Mid-parent Research Articles

Non-additive gene regulation in a citrus allotetraploid somatic hybrid between C. reticulata Blanco and C. limon (L.) Burm

Polyploid plants often produce new phenotypes, exceeding the range of variability existing in the diploid gene pool. Several hundred citrus allotetraploid hybrids have been created by somatic hybridization. These genotypes are interesting models to study the immediate effects of allopolyploidization on the regulation of gene expression. Here, we report genome-wide gene expression analysis in fruit pulp of a Citrus interspecific somatic allotetraploid between C. reticulata cv 'Willowleaf mandarin'+C. limon cv 'Eureka lemon', using a Citrus 20K cDNA microarray. Around 4% transcriptome divergence was observed between the two parental species, and 212 and 160 genes were more highly expressed in C. reticulata and C. limon, respectively. Differential expression of certain genes was confirmed by quantitative real-time RT-PCR. A global downregulation of the allotetraploid hybrid transcriptome was observed, as compared with a theoretical mid parent, for the genes displaying interspecific expression divergence between C. reticulata and C. limon. The genes underexpressed in mandarin, as compared with lemon, were also systematically repressed in the allotetraploid. When genes were overexpressed in C. reticulata compared with C. limon, the distribution of allotetraploid gene expression was far more balanced. Cluster analysis on the basis of gene expression clearly indicated the hybrid was much closer to C. reticulata than to C. limon. These results suggest there is a global dominance of the mandarin transcriptome, in consistence with our previous studies on aromatic compounds and proteomics. Interspecific differentiation of gene expression and non-additive gene regulation involved various biological pathways and different cellular components.

Genetic Distance and Heterosis through Evaluation Index in the Silkworm, Bombyx mori (L.)

Problem statement: Synthesis of new-gene combinations by genetic manipulation is one of the powerful tools in exploiting the commercial qualities of plants and animals. Hybrid performance is evaluated from extensive yield trials that are costly and time consuming. Approach: Four silkworm races belonging to two different voltine groups (two multivoltine races namely Pure Mysore and Nistari and two bivoltine races namely C108 and NB4D2) and the twelve regular and reciprocal hybrids derived from them were reared under standard laboratory condition analyzing six quantitative traits namely cocoon weight, shell weight, shell ratio, filament length, denier and renditta. The data of the pure races was analysed for the estimation of evaluation index to study the genetic divergence between the races, where as evaluation index, heterosis and overdominance effects were studied in twelve hybrid combinations. Results: Varied heterotic effects were observed for different traits for hybrid combination. Cocoon weight and shell weight has maximum heterosis over the mid parent in Pure Mysore × Nistari (27 and 42% respectively), whereas C108 × Nistari have shown maximum shell ratio (30%) among the hybrids. The maximum filament length for heterosis was observed in the Nistari × Pure Mysore. Heterosis for cocoon weight, shell weight, shell ratio, filament length, denier and renditta based on evaluation index confirmed the above results. Conclusion: The investigation indicates that optimum level of genetic divergence between parents is necessary to obtain heterosis in F1 generation.

Cane yield attributes and heritability of juice quality characters in sugarcane under moisture deficit conditions

Development of drought tolerant sugarcane varieties for cultivation in drought prone ecologies of the Nigeria savannas is prerequisite to attain self-sufficiency in sugar production in Nigeria. To this end, bi-parental progenies from four sugarcane crosses involving two drought tolerant and two moderately drought susceptible clones were assessed along with their parents for their drought tolerance capacity using three moisture regimes — well watered, moderate and prolonged drought stress respectively. Almost all the traits investigated in the genotypes remained unaffected by moderate drought stress except cane yield which was reduced by 2–35% in the parents and by 5% in one cross. Prolonged drought stress reduced cane yield by 6–21% in the parents and by 13–21% in the crosses. Differences for juice quality attributes (except refractometer brix and % fibre) were significant under prolonged drought stress. Both additive (δ2 A) and dominance (δ2D) genetic variance estimates differed significantly for juice quality attributes but estimates obtained for δ2D were larger in magnitude than δ2 A indicating the usefulness of specific crosses in breeding for drought tolerance. Progenies from drought tolerant parents exhibited positive heterosis over mid-parent values for stalk length and cane yield under moderate drought stress condition confirming the presence of non-additive gene action for these traits in the populations. Heterosis over the better parent were, however, negligible or negative for most of the characters.

Early generation performance of Fragaria species hybrids in crosses with cultivated strawberry

Yield (i.e., fruit number and size) and yield component measurements were collected and destructive growth analysis carried out on lower-ploidy Fragaria species, synthetic octoploids (SO), F1 (SO × cultivar), OC1 (F1 × cultivar) hybrids and cultivars. Plants were grown in two field trials, at the Elora Research Station, Ontario, and at the Wye Research and Education Centre, Queenstown, Maryland, and in one greenhouse trial in Guelph, Ontario. Total plant dry weight (PDW) was highly variable for the species, but the higher vegetative vigour of the SOs compared with mid-parent values suggested a heterotic effect. The shade adapted species (e.g., F. moschata Duch. and F. nubicola) had greater PDWs than the sun adapted species. Yields of the species, SOs and F1 hybrids were low; however, flower number was higher compared with cultivars. The first outcross with F1s and cultivars resulted in a sixfold increase in yield attributed to both increased fruit size and fruit number. Three of the four OC1 hybrids had yields that were comparable with cultivars. Through breeding and intensive selection, genotypes introgressed with SO germplasm can be restored to the pre-cultivar yield levels with only a few outcrosses to the cultivated strawberry.Key words: Growth analysis, heterosis, interspecific hybridization, strawberry, yield, synthetic octoploid

Small RNAs serve as a genetic buffer against genomic shock in Arabidopsis interspecific hybrids and allopolyploids

Small RNAs, including microRNAs (miRNAs), small interfering RNAs (siRNAs), and trans-acting siRNAs (tasiRNAs), control gene expression and epigenetic regulation. Although the roles of miRNAs and siRNAs have been extensively studied, their expression diversity and evolution in closely related species and interspecific hybrids are poorly understood. Here, we show comprehensive analyses of miRNA expression and siRNA distributions in two closely related species Arabidopsis thaliana and Arabidopsis arenosa, a natural allotetraploid Arabidopsis suecica, and two resynthesized allotetraploid lines (F(1) and F(7)) derived from A. thaliana and A. arenosa. We found that repeat- and transposon-associated siRNAs were highly divergent between A. thaliana and A. arenosa. A. thaliana siRNA populations underwent rapid changes in F(1) but were stably maintained in F(7) and A. suecica. The correlation between siRNAs and nonadditive gene expression in allopolyploids is insignificant. In contrast, miRNA and tasiRNA sequences were conserved between species, but their expression patterns were highly variable between the allotetraploids and their progenitors. Many miRNAs tested were nonadditively expressed (deviating from the mid-parent value, MPV) in the allotetraploids and triggered unequal degradation of A. thaliana or A. arenosa targets. The data suggest that small RNAs produced during interspecific hybridization or polyploidization serve as a buffer against the genomic shock in interspecific hybrids and allopolyploids: Stable inheritance of repeat-associated siRNAs maintains chromatin and genome stability, whereas expression variation of miRNAs leads to changes in gene expression, growth vigor, and adaptation.

Gene action analysis by inheritance and quantitative trait loci mapping of resistance to root-knot nematodes in cotton

With 2 figures and 5 tables Abstract Host–plant resistance is highly effective in controlling crop loss from nematode infection. In addition, molecular markers can be powerful tools for marker-assisted selection (MAS), where they reduce laborious greenhouse phenotype evaluation to identify root-knot nematode (RKN) Meloidogyne incognita Kofoid and White (Chitwood) resistant genotypes. To better understand host–plant interactions, we investigated gene action and genomic locations of RKN resistance genes in cotton (Gossypium hirsutum L). Twelve parents, 17 intraspecific (G. hirsutum × G. hirsutum) and four interspecific (G. hirsutum ×G. barbadense L.) F1, and 11 F2 populations were investigated by examining different RKN resistance backgrounds. The F1 and F2 generation means and distributions, and differences between F1 and mid-parent values for Galling Index (GI) indicated that allelic interaction, epistasis and heterosis operated in these crosses. Genetic and quantitative trait loci (QTL) analyses in crosses NemX × SJ-2 and SJ-2 × Clevewilt revealed resistance because of at least one major recessive QTL with strong additive effect, while in PS 7 × NemXresistance was because of at least one major QTL with strong dominant effect. Simple sequence repeat (SSR) markers CIR316 and MUCS088 on chromosomes 11 and 21 showed the association of two different chromosomes with the RKN resistance. This also supported the two-gene model of observed resistant : susceptible ratios in F2 and F3 (PS 7 × NemX) populations. Selection success rate for MAS was >85% for identifying resistant genotypes with GI < 3 from these crosses with SSRS CIR316, BNL1231 and MUCS088, and CAPS (GHACC1). QTL analyses validated the importance of a major genome-telomeric region on chromosome 11, harbouring RKN resistance genes from different backgrounds. We conclude that breeding for optimal resistance must be based on selection of progeny with combinations of genes homozygous for resistance.

Comparative gene expression profiles between heterotic and non-heterotic hybrids of tetraploid Medicago sativa

BackgroundHeterosis, the superior performance of hybrids relative to parents, has clear agricultural value, but its genetic control is unknown. Our objective was to test the hypotheses that hybrids expressing heterosis for biomass yield would show more gene expression levels that were different from midparental values and outside the range of parental values than hybrids that do not exhibit heterosis.ResultsWe tested these hypotheses in three Medicago sativa (alfalfa) genotypes and their three hybrids, two of which expressed heterosis for biomass yield and a third that did not, using Affymetrix M. truncatula GeneChip arrays. Alfalfa hybridized to approximately 47% of the M. truncatula probe sets. Probe set signal intensities were analyzed using MicroArray Suite v.5.0 (MAS) and robust multi-array average (RMA) algorithms. Based on MAS analysis, the two heterotic hybrids performed similarly, with about 27% of genes showing differential expression among the parents and their hybrid compared to 12.5% for the non-heterotic hybrid. At a false discovery rate of 0.15, 4.7% of differentially expressed genes in hybrids (~300 genes) showed nonadditive expression compared to only 0.5% (16 genes) in the non-heterotic hybrid. Of the nonadditively expressed genes, approximately 50% showed expression levels that fell outside the parental range in heterotic hybrids, but only one of 16 showed a similar profile in the non-heterotic hybrid. Genes whose expression differed in the parents were three times more likely to show nonadditive expression than genes whose parental transcript levels were equal.ConclusionThe higher proportions of probe sets with expression level that differed from the parental midparent value and that were more extreme than either parental value in the heterotic hybrids compared to a non-heterotic hybrid were also found using RMA. We conclude that nonadditive expression of transcript levels may contribute to heterosis for biomass yield in alfalfa.

Evidence for coadaptation in geographic populations of Drosophila bipectinata

In order to test whether there is genetic coadaptation in geographic populations of Drosophila bipectinata with respect to body size, reciprocal crosses were made among five strains derived from ecogeographically different localities in India. Wing length was used as an index of body size, and was measured in all the five strains, and their crosses in F and F2 generations. The statistical analysis of the data show that there is significant interpopulation variation in body size and in all the crosses, there is an increase in body size in F1 generation when compared with mid-parent value. Further, there is a decrease in body size in F2 generation as compared to F1 in most of the crosses with increased variability. These results provide evidence for genetic coadaptation in geographic populations of D. bipectinata.

Heterosis in fingerlings from a diallel cross between two wild strains of silver perch (Bidyanus bidyanus)

Cross-breeding was investigated as a strategy to improve performance of the Australian native freshwater fish, silver perch (Bidyanus bidyanus Mitchell) through the exploitation of heterosis during the fingerling phase of production. Growth, and mid and best parent heterosis of two wild strains, Cataract Dam (C< C,) and Murray River (M< M,) and their reciprocal crosses (C< M, and M< C,) were evaluated in cages and ponds through summer, and in tanks in a re-circulating aquaculture system during winter. The M C cross grew significantly faster than the reciprocal cross and pure strains in cages and tanks, had the lowest coefficients of variation of weight and length and was 20.9% and 16.0% heavier than midparent and best-parent average, respectively, when grown in ponds. Differences in growth between the reciprocal crosses were also evident, with C M expressing significantly less heterosis in cages and tanks. Faster growth of M C was attributed to greater appetite; however, at sizes approaching 250 g this feeding vigour diminished. The results of this study suggest that use of the M C cross has the potential to reduce the length of the culture period and lower costs of silver perch production.

Hybrid performance in taro (Colocasia esculenta) in relation to genetic dissimilarity of parents

Taro (Colocasia esculenta) breeding, as other root crop breeding, is based on the production and evaluation of large numbers of hybrids. The selection of parents is based on their phenotypic value in the absence of information concerning general combining ability (GCA), specific combining ability (SCA), or genetic distances between varieties. By combining data from heritability trials and from genetic diversity studies conducted with AFLP and SSR markers, we aimed at studying the relationship between hybrid vigour and genetic dissimilarity between parents. The traits studied included number of suckers, corm weight, corm dimensions, and dry matter content. Correlation coefficients between hybrid gain and dissimilarity values were calculated. The prediction of hybrid performance based on the mid-parent value was compared to the prediction based on a modified expression that takes into account the genetic relationships between parents. Correlations were all but one positive but not statistically significant for all traits, with the exception of the number of suckers, when using SSR markers for dissimilarity calculations. Accordingly, the genetic dissimilarities in the prediction of hybrid performances did not increase the correlation between predicted and observed hybrid vigour values. However, large differences were observed among the residual means from the regression between predicted and observed values when using AFLP or SSR markers, mainly due to the much higher polymorphism revealed by the latter. Models need to be further adapted to the type of molecular marker used, since their ability to reveal different rates of polymorphism will have a direct incidence on the calculation of genetic dissimilarities between genotypes. Nevertheless, since SSR markers are more polymorphic and more informative than AFLP markers, they should be preferentially used for these studies. Low genetic dissimilarity of parents yielded weak heterosis effects and future studies need to be conducted by using a broader genetic base. This is the first study assessing the relationship of hybrid vigour with the genetic distances between parents, conducted on a tropical root crop.

Agronomic Performance of Soybean Hybrids from Single, Three-Way, Four-Way, and Five-Way Crosses, and Backcross Populations

Male-sterility systems combined with insect-mediated cross-pollination in soybean [Glycine max (L.) Merr.] have been shown to produce large quantities of hybrid seed, which can be useful for studying heterosis and agronomic performance in different population types. The procedure was used to obtain large quantities of hybrid seed for replicated yield trials. The objective of our study was to evaluate agronomic performance of soybean single, three-way, four-way, and five-way crosses, and three backcross generations (BC1, BC2, and BC3) to estimate heterosis for yield and other agronomic traits. Parental genotypes were male-sterile, female-fertile lines, selected for excellent insect pollinator attraction, crossed to a group of male parents selected for their agronomic performance. In 2003, F1 seed of single crosses were evaluated in replicated experiments at two locations in Iowa and one location in Indiana. In 2004, three-way crosses and BC1 populations were evaluated at one location in Iowa. In 2005, hybrid seed of single, three-way, and four-way crosses, BC1, and BC2 populations of eight families were planted at one location in Iowa. In 2006, the five-way crosses and BC3 populations were planted at one location in Iowa. In all experiments, hybrids and parents were evaluated. Results showed a range in mid-parent heterosis values (MPH) for yield from −35% to +42%, and in high-parent heterosis (HPH) from −44% to +42%. For yield, backcross populations had higher heterosis estimates than the other population types. For seed protein content, mean MPH ranged from −1% to +7%, and mean HPH from −4% to +7%. For oil content, mean MPH ranged from −10% to +6%, and mean HPH from −13% to +3%. Negative heterosis values were observed, indicating that a large number of different parental combinations need to be evaluated to identify the superior heterotic combinations. These evaluations will determine the feasibility of hybrid soybean production for commercial purposes.

Genetics of intra-gene pool and inter-gene pool hybridization for seed traits in common bean ( Phaseolus vulgaris L.) germplasm from Europe

Due to adaptation to new ecological and manmade conditions, the large diversity evolved in the European common bean germplasm is of particular interest for plant breeding. The knowledge of the genetic relationships within and among races and gene pools and their performance per se will provide bean breeders with a starting point in designing crosses using contrasting and complementary parents to broaden the genetic base within the different commercial classes. A genetic study of seed size variation and protein markers in progeny derived from 16 intraracial, interracial and inter-gene pools European common bean populations was conducted. General and specific combining ability (GCA and SCA) values were significant for seed weight, indicating that both additive and nonadditive genetic effects were involved in conditioning seed weight. Interracial populations showed transgressive values due to the accumulation of large-seeded alleles. Genetic variation inside Andean germplasm, and Chile and Peru races in particular, exhibited useful genetic progress in these populations, providing lines with a large seed size, and so, an excellent market potential. The distribution of incompatibility between both gene pools (Mesoamerican and Andean) of the common bean was explored. Inter-gene pool populations provided lower means of inbred segregants than the mid-parent value. Therefore, a good option it would be select for large seed size according to a recurrent or congruity inbred-backcrossing selection programs. Analysis of allele markers frequencies in inter-gene populations showed segregation distortion with a higher than expected frequency of alleles from the Mesoamerican gene pool, many of which were fixed in the F 7 lines. The presence of a great percentage of markers that showed segregation distortion in these populations (87%) indicated that this phenomenon can be amplified by using distance related common bean genotypes. In addition, a high percentage of heterozygotes for the Phs locus (for the seed storage protein phaseolin) was found, which suggest that the Andean homozygous TT could not be expressed in Mesoamerican genetic background due to the action of some form of female specific mechanisms that affected gene exchange between parental germplasm in inter-gene pool populations. The present work provides useful information in the establishment of large seed size germplasm that could have a great deal of interest among breeders and may offer some possibilities to exploit existing variation within and between common bean races.

Heterosis in Some Crosses of Bread Wheat under Irrigation and Drought Conditions

Five bread wheat varieties with different characteristics were crossed in a half-diallel model in 2005/2006 season. The five parents and their 10 F1 hybrids were evaluated under normal and water stress conditions during 2006/2007 season, to estimate heterosis of some wheat crosses for drought tolerance and selecting the crosses which could be useful in breeding programs for drought tolerance. The results indicated that, the best crosses over their mid parents at water stress condition for days to heading was Sakha-61 x Sakha-93; for flag leaf area were Giza-168 x Gemmeiza-9 and Sakha-61 x Gemmeiza-9 and for plant height was Sakha-61 x Sakha-93. The best crosses over their mid parents at both normal and stress conditions for days to maturity was Sakha-61 x Gemmeiza-9; for flag leaf area were Giza-168 x Sakha-61, Sakha-8 x Gemmeiza-9 and Sakha-93 x Gemmeiza-9; for spikes/plant were Sakha-8 x Sakha-61, Sakha-8 x Gemmeiza-9 and Sakha-61 x Sakha-93; for kernels/spike were Giza-168 x Sakha-8, Giza-168 x Sakha-61, Giza-168 x Sakha-93 and Sakha-8 x Gemmeiza-9; for 100-kernel weight were Giza-168 x Gemmeiza-9, Sakha-61 x Sakha-93 and Sakha-93 x Gemmeiza-9 and for grain yield/plant were Giza-168 x Sakha-93, Sakha-8 x Gemmeiza-9 and Sakha-93 x Gemmeiza-9. The best crosses over their better parents at water stress condition for flag leaf area were Giza-168 x Sakha-8, Giza-168 x Gemmeiza-9 and Sakha-8 x Gemmeiza-9; for plant height were Giza-168 x Gemmeiza-9 and Sakha-8 x Sakha-61. The best crosses over better parents at both normal and stress conditions for plant height were Giza-168 x Sakha-8, Sakha-8 x Gemmeiza-9 and Sakha-93 x Gemmeiza-9; for spikes/plant were Sakha-8xSakha-61, Sakha-61 x Sakha-93 and Sakha-8 x Gemmeiza-9; forkernels/spike were Giza-168 x Sakha-61 and Giza-168 x Sakha-93 and for grain yield/plant were Sakha-61 x Sakha-93 and Sakha-93 x Gemmeiza-9. Estimation of useful heterosis over better parent for grain yield/plant proved that it never exceeds 10.16% at normal condition (cross Giza-168 x Gemmeiza-9) and 12.76% at stress condition (cross Sakha-93 x Gemmeiza-9). Useful segregate could be selected from such hybrids as hybrids wheat are still under experimentation in Egypt.

Correlation Between Parents and F 1 and Combining Ability of Parents on Seed Dormancy in indica Rice ( Oryza sativa)

Dormancy indices of hulled and dehulled seeds were investigated by using 19 cytoplasmic male sterile (CMS) lines, 9 restorer lines and their 109 F 1 hybrids of indica hybrid rice. The seeds of each F 1 and the parents were harvested on 35 days after flowering. Combining ability was analyzed in 25 combinations made by 5 CMS lines and 5 restorer lines (North Carolina II mating design). The seed dormancy index of F 1 was positively and highly significantly correlated with those of their parents and mid-parent value. Out of the 109 combinations, 82 combinations showed mid-parent heterosis, and 43 heterobeltiosis. Seed dormancy indices of F 1s and their parents declined dramatically in dehulled seeds compared with hulled seeds, indicating that the hull played an important role in seed dormancy. However, the trends were similar in hulled seeds and dehulled seeds in terms of relationships between the seed dormancy indicices in F 1 and their parents. The influence of hull on seed dormancy mainly depended on F 1 genotype, not on the hull from maternal parent. The variances of general combining ability (GCA) in female and male parents occupied 59.2% and 31.1% of total variance, respectively. The variance of specific combining ability (SCA) in combinations occupied 9.7% of total variance, indicating that gene additive effects were principal. Among the 5 CMS lines, II112A had the highest GCA effect for seed dormancy, followed by D62A. Among the 5 restorer lines, IR112 had the highest GCA effect for seed dormancy, followed by 2786. These lines are elite parental materials for breeding F 1 hybrid rice with stronger seed dormancy.

GENETIC ANALYSIS OF EARLINESS COMPONENTS IN SOME BREAD WHEAT GENOTYPES

The main objectives of this investigation were to study the inheritance of earliness traits in wheat, (Triticum aestivum L.) also to evaluate and study some early and late mature parents and their resulted crosses. This investigation included eight bread wheat parental genotypes differed in their earliness components. Half diallel cross was made between these genotypes. The eight parents and their 28 F1 crosses were planted in two sowing dates, early and normal. The collected data were analyzed using Griffing 1956 procedure, Method 2, model 1.The collected data of this experiment were days to first node emergence, days to booting, days to heading, days to anthesis, days to maturity, grain filling period and grain filling rate. Mean performance of most earliness components was low at early sowing date comparing with those at normal one for most genotypes. The parental genotypes Line 1 and Line 2 and most of their crosses gave the most desirable values in most earliness traits. The crosses Line 1 × line 2, Line 1× Sonalica, Giza 163 × Gemmeiza 9 and Sakha 61 × Giza 163 gave the lowest mean values of earliness traits in early sowing date. Meanwhile, the crosses Line 1 × Line 2, Line 2 × Sonalica and Line 1 × Line 3 gave the best values toward earliness at normal sowing date. The cross between Line 1 and Line 2 was the most superior one in its earliness traits at the two sowing dates. Genotypes mean squares for all earliness traits were highly significant at the two sowing dates. The highest and desirable values of heterosis percentage relative to the mid parent for days to first node, to booting and days to heading were obtained from cross Giza 163 × Sids 1 at the two sowing dates, for days to anthesis from cross Giza 163 × Sids 1 under early sowing date and from cross Line 1 × Giza 163 at normal sowing one and, for days to maturity from cross Line 1 × Giza 163 at the two sowing dates. The best crosses over better parent for grain filling period was cross Giza 163 × Sids 1 under the two sowing dates, for grain filling rate was crosses Sakha 61× Giza 163 and Line 2 × Line 3 at the two sowing dates, respectively. General and Specific combining ability mean squares were highly significant for all traits under study at early and normal sowing dates. The GCA/SCA ratios were more than unity for all earliness traits at both sowing dates except for grain filling rate under normal sowing date. Based on general combining ability estimates, the best combiners at early and normal sowing dates for days to first node, to booting, to heading, to anthesis and for days to maturity were Line 1 and Line 2; and for grain filling period and grain filling rate were Giza 163 and Gemmeiza 9. Based on the estimates of specific combining ability estimates, the best cross for days to first node, to booting, and days to heading was cross Giza 163 × Sids 1 at both sowing dates, for days to anthesis was Giza 163 × Sids 1 at early sowing date and Sonalika × Giza 163 at normal sowing date; for days to maturity was Line 1× Giza 163 at early sowing date and Sakha 61 × Sonalika at normal sowing date, for grain filling period were Sakha 61× Giza 163 and Sakha 61× Sonalika at both sowing dates, respectively. For grain filling rate, the best crosses were Sakha 61 × Giza 163 and Line 2 × Line 3 under the two sowing dates, respectively.

Evaluation of Soybean [Glycine max (L.) Merr.] F1 Hybrids

Heterosis is an important factor in development of hybrid cultivars. Few heterosis studies have been done in soybean [Glycine max (L.) Merr.]. This is because manual cross-pollination is difficult and time-consuming, and not economical to produce large quantities of hybrid seed. Male-sterility systems identified in soybean, combined with insect-mediated cross-pollination, have been shown to produce large quantities of hybrid seed. This procedure was used in this study to produce hybrid seed for replicated yield trials with the objectives to: 1) evaluate the agronomic performance of soybean F1 hybrids; and 2) estimate heterosis for yield and other agronomic traits of the F1 hybrids. Parental genotypes were two male-sterile, female-fertile lines with the ms3 and ms9 mutations, and a group of six high-yielding male-parent lines. The experiment was conducted in two years at several locations. In 2005, twelve F1 hybrids were evaluated along with parent lines. Mid-parent heterosis (MPH) ranged from −29% to +32%, and high-parent heterosis (HPH) from −23% to +1%. In 2006, eleven hybrids were evaluated. MPH values ranged from −53% to −21%, and HPH from −66% to −35%. Seed size and seed protein content showed HPH for some combinations. For traits related to vegetative growth, such as height and lodging, positive MPH and HPH were observed. In general, depending on the year and parent combinations, there were hybrids that performed better than the mid-parent values, suggesting that heterosis was identified in soybean. Significant differences for yield between hybrids of the ms3 and ms9 groups also were observed.

Cross-fostering experiments to compare carotenoid- and melanin-based plumage traits and long-term parental effects in post-moulted great tits

A current hot topic in the study of plumage coloration refers to whether melanin- and carotenoid-based plumage traits differ in the factors which determine ornament expression. However, approaches and results are mixed and controversial. The present study aims to apply a cross-fostering experiment in the great tit (Parus major) to compare melanin- and carotenoid-based traits of both genetic and foster parents with those of their offspring after completing post-juvenile moult. The size of the melanin-based black tie area of yearling great tits was significantly correlated to that of their genetic father. Conversely, the chroma of the carotenoid-based yellow breast colouration of yearling offspring was positively correlated to the mid-parent value of the foster parents and to the value of each foster parent separately. Our results suggest that melanin-based traits are mainly influenced by genetic factors, while carotenoid-based colouration is environmentally dependent, supporting the view that different factors determine ornament expression of the two traits. Our results also emphasize the long-term parental effect of carotenoid-based plumage colouration.

Heterosis among Hybrids Derived from Genetically Improved and Unimproved Alfalfa Germplasm

Commercially competitive forage yields, and in some cases high‐parent heterosis, were previously reported for several alfalfa (Medicago sativa L.) diallel hybrids derived from nine unimproved germplasm sources that have been important contributors to North American cultivars. This study evaluated biomass production of genetically unimproved and improved sets of nine of those hybrids, and their respective parents, over three years near Las Cruces, NM. Our objectives were to determine if the performance of unimproved ancestral populations provided useful information to construct superior hybrids using more elite descendant materials, and if such improved hybrids exhibited high‐parent heterosis. All improved hybrids performed either similar to, or superior to, five check cultivars. High‐parent heterosis was detected among the top four yielding improved hybrids. Unimproved hybrid performance and midparent value rankings provided reasonable indicators of potential hybrids that should be attempted among related elite populations. The results indicated that opportunities to exploit hybrid vigor still appear to exist among some elite alfalfa populations that possess a predominating germplasm source.

Creation of salt tolerant wheat doubled haploid lines from wheat × maize crosses

Salinity is one of the most serious agricultural problems throughout the world. The objectives of these studies were: 1. to determine if salt tolerance can be enhanced by combining characters related to salt tolerance (salt exclusion, and high growth rate and grain yield in saline conditions) and 2. to study the genetic basis of salt tolerance in doubled haploid (DH) lines developed using wheat (Triticum aestivum L.) × maize (Zea mays L.) crosses. The 47 DH lines in experiment 1 and 22 DH lines in experiment 2 and their parents were grown in a controlled environment cabinet in nutrient solution with or without addition of 150 mM NaCl. Under the saline condition, the DH lines mean was significantly higher than mid-parental values for shoot fresh weight (SFW), shoot dry weight (SDW), root fresh weight (RFW), whole plant fresh weight (PFW), plant height (PH), number of tillers per plant (TNP), number of spikelets per spike (SNS), number of grains per spike (GNS), grain yield per plant (GYP), 100-grain weight (GW) and plant biomass (PB). Some DHs showed trangressive segregation for salt tolerance as determined by greater SFW, SDW, RFW, PFW, PH, TNP, SNS, GNS, GYP, GW and PB than the better parent. The genetic variances were greater than the error variances for all measured characters except K content in saline conditions. Moderate to high heritability estimates were found for all the characters studied in saline and control conditions. Salt exclusion was an important aspect of salt tolerance as Na content of leaves was negatively correlated with all growth characters at an early stage of growth, and with grain yield and yield components. We concluded that the higher salt tolerance of some DHs was due to the combination of genetic characters responsible for salt tolerance and salt tolerance is an inherited character.

Effect of short-term pre-hatch heat shock of incubating eggs on subsequent

The aim of this study was to investigate the effect of thermal conditioning of broiler chickens during embryonic development on subsequent performance under standard rearing conditions. During incubation eggs from 32-, 45- and 56-week old Ross 308 broiler parent stock were subjected to a 2 h heat shock of 39 °C on days 14 and 15 of incubation. Eggs in the control were incubated throughout incubation at 37 °C. Chicks were feather sexed and equal numbers of each sex were placed in each pen per treatment, and reared for 42 days. Live weight, mortality and feed conversion ratio (FCR) were used as measures of performance. The final (six-week) live weights of broilers from young, mid and older parents for the treatment and control groups were 2113 ± 13.8 vs. 2159 ± 20.0, 2084 ± 29.2 vs. 2139 ± 20.0 and 2096 ± 17.6 vs. 2131 ± 24.3 g, respectively. The six-week live weight of the heat-treated group (2098 ± 12.0 g) was significantly lower than that of the control (2143 ± 12.2 g). The 1-6 week mortality figure was significantly lower in the heat-treated group of chickens from the young (83) and mid parent (77) groups compared to their controls (130 and 119), respectively. However, in the treatment group the incidence of mortality in broilers from the older parent group was significantly higher (105) than that of the control (79). The overall mortality without considering the parent age group was significantly lower in the treatment group (265) than in the control group (328). Mean FCR (g feed/g gain) of the chickens of the three parent groups was 1.79 ± 0.02 vs. 1.75 ± 0.03, 1.85 ± 0.03 vs. 1.77 ± 0.02 and 1.80 ± 0.03 vs. 1.77 ± 0.03 for the treatment vs. control groups, respectively, but the difference was significant only in the mid age parent group. These results suggest that prenatal thermal conditioning is not detrimental to broiler growth under standard rearing conditions in the absence of thermal stress. However, survival rate was improved but live weight and FCR were in some cases significantly poorer. Keywords: Heat stress, incubation, parent age, live weight, mortalitySouth African Journal of Animal Science Vol. 38 (1) 2008: pp. 58-64