Strong Heterosis Research Articles

Evaluation of the relationship between DNA methylation status and heterosis in soybean with MethylRAD technique

Heterosis plays an important role in the breeding of commercial crops, but the molecular mechanism behind this phenomenon is still unclear. To better understand the molecular basis of heterosis in soybean, the correlation between DNA methylation status and heterosis in soybean was tested. From three soybean varieties used as parents, six hybrid combinations were generated. Twelve traits of the nine materials were investigated to study the relationship between DNA methylation level differences and heterosis. In this study, MethylRAD technique was used to evaluate the genomic methylation status among the six reciprocal soybean F1 hybrids and their parents in the immature grains. Results showed that the total site number of methylation and methylation levels of the F1 hybrids with strong heterosis were in a status between the two parents and the ones with weak heterosis were generally below that of two parents. Thus, it was beneficial to promote heterosis when the numbers of methylation sites and methylation levels were between two parents. Among three types of methylation variations, the type that parental demethylated and the progeny methylated (type A) may be relative to improve heterosis of some traits. The type A of methylation variations was significantly positively correlated with the mid-parent heterosis (MPH) of the fat content (r = 0.98**), the branch number per plant (r = 0.84), and also was significantly positively correlated with the BPH of the branch number per plant (r = 0.82*) and the stems thick (r = 0.81*). These results implied that both the methylation and demethylation in hybrids relative to their parents may control the expression of the genes that were associated with partial phenotypic variation in hybrids.

Large-Scale Analysis of Combining Ability and Heterosis for Development of Hybrid Maize Breeding Strategies Using Diverse Germplasm Resources.

Understanding combining ability and heterosis among diverse maize germplasm resources is important for breeding hybrid maize (Zea mays L.). Using 28 temperate and 23 tropical maize inbreds that represent different ecotypes and worldwide diversity of maize germplasm, we first developed a large-scale multiple-hybrid population (MHP) with 724 hybrids, which could be divided into three subsets, 325 temperate diallel hybrids and 136 tropical diallel hybrids generated in Griffing IV, and 263 temperate by tropical hybrids generated in NCD II. All the parental lines and hybrids were evaluated for 11 traits in replicated tests across two locations and three years. Several widely used inbreds showed strong general combining ability (GCA), and their derived hybrids showed strong specific combining ability (SCA). Heterosis is a quantifiable, trait-dependent and environment-specific phenotype, and the response of parental lines and their hybrids to environments resulted in various levels of heterosis. For all the tested traits except plant height and hundred grain weight (HGW), NCD II (temperate × tropical) hybrids showed higher average heterosis than the temperate and tropical diallel hybrids, with higher hybrid performance for ear length, ear diameter, and HGW. Tropical maize germplasm can be used to improve the yield potential for temperate lines. Grain number per row and grain number per ear were two most important traits that determined yield heterosis, which can be used as direct selection criteria for yield heterosis. The hybrids from heterotic groups, Reid × SPT, Reid × LRC, SPT × PA, and Lancaster × LRC, contributed highly significant positive SCA effects and strong heterosis to yield-related traits, and the heterotic patterns identified in this study were potentially useful for commercial maize breeding. Heterosis was more significantly and positively correlated with SCA than GCA, indicating that SCA can be used in heterosis prediction to develop potential hybrids in commercial maize breeding. The results of the present study not only contribute to developing breeding strategies, but also improve targeted breeding efficiency by using both temperate and tropical maize to broaden genetic basis. Large sets of parental lines with available genotypic information can be shared and used in worldwide hybrid breeding programs through an open-source breeding strategy. Potential applications of the reported results in developing hybrid maize breeding strategies were also discussed.

Genome-wide identification and analysis of heterotic loci in three maize hybrids.

SummaryHeterosis, or hybrid vigour, is a predominant phenomenon in plant genetics, serving as the basis of crop hybrid breeding, but the causative loci and genes underlying heterosis remain unclear in many crops. Here, we present a large‐scale genetic analysis using 5360 offsprings from three elite maize hybrids, which identifies 628 loci underlying 19 yield‐related traits with relatively high mapping resolutions. Heterotic pattern investigations of the 628 loci show that numerous loci, mostly with complete–incomplete dominance (the major one) or overdominance effects (the secondary one) for heterozygous genotypes and nearly equal proportion of advantageous alleles from both parental lines, are the major causes of strong heterosis in these hybrids. Follow‐up studies for 17 heterotic loci in an independent experiment using 2225 F2 individuals suggest most heterotic effects are roughly stable between environments with a small variation. Candidate gene analysis for one major heterotic locus (ub3) in maize implies that there may exist some common genes contributing to crop heterosis. These results provide a community resource for genetics studies in maize and new implications for heterosis in plants.

Resequencing core accessions of a pedigree identifies derivation of genomic segments and key agronomic trait loci during cotton improvement.

SummaryUpland cotton (Gossypium hirsutum) is the world's largest source of natural fibre and dominates the global textile industry. Hybrid cotton varieties exhibit strong heterosis that confers high fibre yields, yet the genome‐wide effects of artificial selection that have influenced Upland cotton during its breeding history are poorly understood. Here, we resequenced Upland cotton genomes and constructed a variation map of an intact breeding pedigree comprising seven elite and 19 backbone parents. Compared to wild accessions, the 26 pedigree accessions underwent strong artificial selection during domestication that has resulted in reduced genetic diversity but stronger linkage disequilibrium and higher extents of selective sweeps. In contrast to the backbone parents, the elite parents have acquired significantly improved agronomic traits, with an especially pronounced increase in the lint percentage. Notably, identify by descent (IBD) tracking revealed that the elite parents inherited abundant beneficial trait segments and loci from the backbone parents and our combined analyses led to the identification of a core genomic segment which was inherited in the elite lines from the parents Zhong 7263 and Ejing 1 and that was strongly associated with lint percentage. Additionally, SNP correlation analysis of this core segment showed that a non‐synonymous SNP (A‐to‐G) site in a gene encoding the cell wall‐associated receptor‐like kinase 3 (GhWAKL3) protein was highly correlated with increased lint percentage. Our results substantially increase the valuable genomics resources available for future genetic and functional genomics studies of cotton and reveal insights that will facilitate yield increases in the molecular breeding of cotton.

Genome-wide proteomic profiling reveals the role of dominance protein expression in heterosis in immature maize ears

Heterosis refers to the phenomenon in which hybrid progeny show superior performance relative to their parents. Early maize ear development shows strong heterosis in ear architecture traits and greatly affects grain yield. To explore the underlying molecular mechanisms, genome-wide proteomics of immature ears of maize hybrid ZD909 and its parents were analyzed using tandem mass tag (TMT) technology. A total of 9,713 proteins were identified in all three genotypes. Among them, 3,752 (38.6%) proteins were differentially expressed between ZD909 and its parents. Multiple modes of protein action were discovered in the hybrid, while dominance expression patterns accounted for 63.6% of the total differentially expressed proteins (DEPs). Protein pathway enrichment analysis revealed that high parent dominance proteins mainly participated in carbon metabolism and nitrogen assimilation processes. Our results suggested that the dominant expression of favorable alleles related to C/N metabolism in the hybrid may be essential for ZD909 ear growth and heterosis formation. Integrated analysis of proteomic and quantitative trait locus (QTL) data further support our DEP identification and provide useful information for the discovery of genes associated with ear development. Our study provides comprehensive insight into the molecular mechanisms underlying heterosis in immature maize ears from a proteomic perspective.

Breeding and study of two new photoperiod- and thermo-sensitive genic male sterile lines of polyploid rice (Oryza sativa L.)

Male sterile lines play an important role in the utilization of heterosis. To explore and exploit the heterosis of polyploid hybrid rice, two photoperiod- and thermo-sensitive genic male sterile lines of polyploid rice, PS006 and PS012, were bred via chromosome doubling, complex hybridization and self-breeding. The characteristics of these two lines, including the agronomic traits, growth, development, fertility transformation and combining ability, were investigated. Both lines had good agronomic characteristics and flowering habits, a high outcrossing rate, obvious fertility alterations and good combining abilities. Their hybrids showed strong heterosis and great potential for increasing rice productivity and quality. The new polyploid rice photoperiod- and thermo-sensitive genic male sterile lines will provide material for further research into polyploidy and hybrid vigour in rice and promote the exploitation of polyploid hybrid rice.

Genetic analysis of Upland cotton dynamic heterosis for boll number per plant at multiple developmental stages.

Yield is an important breeding target. As important yield components, boll number per plant (BNP) shows dynamic character and strong heterosis in Upland cotton. However, the genetic basis underlying the dynamic heterosis is poorly understood. In this study, we conducted dynamic quantitative trait loci (QTL) analysis for BNP and heterosis at multiple developmental stages and environments using two recombinant inbred lines (RILs) and two corresponding backcross populations. By the single-locus analysis, 23 QTLs were identified at final maturity, while 99 QTLs were identified across other three developmental stages. A total of 48 conditional QTLs for BNP were identified for the adjacent stages. QTLs detected at later stage mainly existed in the partial dominance to dominance range and QTLs identified at early stage mostly showed effects with the dominance to overdominance range during plant development. By two-locus analysis, we observe that epistasis played an important role not only in the variation of the performance of the RIL population but also in the expression of heterosis in backcross population. Taken together, the present study reveals that the genetic basis of heterosis is dynamic and complicated, and it is involved in dynamic dominance effect, epistasis and QTL by environmental interactions.

Progress of <italic>indica-japonica</italic> hybrid sterility and wide-compatibility in rice

As a main staple food for world population, utilization of heterosis in rice has increased crop productivity tremendously. The Asian cultivated rice ( Oryza sativa L.) consists of two subspecies, indica and japonica . Genetic differentiation between indica and japonica subspecies appears to be a major source of genetic diversity in the cultivated rice gene pool. A strategic plan for utilization of inter-subspecific heterosis was proposed half a century ago, indicating that strong heterosis in indica-japonica hybrids provides an effective approach to increase the yield potential for rice breeding. Hybrid sterility that caused by postzygotic reproductive isolation has been a major barrier for utilization of such heterosis between indica and japonica . Genetic analyses have identified a large number of loci conditioning hybrid sterility in rice, which regulate fertility in heterozygous genetic background by complex allelic and epistasis interactions. Six locus-pairs regulating hybrid embryo-sac or pollen sterility have been cloned recently in rice, providing fresh understandings in mechanism of hybrid sterility. The molecular and evolutionary mechanisms underlying reproductive isolation are summarized with respect to the rice hybrid sterility genes, which reveal three evolutionary genetic models including the parallel divergence model, the sequential divergence model, and the parallel-sequential divergence model. There also exists a special group of rice germplasm, referred to as wide-compatibility varieties that produce fertile hybrids when crossed to both indica and japonica varieties. The wide-compatibility genes in these varieties enable hybridization and provide valuable genetic resources for utilization of inter-subspecific heterosis, which take diverse forms owing to the divergent mechanisms in reproductive barriers. Therefore, understanding in hybrid sterility and reproductive isolation in rice would greatly facilitate the utilization of heterosis in breeding programs. This paper summarized the progress in genetic and molecular mechanisms regulating rice hybrid sterility, and discussed the recent understanding in wide-compatibility genes and their utilizations in breeding of wide-compatibility varieties. These advances may greatly facilitate the exploration of inter-subspecific heterosis in breeding programs.

Vigor híbrido en cruzamientos de líneas endocriadas de gusanos de seda (Bombyx mori L)

Productive characteristics of hybrids, from the crossing of a FA-UBA line and other one of a European origin, have been assessed. Three quantitative variables have been measured: length and weight of the entire cocoon and of the cocoons without pupa. Weight and silk weight of 20000 cocoons and raw silk percentage were also determined. This data was analyzed through ANOVA and several comparisons were performed for each variable analyzed. For all the variables tested, highly significant differences were found between genotype media (breeds and hybrids). For the three features tested, the heterosis effect was very strong. For the cocoon length (mm) the differences were de following: 30.2 parental average vs. 36.05 the direct hybrid and 34.53 the reciprocal hybrid. For the entire cocoon weight (g): 1.17 parental average vs. 1.57 the direct hybrid and 1.54 the reciprocal hybrid. For the bark weight: 0.21 parental hybrid vs. 0.30 the direct hybrid and 0.29 the reciprocal hybrid. The raw silk percentage was between the species ranges (16 to 24%) but the hybrid average turned to be higher than the parents average. The hybrids silk production was 39% higher than the parents production media. In conclusion, the crossing of the two lines used showed strong heterosis effect for all the variables analyzed.

Progress in understanding molecular genetic basis of heterosis in rice

The exploitation of rice heterosis has made great success in China in the last 40 years. Since 1990s, a series of progress has been made in the dissection of genetic basis of rice heterosis. Different hybrid systems such as three-line hybrid and two-line hybrid have been included into heterosis study. Moreover, all kinds of hybrids including indica intra-subspecies hybrid, japonica intra-subspecies hybrid and inter-subspecies hybrid were widely used for generating populations. Based on various populations such as diallelcross design, F2:3, backcross population, “immortalized F2” population, and collection of commercial hybrids, evidences at the level of molecular genetics were obtained to support the hypotheses for genetic basis of heterosis such as dominance, overdominance and epistasis in rice, which all play important roles in controlling heterosis. The importance of each genetic component varied with hybrids either in intra-subspecific or inter-subspecific hybrids or even in different traits in the same hybrid. However, at single gene level, none of dozens of known functional genes exhibited overdominance in rice. The inconsistent results between population level and single gene level probably indicate that overdominance is dependent on genomic background. Pure genetic background likely eliminated overdominance by blocking gene interaction. In addition, no single-gene overdominance was in agreement with the fact that it is not easy to develophybrids with strong heterosis because it is expected that single-gene overdominance should make hybrids possessing better parent heterosis. Besides QTL for agronomy traits, other types of traits such as metabolites and gene expression were also used for QTL mapping, and amounts of resources were available. Data from multiple omics such as genomics (including DNA marker and quantitative trait loci), metabolomics and transcriptomics provided chance to predict heterosis. Manipulating heterosis following the strategy based on the prediction is encouraging and very promising with a large number of new knowledge on heterosis being accumulated. Hybrid exhibits heterosis not only in yield but also in adaptation to eco-geographical regions. However compared to yield heterosis, the genetic basis of heterosis in adaptation is less touched and needs to be emphasized in future. Currently, making a proper experimental design for evaluating adaptation is a big challenge because there is no commonly accepted trait to estimate eco-geographical adaptation. Isolation of more heading date genes would probably help us to understand adaptation. Unveiling the molecular mechanism of key yield related genes will better understand the mechanism underlying dominance and overdominance and enhance the efficiency of breeding hybrids with strong heterosis.

Genetic Linkage Map Construction and QTL Analysis of Two Interspecific Reproductive Isolation Traits in Sponge Gourd.

The hybrids between Luffa acutangula (L.) Roxb. and L.cylindrica (L.) Roem. have strong heterosis effects. However, some reproductive isolation traits hindered their normal hybridization and fructification, which was mainly caused by the flowering time and hybrid pollen sterility. In order to study the genetic basis of two interspecific reproductive isolation traits, we constructed a genetic linkage map using an F2 population derived from a cross between S1174 [L. acutangula (L.) Roxb.] and 93075 [L. cylindrica (L.) Roem.]. The map spans 1436.12 CentiMorgans (cM), with an average of 8.11 cM among markers, and consists of 177 EST-SSR markers distributed in 14 linkage groups (LG) with an average of 102.58 cM per LG. Meanwhile, we conducted colinearity analysis between the sequences of EST-SSR markers and the genomic sequences of cucumber, melon and watermelon. On the basis of genetic linkage map, we conducted QTL mapping of two reproductive isolation traits in sponge gourd, which were the flowering time and hybrid male sterility. Two putative QTLs associated with flowering time (FT) were both detected on LG 1. The accumulated contribution of these two QTLs explained 38.07% of the total phenotypic variance (PV), and each QTL explained 15.36 and 22.71% of the PV respectively. Four QTLs for pollen fertility (PF) were identified on LG 1 (qPF1.1 and qPF1.2), LG 3 (qPF3) and LG 7 (qPF7), respectively. The percentage of PF explained by these QTLs varied from 2.91 to 16.79%, and all together the four QTLs accounted for 39.98% of the total PV. Our newly developed EST-SSR markers and linkage map are very useful for gene mapping, comparative genomics and molecular marker-assisted breeding. These QTLs for interspecific reproductive isolation will also contribute to the cloning of genes relating to interspecific reproductive isolation and the utilization of interspecific heterosis in sponge gourd in further studies.

Identification of QTL for Early Vigor and Stay-Green Conferring Tolerance to Drought in Two Connected Advanced Backcross Populations in Tropical Maize (Zea mays L.).

We aimed to identify quantitative trait loci (QTL) for secondary traits related to grain yield (GY) in two BC1F2:3 backcross populations (LPSpop and DTPpop) under well-watered (4 environments; WW) and drought stressed (6; DS) conditions to facilitate breeding efforts towards drought tolerant maize. GY reached 5.6 and 5.8 t/ha under WW in the LPSpop and the DTPpop, respectively. Under DS, grain yield was reduced by 65% (LPSpop) to 59% (DTPpop) relative to WW. GY was strongly associated with the normalized vegetative index (NDVI; r ranging from 0.61 to 0.96) across environmental conditions and with an early flowering under drought stressed conditions (r ranging from -0.18 to -0.25) indicative of the importance of early vigor and drought escape for GY. Out of the 105 detected QTL, 53 were overdominant indicative of strong heterosis. For 14 out of 18 detected vigor QTL, as well as for eight flowering time QTL the trait increasing allele was derived from CML491. Collocations of early vigor QTL with QTL for stay green (bin 2.02, WW, LPSpop; 2.07, DS, DTPpop), the number of ears per plant (bins 2.02, 2.05, WW, LPSpop; 5.02, DS, LPSpop) and GY (bin 2.07, WW, DTPpop; 5.04, WW, LPSpop), reinforce the importance of the observed correlations. LOD scores for early vigor QTL in these bins ranged from 2.2 to 11.25 explaining 4.6 (additivity: +0.28) to 19.9% (additivity: +0.49) of the observed phenotypic variance. A strong flowering QTL was detected in bin 2.06 across populations and environmental conditions explaining 26–31.3% of the observed phenotypic variation (LOD: 13–17; additivity: 0.1–0.6d). Improving drought tolerance while at the same time maintaining yield potential could be achieved by combining alleles conferring early vigor from the recurrent parent with alleles advancing flowering from the donor. Additionally bin 8.06 (DTPpop) harbored a QTL for GY under WW (additivity: 0.27 t/ha) and DS (additivity: 0.58 t/ha). R2 ranged from 0 (DTPpop, WW) to 26.54% (LPSpop, DS) for NDVI, 18.6 (LPSpop, WW) to 42.45% (LPSpop, DS) for anthesis and from 0 (DTPpop, DS) to 24.83% (LPSpop, WW) for GY. Lines out-yielding the best check by 32.5% (DTPpop, WW) to 60% (DTPpop, DS) for all population-by-irrigation treatment combination (except LPSpop, WW) identified are immediately available for the use by breeders.

Relationship between parental genetic distance and offspring’s heterosis for early growth traits in Liriodendron: implication for parent pair selection in cross breeding

Parent-pair selection is one of crucial factors that generate progenies with strong heterosis in tree cross-breeding programmes. In our Liriodendron breeding programme, we conducted a very effective strategy on selecting elite parental combinations with strong heterosis on the basis of a large number of crosses and progeny tests. In the past two decades, we have conducted dozens of interspecies crosses in Liriodendron and the hybrids with good performance have been broadly planted for both ornamental and industrial utilization in southern China. In contrast to the application, the genetic mechanism of heterosis in Liriodendron still remains unknown. Genetic distance is one key parameter which has been considered for parent-pair selection. Here, we reported the relationship between parental genetic distance and offspring heterosis by analyzing early growth traits of progenies from intra- and inter-specific crosses in Liriodendron. The genetic distances among 13 parental trees were assessed based on polymorphisms generated from 24 microsatellites loci. Offspring heterosis was estimated based on a 6-year-old progeny test. No significant correlations were found between parental genetic distance and offspring heterosis. However, we found that the offspring heterosis of growth reached the maximum value when parental genetic distance was 1.07, which was validated in another batch of crosses based on 2-year-old growth. Our findings may be helpful for the future parent-pair selection in Liriodendron cross-breeding programmes.

Remnants of populations provide effective source material for reintroduction of an endangered Hawaiian plant, Schiedea kaalae (Caryophyllaceae).

Reintroductions may be essential to prevent extinction of many critically endangered species. Ideally, reintroduction efforts rely on adjacent source populations, but limited source material may necessitate crossing individuals from different and possibly distant populations. To determine the consequences of integrating multiple populations in reintroductions, we investigated levels of inbreeding depression, outbreeding depression, and heterosis for populations of Schiedea kaalae (Caryophyllaceae), an endangered species endemic to the Wai'anae and Ko'olau Mountains of O'ahu, Hawai'i. The possibility of gene flow among plants was explored through pollinator observations. Individuals from ex situ living collections of nine populations were hand-pollinated with pollen from the same plant, plants from the same population (for three populations only), or plants from different populations. Progeny were outplanted into two common gardens, one in each mountain range on O'ahu. Cumulative fitness was estimated using several independent life history stages. Inbreeding depression was minimal, and no outbreeding depression was detected. In contrast, strong heterosis was evident in progeny from between-population crosses, which had higher relative fitness than progeny from self-pollinations or within-population crosses. Observations of floral visitors provided the first evidence that biotic pollination may be important for this species. Results demonstrate the ability to conduct genetic rescue of rare species and suggest that reintroductions may be most successful using heterotic individuals from crosses between populations and at sites where pollinators are present and promote outcrossing.

Genotype differences in photosynthetic characteristics and nitrogen efficiency of new-type oilseed rape responding to low nitrogen stress

SUMMARYNew-type oilseed rape (Brassica napus, ArArCcCc) with introgressed exotic subgenomic components from Brassica rapa (ArAr) and Brassica carinata (BcBcCcCc) showed strong heterosis in both vegetative and reproductive growth. The aim of the current study was to analyse the tolerance of the new-type B. napus with different exotic subgenomic contents to low nitrogen (N) stress. Under hydroponic culture and pot experiments, root system parameters, photosynthetic parameters, relative chlorophyll concentration (SPAD values), biomass, seed yield, seed yield components, N concentration and expressions of genes involved in N transport and assimilation were determined with two new-type B. napus genotypes (N-efficient genotype D4-15 and N-inefficient genotype D1-1) under high-N and low-N levels. Furthermore, N accumulation, N transfer efficiency and N use efficiency (NUE) were analysed in the two genotypes. The hydroponic and potted growth tests showed consistent characteristics in N uptake and utilization efficiency at the seedling stage, and N-efficient genotype (D4-15) showed better growth phenotypes across cultured conditions and N levels. Under the low-N condition, D4-15 produced a larger root system and accumulated more N, and had higher N transfer efficiency and NUE than D1-1. Moreover, D4-15 had significantly higher photosynthetic parameters, photosynthetic NUE and expression levels of the N transporter genes, BnNRT1·1, BnNRT2·5, BnNRT2·7 and BnAMT1·1, in roots or leaves, as well as higher seed yield than that of D1-1 under low-N supply. These results indicated that the N-efficient new-type B. napus D4-15 possessed excellent adaptability to low-N stress, which may be attributed to the highly introgressed exotic subgenomic components from B. rapa and B. carinata, suggesting the possibility of identifying high-nutrient-efficiency germplasm from inter-specific hybrids.

Temperature‐specific acclimation effects on adult locomotor performance of inbred and crossbredDrosophila melanogaster

AbstractClimate change poses a serious threat to the existence of many species. The combination of habitat fragmentation and increasing temperatures is of particular concern because it can alter demographic and population genetic processes, which may ultimately lead to extinction. Locomotion is very important in mitigating the negative impacts of these processes by upholding migration and contributing to random mating within and between populations. In the present study, aT‐maze, constituting a relatively complex laboratory assay, is used to investigate whether inbreeding affects the capacity to reach a food source in maleDrosophila melanogasterMeigen 1830 (Diptera:Drosophilidae) reared at 20, 25 or 30 °C, respectively. The effects of inbreeding and crossbreeding are highly temperature‐specific. Strong heterosis for the ability to reach food in the maze is observed in flies developed and maintained at 30 °C, whereas inbred flies locate the food significantly faster than crossbreds when reared at 25 °C in four of six runs. No clear pattern is evident in flies reared at 20 °C. The results suggest that complex traits such as locomotor performance in a maze are highly informative in the evaluation and detection of inbreeding depression under different thermal conditions. The effect of inbreeding is most pronounced at high temperature, which is a characteristic of the conditions that many natural populations may have to face under climate change.

Performance of Restorer Lines with Salt Tolerance in Whole Growth Period under Normal Irrigated Condition and Development of Hybrid Rice with Salt Tolerance

Four introgression line populations derived from the recurrent parent Minghui 86 and four donor parents (Gayabyeo, Shennong 265, Zaoxian 14, and Y134) were screened and evaluated for salt tolerance (ST) under the stress of 0.5% salt concentration over the whole growth stages in Sanmen County of Zhejiang Province. A total of 150 restorer lines with ST were selected. These 150 restorer lines with ST and their test-crossing hybrids with cytoplastic male sterile lines Ⅱ-32A and Chuan 345A were investigated for grain yield and its related agronomic traits under normal irrigated condition. Segregations presented in yield and its related traits among those lines, showing various types with different populations and traits. Thirty promising restorer lines with significantly higher yield and ST were selected. Most of them showed decreases in panicle length (PL), plant height (PH),and thousand-grain weight (TGW), but significant increases in panicle number per plant (PNP) and seed setting rate (SSR), thus resulting in significantly higher yield. As compared with hybrids crossed between Minghui 86 and the two sterile lines, test-crossing populations derived from the crosses between the restorer lines with ST and the two sterile lines showed reduces PL and PH, similar PNP, but significantly increased TGW when tested with Ⅱ-32A, indicating there were partial differences in trait performance between salt-tolerant restorer lines and their hybrids. Twenty-two and 23 hybrid combinations showed stronger heterosis as compared with the hybrids derived from Minghui 86 and the two corresponding sterile lines. Among them, seven (from Ⅱ-32A) and four (from Chuan 345A) hybrids significantly surpassed the commercial check combination Shanyou 10 in yield. It was indicated that ST screening in the field under salt stress combined with selections of yield and its related traits in normal irrigated condition for introgression line populations with an elite restorer background will efficiently improve the ST of restorer lines and possibly facilitate to develop the ST-improved hybrid rice.

Selection and Characterization of a Novel Photoperiod‐Sensitive Male Sterile Line in Upland Cotton

Upland cotton (Gossypium hirsutum L.) shows strong heterosis. However, heterosis is not widely utilized owing to the high cost of hybrid seed production. Creation of a photoperiod-sensitive genetic male sterile line could substantially reduce the cost of hybrid seed production in upland cotton. Such a mutant with virescent marker was found by space mutation in near-earth orbit and its traits had been stable after 4 years of selection in Anyang and Sanya, China. This mutant was fertile with an 11-12.5 h photoperiod when the temperature was higher than 21.5 °C and was sterile with a 13-14.5 h photoperiod. Genetic analysis indicated that both traits were controlled by a single recessive gene or two closely linked genes. Also, the cytological observations and transcriptome profiling analysis showed that the degradation of pollen grain cytoplasm should be the primary reason why the mutant line were male sterile under long-day conditions.

The relationship between the morphological fertility of pollen and marker gene Est9

Many indica-japonica hybrids exhibit a low seed set. In cases where female gamete fertility is normal, the lowered seed set can be attributed to pollen sterility. To use the strong heterosis of indica-japonica hybrids, we must overcome the barrier of pollen sterility.

Characteristics of F1 Hybrids and Inbred lines in Octoploid Strawberry (Fragaria × ananassa Duchesne)

With 4 figures and 3 tablesAbstractThe strawberry (Fragaria × ananassa Duchesne) plant is an octoploid vegetative propagated plant, and its cultivation is labour intensive in comparison with other plants propagated from seeds. The aims of this study were to develop an inbred line from octoploid strawberry and to generate an F1 hybrid cultivar through the combination of inbred lines. All inbred lines were obtained through selfing using five cultivars. Inbred lines were produced by selecting the best individuals for further inbreeding from each of the previous generations. Plant vigour and yield in inbred lines were low compared with the original cultivar, but completely recovered in the F1 hybrid. Breeding of inbred lines in octoploid strawberry can be achieved if individuals showing inbreeding depression are eliminated and vigorous individuals are selected, resulting in a strong heterosis of F1 hybrids through crossing between inbred lines.