The gradual change in climatic conditions particularly rainfall receipt and distribution in tropical and subtropical regions of the world necessitates productivity enhancement of stress tolerant crops such as small millets as one option for food security. Little millet (Panicum sumatrense Roth. ex. Roem. and Schultz.) is an important indigenous small millets crop. It is well known for its drought tolerance and is considered as one of the least water demanding crops. Micronutrient malnutrition resulting from the consumption of diets deficient in minerals, vitamins and essential amino acids, affects more than one-half of the world’s population especially women and children in developing countries [1]. The nutritional quality of little millet grain is superior to many other major cereals. It is also contains B vitamins, especially niacin, B6 and folic acid calcium, iron, potassium, phosphorus, magnesium and zinc [2]. Iron deficiency is the most common nutritional disorder in the world affecting over 4 billion people, with more than 2 billion people, mainly in developing countries, actually being anemic [3]. Zinc deficiency in humans reduces growth, sexual maturity and the immune defence system [4]. Whole grains of little millet may have health promoting effects equal to or even in higher amount than fruits and vegetables and have a protective effect against insulin resistance, heart diseases, diabetes, ischemic stroke, obesity, breast cancer, childhood asthma and premature death [5].

Very little efforts have been made from the green revolution time for the genetic enhancement of this crop although it contributes to the food security for the poor as well as tribal population. Wide spread reports on energy and micronutrient malnutrition in tribal population have raised concerns on the food and nutritional security. In the present climate changing scenario and in the context of micronutrient malnutrition, this crop has a large hidden potential as a promising crop of the future. This untapped potential should be properly exploited for our food and nutritional security in the coming years. The first pre requisite for initiating a breeding programme to develop micronutrient rich genotypes, is to screen the available germplasm and to identify the source of the genetic variation for the target trait which can be used in crosses, genetic variation, molecular marker development and to understand the basic enhancement of micronutrient. This study mainly focused to identify sources and improve zinc, iron and calcium contents in little millet which would be a pertinent approach to combat wide spread malnutrition.

The experimental material consisted of 110 little millet genotypes having their origin from different geographical regions maintained at the Small Millets Germplasm Unit of Department of Millets, Tamil Nadu Agricultural University, and Coimbatore (Table 1). The 110 genotypes comprised of 105 germplasm accessions and five check varieties viz., CO₂, CO₃, Paiyur 1, CO (Samai) 4 and OLM 203. They were evaluated during kharif, 2012 and observations on 12 quantitative traits [days to 50 per cent flowering, plant height, basal tillers per plant, culm branches per plant, peduncle length (cm), panicle length (cm), panicle exertion (cm), flag leaf length (cm), flag leaf width (cm), thousand grain weight (g), single plant dry fodder yield (g) and single plant grain yield (g)] were recorded on five randomly selected competitive plants descriptor for Panicum sumatrense [6]. Based on the data for high single plant yield and bold seeds, 30 genotypes were selected. The 30 genotypes comprised of 26 germplasm accessions and four check varieties viz., CO₂, CO₃, CO (Samai) 4 and OLM 203 and the experiment was laid out in a Randomized Complete Block Design (RCBD) with three replications during summer, 2013 (Jan- May) at Millets Breeding Station, Tamil Nadu Agricultural University, Coimbatore. Recommended agronomic practices were followed to maintain a good crop stand. All the 30 genotypes were subjected to grain nutrient analysis (zinc, iron and calcium). Nutrient analysis was carried out in BRAIC-VFX-130 Atomic Absorption Spectrophotometer model with Iron Hallow cathode lamp at wavelength 248.3 nm. Nutrient analysis was carried out on triplicate ground samples of grains from individual plant by digestion with 9:4 diacid mixture (HNO₃: HCLO₄) followed by atomic absorption spectrometry (AAS) method using ECIL AAS (Perkin Elmer) as per the protocol described by [7,8].

Table 1: List of little millet genotypes used for evaluation.

Generally iron and zinc contents in major food crops range from 5 to 150 μg/g [9]. Nutrient analysis results revealed that zinc, iron and calcium contents in dehusked grains of little millet genotypes differed significantly among the genotypes (Table 2).

Table 2: Variability for grain nutrient content in selected 30 littlemillet genotypes.

The zinc content varied from 2.04 to 8.00 mg/g with a mean of 5.23 mg/g (Figure 1). The genotypes TNPsu 25 had the highest grain zinc content of 8.00 mg/g followed by TNPsu 23 (7.42 mg/g), TNPsu 21(6.95 mg/g) and TNPsu 9 (6.85 mg/g) whereas the lowest zinc content was found in CO (Samai) 4 (2.04 mg/g).

Figure 1: Variation for iron and zinc contents in littlemillet genotypes.

Wide variation in iron content was observed and it ranged from 1.49 to 23.38 mg/g with a mean of 4.95 mg/g (Figure 2). Two of the little millet genotypes viz., TNPsu 23 (23.38 mg/g) and TNPsu 22 (19.22 mg/g) had very high iron content genotypes that had not been reported earlier. In contrast MS 4700 had the lowest grain iron content (1.49 mg/g).

Figure 2: Variation for iron and calcium contents in littlemillet genotypes.

The grain calcium content varied from 1.14 to 13.15 mg/g with a mean of 3.90 mg/g (Figure 3). The genotype CO₃ had the highest calcium content (13.15 mg/g) followed by CO₂ (8.45 mg/g), TNPsu 141 (8.23 mg/g) and CO (Samai) 4 (6.52 mg/g) while the genotypes viz., TNPsu 28 (1.14 mg/g) and TNPsu 27 (1.35 mg/g) had the lowest calcium content.

Figure 3: Variation for zinc and calcium contents in littlemillet genotypes.

The maximum grain calcium, iron and zinc contents in little millet grains were 13 mg/g, 9.3 mg/g and 3.7 mg/g respectively which was reported by FAO [10]. A few of the genotypes like TNPsu 25, TNPsu 23 and TNPsu 22 were rich in both zinc and iron contents and TNPsu 141wass rich in zinc and calcium content. Nambi et al. [11] also reported high iron and calcium contents in little millet. Past attempts by Shashi et al. [12] and Upadhyaya et al. [13] to detect and estimate wide genetic variability for grain nutrients (zinc, calcium and iron) in finger millet were based on a relatively fewer numbers of accessions. Basanti Brar et al. [14] reported wide range of iron and zinc contents in dehusked rice grains within 220 rice genotypes. These genotypes having high nutrient contents could possibly be used in breeding programmes, promotion of large scale cultivation and consumption. Under- utilized species like little millet is likely to be useful in fighting malnutrition and hidden hunger, both in areas of cultivation and outside.

The results implied that in general the little millet genotypes exhibited high variation for the grain nutrient contents viz., iron, and zinc and calcium contents. This type of large genotypic variation especially for iron content in little millet has not been reported earlier. The large genotypic variation of iron, calcium and zinc in little millet grains could be due to tightly controlled homoeostatic mechanisms that regulate metal absorption, translocation and redistribution in plants allowing adequate, but non-toxic levels of these nutrients to accumulate in plant tissues [15]. Iron, zinc and calcium contents in edible portions also depend on the efficiency of translocation of minerals from root tissues to edible plant organs and accumulation thereof.

Zinc, iron and calcium rich genotypes viz., TNPsu 25, TNPsu 23, TNPsu 22 and TNPsu 141 could be involved in hybridization with agronomically superior accessions / breeding lines to combine grain nutrients (zinc, iron and calcium) and grain yield. Genotypes with poor content of nutrients viz., TNPsu 28, TNPsu 27, MS 4700 and MS 1003/1 identified in this study could be an ideal material for molecular understanding of the metal homeostasis in little millet. Even though some of the genotypes had lower calcium content than that of the the standard check varieties but those genotypes were superior in zinc and iron contents. Thus little millet could be a good source of nutrients which need to be exploited properly. This research findings could help in promoting the little millet consumption and thereby nutritional intake of the consumers significantly. This would also contribute to the food basket of the nation in addressing the food security.

The authors would like to acknowledge PPV & FRA, Ministry of Agriculture, GOI, New Delhi and the Project coordinator, AICSMIP, Bangalore for funding the research work.