₃ cytoplasm was a better general combiner than the A₂ cytoplasm for grain yield and both A₂ and A₃ cytoplasms were better general combiners for leaf length and peduncle length. In addition, superiority of A₃ cytoplasm for gca was observed for plant height and ear characters over the A₂ cytoplasm in set II. A differential behaviour of cytoplasms, both in combination with a common pollinator and across pollinators, was observed for several traits. The results provide evidence for the distinctiveness of different cytoplasmic sources in pearl millet and for the influence of cytoplasmic factors on the phenotypic expression of nuclear genes. A diversification of male sterility sources in the breeding of pearl millet hybrids is suggested.     

Downy mildew incidence of pearl millet hybrids with different male-sterility inducing cytoplasms

The use of different sources of cytoplasmic male sterility (CMS) in hybrid seed production of pearl millet [Pennisetum glaucum (L.) R. Br.] is advocated to avoid possible disease epidemics occurring due to cytoplasmic uniformity. The effects of commercially unexploited, but potentially exploitable, sources of CMS, like A₂, A₃ and A₄, on downy mildew [Sclerospora graminicola (Sacc.) Schroet] incidence were studied by using the disease incidence of isonuclear hybrids with male-sterile and fertile cytoplasm. The mean downy mildew incidence of hybrids carrying different male-sterile cytoplasm was similar to that of hybrids retaining the fertile cytoplasm. The cytoplasm accounted for only 0.6% of the total variation and its effect was non-significant; pollinators could explain most of the variation in determining the disease incidence of hybrids. This suggested that these male-sterile cytoplasms are not linked to downy mildew susceptibility and thus can be exploited commercially to broaden the cytoplasmic base of the male-sterile lines and, ultimately, of hybrids.     

Cytogenetics of double cross hybrids between Pennisetum americanum — P. purpureum amphiploids and P. americanum x Pennisetum squamulatum interspecific hybrids

Summary Pearl millet, Pennisetum americanum L. Leeke-napiergrass, Pennisetum purpureum Schum. amphiploids (2n=42) were crossed with pearl millet X Pennisetum squamulatum Fresen. interspecific hybrids (2n=41) to study the potential of germplasm transfer from wild Pennisetum species to pearl millet. These two interspecific hybrids were highly cross-compatible and more than two thousand trispecific progenies were produced from 17 double crosses. All doublecross hybrids were perennial and showed a wide range of morphological variations intermediate to both parents in vegetative and inflorescence characteristics. Some crosses resulted in sublethal progenies. Chromosomes paired mainly as bivalents (¯x15.88) or remained as univalents. At metaphase I, trivalents, quadrivalents, an occasional hexavalent and a high frequency of bivalents indicated some homeology among the genomes of the three species. Delayed separation of bivalents, unequal segregation of multivalents, lagging chromosomes, and chromatin bridges were observed at anaphase I. Although approximately 93% of the double-cross hybrids were male-sterile, pollen stainability in male-fertile plants ranged up to 94%. Seed set ranged from 0 to 37 seed per inflorescence in 71 plants under open-pollinated conditions. Apomictic embryo sac development was observed in double-cross progenies when crosses involved a pearl millet x P. squamulatum apomictic hybrid as pollen parent. These new double-cross hybrids may serve as bridging hybrids to transfer genes controlling apomixis and other plant characteristics from the wild Pennisetum species to pearl millet.     

Transfer of germ plasm from the secondary to the primary gene pool in pennisetum

Summary Germ plasm from the A-genome of Pennisetum purpureum Schum. (AABB) of the secondary gene pool was transferred to cultivated pearl millet (AA) [P. glaucum (L.) R. Br.] by pollinating cytoplasmicnuclear male-sterile (cms) pearl millet with fertile allohexaploid pearl millet x P. purpureum hybrids (AAAABB). Certain allohexaploids used as pollinators on cms pearl millet resulted in 14-chromosome diploid pearl millet progenies. Three types of diploid pearl millet plants were produced in addition to the expected 28-chromosome AAAB-genome plants: (1) cms plants with only the A-genome, (2) cms plants with the A- and A-genomes, and (3) fertile plants with the A- and A-genomes. The latter group has allowed the utilization of genes for fertility restoration, stiff stalk, maturity, height, and morphological characteristics from the A-genome of P. purpureum in the pearl millet breeding program. Production of monoploid gametes by the allohexaploids appeared to be genetically controlled.     

Cytoplasmic-nuclear male sterility in pearl millet: comparative RFLP and transcript analyses of isonuclear male-sterile lines

The identification of diagnostic cytoplasmic molecular markers is of prime interest to pearl millet breeders wishing to identify sources of cytoplasmic-nuclear male sterility (CMS) which can be used as an alternative to the single source currently used in the production of F₁ hybrid seed. Here, we report the classification of five pearl millet CMS sources based on RFLP analysis of isonuclear lines carried out using mitochondrial gene-specific DNA probes in combination with eight restriction endonucleases. On the basis of RFLP data, the five CMS cytoplasms can be distinguished from each other and from the isonuclear fertile cytoplasm. In addition, based on cox1, cox3, atp6 and atp9 polymorphisms, these lines can be classified into two major groups: one corresponds to A₅, A_egp, A_v and A₁ cytoplasms, and the other consists of the A₄ cytoplasm. Our results suggest that a rearrangement involving the cox1 gene might be related to CMS in the first group (A₅, A_egp, A_v and A₁), whereas a rearrangement within the atp6/cox3 cluster region might be related to CMS in the second group (A₄).     

Mitochondrial DNA Polymorphisms Revealed by RAPD Assays Distinguish the Male-sterile and Male-fertile Cytoplasms in Pearl Millet

Diversification of cytoplamic male sterile (CMS) sources is of considerable significance in pearl millet, considering that almost all the commercially cultivated hybrids, particularly in India, are based on a single CMS source, A₁. We analyzed the mitochondrial DNA (mtDNA) polymorphisms among five pearl millet CMS sources (A₁ to A₅) and a male-fertile maintainer (B) line, all in an isonuclear background. Analysis using 21 random primers led to identification of polymorphic bands specific to the A₁, A₂, A3 and A₅ CMS lines. Two RAPD primers, OP-G12 and OP-G19, in combination were able to distinguish all the male-sterile and male-fertile cytoplasms. Highly effective for this purpose also were four RAPD markers, OP-B7, OP-D8, OP-F10 and OP-G12. Cluster analysis, followed by bootstrap analysis, of the mtDNA dataset revealed two distinct clusters: cluster-I comprising the A₁, A₂, A₃ CMS lines and the male-fertile line, and cluster-II comprising the A₄ and A₅ CMS lines.     

<Emphasis Type="Italic">Fusarium</Emphasis> species of the <Emphasis Type="Italic">Gibberella fujikuroi</Emphasis> complex and fumonisin contamination of pearl millet and corn in Georgia,USA

This study was designed to identify and compare the Fusarium species of the Gibberella fujikuroi complex on pearl millet (Pennisetum glaucum (L.) R. Br) and corn (Zea mays L.) crops grown in southern Georgia, and to determine their influence on potential fumonisin production. Pearl millet and corn samples were collected in Georgia in 1996, 1997 and 1998. Three percent of the pearl millet seeds had fungi similar to the Fusarium species of the G. fujikuroi species complex. One hundred and nineteen representative isolates visually similar to the G. fujikuroi species complex from pearl millet were paired with mating population A (Fusarium verticillioides (Sacc.) Nirenberg), mating population D (F. proliferatum (Matsushima) Nirenberg) and mating population F (F. thapsinum (Klittich, Leslie, Nelson and Marasas) tester strains. Successful crosses were obtained with 50.4%, 10.1% and 0.0% of these isolates with the A, D and F tester strains, while 39.5 of the isolates did not form perithecia with any tester strains. Two of the typical infertile isolates were characterized by DNA sequence comparisons and were identified as Fusarium pseudonygamai (Nirenberg and ODonnell), which is the first known isolation of this species in the United States. Based on the pattern of cross-compatibility, conidiogenesis, colony characteristics and media pigmentation, a majority of the infertile isolates belong to this species. Fumonisins FB₁ and FB₂ were not detected in any of the 81 pearl millet samples analyzed. The species of the G. fujikuroi species complex were dominant in corn and were isolated from 84%, 74% and 65% of the seed in 1996, 1997 and 1998, respectively. Representative species of the G. fujikuroi species complex were isolated from 1996 to 1998 Georgia corn survey (162, 104 and 111 isolates, respectively) and tested for mating compatibility. The incidence of isolates belonging to mating population A (F. verticillioides) ranged from 70.2% to 89.5%. Corn survey samples were assayed for fumonisins, and 63% to 91% of the 1996, 1997 and 1998 samples were contaminated. The total amount of fumonisins in the corn samples ranged from 0.6 to 33.3 g/g.     

The effect of genome and sex on recombination rates in Pennisetum species

The effects of homoeology and sex on recombination frequency were studied in crosses between cultivated pearl millet, Pennisetum glaucum, and two wild subspecies, P. violaceum and P. mollissimum. For the two wild x cultivated crosses, reciprocal three-way crosses were made between the F₁ hybrid and an inbred line (Tift 23DB₁). The three-way cross populations were mapped to produce a female map of each wide cross (where the F₁ was the female) and a male map (where the F₁ was the male). Total genetic map lengths of the two inter-subspecies crosses were broadly similar and around 85 % of a comparable intervarietal map. In the P. glaucumxP. mollissimum crosses, the map was further shortened by a large (40 cM) inversion in linkage group 1. Comparison of the recovered recombinants from male and female meiocytes showed an overall trend for the genetic maps to be longer in the male (10%) in both inter-subspecific crosses; however, analysis of individual linkage intervals showed no significant differences. Gametophytic selection was prevalent, and sometimes extreme, for example 121 in favour of wild alleles in the P. glaucumxP. mollissimum male recombinant population. One of the loci which determines panicle type in cultivated pearl millet and wild relatives, H, was mapped 9 cM from Xpsm812 on linkage group 7 in the P. violaceum cross.     

Evolution of Ac and Dsl elements in select grasses (Poaceae)

We present data on evolution of the Ac/Ds family of transposable elements in select grasses (Poaceae). An Ac-like element was cloned from a DNA library of the grass Pennisetum glaucum (pearl millet) and 2387 bp of it have been sequenced. When the pearl millet Ac-like sequence is aligned with the corresponding region of the maize Ac sequence, it is found that all sequences corresponding to intron II in maize Ac are absent in pearl millet Ac. Kimura's evolutionary distance between maize and pearl millet Ac sequences is estimated to be 0.429±0.020 nucleotide substitutions per site. This value is not significantly different from the average number of synonymous substitutions for coding regions of the Adh1 gene between maize and pearl millet, which is 0.395±0.051 nucleotide substitutions per site. If we can assume Ac and Adh1 divergence times are equivalent between maize and pearl millet, then the above calculations suggest Ac-like sequences have probably not been strongly constrained by natural selection. The level of DNA sequence divergence between maize and pearl millet Ac sequences, the estimated date when maize and pearl millet diverged (25–40 million years ago), coupled with their reproductive isolation/lack of current genetic exchange, all support the theory that Ac-like sequences have not been recently introduced into pearl millet from maize. Instead, Ac-like sequences were probably present in the progenitor of maize and pearl millet, and have thus existed in the grasses for at least 25 million years. Ac-like sequences may be widely distributed among the grasses. We also present the first 2 Dsl controlling element sequences from teosinte species: Zea luxurians and Zea perennis. A total of 10 Dsl elements had previously been sequenced from maize and a distant maize relative, Tripsacum. When a maximum likelihood network of genetic relationships is constructed for all 12 sequenced Dsl elements, the 2 teosinte Dsl elements are as distant from most maize Dsl elements and from each other, as the maize Dsl elements are from one another. Our new teosinte sequence data support the previous conclusion that Dsl elements have been accumulating mutations independently since maize and Tripsacum diverged. We present a scenario for the origin of Dsl elements.     

甘蔗与斑茅BC1分子鉴定、抗黑穗病和花叶病初步评价

为了解甘蔗(Saccharum)与斑茅(Erianthus arundinaceus)杂交后代作为抗病亲本的利用价值,通过特异引物PCR鉴定出78份甘蔗与斑茅杂交BC_1真实杂种;通过人工接种花叶病毒和黑穗病菌,初步评价了甘蔗和斑茅杂交BC_1的抗病表现。结果表明,甘蔗和斑茅杂交BC_1的抗花叶病具有普遍性,而黑穗病抗性则出现分离。初步筛选出BC_1无性系YCE01-48、YCE01-71、YCE01-105、YCE01-125、YCE02-184和YCE01-118可同时抗花叶病和黑穗病,有望成为甘蔗杂交利用的高抗病源亲本。     

Molecular evolutionary characterization of an Activator (Ac)-like transposable element sequence from pearl millet (Pennisetum glaucum) (Poaceae)

We present data on the evolution of the Ac/Ds family of transposable elements in select grasses (Poaceae). A defective Ac-like element was cloned from a DNA library of the grass Pennisetum glaucum (pearl millet) and its entire 4531 bp sequence has been determined. When the pearl millet Ac-like sequence is aligned with the maize Ac sequence, it is found that there is approximately 70% DNA similarity in the central region spanning most of maize Ac exon II and all of exon III. In addition, there are two smaller regions of similarity at the Ac terminii. Besides these three major structural similarities, Pennisetum Ac has two large regions, one 5 and one 3, that show little similarity to Zea Ac. Furthermore, most of the sequences corresponding to intron II in maize Ac are absent in pearl millet Ac. Kimura's evolutionary distance between the central region of maize and pearl millet Ac sequences is estimated to be 0.429±0.020 nucleotide substitutions per site. This value is not significantly different from the average number of synonymous substitutions for coding regions of the Adh1 gene between maize and pearl millet, which is 0.395±0.051 nucleotide substitutions per site. If we assume Ac and Adh1 divergence times are equivalent between maize and pearl millet, then the above calculations suggest Ac-like sequences have probably not been strongly constrained by natural selection. Conserved DNA and amino acid sequence motifs are also examined. The level of DNA sequence divergence between maize and pearl millet Ac sequences, the estimated date when maize and pearl millet diverged (25–40 million years ago), coupled with their reproductive isolation/lack of current genetic exchange, all support the theory that Ac-like sequences have not been recently introduced into pearl millet from maize. Instead, Ac-like sequences were probably present in the progenitor of maize and pearl millet and have thus existed in the grasses for at least 25 million years.     

Crossing maize with sorghum,Tripsacum and millet: the products and their level of development following pollination

Summary Maize was crossed with sorghum, Tripsacum and millet with the aim of introgressing desirable alien characteristics into maize. The products of crosses were analyzed as to their level of differentiation following pollination; their further development on artificial culture medium was compared. In spite of a stimulation rate close to 5%, no evidence of hybridization between maize and sorghum or millet could be obtained. The plants recovered proved to be of maternal origin. However, with an appreciable frequency, stimulation leading to hypertrophic growth of nucellar tissue was observed. This phenomenon is bound to pollination, never occurring in non-pollinated ears. In crosses involving Tripsacum, more than 140 true hybrids were isolated. The influence of the genotypes used as well as factors such as climatic conditions or in vitro techniques are discussed. Except for one haploid maize plant, all the plants recovered proved to be classical hybrids, most of them showing the expected complement of chromosomes from each parent (10 + 36 chromosomes), a few others being slightly hyperploid (2n = 47 to 50 chromosomes). No non-classical hybrids constituted by a nonreduced female gamete and a reduced male gamete were obtained.     

Tuareg, a novel miniature-inverted repeat family of pearl millet (Pennisetum glaucum) related to the PIF superfamily of maize

Miniature-inverted repeat transposable elements (MITEs) are abundantly repeated in plant genomes and are especially found in genic regions where they could contribute regulatory elements for gene expression. We describe with molecular and cytological tools the first MITE family reported in pearl millet: Tuareg. It was initially detected in the pearl millet ortholog of Teosinte-branched1, an important developmental gene involved in the domestication of maize. The Tuareg family was amplified recently in the pearl millet genome and elements were found more abundant in wild than in domesticated plants. We found that they shared similarity in their terminal repeats with the previously described mPIF MITEs and that they are also present in other Pennisetum species, in maize and more distantly related grasses. The Tuareg family may be part of MITEs activated by PIF-like transposases and it could have been mobile since pearl millet domestication. Electronic supplementary material Electronic supplementary material is available for this article at and accessible for authorised users. O. Robin contributed the FISH and fiber-FISH hybridizations.     

Cytogenetics of pearl millet

Summary The somatic karyotype of pearl millet Pennisetum americanum (L.) Leeke. (2n = 14) has been studied in several cultivars, but few cytological markers have been discovered which could help in the easy identification of the chromosomes. Analysis of pachytene bivalents permits such identification but is feasible only in a few cultivars. Recently, several lines having telocentric chromosomes have been produced and classified but their potentialities as cytogenetic tools have yet to be explored. Some African populations of pearl millet carry B-chromosomes in their karyotype. Cytogenetics of B-chromosomes has been reported in great detail. Bs undergo spontaneous changes to produce deficient- and iso-chromosomes. The main effect of B-chromosomes is on chiasma frequency which is exerted by the relative amounts of chiasma promoting euchromatin and the chiasma depressing heterochromatin in the Bs. Haploid plants occur occasionally and sometimes show a low degree of seed set, offering a possibility of establishing homozygous inbred lines. Cytogenetics of several spontaneous and induced autotetraploids have been reported. In general quadrivalent formation between the seven sets of four homologues was random. Seed set of the autotetraploids could be improved by selection; improved seed fertility was found to be associated with increased chiasma frequency, increased quadrivalent frequency and regular distribution of chromosomes at anaphase I. Genes controlling morphological characters of plant phenotype segregate independent of those controlling fertility and in pearl millet polyploidy per se is not limiting to plant vigour. Primary trisomics represent the best studied among the aneuploids of pearl millet. All the seven primary trisomics have been identified and described. Some were used in assigning genes to specific chromosomes but in general trisomies have poor vigour and fertility, and show low frequency of transmission. Apart from B-chromosomes, cytogenetics of interchanges has been the best studied aspect of pearl millet. The frequency of co-orientation of an interchange complex at metaphase I, which determines the fertility or sterility of the interchange heterozygote, is influenced by the genetic background and thus is theoretically amenable for selection leading to improved fertility of the heterozygote. Interchange tester-stocks have been assembled which can be used to identify the chromosomes involved in any newly obtained interchange. A complex interchange line involving all the chromosomes of the complement has also been produced, but the ring-of-fourteen produces total male and female sterility.Genotypic control of mitosis and meiosis has been reported, with reference to chromosome numerical mosaicism, multiploid sporocytes, desynapsis and chromosome fragmentation, and male sterility. Pearl millet being a largely outbreeding species, forced inbreeding was mainly found to result in loss of morphological vigour and reduction in mean chiasma frequency per PMC. Interspecific hybrids between pearl millet and several related species have been cytologically investigated and homology of the seven chromosomes of pearl millet with seven of the fourteen chromosomes of P. purpureum has been demonstrated. Cytogenetic evidence from haploids, autopolyploids and interspecific hybrids has indications to suggest that the haploid number of x = 7 is derived from x = 5, but the evidence is inconclusive and needs critical evaluation.     

Rust and Downy Mildew Resistance in Pearl Millet (Pennisetum glaucum) Mediated by Heterologous Expression of the afp Gene from Aspergillus giganteus

The cDNA encoding the antifungal protein AFP from the mould Aspergillus giganteus was introduced into two pearl millet (Pennisetum glaucum) genotypes by particle bombardment. Stable integration and expression of the afp gene was confirmed in two independent transgenic T₀ plants and their progeny using Southern blot and RT-PCR analysis. In vitro infection of detached leaves and in vivo inoculation of whole plants with the basidomycete Puccinia substriata, the causal agent of rust disease, and the oomycete Sclerospora graminicola, causal agent of downy mildew, resulted in a significant reduction of disease symptoms in comparison to wild type control plants. The disease resistance of pearl millet was increased by up to 90% when infected with two diverse, economically important pathogens. This is the first report of genetic enhancement of Pennisetum glaucum against fungal infections.     

Analysis of recombination rate in female and male gametogenesis in pearl millet (Pennisetum glaucum) using RFLP markers

Sex as a factor affecting recovered recombination in plant gametes was investigated in pearl millet, Pennisetum glaucum, by using reciprocal three-way crosses [(AxB)xCvCx(A x B)]. The two populations were mapped at 42 loci pre-selected to cover the majority of the genome. No differences in recombination distances were observed at the whole-genome level and only a few individual linkage intervals were found to differ, all in favour of increased recombination through the male. Distorted segregations found in the three-way crosses provide evidence of post-gametic selection for particular gene(s) or chromosome regions. The significance of these results for the design of pearl millet breeding programmes and inheritance experiments, as well as for other experimental strategies, is discussed.     

Genetic studies of self-fertility in rye (Secale cereale L.). 1. The identification of genotypes of self-fertile lines for the Sf alleles of self-incompatibility genes

Segregation for self-fertility has been studied in progenies from the crosses of self-sterile (SS) plants with interline hybrids obtained by a diallel scheme of pollinations between seven self-fertile (SF) lines (nos. 2–8) and with F₁ (SS plant x SF line) hybrids. All the offspring families from the SS plant x F₁ (SS plant x SF line) crosses demonstrated a 1SF1SS segregation. The crosses of SS plants with some interline hybrids gave only self-fertile plants, whereas the crosses with other interline hybrids gave a segregation of 3SF:1SS expected in the case of digenic segregation. The data obtained permitted us to identify three different S loci (S1, S2, S5) and to estimate the genotypes of self-fertile lines for their Sf alleles: lines 5, 6, 7 and 8 are S1f/S1f S2n/S2n S5m/S5m, line 4 is S1n/S1n S2f/S2f S5m/S5m, and lines 2 and 3 are S1n/S1n S2m/S2m S5f/S5f(Sn, Sm designate active alleles of the incompatibility genes). The identification of the particular S gene which is presented by the Sf allele in each line has been made on the basis of our data concerning the linkage of the Sf mutation with isozyme markers of particular rye chromosomes, which is reported in an accompanying paper.     

Intergeneric hybridization between Diplotaxis siifolia,a wild species and crop brassicas

Summary Attempts were made to obtain intergeneric hybrids between Diplotaxis siifolia, a wild species, and cultivars of Brassica (B. campestris, B. juncea, and B. napus). The crosses showed unilateral incompatibility. When the wild species was used as female parent, pollen germination and pollen tube growth were normal, but hybrid seeds aborted due to post-fertilization barriers. Reciprocal crosses (cultivars as female parent) showed strong pre-fertilization barriers; although pollen grains showed germination, pollen tubes failed to enter the stigma. Hybrids were realized in two of the crosses, D. siifolia x B. juncea and D. siifolia x B. napus, through ovary culture. The hybrids were multiplied in vitro by multiplication of axillary shoots, or somatic embryogenesis. Detailed studies were carried out on the hybrid D. siifolia x B. juncea. F₁ hybrids had shrivelled anthers and were pollen sterile. Amphiploids of this hybrid showed 60% pollen fertility and produced seeds upon self-pollination as well as backcross pollination with the pollen of B. juncea.     

Intersubgenomic heterosis in seed yield potential observed in a new type of Brassica napus introgressed with partial Brassica rapa genome

This paper reports the observation on the intersubgenomic heterosis for seed yield among hybrids between natural Brassica napus (AⁿAⁿCⁿCⁿ) and a new type of B. napus with introgressions of genomic components of Brassica rapa (A^rA^r). This B. napus was selected from the progeny of B. napus × B. rapa and (B. napus × B. rapa) × B. rapa based on extensive phenotypic and cytological observation. Among the 129 studied partial intersubgenomic hybrids, which were obtained by randomly crossing 13 lines of the new type of B. napus in F₃ or BC₁F₃ to 27 cultivars of B. napus from different regions as tester lines, about 90% of combinations exceeded the yield of their respective tester lines, whereas about 75% and 25% of combinations surpassed two elite Chinese cultivars, respectively. This strong heterosis was further confirmed by reevaluating 2 out of the 129 combinations in a successive year and by surveying hybrids between 20 lines of the new type of B. napus in BC₁F₅ and its parental B. napus in two locations. Some DNA segments from B. rapa were identified with significant effects on seed yield and yield components of the new type of B. napus in BC₁F₅ and intersubgenomic hybrids in positive or negative direction. It seems that the genomic components introgressed from B. rapa contributed to improvement of seed yield of rapeseed.