Browsing by Subject "Hybrid breeding"

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Effective pollen-fertility restoration is the basis of hybrid rye production and ergot mitigation
(2022) Miedaner, Thomas; Korzun, Viktor; Wilde, Peer
Hybrid rye breeding leads to considerably higher grain yield and a higher revenue to the farmer. The basis of hybrid seed production is the CMS-inducing Pampa (P) cytoplasm derived from an Argentinean landrace and restorer-to-fertility (Rf) genes. European sources show an oligogenic inheritance, with major and minor Rf genes, and mostly result in low-to-moderate pollen-fertility levels. This results in higher susceptibility to ergot (Claviceps purpurea) because rye pollen and ergot spores are in strong competition for the unfertilized stigma. Rf genes from non-adapted Iranian primitive rye and old Argentinean cultivars proved to be most effective. The major Rf gene in these sources was localized on chromosome 4RL, which is also a hotspot of restoration in other Triticeae. Marker-based introgression into elite rye materials led to a yield penalty and taller progenies. The Rfp1 gene of IRAN IX was fine-mapped, and two linked genes of equal effects were detected. Commercial hybrids with this gene showed a similar low ergot infection when compared with population cultivars. The task of the future is to co-adapt these exotic Rfp genes to European elite gene pools by genomic-assisted breeding.
Optimum strategies to implement genomic selection in hybrid breeding
(2022) Marulanda Martinez, Jose Joaquin; Melchinger, Albrecht E.
To satisfy the rising demand for more agricultural production, a boost in the annual expected selection gain (ΔGa) of traits such as grain yield and especially yield stability has to be rapidly achieved. Hybrid breeding has contributed to a notable increment in performance for numerous allogamous species and has been proposed as a way to match the increased demand for autogamous cereals such as rice, wheat, and barley. An additional tool to increase the rate of annual selection gain is genomic selection (GS), a method to assess the merit of an individual by simultaneously accounting for the effects associated with hundreds to thousands of DNA markers. Successful integration of GS and hybrid breeding should go beyond the study of GS prediction accuracy and focus on the design of breeding strategies, for which GS maximizes ΔGa and optimizes the allocation of resources. The main goal of this thesis was to examine strategies for optimum implementation of GS in hybrid breeding with emphasis on estimation set design to perform GS within biparental populations and on the optimization of hybrid breeding strategies through model calculations. One strategy, GSrapid, with moderate nursery selection, one stage of GS, and one stage of phenotypic selection, reached the greatest ΔGa for single trait selection regardless of the budget, costs, variance components, and accuracy of genomic prediction. GSrapid was also the most efficient strategy for the simultaneous improvement of two traits regardless of the correlation between traits, selection index chosen, and economic weights assigned to each trait. The success of this strategy relies principally on the reduction of breeding cycle length and marginally on the increase in selection intensity. Moving from traditional breeding strategies based on phenotypic selection to strategies using GS for single trait improvement in hybrid breeding could lead not only to increments in ΔGa but also to large savings in the budget. The implementation of nursery selection in breeding strategies boosted the importance of efficient systems for inbred generation accompanied by improvements in the methods of hybrid seed production for experimental tests. When it comes to multiple trait improvement, the choice between optimum and base selection indices had minor impact on the net merit. However, considerable differences for ΔGa of single traits were observed when applying optimum or base indices if the variance components of the traits to be improved differed. The role of the economic weights assigned to each trait was determinant and small variations in the weights led to a remarkable genetic loss in one of the traits. The optimum design of estimation sets to perform GS within biparental populations should be based on phenotypic data, rather than molecular marker data. This finding poses major challenges for GS-based strategies aiming to select the best new inbreds within second cycle breeding populations, as breeding cycle length might not be reduced. Then, the ES design to optimize GS within biparental populations would have a defined application on the exploitation of within-family variation by increasing selection intensity in biparental populations with the largest potential of producing high-performing inbreds. Based on the results of this thesis, future challenges for the optimum implementation of GS in hybrid breeding strategies include (i) reductions in breeding cycle length and increments in selection intensity by refinements of DH technology or implementation of speed breeding, (ii) improvements in the methods for hybrid seed production, facilitating the reallocation of resources to the production of more candidates tested during the breeding cycle, and (iii) precise estimation of economic weights, reflecting the importance of the traits for breeding programs and farmers, and maximizing long term ΔGa for the most relevant traits.
Phenotypic and genotypic assessment of traits with relevance for hybrid breeding in European winter wheat
(2015) Langer, Simon Martin; Würschum, Tobias
Hybrid breeding in wheat has recently received increased interest, especially in Europe, and large public and private projects investigating hybrid wheat breeding have been launched. Hybrid breeding has been a great success story for allogamous crops and is seen as a promising approach to increase the yield potential in wheat. Wheat covers more of the world’s surface than any other food crop and is the second main staple crop for human consumption. It can be produced under widely varying conditions and is grown all around the globe, yet, yield gain has declined and is lagging behind the needs of the constantly growing human population. Future challenges in wheat breeding such as the establishment of hybrid varieties and the adaptation of breeding germplasm to increasing stresses caused by climatic changes also in Europe require knowledge-based improvements of relevant traits and phenotyping approaches suited for applied high-throughput plant breeding. A major limitation for the establishment and the production of hybrid wheat is the lack of a cost-efficient hybrid seed production system. This requires the generation of parental ideotypes which maximize the cross-fertilization capability. Male parents should have an extended time of flowering, extrude anthers and widely shed large amounts of viable pollen. Females need increased receptivity for male pollen by opening the glumes and extruding stigmatic hair. Furthermore, male plants should be taller than females and a synchronized timing of flowering between the two parents is also of utmost importance. Employing a set of European elite winter wheat lines, we developed and evaluated phenotyping methods for important floral and flowering traits with relevance for improved cross-pollination (Publication I). We observed high heritabilities for important traits such as ‘pollen mass’ (h2=0.72) and ‘anther extrusion’ (h2=0.91). In addition, genotypic variances were significant which warrants further breeding success. Positive correlations were found among important flowering and floral characteristics which enables the improvement of outcrossing by indirect selection. ‘Pollen mass’ for example, was associated with ‘anther extrusion’, ‘anther length’ and ‘plant height’. Our findings suggest the utility of the developed phenotyping approaches for applied plant breeding and the potential of the traits to assist in the design of the male ideotype for increased cross-fertilization. We investigated the genetic architecture of flowering time and plant height (Publication II and III). A panel of 410 European winter wheat varieties was genotyped by a genotyping-by-sequencing approach and in addition, analyzed for the effects of specific candidate genes. The major factor affecting flowering time was the photoperiod regulator Ppd-D1 (58.2% of explained genotypic variance) followed by Ppd-B1 copy number variation (3.2%). For plant height, the two candidate loci Rht-D1 (37.0%) and Rht-B1 (14.0%) had the largest effects on the trait but contrary to reports in the literature did not contribute to flowering time control. In addition, we identified several small effect QTL and epistatic QTL responsible for fine-adjustments of these two traits. Population structure and genetic relatedness in European elite wheat lines was assessed using different types of markers (Publication IV). Results for relatedness differed for the marker types but consistently showed the absence of a major population structure. Regarding the large wheat genome our results revealed that a high number of markers is necessary as there are regions with only low coverage. Concordantly, we were not able to identify the major flowering locus Ppd-D1 without targeted candidate gene analysis. Observations on the findings on population structure could be confirmed in Publication II and III and in addition, the geographical distribution of important flowering time and plant height genes displayed the historical development of wheat breeding in Europe. This information on genetic relatedness among lines can also be employed to assist the establishment of hybrid wheat.
Strategies for sustainable pearl millet hybrid breeding in West Africa
(2020) Sattler, Felix; Haussmann, Bettina
Pearl millet [Pennisetum glaucum (L.) R. Br.] is grown by >90 million subsistence farmers, mostly in the drylands of Sub-Saharan Africa and India for human consumption and provides additionally fodder and building material. It is commonly grown in regions with 300 – 500 mm of precipitation, low soil phosphorus levels, and temperatures of >42°C), like its center of origin in West Africa (WA). Pearl millet is a highly heterozygous, diploid (2n = 2x = 14) C4 plant species with outcrossing rates of >70%. Yield levels increased largely in India and the US, while they almost stagnated in WA. Challenging, highly variable environments and a weak seed sector are largely contributing to these differences. To suggest a way forward this thesis was meant to guide heterotic group development for sustainable WA pearl millet breeding. The specific objectives were to (I) facilitate efficient use of pearl millet gene bank accessions, (II) identify diversity patterns, (III) validate the yield superiority and stability of pearl millet population hybrids over OPVs, (IV) derive a more comprehensive picture about combining ability patterns, and (V) develop a unified strategy for heterotic grouping and sustainable hybrid breeding. A total of 81 accessions acquired from the pearl millet reference collection was evaluated for resistance to Striga hermonthica (Del.) Benth. in one artificially infested field in Niger. A subset of 74 accessions was characterized in 2009 in multi-environment trials (MET) under low-input and fertilized conditions. The general superiority of local check varieties compared to the genebank accessions highlighted the importance of local adaptation, possibly lost during the ex situ conservation and regeneration. Nevertheless, the development and preservation of germplasm collections are important to maintain the rich genetic diversity. The MET identified several accessions as sources for specific traits of interest and revealed an immense diversity but also strong admixture. This admixture underlines the need to develop heterotic groups. Therefore, 17 WA open-pollinated varieties (OPVs) were crossed in a diallel mating design and tested together with their offspring in nine environments over two years in Niger and Senegal. Results from these MET verified large panmictic better parent heterosis (PBPH) effects with an average of 18% (1–47%) for panicle yield. A large G × E interaction variance was confirmed and it was not possible to define repeatable mega-environments. Importantly, yield stability was more pronounced in the population hybrids compared to their parental OPVs. Furthermore, a superior combining ability among selected OPVs from Niger vs. Senegal was revealed and the evaluated OPVs were clearly grouped by origin based on genetic information. Nevertheless, there was no significant relationship between genetic distance among OPVs and PBPH. These and earlier studies showed a large diversity, sufficiently large heterosis effects and high yield stability in experimental pearl millet population and topcross hybrids, offering a great opportunity for a regionally coordinated hybrid breeding approach. Therefore, we suggested a unified strategy with a continuous output of different hybrid types, specifically tailored to WA. First, existing diversity and combining ability pattern information on western WA and eastern WA cultivars forming loose groups that combine well with each other should be used. Selected genotypes with high general combining ability (GCA) and per se performance from eastern and western WA, respectively, are promising founder populations. Initiating a reciprocal recurrent selection (RRS) program, possibly supported by modern breeding tools, will diverge the two groups further, while improving the inter-pool per se performance. RRS in combination with continuous diversification of both pools allows distinct female and male pool development, line development and introgression of a cytoplasmic male sterility system. Creating OPVs and population hybrids early and aiming for long-term development of topcross hybrids from improved OPVs and newly derived lines is possible alongside the heterotic pool development. Additionally, the RRS lays the foundation for possible future single-cross hybrid breeding programs. The suggested framework is highly ambitious and requires long-term commitment, vision and financial resources. Considering the flexibility regarding single steps and the possibility to develop different types of varieties at every stage of the pool diversification, it has the potential to enhance gains from selection and, with the continuous output of new high-yielding and stable cultivars, to improve the livelihood of WA subsistence farmers substantially.