Introduction

Impacts of climatic conditions result changing in global temperature, low rainfall, loss of biodiversity, multiple biotic and abiotic stresses on livestock, crops and land degradation (Reddy 2015). By 2050, it is estimated that people are now moving towards South Asia and Sub-Saharan Africa that makes these regions more saturated by addition of 2.4 billion of people. Agriculture is the main economic sector for these regions and also provides employment to the people of these regions. A study reveals that on an average about 20% of population is food insecure (Lipper et al. 2014). At present, new plants are being introduced by breeders and agronomists that have more adoptability potential to grow in all types of terrestrial environment on the earth. So, it is need of hour to introduce naturally stress resilient plants (NSRPs) that can survive under all type of stress conditions and unfavorable environment that are unfriendly for most of the crops.

The NSRPs are sometimes known as extremophiles plant like pearl millet (Pennisetum glaucum), quinoa (Chenopodium quinoa) and grain amaranth (Amaranthus hypochondriacus) (Zhang et al. 2018) because these plants can survive under harsh stressful environmental conditions. These crops are also known as superfood crops, so they are helpful to minimize the pressure of food insecurity (Massawe et al. 2016). In most areas of the world, amaranth is being increasingly recognized that has a more potential to play an important role as alternative food grain. Because of its more degree of phenotypic plasticity, nutritional profile, high adaptability in various environmental conditions and ability to improve food security, it can be grown in marginal lands (Achigan-Dake et al. 2014; Alemayehu et al. 2014). In maximum areas of Asia and Africa, amaranth is consumed as a food crop in the form of both leafy vegetables and grains (Brenner et al. 2000). There are more than 87 species of amaranth are globally exist and three species are area characterized as a grain and about 17 species as an edible leaf form (Grabben and Denton 2004). Amaranthus cruentus and Amaranthus hypochondriacus of these grain species are originated from North and Central America and remaining one grain specie that is Amaranthus caudatus is originated from South America (Rosa et al. 2009). Main proteins in amaranth are albumin and globulin and their concentration varies from 13–19% (Gorinstein et al. 2002).

On the basis of nutritional value some essential bioactive compounds, flavonoids, tannins, anthocyanins, phytosterols and phenolic acids are also present in grains of amaranth (Ryan et al. 2007). In amaranth, bioactive compounds play an important role as a preventive agent in different chronic diseases like diabetes, urinary problems, cancer, cardiovascular problems and hypercholesterolemia (Abugoch 2009). Amaranth grains are more effective in hypo-cholesterolemic index and have more antioxidant value (Gorinstein et al. 2002). About 5 to 13% of lipids are present in it and a high amount of unsaturated fatty acid (linoleic acid) is also present (Schoenlechner et al. 2008; Alvarez-Jubete et al. 2010). In amaranth, maximum amount of vitamins and minerals are present like sodium (Na), calcium (Ca), magnesium (Mg), sulphur (S), phosphrous (P), potassium (K), manganese (Mn) and iron (Fe) and Vitamin B complex (Alvarez-Jubete et al. 2010).

Amaranth is a C4 plant, a pseudo-cereal crop and can raised under warm and bright light environmental conditions. Temperature needed for amaranth growth is varies from 25–30°C (Schippers 2000). Amaranth species are able to survive under high drought and heat because of C₄ photosynthetic machinery due to lack of photorespiration damages and better CO₂ reserves Amaranth plant shows good recovery under water-deficient soil by conserving water through minimizing the transpiration water losses and lack of photorespiration (Louh et al. 2014). In the study of Omami et al. (2006) and Costa et al. (2008) it is clear that mild to moderate salinity does not adversely affect the yield of amaranth plant. Amaranth is considered as a high valuable crop because of its climate proof nature and good quality of nutritional profile.

Amaranth can replace the wheat (Triticum aestivum L.) crop in areas from which it has already disappeared due to the abiotic stresses and help to improve the quality of food intake. Due to wider adaptability in diverse soil and climatic conditions and unique nutritional profile, exotic germplasm of this crop was tested to check adaptability and yield potential in agro-climatic conditions of Faisalabad- Pakistan.

Materials and Methods

Plant material and design

The seeds of ten genotypes were collected from United States Department of Agriculture (USDA). Ten genotypes were assessed for their adaptability and yield potential under agro-climatic conditions of Faisalabad. Origin and complete detail of genotypes are given in Table 1. The experimental design was randomized complete block design having three replications.

Table 1: Genotypes, passport data and phenotypic characteristics of amaranth species used in the experimentation

Table 2: Physical and chemical analysis of soil of field trial site

Experimental details

This two years field trial (2017-18 and 2018-19) was executed at Directorate of Farms in University of Agriculture, Faisalabad Pakistan (73.87°E, 31.87°N; altitude 184.3 m.a.s.l.). The climate of Faisalabad is semi-arid and sub-tropical. Under experiment, all of the weather data regarding rainfall, temperature and relative humidity are presented in Fig. 1. Chemical and physical characteristics of the soil are presented in Table 2 and analysed according to the standard protocols described by the Estefan et al. (2013).

For conserving soil moisture and obtaining maximum emergence two ploughing at a depth of 12 cm was done followed by one planking. Amaranth crop was sown on the tip of each ridge spaced apart by 22.5 cm with hand dibbled method on 21 November 2017 and 25 November 2018. Seeds were sown at a depth of 2-3 cm using seeding rate of 7.5 kg ha^-1. Each experimental unit was consisted of four ridges with each ridge length of 5 m and ridge to ridge distance was 75 cm. The two outer ridges were acting as guard rows, and the terminal amaranth plant was placed at the beginning and end of central rows also act as guard plants. Urea (46% N), diammonium phosphate (18% N and 46% P₂O₅), and sulphate of potash (50% K₂SO₄) were used as fertilizers and applied at the rate of 75:50:50 NPK kg ha^-1, respectively. During the land preparation the half dose of N and full dose of P and K were added. At the time of flowering phase, remaining dose of N was applied. Two weed hoeing were done manually 30 and 60 days after sowing from experimental field. Yield was calculated from a total plot size of two ridges by 4.75 m in length. Harvesting was done on 16 April 2018 and 18 April 2019.

Phenological traits

On the basis of daily field visits, all phenological traits such as, total crop duration, bud initiation, milking stage and seed setting were observed.

Leaf Chlorophyll and carotenoid contents analysis

For chlorophyll determination procedure of Nagata and Yamashta (1992) was followed, while carotenoids were measured using the standard protocol of Davies (1976). At the time of panicle emergence stage, fully expanded young leaves were harvested from each experimental unit. A 0.5 g leaf sample was grounded in 10 mL of 80% acetone using pestle and mortar, grounded material was put in falcon tube and centrifuged for 15 minutes at 4000 rpm, resulted supernatant was subjected to take absorbance at 663, 645 and 480 nm using spectrophotometer (UV 4000). Later on, chlorophyll a, b, total chlorophyll and carotenoids were calculated using following formulae:

Seed protein contents

Nitrogen content in flour samples was estimated by Kjeldahl's method. Nitrogen percentage was calculated using Equation:

Seed protein percentage was calculated by multiplying percent nitrogen with 5.7.

Yield and related traits

At harvest, ten plants were tagged in each plot to record the yield related attributes such as plant height, number of panicles per plant, terminal panicle length, terminal panicle dry weight and terminal panicle grain yield. After harvesting in each experimental unit, crop plants were tied into bundles and sun-dried in the field for 5 days within respective experimental unit. Plant biomass was recorded by using a spring balance, and by manual threshing grain yield was obtained and recorded with an electric balance. Harvest index (HI) was recorded as the ratio of grain yield to biological yield, expressed as a percentage. From grain yield of each experimental unit, grain sample was taken, and 1000 grain was counted by seed counter and the 1000-grain weight was determined with an electric balance.

Statistical analysis

Data of all traits recorded for two years were pooled and used in further statistical analysis. All recorded data for each parameter were subjected to the SAS 9.1 software to work out an analysis of variance (ANOVA). Data regarding phenological, leaf chlorophyll analysis and yield related attributes are presented in tables with critical values to compare genotypes using Tuckey HSD test at the 5% level of probability. Correlation (Pearson) among studied traits was also calculated using statistical package Statistix 8.1.

Results

Yield related attributes

Significant variations (P ≤ 0.001) were observed among the genotypes for yield related attributes such as plant height, number of panicles per plant and biomass (Tables 3, 4). Among the genotypes, maximum plant height was recorded in ‘Ames 18034’ followed by ‘PI 642733’, ‘Ames 1970’ and ‘PI 481272’, while maximum number of panicles per plant were recorded in Ames 15204 followed by Ames 1970, PI 642733 and Ames 2031 (Table 3). Genotype ‘PI 619265’ produced maximum biomass followed by ‘PI 481272’, ‘PI 636194’ and ‘Ames 1970’ (Table 4).

Table 3: Mean values for yield related attributes in 10 genotypes of amaranth over two years

Different letters within the same column indicate statistically significant differences at P ≤ 0.05

Fig. 1: Temperature, Relative humidity and rainfall during experimental period (Nov–April 2018 and 2019)

 Moreover, significant variations (P ≤ 0.001) were recorded among the genotypes for terminal panicle length, terminal panicle dry weight and thousand grain weight and harvest index (Tables 3 and 4). Maximum terminal panicle length was recorded in ‘Ames 2031’ and remaining all genotypes had statistically similar terminal panicle lengths (Table 3). Maximum terminal panicle dry weights was produced by ‘PI 642733’ followed by ‘PI 619265’, ‘Ames 18034’ and ‘PI 636194’ while minimum value was noted in ‘PI 654390’ (Table 3). Furthermore, maximum value of 1000-grain weight was found in ‘Ames 18034’ followed by ‘PI 654390’ and ‘PI 642733’ that was statistically similar and minimum value for this trait was observed in ‘PI 636194’ (Table 4). Maximum harvest index was noted in ‘PI 649305’ followed by ‘Ames 15204’ (Table 4). While among the genotypes, maximum grain yield was produced by ‘PI 642733’ followed by ‘PI 619265’, ‘PI 636194’ and ‘Ames 15204’ (Table 4).

Panicle and seed colour

Genetic diversity was observed between the genotypes for panicle and seed colour (Table 5). Panicle colours of ‘PI 636194’, ‘PI 649305’, ‘PI 481272’ and ‘PI 654390’ were found yellow (Table 5). Genotype ‘Ames 2031’ and ‘Ames 18034’ showed brown panicle colour (Table 5); while ‘Ames 15204’ had light brown panicle colour. Genotype ‘PI 642733’, ‘PI 619265’ and ‘Ames 1970’ produced green, purple and dark pink colour panicles respectively (Table 5). Moreover, ‘PI 481272’, ‘PI 654390’, ‘PI 642733’, ‘PI 619265’ and ‘Ames 1970’ produced black colour seeds (Table 5).

Table 4: Mean values for yield related attributes in 10 genotypes of amaranth over two years

Different letters within the same column indicate statistically significant differences at P ≤ 0.05

Table 5: Mean values for phenological stages in 10 genotypes of amaranth over two years

Different letters within the same column indicate statistically significant differences at P ≤ 0.05

Table 6: Mean values for biochemical attributes in 10 genotypes of amaranth over two years

Different letters within the same column indicate statistically significant differences at P ≤ 0.05

Phenologial traits

Significant variations were observed among genotypes in terms of phenology (Table 5), genotypes initiated their bud growth between 40-48 days after emergence while genotypes reached milking stage 100-114 days after emergence (Table 5). Genotypes completed seed setting between 112 to 128 days. Genotypes ‘PI 642733’, ‘PI 481272’, ‘PI 636194’, ‘PI 619265’ were appeared as late maturing (Table 5).

Seed protein contents (%)

Significant (P ≤ 0.001) genetic variations were noted among the genotypes for seed protein contents. Maximum value of seed protein was found in ‘PI 654390’ followed by ‘Ames 15204’, ‘PI 636194’ and ‘Ames 18034’ (Table 4). Minimum value of seed protein was recoded in ‘PI 642733’ (Table 6).

Leaf biochemical analysis

Significant variations were observed among genotypes in terms of leaf chlorophyll contents (Table 6); genotypes ‘PI 642733’, ‘PI 642733’, ‘PI 636194’ and ‘PI 619265’ had maximum leaf chlorophyll contents (Chl a, Chl b and Total Chl) while genotype ‘PI 654390’ had minimum leaf chlorophyll contents. Leaf carotenoid contents were also found different among amaranth genotypes (Table 6). Maximum leaf carotenoid contents were found in ‘PI 649305’ which was statistically at par with values of genotypes ‘PI 642733’, ‘PI 636194’ and ‘PI 481272’.

Discussion

In order to mitigate climate changes and malnutrition, FAO has selected some crops to be promoted and adopted in existing cropping systems and named these crops as Future Smart Food (Li and Siddique 2018). Amaranth is one of them. Therefore, for its introduction in Pakistan, its germplasm adaptability was explored in Faisalabad. Out for 10 genotypes, four genotypes were found good in terms of grain yield (Table 4). Amaranth grain yield ranged between 961.98-1280.69 kg ha^-1. It showed that amaranth exhibits high degree of plasticity as earlier explained by Shukla et al. (2010). Phenotypic plasticity can be defined as ability of an individual to change its phenotype in response to variable environments (Fazlioglu and Bonser 2016). Due to this character this crop can be adapted in adverse and variable environments (Khanam and Oba 2014). These variations might be due to changes in weather conditions (Fig. 1) especially rise in temperature and increased day length during reproductive stages. In our study, it seemed that increased temperature influenced yield (Fig. 1) and genotypes experienced high temperature and showed different adaptability. Genotypes which produced high grain yield seemed more heat tolerant as well. Grain yield is a result of association and expression of many plant growth components and environmental conditions (Anjum et al. 2011). Abiotic stresses such as high temperature is also most important factor which restricts growth and productivity of major cereals (Umar 2006; Shwabe et al. 2013).

Furthermore, it is evident from time of seed setting (Table 5) that genotypes which were high yielder matured late, it can be linked to “stay green” character of genotypes; stay green character has been considered an important character for heat tolerance. It has also been observed that heat tolerant wheat genotypes had also high chlorophyll contents (Farooq et al. 2011) which is directly linked to stay green character. Moreover, adapted crop genotypes might also have good antioxidant system to detoxify toxic ROS which may otherwise be detrimental to macro molecules including chlorophylls (Hussain et al. 2018). The grain filling process is a reserve accumulation in developing grain which is sensitive to environmental factors which ultimately affect final seed yield (Yang and Zhang 2006). The most significant factor limiting seed yield is high temperature in cereals, high temperature induces shortening of vegetative phases, less light perception due to shortened life cycle and perturbation of carbon assimilation processes (photosynthesis, transpiration and respiration) (Stone and Basra 2001). So, it seems that low yielder genotypes were heat sensitive that’s why they matured earlier (Table 5). Heat stress induces metabolic changes especially excess ethylene production leading to early senescence and chlorophyll degradation. Thus, maintenance of stay green character is very important and considered as best indicator of thermo tolerance (Farooq et al. 2011). In our case study such type of results are evident (Table 6); genotypes which produced high grain yield had also more leaf chlorophyll contents (Table 6). Strong correlations were found between leaf chlorophyll contents and grain yield.

Phenological traits have key importance in crop production it directly influences the overall yield of a crop. In current study days taken to milk stage and days taken to seed setting were recorded. It was observed that genotypes reached at seed setting stage in 113 to 130 days after emergence, it seems large differences. Genotypes in which seed setting was late, might also took advantage of more grain filling period and produced grain yield. Adaptability of any genotype is influenced by environmental (as discussed earlier) and its own genetic factors. Like in cereals different yield contributing factor contribute final yield, so some plant characters of amaranth genotypes were also studied (Table 4) which might influence final grain yield. It is evident from Pearson correlation that haveir terminal panicles contribute to final grain yield.

For successful acclimatization of any crop in new environment, grain quality is also another important element which should not be neglected; therefore, grain protein contents were also measured in harvested grain of different genotypes. Grain protein contents ranged between 11.7 to 19.0% which is comparable with international published reports (Li and Siddique 2018).

Conclusion

Huge phenotypic plasticity was found among amaranth genotypes which were found beneficial to successful acclimatization of this crop in semiarid conditions of Faisalabad, Pakistan. Among the genotypes, maximum grain yield was produced by ‘PI 642733’ followed by ‘PI 619265’, ‘PI 636194’ and ‘Ames 15204’. This was linked with stay green character (more leaf chlorophyll contents) of genotypes for longer period, as depicted by more seed setting periods of high yielder genotypes. Furthermore, seed protein contents ranged between 11.7 to 19.0% which were comparable with already published report.

Author Contributions

Samreen Nazeer: Data analysis, initial draft, review and editing; Shahzad M.A. Basra: Conceptualization, supervision, review and editing; Shahid Iqbal: Conceptualization, supervision, review and editing; Muhammad Bilal Hafeez: Methodology, review and editing; Ahmed Mateen: Data analysis using statistical package; Muhammad Zubair Akram: Methodology; Noreen Zahra: Methodology; review and editing; Shahbaz Khan: Review and editing; Jahanzaib: Methodology; Muhammad Sohail Saddiq: Formal analysis, review and editing.

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