Cytoplasmic-genic Male Sterility Research Articles

Insights into cellular crosstalk regulating cytoplasmic male sterility and fertility restoration.

Cytoplasmic male sterility has been a popular genetic tool in development of hybrids. The molecular mechanism behind maternal sterility varies from crop to crop. An understanding of underlying mechanism can help in development of new functional CMS gene in crops which lack effective and stable CMS systems. In crops where seed or fruit is the commercial product, fertility must be recovered in F1 hybrids so that higher yield gains can be realized. This necessitates the presence of fertility restorer gene (Rf) in nucleus of male parent to overcome the effect of sterile cytoplasm. Fertility restoring genes have been identified in crops like wheat, maize, sunflower, rice, pepper, sugar beet, pigeon pea etc. But in crops like eggplant, bell pepper, barley etc. unstable fertility restorers hamper the use of Cytoplasmic genic male sterility (CGMS) system. Stability of CGMS system is influenced by environment, genetic background or interaction of these factors. This review thus aims to understand the genetic mechanisms controlling mitochondrial-nuclear interactions required to design strong and stable restorers without any pleiotropic effects in F1 hybrids.

Development of alloplasmic male sterile lines and their assessment for heterotic potential in eggplant (Solanum melongena L.)

ABSTRACT The use of Solanum aethiopicum as the female parent with S. melongena led to the development of a cytoplasmic-genic male sterility system (CGMS) in eggplant. The male sterility was complete and expressed as rudimentary anthers with no pollen grains. Ten backcross progenies of male sterile lines in diverse genetic backgrounds of S. melongena were characterised after BC7 generation for 14 horticultural traits. It was observed that male sterile lines and their respective maintainer parents were isogenic for all the traits, except stamen size and days to 50% flowering. The fertility of male sterile lines was restored after hybridising with plants derived from an S. melongena × S. aethiopicum cross. The fertility restoration was governed by a single dominant gene. The maternal cytoplasm of S. aethiopicum in male sterile lines and of S. melongena in maintainers and restorers was confirmed with mitochondria and chloroplast DNA-specific molecular markers. Further, to assess the heterotic potential, 10 cytoplasmic male sterility lines were crossed with three restorers to develop 30 F1 hybrids, out of which D−67A × R−6 and D−104A × R−6 were found consistently better than the standard check for yield plant−1 over two years. In this manuscript a comprehensive study on development and utilisation of an alloplasmic CGMS system in eggplant has been discussed.

Marker-Assisted Selection of Male-Sterile and Maintainer Line in Chili Improvement by Backcross Breeding

Cytoplasmic genic male sterility (CGMS) is a male sterility system that uses the maternal line for hybrid production, ensuring no obscurity of F1 seed purity and reducing the cost of hybrid seed production. Identification of the male sterility gene is important for plant improvement and classification when using the molecular marker-assisted selection (MAS) method. This study aimed to produce a new maternal line (A-line) and its maintainer line (B-line) by transferring a male-sterile line (A-line) and its maintainer line (B-line) gene from another variety to restorer lines (C-line) to achieve future hybrid seed production. In the process, the CGMS line (A-line) and B-line transferred to C1 and C3 lines, which finally resulted in new A-line (BC2F2A1 × C1, BC2F2A1 × C3), and B-line (BC1F2B1 × C1, BC1F2B1 × C3), and then used the MAS method for detecting genes and pollen viability test in the newly improved lines. The results indicated that the 3336-last2-SCAR (1639 bp) and 4162-SCAR (1046 bp) DNA markers classified the Rf locus, and the CMS-SCAR130/140 marker confirmed the S or N cytoplasm. The BC2F2A1 × C1 and BC2F2A1 × C3 lines represented both male-fertile (SRf_) and male-sterile (Srfrf) progenies in a Mendelian ratio of 3:1. Moreover, stained pollen grains with 1% acetocarmine confirmed abnormal pollen in male-sterile plants. The molecular markers that detect maintainer lines (Nrfrf) are BC1F2B1 × C1-14, BC1F2B1 × C3-10, and BC1F2B1 × C3-11. The 3336-last2-SCAR (1639 bp) and CMS-SCAR130/140 markers successfully identified the male-sterile line (Srfrf) and maintainer line (Nrfrf), and 4162-SCAR (1046 bp) detected the presence of the RfRf or Rfrf genotype in chilies at the seedling stage. The use of these markers was highly accurate and confirmed the results at the early generation stage of a conventional breeding program. It can be concluded that the CGMS and maintainer gene in chilies were successfully transferred during early generation using the backcross method.

Characterization, inheritance of male sterility and development of male sterile and maintainer lines in ridge gourd (Luffa acutangula (Roxb.) L.)

Two male sterile mutants IIHRRG-12MS (long fruited) and IIHRRG-28MS (medium long fruited) were identified from the ridge gourd germplasm IIHR-12 and IIHR-28 respectively at ICAR-IIHR, Bengaluru. These two male-sterile (ms) sources were characterized by the production of rudimentary male flowers in the racemes in contrast to the bright yellow flowers with fertile pollen and healthy anthers in male fertile, monoecious plants. Using these ms lines the inheritance of male sterility was worked out, which is cytoplasmic genic male sterility (CGMS) type, with single dominant gene either in homozygous or heterozygous condition restoring male fertility in the presence of sterile cytoplasm. In order to develop F1 hybrids using male sterility, several male sterile and maintainer lines were developed in different genetic back grounds such as green/dark green fruit colour and short/medium long/long fruit length.

The Unstable Restorer-of-fertility locus in pepper (Capsicum annuum. L) is delimited to a genomic region containing PPR genes.

Unstable Restorer-of-fertility (Rfu), conferring unstable fertility restoration in the pepper CGMS system, was delimited to a genomic region near Rf and is syntenic to the PPR-like gene-rich region in tomato. The use of cytoplasmic-genic male sterility (CGMS) systems greatly increases the efficiency of hybrid seed production. Although marker development and candidate gene isolation have been performed for the Restorer-of-fertility (Rf) gene in pepper (Capsicum annuum L.), the broad use of CGMS systems has been hampered by the instability of fertility restoration among pepper accessions, especially sweet peppers, due to the widespread presence of the Unstable Restorer-of-fertility (Rfu) locus. Therefore, to investigate the genetic factors controlling unstable fertility restoration in sweet peppers, we developed a segregation population (BC4F5) from crosses using a male-sterile line and an Rfu-containing line. Segregation did not significantly deviate from a 3:1 ratio for unstable fertility restoration to sterility, indicating single dominant locus control for unstable fertility restoration in this population. Genetic mapping delimited the Rfu locus to a 398 kb genomic region on chromosome 6, which is close to but different from the previously identified Rf-containing region. The Rfu-containing region harbors a pentatricopeptide repeat (PPR) gene, along with 10 other candidate genes. In addition, this region is syntenic to the genomic region containing the largest number of Rf-like PPR genes in tomato. Therefore, the dynamic evolution of PPR genes might be responsible for both the restoration and instability of fertility in pepper. During genetic mapping, we developed various molecular markers, including one that co-segregated with Rfu. These markers showed higher accuracy for genotyping than previously developed markers, pointing to their possible use in marker-assisted breeding of sweet peppers.

Genetics of fertility restoration for the A1 cytoplasmic genic male sterility system in pearl millet (Pennisetum glaucum (L.) R. Br.)

With the objective to investigate the inheritance pattern of fertility restoration of A1cytoplasm in multi-environments, six crosses were developed by crossing two A1 cytoplasm-based male sterile lines (A-lines) with three diverse restorers (R-lines). The parents, 6 F2s and 6 BC1s were evaluated in the rainy season at Delhi and summer season at Delhi and Dharwad. Four crosses viz.,576A1×PPMI 1012, 411A1× PPMI 1012, 576A1× ICMR 06111 and 411A1× ICMR 06111 showed a segregation ratio of fertile: semi-fertile: sterile as 9:3:4 and 1:1:2 in F2 and BC1 generations, respectively, based on pollen fertility and seed set percent data, indicating digenic supplementary gene action. In the other two crosses, i.e., 576A1× HTP 94/54 and 411A1× HTP 94/54, different digenic ratios of 9:7 and 1:3 of fertile and sterile plants were observed in F2 and BC1 generations, respectively, indicating complementary interaction of two genes. The deviation of expected ratios in the summer season at Delhi resulted due to excess sterile plants, as influenced by modifiers and environmental conditions that prevailed during the dry season. Thus, in the present investigation, fertility restoration of A1-based CGMS system was observed to be governed by two major genes. Still, with different types of epistatic interactions, digenic inheritance of A1 cytoplasm suggests that test of allelism and genetic mapping of fertility restorer genes can be taken up in the future.

Male sterility in onion (Allium cepa L.): origin: origin, evolutionary status, and their prospectus

Onion (Allium cepa L.) is the most diversified crop of the family Alliaceae; it is in cultivation since from ancient era for its edible bulbs and verdant foliage due to the immense nutritional and medicinal properties. The increased social acceptance of bulb onion in daily diet could lead to an increase in cultivable area with a similar bulb production. However, the output per unit area had limited due to the lack of exploitation of heterosis for bulb yield. The only possibility to increase the onion productivity is to increase the volume of the individual bulb, and it can achieve by exploiting heterosis for earliness, biotic and abiotic stress resistance, bulb weight, and size by the development of hybrid with the use of male sterility mechanisms like cytoplasmic-genic male sterility or cytoplasmic male sterility system in onion. The male sterility trait is precious in heterosis breeding due to its potential advantages in the development of onion hybrids. In these perspectives, the present review reveals the origin, evolution, maintenance, and prevalence of male sterility systems of onion and the technique of identification of the male sterility systems. The polymorphisms between male-sterile and male-fertile phenotypes difference with morphological-molecular markers with the marker-phenotype linkage of onion.

Morphologic and cytoplasmic assessments of bulb onion (Allium cepa L.) landraces

Today climate change threatens to reduce crop yield and harming the food security. Local landraces have adaptation skills to shifting climatic conditions. Using of this local source in plant breeding programs becoming an alternative strategy. In this study, 97 landraces were collected to initiate the bulb onion breeding program eligible for the current trends. Collected materials were morphologically characterized using 21 descriptors, derived from UPOV (International Union for the Protection of New Varieties of Plants). Clustering which was conducted by the NTSYS (Numerical Taxonomy and Multivariate Analysis System) program using UPGMA (Unweighted Pair Group Method of Arithmetic Averages) method, showed that the genetic similarity rate of the landraces was calculated between 0.06-0.96. Hybrid onion breeding program depends on the cytoplasmic-genic male sterility (CMS) system. Thus, the PCR-markers were applied to identify the cytoplasm types of the landraces. Among landraces N-cytoplasm was found in 78 accessions and S-cytoplasm was found in 19 accessions. At the end of the study, a qualified gene pool has been established consisted of characterized onion genotypes which will might be used in further breeding studies.

Transcriptome analysis identified aberrant gene expression in pollen developmental pathways leading to CGMS in cotton (Gossypium hirsutum L.).

Male sterility (induced or natural) is a potential tool for commercial hybrid seed production in different crops. Despite numerous endeavors to understand the physiological, hereditary, and molecular cascade of events governing CMS in cotton, the exact biological process controlling sterility and fertility reconstruction remains obscure. During current study, RNA-Seq using Ion Torrent S5 platform is carried out to identify ‘molecular portraits’ in floral buds among the Cytoplasmic Genic Male Sterility (CGMS) line, its near-isogenic maintainer, and restorer lines. A total of 300, 438 and 455 genes were differentially expressed in CGMS, Maintainer, and Restorer lines respectively. The functional analysis using AgriGo revealed suppression in the pathways involved in biogenesis and metabolism of secondary metabolites which play an important role in pollen and anther maturation. Enrichment analysis showed dearth related to pollen and anther’s development in sterile line, including anomalous expression of genes and transcription factors that have a role in the development of the reproductive organ, abnormal cytoskeleton formation, defects in cell wall formation. The current study found aberrant expression of DYT1, AMS and cytochrome P450 genes involved in tapetum formation, pollen development, pollen exine and anther cuticle formation associated to male sterility as well as fertility restoration of CGMS. In the current study, more numbers of DEGs were found on Chromosome D05 and A05 as compared to other chromosomes. Expression pattern analysis of fourteen randomly selected genes using qRT-PCR showed high concurrence with gene expression profile of RNA-Seq analysis accompanied by a strong correlation of 0.82. The present study provides an important support for future studies in identifying interaction between cyto-nuclear molecular portraits, to accelerate functional genomics and molecular breeding related to cytoplasmic male sterility studies in cotton.

The use of genetic, manual and chemical methods to control pollination in vegetable hybrid seed production: a review

AbstractProduction of hybrid varieties of vegetable crops is currently a desired breeding goal, due to their remarkable agronomic performance and to the possibility of intellectual property protection. However, efficient hybrid production requires a careful pollination control to guarantee the hybrid nature of F1seed. Several technologies ranging from manual emasculation to genetic transformation are used to inhibit pollen production in mother plants. In this review, we examine the principles underlying strategies like genetically determined systems (genic male sterility, cytoplasmic–genic male sterility, self‐incompatibility) and other methods (manual emasculation, chemical‐hybridizing agents) in different species, considering the benefits and drawbacks of their adoption. Finally, we present the current state of the art for vegetable hybrid seed production.

Fine mapping of Restorer-of-fertility in pepper (Capsicum annuum L.) identified a candidate gene encoding a pentatricopeptide repeat (PPR)-containing protein.

Using fine mapping techniques, the genomic region co-segregating with Restorer - of - fertility ( Rf ) in pepper was delimited to a region of 821kb in length. A PPR gene in this region, CaPPR6 , was identified as a strong candidate for Rf based on expression pattern and characteristics of encoding sequence. Cytoplasmic-genic male sterility (CGMS) has been used for the efficient production of hybrid seeds in peppers (Capsicum annuum L.). Although the mitochondrial candidate genes that might be responsible for cytoplasmic male sterility (CMS) have been identified, the nuclear Restorer-of-fertility (Rf) gene has not been isolated. To identify the genomic region co-segregating with Rf in pepper, we performed fine mapping using an Rf-segregating population consisting of 1068 F2 individuals, based on BSA-AFLP and a comparative mapping approach. Through six cycles of chromosome walking, the co-segregating region harboring the Rf locus was delimited to be within 821kb of sequence. Prediction of expressed genes in this region based on transcription analysis revealed four candidate genes. Among these, CaPPR6 encodes a pentatricopeptide repeat (PPR) protein with PPR motifs that are repeated 14 times. Characterization of the CaPPR6 protein sequence, based on alignment with other homologs, showed that CaPPR6 is a typical Rf-like (RFL) gene reported to have undergone diversifying selection during evolution. A marker developed from a sequence near CaPPR6 showed a higher prediction rate of the Rf phenotype than those of previously developed markers when applied to a panel of breeding lines of diverse origin. These results suggest that CaPPR6 is a strong candidate for the Rf gene in pepper.

Studies on Gene Action and Combining Ability of Cytoplasmic-Genic Male Sterility System based Hybrids in Pigeonpea [<i>Cajanus Cajan</i> (L.) Millsp.

The present investigation was undertaken with different newly developed six cytoplasmic male sterile (A) lines and five pollen fertility restorers (R) lines as testers were crossed in a line x tester mating design for ascertaining their general and specific combining ability for yield and its component traits in pigeonpea [ Cajanus Cajan (L.) Millspaugh.]. The mean sum of squares due to line x testers interaction were significant for all the characters except plant height, revealed the significant contribution of hybrids for specific combining ability variance components. The ratio of σ2gca/ σ2sca being more than unity was found for the traits, days to flowering, days to maturity, plant height and biological yield, which indicated greater role of additive genetic variance for the inheritance for these traits suggesting and indicated to further improvement as a source of favourable genes for earliness and yield improvement through selection of desired transgressive segregants from segregating generation. The ratio σ2gca/ σ2sca being less than unity was found for the traits, number of branches per plant, number of pods per plant, number of seeds per pod, pod length, 100-seed weight, seed yield per plant, harvest index, protein content and leaf area, which exhibited greater role of non- additive genetic variance for the inheritance for these traits and indicated to exploitation of these traits for improvement of yield through heterosis breeding. Among parents, CMS GT 603 A (28.43) and GTR 95 (17.24) were good general combiner for seed yield and its contributing traits viz . pod length, number of branches per plant, number of pods per plant, number of seeds per pod, pod length, biological yield and leaf area, CMS GT 33 A (0.48) and CMS GT 301 A (0.19) for protein content, CMS GT 33 A (-17.93), CMS GT 288 A (-9.03), GTR 52 (-1.40) and GTR 8 (-0.62) recorded for earliness. These parents can be improved further through intensive crossing programme and subsequent selection of transgressive segregants in desired direction. Hybrids CMS GT 33 A X GTR 18 (29.31), CMS GT 302 A X GTR 8 (25.27), CMS GT 601 A X GTR 52 (21.35) and CMS GT 288 A X GTR 95 (20.89) were the best for seed yield per plant . These crosses had also high sca values for its contributing traits viz . number of branches per plant, number of pods per plant, pod length, harvest index, biological yield and leaf area. These crosses involved poor x average, poor x poor and average x poor combining parents and better performance reflected involvement of interaction of dominant and epistasis type gene action for this trait. So, these crosses can be exploited through hybrid breeding programme.

Studies on Gene Action and Combining Ability of Cytoplasmic-Genic Male Sterility System based Hybrids in Pigeonpea <i>Cajanus Cajan</i> (L.) Millsp.

Studies on Gene Action and Combining Ability of Cytoplasmic-Genic Male Sterility System based Hybrids in Pigeonpea <i>Cajanus Cajan</i> (L.) Millsp.

Genomics for greater efficiency in pigeonpea hybrid breeding.

Cytoplasmic genic male sterility (CGMS) based hybrid technology has demonstrated its immense potential in increasing the productivity of various crops, including pigeonpea. This technology has shown promise for breaking the long-standing yield stagnation in pigeonpea. There are difficulties in commercial hybrid seed production due to non-availability of field-oriented technologies such as time-bound assessment of genetic purity of hybrid seeds. Besides this, there are other routine breeding activities which are labor oriented and need more resources. These include breeding and maintenance of new fertility restorers and maintainer lines, diversification of cytoplasm, and incorporation of biotic and abiotic stress resistances. The recent progress in genomics research could accelerate the existing traditional efforts to strengthen the hybrid breeding technology. Marker based seed purity assessment, identification of heterotic groups; selection of new fertility restorers are few areas which have already been initiated. In this paper efforts have been made to identify critical areas and opportunities where genomics can play a leading role and assist breeders in accelerating various activities related to breeding and commercialization of pigeonpea hybrids.

Identification of fertility restorers, stable combiners and heterotic combinations across environments in pigeonpea [<em>Cajanus cajanifolius</em> (L.) Millsp.] in India

Efficient and stable cytoplasmic genic male sterility system is a prerequisite for commercial exploitation of heterosis in any crop improvement program. The present investigation was undertaken to identify fertility restorers, stable combiners and best heterotic crosses in pigeonpea [Cajanus cajanifolius (L.) Millsp]. Totally, 75 crosses were developed by using three A4 cytoplasm-based male sterile lines viz., ICPA 2047, ICPA 2092 and ICPA 2089, and 25 diverse inbred lines. The pollen fertility assay identified 15 good restorers with 85-95% fertility status. The 45, best restored combinations identified were assessed across four seasons (August and September, 2012 and 2013) for their stable heterosis and general and specific combining ability to identify parents possessing desirable genes. Variance for combining ability was significant (p<.05) for lines, testers and line × tester effects. Among the three male sterile lines, ICPA 2047 was stable with a significant general combining ability for most of the traits followed by ICPA 2092, while the general combining ability effects among males was high across seasons for ICPL 20205 and ICPL 20177 (p<0.05). The cross combination of ICPA 2089 × ICPL 20205 had desirable genes for days to the first flowering, 50% flowering and maturity. For yield related traits, cross combinations of ICPA 2047 × ICPL 20128, ICPA 2092 × ICPL 11376 and ICPA 2047 × ICPL 20107 had significant specific combining ability indicating their usability in development of hybrids (p<0.05). With respect to the heterotic ability of crosses, crosses involving parents ICPA 2089 as female and ICPL 88034 and ICPL 81-3 as males showed negative heterosis for flowering and maturity. For yield related traits, crosses with ICPA 2047 as the female parent and ICPL 20128, ICPL 20177 and ICPL 20096 as the male parents showed significant positive heterosis (p<0.05). The identified parents with good combining ability and cross combination`s with significant heterosis could be utilized in producing high yielding hybrids in pigeonpea.

Gene action and stability parameters for yield and yield components, maturity duration and protein content of CGMS lines, pollen fertility restorers and their hybrids in pigeonpea [Cajanus cajan (L.) Millsp.

Cytoplasmic genic male sterility system based hybrids were synthesized by line × tester design and evaluated with check GTH 1 in RBD at Sardarkrushinagar, Jagudan and Khedbrahma during kharif 2007. Analysis of variance in individual and across environments revealed significant differences among genotypes and existence of overall heterosis for seed yield per plant and other thirteen traits. The top ranking on the basis of standard heterosis were CMSGT087A × GTR0525 (116.40 %) followed by CMSGT087A × AGTR0534 (108.93 %), CMSGT0307A × AGTR0538 (99.21 %) and CMSGT 0301A × AGTR 0534 (95.51 %) for seed yield per plant and for one or two of its contributing traits. Combining ability analysis revealed presence of both additive and non-additive gene effects. The specific combining ability variance was found more compaired to general combining ability variance for all the characters under studied. This favored a hybrid breeding programme. In stability analysis, linear portion was considerably high for all the traits except for days to flower and pod length. The best stable hybrids for seed yield per plant over environments were CMSGT 308A × AGTR 0534, CMSGT 307A × AGTR 0543, CMSGT 0308A × AGTR 0536 and CMSGT 0311A × GTR 0525 and also recorded stability in any one or more of its contributing traits viz. pods per plant, branches per plant, seed per pod, pod length and test weight. Top ranking hybrids had high mean performance, high heterosis and desirable sca effects and stability for seed yield per plant. Therefore, these hybrids could be valuable for commercial exploitation.

Visual Versus Marker‐Based Selection of Hybrid Progeny in Fertile × Fertile Beet and Carrot Crosses

ABSTRACTCytoplasmic‐genic male sterility systems (CMS) help control pollination in carrot and table beet breeding programs and hybrid seed production. A challenge common to these breeding programs is identification of F1 hybrid progeny in crosses where both parents carry normal (N) cytoplasm. Such fertile × fertile crosses often produce both F1 and selfed progeny, making identification of F1 hybrids difficult. Such identification has traditionally been accomplished in carrot and table beet by visually scoring roots using heterosis for size. However, if heterosis is lacking, misidentification can result in systematic errors in the breeding process. We sought to determine how effective visual selection of hybrid progeny is in the context of table beet and carrot breeding programs. We used amplified fragment length polymorphisms (AFLP) markers to genotype parents and progeny in a variety of fertile × fertile crosses. Progeny were also grown in the field and evaluated for hybridity based on visual selection using the phenotype of heterosis for size. Two of five fertile × fertile table beet crosses and three of five fertile × fertile carrot crosses showed highly significant differences between visual selection for hybridity and AFLP marker analysis (p < 0.01). Misidentification of roots as F1 hybrids when they were actually self‐pollinated occurred in some crosses as much as 75% of the time. Both type I, a hybrid root scored as an inbred, and type II, an inbred root scored as a hybrid, errors were committed. Across all matings, type I errors occurred on average 40.9% of the time and type II errors occurred on average 8.5% of the time. Type II errors have important consequences because both parents are not represented and recombined in the progeny resulting in further inbreeding. The results of this study indicate that using heterosis for size as a hybrid selection method can be inaccurate for identification of hybrids in certain crosses and may introduce error into breeding programs.

Field evaluation of thermosensitive genic male sterile lines

The use of thermosensitive genic male sterility (TGMS) is well recognized in two-line heterosis breeding. The use of the TGMS system has several advantages over the cytoplasmic genic male sterility system, such as (1) its simple and efficient seed production system, and (2) its greater scope for enhancing heterosis because any genotype can be used as a male parent. To develop hybrids using the TGMS system, it is necessary to identify or develop lines that show a desirable transformation from fertility to sterility and vice versa.

DIVERSITY IN INDIAN AND SOME EXOTIC ONION CULTIVARS AS REVEALED BY GENOMIC AND MITOCHONDRIAL DNA

Cytoplasmic genic male sterility in onion has been associated with the mitochondrial genome. Identification of male sterile lines and its maintainers is a major hurdle in exploitation of male sterility in onion hybrid seed production. In this study, we evaluated genomic and mitochondrial genome diversity to identify type of cytoplasm and male sterility among various onion varieties of Indian and exotic origin employing RAPD, SSR and non-radioactive RFLP molecular markers. Among the 68 used random decamer RAPD primers, 39 primers produced 445 total polymorphic bands with an average of 11.40 bands per primer. A total of 16 SSR primers were screened and 11 showed polymorphism and produced 86 polymorphic bands with an average of 8 polymorphic bands per primer. The RFLP studied using non-radioactive gene probes were cox1, cox2, atp6, atp9 and nad6. These studies demonstrate the diversity in the nuclear and mitochondrial genome of onion cultivars.

Marker-assisted selection of maintainer lines within an onion tropical population

The traditional onion (Allium cepa) hybrid production requires the development of maintainer and male sterile lines and also a pollinator line with good specific combination ability. We report the identification of maintainer and male-sterile onion lines within the Brazilian 'Baia Periforme' derived population, 'Alfa São Francisco', associating random field pairing of male-fertile plants with selected male-sterile plants and PCR-based marker system monitoring S, T and N-cytoplasms. Male-sterile plants produced flowers with light green anthers which were easily detected in the field. A frequency of 2.0% of male-sterile plants was estimated in the 'Alfa São Francisco' sampled population. Male-sterile plants produced the 5'cob-marker 180-bp and the orfA501-marker 473-bp fragments, suggesting the T-cytoplasm type, while the maintainer line produced only the 5'cob-marker 180-bp. These identified lines will be important to develop tropical onion hybrids well-adapted to Brazilian low latitudes and to future comparative studies with other onion cytoplasmic genic male sterility systems.