EFFECTS OF HEAD PRUNING AND DIFFERENT NUTRITIONAL SYSTEMS ( CHEMICAL , BIOLOGICAL AND INTEGRATED ) ON SEED YIELD AND OIL CONTENT IN MEDICINAL PUMPKIN ( CUCURBITA PEPO L . )

To evaluate the effect of head pruning and different nutritional systems (chemical, biological and integrated) on yield and seed oil content in medicinal pumpkin (Cucurbita pepo L.), an experiment was conducted in Kermanshah/Iran during the 2013 growing season. The experimental treatments consisted of two levels – no head pruning, control (Co) and head pruning (C1) allocated to the main plots. Four levels of different fertilizing systems – control (without fertilizer) (T0), chemical (T1), biological (a combination of nitrogen fixing bacteria, Azospirillum brasilense and Glomus mosseae) (T2), and integrated fertilizing system (biological fertilizer + 50% chemical fertilizer) (T3) were assigned to the sub-plots. The experimental treatments were arranged as a split plot based on a randomized complete block design with three replications. The results showed that the highest percentage of seed oil was obtained (37%) in the integrated nutritional system along with the head pruning treatment. The highest grain yields of 53 and 50 g per square meter were obtained in integrated and chemical fertilizing systems, respectively while no pruning was applied. The highest fruit yields of 3,710 and 3,668 kg per hectare were produced by chemical and integrated fertilizing systems, respectively. The biological nutrition system required more time to demonstrate its positive effect on the growth and yield of medicinal pumpkin.


Introduction
Medicinal pumpkin (Cucurbita pepo L.) is an annual and one of the most important oil seed plants of cucurbitaceous family.It is native to tropical and subtropical regions (Gong et al., 2012).The highest percentages of protein and oil in pumpkin seed, reflecting the importance and the nutritional value of the product, have been reported in literature (Mohamed et al., 2009).
A low-input sustainable agricultural system can stabilize and maintain the health of environment (Ibrahim et al., 2013).The over-utilization of chemical fertilizers has caused environmental pollution, ecological damage as well as significant increases in crop production costs.Continuous and sustainable production of healthy food along with environmental health issues have been the major concern of farmers, researchers, politicians and policy makers in recent years (Horrigan et al., 2013).Khorramdel et al., (2010) stated that inoculating Nigella sativa seed with Azotobacter, Azospirillium brasilense and mycorrhiza increased the growth and net assimilation rate in the crop.Seed inoculation by mycorrhiza fungi and its positive effect on the growth and yield of some crops like peppermint, tomatoes and corn have been reported by some researchers (Pourhadi, 2012).Numerous researches have been focused on the synergistic impacts of integrated inoculation of phosphorus solubilizing bacteria and Mycorrhiza on the growth and development of a diversity of crops under different environmental conditions (Zarei et al., 2006).Jahan et al. (2011) reported that biological fertilizers increased protein and oil yield on pumpkin.Also, other researches have showed that the integration of biological fertilizers and manure application will result in the highest protein, oil yield and fresh fruit in the plant (Aghaee et al., 2013).Gholipoori et al. (2007) reported that head pruning had a positive effect on fruit number per plant and seed yield in pumpkin.They also indicated that head pruning between nodes 10 to 14 would have a significant positive effect on the oil and fatty acid concentrations in the plant (Gholipouri and Nazarnejad, 2007).Moradi et al. (2011) reported that sole application of Azotobacter sp. and Pseudomonas sp. would contribute to an increase of 38% and 23% in the economic performance of fennel, respectively.The study of Shabani et al. (2012) on pumpkin showed that the highest fruit yield, seed yield and 1,000-seed weight were obtained when an integrated biological fertilizer was applied along with pruning of head stems.The study results emphasized the positive synergistic effects of biological fertilization along with head pruning to achieve remarkable results in pumpkin production.This study was conducted to evaluate the pruning management and different fertilizer applications on qualitative and quantitative characteristics of pumpkin.

Material and Methods
The experiment was carried out at the Academic Centre for Education, Culture and Research (ACECR), Kermanshah, Iran during the 2013 growing season.The elevation of the site was 1,300 m above the sea level.Soil samples were taken from the top layer of the soil (0 to 30 cm) for the physical and chemical properties (Table 1).
The experimental treatments were arranged as a split plot based on a randomized complete block design with three replications.The experimental treatments consisted of two levels -no head pruning control (Co) and pruning of head (C 1 ) allocated to the main plots.Four levels of different fertilizing systemscontrol (without fertilizer) (T 0 ), chemical (T 1 ), biological (a combination of nitrogen fixing bacteria of Azospirillum brasilense and Glomus mosseae) (T 2 ) and integrated fertilizing system (biological fertilizer + 50% chemical fertilizer) (T 3 ) were assigned to the sub-plots.The plot size was 4 rows of planting (2 m apart) in each experimental plot (8×4 m).Seeds were inoculated in a plastic bag and mixed slowly with a biological fertilizer at room temperature.The amount of the chemical fertilizers (Ammonium phosphate, 16% N, 20% P 2 O 5 at a rate of 500 kg/ha, and urea, 40 kg per 100 litre) in corresponding treatments were calculated based on soil test (Shabani et al., 2012).Phosphorus fertilizer was applied in bands along with each planting line.The seed was sown in late May.Urea application was split and applied in two stages of planting time and blooming stage, on July 15.Seeds were planted by hand at a depth of 5 cm.The first irrigation was applied immediately after planting, while the second irrigation was done three days later.Other irrigation cycle was done weekly (Shabani et al., 2012).The crop was harvested in early September and the measured characteristics included the main stem length, length of lateral branches, and number of lateral branches, 1,000-seed weight, seed yield, fruit yield, and seed oil content.For the purpose of determining the seed oil content, the method by Ghavami and Ramin (2007) was used.
Data was subject to anova using PROC GLM of SAS.When F test showed significant differences, LSD test (p<0.01)was used for means comparison.

Results and Discussion
There was a highly significant (p<0.01)difference between different levels of pruning on the fruit and seed yields.The effect of different nutritional levels on all measured traits was highly significant (p<0.01).The interaction effect of pruning and fertilizer systems on the 1,000-seed weight (p<0.01) was also highly significant.Our findings were also supported by Jahan et al. (2011) and Aghaee Okhcholar and Hassanzadeh Ghorttapeh (2013) who reported the positive effects of different levels of integrated biological and chemical fertilizers on yield and yield components of pumpkin.

1,000-seed weight
The chemical nutritional treatment (125 g) and integrated fertilizing system (121 g) produced the highest 1,000-seed weight (Table 2).It has been reported that the effect of pumpkin stem pruning significantly increased the yield, which supports the findings of this study (Gholipoori et al., 2007;Omidbeygi et al., 2006;Ebadi et al., 2006 andKermani Poorbaghaiy et al., 2014).
In addition, some positive effects of integrated fertilizers and stem pruning on 1,000-seed weight of pumpkin have been reported by Shabani et al. (2012).The available nitrogen in chemical and integrated fertilizers plays an important role in metabolic processes and contributes in plant metabolism leading to an increased rate of dry matter accumulation in plant tissues and seeds (Hamzei and Najari, 2012).
Azotobacter sp. and Azospirillium brasilense by increasing nitrogen availability to the plants can play an important role in increasing the 1,000-seed weight.These probiotics also contribute to higher photosynthesis rate in leaves and stems.The chemical and integrated nutritional systems in both pruning and nonpruning treatments significantly increased the 1,000-seed weight compared to other treatments.These results could probably indicate the higher availability of essential nutrients in these fertilizers.There was a synergetic interaction effect of fertilizing and head pruning on the number of lateral stems and levels of photosynthesis, which could explain the higher 1,000-seed weight.The results reported by Shabani et al. (2012) on the effect of nutritional systems and stem pruning on pumpkin are in line with the results of this study.

Fruit yield
The chemical (3,710 kg/ha) and integrated (3,668 kg/ha) fertilizers significantly produced more fruits than biological and control treatments (Table 2).Also, the interaction effect of pruning with chemical and integrated fertilizers produced the highest fruit yields of 3,899.37 and 3,853.87kg per hectare, respectively (Table 3).The minimum fruit yield of 2,755.3kg per ha was produced in the control treatment (no fertilizer and no pruning treatment) (Table 3).Increasing the number of fruits due to the increased number of female flowers has been reported by Gholipoori et al. (2007).The formation of the first fruit acts as the physiological destination for photosynthetic assimilates which prevents the formation of the next fruit.Munir et al. (2007), assessing the different nutritional treatments of organic, chemical and integrated fertilizers on sunflower, reported the highest grain yield, oil and protein content in the integrated fertilizer treatment.

Seed yield
The highest seed yield was obtained in the chemical (53.23 g/m 2 ) and integrated (50.40 g/m 2 ) fertilizer systems (Table 2).The interaction effect of both chemical and integrated fertilizer treatments with non-pruning of head provided significant advantages by producing 59 and 53 g/m 2 of seed, respectively.The control treatment (without pruning of head) produced the lowest seed yield of 39.33 g/m 2 (Table 2).The chemical and integrated fertilizers, by providing the necessary nutritional elements for growth and development, had a remarkable effect on increasing the number and length of lateral stems (due to pruning of head).This will contribute to a significant increase in the level of photosynthesis in the plant and increase the size and the number of the pumpkin fruits leading to higher seed production.According to the present results, the effect of pruning of head of the main stem was significant on all measured traits of the pumpkin except for the mean fresh fruit weight, number of seeds per fruit and 1,000-seed weight.In contrary to our findings, the results reported by Gholipoori et al. (2007) and Ebadi et al. (2006) showed that pruning of head provided the highest number of fruits per plant, fruit and seed yields by the lopping treatment, after forming the 12th node on the main stem.These differences may be due to the timing and the site of cutting of the main stem and the interaction of other corresponding treatments.The results of Aghaee Okhcholar and Hassanzadeh Ghorttapeh (2013) showed that the integrated application of biological and manure fertilizers produced the highest yield of fresh fruit per plant in pumpkin, which supports the results of this experiment.Jahan et al. (2011) also reported the positive and significant effect of different organic fertilizers on fruit and seed yields of pumpkin.The application of bio-fertilizers increased the seed yield of lentil and its components because of the hormonal activities by probiotic bacteria which stimulated the vegetative growth (Zahir et al., 2004).

Seed oil content
The chemical and integrated fertilizer systems across pruning treatments produced 33.38 and 35.30% of oil, so that the ratio of these treatments to biological and control treatments was highly significant (Table 2).The interaction effect of pruning and integrated fertilizing system produced the highest oil concentration of 36.38.The lowest oil content was produced in the control treatment (no fertilizing application) with and without pruning of head (18.22 and 18.94%, respectively) (Table 3).Different nutritional treatments contain different amounts of nutritional ingredients.The availability of nutritional elements in different nutritional treatments causes a significant difference on oil formation and concentration in oil seed plants.That is why the stem pruning of head was not much effective as the nutritional treatments were on oil content of pumpkin seed in this study.The nutritional treatments of chemical and integrated fertilizer systems have had the same effect on this trait.The combination of pruning of head and integrated fertilizer was the best treatment for oil content, indicating the positive effects of bacteria and Mycorrhiza inoculation on this trait.It is suggested that probiotics adjust the physiologic and metabolic activities in plants resulting in better performance and growth (Ram Rao et al., 2007).Our results on pumpkin seed oil in this experiment supported the findings by Aghaee Okhcholar and Hassanzadeh Ghorttapeh (2013).However, Omidbeygi et al. (2006) reported that seed oil content is not affected by pruning of head.But in another study on pumpkin, the effect of stem pruning of head nodes of 10 to 14 was significant on oil and fatty acids (Gholipouri and Nazarnejad, 2007).
The interaction results showed that the highest oil content was seen in the integrated fertilizer system and pruning of head.The same treatment on lateral stems caused a significant increase in photosynthesis level and thereby the number and size of fruits.The 1,000-seed weight and oil content are highly correlated to the fruit yield.Not only may the correlation coefficient depending on the conditions and treatments vary, but also similarly to the present results, Naeemi et al. (2012) reported that a positive and significant relationship between 1,000-seed weight and seed yield of pumpkin was affected by organic fertilizer treatments.

Conclusion
According to the results of this experiment, the integrated fertilizer system and pruning of the medicinal pumpkin plant head could improve the qualitative and quantitative characteristics of the fruit and its seed yield.Our results showed that the application of integrated fertilizer to substitute the chemical fertilizers could provide the nutrients needed for pumpkin to achieve its optimum growth.Based on the results of this experiment, it can be stated that using the chemical and integrated fertilizer systems along with the pruning of head played a significant role for the grain yield and oil content in pumpkin.It was shown in this study that combining biological and lower amounts (50%) of chemical fertilizer under favourable conditions will lead to increased pumpkin crop quantity and quality.

Table 1 .
Selected physical and chemical characteristics of soil (0-30 cm depth) in the experimental site.

Table 2 .
The main effects of treatments on the traits.
3 : Different nutritional systems, C 0 and C 1 : No pruning of head and pruning of head.Means with the same letter in each column are not significantly different at 5% probability level.

Table 3 .
Interaction between nutritional systems and pruning of head on the traits.Different nutritional systems, C 0 and C 1 : No pruning of head and pruning of head.Means with the same letter in each column are not significantly different at 5% probability level.