Potential of Selenium(Se) accumulation among pearl millet[Pennisetum glaucum(L.) R.Br.) genotypes

Beneficial effects of selenium (Se) can be delivered to humans through enriched plant foods. However, breeding plants to be more efficient at Se accumulation can complement enrichment efforts. This study was aimed at determining the inheritance of Se accumulation for the purpose of developing varieties of pearl millet (Pennisetum glaucum (L.) R. Br.) which accumulate high Se. In doing this the first step involved the determination of the magnitude of genetic variation in the Se content as a proxy for Se accumulation ability of the selected pearl millet genotypes followed by the determination of the gene action and heritability conditioning the Se accumulation trait. Thirty seven genotypes were screened for Se accumulation in a field experiment during 2011/2012 cropping season at University of Zambia (UNZA) Field Station. These genotypes were sprayed with Se in the form of sodium selenate (Na2SeO4) at a rate of 2 mg L-1 (288 m3 ha-1) through foliar application during vegetative stage, 30 days after emergence. The crop was grown to maturity and grains harvested. The grain samples were analysed for Se accumulation using the Atomic Absorption Spectrophotometer fitted with Graphite furnace (AAS-GF). The screened genotypes were further crossed in a North Carolina Design (NCD) II mating scheme, using 12 male and 25 female parents during 2012 offseason at National Irrigation Research Stations (NIRS), Nanga, Southern province of Zambia. The progenies were evaluated for Se accumulation and important agronomic traits in three sets in a Randomised Complete Block Design (RCBD). These progenies were also sprayed with Se and grain samples were analysed for accumulated Se following the same procedure as for parents. The Se analyses for the parental genotypes showed high coefficient of variation (CV) values of 135% for non-sprayed and 156% for sprayed genotypes, indicating the wide inherent genetic variability for grain Se accumulation among pearl millet genotypes. Out of 37 genotypes screened, before spraying, 29 were identified as Se accumulators while 8 were non-accumulators, however after spraying, 35 were designated as Se accumulators and 2 as non- accumulators. The amount of Se accumulated among the non-sprayed parental genotypes ranged from the lowest 0.00 μg g-1 to highest 0.09 μg g-1 for 570028 R1w and SDMV 59009 respectively while among the sprayed genotypes, the lowest was 0.01μg g-1 for 570028 R1w and highest was 0.63μg g-1 for NLC-C3. Significant (P<0.05) differences in Se accumulation were also observed among crosses and the range across sets was 0.08 – 0.62 μg g-1. The overall highest accumulator among all the crosses was ZPMDC x NEC-C3 (0.62 μg g-1) from set I while the overall lowest accumulator was NLBC-C3 x TARAM (0.08 μg g-1) from set III. This result indicated that pearl millet has the potential to accumulate Se and a wide genetic variation in grain Se accumulation exists in pearl millet genotypes. Significant (p<0.05) strong positive correlation (r=0.652) was noted between days to 50% flowering and Se concentration while days to maturity was significantly and negatively correlated (r= -0.926) to Se concentration indicating that selection for high Se content may be possible without significant compromise on grain yield.
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General combining ability (GCA) effects indicated that parent ZPMV 28402, a superior parent can be used in breeding programmes to introgress the Se accumulation trait, without compromising on grain yield. On the other hand, specific combining ability (SCA) revealed that crosses SOSANK x NL0C-C4, SEPO x OKASHANA 1 and ZPMV 24801 x KUOMBOKA could be employed for effective utilisation in hybrid breeding programmes for Se accumulation trait. The variance components using Baker’s ratio (0.36) indicated that non-additive effects were more important in conditioning the Se accumulation trait. Narrow sense heritability (h2) of 0.28 for the Se accumulation trait was found to be very low and, therefore, suggesting a recurrent selection method to be employed in the improvement of this trait. This study has shown that it is feasible to develop pearl millet varieties that contain high Se in the grains. The positive implications for ensuring adequate Se intake for improved nutrition through a pearl millet diet are obvious