Cytoplasmic Male Sterile Lines Research Articles

Analysis of genetic architecture of head yield and biochemical traits in cabbage (Brassica oleracea var. capitata L.) using cytoplasmic male sterile lines

Analysis of genetic architecture of head yield and biochemical traits in cabbage (Brassica oleracea var. capitata L.) using cytoplasmic male sterile lines

Combining Ability and Gene Action Controlling Agronomic Traits for Cytoplasmic Male Sterile Line, Restorer Lines, and New Hybrids for Developing of New Drought-Tolerant Rice Hybrids.

This study aimed to identify new rice lines and hybrids that are tolerant to water deficit and produce high yields under water stress conditions. A line × tester mating design was used to study the lines and testers’ general combining ability (GCA) effects. The specific combining ability (SCA) of the hybrid rice combinations was measured under three different irrigation regimes; 6, 9, and 12 days. The study was carried out at the experimental farm of Sakha Agricultural Research Station, Sakha, Kafr El-Sheikh, Egypt, during the 2018 and 2019 rice growing seasons. Due to the genotypes and their partitions to the parents and the crosses, the mean squares were highly significant for all studied traits under the three irrigation regimes. The additive gene effects play an important role in expressing most of the studied traits. Therefore, the selection procedures based on the accumulation of the additive effect would be successful at improving these traits and the grain yield. The cytoplasmic male sterile (CMS) line G46A (L1) was the best combiner for most yield component traits in the three irrigation regimes. The newly devolved restorer lines T11, T1, T2, T5, T4, and T3, as well as the new hybrids L2 × T10, L2 × T6, L1 × T7, L1 × T5, L1 × T3, L2 × T7, L2 × T9, L2 × T8, L2 × T4, L1 × T4, L2 × T2, L1 × T8, L1 × T9, and L2 × NRL 10, showed good, desirable values of the studied traits such as earliness of flowering, short plant height, number of panicles/plant, panicle length, number of spikelets/panicle, number of filled grains/panicle, panicle weight, 1000-grain weight, hulling percentage, milling percentage, head rice percentage, and grain yield under the irrigation regimes of 6, 9, and 12 days. The hybrids L2 × T10, L2 × T6, L1 × T7, and L1 × T5, showed significant positive SCA effects for grain yield, under all three irrigation regimes.

Growth Regulators Improve Outcrossing Rate of Diverse Rice Cytoplasmic Male Sterile Lines through Affecting Floral Traits.

Cytoplasmic male sterility (CMS) provides an irreplaceable strategy for commercial exploitation of heterosis and producing high-yielding hybrid rice. The exogenous application of plant growth regulators could improve outcrossing rates of the CMS lines by affecting floral traits and accordingly increase hybrid rice seed production. The present study aimed at exploring the impact of growth regulators such as gibberellic acid (GA3), indole-3-acetic acid (IAA), and naphthalene acetic acid (NAA) on promoting floral traits and outcrossing rates in diverse rice CMS lines and improving hybrid rice seed production. The impact of foliar applications of growth regulators comprising GA3 at 300 g/ha or GA3 at 150 g/ha + IAA at 50 g/ha + NAA at 200 g/ha versus untreated control was investigated on floral, growth, and yield traits of five diverse CMS lines. The exogenously sprayed growth regulators, in particular, the combination of GA3, IAA, and NAA (T3) boosted all studied floral, growth, and yield traits in all tested CMS lines. Moreover, the evaluated CMS lines exhibited significant differences in all measured floral traits. L2, L3, and L1 displayed the uppermost spikelet opening angle, duration of spikelet opening, total stigma length, style length, stigma brush, and stigma width. In addition, these CMS lines exhibited the highest plant growth and yield traits, particularly under T3. Consequently, exogenous application of GA3, IAA, and NAA could be exploited to improve the floral, growth, and yield traits of promising CMS lines such as L2, L3, and L1, hence increasing outcrossing rates and hybrid rice seed production.

Development of New Iso-Cytoplasmic Rice-Restorer Lines and New Rice Hybrids with Superior Grain Yield and Grain Quality Characteristics by Utilizing Restorers' Fertility Genes.

This research was carried out at the Experimental Farm of Sakha Agricultural Research Station, Sakha, Kafr El-Sheikh, Egypt, during the 2018–2020 rice-growing seasons to develop and evaluate four iso-cytoplasmic rice-restorer lines: NRL79, NRL80, NRL81, and NRL82, as well as Giza 178, with ten new hybrids in order to estimate genotypic coefficient, phenotypic coefficient, heritability in a broad sense, and advantage over Giza 178 as a check variety (control) of new restorer lines. This study also estimated combining ability, gene action, better-parent heterosis (BP), mid-parents heterosis (MP), and standard heterosis (SH) over Egyptian Hybrid one (IR69A × Giza 178) as a check hybrid (control) for grain yield, agronomic traits, and some grain quality characters in restorer lines and hybrids. The percentage of advantage over commercial-variety Giza 178 (check) was significant, and highly significant among the newly developed restorer fertility lines for all the studied traits. This indicates that the selection is a highly effective factor in improving these traits. New restorer fertility lines showed highly significant positive values over commercial restorer for grain yield; the values ranged from 51% for NRL80 to 100.4% for NRL82, respectively. Meanwhile, in regard to the grain shape of paddy rice, three lines of the promising lines showed highly significant negative desirable values compared with Giza 178; the values ranged from −7.7% for the NRL80 to −15.2% for NRL79, respectively. Based on the superiority of the new lines, the new lines can be used as new restorer fertility lines to breed promising new hybrids and new inbred rice lines or varieties. From the results of the testcross experiment, the four promising lines were identified as effective restorer fertility lines for two cytoplasmic male sterile (CMS) lines. Moreover, the six rice hybrids showed values for SH heterosis of grain yield/plant of more than 15% over the check hybrid variety, with high values of 1000-grain weight and desirable grain shape; these hybrids were G46A × NRL81 (125.1%), G46A × NRL80 (66.9%), IR69A × NRL79 (47.2%), G46A × NRL79 (24.6%), IR69A × NRL81 (23.4%), and IR69A × NRL82 (16.2%).

Agro-morphological and molecular diversity analysis of new cytoplasmic male sterile lines in Indian cauliflower for their use in hybrid breeding

Cauliflower is a typical thermo-sensitive crop, highly responsive to heterosis for yield and stress tolerance. A diverse set comprising of 24 cytoplasmic male sterile (CMS) lines, developed across different maturity groups of Indian cauliflower, using refined Ogura, Can(napus) and Tour sterile cytoplasms was studied to understand the morphometric and molecular changes. The established Ogura-based CMS line of ‘84 series’ (in the nuclear background of snowball cauliflower) was used as an immediate source for conversion of fertile early- and mid-maturity groups lines. Observations on 18 agro-morphological traits revealed significant differences among the CMS lines, however they could not distinguish different CMS systems. The CMS system significantly reduced the floral traits (19) in almost all the transformed lines irrespective of the maturity group, however, the reduction was maximum in CMS line Tour(CMS 394–41–5) having Tour sterile cytoplasm. This CMS line had a peculiar feature of ‘gripping phenomena’ for the style which drastically reduced flower size and eventually seed yield. These CMS lines showed variation with 11 mtDNA markers and 36 genomic simple sequence repeats (gSSR), and of these, BnTR1 perfectly-identified Can(napus) and Tour CMS systems. This is the first detailed report on the extent of diversity observed in 24 new CMS lines developed using three diverse sterile cytoplasms in the nuclear background of different maturity groups of Indian cauliflower. The information will be of immense significance for immediate use in hybrid breeding and/or use as an immediate source of CMS trait for tropical cauliflowers in other regions.

Rapid and Synchronous Breeding of Cytoplasmic Male Sterile and Maintainer Line Through Mitochondrial DNA Rearrangement Using Doubled Haploid Inducer in Brassica napus.

When homozygously fertile plants were induced using doubled haploid (DH) induction lines Y3380 and Y3560, the morphology of the induced F1 generation was basically consistent with the female parent, but the fertility was separated, showing characteristics similar to cytoplasmic male sterile (CMS) and maintainer lines. In this study, the morphology, fertility, ploidy, and cytoplasm genotype of the induced progeny were identified, and the results showed that the sterile progeny was polima cytoplasm sterile (pol CMS) and the fertile progeny was nap cytoplasm. The molecular marker and test-cross experimental results showed that the fertile progeny did not carry the restorer gene of pol CMS and the genetic distance between the female parent and the offspring was 0.002. This suggested that those inductions which produced sterile and fertile progeny were coordinated to CMS and maintainer lines. Through the co-linearity analysis of the mitochondrial DNA (mtDNA), it was found that the rearrangement of mtDNA by DH induction was the key factor that caused the transformation of fertility (nap) into sterility (pol). Also, when heterozygous females were induced with DH induction lines, the induction F2 generation also showed the segregation of fertile and sterile lines, and the genetic distance between sterile and fertile lines was approximately 0.075. Therefore, the induction line can induce different types of female parents, and the breeding of the sterile line and the maintainer line can be achieved through the rapid synchronization of sister crosses and self-crosses. The induction of DH inducer in B. napus can provide a new model for the innovation of germplasm resources and open up a new way for its application.

Competitive ability of sunflower (Helianthus annuus L.) breeding material under Cyperus rotundus infestation

Abstract Weed infestation induces intense competition with the sunflower crop for soil nutrients, space and light causing significant yield losses of the sunflower. Therefore, study was undertaken during the year 2013–15 at College of Agriculture, University of Sargodha, Pakistan to determine the effect of Cyperus rotundus infestation on various morphological and biochemical traits. Initially a screening experiment was carried out to screen against C. rotundus infestation. Later on, cross combinations of selected cytoplasmic male sterile and restorer lines were attempted to develop F1 progenies which were compared with commercial hybrids along with parents. There were 6 parental lines (3 A and 3 R lines) along with 9 single cross combinations obtained from these parents. Experiment was carried out in complete randomized design having factorial arrangement with three replications. Weed in one of regime latter called as control were completely absent, while in weed infestation regimes 5 and 10 plants of C. rotundus were maintained. Results showed that C. rotundus infestation causes significant damage to the sunflower plants. Generally cross combination showed a decrease of leaf area by 440% and 264%, 61% and 49% for chlorophyll contents, 133% and 191% for head weight under low and high weed infestation regime respectively. However, antioxidant activity increased by 44% and 49% under low and high infestation regime induced by C. rotundus. Sunflower genotypes also showed variability in competitive ability against C. rotundus weed. Cross combinations coded as (A10, A7 and A2) showed lower comparative decrease for seed yield and oil contents when compared with standard hybrids under the presence of C. rotundus. Development of sunflower hybrids with better competitive ability under the presence of weeds such as C. rotundus may able to enhance plant development and lower yield losses in sunflower field with minimum the use of herbicide.

The genetic editing of GS3 via CRISPR/Cas9 accelerates the breeding of three-line hybrid rice with superior yield and grain quality

Grain size is one of the major traits that determine rice grain yield and quality. The GS3 gene is the first major quantitative trait locus (QTL) that was identified in regulating rice grain length and weight. It was reported that the gs3 allele with a mutation in the organ size regulation (OSR) domain of the GS3 protein produced longer grains. In this study, we used the CRISPR/Cas9 gene editing technology to introduce an edited gs3 allele into our indica maintainer line, Mei1B, to enhance its grain yield and quality. Through molecular analysis and sequencing, a homologous edited-gs3 mutant line without any transgene was obtained in the T1 generation and was named Mei2B. A superior male sterile line Mei2A was generated by backcrossing the cytoplasmic male sterile (CMS) line Mei1A with Mei2B. Mei2B had a higher grain quality and yield compared to its wild-type Mei1B. Its grain length increased by 7.9%, its length/width ratio increased from 3.89 to 4.19, TGW increased by 6.7%, and grain yield per plant increased by 14.9%. In addition, genetic improvement of other quality traits including brown rice length (6.83 mm), brown rice grain length/width ratio (3.61), matched the appearance standards set for traditional Simiao (silk seedling) type cultivars. Two restorer lines were outcrossed to both Mei1A and Mei2A to produce hybrid rice. Compared to two hybrids of Mei1A, the hybrids of Mei2A had longer grains, higher length/width ratio, TGW, and yield per plant. In addition, the hybrids of Mei2A showed a better grain appearance including better translucency, a lower chalky rice rate, and degree of chalkiness than the hybrids of Mei1A. These results demonstrated that the introduction of an elite gs3 allele into Mei1A via CRISPR/Cas9 gene editing technology led to significant genetic improvement of the rice grain. The resultant CMS line Mei2A(gs3) displayed much higher grain quality and yield than the original Mei1A. Therefore, our study demonstrated that the targeted genetic improvement via gene editing technology can enhance rice breeding, especially the breeding of three-line hybrid rice.

Comparative Analysis of Mitochondrial Genomes between the B-Type Cytoplasmic Male Sterility Line and Its Maintainer Line in Wheat

Cytoplasmic male sterility (CMS) is a complex phenomenon in plants, rendering them unable to produce functional pollen. In general, this is caused by an abnormal or dysfunctional mitochondrial genome. In wheat, however, the systematic structural characteristics of the mitochondrial genome from the CMS line, vis-à-vis its maintainer line, are rarely reported. Here, we identified the morphological characteristics, sequenced, assembled, and characterized the complete mitogenomes of the wheat B-type CMS line (B) and its maintainer line (YS9). The morphological results indicated that the B likely undergoes binucleate microspore abortion. The B and YS9 genomes were assembled into a typical circular molecule 452,794 and 452,453 bp in length, respectively, comprising 34 protein-coding genes (PCGs), 3 ribosomal RNA genes (rRNAs), and 16 transfer RNA genes (tRNAs). The codon usage analysis revealed leucine (Leu) and serine (Ser) as the most frequently used amino acid residues in the B and YS9 mitochondrial proteins. In particular, we uncovered a specific ORF2718, whose length of 501 bp was more 30 bp than that of the atp8 gene in the B genome, which perhaps could affect normal function of ATP8. Further, the existence of SNPs at the atp6 gene is probably associated with the CMS mechanism. This study suggests that sequencing and comparing the genomic features of the B and YS9 mitogenomes provides not only an important opportunity to conduct further genomic breeding studies, but also valuable information for future evolutionary and molecular studies of CMS in wheat.

Identification and expression analysis of phospholipase C family genes between different male fertility accessions in pepper.

Phospholipase C (PLC) is one of the major lipid-hydrolyzing enzymes, involved in lipid-mediating signal pathway. PLCs have been found to play a significant role in the growth and development of plants. In this study, the genome-wide identification and characteristic analysis of CaPLC family genes in pepper were conducted and the expression of two CaPLC genes were investigated. The results showed that a total of 11 CaPLC family genes were systematically identified, which were distributed on five chromosomes and divided into two groups based on their evolutionary relevance. Some cis-elements responding to different hormones and stresses were screened in the promoters of CaPLC genes. Quantitative real-time PCR indicated that the expression of CaPIPLC1 and CaPIPLC5 in flowers were dozens of times higher than in other tissues. In addition, with the development of flower buds, the relative expressions of CaPIPLC1 and CaPIPLC5 gradually increased in fertile materials R1 and F1. However, no expression of CaPIPLC1 and CaPIPLC5 were detected at all developmental stages of cytoplasmic male sterile lines (CMS) compared with fertile accessions. The study revealed the number and characteristics of the CaPLC family genes, which supplied a basic and systematic understanding of CaPLC family. In addition, these findings provided new insights into the role of CaPLC genes in pollen development and fertility restoration in pepper.

High-resolution bin-based linkage mapping uncovers the genetic architecture and heterosis-related loci of plant height in indica-japonica derived populations.

Plant height (PH) is an important trait affecting the plant architecture, seed yield, and harvest index. However, the molecular mechanisms underlying PH heterosis remain unclear. In addition, useful PH-related genes must be urgently identified to facilitate ideal plant architecture breeding in rice (Oryza sativa L.). In the present study, to explore rice quantitative trait loci (QTLs) and heterosis-related loci of PH in rice, we developed a high-generation (>F15 ) population of 272 recombinant inbred lines (RIL) from a cross of two elite varieties, Luohui 9 (indica/xian) × RPY geng (japonica/geng), and two testcross hybrid populations derived from the crosses of RILs and two cytoplasmic male sterile lines (YTA [indica] and Z7A [japonica]). Using deep resequencing data, a high-density genetic map containing 4758 bin markers was constructed, with a total map distance of 2356.41 cM. Finally, 31 PH-related QTLs for different PH component lengths or tiller numbers across five seasons were identified. Two major environment-specific PH QTLs were stably detected in Hainan (qPH-3.1) or Hubei (qPH-5.1), which have undergone significant functional alterations in rice with changes in geographical environment. Based on comparative genomics, gene function annotation, homolog identification, and existing literature (pioneering studies), candidate genes for multiple QTLs were fine-mapped, and the candidate genes qPH-3.1 and qPH-5.1 for PH were further validated using CRISPR-Cas9 gene editing. Specifically, qPH-3.1 was characterized as a pleiotropic gene, and the qPH-3.1 knockout line showed reduced PH, delayed heading, a decreased seed setting rate, and increased tiller numbers. Importantly, 10 PH heterosis-related QTLs were identified in the testcross populations, and a better-parent heterosis locus (qBPH-5.2) completely covered qPH-5.1. Furthermore, the cross results of fixed-genotype RILs verified the dominant effects of qPH-3.1 and qPH-5.1. Together, these findings further our understanding of the genetic mechanisms of PH and offer multiple highly reliable gene targets for breeding rice varieties with ideal architecture and high yield potential in the immediate future.

Molecular Characterization and Genetic Structure Evaluation of Breeding Populations of Fennel (Foeniculum vulgare Mill.)

Fennel, or Foeniculum vulgare Mill., is an important horticultural crop belonging to the Apiaceae family that is cultivated worldwide and used in the agri-food sector and for pharmaceutical preparations. Breeding strategies in this species usually involve three parental lines, including two maternal lines (one cytoplasmic male-sterile line and an ideotype representative maintainer line) that are crossed to obtain an ideotype representative of the cytoplasmic male-sterile line and one paternal line, used as a pollinator in crosses with the progeny of the derived maternal lines. From this cross, F1 hybrid progenies are obtained, which are characterized by high levels of heterozygosity and hybrid vigor. In this study, over 450 plants, representing 8 breeding populations and their respective 3 parental and 1 progeny line, were genotyped by means of codominant molecular markers. The 12 highly polymorphic microsatellites enabled the analyses of the genetic variability, distinctiveness and stability of each breeding line. Moreover, the genetic structure of the core collection was investigated, which, together with the homozygosity, gene flow and genetic similarity results, allowed the identification of unsuitable lines to be used in breeding plans due to their low homozygosity (10.4% in the pollinator line of population 7). Moreover, the Bayesian reconstruction of the core collection’s genetic structure, based on the codominant markers used, allowed us to confirm the distinctiveness results obtained from the genetic similarity investigation and the computed gene flow estimates. Among these, a trend in hybrid heterozygosity was also observed, that increased when the genetic similarity between the respective parental lines decreased. Thus, this research proposes a suitable method for genotyping fennel populations in pre- and post-breeding approaches, such as marker-assisted breeding or breeding line distinctiveness and stability verifications.

Comparative Cytological and Transcriptome Analyses of Anther Development in Nsa Cytoplasmic Male Sterile (1258A) and Maintainer Lines in Brassica napus Produced by Distant Hybridization.

1258A is a new line of B.napus with Nsa cytoplasmic male sterility (CMS) with potential applications in hybrid rapeseed breeding. Sterile cytoplasm was obtained from XinJiang Sinapis arvensis through distant hybridization and then backcrossed with 1258B for many generations. However, the characteristics and molecular mechanisms underlying pollen abortion in this sterile line are poorly understood. In this study, a cytological analysis revealed normal microsporogenesis and uninucleate pollen grain formation. Pollen abortion was due to non-programmed cell death in the tapetum and the inability of microspores to develop into mature pollen grains. Sucrose, soluble sugar, and adenosine triphosphate (ATP) contents during microspore development were lower than those of the maintainer line, along with an insufficient energy supply, reduced antioxidant enzyme activity, and substantial malondialdehyde (MDA) accumulation in the anthers. Transcriptome analysis revealed that genes involved in secondary metabolite biosynthesis, glutathione metabolism, phenylpropane biosynthesis, cyanoamino acid metabolism, starch and sucrose metabolism, and glycerolipid metabolism may contribute to pollen abortion. The down regulation of nine cytochrome P450 monooxygenases genes were closely associated with pollen abortion. These results suggest that pollen abortion in 1258A CMS stems from abnormalities in the chorioallantoic membranes, energy deficiencies, and dysfunctional antioxidant systems in the anthers. Our results provide insight into the molecular mechanism underlying pollen abortion in Nsa CMS and provide a theoretical basis for better heterosis utilization in B.napus.

Selection of nuclear genotypes associated with the thermo-sensitivity of Owen-type cytoplasmic male sterility in sugar beet (Beta vulgaris L.).

Cytoplasmic male sterility in sugar beet becomes thermo-sensitive when combined with specific genotypes, potentially offering a means to environmentally control pollination by this trait. The stability of cytoplasmic male sterility expression in several genetic backgrounds was investigated in sugar beet (Beta vulgaris L.). Nine genetically heterogenous plants from open-pollinated varieties were crossed with a cytoplasmic male sterile line to obtain 266 F1 plants. Based on marker analysis using a multiallelic DNA marker linked to restorer-of-fertility 1 (Rf1), we divided the F1 plants into 15 genotypes. We evaluated the phenotypes of the F1 plants under two environmental conditions: greenhouse rooms with or without daytime heating during the flowering season. Three phenotypic groups appeared: those consistently expressing male sterility, those consistently having restored pollen fertility, and those expressing male sterility in a thermo-sensitive manner. All plants in the consistently malesterile group inherited a specific Rf1 marker type named p4. We tested the potential for thermo-sensitive male sterile plants to serve as seed parents for hybrid seed production, and three genotypes were selected. Open pollination by a pollen parental line with a dominant trait of red-pigmented hypocotyls and leaf veins resulted in seed setting on thermo-sensitive male sterile plants, indicating that their female organs were functional. More than 99.9% of the progeny expressed the red pigmentation trait; hence, highly pure hybrids were obtained. We determined the nucleotide sequences of Rf1 from the three genotypes: One had a novel allele and two had known alleles, of which one was reported to have been selected previously as a non-restoring allele at a single U.S. breeding station but not at other stations in the U.S., or in Europe or Japan, suggesting environmental sensitivity.

Transcript Profiling Analysis and ncRNAs' Identification of Male-Sterile Systems of Brassica campestris Reveal New Insights Into the Mechanism Underlying Anther and Pollen Development.

Male-sterile mutants are useful materials to study the anther and pollen development. Here, whole transcriptome sequencing was performed for inflorescences in three sterile lines of Chinese cabbage (Brassica campestris L. ssp. chinensis Makino, syn. B. rapa ssp. chinensis), the genic male-sterile line (A line), the Polima cytoplasmic male-sterile (CMS) line (P line), and the Ogura CMS line (O line) along with their maintainer line (B line). In total, 7,136 differentially expressed genes (DEGs), 361 differentially expressed long non-coding RNAs (lncRNAs) (DELs), 56 differentially expressed microRNAs (miRNAs) (DEMs) were selected out. Specific regulatory networks related to anther cell differentiation, meiosis cytokinesis, pollen wall formation, and tapetum development were constructed based on the abortion characteristics of male-sterile lines. Candidate genes and lncRNAs related to cell differentiation were identified in sporocyteless P line, sixteen of which were common to the DEGs in Arabidopsis spl/nzz mutant. Genes and lncRNAs concerning cell plate formation were selected in A line that is defected in meiosis cytokinesis. Also, the orthologs of pollen wall formation and tapetum development genes in Arabidopsis showed distinct expression patterns in the three different sterile lines. Among 361 DELs, 35 were predicted to interact with miRNAs, including 28 targets, 47 endogenous target mimics, and five precursors for miRNAs. Two lncRNAs were further proved to be functional precursors for bra-miR156 and bra-miR5718, respectively. Overexpression of bra-miR5718HG in B. campestris slowed down the growth of pollen tubes, caused shorter pollen tubes, and ultimately affected the seed set. Our study provides new insights into molecular regulation especially the ncRNA interaction during pollen development in Brassica crops.

Evaluation of cytoplasmic male sterile lines for yield, stigma receptivity and influence of floral traits on the outcrossing rate in rice (<em>Oryza sativa </em>L.)

Evaluation of cytoplasmic male sterile lines for yield, stigma receptivity and influence of floral traits on the outcrossing rate in rice (<em>Oryza sativa </em>L.)

Identification of Heterotic Groups and Patterns Based on Genotypic and Phenotypic Characteristics Among Rice Accessions of Diverse Origins.

Identification of the right parental combinations to maximize heterosis is the major goal of hybrid breeding, which could be achieved through identification of heterotic groups. The main objective of this study was to identify promising heterotic groups for future rice breeding programs. A collection of 359 rice genotypes of diverse origins of China and abroad, composed of inbreds, maintainers, restorers, and temperature-sensitive genic male sterile (TGMS) lines were genotyped using 10K SNP chips. The SNP data set was subjected to genomic analyses for estimation of genetic divergence and diversity. Significant variations were observed in the germplasm with the identification of six different genetic groups. These lines were assigned to the genetic groups independent of their origin. Taking an account of commercially used heterotic groups present in each cluster, three cytoplasmic male sterile (CMS) lines and 14 inbred and restorer lines with moderate to high genetic distances selected from five heterotic patterns were crossed and obtained 42 F1 hybrids. A total of 14 hybrids were found with significant maximum mid- and better-parent heterosis, namely, TaifengA × Guang122, TaifengA × Wushansimiao, and TaifengA × Minghui63 for earliness; Guang8A × Huazhan for dwarf stature; and Guang8A × Huanghuzhan-1, TaifengA × Yuexiangzhan, Guang8A × Minhui3301, TianfengA × Guang122, Guang8A × Yahui2115, TianfengA × Huanghuazhan, TianfengA × Minghui63, TianfengA × Minhui3301, TaifengA × Gui99, and Guang8A × Yuenongsimiao for yield and yield-related traits. Mid-parent and better-parent heterotic F1 hybrids were in positive correlation with the genetic distances as that manifested by commercially used heterotic groups, encouraging the use of genotypic data for identification of heterotic groups. Our study provides an informative strategy for the development of early maturing, lodging resistant and high-yielding commercial hybrids and cultivars in future heterosis breeding programs.

Assessment of Genetic Parameters and Gene Action Associated with Heterosis for Enhancing Yield Characters in Novel Hybrid Rice Parental Lines.

The technology of hybrid rice utilizing heterosis is an essential requirement for achieving food security. The current study was aimed at assessing the genetic parameters and the gene actions of 15 yield-component traits associated with heterosis, in 9 new parental lines of hybrid rice and their generated hybrids. Five cytoplasmic male sterile (CMS) lines were crossed with four restorer (R) lines using twenty generated line × tester designation hybrid combinations. The results revealed that all the traits were controlled by additive and non-additive gene actions. However, the additive variance was the main component of the total genotypic variance. Assessment of the general combining ability (GCA) detected the best combiners among the genotypes. The hybrid combinations that expressed the highest-positive specific combining ability (SCA) for grain-yield were detected. The correlation between the GCA and SCA was evaluated. The hybrid crosses with high-positive heterosis, due to having a better parent for grain yield, were detected. The principal component analysis (PCA) recorded the first four principal axis displayed Eigenvalues >1 and existing variation cumulative of 83.92% in the genotypes for yield component characteristics. Three-dimensional plots corresponding to the studied traits illustrated that the genotypes Guang8A × Giza181, Quan-9311A × Giza179, II-32A × Giza181, and II-32A × Giza179 are classified as possessing superior grain yield.

Evaluation of A3 cytoplasmic male sterile forage sorghum lines for resistance to sugarcane aphid.

Three known sugarcane aphid-resistant pollinator parents were sterilized in A3 cytoplasmic male sterility and were confirmed in this study to be resistant to sugarcane aphid allowing for the development of sugarcane aphid-resistant forage hybrids. We utilized A3 cytoplasmic male sterility and converted known sugarcane aphid-resistant sorghum TX 2783, and newly released R. LBK1 (Reg. No. GP-865, PI 687244) and R. LBK2 (Reg. No. GP-866, PI 687245) into A3 sterility to determine if the sterile counterparts would also equally express tolerance and or antibiosis to sugarcane aphid. Free-choice flat screen trials and life-table demographic studies were utilized and compared to know susceptible/fertile entries KS 585, and TX 7000, and known resistant/fertile entries TX 2783 and DKS 37-07. The R. LBK1 fertile entry was more tolerant than the known susceptible entries KS 585 and TX 7000, but was not as resistant as the other resistant entries, sustaining a damage rating of 6.0 across two different screen trials. The sterile A3 R. LBK2 showed a greater tolerance and expressed higher levels of antibiosis during aphid reproductive studies when compared to the known resistant and fertile TX 2783. All other fertile (R. LBK2, TX2783) and the A3 male sterile counterparts (A3 R. LBK2, A3 TX2783) were very similar in expression of high levels of tolerance and exhibited statistically similar damage ratings of 3.3-4.3 when exposed to sugarcane aphids. No entry, either fertile or sterile, was as tolerant as DKS 37-07, a known resistant commercial hybrid. Other plant measurements including percent loss in chlorophyll content, difference in plant height, and number of true leaves for sugarcane aphid infested versus non-infested were very consistent and highly correlated with damage ratings. Antibiosis was also exhibited in both fertile and sterile versions of the resistant lines. There was a 2 × reduction in fecundity between the R. LBK1 fertile and its sterile A3 R. LBK1 when compared to the susceptible KS 585 and TX 7000; however, the remaining fertile and sterile entries had 3.8 × to 5.8 × decrease in fecundity when compared to the susceptible KS 585 and TX 7000. Other measurements in life-table statistics such as nymphs produced/female/d, and the intrinsic rates of increased were significantly lower for all fertile and sterile lines, showing that antibiosis significantly affected sugarcane aphid reproduction. In conclusion, the A3 cytoplasmic male sterility shows consistency for maintaining the single dominant trait SCA-resistant trait of TX 2783 for expressing both antibiosis and tolerance, and great utility in the development of sugarcane aphid-resistant forage sorghums.

Reprint: Investigation of Genetic Divergence in Local Sunflower Hybrids and Inbred Lines by Applying Morphological Markers

Knowledge of genetic diversity is the basic requisite for any plant breeding program. Seventeen sunflower hybrids and fifteen inbred lines including ten Cytoplasm male sterile lines and five restorer lines were evaluated at the experimental area of National Agriculture Research centre, Islamabad, Pakistan during autumn-2011. The objective of study was to investigate the genetic diversity, categorize the proficient cross combiners and approximate characters association among sunflower hybrids and inbred lines. Data was estimated on i.e. flower initiation days, full flowering days, full developmental days, height of plant, disk diameter, stem thickness, leaves per plant, hundred achenes weight, achenes yield and oil content percentage. The maximum achenes yield was contributed by Hysun-33 2119 kg ha-1. Followed by SMH-0924 and SMH-0925, SMH-1028 and SMH-0926 were suggested as potential significant hybrids for future breeding plans to incorporate maximum achenes yield and oil content percentage. The CMS-11, CMS-25 and CMS-10 were long statured with vigorous stem and all the restorers were early maturing recommended for including in hybridization program to generate high heterotic factions. Cluster diagram based on Euclidean dissimilarity matrix grouped hybrids as well as inbred lines in four groups. The group I and IV consist of four whereas group II and group III have three and five hybrids respectively. All the restores were clustered in III and IV and CMS in I and II groups respectively. According to principle component analysis the first two components contribute 64% and 89% in total variation in hybrids as well as in inbred lines respectively.