Mineral Profile and Variability in Vegetable Amaranth ( Amaranthus tricolor

Plant Foods for Human Nutrition 61: 23–28, 2006. c 2006 Springer Science+Business Media, Inc.
DOI: 10.1007/s11130-006-0004-x 23 Mineral Profile and Variability in Vegetable Amaranth (Amaranthus tricolor) SUDHIR SHUKLA,1, ∗ ATUL BHARGAVA,1 A. CHATTERJEE,1 J. SRIVASTAVA,2 N. SINGH 2 & S. P. SINGH1 1 Division of Genetics and Plant Breeding, National Botanical Research Institute,Rana Pratap Marg, Lucknow,226001,India; 2 Biomass Biology Division, National Botanical Research Institute,Rana Pratap Marg, Lucknow,226001,India (∗ author for correspondence; e-mail: s shukla31@rediffmail.com) Published online: 31 May 2006 Abstract. Populations in North India depend on a number of vegetable crops of which Amaranthus spp. is the most important since it is the only crop available in the hot summer months when no other foliage crop grows in the field. However, reports on mineral composition of leaves are rare with absolutely no information on the qualitative improvement of foliage yield with special reference to minerals. Studies on correlation among the minerals as well as with yield and leaf attributes are also lacking. Hence, we report the proximate mineral composition in 30 strains of A. tricolor along with some suggestions for qualitative improvement of the foliage yield with reference to minerals. Our study showed that vegetable amaranth is a rich source of minerals like calcium (1.7 ± 0.04 g/100 g), iron (1233.8 ± 50.02 mg/kg), and zinc (791.7 ± 28.98 mg/kg). The heritability estimates were high for most of the traits, with potassium and calcium showing high values, while comparatively lower values were recorded for magnesium and nickel. Nickel was the only mineral that showed positive correlation with all the minerals, as well as with leaf size and foliage yield. Zinc showed strong positive relationship with iron (0.66∗∗ ) and manganese (0.74∗∗ ), and was the only mineral exhibiting significant positive association with foliage yield. This study would be of use in enhancement of selected minerals in different regions according to local preferences and nutrient deficiency prevalent among the populations. Key words: A. tricolor, Correlation, Foliage yield, Genetic enhancement, Minerals, Selection parameters Introduction An increase in world’s population demands increased production of food crops that should also be nutritionally superior to the existing ones. FAO statistics [1] reveal that there is a high frequency of low birth weight children in the developing countries, which is primarily due to deficiency of micronutrients in mother’s diet. Underutilized crops like chenopods, buckwheat, and amaranth have recently gained worldwide attention in this respect as these contain abundant amounts of all the common nutrients required for normal human growth. Simultaneously, these crops do not require large inputs and can be grown in agriculturally marginal lands [2]. Populations in North India depend on a number of vegetable crops of which Amaranthus spp. is the most important since it is the only crop available in the hot summer months when no other foliage crop grows in the field. The species used as vegetable types have short plants with large smooth leaves, small auxiliary inflorescences, and succulent stems. The leaves of amaranth constitute an inexpensive and rich source of protein, carotenoid, vitamin C, and dietary fiber [3, 4]. Besides this, the plant can also grow successfully under varied soil and agro climatic conditions [5]. In view of the potential beneficial attributes of vegetable amaranth, there is an urgent call to carry out extensive research efforts to ascertain its nutritional composition. Although reports on nutritional aspects in the crop are available [4, 6], but literature on mineral composition of leaves is rare [7, 8]. Also, there is absolutely no information on the qualitative improvement of foliage yield with special reference to minerals and associations among themselves as well as with yield and leaf attributes. Therefore, to fill this knowledge gap, the present investigation was undertaken to ascertain the mineral composition of different strains of vegetable amaranth and to find out possible ways for their enhancement, thereby resulting in qualitative improvement of the foliage. Materials and Methods The material consisted of 30 pure strains of vegetable amaranth (A. tricolor), which are being maintained for several years at the experimental field of National Botanical Research Institute, Lucknow. These strains were evaluated during kharif 2003 at the experimental field of NBRI, Lucknow in a randomized block design with three replications. The plot size for each strain was 2 m2 with row-to-row distance 25 cm and plant-to-plant distance was 15 cm. Normal cultural practices were followed during the experimentation. After 3rd week of sowing, 1st cutting of foliage started and subsequent cuttings were done at the interval of 15 days. A total of four cuttings were done and data on foliage yield (kg) was recorded on plot basis separately for each cutting and then pooled for total foliage cutting. For determination of mineral composition, the leaves were first oven dried and then digested in a 1:4 mixture of HClO3 and HNO3 . Calcium and potassium were determined by flame photometry, while zinc, iron, nickel, magnesium, and manganese were determined using atomic absorption spectrophotometer (Perkin Elmer 5100) [9, 10]. Statistical analysis was done according to Panse and Sukhatme [11]. Genotypic (GCV) and Phenotypic coefficient of variation (PCV), heritability (h2 ) in broad sense, and genetic advance (GA%) were estimated according to 24 Singh and Chaudhary [12] as given below:
σ 2g × 100 GCV = x̄ PCV =
σ2p × 100 x̄ Heritability (h 2 ) = σ 2g σ2p 2 Heritability % = σ g × 100 σ2p Expected genetic advance (GA) = iσ ph 2 GA × 100 x where, σ 2 g: genotypic variance, σ 2 p: phenotypic variance, x̄: general mean of character, i: standardized selection differential, √ a constant (2.06), σ p: phenotypic standard deviation ( σ 2 p) Genotypic and phenotypic correlation coefficients were calculated as proposed by Johnson et al. [13]. GA(%) = Results The analysis of variance revealed significant differences among the strains for all the seven characters, which validated further statistical analysis (data not shown). The mineral content of the leaves of 30 strains of vegetable amaranth is presented in (Table 1). Minerals Potassium. AV-41 had the highest potassium content (6.4 g/100g), followed by AV-43 (6.3 g/100 g) and AV-22 (6.1 g/100 g). The lowest amount of potassium was found in AV-26 (1.7 g/100 g). The mean potassium content for 30 strains was 3.7 ± 0.26 g/100 g. Among all the seven minerals analyzed, coefficient of variability was maximum for potassium (39.1%). Calcium. The calcium content among the strains ranged from 0.73 g/100 g to 1.9 g/100 g with an average of 1.7 ± 0.04 g/100 g. Sixteen strains showed above-average mean values for calcium content. Highest amount of calcium was found in AV-43, while lowest amount in the leaves of AV-26. The coefficient of variability (%) for calcium was less than all the minerals except for magnesium. Magnesium. The magnesium content averaged 2.9 ± 0.01 g/100 g, the highest being found in AV-18 (3.0 g/100 g), followed by AV-28 (3.0 g/100 g) and AV-37 (3.0 g/100 g). The coefficient of variability for magnesium (2.2%) was least among all the minerals analyzed. Out of 30 strains, 17 showed above-average values for magnesium content. Zinc. Zinc content among the strains ranged from 434.7 mg/kg (AV-45) to 1230.0 mg/kg (AV-26) with an average mean of 791.7 ± 28.98 mg/kg. Fourteen strains showed above-average performance for zinc, of which two (AV-26 and AV-43) had zinc in excess of 1000 mg/kg. Iron. The highest amount of iron was found in AV-26 (2306.0 mg/kg), followed by AV-37 (1662.0 mg/kg) and AV-30 (1484.0 mg/kg). The mean iron content in 30 strains was 1233.8 ± 50.02 mg/kg and 11 strains showed values higher than the mean value. Only two strains viz. AV-17 and AV-42 had iron content less than 1000 mg/kg (783.0 and 903.3 mg/kg, respectively). Manganese. Manganese ranged from 66.7 mg/kg to 155.0 mg/kg in all the 30 strains. The mean manganese content among the strains was 108.1 ± 3.82 mg/kg, with 14 strains showing above-average mean value. The richest source of manganese was AV-26 (155.0 mg/kg), followed by AV-16 (145.0 mg/kg) and AV-25 (137.0 mg/kg). Nickel. AV-31 and AV-25 had the highest content of nickel (321.3 and 293.3 mg/kg, respectively), while the lowest amount was found in AV-20 (89.3 mg/kg) that was less than three times the highest yielding strain. The mean nickel content was 222.6 ± 9.51 mg/kg and 18 strains scored aboveaverage mean value. Leaf size. The leaf size varied from 16.3 cm2 (AV-22) to 62.3 cm2 (AV-41) with an overall mean of 29.3 ± 2.04 cm2 . Only 10 out of 30 strains had leaf size higher than the mean value. The coefficient of variability was highest for leaf size. Foliage yield. The strains of A. tricolor under study yielded abundant foliage yield that ranged from 3.9 kg/plot (AV-29) to 5.9 kg/plot (AV-43), with an overall mean of 4.8 ± 0.09 kg/plot. Out of 30 strains, 10 had foliage yield >5.0 kg/plot, while two (AV-20 and AV-29) had low yield (<4.0 kg/plot). Variability Studies Variability plays an important role in crop breeding programs. The extent of diversity in crop determines the limits of selection for improvement. In any crop-breeding program, it is prerequisite to have a large variation in the material at the hand of breeder. The characters of economic importance are generally quantitative in nature and 25 Table 1. Mean values for mineral content, leaf size, and foliage yield in 30 strains of A. tricolor Strains AV-11 AV-12 AV-13 AV-14 AV-15 AV-16 AV-17 AV-18 AV-19 AV-20 AV-21 AV-22 AV-23 AV-24 AV-25 AV-26 AV-28 AV-29 AV-30 AV-31 AV-32 AV-33 AV-36 AV-37 AV-38 AV-40 AV-41 AV-42 AV-43 AV-45 Mean ± SE CV (%) K (g/100 g) Ca (g/100 g) Mg (g/100 g) Zn (mg/kg) Fe (mg/kg) Ni (mg/kg) Mn (mg/kg) Leaf size (cm2 ) Foliage yield (kg/plot) 4.2 4.3 5.3 2.4 3.6 3.7 1.8 3.7 2.1 2.7 3.8 6.1 3.8 3.8 4.3 1.7 1.8 1.8 2.4 2.7 4.4 2.0 3.7 3.6 5.5 5.0 6.4 5.9 6.3 2.5 3.7 ± 0.26 39.1 1.8 1.9 1.9 1.6 1.8 1.7 1.6 1.8 1.6 1.7 1.9 1.7 1.7 1.7 1.6 0.7 1.6 1.6 1.6 1.9 1.8 1.8 1.8 1.4 1.8 1.9 1.8 1.6 2.0 1.4 1.7 ± 0.04 13.6 3.0 2.9 3.0 2.9 2.9 2.9 2.8 3.0 3.0 2.8 2.9 3.0 2.9 2.9 2.9 2.8 3.0 2.8 2.8 2.8 2.9 2.9 2.8 3.0 2.9 2.9 2.9 2.8 2.9 2.9 2.9 ± 0.01 2.2 911.3 886.0 634.0 726.7 792.0 792.7 637.3 682.7 744.0 902.7 860.0 834.7 784.0 708.7 824.7 1230.0 686.7 672.7 984.0 732.0 972.0 682.0 592.0 922.7 664.7 782.0 718.7 842.7 1113.3 434.7 791.7 ± 29.0 20.1 1459.1 1423.9 1061.3 1198.3 1170.7 1247.7 783.0 1168.3 1380.3 1161.3 1151.3 1284.6 1184.0 1166.0 1450.0 2306.0 1273.3 1130.0 1484.0 1040.7 1007.0 1124.0 1023.7 1662.0 1073.3 1341.7 1229.0 903.3 1035.0 1090.7 1233.8 ± 50.02 22.2 238.7 163.7 181.3 270.0 227.7 219.7 153.3 179.0 278.3 89.3 292.7 275.0 269.6 224.0 293.3 223.7 230.0 151.3 231.7 321.3 224.3 211.3 204.7 267.7 231.0 267.0 170.3 170.3 250.0 169.0 222.6 ± 9.51 23.4 130.8 126.5 110.7 97.7 109.7 145.0 83.1 90.2 109.7 105.7 116.0 103.8 115.5 93.7 137.0 155.0 98.8 68.0 107.0 102.2 105.3 98.1 117.0 126.3 93.7 126.7 99.3 66.7 128.3 75.7 108.1 ± 3.82 19.4 20.7 17.7 32.7 18.0 26.3 17.5 18.5 25.3 22.7 25.7 25.8 16.3 43.0 22.3 30.3 34.3 28.0 28.0 42.9 29.3 23.9 25.0 27.3 49.3 23.7 24.7 62.3 21.7 41.7 52.3 29.3 ± 2.0 38.3 4.1 4.3 4.9 4.9 4.4 4.8 5.1 4.5 4.4 4.0 4.9 5.9 5.3 4.5 4.6 5.5 5.6 3.9 5.4 5.0 5.3 4.4 5.0 4.9 4.9 4.4 5.5 4.6 5.9 4.6 4.8 ± 0.09 10.5 exhibit considerable degree of interaction with the environment. Thus, it becomes necessary to compute variability present in the material and its partitioning into genotypic, phenotypic, and environmental effects. The values of phenotypic coefficient of variability (PCV) were greater than the corresponding genotypic coefficient of variability (GCV) values, though in many cases the differences were small. Leaf size and potassium showed high coefficient of variation values, while rest of the minerals exhibited moderate GCV and PCV values (Table 2). The heritability estimates were high for most of the traits, with potassium and calcium showing high values (83.43% and 71.83%, respectively), while comparatively lower values were recorded for magnesium and nickel (Table 2). The expected genetic advance as percentage of mean ranged from 2.63% to 71.52%. Maximum genetic gain was observed for potassium (71.52%), followed by iron (33.30%) and nickel (30.47%). Leaf size also had high genetic gain (59.03%), while foliage yield showed low value (14.84%) (Table 2). Correlation Studies The phenotypic and genotypic correlations among various characters are presented in (Table 3). The genotypic Table 2. Selection parameters for various economic traits in A. tricolor Selection parameters Traits GCVa PCVb Heritability (%) Genetic advance (%) K Ca Mg Zn Fe Mn Ni Leaf size Foliage yield 38.0 12.8 1.9 18.4 20.3 17.3 20.5 35.4 9.4 83.4 71.8 46.5 64.2 63.2 56.9 52.2 65.4 58.3 a Genotypic 41.6 15.0 2.7 23.0 25.6 22.9 28.4 43.8 12.4 coefficient of variation. coefficient of variation. b Phenotypic 71.5 22.3 2.6 30.4 33.3 26.9 30.5 59.0 14.8 26 Table 3. Genotypic (G) and phenotypic (P) correlation coefficients between various minerals, leaf size, and foliage yield in A. tricolor Traits FY K Ca Mg Zn Fe Ni Mn K G P G P G P G P G P G P G P G P 0.28 0.12 Ca −0.11 −0.13 0.50∗∗ 0.41∗∗ Mg −0.11 0.07 0.49∗∗ 0.21 0.52∗∗ 0.25 Zn 0.41∗ 0.18 0.16 0.11 −0.33 −0.21 −0.18 −0.16 Fe 0.11 0.06 −0.20 −0.23 −0.71∗∗ −0.61∗∗ −0.11 −0.08 0.66∗∗ 0.50∗∗ Ni 0.36∗ 0.26 0.12 0.03 0.10 0.07 0.19 0.19 0.23 0.18 0.29 0.17 Mn −0.20 0.21 0.16 0.02 −0.12 −0.10 −0.02 0.06 0.74∗∗ 0.45∗ 0.73∗∗ 0.53∗∗ 0.49∗∗ 0.32 LS 0.52∗∗ 0.22 0.11 0.11 −0.20 −0.15 −0.11 −0.10 0.02 0.02 0.19 0.17 −0.01 −0.06 0.002 0.03 Note. FY: Foliage yield, LS: Leaf size. ∗,∗∗ Significance at 5% and 1%, respectively. 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. The perusal of (Table 3) revealed that foliage yield had significant positive correlation with zinc (0.41∗ ), nickel (0.36∗ ), and leaf size (0.52∗∗ ). Potassium was positively correlated with all other minerals except iron, however, it was significantly associated with calcium (0.50∗∗ ) and magnesium (0.49∗∗ ) while calcium was negatively associated with foliage yield, zinc, manganese, and leaf size and had significant negative correlation with iron ( − 0.71∗∗ ). Magnesium exhibited significantly positive association with calcium (0.52∗∗ ). Nickel was the only mineral that showed positive correlation with all the minerals, however it had significant positive correlation with foliage yield (0.36∗ ) and manganese (0.0.49∗∗ ). Iron was significantly and positively associated with manganese (0.73∗∗ ). Zinc showed significant positive relationship with iron (0.66∗∗ ) and manganese (0.74∗∗ ). Discussion The objective of this study was to assess and compare the various mineral compositions in different strains of A. tricolor, which are being widely consumed as a leafy vegetable in many parts of the world. Minerals are important constituents of human diet as they serve as cofactors for many physiological and metabolic processes. Calcium is required for growth of bones as well as in muscular and neurological functions, while iron is important for hemoglobin development. The study showed that vegetable amaranth is a rich source of a number of macro and micronutrients. In vegetable amaranth, calcium, iron, and zinc content is greater than that reported in the leaves of cassava [14] and beach pea [15]. However, comparison of A. tricolor with another leafy vegetable of the same genus (A. hybridus) shows that A. tricolor is a better source of iron and magnesium, while A. hybridus is rich in calcium (2.0 g/100 g), potassium (4.8 g/100 g), manganese (170 ppm), and zinc (894 ppm) [16]. The study shows that for each trait (mineral) a number of strains are outyielded over their corresponding arithmetic means. AV-32, AV-41, and AV-43 were the strains with >5 kg/plot foliage yield and were also rich source of minerals, except iron, which can be economically useful for nutritional aspects and simultaneously enhancement in its’ yield and mineral contents can also easily be achieved through simple selection methods. The strains AV-22, AV-23, AV-26, and AV-30 had above-average foliage yield (4.8 ± 0.09 kg/plot) along with high content of iron and zinc. These strains can substantiate a rich amount of zinc and iron in human diet and also can serve as a donor parent for introgression of genes of these minerals into other strains, which are low in content of these minerals. Similarly, some of the strains may serve as promising material for selection of plant types with increased yield potential as well as mineral composition for which they showed high mean performance. The strains AV-11 and AV-12 had high amount of all the minerals but were deficient in foliage yield and could be utilized as donor parents for introgression of genes in mineral deficient lines like AV-17, which exhibited high foliage yield performance. The strains AV-18, AV-20, AV-29, AV-33, and AV-45 were low yielding as well as deficient in mineral content and would be of 27 little use in breeding programme. These strains of A. tricolor reportedly contain large amount of protein, carotenoid, and ascorbic acid [17] and the present study shows it a rich source of minerals also. This brings to forth the nutritional superiority of vegetable amaranth, which is presently “underutilized” in terms of consumption and trade, but offers exciting prospects for crop diversification and nutritional needs of the community. The correlation analysis presented some interesting results, perhaps for the first time in any foliage crop. In this study, the genotypic correlation between foliage yield was not significant with any mineral except zinc and nickel, indicating that selection for increased mineral content might be possible without hampering yield. Likewise, no significant association was observed between leaf size and any of the minerals. On the other hand, leaf size showed significant positive correlation with foliage yield that is corroborated by our earlier work in A. tricolor (Shukla et al., unpublished) and vegetable Chenopodium (Bhargava et al., unpublished). In any crop-breeding program, it is prerequisite to have a large amount of variation in the material at the hand of a breeder. The extent of diversity in crop determines the limits of selection for improvement. 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 variability present in the material and its partitioning into genotypic, phenotypic, and environmental effects. In the present study, potassium, nickel, and iron had high genotypic coefficient of variability (GCV) and phenotypic coefficient of variability (PCV) values, which indicate scope for improvement in these traits through selection. Lower estimate for both these parameters observed in magnesium and calcium implies that chances of getting substantial gains under selection are likely to be less. Variability alone is not of much help in determining the heritable portion of variation. The amount of gain expected from a selection depends on heritability and genetic advance in a trait. Heritability has been widely used to assess the degree to which a character may be transmitted from parent to offspring. Knowledge of heritability of a character is important as it indicates the possibility and extent to which improvement is possible through selection [18]. However, high heritability alone is not enough to make sufficient improvement through selection generally in advance generations unless accompanied by substantial amount of genetic advance [19]. The expected genetic advance is a function of selection intensity, phenotypic variance, and heritability and measures the differences between the mean genotypic values of the original population from which the progeny is selected. It has been emphasized that genetic gain should be considered along with heritability in coherent selection breeding programmes. It is considered that if a trait is governed by nonadditive gene action it may give high heritability but low genetic advance, which limits the scope for improvement through selection, whereas if it is governed by additive gene action, heritability and genetic advance would be high, consequently substantial gain can be achieved through selection. The heritability and genetic advance values were high for potassium and iron, which suggests that these traits are under genetic control and significant improvement can be obtained for these traits. However, strong positive association of potassium with calcium and magnesium could lead to a concomitant increase in these minerals if selection for potassium is carried out. Likewise, selection for greater iron content could indirectly increase zinc and magnesium content in the foliage, but decrease calcium. Thus, the suggested selection programme for enhancement of selected minerals should be carried out in different regions, taking into account local preferences and nutrient deficiency prevalent among the populations. The present study screened out a strain AV-43 that can substantiate all the minerals in rich quantities in human diet and also have potential to yield high foliage. Acknowledgments The authors are thankful to Director N.B.R.I. for providing the necessary facilities and constant encouragement to carry out the present investigation. References 1. Swaminathan MS (1999) Enlarging the basis of food security: Role of unutilized species. 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