Browsing by Subject "Heterosis"
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Item Evaluation of the heterotic potential of sorghum [Sorghum bicolor (L.) Moench] adapted to the southern Africa region(Texas A&M University, 2007-04-25) Mpofu, Leo ThokozaSorghum [Sorghum bicolor (L.) Moench] production in Africa is widespread with low yields due to low inputs and the lack of sorghum hybrids. This situation has forced most of these farmers to grow maize hybrids since they are readily available in the seed market. Sorghum hybrids could be used if their potential was demonstrated. The objective of this study is to document the level of heterosis in Southern Africa sorghum germplasm. The performance of 52 F1 grain sorghum hybrids and their parental lines was evaluated in four environments. Measurements for grain yield, panicle exsertion, days to mid anthesis and plant height were analyzed to obtain estimates of high parent heterosis. High parent heterosis was observed to be 37.18% for yield, 82.77% for exsertion, -0.02% for days to mid anthesis and 23.7% for height. ICSR-939 and (87EON366*90EON328)-LD30 can be used as testers to develop more female lines for further hybrid seed production in breeding programs because they had the highest general combining ability. Protein content averaged 11.69%. ATx635 had significantly higher protein content than ATx631 (13.49% compared to 9.69%, respectively) and its hybrids had more protein than ATx631 hybrids (11.6% compared to 10.67% for ATx631). Mean heterosis for protein content was negative at -12.5%. This shows that hybrids had lower protein content than their parents since protein content is negatively correlated to grain yield (-0.35**). Starch content averaged 72.13% and ATx631 hybrids had more starch than ATx635 hybrids (73.16 compared to 72.37% respectively). Two hybrids, ATx.631/(87EON366*90EON328)-LD30 and ATx631/ ((TAM428*SV1)*CE151)-LD3 had the highest yields (5.04 t/ha and 4.93 t/ha, respectively). These hybrids also had small grains with good hardness and acceptable whiteness. They had good exsertion, flowered in good time and had acceptable plant heights. These two hybrids were compared to regional check varieties Macia and Tegemeo for all traits and they were either superior or within an acceptable range. These two hybrids are therefore recommended for release in the region. There is need therefore to start working on the various components of seed systems in the region so that seed of these two hybrids is made available to farmers who need the seed.Item General and specific combining abilities in upland cotton (Gossypium hirsutum L) intraspecific crosses utilizing G. harknessii Brandegee male sterile cytoplasm(Texas Tech University, 1984-12) Sheetz, Richard HallRecent technological advances have created renewed interest in the development and production of hybrid cotton seed. Major technical obstacles which have been cited are: 1) complete male fertility restoration in the F1s, 2) adequate pollen transfer between parental rows in commercial production fields, and 3) identification of superior parental combinations. The present study was conducted to determine the levels of heterosis and the relative magnitudes of general and specific combining abilities in crosses between cytoplasmic male sterile lines derived from relatively modern cotton cultivars, and male lines representing the major sources of fertility restorers now publicly available to cotton breeders. Incomplete sets of crosses involving 3 male and 13 female lines were grown in replicated trials at three locations. Estimates of heterosis, analyses of variance and combining ability estimates are presented for lint yield, and for fiber length, strength and fineness. Positive estimates of heterosis for lint yield ranged from 100 to 133% over high parents. Maximum observed heterotic responses over high parent were 109% for fiber length, 104% for fiber fineness and 106% for fiber strength. Statistically significant male x female interactions were observed for yield, fiber length and fiber fineness indicating the presence of significant non-additive genetic effects within the group of crosses studied for these traits. Observed male x female interactions for fiber strength, however, were non-significant indicating a predominantly additive genetic component. The consistent non-significance in lint yield for the estimated location x males x females interactions is interpreted as an indication of potentially increased environmental stability in some F, hybrids. Combining ability estimates for lint yield tend to support the conclusions that within the group of hybrids studied, specific combining ability accounted for a relatively large proportion of the differences between hybrid yields. Previously reported levels of heterosis for the traits studied are apparently repeatable in crosses involving modern Upland cotton cultivars.Item Heterosis and heterosis retention for reproductive and maternal traits in Brahman - British crossbred cows(Texas A&M University, 2005-02-17) Key, Kelli LorenReproductive, maternal, and weight traits were analyzed for Angus (A), Brahman (B), and Hereford (H) straightbred cows; F1 and F2 BA and BH cows; and 3/8 B 5/8 A first (Bn) and second (Bn2) generation cows in Central Texas. Heterosis was estimated for calf crop born (CCB), calf crop weaned (CCW), and cow weight at palpation (PW) by linear contrasts within cow breed groups. F1 BA cows expressed heterosis (P<0.01) for CCB (0.10) and CCW (0.11), while F2 BA cows expressed negative heterosis (P<0.10) for CCB (-0.06) and CCW (-0.07). F1 BH cows expressed heterosis (P<0.001) for CCB (0.15) and CCW (0.16), and F2 BH cows retained F1 heterosis (P<0.001) for CCB (0.13) and CCW (0.15). Bn2 cows expressed heterosis (P<0.01) for CCB (0.14), but Bn cows did not express heterosis (P>0.10) for CCB or CCW. Only the F1 BA (22.9 kg) and F2 BH (42.1 kg) groups expressed heterosis (P<0.10) for PW. Bn2 cows (-65.7 kg) expressed negative heterosis (P<0.01) for PW. Heterosis for calf survival (CS), birth weight (BW), and weaning weight (WW) was estimated by linear contrasts within calf breed groups for B- and H-influenced calves. F1 BH (0.11) and F2 BH (0.14) calves expressed heterosis (P<0.01) for CS. None of the groups expressed heterosis (P>0.10) for BW, but B-sired F1 BH calves were 5.5 kg heavier (P<0.01) than H-sired F1 calves at birth. F1 BH (22.4 kg) and F2 BH (26.2 kg) calves expressed heterosis (P<0.001) for WW, and H-sired F1 BH calves were 20.7 kg heavier (P<0.10) than B-sired F1 calves at weaning.Item Heterosis and Heterosis Retention for Reproductive and Maternal Traits in Brahman x Hereford Crossbred Cows(2012-02-14) Boenig, LydiaCalf crop born, calf crop weaned, calf birth weight, calf weaning weight, and cow weight at weaning were evaluated from 1996 to 2009 in Brahman (B) and Hereford (H) straightbred and crossbred cows (n = 1,515). The objective of these analyses was to estimate heterosis for F1 and F2 females for these reproductive and maternal traits. Breed groups included B, H, F1 Hereford-sired (HB) and Brahman-sired (BH) cows (n = 114 purebreds, 55 F1, 52 F2). Second generation breed groups included cows sired by HB and out of HB dams (F2HB) and BH dams (HBxBH); and cows sired by BH and out of HB dams (BHxHB) and BH dams (F2BH). Least squares means were calculated for calf crop born, calf crop weaned, and calf birth and weaning weights, using numerous different models, where the trait was the dependent variable. Previous research and these preliminary analyses showed that the effects of year and cow age are real as is their interaction each other and with breed type. In each attempted model designed to remove these effects, different breed groups received excessive adjustments, rendering the resultant heterosis estimates inappropriate. To more clearly assess differences, presentation and visual evaluation of unadjusted means were conducted. The model for mature cow weight (cows at 6 years of age) included breed group as fixed effects and cow within breed group and year as random effects. F2 cows appeared to retain approximately 39% of F1 heterosis for calf crop born and approximately 50% for calf crop weaned. HB x BH cows delivered the lightest calves at 33.9 (4.74) kg and F2BH had the heaviest calves at birth at 36.6 (5.37) kg. BH cows weaned the heaviest calves at 240.9 (38.1) kg and F2BH cows weaned the lightest calves at 208.4 (31.9) kg. Sire breed of calf and age of cow appear to be important factors regarding weight traits. Retained heterosis for cow weight at weaning was higher than expected at 73%. Sire breed group differences (HB vs. BH) for these traits in F2 cows may merit further investigation.Item Heterosis and Heterosis Retention for Reproductive and Maternal Traits in Nellore-Angus Crossbred Cows(2013-07-08) Obeidat, Mohammad Diya Talal HamedCalving rate, weaning rate, birth weight, weaning weight, and ADG from 1997 to 2011 were investigated in Angus, Nellore, F_(1) Nellore-Angus, first generation 3/8 Nellore 5/8 Angus produced as following: (1/2 Nellore 1/2 Angus sires and 3/4 Angus ? Nellore dams, 3/4 Angus 1/4 Nellore sires and 1/2 Angus 1/2 Nellore dams, and ? Nellore 1/4 Angus sires and Angus dams), and second generation 3/8 Nellore 5/8 Angus cows. The objectives were to estimate heterosis in Nellore-Angus crosses for cow reproductive traits and maternal effects on traits of their calves. The F_(1) cows expressed 0.20 ? 0.02 heterosis for calving rate, while both first and second generation 3/8 Nellore 5/8 Angus expressed 0.13 ? 0.02. the first generation 3/8 Nellore 5/8 Angus produced out of 3/4 Angus 1/4 Nellore sires and 1/2 Nellore 1/2 Angus dams expressed 0.14 ? 0.03 heterosis for calving rate. The F1 Nellore-Angus expressed 0.23 ? 0.03 heterosis for weaning rate and the 3/8 Nellore 5/8 Angus produced out of 3/4 Angus 1/4 Nellore sires ? 1/2 Nellore 1/2 Angus dams and the second generation 3/8 Nellore 5/8 Angus expressed 0.14 ? 0.07 and 0.15 ? 0.05, respectively. No heterosis was expressed for birth weight in any breedtype group. Multiple attempts to analyze weaning weight and ADG and estimate heterosis resulted in excessive adjustments to least squares means. Young and oldest cows weaned lighter calves than others. F_(1) cows weaned heavier calves at most ages. Nellore-sired F_(1) calves were heavier at weaning than the reciprocal cross. Calves out of cows of intermediate ages had larger preweaning ADG than calves born to 2- and 3-yr-old and to aged cows. Generally, calves out of F_(1) Nellore-Angus cows had larger ADG than those out of cows of other breedtypes. Nellore-sired F_(1) heifers had lower ADG than Angus-sired F_(1) heifers. In general, bull calves had larger ADG than heifers. Non-F_(1) crossbred cows expressed slightly larger heterosis than what would be expected by the dominance model. Heterosis expressed by second generation 3/8 Nellore 5/8 Angus for calving and weaning rate did not appear to differ from the first generation.Item Heterosis, backcross analysis, and breeding potential of one exotic cultivar for grain yield in sorghum (Sorghum bicolor (L.) Moench)(Texas Tech University, 2002-05) Teme, NiabaLian Tang Ai, a Chinese landrace cultivar donor parent and Tx2783, an elite US restorer parental line and, the recurrent parent, were used to develop BC2 derived lines which were evaluated for grain yield potential. The hypothesis of this research was that some of the BC2 derived lines themselves could have higher grain yield potential in BC2F2 and in hybrid combination with ATx623, respectively, than Tx2783 and the hybrid of ATx623xRTx2783. Grain yield of the derived lines and their hybrids grain yield was normally distributed. Five (3.7%) and 46(32.4%) derived lines (P=0.05) produced significantly higher grain yield than the recurrent parent in limited and fully irrigated combined analysis trials, respectively. In the combined analysis of fully irrigated trials, 132(89.2%) hybrids produced significantly higher grain yield than the recurrent parent hybrid. In the combined full irrigation trials, the average heterosis values was 50% over the midparent, heterosis of the best hybrid over the best parent was 60.2%, the best parent over the mid-parent was 78.0% and the worst hybrid had 23.3% over the mid-parent. Highest heterosis of the best hybrid over the best parent was 90.5% at Halfway 2001. Under full irrigation trials, five, four and nine derived lines, respectively, from Lubbock 2000, 2001 and Halfway 2001, were among the top 10% highest grain producing derived lines while four hybrids from Lubbock 2000, 2001 and Halfway 2001 were consistent in producing high grain yield across environments. Across irrigation levels, four derived lines and two hybrids produced consistently and significantly higher grain yield than the recurrent parent and its hybrid. Three high grain yielding derived lines produced high grain yield in hybrids and were significantly superior to the recurrent parent and its hybrids. Five hybrids from the combined limited trials and 7 hybrids from Lubbock 200l fully irrigated trial produced significantly higher grain yield than the standard commercial hybrid check. When using fully irrigated combined analysis, however, no hybrid produced significantly more grain than the standard commercial hybrid. Other derived lines and hybrids had erratic grain yield distribution. Higher grain yield was expressed at Halfway than at Lubbock. There was a significant low and negative correlation between grain yield and maturity in general. Grain yield of derived lines did not accurately predict well their respective hybrid grain yield in individual environments (trials). However, across environments in full irrigation combined trials, grain yield of derived lines was positively and highly correlated to grain yield of hybrids (r=0.419). Introgression of useful yield genes from Lian Tang Ai into Tx2783 was a success. However, genotype by environment interaction made the selection for high yielding and widely adapted derived lines for hybrid productivity a difficult task.Item Molecular Basis of Heterosis in Maize: Genetic Correlation and 3-Dimensional Network Between Gene Expression and Grain Yield Trait Heterosis(2012-02-14) Zhi, HuiHeterosis, or hybrid vigor, refers to the superiority of F?hybrid performance over the mean of its parents (mid-parent heterosis) theoretically, or the performance of better parents. It has been discovered in many species of plants and animals as well as in humans, and played an important role in enhanced agricultural production, especially in maize, rice and sorghum although the mechanism have not been elucidated. We studied the molecular basis of heterosis with a combined genomics and systems biology approach using model organism maize. We profiled the expression of 39 genes that were most differentially expressed (DG) between the mid-parents and their F1 hybrid (Mo17 x B73) in the 13V-satged, developed whole ear shoots of 13 inbred lines and their 22 F1 hybrids grown in the field trails and phenotyped their 13 traits significant for grain yield. The results showed that gene expression varies significantly among inbreds, among hybrids and in heterosis. The gene clustering heat map and gene action networks in inbreds and hybrids were constructed respectively based on their gene expression profile. According to these pattern analyses, we find dramatically difference between inbreds and their hybrids, although the differential expression varies across different hybrids. Our results also suggest that gene networks are altered from inbreds to hybrids, including their gene contents and wire structures. Last but not least, we have determined the genetic variation correlations between the gene expression and trait performance and constructed the gene networks for the development of 12 of the 13 traits that varied significantly among genotypes. This has led to identification of genes significantly contributing to the performances of the traits, with 1 ? 16 genes per trait. These results have indicated that heterosis results not only from altered expression level of corresponding genes between inbreds and their hybrids, importantly, also from the altered gene action networks and expression patterns. These alternations could be derived from gene actions in a manner of additivity, dominance, over dominance, pseudo-overdominance, epistasis and/or their combinations. Therefore, our findings provide a better understanding of the underlying molecular basis of heterosis. The genes identified for the traits will provide tools for advanced studies of the trait heterosis and could be used as tools for their heterosis breeding in maize. The strategy developed in this study will provide an effective tool for studies of other complicated, quantitative traits in maize and other species.Item Phenotypic and genotypic characterization of white maize inbreds, hybrids and synthetics under stress and non-stress environments(Texas A&M University, 2006-10-30) Makumbi, DanMaize is susceptible to biotic and abiotic stresses. The most important abiotic stresses in Africa are drought and low soil fertility. Aflatoxin contamination is a potential problem in areas facing drought and low soil fertility. Three studies were conducted to evaluate maize germplasm for tolerance to stress. In the first study, fifteen maize inbred lines crossed in a diallel were evaluated under drought, low N stress, and well-watered conditions at six locations in three countries to estimate general (GCA) and specific combining ability (SCA), investigate genotype x environment interaction, and estimate genetic diversity and its relationship with grain yield and heterosis. GCA effects were not significant for grain yield across environments. Lines with good GCA effect for grain yield were P501 and CML258 across stresses. Lines CML339, CML341, and SPLC7-F had good GCA effects for anthesis silking interval across stresses. Additive genetic effects were more important for grain yield under drought and well-watered conditions. Heterosis estimates were highest in stress environments. Clustering based on genetic distance calculated using marker data from AFLP, RFLP, and SSRs grouped lines according to origin. Genetic distance was positively correlated with grain yield and specific combining ability. In the second study, synthetic hybrids were evaluated at seven locations in three countries to estimate GCA and SCA effects under low N stress and optimal conditions and investigate genotype x environment interaction. GCA effects were significant for all traits across low N stress and optimal conditions. The highest yielding synthetic hybrids involved synthetics developed from stress tolerant lines. Synthetics 99SADVIA-# and SYNA00F2 had good GCA for grain yield across low N stress conditions. Heterosis was highly correlated with grain yield. Optimal environments explained more variation than stress environments. The third study evaluated the agronomic performance and aflatoxin accumulation of single and three-way cross white maize hybrids at five locations in Texas. Inbreds CML343, Tx601W, and Tx110 showed positive GCA effects for grain yield. Significant GCA effects for reduced aflatoxin concentration were observed in lines CML269, CML270, and CML78 across locations. Differences in performance between single and three-way crosses hybrids were dependent mostly on the inbred lines.Item Roles for polyploidy, circadian rhythms, and stress responses in hybrid vigor(2014-05) Miller, Marisa Elena; Chen, Z. JeffreyHybrid plants and animals, like corn and the domestic dog, grow larger and more vigorously than their parents, a common phenomenon known as hybrid vigor or heterosis. In hybrids between Arabidopsis ecotypes or species (in allotetraploids), altered expression of circadian clock genes leads to increased starch and chlorophyll content and greater biomass. In plants and animals, circadian clock regulation plays a key role in optimizing metabolic pathways, increasing fitness, and controlling responses to biotic and abiotic stresses. In the allotetraploids, the increased level of heterosis is likely caused by interspecific hybridization as well as genome doubling. However, it is unknown how genome dosage and allelic effects influence heterosis, and whether additional clock output traits, such as stress responses, are altered in hybrids. In three related projects, the effects of genomic hybridization (including parent-of-origin effects) and genome dosage on heterosis were elucidated. In my first project, I found that although ploidy influenced many traits, including seed and cell size, biomass and circadian clock gene expression were most strongly influenced by hybridization. Additionally, parent-of-origin effects between reciprocal hybrids were frequently observed for many traits. In my second project, I described a unique role for RNA-directed DNA methylation (mainly CHH methylation) in mediating the parent-of-origin effect on expression of the circadian clock gene CCA1 in reciprocal hybrids. Altered CCA1 expression peaks were associated with heterosis of biomass accumulation in the reciprocal hybrids. Lastly, I used transcriptome sequencing in hybrids at different times of day to examine changes in downstream clock-regulated pathways. In the hybrids, many genes in photosynthetic pathways were upregulated, while many genes involved in biotic and abiotic stresses were repressed during the morning and afternoon, respectively. Additionally, natural variation between parents in stress-responsive gene expression was found to be crucial for producing vigorous hybrids. These conceptual advances increase the mechanistic understanding of heterosis, and may guide selection of parents for making better hybrids.Item The heterotic effects of dwarf A lines in hybrid sudangrass(Texas Tech University, 1967-05) Clement, Edward LeonThe purpose of this study was to compare the various heights of the male-sterile Rhodesian sudangrass lines, with their respective number of genes for dvrarfness, from the following points of view. 1. To determine the effects of the various dvrarf A lines on the forage yield of their respective hybrids. 2. To determine the effects of the various dwarf A lines on the leaf-stem ratio of their respective hybrids. 3. To determine the effects of the various dwarf A lines on the percent protein content of their respective hybrids. 4. To compare the performance of the hybrids, A lines, and the H line (Tift). 5. To compare the performance of the Lubbock planting and the Beaumont planting in order to determine the climatic effects on the hybrids, A lines, and the R line (Tift).Item The link between small RNA-directed gene regulation and heterosis in Arabidopsis allotetraploids(2016-12) Johnson, Thomas MacElliot; Chen, Z. Jeffrey; Qiao, HongHybridization between different species of plants and animals commonly leads to superior levels of biomass, growth rate and stress resistance, because of a phenomenon known as hybrid vigor or heterosis. Despite the evolutionary significance and agricultural importance of this vigor, a true understanding of the genetic and molecular parameters remains unknown. Genome-wide changes in gene expression are well documented in hybrids, and could be under the control of a multitude of epigenetic factors. To examine the relative impact that small RNA (sRNA) directed cleavage of target transcripts has on Arabidopsis hybrid vigor, transcriptome, degradome and small RNA-sequence libraries were produced for five Arabidopsis lines: A. thaliana autotetraploids, A. arenosa, F1 resynthesized allotetraploids, F8 allotetraploids, and the natural allotetraploid A. suecica. Together these RNA libraries allowed for degradome analysis to be performed. This genome-wide approach allows for direct detection of sRNA-directed cleavage of target mRNAs without the need for prior predictions or sequence knowledge. The analysis output provides evidence of sRNA-target pairs that are biologically functioning in vivo at a particular spatial or temporal capacity. When transcriptome or protein expression data is incorporated with degradome analysis, an overall model of expression and regulation patterns can be devised. During this investigation I detected novel and significantly differentiated sRNA-target interactions between the allotetraploids and their parents. Allelic expression frequencies within the allotetraploids allowed for the identification of homoeolog cleavage silencing modifications, along with the classification of cleavage events as being additive, exhibiting parental level dominance, or manifesting transgressive up- or down-regulation. I found that there is a significant amount of homoeolog expression bias that is being influenced by sRNA-mediated cleavage. Bias cleavage was found to not only preferentially eliminate homoeologous transcripts, but also function a buffering action to control threshold concentrations of target mRNA productions. Results from this investigation indicates that sRNA-directed cleavage is contributing to the stimulation of heterosis within Arabidopsis allotetraploids. Integration of what we learned about this sRNA influence with previous reports on circadian rhythm, methylation and histone modification will better our knowledge of the mechanisms driving heterosis.