​Influence of Zn, Fe and Ag Nanoparticles on Growth, Yield Attributes and Profitability in Tomato (Solanum lycopersicum mill)

Tomato is one of the most popular and widely grown vegetable in the world, has second position in importance after potato in many countries. In India, the estimated area and production of tomato is 0.81 mha and 20.57 mt respectively (NHB, 2019-20). Fresh fruits are the good source of potassium, folate, soluble and insoluble dietary fibers and minerals. Tomatoes are major contributors of antioxidants such as carotenoids (especially, Lycopene and β-carotene), phenolics, ascorbic acid (vitamin C) and small amounts of vitamin E in daily diets. Tomato is considered as an important protective food.
       
Despite all the technological, varietal and mechanization interventions in tomato cultivation, its productivity in the country is very low. The major constraints for low productivity include: climatic variations resulting in drought or excess water; increased pressure of diseases and pests; low adoption of hybrid; small farm holdings and limited resource availability; limited adoption of improved production-protection technologies; which deprives crop from proper nutrients, especially micronutrients availability. Unsustainable intensification accompanied by imbalanced soil nutrient management is one of the major causes of declining productivity of crops in the country. An increase in the productivity of a crop can be achieved either by increasing the area under cultivation or by increasing the productivity per unit area. Since the area is limited, yield level per unit area needs to be augmented to ensure food and nutrition security of nation. Micronutrients play a significant role in plant growth and metabolic processes associated with photosynthesis, chlorophyll formation, cell wall development, respiration, water absorption and resistance to plant diseases, enzyme activities involved in the synthesis of primary and secondary metabolites.

Innovation in development of new fertilizers and pesticides are required to provide sustainable agri-inputs for higher production of agricultural crops. Currently, Nanotechnology is working with the smallest possible particles which increase hopes for improving agricultural productivity through encountering problems unsolved conventionally and have the potential to change agricultural production by allowing better management and conservation of inputs of plant. It provide a great scope of novel applications in the plant nutrition fields to achieve the future request of the rising population because nanoparticles have exclusive physicochemical characters i.e. high surface area, high reactivity and tunable pore size. The ambition of nanoparticles in agriculture is to reduce the amount of spread chemicals, minimize nutrient losses in fertilization and increased yield through pest and nutrient management. The recent advances in nanotechnology and its use in the field of agriculture are astonishingly increasing therefore it is tempting to understand the role of Zn, Fe and Ag nanoparticles on growth and yield of tomato.

A field experiment was carried out during Rabi 2018-19 at the Protected Cultivation Unit of Department of Vegetable Science, College of Horticulture and Forestry, Jhalawar (Rajasthan). The tomato cv. Arka Rakshak was used as an experimental material for this study. Three nanoparticles viz. Zn, Fe and Ag NPs were used at four different concentrations (200, 400, 600, 800 ppm for Zn and Fe NPs) and (25, 50, 75, 100 ppm for Ag NPs) in the experiment. Synthesized different nanoparticles at different concentrations were suspended directly in deionized water and dispersed ultrasonic vibration (100 W, 40 KHz) for 30 minutes. Small magnetic bar was placed in the suspension for stirring through Ultrasonicator to avoid aggregation of the particles. Several suspensions of concentration range up to maximum possible limit were tried for uniform particle dispersion, stability and clear suspension (trial and error method). Tomato seeds were treated with mentioned concentrations of Zn, Fe and Ag NPs for 4 hour as well as control. After soaking, seeds were dried to near original moisture content and sown in pro-trays for raising seedling in nursery.
       
Field was ploughed by mould board plough twice and then levelled properly with heavy wooden planker to bring the field to a good tilth. Raised beds of 20 cm height and 1 m width were prepared with the space of 50 cm between the beds. Well decomposed vermicompost @ 5 kg/m² was uniformly mixed in the soil a fortnight before transplanting. The recommended dose of NPK fertilizers (150:100:120 kg/ha) were applied as basal dose. Nitrogen was given into two split doses, first as basal dose and another was given after one month of transplanting to each treatment plot. After that, 25 days old vigorous and uniform seedlings were transplanted on the raised beds according to treatment at the spacing of 60 × 45 cm in three replications. All the recommended package of practices was uniformly followed in all treatments. The necessary plant protection measures were adopted to raise healthy crop.
       
The observations on growth attributes viz. plant height (cm), number of leaves per plant, intermodal length (cm), shoot diameter (cm), number of flower/plant, days to 50 per cent flowering, total chlorophyll content at 45 and 90 DAT and yield contributing characters i.e. number of fruit set/plant, number of fruits/plant, fruit weight (g), fruit weight/plant (g), fruit yield/ha (kg), seed yield/plant (g) were recorded at maturity from randomly selected 10 plants from each treatment plots. B:C ratio was also computed by dividing gross returns with cost of cultivation for each treatment. The data on quantity observations recorded during the course of investigation for various characters were subjected to statistical analysis by adopting randomized block design (RBD) with three replications as per the technique suggested by Panse and Sukhatme (1995). Significance of difference in the treatment effect was tested through ‘F’ test at 5 percent level of significance.

Performance of growth attributes
 
Application of nanoparticles as seed treatment significantly influenced growth attributes in tomato (Table 1). Plant height was significantly increased with Zn NPs treated seeds (800 ppm) and treatments, viz. T₄, T₃, T₂ and T₁ registered higher plant height (144.2, 135.84, 133.2 and 129.78, respectively). The increased in plant height in Zn NPs treatment might be due to the enhanced biosynthesis of auxins (IAA) and better nutrient uptake activity, which lead to increase in plant height (Faizan and Hayat, 2019). The results are in conformity with the reports of Velasco et al., (2020) in tomato, siddiqui et al., (2014) in summer squash. Significantly higher number of leaves/plant (161.88), intermodal length (7.10 cm) and shoot diameter (1.98 cm) were reported in Zn NPs 800 ppm treatments than control (129.12, 4.34 cm and 1.21 cm, respectively). The significant increase in these attributes with application of Zn NPs could be due to enhanced photosynthesis and related attributes along with the CA activity. Moreover, ZnO-NPs enhanced the assimilatory rate of CO₂, increasing metabolism and enzymatic action which leads the increased cell division and ultimately enhanced growth and development of plant. These results are in conformity with the finding of Burman et al., (2013) in chick pea, Elizabath et al., (2016) in carrot, Mahdieh et al., (2017) in bean, Sarkar et al., (2017) in water spinach, Salama et al., (2019) in bean, Lopez et al., (2018) in pepper, Faizan and Hayat (2019) in tomato. NPs seed treatment particularly Zn NPs significantly increased the number of flowers/plant (Table 2). The significantly higher number of flowers was recorded in T₄ (129.42) followed by T₃ (121.29) and T₂ (116.65) than control (T₀) (80.12). This may be due to use of Zn nanoparticles helped in chlorophyll synthesis which increases in photosynthetic rate resulting more accumulation of carbohydrates leading to profuse flowering (Dhruve et al., 2018). The results are in conformity with the finding of Laware and Raskar (2014) in onion and Lopez et al., (2018) in pepper. Nanoparticles application changes the days taken to 50% flowering. Significantly lesser days taken to 50% flowering was observed in T₄ (38.87) followed by T₃ (39.84) and T₂ (40.18). However, Zn NPs application significantly reduced the days taken to 50% flowering which might be due to ZnNPs provided essential plant growth promoting substance which promoted reproductive phase resulting in lesser time required for 50 per cent flowering (Laware and Raskar 2014). The results are in agreement with the finding of Sarkar et al., (2017) in spinach and Kumar et al., (2017) in strawberry.
 

 


Significantly higher value of chlorophyll content (1.71 and 2.01 mg/100 g) in T₄ treatment (ZnNPs at 800 ppm) while, the lesser value of chlorophyll content (1.11 and 1.23 mg/100 g) was recorded in T0 (control) at 45 and 90 DAT respectively. However, the treatment T₃ (Zn NPs suspension 600 ppm) with 1.68 and 1.88 mg/100 g were found at par with treatment T₄ at 45 and 90 DAT respectively. The observed increases in the chlorophyll content are attributed to the fact that Zn plays an essential role in the activity of carbonic anhydrase enzyme that catalyzes the hydration of CO₂ that facilitates the diffusion of carbon dioxide to the carboxylation sites in plant. The similar results were also reported by Pullagurala et al., (2013) in coriander and Raliya and Tarafdar (2013) in cluster bean.
 
Yield contributing characters
 
The data presented in Table 2 showed that application of nanoparticles as seed treatment significantly influenced yield and yield contributing attributes in tomato. Yield contributing attributes i.e. number of fruit set/plant (117.99), number of fruit/plant (99.62), fruit weight (87.7 g), fruit weight/plant (8.7 kg), fruit yield (322.54 q/ha) and seed yield per plant (65.52 g)  were recorded significantly high under treatment T₄ (Zn NPs 800 ppm) and the minimum value for yield parameters i.e. number of fruit set/plant (68.73), number of fruit/plant (55.10), fruit weight (61.79 g), fruit weight/plant (3.39 kg), fruit yield (125.00 q/ha) and seed yield per plant (26.35 g) were recorded under treatment T₀. This might be due to better absorption of Zn NPs which ultimately increase more accumulation of photosynthates which were synthesized in the leaf and translocated towards the fruit and provide better environment for growth and developmental processes, thus, better results were obtained due to the availability of favorable conditions and more number of fruit set and development per plant. The similar results were also obtained by Kole et al., (2013) in bitter melon, Laware et al., (2014) in onion, Lopez et al., (2019) in pepper, Osman et al., (2019), Faizan and Hayat (2019) in tomato.

Seed yield per plant was significantly higher in treatment T₄ (Seed treated with ZnNPs at 800 ppm). The highest (65.52 gm) seed yield per plant was recorded under treatment T₄ while minimum seed yield (26.35) was recorded in T₀. It might be due to ZnNPs play a decisive role in improving the productivity of the crop. In fact zinc is recognized as key element in protein synthesis and also involved in various types of enzyme activity, carbohydrate metabolism nitrogen fixation that lead the higher number of seed per plant (Elham et al., 2020). The results are in conformity with the finding of Laware and Raskar (2014) in onion and Masuthi et al., (2009) in cowpea.
 
Cost of economics
 
The data regarding to net return and B: C ratio is presented in Table 3 and Fig 1 and showed that increase in net return and B: C ratio was obtained with application of nanoparticles. Treatment T₄ (Zn NPs 800 ppm) resulted maximum net profit of Rs. 259918.00 with B:C ratio (5.15), followed by Rs. 214693 net return and 4.42 B:C ratio under treatment T₃ (Zn NPs 600 ppm) than control (Rs. 62478.00 and 1.99, respectively).