In sorghum, a predominantly self-pollinated crop, hybrid seed production relies exclusively on the cytoplasmic-genetic male sterility system. The system of hybrid development has caused sorghum breeding programs to develop two breeding groups: a male-parent group (R-line/ fertility-restorer) and a female-parent group (an A/B line, lacking the fertility-restoring gene of the A1 male-sterility system). These have served as heterotic groups in the absence of more information with reference to genetic diversity. Efforts to determine heterotic groups in sorghum have not been successful in clearly delineating any patterns. However, in a recent molecular marker-based study of 50 elite sorghum parental lines, groups similar to the working group system were observed, as was an absence of a consistent delineation, characteristic of heterotic groups, between the A/B- and R-lines. This study was conducted with the objective of evaluating the groups observed and assessing their potential as heterotic groups. Two parental lines from each of the five groups, and two lines from those not conforming to any group, were chosen and crossed in a half-diallel. The twelve parents, sixty-six diallel hybrids and three commercial hybrid checks were evaluated for grain yield and other agronomic traits in five environments' College Station, TX in 2003 and 2004, Weslaco, TX in 2003, and Halfway, TX in 2003 and 2004. Within-group crosses exhibited inferior heterotic expression, for grain yield and other traits, in comparison with across-group crosses. Furthermore, genetic similarity estimates for parental line pairs obtained from the molecular study were significantly correlated with specific combining ability and heterosis for yield of the corresponding hybrid combinations, revealing a pattern of correspondence between molecular data and heterosis. Hybrids made among R-lines and among B-lines were significantly lower in yield compared to AxR hybrids, likely to be a result of decades of breeding efforts to develop inbreds within the mutually isolated groups, rather than a consequence of phylogenetic divergence. An examination of the heterotic effects manifested in hybrid combinations reveals a pattern of interactions broadly in agreement with the molecular data, but differential responses between individual members of the proposed groups make it difficult to define distinct heterotic groups.

In sorghum, a predominantly self-pollinated crop, hybrid seed production relies exclusively on the cytoplasmic-genetic male sterility system. The system of hybrid development has caused sorghum breeding programs to develop two breeding groups: a male-parent group (R-line/ fertility-restorer) and a female-parent group (an A/B line, lacking the fertility-restoring gene of the A1 male-sterility system). These have served as heterotic groups in the absence of more information with reference to genetic diversity. Efforts to determine heterotic groups in sorghum have not been successful in clearly delineating any patterns. However, in a recent molecular marker-based study of 50 elite sorghum parental lines, groups similar to the working group system were observed, as was an absence of a consistent delineation, characteristic of heterotic groups, between the A/B- and R-lines. This study was conducted with the objective of evaluating the groups observed and assessing their potential as heterotic groups. Two parental lines from each of the five groups, and two lines from those not conforming to any group, were chosen and crossed in a half-diallel. The twelve parents, sixty-six diallel hybrids and three commercial hybrid checks were evaluated for grain yield and other agronomic traits in five environments' College Station, TX in 2003 and 2004, Weslaco, TX in 2003, and Halfway, TX in 2003 and 2004. Within-group crosses exhibited inferior heterotic expression, for grain yield and other traits, in comparison with across-group crosses. Furthermore, genetic similarity estimates for parental line pairs obtained from the molecular study were significantly correlated with specific combining ability and heterosis for yield of the corresponding hybrid combinations, revealing a pattern of correspondence between molecular data and heterosis. Hybrids made among R-lines and among B-lines were significantly lower in yield compared to AxR hybrids, likely to be a result of decades of breeding efforts to develop inbreds within the mutually isolated groups, rather than a consequence of phylogenetic divergence. An examination of the heterotic effects manifested in hybrid combinations reveals a pattern of interactions broadly in agreement with the molecular data, but differential responses between individual members of the proposed groups make it difficult to define distinct heterotic groups.

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Thesis (M.Sc.) -- University of Adelaide, Depart of Botany, 1977.

Thesis (Ph. D.)--University of Wisconsin, 1965. / Typescript. Vita. eContent provider-neutral record in process. Description based on print version record. Includes bibliography.

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Calf 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.

Hybrid development has become an essential component in many major crop species due to the exploitation of heterosis. However, parental combinations that exhibit high heterotic gains can be difficult to obtain if no prior genetic architecture is known. The current research focuses on heterotic gene pool development using genetic distance and multivariate cluster analysis. Seventy-nine inbred accessions were grouped using three different methods including; 1) phenotypic classification based on 20 qualitative and quantitative traits; 2) Sequence related amplified polymorphisms (SRAP) using 29 forward and reverse primer combinations; 3) genotyping-by-sequencing (GBS) using 80,005 single nucleotide polymorphisms. Both genotypic methods (SRAP and GBS) were compared to each other, and hierarchical clustering produced similar results with 68% homology between the two methods. Heterotic cluster accuracy was investigated between the two genotypic methods through hybrid performance. Forty-four hybrid combinations along with parental cultivars were grown at one location in Winnipeg, MB with three replicates in a randomized complete block design. Hybrid yield and heterosis were regressed against the genetic distance from each genotypic method. GBS was a better predictor of hybrids with high yield (R = 0.47, p <.01); however, SRAP was a better predictor for mid-parent and high-parent heterosis at R = 0.53 and R = 0.61, respectively. This research provides experimental evidence that SRAP and GBS heterotic pool definitions have utility in the prediction of high heterotic parental combinations / May 2016

Sorghum [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.

Reproductive, 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.