Estimates Of Heterosis Research Articles

Estimation of Heterosis and Combining Ability in Single Cross Hybrids Developed from Newly Derived Inbred Lines of Maize (<i>Zea Mays</i> L.)

An experiment was conducted to study the heterosis and combining ability in newly derived inbred lines involving line×tester analysis with ten lines and three testers at All India Co-ordinated Maize Improvement Project, Agricultural Research Station, Arabhavi, UAS, Dharwad. The results revealed that among ten female lines, L2 was the best general combiner for plant height, ear height, ear length, 100-grain weight, grain yield per hectare and fodder yield per hectare. Whereas, among thirty crosses, L8×T3 was the best specific combination for plant height, ear height and grain yield per hectare. Among thirty, three hybrids L2×T1, L1×T2 and L×T3 showed significant positive standard heterosis over both EH434042 and 900M (Commercial checks).

Heterosis for Yield and Yield Components in OKRA (Abelmoschus Esculentus L.)

The present investigation was undertaken with the objective of identifying the high yielding parents and F1 hybrids through Line x Tester mating design to estimate the heterosis. The experiment was conducted by raising four lines and fifteen testers as parents and their 60 F1 hybrids during kharif 2009 and spring summer 2010. The heterosis recorded for fruit and its thirteen component characters. The F1 hybrids, Arka Anamika x IC-331217, Arka Abhay x IC-331217, Arka Anamika x IC-326893, Arka Anamika x IC-443670, Arka Abhay x IC-332454 and Arka Abhay x IC-433675 recorded high degree of standered heterosis for yield and its contributing characters. High estimates of heterosis obtain in hybrid combinations revealed considerable genetic divergence among the parental lines.

Appraisal of Heterosis for Yield and Yield Attributing Components in Maize (Zea Mays L.)

Estimation of heterosis for yield and yield attributing components in maize was carried out involving 45 crosses developed by including 15 lines, 3 testers along with 3 checks and sown in a Randomized Block Design with three replications. The phenomenon of heterosis was of general occurrence for most of the characters under study. Crosses L9 x T1 and L9 x T2 elucidated desirable and significant heterosis both over mid parent and better parent. Line L6, L7 and tester T1 proved out to be the best general combiner for maturity traits. Crosses, L5 x T3 and L6 x T2 were good specific combiner for maturity traits. Line L6, L2 and tester T3 were good general combiners and among the crosses L10 x T1 and L5 x T3 proved, the best specific combiners for plant height. The superior crosses and lines can be used in future breeding programmes to develop synthetic/hybrid varieties.

Heterosis Studies in Chilli (<i>Capsicum annuum </i>L.)

The estimation of heterosis in 72 hybrids for yield and other 13 yield related component traits were studied following Line x tester design in chilli. Maximum heterosis (49.09 %) for dry fruit yield per plant and fruit weight (21.70 %) over standard check was observed in the cross Co-1 x Byadagi dabbi and for plant height and number of primary branches the cross GPC-82 x Singanahalli local. The hybrid Punjab Lal x KDC-1 had more number of fruits per plant, while Puri red x Lokur local and Puri red x KDC-1 were early for days to 50 per cent flowering. The hybrid G-3 x VN-2 exhibited highest heterosis for fruit diameter and pericarp weight. For fruit length and number of seeds per fruit the cross Co-1 x Byadagi dabbi while, S-32 x Lokur local showed maximum standard heterosis for dry fruit yield per plant. The hybrids Co-1 x Byadagi dabbi (40.09 %), Co-1 Lokur local (40.97 %), G-3 x Lokur local (39.92 %), Co-1 x KDC-1 (36.10 %), G-4 x Byadagi dabbi (34.19 %) and Kunkaur-3 x Byadagi dabbi (32.66 %) were considered most heterotic hybrids for yield and yield related components viz., number of secondary branches, number of fruit per plant, fruit length, fruit weight and pericarp weight.

COMBINING ABILITY AND HETEROSIS ESTIMATES FROM LINE X TESTER MATING DESIGN UNDER WATER STRESS CONDITIONS IN RICE (Oryza sativa L.)

A Study on combining ability and heterosis were conducted on 15 F1 hybrids along with eight rice genotypes (five lines and three testers) to understand the pattern of inheritance of yield, its components and some root traits for selecting superior genotypes. The experiment was carried out using line x tester mating design, during 2010-2011 rice growing seasons at the experimental farm of Rice Research and TrainingCenter, Sakha, Kafr El-Sheikh, Egypt. Analysis of variance revealed significant differences among genotypes, lines, testers and line x tester interactions for days to 50% heading, plant height, panicle length and weight, number of filled grains/panicle, number of panicles/plant, number of roots/plant, root length and volume and grain yield/plant traits under water stress conditions, indicated that the genotypes had wide genetic diversity for the studied traits. Significance of the means of sum squares due to lines and testers indicated a prevalence of additive variance. However, significant differences due to interactions of line x tester for the above mentioned traits, indicating the importance of both additive and non-additive variance in the inheritance of these traits. The mean squares due to GCA as well as SCA were significant for all studied traits except 100- grain weight and root/shoot ratio. Thus, the significance of GCA (variances due to lines and testers) and SCA (variances due to lines x testers) implied that both additive and non-additive types of variation was available for all the traits, yet additive genes were more important than the dominant genes because variance due to GCA was higher than that of SCA for all mentioned traits. Moreover, the ratio of GCA and SCA variances was greater than unity for all the traits studied that revealed the preponderance of additive gene action over the non-additive gene action. IET 1444, Morobrekan and Giza 178 rice genotypes were the best general combiners due to highly significant GCA effects for number of roots/plant, root volume and root length traits. Moreover, Wab 450-JR-4-1-1 as tolerant to water stress conditions was the best general combiner for panicle weight, number of filled grains/panicle, otherwise, Sakha 102, rice genotype was the poorest combiner comparing with other rice genotypes for all the studied traits, except days to 50% heading. The crosses, Sakha 105 x IET 1444, Sakha 103 x Sakha 102 and Morobrekan x Wab 450-JR-4-1-1 were found to be the best cross combinations for most of the studied traits; these crosses had high and significant SCA in desirable direction under water stress conditions. Highly significant and positive estimates of heterosis and heterobeltiosis were recorded in Morobrekan x IET 1444, Sakha 105 x IET 1444 and Sakha 104 x Sakha 102 for number of panicles/plant, panicle length and number of roots and their volume/plant, respectively. The highest estimated values of phenotypic (Vph) and genotypic (Vg) variances were observed for number of filled grains/panicle, root number/plant and root volume indicating better scope for the genetic improvement in these three mentioned traits. High broad-sense heritability, coupled with high genetic advance, were observed for plant height, panicle weight, number of panicles/plant, sterility % and grain yield/plant, indicating the role of additive genetic variance in the expression of these traits and direct selection might be highly effective in early generations to improve these traits under water stress conditions.

GENETIC STUDIES ON GRAIN DIMENSION, YIELD AND ITS RELATED TRAITS IN RICE UNDER SALINE SOIL CONDITIONS (Orayza sativa L.)

The present investigation was carried out at the Lysimeter of the Rice Research and Training Center (RRTC), Sakha, Kafr El-Sheikh, Egypt during 2009, 2010 and 2011 summer seasons. The aim of this investigation estimate heterosis, heterobeltiosis, heritability in broad and narrow senses, expected genetic advance, inbreeding depression, phenotypic and genotypic coefficient of variability and nature of gene action for grain dimensions, yield and its related traits in rice using six populations technique, viz., P1, P2, F1, BC1, BC2 and F2 generation of (Nabatat Asmar x Sakha 105) rice cross under both saline soil irrigated with 10.6 dSm-1 of sodium chloride (NaCL2) and calcium chloride (CaCL2) at the ratio of 1: 2, respectively, and normal soil conditions irrigated with tap water (EC, 0.77 dSm-1). The main finds could be summarized as follows: The results indicated that highly significant and positive heterosis and heterobeltiosis were obtained for all the studied traits under saline soil conditions, except 100-grain weight, grain width and grain shape traits, which, showed highly significant and negative estimates of heterosis when it were measured as a deviation from better-parent under normal soil conditions for the first two traits. Highly significant and negative estimates of heterosis when it was measured as a deviation from mid-parent for the third trait. Phenotypic coefficient of variability (P.C.V) was higher than genotypic coefficient of variability (G.C.V) for all the studied traits, indicating that they all affected by environment conditions. High estimates of broad sense heritability coupled with high genetic advance was observed for days to 50 heading, plant height, 100-grain weight, panicle weight, grain length, grain width and grain shape under two conditions. Therefore, direct selection for these characters is recommended in early generations. In addition, incomplete dominance to over-dominance was operative for most the studied traits under two conditions. The estimates of nature of gene action showed that mid-parent values were positively and highly significant for all the studied traits under two conditions except days to 50 % heading, plant height and sterility % under two conditions. Additive gene action was important for all the studied traits except plant height, grain length and grain shape under saline soil conditions. Whereas, dominance gene action was played an important role in the inheritance of 100- grain weight and grain yield/ plant. Moreover, additive x additive type of gene interaction were important for plant height, 100- grain weight and sterility % under normal conditions. On the other hand, grain yield/ plant followed by number of filled grains/ panicle, panicle length, grain length and panicle weight were affected by dominance x dominance gene interaction. The results in general, revealed that days to 50 % heading, plant height, panicle length, grain length, grain width, and grain shape were controlled by almost one pairs of effective genes suggesting that these traits were inherited as simple traits under two conditions. Moreover, number of panicles/ plant and number of filled grains/ panicle under saline soil conditions were probably controlled by two to sixty nine pairs of genes indicating that these traits were inherited as a complicated or quantitative traits, so, selection late generation was important and play an remarkable role in important such traits.

Performance evaluation and crossbreeding effects for body weight and conformation traits in different breeds of ducks

A 3×3 full diallel experiment was carried out using 3 breeds of ducks, viz. Indigenous duck (D), Khaki Campbell (C) and White Pekin (P), to evaluate the juvenile body weights and conformation traits and to estimates different crossbreeding genetic parameters in 609 ducklings from nine genetic groups. Significant differences between different genetic groups were observed for all the traits measured. Direct genetic effects, maternal effects and heterosis were significant for all the traits studied. Heterosis was in desirable direction for all the traits. Overall results revealed that crossbreds performed significantly higher than the purebreds. C × P recorded highest body weight amongst the crossbreds at 8 weeks of age. Heterosis (%) estimates for 8 week body weight, shank length and keel length were positive. Since both additive and non-additive genetic effects are important for the juvenile traits, establishment of pure lines with specialized sire and dam lines followed by crossing is ideal for the production of different crosses for the commercial duck farming.

Heterosis and combining ability for body weight in a diallel cross of three chicken genotypes

The aim of the study was to evaluate heterotic and combining ability effects for growth in nine chicken genotypes. A 3 × 3 complete diallel mating system involving two indigenous breeds named Venda (V) and Naked Neck (N) and one commercial broiler breed named Ross 308 (R) were used. The nine genetic groups of crosses were reared up from hatch to 13 weeks of age in deep litter open house. Body weights of 180 chicks (20 chicks per genetic group), recorded at 0, 3, 5, 7, 9, 11, and 13 weeks of age, were used to estimate heterosis, general combining ability (GCA), and specific combining ability (SCA). Results showed that the Ross 308 had the heaviest body weight at all weeks of measurement except for hatch. With respect to crosses, the V × R and its reciprocal cross, R × V had the heaviest body weights at 13 weeks. Heterosis estimates for body weight were higher in the Venda male × Ross 308 female and Venda male and Naked Neck female crosses. GCA was significant (P ≤ 0.01) for body weight from hatch to 13 weeks of age while SCA and reciprocal effects were both significant (P ≤ 0.05) for body weight at all ages of measurement except for hatch. The Ross 308 gave the highest positive effect of GCA for body weight except for hatch. V × N gave the highest and positive effects of SCA for body weight.

Capacidade combinatória e heterose para resistência a pinta-preta em mamoeiro por meio de análise dialélica

Diallelic crosses were performed between eight papaya genotypes belonging to the 'Solo' and 'Formosa' heterotic groups (four belonging to each group). The 56 hybrid combinations (F1's and reciprocals) along with their parents were evaluated in a complete randomized block design for resistance to black spot disease, caused by Asperisporium caricae. The severity of black spot in leaves and fruits was quantified in two occasions, March and May 2010. When the genotype effect was significant, heterosis as well as general and specific combining ability were estimated from the severity data. The genotypes 'JS12-N', 'Sekati', 'Golden' and 'Sunrise Solo 72/12' displayed better general combining ability for both characteristics. Twelve hybrids displayed promising results for selection, with low values of specific combining ability for resistance to black spot leaves and fruits. The heterotic group did not affect hybrid performance or heterosis estimates. Heterosis in papaya for resistance to black spot may provide significant genetic gains from both inter-and intra-heterotic crosses, and especially from hybridizations involving genotypes of the 'Solo' group.

Estimation of Heterosis and Heritability in Bread Wheat (Triticum aestivum L.)

Six varaieties of bread wheat Triticum aestivum L.(Sham 4, Adnaniya, Iba 95, Tamoz 2, Eratom, Abo-Graib) and their half diallel crosses were used to estimate heterosis, broad and narrow sense heritability for the following quantitative characters: heading time, number of tillers per plant, plant height, flag leaf area, number of spikes per plant, spike length, number of spiklet per spike, number of grains per spike, 100 grain weight, grain yield per plant and the harvest index. Most hybrids appeared significant and desirable values for heterosis. The broad sense heritability was high for plant height, spike length and number of spiklet per spike while, it was modrate for harvest index, and low for heading time, number of tillers per plant, flag leaf area, number of spike per plant, number of grains per spike, 100 grain weight and grain yield per plant. The narrow sense heritability was high for plant height and harvest index, and moderate for heading time, spike length, number of spiklet per spike,100 grains weight while it was low for number of tillers per plant, flag leaf area, number of spike per plant, number of grains per spike and grain yield per plant.

Preliminary observations on growth and survival ofOreochromis spilurusx GIFTOreochromis niloticusF1reciprocal hybrids in fresh and seawater

Tilapia has a significant potential for culture in saline environments. There is an increasing demand among tilapia producers to develop a tilapia hybrid that can survive well in marine water conditions. This study compared mean weight (MWT), daily growth rate (DGR), specific growth rate (SGR), survival, feed conversion ratio (FCR), condition factor (K), production rate (PR) and rate of skin lesions, and tail and fin rot as well as eye cataract in the Genetically Improved Farmed Tilapia strain (GIFT) of the Nile tilapia, Oreochromis niloticus (NN) and the salt-tolerant Oreochromis spilurus (SS), and their F1 reciprocal hybrids; O. niloticus ♀ x O. spilurus ♂ (NS) and O. spilurus ♀ x GIFT O. niloticus ♂ (SN) in freshwater (0 g L−1) and seawater (40 g L−1). Fish (3.5 g) were stocked at 150-fish m−3 and fed with sea bream pellets (47% protein) for 180 days. Results showed that in seawater, the SN hybrid had the highest values for MWT (165.9 g), DGR (0.9 g fish−1 day−1), SGR (2.14% day−1), survival (96.3%), PR (23.9 kg m−3) and best FCR (1.53) followed by the NS hybrid and the NN parent. Both hybrids had significantly lower rates of skin lesions and fin and tail rot than the NN genotype. In freshwater, the NN had the highest values for MWT (255.1 g), DGR (1.40 g fish−1 day−1), SGR (2.38% day−1), K (2.13%) and PR (34.9 kg m−3) followed by the NS and SN hybrids. High estimate of heterosis for MWT (41.3%), DGR (42.5%), SGR (10.7%) and survival (22.1%) was obtained in the hybrids reared in seawater, indicating that a hybrid vigor was produced and the fast growth trait from the GIFT parent was successfully combined with the salinity tolerance trait from the O. spilurus parent. The better growth performance and survival of the SN hybrid in seawater indicate that this hybrid is more suitable for culture in seawater than its reciprocal hybrid.

Genetic effects on carcass quantity, quality, and palatability traits in straightbred and crossbred Romosinuano steers1,2

The objectives of this work were to estimate heterosis and breed genetic effects for carcass quantity, quality, and palatability traits of steers (Bos spp.) produced from matings of Romosinuano, Brahman, and Angus cattle. Steers (n = 464) were weaned at 7 mo of age and transported to the Southern Great Plains where they grazed winter wheat for 6 mo and were then fed a finishing diet until serial slaughter after different days on feed (average 130 d). Carcass quality and quantity traits were measured; steaks (aged 7 d) were obtained for palatability evaluation. Heterosis was detected for BW, HCW, dressing percentage, LM area, and yield grade for all pairs of breeds. Generally, Romosinuano-Angus heterosis estimates were smallest, Romosinuano-Brahman estimates were intermediate, and Brahman-Angus heterosis estimates were largest. The direct Romosinuano effect was to decrease (P < 0.05) BW (-67 ± 16 kg), HCW (-48 ± 10 kg), dressing percentage (-1.4 ± 0.5 units), 12th rib fat thickness (-5.2 ± 0.8 mm), and yield grade (-0.9 ± 0.1), and to increase LM area per 100 kg HCW (3.6 ± 0.3 cm(2)/100 kg). Significant Brahman direct effects were detected for BW (34 ± 17 kg), HCW (29 ± 10 kg), dressing percentage (1.6 ± 0.6 %), LM area per 100 kg HCW (-3.3 ± 0.4 cm(2)/100 kg), and yield grade (0.6 ± 0.1). Significant Angus direct effects were to increase 12th rib fat thickness (3.8 ± 1 mm). Among sire breed means, Romosinuano had reduced (P = 0.002) marbling score (393 ± 9) than Angus, but greater mean sensory tenderness scores (5.8 ± 0.1), and reduced percentage Standard carcasses (10 ± 2%) than Brahman (P < 0.002). Angus sire breed means for marbling score (475 ± 10), overall tenderness (5.8 ± 0.1), and percentage Choice carcasses (75 ± 5%) were greater (P < 0.05) than Brahman sire breed means (360 ± 11, 5.4 ± 0.1, 31 ± 5%). From consideration only of characteristics of the end product of beef production, Romosinuano did not provide a clearly superior alternative to Brahman for U.S. producers, as they had some quality and palatability advantages relative to Brahman, but at lighter HCW.

Progress on breeding for best-hybridized crossing of meat rabbits

Best-hybridized crossing should ideally result in optimal exploitation of heterosis of lines and capitalize on expressed heterosis. Rabbit breeding is heading in the direction of breeding for best-hybridized crossing of meat rabbits. Most special sire lines are selected for post-weaning average daily gain and marketing weight. Post-weaning growth has a negative and favorable genetic correlation with the feed conversion ratio, which is used in indirect selection for feed conversion ratio. The most common selection criteria for special maternal lines are related to litter size at birth or at weaning. Since the heritability of most reproductive traits is low, we must collect as many individual and relative records as possible in the genetic evaluation of rabbits. The BLUP procedure under an animal repeatability model is the most common procedure used for evaluation of animals in selection programs for special lines of meat rabbits. Direct selection for litter size is less efficient than selection for post-weaning growth, but the estimation of heterosis is generally higher for litter size than that for the post-weaning growth. Evaluation of heterosis could be performed by estimating crossbreeding parameters in the cross or comparing contemporary productivity among purebreds and crossbreds. Here, we reviewed breeding of special lines, exploitation of heterosis of crossbreds, and establishment of crossbreeding system of hybrid meat rabbits and summarized the methodologies of breeding special lines, criteria in selection programs, and the result of heterosis estimates.

Diallel cross among fresh market tomato inbreeding lines

The general combining ability (GCA), specific combining ability (SCA), and heterosis were studied in a complete diallel cross among fresh market tomato breeding lines with reciprocal excluded. Fifteen genotypes (five parents and ten hybrids) were tested using a randomized complete block design, with three replications, and the experiments were conducted in Itatiba, São Paulo state, Brazil, in 2005/06. The yield components evaluated were fruit yield per plant (FP), fruit number per plant (FN), average fruit weight (FW); cluster number per plant (CN); fruit number per cluster (FC), fruit wall thickness (FT) and number of locules per fruit (NL). Fruit quality components evaluated were total soluble solids (SS); total titratable acidity (TA); SS/TA ratio, fruit length (FL); fruit width (WI); length to width ratio (FL/WI). The data for each trait was first subjected to analysis of variance. Griffing's method 2, model 1 was employed to estimate the general (GCA) and specific (SCA) combining abilities. Parental and hybrid data for each trait were used to estimate of mid-parent heterosis. For plant fruit yield, IAC-2 was the best parental line with the highest GCA followed by IAC-4 and IAC-1 lines. The hybrids IAC-1 x IAC-2, IAC-1 x IAC-4 and IAC-2 x IAC-4 showed the highest effects of SCA. High heterotic responses were found for fruit yield and plant fruit number with values up to 49.72% and 47.19%, respectively. The best hybrids for fruit yield and plant fruit number were IAC-1 x IAC-2, IAC-1 x IAC-4 and IAC-2 x IAC-5, for fruit yield and plant fruit number, the main yield components.

Genetic Improvement of Jatropha for Biodiesel Production

Jatropha curcas L. is a perennial oilseed crop belonging to the Euphorbiaceae family, whose oil content in seeds varies from 33 to 38%, giving a yield potential of over 1200 kg of oil per hectare. However, it is a non-domesticated species and research is required for commercial exploration of this species for biodiesel production. The strategies of Embrapa’s jatropha breeding program aim at developing cultivars with high yield and oil content, non-toxic (absence of phorbol esters), resistant to biotic and abiotic stresses and adapted to the main producing regions of Brazil. The program activities started with the enrichment and characterization of the germplasm bank, currently with over 200 accessions from different regions of Brazil. Depending on the specific objectives of the program, different selection and breeding methods are employed. In order to understand the genetic control of specific traits and to generate segregating populations, experimental designs such as diallel crosses, which allow the estimation of heterosis, general combining ability and specific combining ability among genotypes, have been adopted. In addition, molecular markers such as SSR and SNPs are being developed and may help in early selection for characters such as the absence of toxicity in the grains. The program also includes the study on genotype × environment interaction with the evaluation of the progenies/improved clones in different regions of Brazil, which is essential for recommending cultivars for specific or broad climatic conditions. In conclusion, considering that J. curcas is a perennial species and still not domesticated, approximately 5-7 years will be required to obtain improved cultivars and evidence-based information on crop production systems to support commercial cultivation.

Estimation of heterosis in root length of wheat under different saline environment

A 6 × 6 diallel cross among three sensitive (18180-II, 18205-I, 18205-I and DN-18) and three tolerant (18194-II, DN-4, and LU-26S) wheat genotypes was analyzed. Thirty-six genotypes were sown in a triplicates completely randomized design in hydroponics culture. Data for root length was recorded in three salinity levels, i.e. control, 10 and 15 dSm−1. Combining ability effects controller tolerance in the two salinity levels (10 and 15 dSm−1). The genotypes 18194-II and LU-26S exhibited highest general combining abilities under10 and 15 dSm−1. The cross combinations with highest specific combining ability for root length were 18194-II × DN-4, 18180-II × 18205-I and LU26S × DN-18 under salinity levels. In reciprocals the crosses DN-18 × DN-4 and DN-4 × 18205-I appeared to be superior to the others under high salinity levels. DN-4 × LU26S produced significantly longer roots than its better parent and thus showed highest heterobeltiosis in high salinity level.

Developmental Stability in Chickens Local to Warm Climatic Region 2. Variation in Blood Metabolites Due to Genetic Selection and Crossing

An experiment was conducted to assess the variation in blood metabolic constituents in a local chicken line (CE1) selected five generations for increased 6-wk body weight. Also, line CE1 was reciprocally crossed with a Slow-Growing Commercial Broiler Strain (SGB). The local genetic control line (CRB) was used for genetic comparison. No significant differences were observed in the blood levels of total proteins, albumin, globulin and Albumin/Globulin (A/G) ratio among lines CE1 and CRB in both parental (P) and progeny (F1) generations. In P generation, total protein levels of 2.22 and 2.16 g/dl were obtained for lines CE1 and CRB and were significantly higher than 1.78 g/dl for strain SGB. Line CE1 had triglyceride level of 178.76 mg/dl which was significantly higher than 122.13 mg/dl for line CRB. Similar trend for the blood lipid metabolites were obtained in F1 generation. Sex variation in body weight although was obvious, the selection pressure on sex variation in metabolic activity was not existed. Significant heterosis estimates of -22.56 and 5.0% were obtained for the levels of total lipids and cholesterol. The heterosis estimates in the levels of total proteins, albumin, globulin, A/G ratio and triglycerides were -23.71, 9.94, -33.66, 14.97 and -3.63%, but lacked significance. Although heterosis estimates were mostly insignificant, they indicated that the metabolic activity could be drastically changed by crossing. The drastic change in the metabolic activity was too early to be noticeable in a short-term selection program. Selection pressure was more obvious in lipid metabolites, particularly triglycerides, than in protein metabolites. Highly moderate negative and significant correlation coefficient was obtained between globulin level and cholesterol level. The variable correlation relationships among blood metabolites and the insignificant correlations between blood metabolites and body weights did not reflect the continuous metabolic and tissue remodeling associated with growth. This could be due to the small size that characterizes local chickens of warm regions or the shortness of selection scheme that did not result in an obvious change in the metabolic activity.

Heterotic parameterizations of crosses between tropical and temperate lines of popcorn

We examined the heterotic parameterizations of diallel crosses among 10 popcorn inbred lines in two different environments (municipalities of Campos dos Goytacazes and Itaocara, Rio de Janeiro State) and originating from tropical, temperate and subtropical germoplasm. Traits, including grain yield (GY), plant height (PH), ear height (EH), days to silking (FL) and popping expansion (PE), were measured. The inbred lines and the hybrids were evaluated in a randomized complete block design with three replications. The sources of genotypic variation, inbred lines and heterosis had significant effects on all traits. When the sources of heterotic variation were compared separately, estimated mean heterosis was found to be significant for all traits. When inbred lines and specific heterosis was investigated, only popping expansion was not significantly different, demonstrating that heterotic effects are favorable for developing superior hybrids. A direct relation between ĝi and was made clear, especially for traits that were slightly influenced by the effects of dominance. Additivity was determined to have the best effect for improving popping expansion. The hybrid combinations had positive estimates of heterosis for the GY but not for PE. The hybrids P1 x P3 and P2 x P4 had the best responses for the GY and PE. The superiority of the combination P1 x P3 shows that the addition of genomes with different edaphoclimatic adaptations is an important factor in obtaining superior hybrids.

Estimates of strain additive genetic, heterosis and reciprocal effects for male proportion in Nile tilapia, Oreochromis niloticus L.

Data from the GIFT complete diallel cross with eight strains of Nile tilapia reared at seven different grow out environments were analyzed to evaluate the feasibility of using breeders from the best performing strains or strain combinations to increase male proportion in the population. Of the three strain genetic by test environment interaction effects evaluated, i.e., strain additive, strain reciprocal and strain heterosis, only the latter was found to be significantly different from zero ( P < 0.05). However, it was difficult to see any trend with respect to the ranking of the strain total heterosis estimates across different environments, a prerequisite for a commercial utilization of these heterosis effects in a breeding program. Of those effects found to have a significant effect ( P < 0.05) on male proportion, the environment effect accounted for 0.12%, the batch effect for 0.23%, the strain additive genetic effect for 0.06%, the strain reciprocal effect for 0.25% and the strain total heterosis effect for 0.42% of the total variation in male proportion. The largest difference between two strains was 13.3 ± 4.6 percentage points ( P < 0.001) for the additive genetic effect, 12.0 ± 2.2 percentage points ( P < 0.001) for the reciprocal effect and 5.7 ± 2.2 percentage points ( P < 0.01) for the general heterosis effect. Average heterosis for male proportion was not significantly different from zero (1.8 ± 1.2 percentage points; P > 0.05), however for some strain crosses the total strain heterosis effect was substantial with 19.7 ± 4.4 percentage points ( P < 0.001) as the largest difference between two strain crosses. The strain additive effect explained only 3%, the strain reciprocal effect 25% and the strain total heterosis effect 59% of the variation in total performance (strain additive + strain reciprocal + strain total heterosis) in male proportion. However, most of the variation in total heterosis was due to the specific heterosis effect which explained a large proportion (53%) of the variation in total performance in male proportion among the crosses, and thus is more important than any of the other studied strain genetic effects; i.e. the strain additive, reciprocal and general heterosis effects. Therefore to maximize gain in male proportion the strain cross or crosses with highest total performance should be chosen. It can be concluded that genetic improvement of male proportion through the use of breeders from the strain and strain crosses with highest male proportion in this study will have an insufficient impact for the immediate commercial applications under the tested farming conditions in the Philippines.

Combining ability, heterosis and genetic diversity in tropical maize (Zea mays L.) under stress and non-stress conditions

Drought and low soil fertility are considered the most important abiotic stresses limiting maize production in sub-Saharan Africa. Knowledge of the combining ability and diversity of inbred lines with tolerance to the two stresses and for those used as testers would be beneficial in setting breeding strategies for stress and nonstress environments. We used 15 tropical maize inbred lines to (i) evaluate the combining ability for grain yield (GY), (ii) assess the genetic diversity of this set of inbred lines using RFLP, SSR, and AFLP markers, (iii) estimate heterosis and assess the relationship between F1 hybrid performance, genetic diversity and heterosis, and (iv) assess genotype × environment interaction of inbred lines and their hybrids. The F1 diallel hybrids and parental inbreds were evaluated under drought stress, low N stress, and well-watered conditions at six locations in three countries. General combining ability (GCA) effects were highly significant (P < 0.01) for GY across stresses and well-watered environments. Inbred lines CML258, CML339, CML341, and CML343 had the best GCA effects for GY across environments. Additive genetic effects were more important for GY under drought stress and well-watered conditions but not under low N stress, suggesting different gene action in control of GY. Clustering based on genetic distance (GD) calculated using combined marker data grouped lines according to pedigree. Positive correlation was found between midparent heterosis (MPH) and specific combining ability (SCA), GD and GY. Hybrid breeding program targeting stress environments would benefit from the accumulation of favorable alleles for drought tolerance in both parental lines.