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New Role for the World Sugar Economy in a Changed Political and Economic Environment


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International Conference on:

New Role for the World Sugar Economy in a Changed Political and



Economic Environment ”


Allelopathic Interference of Certain Weed Species with the Germination and Growth of Sugarcane
Ahmed S.A, A.A. Abdel-Wahab, A.M. El-Gareeb and M.S.S. El-Taeb
Plant Prot. Dept., Fac. Agric., Assiut Univ., Assiut 71526, Egypt

Abstract:


A study was conducted the Agricultural Research Station at Kom-Ombo, Aswan, Egypt to study the allelopathic interference of the most common weeds in the area (Digitaria sanguinalis "hairy crabgrass", Cynanchum acutum "stranglewort" and Euphorbia geniculata "common spurge") with germination and growth of sugarcane "G T 45/9" plants grown in plastic bags 24 kg capacity in completely randomized design. Planting was carried out using three parts of sugarcane segments (terminal, medial, basal). Weed plants collected from the field were extracted with water after washing and cutting into small pieces and blended in an electric blender (250 or 500 gm/l) then filtered through several layers of motheline cloth. Irrigation was done at planting with the aqueous extract of each weed except control treatment that was irrigated with water at the same amount.

All weed extracts enhanced the sugarcane germination compared to the control, all extracts caused an increase in plant height after 45 days compared to the control. The highest plants were recorded in the D. sanguinalis 250 g/l followed by E. geniculata 500 g/l extract treatment then C. acutum 250 g/ l extract. At the end of experiment, weed extracts significantly affected the determined sugarcane root weight. Both the low concentration of D. sanguinalis and E. geniculata caused a higher sugarcane root weight comparing to the control. All treatments led to a decrease in sugarcane plant height, the most inhibiting treatments were E. geniculata low concentration extract and the least inhibiting treatment was the high concentration of the same weed. Weed extracts significantly decreased sugarcane green parts' weight compared to the control. The number of green or dry leaves, total leaf number and number of tillers were not affected at the end of experiment. All extracts significantly affected the mean tillers weight, the most inhibiting treatments were the low and high concentrations of D. sanguinalis then the low concentration of C. acutum compared to the control.

These results indicated the possibility of some germination stimulants occurrence in the aqueous extract of the tested weeds that led to encouraging sugarcane bud germination and plant height after 45 days, and sugarcane root weight after 90 days. At the same time, there was evidence concerning the occurrence of allelohemical substance/ substances in these weeds, as the sugarcane plant height and its green parts and tillers weight were affected at 90 days after treatment.

Keywords: sugarcane, sugarcane weeds, allelopathic interference, Digitaria sanguinalis, Cynanchum acutum, Euphorbia geniculata.

Introduction


Sugarcane is considered one of the main economic crops in Egypt and it is grown primarily in Upper Egypt. According to the "USDA Foreign Agricultural Service", cane production continues to be stable, while beet production is increasing at a dramatic rate, i.e. even though beet production is growing, cane production is still 60 per cent of total sugar output (Gressel et al, 2010).

Total cane area harvested in 2009/10 is estimated at 183,000 ha, unchanged from the previous year. However, the amount of cane crop actually delivered to crushers is estimated to come from only about 112,000 ha; the difference (about 70,000 ha) represents non-official deliveries utilized in manufacturing sugar cane syrup in small rural plants, or otherwise consumed fresh or not harvested due to infestation.

Many weed species can invade sugarcane fields causing, in many cases, a considerable loss in cane yield. Molisch (1937) proposed the term ‘allelopathy’ for expressing the harmful effects that one plant species may have on another through the mechanism of chemical retardants escaping into the environment. In other words, allelopathy is the direct influence of a chemical released from one living plant in the development and growth of another plant.

The definition of "Allelopathy" accepted by the International Allelopathy Society is 'any process involving secondary metabolites produced by plants, algae, bacteria and fungi that influence the growth and development of agricultural and biological systems' (Anonymous, 1996).

Chemicals that impose allelopathic influences are called allelochemicals or allelochemics. In a review of the potential use of allelochemicals as herbicides (Bhadoria, 2011), Putnam (1988) listed 6 classes of allelochemicals namely alkaloids, benzoxazinones, cinnamic acid derivatives, cyanogenic compounds, ethylene and other seed germination stimulants, and flavonoids which had been isolated from over 30 families of terrestrial and aquatic plants. All these chemicals possess actual or potential phytotoxicity.

Green plants are known to produce hundreds of thousands of compounds that are not involved in the primary metabolism of the plant (secondary products), the compounds involved in interspecific chemical interactions (allelopathy) with higher plants are often phytotoxic or herbicidal to other species or even to the species producing them (Duke, 1986).

However, according to Lavabre (1991), allelopathic effects are controversial and still poorly understood. Allelochemicals (inhibitors) are produced by plants as end products, by-products and metabolites and are contained in the stem, leaves, roots, flowers, inflorescence, fruits and seeds of the plants. Of these plant parts, leaves seem to be the most consistent producers of these allelochemicals.

According to Rice (1984) tens of thousands of secondary substances out of several hundreds of low molecular weight compounds of primary metabolism are known today, but only a limited number has been recognized as allelochemicals. Rainfall causes the leaching of allelopathic substances from leaves which fall to the ground during period of stress; leading to inhibition of growth and germination of crop plants (Rice, 1974; Mann, 1987).

The four ways in which allelochemicals escape from a plant are: (i) volatilization, during which the terpenes are released from the leaves of some plant species; (ii) leaching (which has shown that living or dead leaves of many plants contain growth inhibitors); (iii) exudation in which case roots of several crop and non-crop species release large quantities of organic compounds that inhibit the growth of other plants; and (iv) decomposition, through which allelochemicals are released from the plant residue (Sisodia & Siddiqui, 2010).



The aim of this work was directed toward investigating the possible occurrence of allelochemical(s) might present in weed aqueous extracts of the most common weeds in the area, i.e. Digitaria sanguinalis. Euphorbia geniculata and Cynanchum acutum on the germination and growth of sugarcane plants.

Materials and Methods


A completely randomized block design with three replicates was used to study the effect of aqueous extract of certain weeds on growth traits of cane "G.T. 54/9 variety" grown in polyethylene bags of 25 kg capacity. Planting was carried out using three cane segments (terminal – medial – basal) in each bag. Irrigation at planting was done using the aqueous extract of weeds while the control treatment was irrigated with water at equivalent amounts.

  1. Extract preparation

The tested weeds that represent the most common weeds in the area were: Digitaria sanguinalis, Cynanchum acutum and Euphorbia geniculata. Plants of these weed species were collected from the field, rinsed with water and cut into small pieces. 250 or 500 gm of the segment material were blended with water in an electric blender then squeezed through 4 layers of cheesecloth.

  1. Sugarcane characters recorded

After irrigation with the extracts, the following characters were recorded:

  • The average date of seedling emergence.

  • Plant length after 45 days from treatment.

  • Weight of green parts, root weight, number of green leaves, number of dry leaves, number of green and dry leaves (total leaves), plant length, average of tillering, and the average weight of each tillering after 90 days of treatment.

Results and Discussion


The average days for sugarcane seedling emergence, plant length after 45 days and root weight, plant length, weight of green part, number of green leaves, number of dry leaves, total leaves (green and dry leaves), number of tillers and weight of tillers as affected by weed aqueous extracts by 90 days after treatment are given in Table 1.

Table (1) : Effect of aqueous extracts of three weed species, on average days for sugarcane seedling emergence, plant length after 45 days from treatment and root weight, plant length, weigh of green part, number of green leaves, number of dry leaves, total leaves, no. of tillers/plant and weight of tillers by 90 days after treatment*.



No

Treatment

Conc.

Days for seedling emergence

Plant length after 45 days (cm)

Root weight after 90 days (gm)

Plant length after 90 days (cm)

Weight of green part after 90 days (gm)

Number of green leaves after 90 days

Number of dry leaves after 90 days

Total leaves after 90 days

No. of tillers after 90 days

Weight of tillers after 90 days (gm)

1

Digitaria sanguinalis

250 g/L

15.83b

16.33a

4.68a

25.44bc

48.33b

4.83b

2.82a

7.67a

1.50b

1.50c

2

Cynanchum acutum

250 g/L

15.67b

15.33ab

2.07c

26.33b

42.19b

5.00a

3.67a

8.67a

2.50ab

2.14c

3

Euphorbia geniculata

250 g/L

17.67b

12.67bc

3.53ab

15.50d

35.14b

5.83a

2.17a

8.00a

3.17a

3.60b

4

Digitaria sanguinalis

500 g/L

16.00b

12.83b

2.22c

23.67c

42.34b

6.17a

3.50a

9.67a

1.17b

1.32c

5

Cynanchum acutum

500 g/L

18.00b

13.00bc

2.80bc

24.00c

41.28b

6.50a

3.17a

9.67a

3.00ab

4.42b

6

Euphorbia geniculata

500 g/L

14.17b

16.00a

2.92bc

26.83b

42.05b

6.00a

3.00a

9.00a

2.67ab

6.20a

7

Control




25.83a

11.00c

2.16c

33.00a

73.13a

6.17a

3.33a

9.50a

2.17ab

7.13a

F Significance at


*

*

*

*

*


n.s.

n.s.

n.s.

n.s.

*



* Means within a column followed by the same letter are not statistically different using Duncan's multiple range test at 5% probability level.

  1. Days for cane seedling emergence

Data in Table (1) revealed that the extracts of weeds significantly affected the average days for cane seedling emergence. The extracts of weeds considerably enhanced seedling emergence (14-18 days) relative to the control treatment (25.83 days).

  1. Cane plant length after 45 days

Data in Table (1) revealed that the extract of the tested weeds significantly affected cane length after 45 days from treatment. All weed extracts gave taller plant length (12.7-16.3 cm) than the control treatment (11.0 cm). The tallest plants were recorded with D. sanguinalis low concentration (16.33 cm) followed by E. geniculata high concentration (16 cm) and C. acutum low concentration (15.33 cm).

  1. Cane root weight after 90 days

Data in Table (1) revealed that the extract of weeds significantly affected the root weight measured 90 days after treatment. The low concentration of D. sanguinals and E. geniculata extracts gave higher cane root weight (4.68 and 3.53 gm) than the control (2.16 gm). The other weed extract treatments gave slightly higher cane root weight than the control but with no significant difference.

  1. Cane plant length after 90 days

Data in Table (1) revealed that the extract of the weeds significantly affected cane plant length after 90 days from treatment. All treatments gave lower cane plant length (15.5 – 26.83 cm) than the control treatment (33.0 cm). The most inhibitory treatment was the extract of E. geniculata low concentration (15.5 cm) and the least inhibitory one was the extract of E. geniculata high concentration (26.83 cm).

  1. Weight of green part after 90 days

Data in Table (1) revealed that the extract of weeds significantly affected the weight of green part after 90 days from treatment. The weed extracts considerably reduced the weight of green part (35.14 – 48.33 gm) relative to the control (73.13 gm).

  1. Number of green leaves, number of dry leaves, total leaves and number of tillers after 90 days

Data in Table (1) revealed that the extract of weeds had no significant effect on the number of green and dry leaves, total leaves and average number of tillers.

  1. Weight of tillers after 90 days

Data in Table (1) revealed that the extract of weeds significantly affected the average weight of tillers after 90 days from treatment. The most inhibitory treatments were the extracts of D. sanguinalis (low and high concentrations) (1.50 – 1.32 gm), C. acutum low concentration (2.14 gm) followed by E. geniculata low concentration (3.60 gm) and C. acutum high concentration (4.42 gm); while the least inhibitory treatment was the extract of E. geniculata high concentration (6.20 gm) that had no significant difference with the control (7.13 gm).

The above mentioned results reveal the possible occurrence of certain stimulants in the aqueous extracts of the tested weeds that enhanced cane bud germination, cane plant length after 45 days and cane root weight after 90 days. Meanwhile, there is an evident of allelochemical(s) occurrence in these weeds, in terms of their effect on cane plant length, cane green part weight and weight of tillers after 90 days from treatment.

The inhibition effect was found to be increased with increasing concentrations of different aqueous extracts (Sisodia & Siddiqui, 2008, 2009). Some recent studies indicating the phytotoxic/allelopathic effect of aqueous extracts of weeds include Mikania micrantha (Ismail & Kumar, 1996), Vulpia sp. (An et al., 1999), Cyperus rotundus (Quayyaum et al., a2000), Cardaria draba (Kiemnec & McInnis, 2002), Parthenium hysterophorus (Batish et al., 2002a; Singh et al., 2003a), Brassica nigra (Tawaha & Turk, 2003), Raphanus raphanistrum (Norsworthy, 2003) and Ageratum conyzoides (Batish et al., 2002b; Singh et al., 2003b,c). All these studies indicate the release of phototoxic chemicals during the preparation of aqueous extracts.

To establish the cause and effect relationship of allelopathy one needs to demonstrate the production of allelochemicals by a given plant, their transport from this plant to the affected plants in the surroundings, and exposure of affected plants to these chemicals in sufficient quantity for a sufficient time to cause the observed allelopathy (Einhelling, 1995).

Biodegradable natural plant products rarely contain halogenated atoms and possess structural diversity and complexity, constituting one such class of chemicals and these can act directly as herbicides or may provide lead structures for herbicidal discovery (Duke et al., 2000). Selection of allelopathic plants is a good and commonly used approach for identification of plants with biologically active natural products (Duke et al., 2000).



The allelopathic compounds can be used as natural herbicides and other pesticides, they are less disruptive of the global ecosystem than are synthetic agrochemicals. Many important crops, such as rice, sugarcane are affected by their own toxic exudates or by phytotoxins produced when their residues decompose in the soil (Einhelling, 1995). Eliminating or preventing the formation of the phytotoxins through field treatments can minimize autointoxication. These treatments may be a combination of crop rotation, water draining, water flooding and the polymerization of phytotoxic phenolics into a humic complex.

Allelopathy is considered a natural phenomenon and may be employed as an alternative weed control technique. It is environmentally safe, can conserve the available resources and also may mitigate the problems raised by synthetic chemicals (Rizvi & Rizvi, 1992; Duke et al., 2001).

On the other hand, the organic chemical compounds having herbicidal properties may be combined with allelopathic water extracts at lower doses (Cheema et al., 2005; Iqbal & Cheema, 2007). This, on one side, may improve the efficacy of allelopathic extracts and may provide the opportunities of reducing the herbicidal doses on other. Hence the cost of weed control could be lowered and promoting sustainable environmental safety (Hussain et al., 2007).

For sugarcane crop, further studies still needed to identify the stimulants and allelochemicals might occur in the most common weeds in cane fields and to clarify their possible role in cane plantations.

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