Browsing by Subject "Selection strategy"

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Towards understanding the genetics of tolerance to low soil phosphorus conditions in West African pearl millet
(2015) Gemenet, Dorcus Chepkesis; Haussmann, Bettina
About two hundred and twenty three million people are undernourished in Sub-Saharan Africa (SSA) with 11 million people being food insecure in the Sahel region of West Africa (WA). A growing global population and climate change are expected to exacerbate this situation and present new challenges on global food production. Phosphate rock, a non-renewable resource is expected to be depleted in about 40-400 years depending on the source of information but a phosphorus (P) peak (where P demand exceeds P supply) is likely to occur before 2040. The effects of limited global P supply are expected to be felt more by resource poor smallholder farmers in SSA. This is also the region already with the lowest inorganic fertilizer use and highly weathered P deficient soils. Given these factors, breeding for low-P tolerance in crop plants offers the main environmental friendly and economically feasible strategy for improving crop productivity under low-P soils for smallholder farmers in WA conditions. This will not only contribute towards food security in the short term but also in the long term by contributing towards the efficient use of a scarce resource. In the Sahel region of WA where pearl millet is the staple cereal, it contributes to food security by providing calories as well as contributing towards nutritional security by providing higher iron and zinc levels than most staple cereals. Despite this fact, the available pearl millet germplasm had never been evaluated for grain yield performance under low-P conditions within this region prior to this study and the magnitude of the genetic component of variation had not been tested from a breeding perspective. To fill in this knowledge gap, three genotype groups: open-pollinated varieties, inbred lines and their testcrosses were evaluated in large-scale multi-environment trials in four countries under two P-levels between 2010 and 2012. In addition, the open-pollinated varieties and inbred lines were evaluated for P-efficiency related traits at early growth stage in pot conditions and at mature plant stage under field conditions (inbred lines only). The main aim of these evaluations was to explore the prospects of plant breeding for improving pearl millet grain yield under low-P conditions in WA. We sought to achieve the following specific objectives: (i) to estimate quantitative-genetic parameters for grain yield in order to establish a selection strategy for pearl millet targeting P-limited environments in WA; (ii) to determine the relationship between P-efficiency related traits and grain yield in order to make inferences on which target traits should be considered in adapting pearl millet to low-P conditions in WA; and (iii) to identify genetic regions underlying quantitative traits which are related to P-efficiency based on diversity array technology (DArT) markers. There is significant genetic variation for pearl millet performance in low-P soils; hence genetic improvement for low-P conditions should be possible. Both wide and specific adaptation can be followed in breeding pearl millet varieties for low-P conditions in WA. Direct selection of pearl millet under low-P conditions is more efficient and should be carried out in breeding activities targeting low-P environments. Pearl millet in WA exhibits a wide genetic variation for P-uptake and internal use efficiency. P-uptake efficiency is more correlated to grain yield in pearl millet than P-utilization efficiency, and given the interactions among P, drought and other soil characteristics evident within the region, P-uptake efficiency under these conditions should be selected for. However, given the already low P content of the soils in the region and the low input conditions, genotypes selected for low-P environments should combine both P-uptake efficiency and internal P-utilization efficiency to avoid further depletion of the soils. Nine markers were associated with different P-efficiency-related traits such as P concentration in stover, P concentration in grain, P uptake and P utilization efficiency. Nine markers and thirteen markers were found to be associated with flowering time and grain yield respectively. Each of these markers individually explained between 5.5 to 15.9 % of the observed variations indicating the polygenic nature of low P tolerance in pearl millet. The results presented in the current study indicate potential of improving pearl millet grain yield under P-limited conditions through breeding both conventionally and through molecular technologies. Given the global P crisis, other agronomic, socio-economic and policy approaches need to be effected alongside breeding activities if the pearl millet production system should be made sustainable to ensure food security for current and future generations.