Cytoplasmic Sources Research Articles

Transcriptomic Communication between Nucleus and Mitochondria during the Browning Process of Lentinula edodes.

To explore the reason for cytoplasmic replacement's significant effect on browning, transcriptomic data of nuclear (N) and mitochondrial (M) mRNAs and long noncoding RNAs (lncRNAs) in L808 and two cytoplasmic hybrids (cybrids) (L808-A2 and L808-B) of Lentinula edodes at three different culturing times (80, 100, and 120 days) were obtained. The results showed that the expression of N and M genes and lncRNAs changed with the culture time and cytoplasmic source. Cytoplasmic replacement significantly affected some M and N genes related to the internal mechanism and external morphological characteristics of L. edodes browning. The internal browning mechanism should be the nicotinamide adenine dinucleotide phosphate (NADPH)-mediated antioxidant machinery to protect mycelia against oxidative stress induced by the generation of reactive oxygen species under light irradiation. External morphological characteristics were the changing features of brown films by melanin (an antioxidant) aggregation on the surface of the mycelia of the bag or log. Especially, some genes were related to the remodeling of the plasma membrane, extracellular enzymes of celluloses and hemicellulases, small molecules, and NADPH metabolic processes. Additionally, communication between the nucleus and mitochondria mediated by M-rps3 was reported for the first time, and it is mainly appreciated in M structural assembly, functional implementation, and cooperation with other organelles.

Identification of stable restorers and high-yielding hybrids using diverse sorghum male sterile cytoplasmic sources and established pollen parents under different water regimes

Sorghum hybrids demonstrated increased productivity and helped offset the decreasing cultivated areas, particularly in Asia. The diversity in cytoplasmic male sterility systems, stability of restorers and high yield of sorghum is an important factor for achieving food security and sustainability. In sorghum, hybrid production has been limited to A1 cytoplasmic source to date, primarily due to limited number of restorers on other cytoplasmic sources. This work aimed at filling this gap through diversifying and assessing the producibility and stability of cytoplasmic backgrounds across environments, evaluating the stability of restorers across cytoplasms and environments, and evaluating the performance of the hybrid F1 products under different water regimes across cropping seasons. The effects of genotypes and interactions between the genotypes and the tested environments were shown visually using GGE biplot, which also categorized the genotypes based on performance per se and stability. Analysis of variance revealed significant (P< 0.001) differences between genotypes, environments and their interaction components for all the plant characteristics studied. The various GGE biplot patterns revealed that the restorers G4 (IS 33844-5), G5 (M 35-1-19), G8 (ICSV 15014), and G10 (ICSR 13009) were stable across environments and cytoplasms. We observed the following order of superiority in cytoplasmic restoration and seed producibility, A2 >A1>A3 >A4. The A2 cytoplasm can therefore reliably offer seed producibility advantage to commercial seed producers. Furthermore, the which-won–where model for hybrid grain yield revealed specific adaptations of hybrid genotypes G143, G195 and G215 to first mega environment (E1 and E3), whereas G167, G110, and G112 were adapted to the second mega-environment (E2 and E4). With a GGE biplot goodness of fit of 70% the best possible yield- and stability-based ranking of hybrid genotypes was G143, G215, G189, G200, G69, G162, G119, G54, and G81. The newly uncovered hybrid products should therefore be considered for downstream testing stages and candidates for release and commercial cultivation. Clearly, this work resulted in novel findings particularly in terms of seed producibility, universal restorers across the 4 cytoplasms and environments, and superior and stable hybrid products, all of which are expected to add value to conventional and heterosis breeding in the process of sorghum cultivar development.

Development of CGMS Systems in Pigeonpea with Special Reference to A2 Source of Cytoplasm

Development of CGMS Systems in Pigeonpea with Special Reference to A2 Source of Cytoplasm

Early generation combining ability of maldandi restorers in rabi sorghum [Sorghum bicolor (L.) Moench

In this study, a reported restorer on maldandi cytoplasm DSMR 8 was used to identify combining ability in early segregating generation. A large F2 population of the cross M31-2A × DSMR 8 was raised. Among them, fifteen superior restoring plants were selected and forwarded to the F3 generation. These fifteen F3 plants were crossed to three male sterile lines having both milo and maldandi cytoplasmic sources (M31-2A, 401A, and 104A) in L × T design. Among lines, MR 4 showed significant positive gca effects for six traits. Among 45 crosses 18 recorded high sca and the remaining 27 crosses showed low sca. The crosses M 31-2A × MR 12 and M 31-2A × MR 14 showed maximum overall sca status as they were having significant positive sca effects. Out of 15 lines, only five lines viz., MR 4, MR 12, MR 1, MR 13, and MR 2 could be forwarded to the next generation as these lines were transgressive seggregants for combining ability because of good gca and better per se performance when crossed to maldandi cytoplasm.

Transcriptome Analysis Reveals the Genes Related to Pollen Abortion in a Cytoplasmic Male-Sterile Soybean (Glycine max (L.) Merr.).

Cytoplasmic male sterility (CMS) lays a foundation for the utilization of heterosis in soybean. The soybean CMS line SXCMS5A is an excellent CMS line exhibiting 100% male sterility. Cytological analysis revealed that in SXCMS5A compared to its maintainer SXCMS5B, its tapetum was vacuolated and abnormally developed. To identify the genes and metabolic pathways involving in pollen abortion of SXCMS5A, a comparative transcriptome analysis was conducted between SXCMS5A and SXCMS5B using flower buds. A total of 372,973,796 high quality clean reads were obtained from 6 samples (3 replicates for each material), and 840 differentially expressed genes (DEGs) were identified, including 658 downregulated and 182 upregulated ones in SXCMS5A compared to SXCMS5B. Among them, 13 DEGs, i.e., 12 open reading frames (ORFs) and 1 COX2, were mitochondrial genome genes in which ORF178 and ORF103c were upregulated in CMS lines and had transmembrane domain(s), therefore, identified as CMS candidate mitochondrial genes of SXCMS5A. Furthermore, numerous DEGs were associated with pollen wall development, carbohydrate metabolism, sugar transport, reactive oxygen species (ROS) metabolism and transcription factor. Some of them were further confirmed by quantitative real time PCR analysis between CMS lines with the same cytoplasmic source as SXCMS5A and their respective maintainer lines. The amount of soluble sugar and adenosine triphosphate and the activity of catalase and ascorbic acid oxidase showed that energy supply and ROS scavenging decreased in SXCMS5A compared to SXCMS5B. These findings provide valuable information for further understanding the molecular mechanism regulating the pollen abortion of soybean CMS.

Bunyaviral N Proteins Localize at RNA Processing Bodies and Stress Granules: The Enigma of Cytoplasmic Sources of Capped RNA for Cap Snatching

Most cytoplasmic-replicating negative-strand RNA viruses (NSVs) initiate genome transcription by cap snatching. The source of host mRNAs from which the cytoplasmic NSVs snatch capped-RNA leader sequences has remained elusive. Earlier reports have pointed towards cytoplasmic-RNA processing bodies (P body, PB), although several questions have remained unsolved. Here, the nucleocapsid (N) protein of plant- and animal-infecting members of the order Bunyavirales, in casu Tomato spotted wilt virus (TSWV), Rice stripe virus (RSV), Sin nombre virus (SNV), Crimean-Congo hemorrhagic fever virus (CCHFV) and Schmallenberg virus (SBV) have been expressed and localized in cells of their respective plant and animal hosts. All N proteins localized to PBs as well as stress granules (SGs), but extensively to docking stages of PB and SG. TSWV and RSV N proteins also co-localized with Ran GTPase-activating protein 2 (RanGAP2), a nucleo-cytoplasmic shuttling factor, in the perinuclear region, and partly in the nucleus when co-expressed with its WPP domain containing a nuclear-localization signal. Upon silencing of PB and SG components individually or concomitantly, replication levels of a TSWV minireplicon, as measured by the expression of a GFP reporter gene, ranged from a 30% reduction to a four-fold increase. Upon the silencing of RanGAP homologs in planta, replication of the TSWV minireplicon was reduced by 75%. During in vivo cap-donor competition experiments, TSWV used transcripts destined to PB and SG, but also functional transcripts engaged in translation. Altogether, the results implicate a more complex situation in which, besides PB, additional cytoplasmic sources are used during transcription/cap snatching of cytoplasmic-replicating and segmented NSVs.

Elucidating Mitochondrial DNA Markers of Ogura-Based CMS Lines in Indian Cauliflowers (Brassica oleracea var. botrytis L.) and Their Floral Abnormalities Due to Diversity in Cytonuclear Interactions.

Mitochondrial markers can be used to differentiate diverse mitotypes as well as cytoplasms in angiosperms. In cauliflower, cultivation of hybrids is pivotal in remunerative agriculture and cytoplasmic male sterile lines constitute an important component of the hybrid breeding. In diversifying the source of male sterility, it is essential to appropriately differentiate among the available male sterile cytoplasms in cauliflower. PCR polymorphism at the key mitochondrial genes associated with male sterility will be instrumental in analyzing, molecular characterization, and development of mitotype-specific markers for differentiation of different cytoplasmic sources. Presence of auto- and alloplasmic cytonuclear combinations result in complex floral abnormalities. In this context, the present investigation highlighted the utility of organelle genome-based markers in distinguishing cytoplasm types in Indian cauliflowers and unveils the epistatic effects of the cytonuclear interactions influencing floral phenotypes. In PCR-based analysis using a set of primers targeted to orf-138, 76 Indian cauliflower lines depicted the presence of Ogura cytoplasm albeit the amplicons generated exhibited polymorphism within the ofr-138 sequence. The polymorphic fragments were found to be spanning over 200–280 bp and 410–470 bp genomic regions of BnTR4 and orf125, respectively. Sequence analysis revealed that such cytoplasmic genetic variations could be attributed to single nucleotide polymorphisms and insertion or deletions of 31/51 nucleotides. The cytoplasmic effects on varying nuclear-genetic backgrounds rendered an array of floral abnormalities like reduction in flower size, fused flowers, splitted style with the exposed ovule, absence of nonfunctional stamens, and petaloid stamens. These floral malformations caused dysplasia of flower structure affecting female fertility with inefficient nectar production. The finding provides an important reference to ameliorate understanding of mechanism of cytonuclear interactions in floral organ development in Brassicas. The study paves the way for unraveling developmental biology of CMS phenotypes in eukaryotic organisms and intergenomic conflict in plant speciation.

A5 cytoplasm: way to three way forage pearl millet hybrids

In the present study, two CMS lines viz., ICMA 03333 and ICMA 01777 based on A5 cytoplasm were used. These A5 lines were crossed with maintainers of different cytoplasmic sources during kharif 2016. The maintainer lines belong to A1, A4 and Violaceum cytoplasmic sources. The 15 F1 hybrids developed from the crosses were found to be fully sterile and could be used as potential seed parents to develop three way forage hybrids.

Gene action for oil content and quality in diverse cytoplasmic sources in sunflower under varied moisture environments

Abstract Sunflower breeding aims to developing good heterotic hybrids which can be achieved by tapping combining ability of hybrids belongs to diverse parents. Nine diversified CMS lines along with one maintainer lines were hybridized with four male lines in a line × tester manner thereby, developing a total 40 hybrids. The experimental material was grown over two environments i.e. recommended irrigation and other moisture stress environments continuously for two years 2011 and 2012 in randomized complete block design with three replications at Punjab Agricultural University, Ludhiana, Punjab, India. The experiment was design to estimate combining ability of parental lines, gene effects and effect of divers CMS sources on oil content and quality traits. It was observed that the non-additive component of genetic variance played major role in inheritance of these traits as recommended by analysis of variance of combining abilities and analysis of genetic variance components. Further supporting this conclusion was the fact that the GCA/SCA ratio for oil content and quality traits observed in F1 generation was less than one under both the environments. These results indicated the preponderance of dominant gene action and the feasibility of hybrid sunflower development. GCA estimates revealed that CMS analogues CMS-XA (Unknown), ARG-2A (H. argophyllus) and PRUN-29A (H. praecox spp. runyonic) were very good combiner for oil content under both the environments. The pollen parents RCR-8297 and P69R were observed as very good combiners for oil content and stearic acid under moisture stress condition. The male parent P100R was recorded very good combiner for oil content under normal environment while, RCR-8297 and P100R were very good combiners for oleic acid under both the environments. A total seven crosses were identified for oil content and eight crosses for oleic acid as having high SCA effects under both the water regimes.

Combining ability and gene action in relation to alloplasmic isonuclear lines in pearl millet [Pennisetum glaucum (L.) R. Br.

The Line × Tester analysis involving two CMS lines with diverse (A1, A4 and A5) cytoplasmic sources and six testers (males) of pearl millet was carried out at JAU, Jamnagar (Gujarat) during Kharif 2018 to identify crosses and good combiners for developing new hybrids to achieve higher yield. The variance due to GCA and SCA showed that the non-additive components were pre-dominant for the expression of days to 50% flowering, plant height (cm), number of effective tillers per plant (no.), ear head diameter (cm), grain yield per plant (g) and Fe and Zn content (ppm) Whereas, additive components were predominant for the expression of days to maturity and ear head diameter (cm). Among the female parents ICMB 96222 were identified as good general combiner for grain yield per plant and some other component traits. Among the male parents J-2597, J-2598 and J-2603 was good general combiner for most of the characters. Among the 36 hybrids, five crosses (ICMA5 95222 x J-2597, ICMA4 95222 x J-2597 ICMA5 96222 x J-2596, ICMA4 96222 x J-2584 and ICMA1 96222 x J-2597) were identified as good specific combiners based on significant and positive sca effect for grain yield per plant.

Identification of stable restorers for diverse cytoplasmic source in Sorghum [Sorghum bicolor (L.) Moench.

In sorghum [Sorghum bicolor (L.) Moench.], milo is the lone source of cytoplasmic male sterility (CMS) extensively used in production of commercial hybrids. The hazards of such a narrow cytoplasmic base are apparent and consequently new diverse sources like A2, A3, A4, maldandi, VZM and G1 were identified. However, the commercial exploitation of these sources has not been possible because of the difficulty in fertility restoration on these sources. The present study was, therefore, undertaken to test different sorghum germplasm lines for their fertility restoration/maintenance on maldandi and milo cytoplasm. Twenty-five diverse accession were selected from minicore collection and crossed with two male sterile lines viz., 104A (milo) and M 31-2A (maldandi). The resulting F1s were classified as fertility restorers and maintainers based on seed set on bagged ear heads. The restoration studies indicated that 2 lines on maldandi and 6 on milo cytoplasm showed strong fertility restoration (&gt; 90 % seed set).

Insight into genetic potential of male sterile sweet sorghum A-lines for agroindustrial traits using tester R-lines

There is a growing demand for the development of alternative fuels from renewable sources, thus sweet sorghum an autogamous species has potential for bioethanol production. Traditionally recommended cultivars were varieties, however, with the development of cytoplasmic male sterile sweet sorghum lines, sweet sorghum hybrids have become economically viable. The sweet sorghum breeding program of the Brazilian Agricultural Research Corporation (Embrapa Milho e Sorgo) has been developing sweet sorghum hybrids for bioethanol production according to the scheme of A, B and R-lines are used, where A-lines are used as females in the production of hybrid seeds. A and B-lines are isogenic, which differ only its cytoplasm source, sterile and normal, respectively, and fertility restorers R-lines. Thus the objective of this work was to evaluate the genetic potential of new male-sterile sweet sorghum A-lines using testcross hybrids developed with two sweet sorghum R-line as testers for agroindustry characteristics for bioethanol production. Forty testcross hybrids were developed using 20 experimental A-lines and two testers sweet sorghum R-lines. Experiments were conducted at experimental stations in Sete Lagoas-MG and Nova Porteirinha-MG, to evaluate 20 A-lines, two 2 R-lines, the resulting 40 testcross hybrids, and two controls. The 64 treatments were evaluated for days to flowering, fresh biomass yield and total soluble solids (Brix). The data obtained were analyzed using the ASReml package, for the estimation of variance components and the prediction of genetic and non-genetic values via REML/BLUP. Two models were adopted, called Multi-Tester and Single-Tester. The genotypic values of the A-lines when crossed with tester T2, were positive for nine A-lines (12, 17, 6, 20, 18, 16, 19, 11 and 3) with emphasis on A-lines 12, 17 and 6, which were the highest values, respectively, the same tester for the trait FLOW, ten A-lines were positive values (3, 16, 17, 4, 12, 15, 5, 6, 8, 20) with emphasis on 3, 16 and 17. The genotypic values for TSS (Brix) trait of the A-lines when crossed with tester T1 were positive for A-lines (19, 18, 20, 16, 1, 5, and 6) with emphasis on lines 19, 18, 20, and 16, with the highest values, respectively. Only two A-lines showed positive genotypic values for three traits, A-line 16 and 20. These results indicate the need for continuing simultaneous improvement of A-lines for FLOW, FBY, and TSS. A-lines from the sorghum breeding program of Embrapa Milho e Sorgo have the potential for use as parents in the development of superior sweet sorghum hybrids for bioethanol production. The A-lines 6 and 20 have positive genotypic values for three traits, this A-lines has a potential for producing hybrids dedicated to bioethanol production. The T1-L tester was more efficient in discriminating the genetic values between the A lines for TSS, while the T2-L tester for FBY and FLOW. The development of a tester with genotype "drydry" and "Ma1Ma1" is important in order to develop superior hybrids to produce bioethanol involving the A, B and R scheme.

Identification and evaluation of tobacco cytoplasmic male sterile line Nta(gla)S K326 generated from asymmetric protoplast fusion of Nicotiana glauca and N. tabacum followed by backcrossing with N. tabacum K326

Cytoplasmic male sterile (CMS) lines are valuable resources in plant breeding for heterosis utilization, guaranteeing quality of hybrid seeds, and genetic integrity. Nta(sua)S K326, which contains the nuclei of Nicotiana tabacum cv. K326 and cytoplasm of N. suaveolens, is currently the dominant CMS source used in tobacco leaf production in Yunnan, China. Therefore, the alternative CMS lines are required. Here, the Nta(gla)S K326 with cytoplasm of N. glauca has been generated from asymmetric somatic hybridization between protoplasts of K326 and N. glauca followed by backcrossing with K326. Flow cytometry analysis revealed that Nta(gla)S has almost identical ploidy level as that in K326. Moreover, Nta(gla)S, Nta(sua)S, and K326 plants showed similar relative growth rate, yield, and contents of several chemical components in the field. Further scaning electron microscopic observation of floral organs revealed that the Nta(gla)S has shortened filaments and shrivelled stamens, whereas the Nta(sua)S has severe degenerated and carpel-liked stamens, compared with fertile K326 plants. In addition, the expression patterns of several mitochondrial genes in Nta(gla)S, Nta(sua)S, and K326 plants were compared. Furthermore, the cytoplasm source of Nta(gla)S and Nta(sua)S could be distinguished by cleaved amplified polymorphic sequence (CAPS) analysis with chloroplast-specific universal primers. Taken together, these results showed the development of a Nicotiana CMS hybrid via asymmetric somatic hybridization, suggesting that flow cytometry analysis at early stage could facilitate and accelerate the selection process of generating CMS lines. Importantly, the Nta(gla)S provides a valuable germplasm as an alternative CMS line instead of Nta(sua)S in Nicotiana hybrid breeding. The Nicotiana CMS hybrid Nta(gla)S has been generated by asymmetric protoplast hybridization. The Nta(gla)S provides a valuable germplasm as an alternative CMS line instead of Nta(sua)S in Nicotiana hybrid breeding.

Interactions between cytoplasmic and nuclear genomes confer sex-specific effects on lifespan in Drosophila melanogaster.

Genetic variation outside of the cell nucleus can affect the phenotype. The cytoplasm is home to the mitochondria, and in arthropods often hosts intracellular bacteria such as Wolbachia. Although numerous studies have implicated epistatic interactions between cytoplasmic and nuclear genetic variation as mediators of phenotypic expression, two questions remain. Firstly, it remains unclear whether outcomes of cyto-nuclear interactions will manifest differently across the sexes, as might be predicted given that cytoplasmic genomes are screened by natural selection only through females as a consequence of their maternal inheritance. Secondly, the relative contribution of mitochondrial genetic variation to other cytoplasmic sources of variation, such as Wolbachia infection, in shaping phenotypic outcomes of cyto-nuclear interactions remains unknown. Here, we address these questions, creating a fully crossed set of replicated cyto-nuclear populations derived from three geographically distinct populations of Drosophila melanogaster, measuring the lifespan of males and females from each population. We observed that cyto-nuclear interactions shape lifespan and that the outcomes of these interactions differ across the sexes. Yet, we found no evidence that placing the cytoplasms from one population alongside the nuclear background of others (generating putative cyto-nuclear mismatches) leads to decreased lifespan in either sex. Although it was difficult to partition mitochondrial from Wolbachia effects, our results suggest at least some of the cytoplasmic genotypic contribution to lifespan was directly mediated by an effect of sequence variation in the mtDNA. Future work should explore the degree to which cyto-nuclear interactions result in sex differences in the expression of other components of organismal life history.

Complete organelle genomes of Sinapis arvensis and their evolutionary implications

Sinapis arvensis, belonging to the genus Sinapis of the family Brassicaceae, has good agronomic characters that make it a valuable genetic resource for crop improvement and is a cytoplasmic source of heterologous cytoplasmic male sterility (CMS). In addition, S. arvensis has played an important role in the evolution of the six major cultivated Brassica species involved in the triangle of U. Using next-generation sequencing, we assembled and revealed the gene composition of S. arvensis cytoplasmic genome. The chloroplast genome comprises 153,590 bp, with 112 individual genes, including 4 rRNA, 29 tRNA, and 79 protein-coding genes. The mitochondrial genome comprises 240,024 bp, with 54 genes, including 18 tRNA, three rRNA and 33 protein-coding genes. Genome structure and evolutionary analysis indicated that the sequences of the S. arvensis organellar genomes were more similar to those of Brassica nigra and B. carinata than to those of other Brassicaceae species. Four mitochondrial open reading frames displaying chimeric structural features and encoding hypothetical proteins with transmembrane domains may account for the infertility of Nsa CMS previously derived from somatic cell hybridization between B. napus and S. arvensis. These results will not only contribute to utilize the germplasm resource of S. arvensis, and comprehend the evolution of organelle genomes within the Brassicaceae family, but also help to identify genes conditioning the alloplasmic male sterility of Nsa CMS in B. napus.

Genetic Diversity and Classification of the Cytoplasm of Chinese Elite Foxtail Millet [Setaria italica (L.) P. Beauv.] Parental Lines Revealed by Chloroplast Deoxyribonucleic Acid Variation.

Due to the maternal inheritance of cytoplasm, using foxtail millet [Setaria italica (L.) P. Beauv.] male sterile lines with a single cytoplasmic source as the female parent will inevitably lead to a narrow source of cytoplasm in hybrids, which may make them vulnerable to infection by cytoplasm-specific pathogens, ultimately leading to destructive yield losses. To assess cytoplasmic genetic diversity in plants, molecular markers derived from chloroplast DNA (cpDNA) have been used. However, such markers have not yet been applied to foxtail millet. In this study, we designed and screened nine pairs of polymorphic foxtail millet-specific primers based on its completely sequenced cpDNA. Using these primers, we analyzed the genetic diversity and cytoplasmic types of 130 elite foxtail millet parental lines collected in China. Our results revealed that the cytoplasmic genetic diversity of these accessions was low and needs to be increased. The parental lines were divided into four cytoplasmic types according to population structure analysis and a female parent-derivative evolutionary graph, indicating that the cytoplasmic types of elite foxtail millet lines were rather limited. A principal component analysis (PCA) plot was linked with the geographic and ecological distribution of accessions for each cytoplasmic type, as well as their basal maternal parents. Collectively, our results suggest that enriching cytoplasmic sources through the use of accessions from diverse ecological regions and other countries as the female parent may improve foxtail millet breeding programs, and prevent infection by cytoplasm-specific pathogens.

Current understanding of male sterility systems in vegetable Brassicas and their exploitation in hybrid breeding.

Overview of the current status of GMS and CMS systems available in Brassica vegetables, their molecular mechanism, wild sources of sterile cytoplasm and exploitation of male sterility in hybrid breeding. The predominantly herbaceous family Brassicaceae (crucifers or mustard family) encompasses over 3700 species, and many of them are scientifically and economically important. The genus Brassica is an economically important genus within the tribe Brassicaceae that comprises important vegetable, oilseed and fodder crops. Brassica vegetables display strong hybrid vigor, and heterosis breeding is the integral part in their improvement. Commercial production of F1 hybrid seeds in Brassica vegetables requires an effective male sterility system. Among the available male sterility systems, cytoplasmic male sterility (CMS) is the most widely exploited in Brassica vegetables. This system is maternally inherited and studied intensively. A limited number of reports about the genic male sterility (GMS) are available in Brassica vegetables. The GMS system is reported to be dominant, recessive and trirecessive in nature in different species. In this review, we discuss the available male sterility systems in Brassica vegetables and their potential use in hybrid breeding. The molecular mechanism of mt-CMS and causal mitochondrial genes of CMS has been discussed in detail. Finally, the exploitation of male sterility system in heterosis breeding of Brassica vegetables, future prospects and need for further understanding of these systems are highlighted.

Cytoplasmic and nuclear genetic components of membrane stability of winter wheat plants exposed to sub‐zero temperatures

AbstractWinter wheat (Triticum aestivum L.) is seeded in the autumn and harvested the following summer, and therefore, must survive multiple episodes of subfreezing temperatures throughout the winter months. Cellular membrane stability following exposure to subfreezing temperatures contributes to the ability to survive these episodes. This study investigated the inheritance of the ability to tolerate subfreezing temperatures with a seven‐parent diallel cross analysis of cellular membrane integrity as measured by electrolyte leakage after exposure to −10 or −14 °C. Significant differences in membrane stability were found among the parent lines. The inheritance of the freezing tolerance as measured by electrolyte leakage was complex and characterized by significant additive, dominant and cytoplasmic effects. General combining ability, indicative of additive genetic effects, were significant at both test temperatures, but accounted for 25.5% of the variance at the −10° C test temperature, and only 4% of the variance at the −14 °C test temperature. Specific combining ability, indicative of genetic dominance effects, were significant at both test temperatures, but accounted for only 14.6% of the variance at the −10 °C test temperature, and 38% of the variance at the −14 °C test temperature. Reciprocal (cytoplasmic) effects were significant and accounted for about 20% of the variance at both test temperatures. Cytoplasmic effects contributing to greater membrane stability were especially apparent in the cultivar Tiber when crossed to Masami, Lewjain, or Hatton. These results suggest that efforts to improve freezing tolerance are complicated by differing gene action at different test temperatures and also may benefit from identifying specific combinations of nuclear and cytoplasm sources that are most conducive to membrane stability following freezing.

Identification of fertility restorer and sterility maintainer lines for diversified CMS lines in sunflower (Helianthus annuus L.)

Six diversifiedCMS lines ARG-6-3-1-4, PKUZ, ARG-3, ARG-2-1-2, PRUN-29 and MUT2-8-3-2 were crossed with ninety six inbred lines in a line x tester fashion to study their sterility maintenance or fertility restoration reaction. Out of 96 inbreds tested, 48 inbreds restored fertility in the diversified CMS lines viz., ARG-6-3-1-4, PKUZ, ARG-3, ARG-2-1-2, while 47 and 45 inbreds restored fertility in MUT2-8-3-2 and PRUN-29, respectively. On the other hand, 39, 46, 45, 43, 44 and 46 inbreds maintained sterility in the diversified CMS lines ARG-6-3-1-4, MUT-2-8-2, PUKZ, ARG-3, PRUN-29 and ARG-2-1-2, respectively. Among 96 inbreds, as many as 38 inbreds were identified as common maintainers for all the six diverse CMS lines. Similarly, 39 inbreds were identified as common restorers for all the six diverse CMS lines. Effective restorer lines identified for alternate sources of cytoplasm could be exploited in developing hybrids with better heterosis and it can pave way for broadening the CMS sources used in commercial hybrid development. Identified promising maintainer lines could be used in development of new CMS lines through conversion.

Characterization for Drought Tolerance and Physiological Efficiency in Novel Cytoplasmic Male Sterile Sources of Sunflower (Helianthus annuus L.)

Sunflower is sensitive to drought, and furthermore, sunflower hybrids display limited cytoplasmic diversity. In addition, the wild cytoplasmic sources of sunflower are not well explored for their potential to introduce drought tolerance into newly developed hybrids. Therefore here, we carried out a Line × Tester-based genetic study using 19 sunflower genotypes representing, 13 cytoplasmic male sterile (CMS) lines from wild and conventional sources, 2 maintainer lines, and 4 restorer lines. The CMS and maintainer lines were crossed with restorer lines to develop sixty F1 hybrids. The parents and their hybrids were evaluated under two water regimes, normal irrigation and drought stress (i.e., withholding water). A total of twelve important plant descriptors were studied over a period of two years and the significant differences between parents and hybrids are reported here. More specifically, hybrid lines were higher in average values for all the descriptors. The contribution of female parent was more prominent in the expression of traits in hybrids as compared to male parents. The CMS sources varied significantly regarding seed yield per plant and other physiological traits. Proline content in the leaves of all the genotypes was three times higher in the water stress regime. Accession CMS-PKU-2A was identified as the best general combiner for leaf area and specific leaf weight., whereas CMS-234A was the best general combiner for biological yield and photosynthetic efficiency under both conditions. The cross combinations CMS-ARG-2A × RCR-8297, CMS-234A × P124R, and CMS-38A × P124R were found significant for biological yield, seed yield and oil content under both environments. Overall, this study provides useful information about the cytoplasmic effects on important sunflower traits and drought stress tolerance.