Positive Mid-parent Heterosis Research Articles

Profiling volatile compounds in fresh leaves of 22 major oolong tea germplasm cultivated in Fujian of China

Tea is highly esteemed by consumers due to its distinct aroma and the abundance of nutrients that contribute to human well-being. While volatile compounds in fresh tea leaves serve as the essential foundation for tea aroma, the understanding of cultivar-specific aroma constituents and their genetic regulation remains a research gap. In this study, we extracted and profiled the volatile compounds in fresh leaves from 22 major oolong tea cultivars using gas chromatography-mass spectrometry. A total of 140 volatile compounds were identified, of which 61 were consistently found in all tea cultivars. The volatile profiles of the 22 tea cultivars exhibited considerable dissimilarity, with several distinct cultivar-specific volatiles identified. Subsequent analysis of nonadditive volatiles in tea hybrids revealed a noteworthy positive mid-parent heterosis (MPH) in ‘Mingke 1’ (also known as ‘Jinguanyin’) and ‘Huangmeigui’. Comprehensive heterosis across various volatile compounds was also documented. Our study elucidated the composition of volatile compounds in the fresh leaves from the major oolong tea cultivars and provided an extensive exploration of volatile heterosis in tea plants. These cultivar-specific volatile variations will offer essential insights for enhancing the genetic aspects of tea aroma flavor and deepen our understanding of the molecular mechanisms underlying volatile compound formation in fresh tea leaves.

Heterotic capability of five crosses for quantitative traits in bread wheat (Triticum aestivum L.) with inbreeding depression studies using generation mean analysis

Six generations, namely P1, P2, F1, F2, BC1 and BC2 of five crosses of bread wheat viz., AKAW 4842 x Raj 4238, AKAW 4924 x RW5, DBW 39 x MP 3353, GW 11 x DWAP 1540 and GW 455 x UP 2968 were developed to estimate the extent of heterosis andinbreeding depression and underlying genetic causes for different characters in bread wheat. The analysis of variance betweenfamilies (crosses) revealed that the mean square due to crosses were highly significant for all the characters. The analysis of varianceamong progenies (generations) within each family (cross) indicated significant differences among six basic generation means for all the characters studied in all the five crosses. In the present study all the crosses depicted significant and positive mid parent heterosis and heterobeltiosis for grain yield per plant and almost all the component traits. Among which crosses AKAW 4842 x Raj 4238, AKAW 4924 x RW 5, GW 11 x DWAP 1540 and GW 455 x UP 2968 depicted negative inbreeding as well as significant and positive mid parent heterosis and heterobeltiosis for grain yield per plant therefore, intermating in F2 generation may be advantageous for improving particular character for above mentioned crosses. Generally, the character like grain yield per plant governed by fixable additive gene effect can be improved through pedigree selection method.

Three-way cross hybrid abalone exhibit heterosis in growth performance, thermal tolerance, and hypoxia tolerance

Abalone is an economically important aquaculture resource worldwide, with high commercial value. Abalone productivity, stress resistance, and profitability have been improved by interspecific and intraspecific hybridization. In this study, a systematic comparative assessment of heterosis for survival, growth, thermal tolerance, and hypoxia tolerance in Haliotis gigantea (SS), H. discus hannai (DD), H. discus hannai♀ × H. fulgens♂ (DF), and three-way cross hybrids SS♀ × DF♂ and DF♀ × SS♂ was conducted. Two three-way cross hybrids, SS × DF and DF × SS, showed positive mid-parent heterosis in the growth rates of shell length and total wet weight in different months. The proportion of large individuals with higher total wet weight or shell length in DF × SS and SS × DF was higher than in other abalone species. The thermal and hypoxia tolerance of these abalone were assessed using Arrhenius break temperatures (ABT) and the breakpoint of dissolved oxygen (BPDO) of cardiac performance, respectively. The mid-parental heterosis values of ABT in SS × DF and DF × SS were 2.29% and 1.38%, respectively, while the BPDO values in SS × DF and DF × SS were − 11.48% and − 11.96%, respectively, confirming heterosis for thermal and hypoxia tolerance in these three-way cross hybrids. Overall, this is the first three-way interspecific cross of abalone, and the improvement of commercial traits can be achieved through a combination of selection and further hybridization among purebred and hybrid abalone.

Heterosis for seed and seedling traits in papaya

The current study was aimed to explore the heterosis expressed in the seed and seedlings of 36 papaya hybrids originating from the 6 inbred lines. The results revealed the manifestation of heterosis, occurred in the seed and seedling stage of papaya. The cross combinations, P-9-5 × P-7-2, P-9-12 × PN and PN × P-9-5 exhibited positive average heterosis and heterobeltiosis for physical seed traits. The genotypes, P-9-5, P-9-12, P-9-5 × P-9-12 and P-9-12 × P-9-5 were observed with positive mid-parent heterosis and heterobeltiosis for the seedling traits. The hybrid, P-7-9 × PN and PS3 × P-7-9 showed positive average heterosis (5.89% and 9.91%) and heterobeltiosis (3.41% and 2.09%) for germination percentage, respectively. Whereas in case of seedling length and weight (fresh and dry), the hybrid combination, P-9-5 × P-9-12 exhibited the positive heterosis. The heterosis effect estimated helped us to identify the superior performing hybrids like, PN × P-7-2, PN × P-9-5, P-7-2 × PN, P-7-2 × P-7-9, P-7-9 × P-9-5, P-9-5 × P-7-2, P-9-5 × P-9-12, P-9-12 × PN, P-9-12 × P-7-2, P-9-12 × P-95and PS3 × P-7-9, in the initial stage of seedling development.

Dissecting Bread Wheat Heterosis through the Integration of Agronomic and Physiological Traits.

Simple SummaryTo meet the challenge of feeding almost 10 billion people by 2050, wheat yield has to double by 2050. However, over the past 20 years, yield increase has slowed down and even stagnated in the main producing countries. Similar to what has been observed in maize, hybrids have been suggested as a solution to overcome yield stagnation in wheat. However, wheat heterosis, i.e., the fact that a progeny surpasses the performances of its parents, is still limited and poorly understood. To better characterize this phenomenon, we developed and phenotyped for physiological and agronomic traits 91 hybrids and their nineteen female and sixteen male parents. We showed that hybrids had a longer grain filling phase that led to bigger grains and an increased thousand kernel weight. This resulted in a better yield for 86% of hybrids compared to the average yield of their parents. In addition, hybrids appeared to be less affected by the negative correlation between protein content and yield compared to pure lines. These results shed light on the physiological bases underlying yield heterosis in wheat, paving new ways to breed for better wheat hybrids that can help to meet agriculture’s challenges.To meet the challenge of feeding almost 10 billion people by 2050, wheat yield has to double by 2050. However, over the past 20 years, yield increase has slowed down and even stagnated in the main producing countries. Following the example of maize, hybrids have been suggested as a solution to overcome yield stagnation in wheat. However, wheat heterosis is still limited and poorly understood. Gaining a better understanding of hybrid vigor holds the key to breed for better varieties. To this aim, we have developed and phenotyped for physiological and agronomic traits an incomplete factorial design consisting of 91 hybrids and their nineteen female and sixteen male parents. Monitoring the plant development with normalized difference vegetation index revealed that 89% of the hybrids including the five higher yielding hybrids had a longer grain filling phase with a delayed senescence that results in larger grain size. This average increase of 7.7% in thousand kernel weight translated to a positive mid-parent heterosis for grain yield for 86% of hybrids. In addition, hybrids displayed a positive grain protein deviation leading to a +4.7% heterosis in protein yield. These results shed light on the physiological bases underlying yield heterosis in wheat, paving new ways to breed for better wheat hybrids.

PERFORMANCE ASSESSMENT OF CROSSES BETWEEN GADAM AND HARDCORE TANNIN SORGHUM IN HYBRID LINES PRODUCTION

Gadam cultivar of sorghum has been characterized by low yields compared to the international yield levels of sorghum. In this research, Gadam was crossed with Serena, Seredo, and Kari/Mtama-1 in an attempt to increase yield through heterosis. The objective of this study was to determine the level of compatibility and heterosis in crosses between Gadam and the three sorghum lines in a reciprocal crossing. Gadam was crossed with the three lines and their reciprocals to make six treatments that were subjected to compatibility and heterosis tests. The F1 hybrid lines and their parental controls were sown in a randomized complete block design in three replicates. Compatibility and heterosis data variances were analyzed using R statistical software. The cross between Gadam x Serena, Serena x Gadam and the parent Gadam exhibited moderate mean plant height ranging from 99.5 cm to 120.5 cm. The cross Gadam x Serena recorded a desirable negative mid-parent heterosis of -19.89 and -16.16 for plant height and days to maturity respectively. All F1 hybrids recorded positive mid-parent heterosis for the panicle length, the number of reproductive tillers, a thousand seed weight, and the number of tillers per plant. The crosses Gadam x Seredo, Seredo x Gadam, Gadam x Serena and Kari/Mtama-1 x Gadam recorded significantly lower grain filling percentages compared to their parents. In conclusion, the F1 hybrids differed significantly from their reciprocal crosses especially in days of heading, flowering, and maturity indicating a significant maternal influence in these traits. Also, the mid-parent and better parent heterosis had a nonsignificant difference in quantitative traits assessed except for the plant height and grain filling percentage.

Characterization of heterosis and genomic prediction-based establishment of heterotic patterns for developing better hybrids in pigeonpea.

Whole-genome resequencing (WGRS) of 396 lines, consisting of 104 hybrid parental lines and 292 germplasm lines, were used to study the molecular basis of mid-parent heterosis (MPH) and to identify complementary heterotic patterns in pigeonpea [Cajanus cajan (L.) Millsp.] hybrids. The lines and hybrids were assessed for yield and yield-related traits in multiple environments. Our analysis showed positive MPH values in 78.6% of hybrids, confirming the potential of hybrid breeding in pigeonpea. By using genome-wide prediction and association mapping approaches, we identified 129 single nucleotide polymorphisms and 52 copy number variations with significant heterotic effects and also established a high-yielding heterotic pattern in pigeonpea. In summary, our study highlights the role of WGRS data in the study and use of heterosis in crops where hybrid breeding is expected to boost selection gain in order to ensure global food security.

Genomic Prediction of Yield Traits in Single-Cross Hybrid Rice (Oryza sativa L.).

Hybrid rice varieties can outyield the best inbred varieties by 15 – 30% with appropriate management. However, hybrid rice requires more inputs and management than inbred rice to realize a yield advantage in high-yielding environments. The development of stress-tolerant hybrid rice with lowered input requirements could increase hybrid rice yield relative to production costs. We used genomic prediction to evaluate the combining abilities of 564 stress-tolerant lines used to develop Green Super Rice with 13 male sterile lines of the International Rice Research Institute for yield-related traits. We also evaluated the performance of their F1 hybrids. We identified male sterile lines with good combining ability as well as F1 hybrids with potential further use in product development. For yield per plant, accuracies of genomic predictions of hybrid genetic values ranged from 0.490 to 0.822 in cross-validation if neither parent or up to both parents were included in the training set, and both general and specific combining abilities were modeled. The accuracy of phenotypic selection for hybrid yield per plant was 0.682. The accuracy of genomic predictions of male GCA for yield per plant was 0.241, while the accuracy of phenotypic selection was 0.562. At the observed accuracies, genomic prediction of hybrid genetic value could allow improved identification of high-performing single crosses. In a reciprocal recurrent genomic selection program with an accelerated breeding cycle, observed male GCA genomic prediction accuracies would lead to similar rates of genetic gain as phenotypic selection. It is likely that prediction accuracies of male GCA could be improved further by targeted expansion of the training set. Additionally, we tested the correlation of parental genetic distance with mid-parent heterosis in the phenotyped hybrids. We found the average mid-parent heterosis for yield per plant to be consistent with existing literature values at 32.0%. In the overall population of study, parental genetic distance was significantly negatively correlated with mid-parent heterosis for yield per plant (r = −0.131) and potential yield (r = −0.092), but within female families the correlations were non-significant and near zero. As such, positive parental genetic distance was not reliably associated with positive mid-parent heterosis.

Temporal Regulation of the Metabolome and Proteome in Photosynthetic and Photorespiratory Pathways Contributes to Maize Heterosis.

Heterosis or hybrid vigor is widespread in plants and animals. Although the molecular basis for heterosis has been extensively studied, metabolic and proteomic contributions to heterosis remain elusive. Here we report an integrative analysis of time-series metabolome and proteome data in maize (Zea mays) hybrids and their inbred parents. Many maize metabolites and proteins are diurnally regulated, and many of these show nonadditive abundance in the hybrids, including key enzymes and metabolites involved in carbon assimilation. Compared with robust trait heterosis, metabolic heterosis is relatively mild. Interestingly, most amino acids display negative mid-parent heterosis (MPH), i.e., having lower values than the average of the parents, while sugars, alcohols, and nucleoside metabolites show positive MPH. From the network perspective, metabolites in the photosynthetic pathway show positive MPH, whereas metabolites in the photorespiratory pathway show negative MPH, which corresponds to nonadditive protein abundance and enzyme activities of key enzymes in the respective pathways in the hybrids. Moreover, diurnally expressed proteins that are upregulated in the hybrids are enriched in photosynthesis-related gene-ontology terms. Hybrids may more effectively remove toxic metabolites generated during photorespiration, and thus maintain higher photosynthetic efficiency. These metabolic and proteomic resources provide unique insight into heterosis and its utilization for high yielding maize and other crop plants.

Heterosis and combining ability for grain Fe and Zn concentration and agronomic traits in sorghum [Sorghum bicolor (L.) Moench

Studies on genetics and trait relationships with grain yield and other agronomic traits are critical for improving the micronutrients content in the grain and it forms an effective strategy for breeding bio fortified sorghum. It greatly contributes to addressing micronutrient malnutrition in poor people who are dependent on sorghum as a staple food. Development of hybrids with high grain Fe and Zn and higher yield enables delivery of commercial products that address both food and nutrition while bringing profits to farmers. The present study was aimed at developing suitable breeding strategy and improving breeding products using gene action, heterosis and combining ability analysis for improving the grain Iron (Fe) and Zinc (Zn) concentration and grain yield in sorghum. This study was conducted in Line × Tester mating design involving seven parents. A total of 12 new hybrids were developed by mating three lines with four testers. The combining ability of the crosses indicated predominance of dominance variance than additive variance for the agronomic traits such as days to 50% flowering, grain yield, grain Fe and Zn concentrations except for plant height and 100 seed weight. Higher magnitude of SCA than GCA variance for grain iron and zinc concentrations indicated the importance of non-additive gene action in the improvement of nutritional traits. Hybrids exhibited heterosis for agronomic traits and for grain Fe concentration and grain Zn. Most of the traits showed significant positive heterosis over mid parent value indicating the predominance of dominant gene action except the trait 100 seed weight. Significant positive mid-parent heterosis for grain iron indicated that there would be an opportunity to exploit heterosis in improving for grain Fe. But for Zn concentration, there is a limited possibility for exploitation of heterosis. This study suggested that simple selection will improve plant height and 100 seed weight in sorghum but heterosis breeding is more useful for improving grain yield. While both parents need to be improved for improving grain Zn concentration, there is good scope for exploiting heterosis for improving grain Fe concentration in sorghum.

Gene effects and heterosis for grain Fe and Zn content in barnyard millet (Echinochloa frumentacea (Roxb.) link)

Barnyard millet (Echinochloa frumentacea) is an unexplored nutri-rich crop that thrives well in harsh environments and supports many small farmers in Southern and Eastern Asia. Although it has rich sources of micronutrients, the genetic studies are very limited which further impedes in its genetic improvement. Therefore, we attempted to assess the genetic diversity for Fe and Zn content in 40 barnyard millet germplasm and to evaluate the combining ability and heterosis in sixteen F1 cross combinations through line × tester model. The Mahalanobis D2 analysis grouped the 40 genotypes into nine different clusters. Cluster III and I were the largest groups containing 22 and 6 genotypes, respectively and the rest of seven clusters were the lowest group containing one or two genotypes. Positive correlation was observed between Fe and Zn content though both had a non-significant association with grain yield. This indicate that there would not be any compromise on increase or decrease of grain yield while breeding for varieties high in micronutrient content. Combining ability analysis revealed that lines, testers, and their interaction components are significant. The predictability ratio indicated the predominance of additive variance for Fe and Zn content and non-additive variance in the inheritance of yield components. Genotypes, ACM 331, ACM 333, ACM 335 and MA 10 exhibited positive gca effects for Fe and Zn content and grain yield. Two cross combinations, ACM 331 × ACM 335 and ACM 331 × MA 10 involved one or both the parents with good gca effects exhibited, high mean, positive mid-parent heterosis and sca effects for Fe, Zn content and yield components. Thus, the present investigation provided a significant understanding of the gene action and the possibility of utilizing the selected parents and cross combination for exploiting micronutrient traits in barnyard millet crop.

Heterosis for growth, yield and fruit quality traits in papaya

An experiment was conducted during 2016–2017 to determine the magnitude of heterosis in papaya for growth, yield and fruit quality traits. A total of eight genotypes consisting three hybrids along with their five parents were evaluated in a Randomized Block Design with three replications. Appreciable heterosis was found over better over mid parent in traits like days to fruit maturity, number of fruits per plant, fruit yield, fruit shelf life, fruit firmness, antioxidant activity of fruit, total carotenoid content and lycopene content in desirable direction. A hybrid, of progeny of Red Lady (Self) × Pusa Nanha (14.57%) showed significant relative heterosis for yield, whereas none of the hybrids were recorded with better parent heterosis. Two hybrids, Red Lady (Self) × Pusa Nanha (2.93%) and Pune Selection 3 × P-7-9 (22.13%) was observed with high heterosis for number of fruits per plant. All three hybrids exhibited heterosis in negative direction for days to fruit maturity. For fruit shelf life at ambient temperature, hybrid Red Lady (Self) × P-9-5 (3.12%) exhibited better parent heterosis, whereas all three hybrids showed positive mid parent heterosis for the same trait. All three hybrids showed positive mid-parent heterosis for traits like number of fruits per plant, shelf-life, total phenolic content and antioxidant activity. The hybrid Red Lady (Self) × Pusa Nanha exhibited better parent and mid parent heterosis for total carotenoid and lycopene content along with total phenolic content and antioxidant activity. Moreover, none of the hybrids showed positive heterosis for TSS, leaf length, fruit weight, fruit diameter and fruit length. However, hybrid Red Lady (Self) × Pusa Nanha has shown moderate heterosis for important economic traits and same may be exploited further to develop a commercial hybrid of papaya.

Environmental stress tolerance and immune response for the small abalone hybrids

Recently, mass mortality affected the cultured small abalone, Haliotis diversicolor diversicolor, which was the dominant cultured abalone species in southern China. Prior studies revealed that survivorship varied significantly between different stocks and crosses. However, the immunological basis for differences in susceptibility has not been well understood to date. Herein, low temperature, air exposure tolerance tests, and pull-off force measurement were assessed in the three groups (Japan, Taiwan, and their Hybrid stock). The results showed that the critical thermal minimum (CTMin) at 50% was 15.6 °C for the Taiwan stock, 12.1 °C for the Japan stock, and 13.2 °C for the Hybrid stock. Upon air exposure challenge, 100% abalones from the Taiwan group died after 8 h at 24 °C, while the survival rate in the Japan and Hybrid groups were 37.8% and 29.4%, respectively. The detachment stress for the Japan group was 42.3 kPa, which was 2.78-fold and 1.43-fold higher compared to the Taiwan and Hybrid groups, respectively. Variation in susceptibility to disease may be based on the effectiveness of the innate immune responses. Therefore, total hemocyte count, phagocytosis, respiratory burst, superoxide dismutase activity, acid phosphatase activity, alkaline phosphatase activity, and myeloperoxidase activity were determined for the healthy abalones in each group. Positive mid-parent heterosis on immunological parameters was consistent with the prior knowledge on the positive mid-parent heterosis for survival rate, which indicated the improvement on immune reaction and disease resistance through hybridization methods. The current study will be useful in efficient design of breeding programs for the development of sustainable abalone aquaculture.

Genetic Control and Heterosis of Quantitative Traits in Several Local Eggplant Genotypes

The present study was performed to assess the nature of gene action governing inheritance of agronomic traits in eggplant genotypes and extent of mid parent heterosis (MPH) and better parent heterosis (BPH) in six eggplant hybrids generated from four superior and optimally divergent genotypes of eggplant namely ‘Yalo’, ‘Uyo’, ‘K3’ and ‘Iyoyo’ selected from the germplasm and were crossed in 4×4 half diallel mating design. The six hybrids were found to show a significant (p< 0.05) positive MPH in yield traits and the highest was obtained in the hybrid ‘Yalo’ × ‘K3’ for number of fruits per plant (158.90%) and ‘K3’ × ‘Iyoyo’ for fruit yield per plant (63.14%) and fruit yield per hectare (62.20 %). The hybrid combinations ‘Yalo’ × ‘K3’ and ‘K3’ × ‘Iyoyo’ had significant positive BPH for the number of fruits per plant, 104.08% and 42.43%, respectively. For fruit yield per plant, the hybrid combination ‘Yalo’ × ‘K3’ (7.93%), ‘Uyo’ × ‘K3’ (8.48%) and ‘K3’ × ‘Iyoyo’ (12.26%) had significant positive BPH. However, the hybrid ‘K3’ × ‘Iyoyo’ (11.51%) showed significant positive BPH in fruit yield per hectare. Dominance and dominance × dominance gene effect were found to be positively higher in magnitude in all crosses for number of fruits per plant, fruit yield per plant and fruit yield per hectare. The prevalence of dominance and dominance × dominance gene effect in the yield traits indicate heterosis breeding as the best breeding method to improve the productivity of eggplant.

Estimation of heterosis in yield and yield attributing traits in single cross hybrids of maize

A field experiment was conducted at National Maize Research Program, Rampur, Chitwan, Nepal during winter season from 6th October, 2015 to 5th March 2016 to estimate different heterosis on single cross maize hybrids . Thirteen maize hybrids were tested randomized complete block design with three replications. Hybrid namely RML-98/RL-105 gave the highest standard heterosis (57.5%) for grain yield over CP-666 followed by RML-4/NML-2 (32.6%), RML-95/RL-105 (29%) and RML-5/RL-105 (20.6%). The hybrid RML-98/RL-105 produced the highest standard heterosis (75.1%) for grain yield over Rajkumar followed by RML-4/NML-2(50.2%), RML-95/RL-105(46.6%), RML-5/RL-105 and (35.7%). Mid and better parent heterosis were significantly higher for yield and yield attributes viz. ear length, ear diameter, no of kernel row per ear, no of kernel per row and test weight. The highest positive mid-parent heterosis for grain yield was found in RML-98/RL-105 followed by RML-5/RL-105, RML-95/RL-105, and RML-4/NML-2. For the grain yield the better parent heterosis was the highest in RML-98/RL-105, followed by RML-5/RL-105, RML-95/RL-105, and RML-4/NML-2. These results suggested that maize production can be maximized by cultivating hybrids namely RML-98/RL-105, RML-5/RL-105, RML-95/RL-105, and RML-4/NML-2.

Genetic Effects and Heterosis of Yield and Yield Component Traits Based on Gossypium Barbadense Chromosome Segment Substitution Lines in Two Gossypium Hirsutum Backgrounds.

We hybridized 10 chromosome segment substitution lines (CSSLs) each from two CSSL populations and produced 50 F1 hybrids according to North Carolina Design II. We analyzed the genetic effects and heterosis of yield and yield components in the F1 hybrids and parents in four environments via the additive-dominance genetic model. Yield and yield components of the CSSLs were controlled by combined additive and dominance effects, and lint percentage was mainly controlled by additive effects, but boll weight, boll number, seedcotton yield and lint yield were mainly controlled by dominance effects. We detected significant interaction effects between genetics and the environment for all yields traits. Similar interactions were detected between two CSSL populations (Pop CCRI 36 and Pop CCRI 45). Significant positive mid-parent heterosis was detected for all yield traits in both populations, and significant positive better-parent heterosis was also detected for all yield traits except lint percentage. The differences among parents were relatively small, but significant heterosis was detected for yield and yield components. Therefore, the relationship between heterosis and genetic distance for yield traits is complicated and requires further study. These CSSLs represent useful tools for improving yield and yield components in cotton.

Dissection of heterosis for yield and related traits using populations derived from introgression lines in rice

Despite the great success achieved by the exploitation of heterosis in rice, the genetic basis of heterosis is still not well understood. We adopted an advanced-backcross breeding strategy to dissect the genetic basis of heterosis for yield and eight related traits. Four testcross (TC) populations with 228 testcross F1 combinations were developed by crossing 57 introgression lines with four types of widely used male sterile lines using a North Carolina II mating design. Analysis of variance indicated that the effects of testcross F1 combinations and their parents were significant or highly significant for most of the traits in both years, and all interaction effects with year were significant for most of the traits. Positive midparent heterosis (HMP) was observed for most traits in the four TC populations in the two years. The relative HMP levels for most traits varied from highly negative to highly positive. Sixty-two dominant-effect QTL were identified for HMP of the nine traits in the four TC populations in the two years. Of these, 22 QTL were also identified for the performance of testcross F1. Most dominant-effect QTL could individually explain more than 10% of the phenotypic variation. Four QTL clusters were observed including the region surrounding the RM9–RM297 region on chromosome 1, the RM110–RM279–RM8–RM5699–RM452 region on chromosome 2, the RM5463 locus on chromosome 6 and the RM1146–RM147 region on chromosome 10. The identified QTL for heterosis provide valuable information for dissecting the genetic basis of heterosis.

Pearl Millet Inbred and Testcross Performance under Low Phosphorus in West Africa

ABSTRACTPearl millet [Pennisetum glaucum (L.) R. Br] is a food security crop for millions living in drylands of Africa and Asia. Its production on acid sandy soils of the Sahel is limited by erratic rainfall and poor soil fertility, especially low P soils. We sought to elucidate the genetic variation in West and Central African landrace‐derived inbred lines for grain yield under low P conditions, to determine their performance as inbred lines per se and in hybrid combinations, and to determine quantitative‐genetic parameters to derive an appropriate breeding strategy to enhance grain yield under low P conditions. We evaluated a total of 155 landrace‐derived inbred lines as well as their testcrosses in four locations during two years under two treatments, high P (HP; with P fertilization) and low P (LP; without P fertilization). Results revealed significant effects for genotypes, P‐level, genotype × P‐level, as well as genotype × environment interactions. Grain yield reductions under LP treatment ranged from 7.9 to 35.5%, and 11.2 to 60.9% for inbred lines and testcrosses respectively, with positive midparent heterosis averaging 43.5% under LP. We conclude that direct selection of testcrosses under LP is more effective and that indirect selection for testross performance from inbred line performance is not desirable.

Short communication: Heterosis and combining ability of Nepalese yellow maize (Zea mays L.)

Nepalese yellow maize inbred lines were characterized for general combining ability (GCA) and specific combining ability (SCA) of their crosses and parents were identified having high combining ability for determining the heterotic effects on yield and other quantitative traits of hybrids. A line x tester mating design was used for making the crosses in the winter season of 2008 and the hybrids along with their parents and four checks were evaluated in Randomized Complete Block Design (RCBD) with three replications in the spring season of 2009 at the experimental farm of the National Maize Research Program, Chitwan. Significant variations were found among the treatments for grain yield and other traits which indicated presence of high magnitude of genetic variations among tested inbred lines. The cross between RML-32 and RML-17 produced the highest grain yield (15870 kg/ha) among the crosses. Hybrids such as RL-194 x RL-84 (10770 kg/ha), RML-21 x RML-17 (9270 kg/ha), RL-180 x RML-17 (9270 kg/ha) and L-1 x RL-84 (8785 kg/ha) were found superior grain yielder. Thirty-nine hybrids showed positive mid-parent heterosis for grain yield among 40 crosses. The highest positive mid-parent heterosis for grain yield was found 880% in cross between RML-32 and RML-17, followed by RL-98X RML-17 (507%), RL-103 x RML-17 (403%), PUTU-18 x RML- 17 (351%) and RL-180 x RL 84 (316%). Agronomy Journal of Nepal (Agron JN) Vol. 3. 2013, Page 172-180 DOI: http://dx.doi.org/10.3126/ajn.v3i0.9020

Heterotic performance of quality characteristics of bread wheat cultivars

Heterosis has made a significant contribution to the improvement of many crops regarding yield, quality and resistance to pests. The low wheat ( Triticum aestivum L.) productivity in Lesotho has necessitated exploitation of heterosis in commercial cultivars. Heterotic performance of 38 F1 and F2 progenies from 5 x 5 diallel crosses of wheat cultivars were estimated for mid-parent and best-parent values. There were significant differences between F1 and F2 progenies for all characteristics. In F1 progeny, a positive mid-parent heterosis was observed in Sodium dodecyl sulphate (SDS) sedimentation volume, kernel hardness, break flour yield and kernel weight. Positive best-parent heterosis was obtained in all the above parameters. In F2 progeny, characteristics that showed positive mid-parent heterosis were mixograph development time, hardness index and SDS sedimentation volume; while positive best-parent heterosis was observed in mixograph development time, hardness index, kernel diameter and weight. A significant increase in mid-parent heterosis was observed for five characteristics in Sceptre x Wanda and SST124 x Nata. Another significant increase in mid-parent heterosis occurred for four characteristics in Nata x Wanda, Nata x Sceptre, Sceptre x Kariega, Sceptre x SST 124, Wanda x SST 124 and Sceptre x Nata. SST 124 x Sceptre, Nata x Wanda, SST 124 x Kariega and Kariega x Nata revealed a significant increase in best-parent heterosis for all characteristics. Keywords: Best-parent heterosis, Triticum aestivum African Crop Science Journal , Vol. 21, No. 4, pp. 283 - 289