Allelopathic Effect of Echinochloa colona L . and Cyperus iria L . Weed Extracts on the Seed Germination and Seedling Growth of Rice and Soyabean

The present study was undertaken to assess the allelopathic effect of Echinochloa colona L. and Cyperus iria L. in relation to the germination and primary growth of Oryza sativa L. (rice) and Glycine max L. (soyabean). Effects of dichloromethane (DCM) and double distilled water soluble (DDW) fractions of E. colona L. and C. iria L. root and aerial part extracts reduced germination and suppressed early seedling growth of rice and soyabean. With increase in extract concentration from 1 to 100mg/mL, a gradual decrease in seed germination and seedling length occurred. The highest growth of G. max seedling was recorded in DDW fraction of E. colona aerial part extract at 1mg/mL concentration with 94% germination and the lowest length was found in DCM fraction of C. iria root extract at 100mg/mL concentration with 65% germination. In O. sativa, the highest length was noted at 1mg/mL concentration in DDW fraction of E. colona aerial part extract with 82% germination and the lowest length was found in DCM fraction of C. iria and E. colona root extracts with germination 57% and 62%, respectively, at 100mg/mL concentration.The results suggested that these weeds had good allelopathic potential which reduces germination and plant growth.


Introduction
Allelopathy is the direct or indirect effect of plants with one another through producing chemical compounds [1].Allelopathic compounds generally occur in natural plant communities and are suggested to be one mechanism by which weeds interfere with crop growth [2].Several weed species are reported to have allelochemicals that affect germination and growth of crops due to toxicity [3].Allelopathic effects of weeds on rice as well as competition of weeds with rice for water, light, physical space, and nutrient thus reduce yield, lowering grain quality and cash value of the crop [4].
According to Karim et al. [5], the annual rice yield loss due to weed infestation is about 15-21%.Weed management has been a challenge for the rice farmers as weed is one of the major problems in rice production [6].Annual loss of 10 million metric tons of rice production due to weed competition has been reported from China [7].Rice grain yield loss of about 42% has been observed in uncontrolled field due to infestation of Fimbristylis miliacea [8].
The most important oilseed crop soyabean is grown worldwide.In soyabean, reduction of yield recorded more than 50% because of variety and intensity of weed [9].Soyabean and maize were observed to be sensitive to different weed species [10,11], while sorghum and sunflower showed allelopathic potential against weeds [12,13].
Cyperus iria L. is one of the three most common weeds of rice in Sri Lanka, India, and Philippines, reported by Holm et al. [14].It is found to be a host for several pests of rice and rice nematodes: Pratylenchus zeae and Hirschmanniella spinicaudata [15].Further, Criconemella onoensis is a rice nematode which uses C. iria as a host.Echinochloa colona is a common weed in many crops (mainly rice, maize, and vegetables), gardens, roadsides, disturbed sites, waste areas, and pastures.E. colona is often the dominant weed of rice.Holm et al. [14] have reported that E. colona is associated with 2 Advances in Agriculture 35 crops in more than 60 countries and is the second most common weed of rice.To the best our knowledge, no work has been done on allelopathic effect of E. colona and C. iria weed extract on rice and soyabean in Uttarakhand.Therefore, the present study was carried out to investigate the possible allelopathic effect of C. iria and E. colona extracts on seed germination and seedling growth of O. sativa and G. max.

Materials and Methods
2.1.Preparation of Plant Extracts.Field-grown rice (Oryza sativa L.) and soyabean (Glycine max L.) along with weed species Rice Flatsedge (Cyperus iria L.) and Cock Spur-Grass (Echinochloa colona L.) were collected from the agriculture fields of Nainital district.Plants were chopped into pieces with a fodder cutter and oven-dried at 48 ∘ C for 72 hours.The aerial and root part of weed species were crushed into powder form.Fifteen gram powdered plant material was suspended in 150 mL double distilled water (DDW) and dichloromethane (DCM) and mixed for 24 hours by a horizontal rotary shaker for producing uniform extract.The extracts were filtered through filter paper (Whatman number 1).

Experimental Treatments.
Three different concentrations of weeds, that is, 1, 35, and 100 mg/mL, with double distilled water (DDW) and dichloromethane (DCM) were taken to observe allelopathic effects of weed species on test crops in triplicates.

Experimental
Procedure.The germination of rice and soyabean seeds was studied by Petri dish method.Ten seeds of each test crops were placed in Petri dish lined with double layer of filter paper and treated with weed extracts in three concentrations.These Petri dishes were then kept for 7 days and 15 days for soyabean and rice, respectively, at room temperature (28 ± 1 ∘ C) and kept constantly moist with distilled water.After that seed germination and seedling growth were determined for different treatments.

Results
Results with respect to the effect of different concentrations of extracts on seed germination performance were measured in terms of growth.With increase in extract concentration, there was a gradual decrease in seedling length and germination percentage.The mean values of seed germination and seedling growth were observed maximum in aerial part extract as compared to root extract in test crops (Figures 1 and  2).

Effects of DDW and DCM Fractions of E. colona L. and C. iria L. Extracts on O. sativa L. and G. max. L. Seed Germination.
The allelopathic effect of the DDW and DCM extracts of E. colona and C. iria on the seed germination of rice and soyabean was given in Figure 1.It was noted that the germination was delayed by increasing the concentration.The time, at which germination started, was recorded maximum in rice as in comparison to soyabean.Among both weeds, rice showed the maximum reduction in seed germination (58%) when treated with root extract of C. iria with DCM fraction.Maximum percent germination was observed in soyabean seeds (94%) in DDW fraction and in DCM fraction (82%) at 1 mg/mL concentration of E. colona aerial part extract followed by rice seeds, that is, 82% with DDW fraction and 79% in DCM fraction.In C. iria aerial part extract, maximum seed germination was also observed in soyabean seeds (90% in DDW fraction and 88% in DCM) followed by rice seeds (79% in DDW and 74% in DCM).With increasing concentration a gradual decrease in germination percentage was recorded in the aerial and root part extracts of E. colona and C. iria (Figure 1).

Effects of DDW and DCM Fractions of E. colona and C. iria Extracts on Seedling Length of O. sativa and G. max.
The seedling length of rice and soyabean was significantly ( < 0.05) reduced by aerial part of E. colona in all three concentrations and at 100 mg/mL by root extracts (Figure 1).Seedling length of rice and soyabean was also significantly ( < 0.05) reduced by root part of C. iria at 100 mg/mL concentration.In C. iria root extract, seedling growth of soyabean at 1 mg/mL and rice at 35 mg/mL was significantly ( < 0.05) reduced.
Root extract of both weeds with DCM fraction had more adverse effect on the seedling growth of rice.In DDW fraction of both weeds, the seedling growth of soyabean (2.1 ± 0.1 cm) was observed to be the highest in aerial part extract of E. colona at 1 mg/mL concentration and lowest in root part extract of C. iria (0.7± 0.1 cm) at 100 mg/mL concentration.Similarly, in DCM fraction of both weeds, the seedling growth of soyabean (2.0 ± 0.3 cm) was observed to be the highest in aerial part extract of E. colona at 1 mg/mL concentration and the lowest in root extract of C. iria (0.6 ± 0.1 cm) at 100 mg/mL concentration.
In DDW fraction of both weeds, the seedling growth of rice (1.9 ± 0.1 cm) was observed to be the highest in aerial part extract of E. colona at 1 mg/mL concentration and the lowest in root part extract of E. colona (0.6 ± 0.1 cm) at 100 mg/mL concentration.Similarly, in DCM fraction of both weeds, the seedling growth of rice (1.8 ± 0.1 cm) was noted to be the highest in aerial part extract of E. colona at 1 mg/mL concentration and the lowest in root part extract of E. colona and C. iria both (0.4 ± 0.1 cm) at 100 mg/mL concentration.In control conditions the mean maximum seedling length was observed in G. max (2.8 ± 0.2 cm) compared to O. sativa (2.4 ± 0.2 cm).
The mean of rice seedling length was significantly different in all three concentration of E. colona aerial part extract (DDW and DCM) and in root part extract of C. iria (DDW).The mean of soyabean seedling length was observed to be  significantly different in all three concentrations of root and aerial part extract of E. colona (DDW and DCM) and aerial part of C. iria (DCM) (Figure 2).

Discussion
Seed germination and seedling growth were more affected by root extract with DCM fraction than the aerial part, whereas with increase in concentration from 1 to 100 mg/mL, there was a decrease in germination percentage and seedling growth.Germination of both crops was affected slightly by the lower concentration of weed extracts but at next one, the germination and seedling length of rice and soyabean were more affected by the highest concentration.
From the results, it appeared that the germination and primary growth differed significantly due to the effect of extracts of different plant parts of two weed species (Figures 1 and 2).Primary growth of soyabean seedlings was reduced significantly by the allelopathic effect of different plant parts.In DDW fraction, the highest mean growth of soyabean seedling was observed in E. colona aerial part extract at 1 mg/mL concentration and the mean lowest length was found in C. iria root extract at 100 mg/mL concentration.In DCM fraction of E. colona aerial part extract, the highest mean growth of soyabean seedling was observed at 1 mg/mL concentration and the mean lowest length was found in C. iria and E. colona root extract at 100 mg/mL concentration.
Rice seedling in DDW fraction showed the highest mean growth in aerial part extract at 1 mg/mL concentration and the mean lowest length was found in root extract of E. colona at 100 mg/mL concentration.While considering the DCM fraction, the highest primary growth of rice was observed in aerial part extract of E. colona at 1 mg/mL concentration and the lowest length was found in the root extract of E. colona and C. iria at 100 mg/mL concentration.
The results indicated that the effects of weed extracts on the test species were concentration-dependent.Our results agree with the findings of some earlier studies.Swain et al. [16] pointed out that rice root growth was completely inhibited with 10% w/v leachates of 60-day-old plant and that the decomposing and decomposed leachates reduced rice shoot growth by 57% and 84%, respectively, which indicated that lower concentrations can stimulate plant growth, while higher concentrations cause inhibition [8,17].This can be attributed to the fact that low dose of phenolic compounds stimulates protein synthesis and activation of antioxidant enzymes [18] which are effective in plant protection [19], while high levels of phenolic application result in plant damage [20].Ashfaq et al. in 2014 [21] reported that the interaction between C. esculentus and P. hysterophorus showed a significant effect on germination rate, plumule length, radicle length, fresh weight, and dry weight of seeds.Awan et al. [22] suggested that the growth of C. iria can be suppressed by high rice density (400 plants/m 2 ) even at high N rates.V. Singh and H. Singh [23] concluded that Caesulia axillaris Roxb.was found to be the most phytotoxic weed, followed by Echinochloa cruss galli L. Beauv and Echinochloa colonum L. Link, while Fimbristylis miliacea L. Vahl and Cyperus iria L. were observed moderate weeds of the rice fields.
The germination and seedling growth responses of rice and soyabean to root and aerial part extracts of E. colona and C. iria was significantly different.This uneven suitability to both extracts could be due to inherent differences in various biochemicals involved in the process.

Conclusion
The present study revealed that the extracts of E. colona and C. iria weed were highly effective against seed germination and seedling growth of rice and soyabean.From the above findings of the present experiment it could be suggested that E. colona and C. iria had strong and moderate detrimental effect on rice and soyabean, respectively.Results showed that seed germination and seedling growth were highly affected in rice, root part, and DCM rather than soyabean, aerial part, and DDW, respectively (Figures 3 and 4).There is a high need to carry out such type of studies to test the efficacy of these weed extracts under field conditions.Therefore, the cited weeds must be taken into better care and should be avoided in seed bed for growing rice and soyabean seedlings.Furthermore, the allelochemicals responsible for germination and growth reduction of different crops should be isolated and identified.

Figure 1 :Figure 2 :
Figure 1: Difference between germination percentage in DDW and DCM extract with respect to different concentration.
Figure 4: Effects of extracts E. colona and C. iria on seedling growth.