Independent Dominant Genes Research Articles

Genetic Mapping of a Novel Gene PmAege7M from Aegilops geniculata Conferring Resistance to Wheat Powdery Mildew.

Powdery mildew, caused by Blumeria graminis f. sp. tritici (Bgt), is one of the most damaging foliage diseases of wheat across the world. Aegilops geniculata Roth is a valuable gene resource for enhancing wheat resistance to powdery mildew. This study identified Ae. geniculata accession PI 487224 as immune and PI 487228 as susceptible to powdery mildew. Genetic analysis of the F1, F2, and F2:3 progeny derived from PI 487224 × PI 487228 showed that powdery mildew resistance in PI 487224 was controlled by two independent dominant genes located on two different nonhomologous chromosomes. By combing bulked segregant RNA-Seq, genetic linkage analysis of a single resistance gene segregation population, and marker analysis of a set of 14 wheat-Ae. geniculata chromosome addition lines, one of the resistance genes, temperately designated PmAege7M, was mapped to a 4.9-cM interval flanked by markers STS7-55926 and SNP7-45792/STS7-65911 on the long arm of chromosome 7 Mg of PI 487224, spanning 604.73 to 622.82 Mb on the 7D long arm based on the Ae. tauschii reference genome (Aet_v4.0). The map and closely linked markers of PmAege7M from Ae. geniculata in this study will facilitate the transfer of PmAege7M into common wheat and fine mapping of the gene.

Inheritance of seed protein in two interspecific pigeonpea (Cajanus cajan) crosses

AbstractPigeonpea is one of the primary sources of protein for most rural communities of south Asia and Africa. The enhancement of protein from the present level of 20–22% will help masses in their nutritional well‐beings. Breeders have identified high‐protein (28–30%) germplasm amongst the wild relatives of pigeonpea; and these can serve as donors in breeding high‐yielding high‐protein cultivars. To achieve this, information on the inheritance of seed protein will be useful in organizing interspecific matings, generation advancement, and selection schemes. In the present study, two interspecific crosses, involving two pigeonpea cultivars ('Pant A2' and 'ICP 6997') and a wild species (Cajanus albicans (W. & A.)), were made to study the inheritance of seed protein in F1, F2, and BC1F1 generations. The high‐protein trait was found to be controlled by two independent dominant genes with complementary effects. These genes are tagged with symbols “HPt1” and “HPt2”. The authors believe that now opportunities exist for enhancing the protein levels in pigeonpea through breeding approaches.

Inheritance and Allelic Relationships of Alectra vogelii Benth. Resistance Genes in Cowpea Genotypes B301 and KVx414-22-2

Alectra vogelii Benth. is the second most important parasitic weed in cowpea [Vigna unguiculata (L.) Walp.] production in Burkina Faso. Several resistant varieties to this weed have been identified in the country among which are B301 and KVx414-22-2. The inheritance and allelic relationships of the resistance genes in the two varieties have not been studied with A. vogelii strains in Burkina Faso. The objective of this study was to determine the inheritance and allelic relationship of the resistance genes in B301 and KVx414-22-2. To determine the inheritance of the genes for resistance, the resistant varieties (B301 and KVx414-22-2) were each crossed to a susceptible variety IT82D-849 to generate F1 and F2 populations. For the allelic relationship study the two resistant genotypes were crossed among themselves to generate F1 and F2 offspring. The parents and their F1 and F2 progenies were screened in artificially infested pots with Alectra seed in a screen house at Kamboinsé Research Station in Burkina Faso. Resistance/susceptibility of genotypes was assessed by recording the number of emerged Alectra shoots. The data were subjected to the Chi-Square goodness-of-fit test for one, two and three genes segregation ratios. The results revealed that two independent dominant genes confer resistance in the variety B301 and a single dominant gene confers resistance in variety KVx414-22-2. The single dominant gene in KVx414-22-2 is non-allelic to the two genes in B301. The two resistance genes in variety B301 have already been named Rav1 and Rav2 whilst Rav3 is the name of the resistance gene in variety IT81D-994. Therefore, we propose the symbol Rav4 as the name for the resistance gene in variety KVx414-22-2.

QTL-seq for identification of loci associated with resistance to Phytophthora crown rot in squash

Phytophthora capsici Leonian, the causal agent of foliar blight, root rot, fruit rot and crown rot syndromes in squash (Cucurbita moschata), is a devastating pathogen worldwide. Resistance to Phytophthora crown rot in University of Florida breeding line #394-1-27-12 (C. moschata) is conferred by three independent dominant genes (R1R2R3). Availability of DNA markers linked to R1R2R3 genes would allow efficient breeding for Phytophthora crown rot resistance through marker-assisted selection (MAS). The goal of the current study was to identify quantitative trait loci (QTLs) associated with resistance to Phytophthora crown rot in an F2 population (n = 168) derived from a cross between #394-1-27-12 (R) and Butter Bush (S) using QTL-seq bulk segregant analysis. Whole-genome resequencing of the resistant (n = 20) and susceptible (n = 20) bulk segregants revealed ~900,000 single nucleotide polymorphisms distributed across C. moschata genome. Three QTLs significantly (P < 0.05) associated with resistance to Phytophthora crown rot were detected on chromosome 4 (QtlPC-C04), 11 (QtlPC-C11) and 14 (QtlPC-C14). Several markers linked to these QTLs are potential targets for MAS against Phytophthora crown rot in C. moschata. The present study reports the first QTLs associated with Phytophthora crown rot resistance in C. moschata.

Genetic analysis and fine-mapping of Soybean mosaic virus SC7 and SC13 resistance genes in soybean (Glycine max)

Soybean mosaic virus (SMV) is one of the most destructive pathogens of soybean (Glycine max (L.) Merr.) worldwide. In this study, 184 F7:11 recombinant inbred line (RIL) populations derived from Kefeng No. 1 × Nannong 1138-2 were used to study the inheritance and linkage mapping of resistance genes against SMV strains SC7 and SC13 in Kefeng No. 1. Two independent dominant genes (designated Rsc7 and Rsc13) that control resistance to SC7 and SC13 were located on a molecular linkage group (MLG) of chromosome 2 (D1b). A mixed segregating population was developed by self-pollination of three heterozygous plants of residual heterozygous lines (RHL3-27, RHL3-30, RHL3-53) with five markers linked to the loci, and was used in fine-mapping of Rsc7 and Rsc13. In addition, Rsc7 was fine-mapped between BARCSOYSSR_02_0667 and BARCSOYSSR_02_0670 on MLG D1b. The genetic distance between the two closest markers was 0.7 cM and the physical distance of the interval was ~77 kb, which included one LRR gene and another gene containing an F-box region. Two SSR markers (BARCSOYSSR_02_0610 and BARCSOYSSR_02_0621) were closely linked to the SC13 resistance gene. The physical distance where Rsc13 was located was ~191 kb. Sequence analysis showed that there were two K-box region types of transcription factor genes; GmHSP40 and two serine/threonine protein kinase (STK) genes were the most likely candidate genes. These results will facilitate map-based cloning of the Rsc7 and Rsc13 genes and development of transgenic disease-resistant varieties, and will provide SMV-resistance breeding systems with excellent resistance germplasm.

Resistance Against Melon Chlorotic Mosaic Virus and Tomato Leaf Curl New Delhi Virus in Melon.

Thirty-one melon accessions were screened for resistance to the begomoviruses Melon chlorotic mosaic virus (MeCMV) and Tomato leaf curl New Delhi virus (ToLCNDV). Five accessions presented nearly complete resistance to both viruses. Accession IC-274014, showing the highest level of resistance to both viruses, was crossed with the susceptible cultivar Védrantais. The F1, F2, F3/F4, and both backcross progenies were mechanically inoculated with MeCMV. Plants without symptoms or virus detection by enzyme-linked immunosorbent assay and/or PCR were considered as resistant. The segregations were compatible with two recessive and one dominant independent genes simultaneously required for resistance. Inheritance of resistance to ToLCNDV in the F2 was best explained by one recessive gene and two independent dominant genes simultaneously required. Some F3 and F4 families selected for resistance to MeCMV also were resistant to ToLCNDV, suggesting that common or tightly linked genes were involved in resistance to both viruses. We propose the names begomovirus resistance-1 and Begomovirus resistance-2 for these genes (symbols bgm-1 and Bgm-2). Resistance to MeCMV in IC-274014 was controlled by bgm-1, Bgm-2, and the recessive gene melon chlorotic mosaic virus resistance (mecmv); resistance to ToLCNDV was controlled by bgm-1, Bgm-2, and the dominant gene Tomato leaf curl New Delhi virus resistance (Tolcndv).

Genetic analysis and molecular mapping of stripe rust resistance genes in Chinese native wheat (Triticum aestivum) Lankao 5

Lankao 5 is a common wheat (Triticum aestivum) landrace collected from Henan province, China, which exhibits a high level of resistance to stripe rust (Puccinia striiformis f.sp. tritici, ‘Pst’) in field trials over many years. To analysegenetic of resistance in Lankao 5, F1 and F2 progenies were obtained from a cross between wheat genotypes Lankao 5 and Chinese Spring (CS). Parents, F1 and F2 plants, were planted in greenhouse and tested at the seedling stage with Pst races CYR29, CYR30, CYR31, CYR32, Sun11-4, and Sun11-11. Genetic analysis showed that the resistance of Lankao 5 to race CYR30 were conferred independently all by one dominant gene and one recessive gene, independently, resistance to Sun11-11 by one dominant gene, resistance to CYR31, CYR32, and Sun11-4 all by two independent dominant genes, and resistance to CYR29 by two recessive genes of independent action. Using F2 progenies from crosses between Lankao 5 and a set of 20 CS monosomic lines, the resistance gene in Lankao 5 to Pst race Sun11-11 was cytogenetically located on chromosome 7B. Using 141 F2 plants and their F3 generations with 7B specific simple sequence repeat (SSR) markers, a linkage map consisting of five SSR loci and the resistance gene locus YrLk was constructed. The linkage map spanned a genetic distance of 21.6 cM, and the SSR markers Xwmc396 and Xbarc267 were closely linked to YrLk with genetic distances of 3.3 and 4.4 cM, respectively. Analyses of chromosomal positions, reaction types to Pst race, and gene origin suggested that YrLk was very likely a novel resistance gene for stripe rust in wheat. Genetic analysis of the stripe rust resistance gene in Lankao 5 and closely linked markers for YrLk will facilitate the use of resistance in breeding programs to control wheat stripe rust.

Identification of fertility restorers among Assam rice cultivars by phenotyping and molecular screening approaches

In three line hybrid rice seed production the combination of a CMS line, maintainer line and restorer line are involved in the development of hybrids. The wild abortive CMS is extensively used in commercial hybrid seed production. The fertility restoration of wild abortive CMS is governed by two independent dominant Rf genes viz., Rf4 and Rf3. The present study was conducted with the objective of molecular characterization rice genotypes from Assam, India and to identify restorers for hybrid rice breeding programme. A total one hundred and eleven hybrids were generated and evaluated for their pollen and spikelet fertility. Based on molecular screening twenty five genotypes were identified to carry only Rf4 gene and three genotypes identified to carry both Rf3 and Rf4 genes. These identified restorers in the present study would be a usable restores for hybrid rice breeding in north east India. Molecular diversity for fertility restoration using NTSYS package formed two clusters among the tested genotypes, cluster A represented a landrace Terabali from Assam and cluster B with all other genotypes.

Differential reaction of selected restorers/maintainers with WA based CMS lines and genetics of fertility restoration in hybrid rice (Oryza sativaL.)

Investigation was carried out to identify restorers/maimtainers with WA based CMS lines. Various inbred lines behaved differently in four CMS back grounds in respect of their maintainer/restorer reaction. Lines R-42, R-43, R-44, R-46, R- 47, R-56, R-51, R-52, R-54, IR-64, IR-66, DRR-714, IR10198, IR 13419 and JGL 11118 identified as potential restorers at over the locations and these lines can be utilized for developing new potential hybrids. Fertility restoration studies indicated that restorer lines (R-43, R-44, R-52 and R-54) were governed by two independent dominant genes. A restorer with more than one independent gene is likely to produce the hybrids with higher fertility restoration and consequently increased yield.

Identification of three major R genes responsible for broad-spectrum blast resistance in an indica rice accession

An indica rice accession HR4 was found to exhibit good resistance to rice blast in previous research. Inoculation with 116 different M. oryzae isolates revealed that HR4 has the broadest resistance spectrum of the six rice cultivars used in this study, which included two well characterized broad-spectrum resistance sources. To uncover the genetic mechanism of the broad-spectrum resistance in HR4, genetic analysis was carried out with three stable isolates. The results showed that a single dominant gene controlled its resistance to isolates GD93286 and GD00193, whereas two independent dominant genes were responsible for its resistance to isolate GD08T4. The resistance (R) gene in HR4 corresponding to isolate GD93286, named Pi-h1(t), was found to reside in a region of ~235.9 kb on the long arm of chromosome 11, while the other two R genes identified with isolate GD08T4, named Pi-h2(t) and Pi-h3(t), were linked to markers on chromosomes 1 and 12, respectively. The results indicated that the broad-spectrum resistance to rice blast in HR4 could be ascribed to multiple R genes. Identification of such multiple R genes will allow us to use markers more effectively for resistance improvement in rice breeding programs.

Genetic diversity for adult plant resistance to leaf rust in bread wheat (Triticum aestivumL.)

There is an increasing worldwide interest in adult plant resistance (APR) since most examples of durable resistance to leaf rust in wheat are this kind. Twelve bread wheat genotypes were studied for inheritance of APR to leaf rust using pathotype 77-5 (121R63-1), the most prevalent and widely virulent one on bread wheat germplasm in India. Resistance was controlled by a pair of dominant and recessive genes each in CPAN 1676 and CSP 44 and by two independent dominant genes each in CPAN 1796, Frontana, HD 2009, HD 2135, HUW 37, HW 517, Nainari 60, Pavon 76,VL 404 and WG 138. Segregation patterns observed in their intercrosses showed the presence of at least four genes, including a recessive one, among these genotypes in addition to known APR genes Lr34, Lr46, Lr48, Lr49 and Lr68. The present findings are expected to contribute toward enriching diversity for leaf rust resistance in bread wheat improvement programmes.

Genetic Analysis of Resistance to Rice Blast: A Study on the Inheritance of Resistance to the Blast Disease Pathogen in an F3 Population of Rice

AbstractBlast caused by the fungus Magnaporthae grisea (Herbert) Borr. (anamorphe Pyricularia oryza Cav.) is a serious disease of rice (Oryza sativa L.). One method to overcome this disease is to develop disease resistant cultivars. Due to the genetic plasticity in the pathogen genome, there is a continuous threat to the effectiveness of the developed cultivars. Additional studies of the genetics of resistance, virulence stability and functional genomics are required to accelerate research into understanding the molecular basis of blast disease resistance. In this study, individual plants of the F3 population derived from Pongsu Seribu 2 and Mahsuri were used for pathogenesis assays and inheritance studies of blast resistance. The study was performed with two of the most virulent Malaysian M. grisea pathotypes: P7.2 and P5.0. For blast screening, plants were scored based on the IRRI Standard Evaluation System (SES). F3 populations showed a segregation ratio of 3R:1S for pathotype P7.2, indicating that resistance to this pathotype is likely controlled by a single nuclear gene. Chi‐square analysis showed that the F3 families segregated in a 15R:1S ratio for pathotype P5.0. Therefore, locus interactions or epitasis of blast resistance occur against pathotype P5.0 in the F3 population derived from Pongsu Seribu 2 and Mahsuri. This can be explained by the presence of two independent dominant genes that when present simultaneously, provide resistance to the M. gresia pathotype P5.0. These results indicated that blast resistance in rice is due to the combined effects of multiple loci with major and minor effects. The genetic data generated here will be useful in the breeding of local cultivars for resistance to field blast. The methodology reported here will facilitate the mapping of genes and quantitative trait loci (QTLs) underlying the blast resistance trait.

Fertility restoration in three CMS systems of eggplant by the Rf genes of each other's systems and their SCAR marker

Three pollen non-formation type cytoplasmic male sterility (CMS) systems of eggplant (Solanum melongena L.) were developed in our previous study, through repeated backcrossing, by using wild Solanum species Solanum aethiopicum L. Aculeatum Group, Solanum anguivi Lam. and Solanum grandifolium C. V. Morton as the cytoplasm donor and eggplant ‘Uttara’ as the recurrent pollen parent. Each CMS system has male fertile (MF) line which carries the fertility restorer (Rf) genes for the pollen non-formation type sterility. In the present study, fertility restoration ability in three CMS systems of eggplant by the Rf genes of each other's systems was evaluated. The male sterile (MS) line of each CMS system was pollinated with the pollen of MF lines of other CMS systems as well as its own CMS system. Among the nine cross combinations, six groups were obtained from crossing MS lines with MF lines of other CMS systems and three groups were obtained from crossing MS lines with MF lines of their own CMS system. The segregation of MF and MS plants was fitted well with a 3:1 ratio in almost all cross combinations. The segregation patterns revealed that two independent dominant Rf genes restore fertility in each CMS system. Pollen stainability and in vitro pollen germination rate of the progenies obtained from different cross combinations were varied from 61.0 to 89.8% and 0.7 to 8.0%, respectively. Each Rf gene of three CMS systems restores fertility of other CMS systems as well as its own CMS system. Moreover, fertility recovery action in these three kinds of CMS is similar. DNA markers linked to Rf genes were screened by bulked segregant analysis (BSA) using random amplified polymorphic DNA (RAPD). A total of 420 primers were used, and more than 65% of the primers yielded a considerable number of RAPD fragments in both MF and MS bulks. Only one Operon primer OPAB10 gave a reproducible polymorphic band of 1.9kbp (OPAB101900) between bulks and was identified as linked to the Rf genes. Additionally, the RAPD marker OPAB101900 was converted to sequenced characterized amplified region (SCAR) marker designated as SCAB101900 by nucleotide sequencing. Findings of the present study may give us a potential way to explore CMS and the corresponding Rf genes from wild Solanum resources for the breeding program of eggplant.

Heterosis and inheritance of fertility-restorer genes in rice

Three-line hybrid rice technology can increase rice yield. This study aims to identify restorers and maintainers, to estimate heterosis of hybrid rice, and to identify fertility-restorer genes of F2 populations. The analysis of 31 test crosses revealed 6 restorers and 9 maintainers based on pollen fertility. The estimation of heterosis to select superior genotypes was conducted on 12 hybrids resulting from crosses between 6 restorers and 2 male sterile lines. The results show that two hybrids had a high heterobeltiosis and standard heterosis, with yields of 7940 and 6810 kg/ha, respectively. The inheritance of fertility-restorer genes of F2 populations in crosses IR80151A/CH1 and IR80151A/CH4 was evaluated at heading to flowering stage based on pollen fertility and seed setting rate (SSR). The segregation ratio of pollen fertility was 15:1 (fertile: sterile), representing two nuclear independent dominant genes controlling the trait with sporophytic abortive fertility. The SSR, however, could not be used to study fertility-restorer genes, as it is influenced by physiological and environmental factors.

Development of Novel Cytoplasmic Male Sterile Source from Dongxiang Wild Rice (Oryza rufipogon)

This study was conducted to develop and characterize a novel cytoplasmic male sterile (CMS) source which was identified from Dongxiang wild rice (Oryza rufipogon) by crossing Dongxiang wild rice as female with Zhongzao 35, an indica inbred variety, as male and continuous backcrossing with Zhongzao 35. Observation under optical microscope manifested that this novel CMS belonged to typical abortion type with less pollen compared with wild abortive type cytoplasm (CMS-WA). Sequential planting showed that this novel CMS has complete and stable male sterility. Testcross experiment showed that all the 24 tested materials including maintainer and restorer lines of CMS-WA and Honglian type cytoplasm (CMS-HL) and other indica inbred varieties are the maintainers with complete maintaining ability, suggesting that this novel CMS has fertility restoration totally different from CMS-WA and CMS-HL and belongs to a novel type of CMS. So far, we only discovered a unique fertility restoration source for this novel CMS. Inheritance analysis showed that the fertility restoration of this CMS was governed by three pairs of independent dominant genes. Prospect for application of this novel CMS system in hybrid rice breeding was also discussed.

Evidence of a unique inter-allelic epistatic interaction for seed coat color in pigeonpea [Cajanus cajan (L.) Millspaugh

For enhancing productivity and profitability of pigeonpea (Cajanus cajan (L.) Millsp.) a hybrid breeding technology based on a cytoplasmic nuclear male-sterility (CMS) system was developed at International Crops Research Institute for the Semi-Arid Tropics (ICRISAT). Among the elite hybrids ‘ICPH 2671’ was most out-standing with 30–35% yield advantage over local varieties. Despite its commercial release in 2010, this hybrid could not attract many growers due to its less preferred seed color. Both the parents (ICPA 2043 and ICPR 2671) of this hybrid and their crossed seeds had Greyed-orange [code no*: 167B/C (* The standard identification numbers of Royal Horticultural Society)] color. However, the commercial seeds produced on the hybrid plants surprisingly have Greyed-purple (code no: 183C) color that fetches relatively less profits. To understand the genetics of this phenomenon a cross combination was studied for seed color in F1, F2, and B1C1F1 generations. The data suggested that three independent dominant genes controlled the expression of seed coat color. The observations further suggested the presence of two dominant genes (Brsd1 and Brsd2) in the male-sterile line ‘ICPA 2043’, ‘ICPR 2671’ and another dominant gene (Brsd3) in the restorer line. In the hybrid plants genes Brsd1 and Brsd2 act in complementation with the third gene Brsd3, this also acts as a modifier. The presence of Brsd3 gene in a genotype together with Brsd1 and/or Brsd2 produces a strong inter-allelic epistatic interactions resulting in the Greyed-purple (183C) seed color. It was further postulated that the genetic constitution of ‘ICPA 2043’ is Brsd1Brsd1Brsd2Brsd2brsd3brsd3, while the genotype of the restorer line ‘ICPR 2671’ is brsd1brsd1brsd2brsd2Brsd3Brsd3.

Inheritance of stripe rust resistance to predominant Chinese races in six spring wheat cultivars from the pacific Northwest of the United States

Stripe rust, caused by Puccinia striiformis Westend. f. sp. tritici Eriks., is a major disease that causes substantial losses to wheat production worldwide. The utilization of effective resistance genes in wheat cultivars is the preferred control of the disease. To study the inheritance of all-stage resistance in spring wheat cultivars Louise, WA008016, Express, Solano, Alturas and Zak from the Pacific Northwest (PNW) of the United States, the six cultivars were crossed with the Chinese susceptible variety Taichung 29. Single-spore isolates of CYR32 and CYR33, the predominant Chinese races of P. striiformis f. sp. tritici, were used to evaluate F1, F2 and BC1 generations for stripe rust resistance under controlled greenhouse conditions. Genetic analysis determined that Louise had one dominant resistance gene to CYR32, temporarily designated as YrLou. WA008016 had two dominant and one recessive resistance genes to CYR32, temporarily designated as YrWA1, YrWA2 and YrWA3, respectively. Express had a single recessive gene that conferred resistance to CYR32, temporarily designated as YrExp3. The two independent dominant genes in Solano conferring resistance to CYR32 were temporarily designated as YrSol1 and YrSol2. Alturas had two recessive genes for resistance to CYR32, temporarily designated as YrAlt1 and YrAlt2. Zak has one dominant gene for resistance to CYR33, temporarily designated as YrZak1. These six cultivars can be important resistance sources in Chinese wheat stripe rust resistance breeding.

Genetic Analysis of “8101” Soybean Containing Three Genes for Resistance to Soybean Mosaic Virus

ABSTRACTSoybean mosaic virus (SMV) occurs in most soybean [Glycine max (L.) Merr.] growing areas around the world. The use of soybean cultivars with resistance to SMV is the most effective way of controlling this disease. Three independent genetic loci (Rsv1, Rsv3, and Rsv4) with multiple alleles for SMV resistance have been identified. The objective of this study was to evaluate the genetic composition of a Chinese soybean line 8101 for SMV resistance. In this study, 8101 was crossed with susceptible cultivars Lee 68, Essex, and Hefeng No. 25. The genotype 8101 was also crossed with resistant lines PI 96983, L29, and V94‐5152 carrying Rsv1, Rsv3, and Rsv4, respectively, to examine the allelic relationship between the genes in 8101 and the previously reported genes at these three loci. The results indicated that 8101 carries three independent dominant genes for resistance to SMV. One of them is at the Rsv1 locus but carries a different allele than the Rsv1 in PI 96983. This new allele confers resistance to SMV G1 but a susceptible reaction to SMV G7. The second gene is at the Rsv3 locus conferring resistance to SMV G7 but a susceptible reaction to SMV G1. The third gene is at the Rsv4 locus and confers resistance to both SMV G1 and G7. The presence of these three genes in 8101 confers resistance to SMV strains G1 through G3 and G5 through G7. The line 8101 is the first genotype identified as carrying all three SMV resistance genes, Rsv1, Rsv3, and Rsv4 Research is underway to further characterize the three resistance genes in 8101.

Inheritance of somatic embryogenesis using leaf petioles as explants in upland cotton

Somatic embryogenesis (SE) is a critical step leading to plant regeneration in tissue culture of many plant species. The objective of the present study was to analyze the inheritance of SE in cotton (Gossypium hirsutum L.) using leaf petioles as explants. A high embryogenic callus (HEC)—producing line, W10, was selected by petiole callus culture from a commercial Chinese cotton cultivar CRI24 and crossed with a non embryogenic line, TM-1 and a low embryogenic (LEC) commercial Chinese cotton cultivar, CRI12, respectively. The parental lines, F1 and F2 were grown in field conditions for sources of leaf petioles as explants. The F1 plants were similar to the HEC parent in embryogenic callus (EC) induction, indicating that high EC ability is dominant. The classical Mendelian analysis showed that the high EC ability in the HEC line W10 is controlled by two independent dominant genes with complementary effect, designated Ec 1 and Ec 2 , while the LEC line CRI12 contains one dominant gene Ec 2 . A joint segregation analysis confirmed that SE ability in cotton is controlled by two major genes with epistatic effects along with other polygenes. A SSR marker analysis identified three quantitative trait loci (QTLs) on two linkage groups, one of which harbored a major QTL (qEc1) which is assigned to the major gene Ec 1 . This qualitative and quantitative genetic study has provided an incentive to fine map the genes responsible for SE towards the isolation of the SE genes in cotton.

Molecular mapping of genes for opposite leafing in maize using simple-sequence repeat markers

Maize with opposite phyllotaxy (OP) and also initiating ears in opposite pairs is an aberrant mutant and also precious material for maize breeding and plant evolution studies. Mapping and identifying the markers closely linked to genes for the OP trait are essential for cloning the gene and marker-assisted selection in breeding. We established H14D, a near-isogenic line of the OP trait with H53 genetic background. We found that the OP trait is regulated by two independent dominant genes with mutually complementary relations, named Opp-1 and Opp-2. Screening of seven simple-sequence repeat (SSR) markers among the 105 pairs of SSR primers showed polymorphism between the inbred lines H14D and H53. The polymorphic SSR markers were then used to determine linkage with the trait in an F(2) population with 441 progeny, suggesting that SSR marker umc2094 in the Bin2.01 region is linked with Opp-1 at 6.7 cM, and bnlg1831 in Bin2.06 is linked with Opp-2 at 6.1 cM. Further investigation showed that bnlg1092 and umc1028 are linked to Opp-1 and Opp-2 genes, with genetic distances of 12.2 and 1.9 cM. It was also found that the four SSR markers flank the two OP genes, respectively. These results will be useful for marker-assisted selection breeding of OP maize and will also strengthen the basis for cloning of the opposite leafing gene.