Abstract
Most of the maize (Zea mays L.) varieties in developing countries have low content of micronutrients including vitamin A. As a result, people who are largely dependent on cereal-based diets suffer from health challenges due to micronutrient deficiencies. Marker assisted recurrent selection (MARS), which increases the frequency of favorable alleles with advances in selection cycle, could be used to enhance the provitamin A (PVA) content of maize. This study was carried out to determine changes in levels of PVA carotenoids and genetic diversity in two maize synthetics that were subjected to two cycles of MARS. The two populations, known as HGA and HGB, and their advanced selection cycles (C1 and C2) were evaluated at Ibadan in Nigeria. Selection increased the concentrations of β-carotene, PVA and total carotenoids across cycles in HGA, while in HGB only α-carotene increased with advances in selection cycle. β-cryptoxanthine increased at C1 but decreased at C2 in HGB. The levels of β-carotene, PVA, and total carotenoids increased by 40%, 30% and 36% respectively, in HGA after two cycles of selection. α-carotene and β-cryptoxanthine content improved by 20% and 5%, respectively after two cycles of selection in HGB. MARS caused changes in genetic diversity over selection cycles. Number of effective alleles and observed heterozygosity decreased with selection cycles, while expected heterozygosity increased at C1 and decreased at C2 in HGA. In HGB, number of effective alleles, observed and expected heterozygosity increased at C1 and decreased at C2. In both populations, fixation index increased after two cycle of selections. The greatest part of the genetic variability resides within the population accounting for 86% of the total genetic variance. In general, MARS effectively improved PVA carotenoid content. However, genetic diversity in the two synthetics declined after two cycles of selection.
Highlights
Increased susceptibility to several major diseases, such as anemia, diarrhea, measles, malaria and respiratory infections, which accounts for about 70% of childhood deaths throughout the world, is the most disastrous effects of VAD12,13
The present study was conducted to determine the genetic gain for pro-vitamin A (PVA) content and examine the extent of change in genetic diversity in two synthetics
The two synthetics were formed from pro-vitamin A rich maize inbred lines belonging to different heterotic groups developed at IITA and they were improved for pro-vitamin A content through two cycles of MARS
Summary
Increased susceptibility to several major diseases, such as anemia, diarrhea, measles, malaria and respiratory infections, which accounts for about 70% of childhood deaths throughout the world, is the most disastrous effects of VAD12,13. Most maize varieties grown and consumed throughout the world have only 0.5–1.5 μg/g of β-carotene[19] This genetic variability makes it possible to develop maize varieties with increased level of PVA carotenoid content. Synthetics can be released as variety per se besides serving as a source of better performing inbred parents[22] These synthetics were synthesized from provitamin A rich elite inbred lines adapted to low-land tropical environments and are tolerant to major constraints in their target environments. Development of advanced inbred lines for the formation of provitamin A rich maize hybrids with better agronomic performance through recurrent selection has a paramount importance in improving the food and nutritional security of the target population
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