Allelopathic effects of Amaranthus viridis L. on some growth characters of Swiss chard plant ( Beta vulgaris var. Cicla) )

A pot experiment was conducted at Faculty of Education, Alzaiem Alazhari University, Sudan, during 2019/2020 to evaluate the effect of Amaranthus viridis powder on the emergence and growth of Swiss chard ( Beta vulgaris var. cicla). The experiment was set as a completely randomized design (CRD) with four replicates. In the treatments the powder of Amaranthus viridis was incorporated into the soil at rate of (0, 0.5, 1.0. 1.5 and 2.0% w/w) representing T 1 (control), T 2 , T 3 , T 4 and T 5 respectively. Results indicated that Amaranthus viridis powder decrease germination, plant height, number of leaves, leaf area, shoot and root fresh and dry weight, chlorophyll content (a, b) and some chemical elements (P, Ca, Mg, Fe) of Swiss chard ( Beta vulgaris var. cicla).


Introduction
Food shortage and deficiency is considered to be one of the most global problems across the world. Weeds leaf uncontrol may cause great losses in crop yield and these losses exceeded that caused by other pests, Plants growing together compete with each other for sunlight, soil nutrients and water. To reduce competition, plants produce chemicals that affect the germination and growth of neighbouring plants by disruption of various physiological processes [1]. These chemicals are known as allelochemical which released into the environment by plant organs.
Swiss chard (Beta vulgaris var. cicla) is a vegetable which is consumed by the majority of the Sudanese population. The main constrain of Swiss chard production is the weed infestation. Amaranthus viridis is one of the dominant weeds that compete with Swiss chard and other vegetables.
The present study was conducted to evaluate the effect of Amaranthus viridis on the germination growth, yield and some chemical constituents of Swiss chard (Beta vulgaris var. cicla).

Plant material
Amaranthus viridis plants were collected fro the farm of the Faculty of Agriculture, University of Khartoum. The plants were uprooted, washed with distilled water than dried at room temperature (25 o C for 96 hours. Plant then chopped and ground into fine powder. The Swiss chard seeds were obtained from local market (local cultivar).

Pot experiment
Plastic pots (18 × 30 cm) filled with silt soil, were arranged in completely randomized design (CRD) with four replications. Five treatments were used, the first one T1 representing the control where the soil was from Amaranthus residue. The other four treatments were represented by T2, T3, T4 and T5, where soils were incorporated with Amaranthus powder in 10, 20, 30 and 40 g per pot which representing 0.5, 1.0, 1.5 and 2.0% w/w residue (soil0 respectively. Five seeds of Swiss chard were sown in reach pot and later thinned to two seedlings. Pots were irrigated daily with tap water. During the experiment the germination percentage, plant height, numbers of leaves, leaf area were recorded. At the end of the experiment shoot and root fresh and dry weight, chlorophyll content (a, b) and some elements (P, Ca, Mg, Fe) were variance (ANOVA) according to [ 2].

Results and discussion
The germination percentage of Swiss chard plant decreased as the concentration of Amaranthus viridis increased ( Table  1). The reduction of germination percentage was from 83.33% at control to 46.65% at treatment T2 then decreased to 6.60% and 3.33% at treatments T3 and T4 respectively. These results were supported by the findings of [3] who reported that Amaranthus viridis extract significantly decreases the germination of mung bean (Vigna radiata (L.) R. Wilczek). Similar results were reported by [4] they found that the extracts of the whole plant of Amaranthus exhibited severe inhibition of seed germination of tomato as well as of weed seeds of Conyza bonariensis. Also [ 5]) concluded that leaf leachates of Amaranthus viridis, Parthenium hysteroporus and Polygonum plebeinum significantly inhibited the growth of Triticum aestivum. The inhibition in the germination percentage of Swiss chard may be attributed to the presence of phenolic acids. These phenolic acids may inhibit cell division, water and nutrient uptake and consequently germination.
The highest plant height of Swiss chard was observed at control 14.16 cm, then decreased to 10.20, 10.00, 9.50 and 8.80 cm in treatments T2, T3, T4 and T5 respectively. These results were confirmed by the findings of [6 ] who reported that extracts of Amaranthus viridis decreased shoot growth of rye grass compared to control. Similar results were reported by [7] who found that incorporation of powder residue Amaranthus viridis in the soil significantly decreased plant height of common bean (Phaseolus vulgaris L.) cow pea (Vigna sinensis (L.) Walp), pigon pea (Cajanus cajan (L.) Mill sp) and alfalfa (Medicago sativa L.). The number of leaves did not show any significant difference between treatment and control, although some researchers reported a significant decrease in number of leaves of sorghum, millet, maize and wheat. The leaf area of Swiss chard exhibited significant decrease from the control at treatments T3 (1%, w/w), T4 (1.5%, w/w) and T5 (2%, w/w) ( Table 1). Similar results were reported by [8] who showed that irrigation of groundnut and maize with water extract of Eucalyplus globulus reduced leaf area.
The shoot fresh and dry weight of Swiss chard exhibited a significant decrease in all treatments as compared with control ( Table 2). These results were supported by the results of [9] who found that Amaranthus hybiridus inhibited the dry weight of shoot and root of red clover and root of alfalfa. In connection to this [10] assumed that decrease in fresh and dry weight may be attributed to allelochemicals inhibiting protein and carbohydrate synthesis and hence reducing seedling growth.
The root length, root fresh and dry weight showed a significant decrease from control ( Table 2). The root length decrease as the concentration increased. Root growth is characterized by high metabolic rate and for this reason; roots are highly susceptible to environmental stresses such as allelochemicals in soil [11]. These results were supported by the results of [7]) who reported that the incorporated powder of Amaranthus viridis into soil decreased root length as well as root fresh and dry weight of sorghum, millet, maize and wheat. The decrease in root fresh and dry weight of Swiss chard may be attributed to the decrease in root and shoot seedling length which induced by allelochemicals found in Amaranthus powder.
The chlorophyll content (a, b) decreased significantly as the concentration of Amaranthus increased (Table 3). Similar results were reported by [12] and [13] who reported that a reduction was observed in chlorophyll (a) content of the corn treated with Eucalyptus rostrata leaf residue. In this respect [14] attributed the decrease in chlorophyll content to the decreases in the relative water content of leaves which initially induce stomatal closure, imposing a decrease in the supply of Co2 to the mesophyll cells and consequently, photosynthesis could be lowered resulting in the decrease in chlorophyll content.
A significant reduction was observed in content of phosphorus P and calcium Ca, Magnesium, Mg and iron Fe in treatments as compared with control ( Table 3). The reduction in P content was also reported by [13] who found that Eucalyptus allelochemicals reduced the amount of P and N. On the other hand, the decrease in Ca 2+ , Mg 2+ and Fe 2+ was supported by [15] who observed that root exudates of cucumber inhibited the uptake of K + , Ca 2+ , Mg 2+ and Fe 2+ by cucumber seedlings. The reduction in these elements may be attributed to that, root membranes are primary site of action for allelochemicals and the contact of phenolic acid with the root cell membrane leads to depolarization, an efflux of ions and a reduction of hydrolic conductivity, water uptake and net nutrient uptake [16].

Conclusion
The study concluded that Amaranthus viridis residue containing phenolic compunds suppress the germination, the growth and yield of Swiss chard. Field studies are needed to evaluate the suppressive efficacy of Amaranthus viridis under natural conditions.