Browsing by Subject "Combining ability"

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    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.