Studies on the Allelopathic Potential of Corn (Zea mays L.) Aqueous Extracts and Root Exudates






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Journal of Agricultural Science and Technology A 2 (2012) 432-437

Earlier title: Journal of Agricultural Science and Technology, ISSN 1939-1250

Studies on the Allelopathic Potential of Corn (Zea mays

L.) Aqueous Extracts and Root Exudates

Zakiya A. Hassan

Department of Horticulture, School of Plant Production, Faculty of Agriculture and Forestry, University of Duhok, Kurdistan Region, Duhok 273, Iraq

Received: November 21, 2011 / Published: April 20, 2012.

Abstract: This investigation was carried out at Faculty of Agriculture and Forestry-University of Duhok/Kurdistan-Iraq. Three experiments were included in this investigation: (1) First experiment was a bioassay related to the germination performance, shoot and root development of corn (Zea mays L.) and peanut (Arachishypogaea) at two concentrations of root (3% and 1.5%) and shoot (12% and 6%) aqueous extracts of corn medium; (2) The second experiment dedicated to the intercropping of corn and peanut at four treatments; (3) While the third experiment involved the effect of peanut root exudation on growth of corn. Experiment results revealed that corn shoot and root water extracts highly inhibited seed germination of both corn and peanut, the inhibitory of shoot extract was more than root aqueous extract. While its effect on the seedling growth was vice versa as compared with control treatment, there was an increase in root and shoot length of both corn and peanut when grown in corn aqueous extracts. Intercropping experiment results has stimulated most traits of peanut under studying. Also for corn, there was apparent and significant increase in all characteristics as compared with control. It was further confirmed from the results of peanut root exudates that had all studied characters of corn were stimulated than the control treatment.

Key words: Allelopathic potential, corn, peanut, aqueous extracts, root exudates.

1. Introduction

Sustainable crop production over long period of time is currently emphasized rather than maximizing yield in a short term [1]. To achieve sustainable agriculture, there is a need to understand ecological interaction occurring within a given agro-ecosystem. In crop association or natural stands, besides nutrients, water, light and space competition there is allelopathic interference, which causes inhibitory or stimulatory effect of one plant on another [2], and plays an important role in the intraspecific and interspecific competition. Chemicals released from the plants are responsible for replacing susceptible specie and new invading species during succession [3, 4]. Additionally, some crop plants have the auto-toxicity, which is a typical type of allelopathy in which plants have an

Corresponding author: Zakiya A. Hassan, lecturer, research fields: field crops, weed control, allelopathy. E-mail:

inhibitory effect on other plants of the same species [5]. Corn is an important crop that is extensively planted in the world for human and animal feed. As a result of widely spaced corn rows, weed competition is one of the most important limiting factors that reduce corn yield and impact economic returns. Hence, corn and legumes are two crops, normally grown in association.

However, there are few research results talking about the allelopathic effect from corn [6], peanut [7] and soybean [8]. Moreover, to the best of our knowledge, both corn and peanut are crops that are characterized by auto-toxicity (intraspecific) [9-11]. In a study [12], the bioassay of employing root exudates collected from wheat and rye (Secale cereal L.) seedling demonstrated that rye exudates inhibited root growth of wild oats (Avena fatua L.), suggested that rye could potentially interfere with the growth of oats in nature, and this interference could be due to the release of Hydroxamic acid to the soil via the root



exudates. Zwain [13] showed that the aqueous extracts of wheat significantly reduced seed germination and seedling growth of rice and mungbean, he also found that the aqueous extracts residues of wheat inhibited the nitrification and nitrogen fixation process. Almezory [14] found that aqueous extracts and decaying residues of corn significantly inhibited seed germination and seedling growth of corn due to the auto-toxicity of corn under monoculturing regime. Multiple cropping is common practice in subtropical and tropical regions [15]. It is also common in Iraq, particularly in Northern region where different crops are grown together in the same field and at the same time for self-sufficiency. The objective of this study is to investigate the plant residues of corn on corn and peanut emergence and seedling growth and to evaluate the root exudates of intercropped corn and peanut.

2. Materials and Methods

The experiments were conducted in the laboratory and greenhouse of Faculty of Agriculture/University of Duhok, Kurdistan-Iraq.

2.1 Bioassay Experiment

To study the effect of aqueous extracts of corn plants (root and shoot systems) on seed germination and growth of corn and peanut, the following experiments were carried out. Plant samples of corn (Zea mays L.) collected from the fields of Faculty of Agriculture/University of Duhok. The plant materials transferred to the laboratory cleaned from the soil particles, the shoot and root separated and air dried in the dark conditions under room temperature then dried by electric oven at 70 ± 1 °C for 48 hours. The dried plant parts were ground by electric grinder into small pieces for extracts preparation Chopped corn was soaked in room temperature (25 ± 2) distilled water (for shoot, 3 gm/100 mL and for root, 3 gm/100 mL) for three days [16]. The mixtures were passed through filter paper. The filtrate extract was completed to the original volume (100 mL) by adding distilled water.

Test solutions of water extracts were prepared by diluting the original extract to obtain the different concentrations of shoot and root (6% and 1.5% respectively). The aqueous concentrations for shoot were (0% distilled water as control, 12% and 6%); while for root aqueous extracts were (0% distilled water as control, 1.5% and 3%). This was the basic medium for seed bioassay.5 mL of the extracts were added to each Petri dish (9 cm), planted with 5-10 seeds of peanut and corn respectively, and same amount of distilled water was used for the control. Four replicates of each treatment were randomly distributed in a growth germinator at 25 ± 1 °C.The germination percentages were recorded after 7 days of cultivation. The shoot and root parts of the seedlings were separated then the length of each system was recorded.

2.2 Intercropping Experiment

In order to study the interaction between plants grown together in the same field. An experiment conducted in the green house in plastic pots containing 7 kg of sand washed with dilute hydrochloric acid and distilled water, each pot was planted with corn and peanut seeds due to the experiment treatments which were the following:

Control for corn; Control for peanut;

Intercropping (4 corn plants + 2 peanut plants); Intercropping (4 corn plants + 4 peanut plants); Intercropping (2 corn plants + 4 peanut plants). Throughout the duration of the experiment, the pots were alternatively irrigated with equal quantities of tap water. The pots were distributed randomly in the greenhouse, in three replications. After two months, the plants took off, the following characters for corn were recorded (plant height, No. of leaves, leaf length, leaf width, stem diameter, shoot dry weight and root dry weight), while for peanut the studied characters were (plant length, No. of branches, No. of leaves, shoot dry weight, root fresh weight, root dry weight). Shoot and root systems for both crops were separated,


then dried at 70 ± 1 °C for 48 hours.

2.3 Root Exudates Experiment

Manual root exudates recirculation used in stair-step technique has been modified by AlSaadawi et al. [3]. The system consisted of a main stand 4 m × 2 m with 4 shelves coming out from both sides at different distances, with wood pierces in equal dimensions covers for setting plastic pots (23 cm × 8 cm) with fixed cannula on their bottoms to adjust the flow of Hoagland and Arnon nutrient solution. The pots were filled with sand washed by a diluted acid and distilled water, and were planted with corn and peanut. The pots were divided into two series (treatment and control) each for three replicates. In treatment series, the nutrient solution (1/10 strength) will flow from container at the top, through pots containing donor plant (peanut) alternated with recipient plant (corn), and finally to the container at the bottom, then recycled manually twice a day. While in control series, the nutrient will pass through pots containing sand without donor plants, alternated with recipient plant. After 35 days the plants are took off and washed carefully and their length, No. of leaves, fresh and dry weights of root and shoot and chlorophyll measurements were recorded.

3. Results and Discussion

Table 1 shows that concentrations 1.5% of roots extract and 6% of shoot extract of corn, which inhibited the germination of corn seeds. This may be due to the due to the auto-toxicity of corn, as the study results of Almezory [14] indicated that ferulic, vanillic, p-coumaric and syringic acids were identified from the aqueous extracts of soil containing corn residues, these phytotoxins did not appear in soil without corn residues. The same results observed by Saied [17], who reported that seed germination is inhibited by allelochemicals released from plant. Regarding the radicle and shoot length, both obtained a significant increase as shoot and root aqueous extracts of corn were used, except the

radical length obtained a decrease with these treatments as compared with control. Among treatments of shoot and root extracts concentrations, treatment 3% of root water extract was more positive and enhanced the growth of corn seedlings and seed germination, while the treatments of shoot extract concentrations (6% and 12%) had decreased the radicle length and seed germination as compared with control but shoot length improved when shoot extract of corn has been used and the diluted concentration was significantly more effective than treatment 12% by which the radical length increased insignificantly and seed germination significantly from treatment 6%. It is clear that the shoot aqueous extracts was inhibitorier to seed germination of interacted plants than root aqueous extracts .the mechanism of growth inhibition by allelopathic substances might be as a result of reducing cell division and elongation.

Seed germination of peanut crops affected by corn material extracts (Table 2). Inhibition percentage increased as the concentration of corn extract increased. The reduction of seed germination was significant as compared with control. On the other hand, shoot and root water extracts enhanced the seedling development when compared with control except treatment 6% which affected negatively and decreased the shoot and radical length. Among the extract types and concentrations, the best treatment was diluted concentration of root aqueous extract (1.5%). In general shoot extract was more inhibitor than root extract for its effect on both corn and peanut growth and seed germination. This agreed with the results of Iman et al. [18]. Results of seed germination indicated the same trend of corn seed germination when planted by shoot extracts, and the inhibition percentage increased as the extract concentration increased. Results of seed germination and seedling growth of the tested plants showed different response to the aqueous extract of interfered plants in this study. This comes in accordance with the study of Ben-Hamouda et al. [19], in that clear differences were present between shoot and root extracts of the same plant


Table 1 The effect of shoot and root aqueous extracts of corn on seed germination and seedling growth of corn.

Shoot extract Root extract

Conc. % Shoot length Radical length Germination % Conc. % Shoot length Radical length Germination %

0 4.59 c 12.97 a 87.5 a 0 4.59 b 12.97 c 87.50 a

6 7.40 a 8.19 b 40.63 c 1.5 8.09 a 15.36 b 50.00 c

12 6.16 c 8.83 b 50.00 b 3.00 8.58 a 18.36 a 75.00 b

Means followed the same letter within a column do not differ from each other according to Duncan's multiple range test at 5% level.

Table 2 The effect of shoot and root aqueous extracts of corn on seed germination and seedling growth of peanut.

Shoot extract Root extract

Conc. % Shoot length Radical length Germination % Conc. % Shoot length Radical length Germination %

0 2.80 b 4.51 a 80 a 0 2.80 a 4.51 b 8o a

6 1.33 c 2.73 b 65 b 1.5 3.06 a 6.97 a 65 b

12 3.19a 4.50a 45c 3 2.47 a 4.64 b 50 c

Means followed the same letter within a column do not differ from each other according to Duncan's multiple range test at 5% level.

concerning their effect on others. This can be explained by the differences of plant parts in accumulation of phytotoxin [20].

Comparison between the effect of shoot and root aqueous extracts on the growth of different studied plants indicated that plant types are different in their effect. This may be explained by one or more of the following reasons: (1) the reservoir of accumulated allelochemicals must differ in different plant types; (2) the allelochemicals which inhibit growth of certain plants could not necessarily be the same which inhibit the growth of other plants. Reduction of seedling growth and seed germination percentage may be due to the presence of allelochemicals which accumulated in shoot and root systems, then released through out the process of extraction and affected the growth of same (autotoxicity) or other plants (telotoxicity).

Table 3 shows the data of experiment (2) which studied the effect of intercropping on growth development of corn plants. Intercropping treatments caused a significant increase in all studies characters of corn especially treatment of intercropping (2 corn + 4 peanut), which considered the best treatment in this experiment. This mean that grain and legume association plants possess positive interaction, and this might due to the substances released from the roots and affect the intact plants. Respective of the intercropping treatments, planting in mixture has the advantages that

more efficient utilization of light, water resources and soil nutrients can be attained by the special arrangement of plants [21]. As the corn plant height increased the suppression of peanut plants increased, this may be due to the competition for available mineral nitrogen [22], or to the utilization of light resources [23] or to the allelopathic inhibitory of corn on peanut [14].

Results of Table 4 indicated that multicropping has enhanced the all tested parameters of peanut except plant length, there was insignificant reduction in all treatments for this character when compared with sole cropping of peanut (control). Treatment (4C + 2P) obtained the highest means for root dry weight, while treatment (2C + 4P) gave maximum means for number of branches/plant, number of leaves/plant and shoot dry weight (2.33, 17.57 and 1.65 respectively). Increasing of corn plant height and leaf length contributed to the crowding as the number of plants per pot increased, the competition for light increased, this is true for the intercropping systems as compared with control. This also can be explained by the idea that corn plants are strong competitor for light and nutrients than weak peanut.

The results of intercropping experiment indicated that the difference between control and treatments of all characters except root dry weight was insignificant and this may certify the idea that corn roots contain less inhibitory materials.


Table 3 Effect of corn and peanut intercropping treatments on the growth of corn plants.


Treatments Plant height (cm)

No. of leaves/plant Leaf length (cm) leaf width (cm) Stem diameter (cm) Shoot dry weight (gm)

Root dry weight (gm)

Control(corn) 98.59 b 4.22 b 64.77 a 2.87 b 0.449 a 2.353 b 0.227 c 4 C + 2P 96.65 b 4.33 b 62.83 a 2.84 a 0.490 a 2.234 b 0.262 bc 4C + 4P 99.53 b 4.53 ab 64.92 a 3.03 b 0.565 a 2.561 b 0.318 ab 2C + 4P 106.83 ab 5.5 a 66.42 a 3.53 a 0.633 a 3.258 a 0.430 a Means followed the same letter within a column do not differ from each other according to Duncan's multiple range test at 5% level.

Table 4 Effect of corn and peanut intercropping treatments on growth of peanut plants.


Treatments Plant length (cm) No. of branches/plant No. of leaves/plant Shoot dry weight (gm) Root dry weight (gm)

Control (peanut) 29.42 a 2.21 a 15.68 a 1.01 a 0.32 b

4 C + 2P 26.25 a 2.00 a 12.63 a 1.04 a 1.693 a

4C + 4P 28.83 a 1.66 a 13.21 a 0.88 a 1.078 ab

2C + 4P 28.91 a 2.33 a 17.57 a 1.65 a 1.125 ab

Means followed the same letter within a column do not differ from each other according to Duncan's multiple range test at 5% level.

Interaction between corn and peanut plants are studied by using root exudates effect of each one on the growth of the other. Fig. 1 revealed apparently the means obtained from the third experiment. The results clearly indicate the promotion of all characters under study for the treatment as compared with control. Leaf length, root fresh weight and root dry weight significantly increased by the root exudates of peanut while the rest characters enhanced and increased but did not interact significantly. Root exudation has not been studied much, yet it can be very important, especially affecting the microorganisms and it can have a direct effect on other plant roots [24]. The experiment results demonstrated that peanut plants intercropped with corn plants might release allelochemical which stimulate the

0 10 20 30 40 50 60 70 80 90 100 Treatment Control 

Fig. 1 Effect of root exudates of peanut on growth of corn seedlings.

growth of corn plants, therefore the root exudation is one of very important ecological method for releasing phytotoxins into the environment which accumulate in soil throughout plant cycle [14, 25-27].


The author wishes to thank Dr. Hassan A. Elmezory, vis president of University of Duhok for his kind assistance and evaluable suggestion during conducting of the research and preparing the paper.


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