Browsing by Subject "Fertility restoration"

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    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.