Significant Mid-parent Heterosis Research Articles

Estimation of genetic components, heterosis and combining ability of elite Pakistani wheat varieties for yield attributing traits and stripe rust response.

Wheat (Triticum aestivum L.) is a staple food and major source of dietary calories in Pakistan. Improving wheat varieties with higher grain yield and disease resistance is a prime objective. The knowledge of genetic behaviour of germplasm is key. To achieve this objective, elite wheat varieties were crossed in 4 by 3, line × tester design, and tested in 2019 in a triplicate yield trial to estimate genetic variance, general and specific combining ability, mid-parent heterosis and stripe rust (Puccinia striiformis L.). High grain 3358 kg·ha-1 was recorded in F1 hybrid (ZRG-79 × PAK-13). Analysis of variance (ANOVA) revealed significant genotypic variance in grain yield. Broad sense heritability (H2) was recorded in the range of 28 to 100 %. General combining ability (GCA) significant for grain yield in parents except FSD-08 and PS-05 was recorded, while specific combining ability (SCA) was recorded to be highly significant for grain yield only in two crosses (ZRG-79 × NR-09 and ZRG-79 × PAK-13). Mid-parent heterosis was estimated in the range of -28 to 62.6 %. Cross combinations ZRG-79 × PAK-13 depicted highly significant mid-parent heterosis (62.6 %). Highly significant correlation was observed among spike length, spikelets per spike, plant height and 1000-grain weight. Rust resistance index was recorded in the range of 0 to 8.5. These findings suggest exploitation of GCA for higher grain yield is important due to the presence of additive gene action and selection in the filial generations will be effective with improved rust resistance, while cross combinations ZRG-79 × PAK-13 high GCA are best suited for hybrid development.

Heterotic gains, transgressive segregation and fitness cost of sweetpotato weevil resistance expression in a partial diallel cross of sweetpotato

Heterosis-exploiting breeding schemes are currently under consideration as a means of accelerating genetic gains in sweetpotato (Ipomoea batatas) breeding. This study was aimed at establishing heterotic gains, fitness costs and transgressive segregation associated with sweetpotato weevil (SPW) resistance in a partial diallel cross of sweetpotato. A total of 1896 clones were tested at two sites, for two seasons each in Uganda. Data on weevil severity (WED), weevil incidence (WI), storage root yield (SRY) and dry matter content (DM) were obtained. Best linear unbiased predictors (BLUPs) for each clone across environments were used to estimate heterotic gains and for regression analyses to establish relationships between key traits. In general, low mid-parent heterotic gains were detected with the highest favorable levels recorded for SRY (14.7%) and WED (− 7.9%). About 25% of the crosses exhibited desirable and significant mid-parent heterosis for weevil resistance. Over 16% of the clones displayed superior transgressive segregation, with the highest percentages recorded for SRY (21%) and WED (18%). A yield penalty of 10% was observed to be associated with SPW resistance whereas no decline in DM was detected in relation to the same. Chances of improving sweetpotato through exploiting heterosis in controlled crosses using parents of mostly similar background are somewhat minimal, as revealed by the low heterotic gains. The yield penalty detected due to SPW resistance suggests that a trade-off may be necessary between maximizing yields and developing weevil-resistant cultivars if the current needs for this crop are to be met in weevil-prone areas.

Introgression of Heterotic Genomic Segments from Brassica carinata into Brassica juncea for Enhancing Productivity.

Interspecific hybridization resulted in the creation of B. juncea introgression lines (ILs) generated from B. carinata with increased productivity and adaptability. Forty ILs were crossed with their respective B. juncea recipient parents to generate introgression line hybrids (ILHs) and the common tester (SEJ 8) was used to generate test hybrids (THs). Mid-parent heterosis in ILHs and standard heterosis in THs were calculated for eight yield and yield-related traits. Heterotic genomic regions were dissected using ten ILs with significant mid-parent heterosis in ILHs and standard heterosis in THs for seed yield. A high level of heterosis for seed yield was contributed by 1000 seed weight (13.48%) in D31_ILHs and by total siliquae/plant (14.01%) and siliqua length (10.56%) in PM30_ILHs. The heterotic ILs of DRMRIJ 31 and Pusa Mustard 30 were examined using polymorphic SNPs between the parents, and a total of 254 and 335 introgressed heterotic segments were identified, respectively. This investigation discovered potential genes, viz., PUB10, glutathione S transferase, TT4, SGT, FLA3, AP2/ERF, SANT4, MYB, and UDP-glucosyl transferase 73B3 that were previously reported to regulate yield-related traits. The heterozygosity of the FLA3 gene significantly improved siliqua length and seeds per siliqua in ILHs of Pusa Mustard 30. This research proved that interspecific hybridization is an effective means of increasing the diversity of cultivated species by introducing new genetic variants and improving the level of heterosis.

Assessment of heterotic and combining ability effects along with genotype × environment factors influencing the variation of yield and quality components in pepper

Peppers hot and sweet are widely grown Solanaceous vegetable, consumed as fresh and spice crops worldwide. Their fruits have high nutritional and antioxidant characteristics especially the bell peppers, which have high vitamin C content and antioxidants such as carotenoids and chlorophylls, while hot peppers have pharmaceutically and industrially important compounds such as capsaicinoids that make it a high-interest crop for both breeders and consumers. The often cross-pollinating nature and availability of male sterility systems make the hybrids more popular in this crop, and because of its wide cultivation over different climatic zones, there is always a need for suitable varieties for specific growing conditions. In the present investigation, eight parents of both hot and bell pepper types were used to produce twelve hybrids through line × tester analysis and tested for sixteen yield and quality attributes under two different growing environments. We found significant differences among parents and hybrids for 9 out of 16 traits across two growing environments. The significant effect of genotype was found for most of the traits in the case of parents, while environmental component was accounted for major variation found in hybrids for most of the traits studied. Significant mid-parent heterosis was found for all the genotypes at least for one of the studied characters. We found higher plasticity for fruit yield and plant spread in parents, while vitamin C content for hybrids. The tester's contribution (59.42%) was highest under line × tester analysis for the studied characters. PCA for the first two dimensions explained 49.91% of the total variation, exhibited differences among evaluated traits and genotypes. This extensive path is used admit to appraise those characters, which exhibit stability in hybrids and help to generate novel and widely adapted hybrids.

Effects of drought stress on grain yield, agronomic performance, and heterosis of marker-based improved provitamin-A maize synthetics and their hybrids

ABSTRACT Provitamin A-enriched maize (Zea mays L.) is an important complementary food staple for combating vitamin A deficiency (VAD) in high maize-producing and maize-consuming countries of sub-Saharan Africa (SSA). However, frequent drought is a major abiotic factor that retards maize growth, resulting in yearly fluctuations in grain yield. Development of provitamin A-enriched maize varieties resilient to recurrent drought stress could enhance and stabilize maize grain yield. This study was conducted to assess the effects of managed drought stress (MDS) on the performance and heterosis of some marker-based improved provitamin A maize synthetics and their varietal-cross hybrids. The maize synthetics and their varietal-cross hybrids, along with a drought-tolerant check (PVASYN13), were evaluated under MDS and well-watered (WW) conditions at Ikenne, Nigeria, for two years. Genotype and year effects were significant for grain yield and some agronomic traits under MDS and WW conditions. Grain yield was reduced by 56% under MDS. Grain yield was significantly correlated with days to anthesis, days to silking and anthesis-silking-interval under MDS but not under WW condition. Under MDS, three varietal-cross hybrids (PVASYNHGBC0/PVASYNHGAC0, PVASYNHGBC2/PVASYNHGAC0, PVASYNHGBC0/ PVASYNHGAC1) had similar grain yields and tolerance indices as the drought-tolerant check, whereas PVASYNHGBC1/PVASYNHGAC2 produced 12.5% more grain yield than the check. Three of the varietal-cross hybrids (PVASYNHGBC0/PVASYNHGAC0, PVASYNHGBC0/PVASYNHGAC1 and PVASYNHGBC1/PVASYNHGAC2) had significant mid-parent heterosis for grain yield under the two test conditions, and were recommended for developing drought-tolerant varieties to combat VAD in drought-prone environments of SSA.

Assessing Effect of Marker-Based Improvement of Maize Synthetics on Agronomic Performance, Carotenoid Content, Combining Ability and Heterosis

Vitamin A deficiency (VAD) is a serious problem in sub-Saharan Africa (SSA) and other parts of the world. Understanding the effect of marker-based improvement (MARS) of two maize synthetics (HGA and HGB) representing different heterotic groups on their agronomic performance, carotenoid content, and combining abilities could help identify suitable sources to develop divergent inbred lines for optimizing heterosis. This study involved three selection cycles each of the two synthetics and their nine varietal-cross hybrids together with a released check variety was conducted across four diverse locations in Nigeria in 2018 and 2019. Environment and hybrid effects were significant on grain yield and other agronomic traits as well as provitamin A content and other carotenoids. Genetic improvement per cycle of MARS in the parental synthetics was 15% for provitamin A, 25% for β-carotene and 26% for lutein in HGA and 4% for grain yield, 3% for zeaxanthin and 5% for α-carotene in HGB. Grain yield and agronomic traits of the two maize synthetics were controlled by additive and non-additive gene effects, while provitamin A content and other carotenoids were mainly controlled by additive gene effects. Some selection cycles which were high in grain yield and provitamin A content were identified as potential sources of new and divergent maize inbred lines in maize breeding programs. Some varietal-cross hybrids expressed significant mid-parent heterosis for grain yield and moderate mid-parent heterosis for provitamin A, β-carotene and xanthophylls. These hybrids could be commercialized at reasonable prices to small-scale farmers in rural areas that are most affected by vitamin A deficiency.

Kernel metabolites depict the diversity of relationship between maize hybrids and their parental lines

As the end products of cellular regulatory processes, metabolites provide the link between genotypes and phenotypes. Although metabolites have been widely applied for functional gene detection and phenotype prediction in maize, there is little research focusing on the genetic information of metabolites per se. Here, we performed genetic analyses for the kernel metabolites of 11 parental inbred lines of six representative maize varieties, including Zhongdan 2, Danyu 13, Yedan 13, Zhengdan 958, Xianyu 355, and Suyu 16, as well as their 26 reciprocal hybrids. We identified a total of 208 metabolites in maize kernels using untargeted metabolite profiling technology. Both cluster analysis and principal component analysis indicated that kernel metabolites could distinguish hybrids from their parents. Analysis of variance further revealed that 163 metabolites exhibited significant differences between parents and hybrids, and 40 metabolites showed significant differences between reciprocal crosses. We also investigated the genetic effects and heterosis for each metabolite. By taking all hybrids into consideration, about two-thirds of all metabolites displayed overdominant with 36.8% and 31% of them displaying positive overdominant and negative overdominant, respectively. Besides, 27.5% and 20.4% of all hybrid combinations showed significant mid-parent heterosis and over-parent heterosis, respectively. Our findings revealed that kernel metabolites exhibited the diversity of relationship between maize hybrids and their parental lines. Additionally, we identified 25 significant metabolic markers related to 11 agronomic traits using the LASSO method. Seven metabolic markers were associated with more than one trait simultaneously. These results provide a genetic basis for further utilization of metabolites in the genetic improvement of maize.

Dissection of heterotic, genotypic and environmental factors influencing the variation of yield components and health-related compounds in chilli pepper (Capsicum annuum)

Chilli pepper is a widely spread vegetable crop and one of the main spices used all over the world. Its properties comprise high antioxidant capacity and content of several healthy-related compounds including vitamin C, carotenoids and capsaicinoids. In countries of the Mediterranean basin, chilli production is largely based on local varieties traditionally selected for open field conditions, although, the genetic improvement is a rapidly growing sector toward the development of hybrids. In the present study, nine chilli pepper varieties with diverse market destinations including powder consumption, canned production, and blister packaging as well as seven hybrids obtained through half-diallel crosses between the parent varieties were grown in replicated field trials over diverse locations and evaluated in a comprehensive approach regarding twenty-six quantitative agronomic, morphological and health-related phytochemical traits. Significant differences between hybrids and parents were found for 12 out of the 26 traits studied in both environments. Agronomic and chemical traits did not differ significantly except than for total yield and pH. Several biochemical traits differed significantly and carotenoids and ascorbic acid values were mostly linked to the cultivation environment. A significant effect of the genotype (P < 0.01) was found in all traits for both parental lines and hybrids. The phenotypic plasticity revealed high stability for fruit morphological traits in both parents and hybrids. Greater plasticity was found for total yield in the parent lines, while hybrids were more stable for capsaicinoids and more plastic for carotenoids and AsA, compared to parental. Significant mid-parent heterosis was observed in all the hybrids tested for at least one of the trait evaluated. The PCA in the first two dimensions explained 48.26% of the total variance showing a distinction between each hybrid and the related parental lines for the traits analyzed. This comprehensive approach used, allow to dissect those traits which can be successfully introgressed in hybrids and are useful for precision breeding of novel varieties.

Predicting heterosis in grain sorghum hybrids using sequence-based genetic similarity estimates

ABSTRACT The genetic yield potential in grain sorghum [Sorghum bicolor (L.) Moench] hybrids has increased at a slower rate than other cereal crops. While there are many reasons for this lag, increasing heterosis through broadening genetic distance between parents is commonly hypothesized as a mechanism to boost the rate of gain. To assess the relationship between heterotic groups in sorghum, a panel of 435 inbred lines from the Texas A&M program was genotyped using Genotyping-By-Sequencing (GBS). Lines were divided into three groups through K-means clustering based on genetic similarity. Distinct groups of B-lines, R-lines, and forage lines were observed, but they were not highly divergent from one another. In both elite germplasm and a large panel of sorghum lines, less diversity was observed among B-lines than R-lines. From the panel of 435 inbreds, a subset of 24 elite grain-type lines was chosen and crossed to produce 52 hybrids. Hybrids and parental lines were evaluated in four environments for grain yield, plant height, days to flower, and panicle exsertion. Genetic similarity among elite inbred parents of hybrids evaluated ranged from 0.632 to 0.792. For all traits, significant mid-parent heterosis was observed; however, correlations between mid-parent heterosis and genetic similarity were low to non-significant. GBS-based genetic similarity is not a good predictor of heterosis or hybrid performance among elite Texas A&M sorghum inbreds. However, some parental-inbred performance measurements may be predictive of hybrid performance.

Utilization of Combining Ability and Genetic Components for Yield and its Contributing Traits of some Rice (Oryza sativa L.) Genotypes

Twenty-one hybrids developed from crossing seven lines and three testers were assessed for the extent of combining ability effects, heterosis and genetic parameters for yield and related contributing traits. The analysis of variance uncovered that there were highly significant differences for all the studied traits except panicle weight among parents and parents vs. crosses. The two promising lines GZ 9461-4-2-3-1 and GZ 1368-S-5-4 were seen as a good general combiner among lines for most of the traits, while among the testers, the parental variety Sakha S 300 was superior. Two crosses out of hybrids, GZ 9461-4-2-3-1 / Milyang 349 and GZ 1368-S-5-4 / IR14K642 exhibited positive and highly significant SCA effects for grain yield plant-1, respectively. The maximum positive and highly significant mid-parent heterosis and heterobeltiosis for grain yield plant-1 were observed. The five crosses GZ 1368-S-5-4 / Sakha S 300, GZ 1368-S-5-4 / IR14K642, GZ 9461-4-2-3-1 / Milyang 349, GZ 9461-4-2-3-1 / Sakha S 300 and GZ 9461-4-2-3-1 / IR14K642 recorded the highest values and maybe extensively used in rice programs by adopting a heterosis breeding strategy. The additive gene action was noticed for days to 50% flowering, plant height, flag leaf area, number of panicles plant-1, panicle length, panicle weight, panicle density index, spikelets fertility, 1000-grain weight, and grain yield plant-1. Grain yield plant-1 was highly significantly and positively correlated with plant height, flag leaf area, number of panicles plant-1, panicle weight and panicle density index indicating the significance of these traits as determination criteria in yield enhancement.

Phenotypic Data from Inbred Parents Can Improve Genomic Prediction in Pearl Millet Hybrids.

Pearl millet is a non-model grain and fodder crop adapted to extremely hot and dry environments globally. In India, a great deal of public and private sectors’ investment has focused on developing pearl millet single cross hybrids based on the cytoplasmic-genetic male sterility (CMS) system, while in Africa most pearl millet production relies on open pollinated varieties. Pearl millet lines were phenotyped for both the inbred parents and hybrids stage. Many breeding efforts focus on phenotypic selection of inbred parents to generate improved parental lines and hybrids. This study evaluated two genotyping techniques and four genomic selection schemes in pearl millet. Despite the fact that 6× more sequencing data were generated per sample for RAD-seq than for tGBS, tGBS yielded more than 2× as many informative SNPs (defined as those having MAF > 0.05) than RAD-seq. A genomic prediction scheme utilizing only data from hybrids generated prediction accuracies (median) ranging from 0.73-0.74 (1000-grain weight), 0.87-0.89 (days to flowering time), 0.48-0.51 (grain yield) and 0.72-0.73 (plant height). For traits with little to no heterosis, hybrid only and hybrid/inbred prediction schemes performed almost equivalently. For traits with significant mid-parent heterosis, the direct inclusion of phenotypic data from inbred lines significantly (P < 0.05) reduced prediction accuracy when all lines were analyzed together. However, when inbreds and hybrid trait values were both scored relative to the mean trait values for the respective populations, the inclusion of inbred phenotypic datasets moderately improved genomic predictions of the hybrid genomic estimated breeding values. Here we show that modern approaches to genotyping by sequencing can enable genomic selection in pearl millet. While historical pearl millet breeding records include a wealth of phenotypic data from inbred lines, we demonstrate that the naive incorporation of this data into a hybrid breeding program can reduce prediction accuracy, while controlling for the effects of heterosis per se allowed inbred genotype and trait data to improve the accuracy of genomic estimated breeding values for pearl millet hybrids.

Study of heterosis in different cross combinations of tomato for yield and yield components

Abstract The purpose ofconducting present study was to evaluate the performance of different cross combinations of tomato for mid parent heterosis and better parent heterosis regarding yield and yield related traits. Forthe parameters: No of fruits/clusters, No of fruits/plants, Fruitweight, plant height and yield/plant,some of the combinations showed significant positive mid parent heterosis. No positive significant mid-parent heterosis was observed for the parameters like fruit length and fruit size. Significant better-parent heterosis was observed in some cross-combinations for the parameters: No of fruits/clusters, No of fruits/plants and yield/plant. While, no significant positive heterosis was observed for the parameters like fruit-length, fruit diameter,fruit size and fruit weight. For fruit length and fruit diameter all the combinations showed negative value of heterosis. Significant positive heterosis for yield/plant is great achievement in our study as yield/plant is the ultimate goal of tomato growers.

Heterosis and combining ability analysis of slow rusting stem rust resistance and yield and related traits in bread wheat

Bread wheat genotypes with slow rusting stem rust resistance were crossed in a half-diallel mating design to identify superior parents for stem rust resistance combined with high grain yield (GY) and related traits. Significant mid-parent heterosis for area under disease progress (AUDPC) was observed in crosses 7041-1 × Danda’a and Danda’a × Kubsa. H04-2 × Danda’a showed significant mid-parent heterosis for GY, thousand kernel weight (TKW), number of tillers per plant (TPP) and reduced plant height (PLH), and significant better-parent heterosis for GY. Significant general combining ability (GCA) effects for all characters and specific combining ability (SCA) effects for most of the traits indicated the contribution of additive and non-additive genes in the expression of these traits, respectively. GCA and SCA ratios ( $$\sigma_{\text{gca}}^{ 2} /\sigma_{\text{sca}}^{2}$$ ) were less than unity for GY, TKW and PLH, suggesting preponderance of non-additive gene action at F1 for these traits. Additive gene action was predominant in the inheritance of AUDPC, kernels per spike, TPP and days to maturity. H04-2, Digelu and Danda’a showed strong GCA effects for most of the characters investigated. Crosses 231545-1 × H04-2, 7041-1 × H04-2, Digelu × Kubsa and Danda’a × Kubsa were good combinations for AUDPC. H04-2 × Danda’a, Digelu × Kubsa and Danda’a × Kubsa were good combinations for GY and TKW. Overall, H04-2 and Danda’a were good general combiners, and crosses involved these lines performed well for most of the traits. Hence, these lines may be used in breeding programs to develop stem rust resistant and high yielding cultivars.

Carotenoid composition and heterotic effect in selected Italian maize germplasm

Maize (Zea mays L.) is a promising crop for improving the nutritional quality of foods, because of the presence of broad natural variability for the content of carotenoids. One hundred Italian and nine public lines were screened by PCR to identify the alleles of Hydroxylase3 (HYD3) and Lycopene epsilon cyclase (LCYE) genes, codifying for key enzymes of the carotenoid pathway and associated with high or low β-carotene contents. Nineteen selected genotypes carrying different alleles were grown in 2011 and/or 2012, and used to obtain F1 seeds. HPLC analysis highlighted the richness in zeaxanthin and β-cryptoxanthin of Italian germplasm (mean values 12.63 and 2.88 mg/kg d.m., respectively). The percentage of positive and significant mid parent heterosis (MPH) and best parent heterosis (BPH) values (51% and 29%) indicated the presence of a high heterotic response for carotenoids. The compounds on the same branch of the pathway were found to be positively correlated; on the contrary, no consistent correlation was observed between the different HYD3 alleles and β-carotene content. Finally, total antioxidant capacity (TAC) was also measured. These lines resulted therefore as interesting raw materials for the market of maize-based foods.

Relationship between morphological and amplified fragment length polymorphism (AFLP) marker based genetic distance with heterosis in hot pepper (Capsicum annuum L.)

Identification of potential parents that produce the hybrids with superior yield is the most important step in developing hybrids to save the substantial resources. The present study was carried out to assess the morphological and amplified fragment length polymorphism (AFLP) marker based genetic diversity, to estimate mid parent heterosis and to correlate the estimated parental genetic diversity with heterosis chilli. Five CMS B - lines and 30 testers were used for morphological and AFLP marker genetic divergence analysis. 150 hybrids were synthesized through Line × Tester (5 × 30) mating design and were used to estimate the mid-parent heterosis for nine characters at two locations. 35 parents were examined for nine morphological traits and were grouped in to six clusters. These parents were also examined for eight AFLP primers combinations and were grouped into seven clusters. More than 50% of hybrids showed significant mid-parent heterosis for both green and red fruit yield plant-1. Hence, there is a much potential for development of good yielding hybrids. The positive significant correlation was found between morphological and AFLP marker distance of the parents with heterosis for plant height (r = 0.17 and 0.38), green fruit yield plant -1 (r = 0.19 and 0.25) and red fruit yield plant -1 (r = 0.20 and 0.34); however, the correlation coefficients were not strong in these traits. Genetic distance between parents was not strong enough to predict the performance of the hybrids and proved to be of no predictive value. Keywords: Correlation, molecular markers, genetic diversity, chilli

A Dynamic and Complex Network Regulates the Heterosis of Yield-Correlated Traits in Rapeseed (Brassica napus L.)

Although much research has been conducted, the genetic architecture of heterosis remains ambiguous. To unravel the genetic architecture of heterosis, a reconstructed F2 population was produced by random intercross among 202 lines of a double haploid population in rapeseed (Brassica napus L.). Both populations were planted in three environments and 15 yield-correlated traits were measured, and only seed yield and eight yield-correlated traits showed significant mid-parent heterosis, with the mean ranging from 8.7% (branch number) to 31.4% (seed yield). Hundreds of QTL and epistatic interactions were identified for the 15 yield-correlated traits, involving numerous variable loci with moderate effect, genome-wide distribution and obvious hotspots. All kinds of mode-of-inheritance of QTL (additive, A; partial-dominant, PD; full-dominant, D; over-dominant, OD) and epistatic interactions (additive × additive, AA; additive × dominant/dominant × additive, AD/DA; dominant × dominant, DD) were observed and epistasis, especially AA epistasis, seemed to be the major genetic basis of heterosis in rapeseed. Consistent with the low correlation between marker heterozygosity and mid-parent heterosis/hybrid performance, a considerable proportion of dominant and DD epistatic effects were negative, indicating heterozygosity was not always advantageous for heterosis/hybrid performance. The implications of our results on evolution and crop breeding are discussed.

Evaluation of A 1, A 2, A 3, A 4(M), A 4(G) and A 4(VZM) cytoplasms in iso-nuclear backgrounds for grain mold resistance

Breeding for resistance to grain mold, an economically important disease of sorghum, has been only partially successful. Hybrid technology is well developed in sorghum due to availability of the cytoplasm male sterility (CMS) system and at present almost all commercial hybrids are based on the A 1 CMS system. To compare the available alternate CMS systems for grain mold resistance, 72 hybrids were produced by crossing 36 A-lines (six CMS systems; A 1, A 2, A 3, A 4(M), A 4(G), A 4(VZM) each in six nuclear backgrounds) with two common restorers, and were evaluated during the 2006 and 2007 rainy seasons in grain mold nursery at ICRISAT. Data analyses indicated influence of cytoplasm on the responses of hybrids to grain mold infection as measured by panicle grain mold resistance (PGMR) score. The A 1 cytoplasm seemed to contribute to grain mold resistance followed by A 4(VZM) and A 2 cytoplasms. The A 4(M) cytoplasm had superior general combining ability (GCA) effects while the A 1 and A 4(VZM) cytoplasm based hybrids had superior specific combining ability (SCA) effects on the PGMR score. Almost all hybrids had significant mid-parent heterosis. The A 1 cytoplasm is the best suited for the development of sorghum hybrids for the rainy season adaptation with grain mold resistance. However, use of alternate cytoplasms (A 2 and A 4(VZM)) for hybrid development will not increase susceptibility to grain mold in commercial grain production.

Partial diallel analysis of agronomic characters in rice (Oryza sativa L.)

Rice (Oryza sativa L.) breeding seeking to combine high productivity and cold tolerance for the temperate Latin America region is an important challenge. We estimated some useful parameters which can be used to investigate the genetic control of agronomic characters in crosses combining cold tolerance and productivity. A partial diallel design was used in crosses between six tropical indica rice cold susceptible genotypes (group 1) and seven japonica or indica/japonica cold tolerant rice genotypes (group 2). Parents and crosses were evaluated for agronomic characters under field conditions in two different experiments in 2005. The results showed significant mid-parent heterosis for all characters (plant height, tiller number, days to 50% flowering, panicle length, grains per panicle, sterility, and one-hundred grain weight). The predominant direction of dominance effects was negative for days to 50% flowering, and positive for all the other characters. General combining ability (GCA) and specific combining ability (SCA) were significant for all characters, although the GCA effects of the two groups were more important than the SCA effects.

Heterosis and polymorphisms of gene expression in an elite rice hybrid as revealed by a microarray analysis of 9198 unique ESTs

Despite the significant contributions of utilizing heterosis to crop productivity worldwide, the biological mechanisms of heterosis remained largely uncharacterized. In this study, we analyzed gene expression profiles of an elite rice hybrid and the parents at three stages of young panicle development, using a cDNA microarray consisting of 9198 expressed sequence tags (ESTs), with the objective to reveal patterns of gene expression that may be associated with heterosis in yield. A total of 8422 sequences showed hybridization signals in all three genotypes in at least one stage and 5771 sequences produced detectable signals in all slides. Significant differences in expression level were detected for 438 sequences among the three genotypes in at least one of the three stages, as determined by ANOVA validated with 100 permutations at P < 0.05. Significant mid-parent heterosis was detected for 141 sequences, which demonstrated the following features: a much larger number of sequences showed negative heterosis than ones showing positive heterosis; genes functioning in DNA replication and repair tended to show positive heterosis; genes functioning in carbohydrate metabolism, lipid metabolism, energy metabolism, translation, protein degradation, and cellular information processing showed negative heterosis; both positive and negative heterosis were observed for genes in amino acid metabolism, transcription, signal transduction, plant defense and transportation. The results are indicative of the biochemical and physiological activities taking place in the hybrid relative to the parents. Identification of genes showing expression polymorphisms among different genotypes and heterotic expression in the hybrid may provide new avenues for exploring the biological mechanisms underlying heterosis.

Biplot Analysis of Forage Combining Ability in Maize Landraces

ABSTRACTIn Argentina, maize (Zea mays L.) hybrids selected for silage production and local adaptation are not available for most temperate regions where silage maize can be produced. This study sought maize landraces that could be used as germplasm sources to enhance forage yield and quality in warm temperate areas and emphasized eight landraces not previously selected for grain yield. These were crossed in a diallel mating design and the 28 F1 population hybrids, the eight parental populations, and four commercial hybrids were evaluated in four environments in Argentina for combining abilities and to determine heterotic patterns among germplasm sources, using a biplot diallel analysis. Significant midparent heterosis (MPH) was observed for ear yield (EY), stover yield (SY), and whole plant yield (WY). General combining ability (GCA) effects were significant for EY, SY, and WY. Specific combining ability (SCA) effects were not significant for any trait. The graphical representation offered by biplot analysis allowed a rapid and effective overview of GCA and SCA effects of the populations, their performance in crosses, as well as grouping patterns of similar genotypes. Significant variation among checks was observed for EY and SY. On average, commercial hybrids had greater EY, but lower SY, than landraces and population hybrids. Some landrace crosses showed superior or similar WY than commercial checks, indicating the breeding potential of the evaluated germplasm.