Mineral composition in foliage of some cultivated and wild species of Chenopodium

Members of the genus Chenopodium are used as a foliage crop and fodder in many parts of the world. Forty accessions of Chenopodium spp. (C. album, C. berlandieri, C. bushianum, C. giganteum, C. murale, C. quinoa, and C. ugandae) were sown in a randomized block design with 3 replications. For determination of mineral composition, leaves of each accession from each replication were collected from lower, middle and upper regions of the plant, bulked together and transported to the laboratory. All the samples were analyzed in triplicate. The present study showed that Chenopodium spp. is a rich source of minerals like (means, in mg 100 mg) potassium (6,329), sodium (8,350), calcium (1,154) and iron (83.92). The heritability estimates were high for all the minerals, with potassium and nickel showing the highest values (99.49 and 99.16% respectively). Sodium was positively correlated with calcium (0.483**) and copper (0.274*). Copper was negatively correlated with all heavy metals except iron and nickel. Leaf size was negatively correlated with potassium and chromium, and positively correlated with calcium and copper. This study would be of immense importance in enhancement of minerals in chenopod foliage as well as in mitigating nutritional deficiency prevalent among the poor populations in the developing countries. Additional key words: correlation, foliage, genetic advance, heritability, mineral content, qualitative improvement.

A large portion of the population in the developing countries has little access to protein and mineral rich diet, since wheat and rice are the principal food crops.To mitigate this problem, recently attention has centered on the exploitation and utilization of unusual and underexploited plant material for food.However, much of these efforts have laid emphasis on grain while sources of leafy vegetables have been largely overlooked.Green vegetables have long been recognized as the cheapest and most abundant sources of protein, vitamins and minerals (Aletor et al., 2002;Shukla et al., 2006;Bhargava et al., 2007a).In recent years, leafy vegetables have evoked interest, especially as potential food crops for diversification of agriculture to newer areas, environmental sustainability and for combating the nutritional deficiency in many parts of the world (Shukla et al., 2006;Bhargava et al., 2007a).
The genus Chenopodium comprises about 250 species (Giusti, 1970) most of which are colonizing annuals (Wilson, 1990).Chenopodium spp.have been cultivated since centuries as a leafy vegetable and subsidiary grain crop in different parts of the world.Recently, the genus has been recognized to have antitumour, antifungal and antioxidant activity (Nascimento et al., 2006;Kumar et al., 2007).Although only three species are cultivated (Bhargava et al., 2006(Bhargava et al., , 2007a)), the leaves and tender stems of numerous others are consumed as food and fodder (Moerman, 1998;Partap et al., 1998).The foliage of Chenopodium constitutes an inexpensive and rich source of protein, carotenoid and vitamin C (Prakash et al., 1993).Although some reports have described the nutritional and antinutritional factors in the leaves of the some species of the genus (Prakash et al., 1993;Repo-Carrasco et al., 2003), the database of their mineral composition is far from exhaustive.
A number of different species of Chenopodium have been introduced and acclimatized in central mountain regions of North America, Europe and Africa (Mujica et al., 2001;Bhargava et al., 2006Bhargava et al., , 2007b)), but systematic evaluation for different qualitative traits are rare leading to lack of information on many aspects.Genetic variability in the base population plays a very important role in any crop-breeding program (Bhargava et al., 2007b).The characters of economic importance are generally quantitative in nature and exhibit considerable degree of interaction with the environment.Thus, it becomes imperative to compute the variability present in the material and its partitioning into genotypic, phenotypic and environmental ones.Improvement of yield requires an in-depth knowledge of the magnitude of variation present in the available germplasm, interdependence of quantitative characters with yield, heritability and genetic gain of the material.Correlation coefficients show relationships among various traits along with the degree of linear relation between these characters.Although reports on variability and correlation analysis among different minerals are available in other crops (Seiler and Campbell, 2004), such studies on foliage yield in vegetable chenopods are rare (Bhargava et al., 2008) wherein the authors assessed the genetic diversity in the genus using the multivariate analysis.Apart from this study no study mentions the qualitative improvement in chenopods with reference to minerals.The existence of genetic variability in mineral element composition would indicate the potential for selecting for enhanced forage quality.Therefore, the objectives of this study were to: (i) determine the variability for different minerals in the foliage of various wild and cultivated species of Chenopodium, and (ii) examine relationships among mineral concentrations in the foliage and their direct impact on leaf size while exercising selection.
The experiment was conducted at the experimental field of National Botanical Research Institute, Lucknow (altitude = 120 m; 26.5°N latitude, 80.5°E longitude).This subtropical region is situated in the Indo-Gangetic Plains and has sharp differences in summer and winter temperatures.Chenopodium spp.occurs as a winter crop and is harvested before the arrival of summers.The experimental material comprised 40 accessions of Chenopodium spp.whose details have been provided in Table 1.The material was sown in November 2003 in a randomized block design with 3 replications.The plot size for each accession was 4 m 2 , with row-to-row and plant-to-plant distance of 25 and 15 cm, respectively.The soil of the experimental site was sandy loam with a pH of 6.8 ± 0.04, electrical conductivity of 479 ± 1.26 µs cm -1 and organic matter content of 1.06 %.Twenty tons ha -1 of compost was added in the field prior to sowing and no chemical fertilizer or fungicide was used during the experiment.The leaves were collected when the plants had attained an aboveground height of 20 cm.
For determination of mineral composition, leaves of each accession from each replication were collected from lower, middle and upper regions of the plant, bulked together and transported to the laboratory.All the samples were analyzed in triplicate.The leaves were thoroughly washed with tap water and finally rinsed in deionized water (0.2% non-phosphate detergent solution).The leaves were then oven dried for 72 h at 80°C and digested in a 1:4 mixture of HClO 3 and HNO 3 .Calcium, sodium and potassium were determined by flame photometry, while iron, magnesium, zinc, copper, nickel, chromium and cadmium were determined using atomic absorption spectrophotometer (Perkin Elmer 5100).Leaf area (cm 2 ) was measured using the leaf area meter of Delta T Devices Ltd, when the plant was in full bloom.The raw data was compiled by taking the means of all the plants taken for each treatment and replication for different traits.Mean, phenotypic and genotypic coefficients of variation, heritability and genetic advance were analyzed according to Singh and Chaudhary (1985).Correlation analysis was performed according to Johnson et al. (1955a).
Minerals are important in human diet because they serve as cofactors for many physiologic and metabolic functions.Significant genotypic differences are known to exist in the metal uptake by plants (Hocking and McLaughlin, 2000).The analysis of variance revealed significant differences among the accessions for all the 10 variables as well as for leaf size (Table 2).The mean, range and other variability parameters for leaf The potassium content among the accessions ranged from 2,081-8,527 mg 100 mg -1 with an average of 6,329 mg 100 mg -1 .The mean calcium content for 40 accessions was 1,154 ± 0.20 mg 100 mg -1 , while the sodium content of the leaves measured 8,350 ± 544.70 mg 100 mg -1 .The iron content ranged from 75.6-92.33mg 100 mg -1 , with an arithmetic mean of 83.92 ± 0.53 mg 100 mg -1 .The mean values for zinc and copper content were 14.88+1.24and 13.21 ± 0.19 mg 100 mg -1 , respectively.The nickel content among the accessions ranged from 0.00-22.19mg 100 mg -1 , while chromium and copper averaged at 4.32 ± 0.60 and 2.40 ± 0.38 mg 100 mg -1 , respectively.An enormous amount of variation was found in leaf size for which the lowest and the highest values differed by over 13 times (lowest: 3.43 cm 2 ; highest: 46.51 cm 2 ) (Table 2).Our results show that potassium, calcium, sodium, iron and copper contents in Chenopodium were particularly high and moderate consumption of the foliage would satisfy the 'Recommended Dietary Allowance' (RDA), a standard developed in USA which specifies the amount of each nutrient that needs to be consumed daily in order to maintain good health (NRC, 1989).The mineral content of chenopod leaves compares favourably with those reported for other leafy vegetables by Aletor et al. (2002) and Kawashima and Soares (2003).The calcium and iron content in Chenopodium were much higher as compared to amaranth (Barminas et al., 1998) and spinach (Singh et al., 2001), but chenopod foliage is comparatively inferior in magnesium and zinc (Aletor and Adeogun, 1995;Odhav et al., 2007).A comparison with many other uncultivated plant foods also shows that chenopod leaves are rich in calcium, iron, potassium, zinc and sodium (Cook et al., 2000).Earlier studies have shown that the foliage of many species of Chenopodium is rich in protein, carotenoid and ascorbic acid (Prakash et al., 1993;Bhargava et al., 2007a).Thus, chenopod leaves should be included in the diet to overcome the nutritional problems prevalent in different regions of the world.The values of genotypic coeff icient of variation (GCV), phenotypic coefficient of variation (PCV), heritability and genetic advance are presented in Table 2. Highest coefficient of variation values were obtained for nickel, followed by cadmium and chromium.High GCV and PCV values recorded for these metals, as well as for leaf size, indicated good scope for improvement in these traits through selection for isolation of ideal plant types that can contribute in bioleaching of these metals from contaminated soils.Likewise, potassium, sodium and zinc also had moderate GCV and PCV values indicating considerable scope for improvement through selection for plants better suited for edible purposes.The heritability estimates were high for all the minerals as well as for leaf size, with potassium and nickel showing the highest values.Maximum genetic advance was observed for nickel, followed by cadmium and chromium.Low genetic advance values were obtained for iron and copper (Table 2).
The genotypic and phenotypic correlations among various minerals are presented in Table 3.The genotypic correlation coefficients were generally higher than the corresponding phenotypic values for most of the traits.Throughout the remainder of this section, reference will be made only to genotypic correlations.Sodium was significantly correlated: positively with calcium (0.483**) and copper (0.274*), and negatively with iron (-0.229*), zinc (-0.470**), nickel (-0.378**) and chromium (-0.308**).Zinc exhibited strong positive association with iron (0.351**) and magnesium (0.436**).Copper was negatively and significantly correlated with potassium and all heavy metals except iron and nickel.Nickel was positively correlated with zinc and magnesium, the values being significant in both the cases (0.659** and 0.266*, respectively).Chromium and cadmium showed strong positive association with magnesium, zinc and nickel, while cadmium and chromium were also strongly correlated with each other (Table 3).Leaf size was negatively correlated with potassium and chromium, and positively correlated with calcium and copper.Correlation studies show that attempts to increase leaf size for fodder use would lead to an increase in calcium and copper content, but a reduction in potassium and chromium levels in the leaves.Improvement of nutritional quality must go hand in hand with improvement of agronomic characters.Knowledge of heritability of a character is important as it indicates the possibility and extent to which improvement is possible through selection.The heritability values for most of the traits were high suggesting that these traits are under genotypic control.Such high heritability values for various traits have also been reported earlier in vegetable chenopods (Bhargava et al., 2003).However, high heritability alone is not enough to make sufficient improvement through selection generally in advance generations unless accompanied by substantial genetic advance (Johnson et al., 1955b).In the present study, moderate to high genetic advance values for most of the minerals indicate that improvement can be made in the aforesaid characters.The genetic advance for some minerals were extremely high because of the extreme variation in the material investigated, and smaller values are expected in further selection cycles in a more improved material.The heritability and genetic advance values were high for sodium, potassium and heavy metals like zinc, nickel, cadmium and chromium, suggesting that these traits are under genetic control.The abovementioned heavy metals also share significant positive correlation among themselves, which suggests that selection for improvement in any one mineral would lead to a concomitant increase in the other three.Likewise, strong negative association of copper with all heavy metals shows that attempts to increase copper could result in decrease in the concentration of other heavy metals, which would be more desirable for edible purposes.
The genetic variation of the minerals in different chenopod species should allow for the selection of individuals for improving mineral elements in the forage.The selection program for enhancement of selected minerals should be carried out in different regions, taking into account local preferences and mineral deficiency prevalent among the populations.This would allow the inhabitants of different regions to utilize these species to supplement their diet so as to optimize the nutritional value of their diets.

Table 1 .
Accessions of Chenopodium used in the present study size and different minerals are presented in Table2.

Table 2 .
Mean (mg/100 g dry weight), range and variability parameters for leaf size (cm 2 ) and various minerals (mg/100 g dry weight) in Chenopodium spp.
a Genotypic coefficient of variation.b Phenotypic coefficient of variation.

Table 3 .
Genotypic (G) and phenotypic (P) correlation coefficients between various minerals in Chenopodium spp.