INVESTIGATING PLANT GROWTH AND PHYSIOLOGICAL RESPONSE TO SOIL WETTING WITH GREY WATER UNDER DIFFERENT SHADE REGIMES: A CASE OF FLUTED PUMPKIN (TELFAIRIA OCCIDENTALIS)
DOI:10.30825/5.EJPAU.31.2017.20.4

Beckley Ikhajiagbe¹, Geoffrey Obinna Anoliefo¹, Edokpolor O. Ohanmu², Gloria O. Omoregie³, Thomas Uwagboe^1
1 Environmental Biotechnology and Sustainability Research Group, Department of Plant Biology & Biotechnology, Univ. of Benin, Benin City, Nigeria
² Department of Plant Biology & Biotechnology, Edo University, Iyhanmo, Nigeria
³ Department of Environmental Management and Toxicology, Fed. Univ. of Petroleum Resources, Effurun, Nigeria

ABSTRACT

Limited supplies of freshwater are of concern worldwide. The ever growing demand for water for agricultural purposes warrants the need for alternative water sources for irrigational purposes. Soap-based grey water was used to irrigate fluted pumpkin plants (Telfairia occidentalis) at different frequencies of wetting for a period of 3 months; this was coupled with the concomitant effects of shading conditions. The results obtained showed that grey water had favourable effects on the growth and yield of Telfairia occidentalis, having little or no effect on the proximate content. With regard to yield, determined herein as number of leaflets, since the plant is majorly utilized for its leafy vegetable, was better under partial shade; no significant differences were recorded for leaf area under various shading conditions. Increased superoxide dismutase and catalase activities in higher plants, as reported in this study, is an indication of disturbed physiological stress condition, triggered by biotic stress condition. Thus grey water can serve as alternative source of irrigation while augmenting with fresh water.

Key words: grey water, physiological stress, Telfairia occidentalis, shading regime, proximate content, irrigation, water security.

INTRODUCTION

The world’s population increases at a steady rate, and nearly all the earth’s resources are overstretched to take care of this ever-growing burden. One of such resources is water. Today the world is facing an impending global water scarcity, particularly because the increased demand for water has led to the demand for newer and more distant sources of water  at greater depths, which leads to amplified environmental costs and economic exploitation. The obtainability of plentiful clean freshwater is no longer assured, even in “water-rich” countries like Canada. On a global scale, water scarcity is one of the most significant challenges to human health and environmental integrity. Although the world is covered mostly by water bodies, scarcity of water refers to low availability of useable forms of water, particularly freshwater. This results mainly from man’s activity which guarantees incessant contamination and removal of watersheds and waterbodies in the bid to erect buildings and other structures. As the world’s population grows and prosperity spreads, water demands increase and multiply without the possibility for an increase in supply. An estimated billion people lacking access to portable water worldwide [23] leads to the mounting demand on this finite and invaluable resource. This has inspired creative strategies for freshwater management, including innovative techniques for wastewater recycling. Grey water reuse is one of such strategy, and its usefulness to fulfil non-portable water needs should be thoroughly investigated.

In a report by the Food and Agriculture Organization in 2008, almost three quarters of freshwater consumption is devoted to agricultural operations and activities [15] and this adds more to the stress already created by global water scarcity. The only choice left would be to rely on alternative water sources to replace scarcely available freshwater sources in order to keep up with water demand and supply. Grey water is a wastewater derived from kitchens, bathrooms (i.e., discharges from shower, hand basin, bath), and laundry water. WHO [29] reports the use of grey water for agricultural purposes. Since grey water contains varying concentrations of macro- and micronutrients depending on the source, it has the potential to act as a diluted fertilizer [12].  As reported by Essay [14], reducing stress on the portable supply of water is the main benefit. But there are drawbacks to using waste material to grow plants because households have different proportions of additives that may affect plant growth. The risks are divided into three main categories: possible detrimental effects on the environment that decreases the ability for soil to provide plant growth, subsequent effects on plant growth and yield, and risk to human health.

In a period when available water resources dwindle, the management of wastewater for reuse is promptly becoming a matter of great awareness to researchers. Agricultural water needs imply a significant share of global water use, and wastewater reuse is an attractive alternative with good potential to supplement freshwater supplies. The grey waste water is considered not only a rich source of organic matter and other nutrients but also contains heavy metals like Fe, Mn, Cu, Zn, Pb, Cr, Ni, Cd and Co at high concentrations in receiving soils [19]; thus presenting the possibility of negatively impacting the plants on which it is used, as well as the soil biota, not mentioning biomagnification effects in humans. However, the use of grey water is more predicated on the fact that some of the farmers, particularly vegetable farmers, require regular water supplies to their farms in other to guarantee proper and better yield. One of such vegetable crops is the fluted pumpkin (Telfairia occidentalis), which is one of the most commonly sought-after leafy vegetable in tropical Africa. Therefore, as global water crisis intensifies, investment in alternative supply means for agriculture is imperative. This justifies the current widespread reuse of domestic greywater for irrigation of home gardens in many parts of the world. This is even more important given the widespread availability of fluted pumpkins in home gardens. Although the implications of reusing greywater to water edible crops remain uncertain, the aim of the study is to investigate morphological and physiological responses of Telfairia occidentalis to grey water wetting under varying shade conditions.

MATERIAL AND METHODS

The study was carried out in the Department’s of Plant Biology and Biotechnology Botanic Garden, University of Benin, Benin City, Edo State. The top soil (0–10 cm) was collected, sun-dried to constant weight, and measured into unperforated buckets (20 kg soil/bucket). Grey water was obtained by washing 1 kg of dirty clothes with 20 g of Premier® soap in 10 litres of tap water (pH 6.14–6.92). In this study, the term dirty clothes referred only to dirty T-shits that were worn twice before been sent to the laundry for dry-cleaning. The grey water was used within one week of preparation.

Initially, each bucket was saturated with greywater on the first day; thereafter the buckets were further subjected to periodic wetting with 1500 ml on a daily basis (D), twice a week (2DW), weekly (W), twice within a month (2WM), and monthly (M). The control buckets  (C) were wetted with tap water. The water-holding capacity (WHC) of the soil was previously determined prior to the study to be 293.42 ml/kg soil. Viable seeds of Telfaria occidentalis were sown at a depth of 5 cm below soil level and at a rate of 3 seeds per bucket, but later thinned down to one. These plants were placed under shade constructed to a height of 4m above ground with either cement roofing sheets or with thatched roofing. This therefore provided 2 major shading conditions for the plants – total shade (TS), partial shade (PS) and no-shade (NS) conditions respectively. TS was made possible by placing the plants under cement roof 4 m above ground; whereas, plants exposed to PS were placed under loose thatch roof cover made up of oil palm fronds, 4 m above ground. The third condition was the no-shade condition (NS), where plants were left in the open sun throughout the duration of the experiment. The plants were monitored for selected physical growth and morphological parameters. Foliar chlorophyll content index was measured with the aid of a chlorophyll content meter; CCM-200 plus, a non-destructive chlorophyll content measuring meter, which exploits the distinct optical absorbance characteristics of the chlorophyll in other to determine its relative concentration. The average meter reading of 5 leaves per plant was taken as the CCI.

Percentage foliar chlorosis, necrosis and senescence were determined as the percentage of the total number of leaves produced by the plants that showed significant levels of chlorosis, necrosis, and senescence. For chlorosis and necrosis, > 50% of foliar surface showed the symptoms before they were used to determine the aforementioned parameters.

Estimation of Superoxide Dismutase (SOD) was according to the methods of Misra and Fridovich [18]. Assay of catalase activity was by Sinha [24], whereas proximate contents were accprding to the methods of AOAC [3]; Pearson [21]. Results of the study were presented as means of 5 replicates. By means of the Duncan Multiple range  Test, Least significant differences between determined means were used as tool for mean separation (at 95% confidence limit). Pearson’s correlation coefficient was used in the study to establish bivariate correlationship among selected growth parameters of the test plant at 95% confidence interval. Similarly, linear regression models for these parameters, divided into dependent and independent variables were also presented. All statistical parameters in this study were carried out using the SPSS-16 Statistical Software Package®.

RESULTS

The present study investigated the beneficial as well possible inhibitory effects of grew water usage in the irrigation of fluted pumpkin. Comparative effects of shading have also been presented. The first part of the research was to determine the physicochemical composition of GW (Tab. 1); results showed chloride increases to as much as 12 times that of tap water and a total phosphate content wise that of tap water as well.

Table 1. Physicochemical parameters of materials used for the study

Parameters	Soil [mg/kg]	Grey water [mg/l]	Tap water [mg/l]
TSS	NA	4.04	1.00
Dissolved Oxygen	NA	1.52	0.96
Biochemical Oxygen Demand	NA	1.36	0.24
Chloride	NA	639.80	53.98
Total Phosphate	294.700	118.22	53.98
Available Phosphate	22.350	NA	NA
Nitrate	0.023	2.30	0.62
NA – not applicable

Some above ground plant parameters at 12 weeks have been presented on Table 2. The total number of leaflets per plant was 187 in the control (under total shade) compared to 202 and 224 in 2DW and 2WM respectively, both under total shade conditions. Statistically there were significant differences in the number of leaflets per plant (P < 0.05). There was significant reduction in leaflet area compared to the control (P < 0.05), with values ranging from 29.58 to 35.69 cm².

Table 2. Effects of greywater wetting and shading conditions on some above-ground parameters of Terferia occidentalis at 12 weeks

	No. of leaflets/ plant	Leaflet area [cm2]	Vine length [cm]	Length of longest root [cm]	Root dry wt. / plant [g]	Foliar chlorosis [%]	Foliar necrosis [%]	Senesced leaves [%]	Leaf chlorophyll content index
	Total shade (TS)
C	99.13	30.50	187.04	62.50	8.98	18.18	8.18	0.00	57.32
**D	0	1.33	77.12	11.23	1.76	100.00	100.00	PD	PD
2DW	78.41	36.83	202.12	43.08	11.19	21.63	19.23	0.00	48.32
W	87.17	23.29	189.24	46.87	5.13	29.52	28.57	0.00	42.43
2WM	72.25	29.38	224.13	68.55	14.46	21.32	16.67	0.00	43.23
M	60.42	24.95	147.43	74.09	9.46	25.26	15.79	0.00	36.25
	Partial shade (PS)
C	69.14	35.69	219.25	38.05	4.73	14.38	11.23	0.00	50.32
D	87.34	31.15	213.13	45.46	4.67	52.51	48.15	0.00	56.46
2DW	114.16	31.68	129.42	55.02	4.62	22.94	11.76	0.00	48.36
W	102.25	29.88	173.45	20.33	7.57	26.06	12.12	0.00	42.51
2WM	78.28	23.40	157.42	30.43	9.94	18.35	13.04	0.00	53.86
M	72.13	31.07	172.14	32.03	9.09	22.62	20.83	0.00	40.64
	No shade (NS)
C	84.61	29.58	153.24	52.25	7.23	8.06	0.00	0.00	59.05
**D	0	3.33	28.42	20.72	1.80	100.00	100.00	PD	PD
2DW	99.52	34.15	128.31	48.54	12.27	39.21	33.33	0.00	43.75
W	63.32	31.63	162.25	52.02	9.49	33.46	27.78	0.00	43.58
2WM	81.71	31.21	192.14	57.55	9.94	19.76	14.81	0.00	39.54
M	78.14	30.28	132.34	64.01	9.05	24.29	9.52	0.00	48.32
LSD (0.05)	12.53	7.56	21.58	13.26	3.65	5.96	17.63	0.00	17.31
**Parameter was taken at 8th week during which total plant death occurred. The is no significant difference (p>0.05) between any 2 mean on the same column which difference is less than the least significant difference (LSD) value at 95% confidence limit. C – control, D – daily wetting, 2DW – wetting twice a week, W – weekly wetting, 2WM – fortnight wetting, M – monthly wetting. PD – total plant death at 8th week.

As reported in this study, plants under daily wetting showed stunted growth and total necrosis. Percentage foliar chlorosis was recorded in the course of the study as the percentage of total number of leaves per plant that showed chlorosis. The same was for necrosis. Chlorosis was generally low in the control ranging from 8.06 to 14.38% under all shade conditions. Percentage foliar chlorosis was highest for plant wetted daily under total and no shade conditions respectively (100%); the plants reportedly dried out in the 8 week, amounting to 100% necrosis for both treatments.

There were no significant differences among values obtained for proximate content of pumpkin under the various experimental conditions (Tab. 3). The effects of GW wetting as well as shading proportions did not significantly affect foliar proximate content.

Table 3. Effects of greywater wetting and shading conditions on proximate contents of leaves of Terfaria occidentalis

Treatments	Moisture content [%]	Fibre content [g/100 g]	Fat content [g/100 g]	Crude protein [g/100 g]	Ash content [g/100 g]	Carbohydratecontent [g/100 g]
Total shade
C	84.09	5.20	4.80	3.20	0.94	1.77
D	PD	PD	PD	PD	PD	PD
2DW	84.54	5.53	4.80	2.32	0.96	1.65
W	85.50	5.57	3.90	2.53	0.90	1.60
2WM	84.21	4.69	4.70	3.48	1.20	1.72
M	78.92	7.80	5.38	3.23	1.84	2.83
Partial shade
C	81.40	7.69	4.21	3.31	1.20	2.19
D	82.28	6.80	3.94	2.56	2.10	2.32
2DW	83.64	7.39	4.00	2.69	0.91	1.37
W	84.29	5.21	4.36	2.73	1.30	2.11
2WM	81.19	6.30	5.61	2.83	1.97	2.10
M	85.53	4.38	3.84	3.29	1.22	1.70
No shade
C	84.88	4.69	4.72	3.18	0.90	1.63
D	PD	PD	PD	PD	PD	PD
2DW	81.12	7.73	5.84	2.58	1.00	1.73
W	83.33	6.85	4.81	2.70	1.18	1.13
2WM	85.88	4.82	3.72	3.17	1.13	1.28
M	81.01	7.85	3.92	3.39	1.86	1.97
LSD (0.05)	23.65	2.97	3.01	1.84	1.02	1.26
The is no significant difference (p>0.05) between any 2 mean on the same column which difference is less than the least significant difference value at 95% confidence limit. C – control, D – daily wetting, 2DW – wetting twice a week, W – weekly wetting, 2WM – fortnight wetting, M – monthly wetting. PD – Plant death at 8th week.

Results showed that SOD concentration in the leaves increased from 0.03 to 0.49 grams per protein in the control under total shade and from 0.01 to 0.56 gram per protein under partial shade; whereas an increase from 0.02 to 0.53 U/mg protein was observed under no shade in the control from 4 weeks to 12 weeks (Fig. 1). At 4 weeks the highest concentration of SOD was 0.08 U/mg protein and it was obtained from 2DW under total shade (0.08 U/mg protein) and M treatment under partial shade (0.08 U/mg protein). For catalase activity lower concentrations of catalase in the leaves of the test plant were obtained at the 4th week (13.83 to 19.56 U/mg protein) under the various experimental conditions (Fig. 2).

Fig. 1. Superoxide dismutase activity in the leaves of fluted pumpkin under experimental condition. C – control, D – daily wetting, 2DW – wetting twice a week, W – weekly wetting, 2WM – fortnight wetting, M – monthly wetting.

Fig. 2. Catalase analytical results on the leaves of fluted pumpkin. C – control, D – daily wetting, 2DW – wetting twice a week, W – weekly wetting, 2WM – fortnight wetting, M – monthly wetting.

Figure 3 shows foliar concentration of ascorbate at 12 weeks where results showed that under partial shade concentrations ranged from 454.48 to 559.31 mg per protein. These concentrations were not significantly different from those obtained under total shade (455.17 to 550.65 mg per protein) and under no shade conditions (454.14 to 549.66 mg per protein). For concentrations of proline in the leaves at 12 weeks (Fig. 4), results showed that concentrations were highest in the plants wetted weekly for the various shading conditions; total shade (2.18 mg per protein), partial shade (1.74 mg per protein) and no shade (4.62 mg per protein).  It was generally observed that proline concentrations was higher in the no shade conditions (2.28 to 4.62 mg per protein) compared to other shading conditions.

Fig. 3. Foliar concentration of ascorbate at 12 weeks. C – control, D – daily wetting, 2DW – wetting twice a week, W – weekly wetting, 2WM – fortnight wetting, M – monthly wetting.

Fig. 4. Foliar concentration of proline in the leaves at 12 weeks. C – control, D – daily wetting, 2DW – wetting twice a week, W – weekly wetting, 2WM – fortnight wetting, M – monthly wetting.

There was highly significant (p<0.01) positive correlation between percentage chlorosis and percentage necrosis (r = 0.933); and indication that a possible chlorotic lesion in the leaves of the tested plant may positively imply necrosis (Tab. 4). Similarly, there was positive correlation (p<0.05) between percentage necrosis and foliar ascorbate activity (r = 0.493). However, correlationship was negative between leaf area and SOD activity (r = -0.591, p<0.05), implying that an increase in leaf area of the tested plant implied a reduced SOD activity in the leaves (Tab. 4).

Table 4. Pearson’s correlation coefficient establishing bivariate correlationship among selected growth parameters of the test plant

	LFAR	VNLT	CHLO	NECR	CCI	RTLN	RTWT	ASC	PRO	SOD
VNLT	0.19	1
CHLO	0.046	0.007	1
NECR	0.07	0.209	0.933**	1
CCI	0.125	0.095	-0.131	-0.151	1
RTLN	-0.111	-0.117	-0.043	-0.116	-0.114	1
RTWT	0.066	-0.017	-0.097	-0.065	-0.323	0.2846	1
ASC	0.274	-1E-04	0.5122	0.493*	0.1866	-0.327	-0.356	1
PRO	0.157	-0.337	0.2622	0.2404	-0.104	0.0121	0.1871	0.348	1
SOD	-0.591*	0.076	0.1811	0.1491	-0.021	0.0804	0.121	-0.152	-0.111	1
CAT	-0.063	0.056	0.2886	0.1011	0.257	0.0824	-0.587*	0.383	-0.32	0.176
*. Correlation is significant at the 0.05 level (2-tailed). **. Correlation is significant at the 0.01 level (2-tailed). LFNM – No. of leaves/plant; LFAR – Leaflet area; VNLT – Vine length; INTD – Internodal distance; CHLO – Percentage foliar chlorosis; NECR – Percentage foliar necrosis; CCI – Chlorophyll content index; RTLN – Length of longest root; RTWT – Root dry weight; ASC – Foliar ascorbate content; PRO – Proline content; SOD – Superoxide dismutase content; RTBR – Number of primary root branches; CAT – catalase activity.

The linear regression models for both positively and negatively correlated parameters have been presented (Tab. 5). With an adjusted squared correlation of 0.862, the linear regression model y = 1.046x – 7.789, is reliable to predict the future outcome of percentage foliar chlorosis (x) as long as the independent variable (percentage necrosis, y) was known. The linear regression models for establishing predictive relationship between leaf number and ascorbate activity was not entirely reliable with a low adjusted R. Sq. linear (Tab. 5).

Table 5. Presentation of linear regression models for selected dependent (y) and independent variables (x)

Variables	Regression model	R	R Square Linear	Adjusted R Square
CHLO(x), NECR(y)	y = 1.046x – 7.789	0.933**	0.871	0.862
LFNM(x), ASC(y)	y = 1.046x + 389.381	0.4912*	0.242	0.188
LFAR(x), SOD(y)	y = 1.092 – 1.016x	-0.591*	0.349	0.303
NECR(x), ASC(y)	y = 1.803x + 473.689	0.493*	0.243	0.188
RTWT(x), CAT(y)	y = 184.515 – 3.661x	-0.587*	0.345	0.298
*. Correlation is significant at the 0.05 level (2-tailed). **. Correlation is significant at the 0.01 level (2-tailed). R – Pearson’s correlation coefficient.  LFNM – No. of leaves/plant; LFAR – Leaflet area; CHLO – Percentage foliar chlorosis; NECR – Percentage foliar necrosis; RTWT – Root dry wt; ASC – Foliar ascorbate content; SOD – Superoxide dismutase content; CAT – catalase activity.

DISCUSSION

The present study investigated the beneficial as well possible inhibitory effects of grew water (GW) usage in the irrigation of fluted pumpkin. Comparative effects of shading have also been presented. The first part of the research was to determine the physicochemicals composition of GW; results showed chloride increases to as much as 12 times that of tap water and a total phosphate content wise that of tap water as well. Beaver [5] showed that GW was rich in chloride and phosphate contents. According to the author, these nutrients, when managed properly are important inputs in homestead farming.

The physicochemical composition of GW reveals the possibility for either improvement or retardation of plant development. There is the tendency for GW to raise soil alkalinity and salinity as well as a reduction in the ability of soil to absorb and retain water owing to increased sodium and chloride contents [9]. According to Anwar [2], increased concentration of GW contributes to higher Electrical Conductivity (EC). The EC of aqueous solution indicates the presence of salt and hence the salinity of the soil. However, in this study, EC was higher with daily application of GW to soil; thus implying that the regularity of GW application to soil may have direct implications for the soil’s EC. Generally, after harvest of test crop, EC was higher in the GW-impacted soils compared to the control, confirming the statement of Anwar [2]. There were no comparable changes in soil pH of GW-impacted soils compared with the control soil. The pH of the soil was generally within 6–7. However, it was expected that pH of the GW-wetted soils would increase with impact because of the rapid changes of soil hydraulic properties due to GW.

Having exposed the test plants to GW and the various shading conditions, it was noticed that the plants in the full glarer of sunlight that received daily wetting with GW showed stunted growth. Similarly, plants under total shade and wetted daily also were stunted. These plants eventually became totally necrotic.

Build-up of toxic ions due to increased concentration of GW in soil may be one of the reasons for phytotoxicity. Although reports on the possible effects of GW on plants due to ion toxicity are sketchy, Christova-Boal et al. [7] suggested that high pH and high concentrations of sodium, zinc and aluminium ions in GW may reduce plant growth with direct and indirect effects on soil properties. The effects of surfactants present in GW on the water use efficiency of plants have been reported [1, 11, 22, 25, 30]. These surfactants, which are found as residues of GW, have the capability to significantly modify the hydraulic conductivity of soils [1, 22], thereby making the soils to become water-repellent [22, 30]. This generally affects the plant’s water use efficiency, and may have grave implications for water shortage in plants that are continually exposed to GW. As reported in this study, plants under daily wetting showed stunted growth and total necrosis.

CSBE [9] reported that owing to the presence of harmful constituents like boron, chlorides and peroxides, GW-exposed plants show some degree of phytoxic symptoms. For example, plant impairment from exposure to disproportionate quantities of boron is primarily exhibited by a burnt appearance to the edges of the leaves. Other symptoms of boron toxicity include leaf cupping, chlorosis, and premature leaf drop and reduced plant growth [9]; these were observed in a number of old leaves. Although some authors have attempted to show phytotoxic effects of GW to plants, the basis of GW toxicity is not clearly understood, particularly given the instance where improved plant growth performance was recorded in some treatments in the present study. In terms of yield due to foliar composition, those plants that were exposed to GW on a fortnightly basis had the highest number of leaves per plant. This was under total shade. Under partial shade as well as total exposure the test plant had the least number of leaves per plant. This therefore underscores the Signiant impact of shading in fluted pumpkin farming, as is the usual practise in this part of the world.

Under total shade, plant wetting with GW on a fortnight basis enhanced total plant development. These plants had better leaf size, longer vine length, and least presentation of foliar chlorosis. However, the effects of shading were significant. Generally, plants under no-shade condition were the least in growth and yield performance. The importance of shading in the cultivation of fluted pumpkin is therefore emphasised. Olaniyi and Odedere [20] had earlier opined that conditions that significantly favour the cultivation of fluted pumpkins were a loose, friable soil with ample humus and shade.

There were no significant differences among values obtained for proximate content of pumpkin under the various experimental conditions. The effects of GW wetting as well as shading proportions did not significantly affect foliar proximate content. Effiong et al. [10] reported foliar moisture content of 84%, which compares favourably with the results of the present study (78–85%). However, lower fat contents as well as crude protein were reported in the present study compared with that reported by Effiong et al. [10].

GW, being rich in chloride and sulphate ions as well as in some metals such as Na, B, K, Cu, Co, Cd and Zn, suggest salinity effects in soils upon impact. Salinity stress disrupts the equilibrium in water potential and ion distribution, both on cellular and on whole-plant scales [13]. One of such effects is conformational alteration in protein structure, although the clear-cut underlying mechanisms are not wholly implicit because plant resistance to salinity-induced stress is a multigenic trait [13].

Apart from the possibility for salinity initiation, constituent heavy metals found in GW-impacted soils can also induce oxidative stress which can disrupt normal physiological and cellular functions [6, 27]. Most oxidative stresses result from the accumulation of reactive oxygen species (ROS) like superoxides, hydroxyl radical and singlet oxygen, triggered by the presence of heavy metal in toxic concentrations. However, most plants have evolved various enzymatic and non-enzymatic antioxidant systems which can protect such plant from the toxic action of various ROS. In the present study, the accumulation of proline and ascorbate, as well as superoxide dismutase and catalase, in response to possible stress imposed by GW was determined.

Without taking into cognisance the effects of shading, proline concentration in the GW-exposed plants were higher than the control. This is a typical non-enzymatic defence response against plant damage occasioned by a wide range of stressors such as excessive salinity, as imposed by GW exposure [28]. GW-exposed plants are most likely exposed to metals, which are constituents of GW. Clemens [8] suggested that HM-induced Proline accumulation in plants is not directly emanated from HM stress, but water balance disorder. In this regard, Proline functions as an osmoregulator or osmoprotectant.

Similarly, accumulations of ascorbic acid in plant leaves were indicated by increased exposure of the plant to GW. Athar et al. [4] reported ascorbic acid to be very effective in promoting growth of maize plants under saline stress. Generally, SOD levels in the plant leaves were higher in GW-exposed plants than in the control. This confirms the findings of Hoque et al. [16] that superoxide dismutase activity under salt stress increased, particularly with concomitant increase in proline levels. The authors also reported reduction in catalase activity. This is similar to the results of the present findings. Jaleel et al. [17] and Sulochana et al. [26] also reported reduced catalase activity in catalase activity chloride-stressed plants.

CONCLUSIONS

• The significant impact of GW wetting as well as shading on the growth and development of pumpkin reveal effects mainly on plants morphology than in its proximate content.
• Exposing fluted pumpkin to partial shading rather than total or no shade conditions, seems better for plant total growth and foliar yield.

Acknowledgements

The researchers are grateful to Mr Osazuwa Omoregbee for his lab assistance. The study was funded by the authors.

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Accepted for print: 21.11.2017

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Beckley Ikhajiagbe
Environmental Biotechnology and Sustainability Research Group, Department of Plant Biology & Biotechnology, Univ. of Benin, Benin City, Nigeria

email: beckley.ikhajiagbe@uniben.edu

Geoffrey Obinna Anoliefo
Environmental Biotechnology and Sustainability Research Group, Department of Plant Biology & Biotechnology, Univ. of Benin, Benin City, Nigeria


Edokpolor O. Ohanmu
Department of Plant Biology & Biotechnology, Edo University, Iyhanmo, Nigeria


Gloria O. Omoregie
Department of Environmental Management and Toxicology, Fed. Univ. of Petroleum Resources, Effurun, Nigeria


Thomas Uwagboe
Environmental Biotechnology and Sustainability Research Group, Department of Plant Biology & Biotechnology, Univ. of Benin, Benin City, Nigeria

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