Browsing by Subject "Hybrids"

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Differences in yield performance and yield stability between hybrids and inbred lines of wheat, barley, and triticale
(2015) Mühleisen, Jonathan; Reif, Jochen Christoph
Hybrids of wheat, barley, and triticale are expected to possess higher yield performance and yield stability compared to inbred lines. Assessment of yield performance as well as yield stability requires the evaluation of genotypes in plot-based yield trials across multiple environments. Evaluation of genotypes under stress conditions can be associated with increased field heterogeneity, which may result in imprecise estimates of genotypic values. The assessment of yield stability requires intensive testing in many environments, and it would be interesting to know how many test environments are required to reliably estimate yield stability. The key objectives of the present thesis were to (1) investigate optimal strategies to analyze field trials with high error variance due to spatially varying drought stress, (2) identify the required number of test environments to precisely estimate yield stability of individual barley genotypes, and (3) examine yield performance and yield stability of wheat, barley, and triticale hybrids and lines. Drought stress at two locations of a winter triticale trial caused increased field heterogeneity, resulting in lower heritabilities compared to the four non-stress locations. It was found that heritability could be increased by modeling incomplete block and row effects, by using visual scorings of drought stress intensity as covariates in an analysis of covariance, and by modeling a spatial covariance between adjacent plots. The most suitable model can be identified using the Akaike Information Criterion. In addition, it has to be ensured that the covariate is independent from genotypic effects and that it is linearly related with the response variable. Dynamic yield stability of genotypes was frequently found to depend strongly on the specific set of test environments. When the genotypes were evaluated in different environments, e.g. in the following year, the ranking in yield stability could be different. This would result in a low heritability. Theoretical assumptions and empirical studies showed that heritability can be increased when the number of test environments is increased. Five series of barley registration trials with a reduced number of 16 to 27 genotypes evaluated in 39 to 45 environments were used to investigate the relationship between magnitude of heritability of yield stability and number of test environments. Based on a cross-validation approach, it was found, that at least 40 test environments should be used to obtain a heritability of 0.5. Magnitude of heritability, however, varied strongly within and between series. Therefore, depending on the respective set of environments and genotypes, more or less test environments can be needed. Yield performance of wheat hybrids produced using chemical hybridizing agents (CHA) or cytoplasmic male sterility (CMS) was well investigated in other studies reporting around 10% midparent heterosis for grain yield. In the present thesis, CMS-based barley hybrids were compared with parental inbred lines and unrelated commercial inbred lines in breeding and registration trials. Midparent heterosis was around 10%. The comparison with commercial inbred lines in the registration trials revealed that hybrids could compete with and partially surpass outstanding inbred lines. Triticale hybrids, produced using CMS, were evaluated for grain yield at up to 20 environments with their parents and commercial inbred lines. Midparent heterosis amounted to 3% and no hybrid outyielded the best inbred line. The low yield performance of triticale hybrids is probably associated with CMS-system, since CHA-based triticale hybrids showed a midparent heterosis around 10% in early studies, which is comparable to the midparent heterosis found in wheat and barley. Yield stability of CHA-based wheat as well as CMS-based hybrids of barley and triticale was compared with yield stability of parental and commercial inbred lines on group level. The wheat and barley hybrids showed on average significantly higher dynamic yield stability compared to inbred lines, but the triticale hybrids did not. In the barley registration trials, hybrids had the highest dynamic yield stability on average. The CMS-based triticale hybrids, however, showed on average significantly lower dynamic yield stability as their female parents and the commercial inbred lines across 20 environments. In conclusion, hybrids of wheat and barley possessed an increased yield potential as well as an enhanced dynamic yield stability. In contrast, the CMS-based triticale hybrids showed only marginal yield advantages coupled with low dynamic yield stability. Further research is required to increase economical competitiveness of hybrids in all three crops, to identify and eliminate the reasons for poor performance of CMS-based triticale hybrids and to investigate the suitability of dynamic yield stability measures to identify vigorous and stress tolerant genotypes.
Phenotypic, genetic, and genomic assessment of triticale lines and hybrids
(2017) Losert, Dominik; Würschum, Tobias
Triticale (×Triticosecale Wittmack) is a small grain cereal used for livestock feeding and as renewable energy source. These diverse types of usage lead to different breeding strategies, ideally resulting in continued increase of both, grain and biomass yield. Briefly, the objectives of this thesis were to explore aspects with relevance for line and hybrid breeding in triticale by phenotypic, genetic and genomic assessment of important traits. More specifically, the objectives of this study were to (i) evaluate agronomic traits, assess trait correlations, and investigate the amount of heterosis in triticale hybrids, (ii) examine the potential of line and hybrid cultivars for production of biomass, (iii) assess the phenotypic and genotypic variability in triticale germplasm, (iv) investigate long-term phenotypic trends based on cultivars registered in the past three decades, and (v) identify QTL for agronomical relevant traits. In conclusion, hybrids of triticale possess an increased biomass yield potential compared with their mid-parent values as well as compared with commercial reference cultivars. The findings on triticale germplasm and its breeding history provide important information for breeding programs. Furthermore, based on the obtained results, genomic approaches like marker-assisted or genomic selection appear promising to assist triticale breeding in the future.
Stirring up sorghum hybrid breeding targeting West African smallholder farmers low input environments
(2019) Kante, Papa Ndiaga Moctar; Haussmann, Bettina
Food supply and income in rural areas of West Africa (WA) depend strongly on the local production, and mostly on farmers’ field production of root and tuber crops, and cereals. To feed an ever-increasing population in a context of climate-change and low-input cultural conditions, breeding for resilient crops can guarantee smallholder farmers food security and cash income for a sustainable rural development. Sorghum hybrids for WA were first explored in the early 1970s and hybrid crosses of Malian landraces with introduced Caudatum-race seed parents were evaluated in the early 80s. Although those hybrids exhibited good heterosis for grain yield, their lack of grain quality made them commercially unsustainable. Efforts by the International Crops Research Institute for the Semi-Arid Tropics (ICRISAT) and its partners resulted in the first series of Guinea-race based hybrids. The short statured hybrids were evaluated in several on-farm farmer-managed yield trials, and showed satisfactory grain yield and quality under farmers’ cultivation conditions. Although taller- relative to shorter- height sorghum can help reduce risks of panicle loss by grazing transhumant cattle, no indication on the yield potential of the tall statured hybrids is available. The advances achieved by ICRISAT and its partners in hybrid development justified establishing a long-term hybrid breeding program to provide farmers with hybrids with sufficient grain yield and good grain quality under low input conditions. However, the lack of quantitative genetic information about the genetic value of new experimental hybrids and their parents (Guinea-Caudatum to complete Guinea background, from different WA origins), or about the efficiency of alternative selection methods for targeting yield performance in the predominantly low-input and phosphorous-deficient sorghum production conditions hinders sorghum hybrid development for this region. Sorghum hybrid breeding was commercially feasible only after the identification of a heritable and stable cytoplasmic male sterility (CMS) mechanism. Hybrid breeding in WA can benefit from molecular marker, especially for the fertility restoration/sterility maintenance of the predominant A1-type of CMS. The major outcomes of this thesis are presented as follow: Mean yields of tall hybrids were 3 to 17% (ranging from 6 to 28 g m−2) higher than that of the local check across all 37 on-farm farmer-managed environments and were highest (14–47%) averaged across the seven trials with the lowest mean yields. The yields of the new set of experimental hybrids were substantially superior to farmers’ local Guinea-race varieties, with 20 to 80% higher means over all hybrids in both low phosphorus (LP) and high phosphorus (HP) environments. Average mid-parent and better-parent heterosis estimates were respectively 78 and 48% under HP, and 75 and 42% under LP. Direct selection under LP was predicted to be 20 to 60% more effective than indirect selection under HP conditions, for hybrid performance under LP. The combining ability estimates provide initial insights into the potential benefit of germplasm from further east in West and Central Africa for developing a male parental pool that is distinct and complimentary to the Malian female pool. On chromosome SBI-05, we found a major A1 CMS fertility restorer locus (Rf5) explaining 19 and 14% of the phenotypic variation in either population. Minor quantitative trait loci (QTL) were detected in these two populations on chromosomes SBI-02, SBI-03, SBI-04 and SBI-10. In the third population, we identified one major A1 CMS fertility restorer locus on chromosome SBI-02, Rf2, explaining 31% of the phenotypic variation in the F2 mapping population. Pentatricopeptide repeat genes in the Rf2 QTL region were sequenced, and we detected in Sobic.002G057050 a missense mutation in the first exon, explaining 81% of the phenotypic variation in an F2:3 validation population and clearly separating B- from R-lines. The Guinea-race hybrids’ substantial yield superiorities over well adapted local Guinea-race varieties suggests that a strategy of breeding hybrids based on Guinea-germplasm can contribute to improving the livelihood of many smallholder farmers in WA. Although the usefulness of direct selection under LP for hybrid performance in the predominantly P-limited target environments was proven, companion evaluations of hybrids under HP would be desirable to identify also new hybrids that can respond to improved fertility conditions for sustainable intensification. The developed KASP marker stands as a promising tool for routine use in WA breeding programs.