Effect of nano zinc oxide on morpho physiological yield parameters and quality of finger millet [Eleusine coracana (L.) Garten.]

Introduction

Millets are popularly known as nutri-cereals as they provide most of the nutrients required for human body. These are highly nutritious, non-gluten, acid free having many nutraceutical and health promoting properties. These are the imperative food and fodder crops in semi-arid regions with higher efficiency of water that are gaining more relevance in the world. Millets are an often over looked staple food for millions living in the harshest, food-insecure regions of the developing world. Millets represent a diverse group of small-seeded grasses grown for food, feed or forage. Millets are extraordinarily tolerant to drought and other abiotic stresses viz., high temperatures and poor fertile soils. This makes them "climate smart" and often a good source for genetic characters that can strengthen the resilience of other crops in the scenario of climate change. Millets are known to provide many vitamins such as vit E and vit B which are essential and micronutrients that can support nutrition for those living in dryland areas particularly women and children. Millets are also rich source of phytochemicals which act as antioxidants and detoxifying agents. According to the data from the US Department of Agriculture's Foreign Agricultural Service, as of Febrauary 2023, India produced 39% of the millets worldwide of the year 2022.India produced about 120 Lakh tonnes produced globally in 2022. Among the micronutrients, zinc (Zn) is considered as the major limiting micronutrient which limits the crop yields. Zinc has role in diverse physiological functions in biological systems. Zinc is typically the second most abundant transition metal in organisms after iron and the only metal represented in all six enzyme classes viz., oxidoreductase, transferases, hydrolases, lyases, isomerases and ligases (Auld, 2001) [5] . Further around 200 enzymes responsible for growth, development, immune function and resistance to infections are regulated by zinc in plant system. Hence, zinc deficiency in soils may cause lower yield or sometimes crop failure and poor accumulation of zinc into grains and thus may lead to zinc malnutrition in human. Zinc deficiency in soils strongly correlates to zinc deficiency in humans. Finger millet crop is frequently referred as a "Pandora box of nutrients" for better health because the grains are enhanced with various significant nutritional benefits with 65-75 percent carbs, 15-20 percent dietary fibre, 5-8 percent protein, and 2.5-3.5 percent minerals, finger millet grains are incredibly nutrient-dense. Finger millet, an orphan crop, possesses immense potential in mitigating climate change and could offer threefold security in terms of food, fodder and nutrition. Government of India had proposed to United Nations for declaring 2023 as International Year of Millets (IYoM). The proposal of India was supported by 72 countries and United Nation's General Assembly (UNGA) declared 2023 as International Year of Millets on 5th March, 2021. Nanotechnology is considered the potential solution for solving various agricultural problems and increases agricultural productivity through various delivery agents like nanopesticides, nanofertilizers. Nano particles afford 'magic bullets', which comprise chemicals, and herbicides or genes that target specific crop components for the proclamation of their content (Periakaruppan et al., 2023) [27] . The use of Zinc oxide nano particles (ZnO-NPs) in agriculture also possess some potential adverse effects, including toxicity to non-target organisms, accumulation in the food chain and environmental pollution. These effects are influenced by various factors such as particle size, concentration and exposure time. The application of ZnO-NPs can significantly enhance plant growth, physiological and metabolic activity and yield as well as crop quality. (Seleiman et al., 2023) [34] .

Materials and Methods

A field experiment entitled "Effect of nano zinc oxide on morpho physiological yield Parameters and quality of Finger Millet [Eleusine coracana (L.) Garten.] was conducted during rabi, 2022 at Dryland S.V. Agricultural College, Tirupati campus of Acharya N.G. Ranga Agricultural University, which is geographically situated at 13.5° N latitude and 79.5° E longitude with an altitude of 182.9 m above the mean sea level, in the Southern Agro-Climatic Zone of Andhra Pradesh. According to Trolls classification, it comes under the Semi-Arid Tropics (SAT). The experimental soil was Sandy loam in texture. Zinc was applied in the form of ZnSO 4 .7H 2 O to treatments T 3 and T 5 for soil and foliar for T 4 and T 5 application, respectively. Whereas, foliar application of nano zinc oxide was done in T 6 to T 10 applied at time (30 DAT and 60 DAT) as per treatment details T 1: Absolute control (Water spray), T 2: RDF (Reccomended NPK + FYM),T 3 :T 2 + Soil application ZnSO 4 .7H 2 O @ 50 kg/ha (at sowing),T 4 :T 2 + Foliar ZnSO 4 .7H 2 O @ 0.2% at 30 and 60 DAT ,T 5 :(T 2 + T 3 + T 4 ),T 6: T 2 + Foliar Nano ZnO @ 50 ppm ha -1 at 30 and 60 DAT T 7: T 2 + Foliar Nano ZnO @ 100 ppm ha -1 at 30 and 60 DAT T 8: T 2 + Foliar Nano ZnO @ 150 ppm ha -1 at 30 and 60 DAT, T 9: T 2 + Foliar Nano ZnO @ 200 ppm ha -1 at 30 and 60 DAT T 10: T 2 + Foliar Nano ZnO @ 250 ppm ha -1 at 30 and 60 DAT.

Results and Discussion

Growth parameters Plant height

It was observed from the data presented in Table 1 that significantly a higher plant height (97.10 cm) was recorded with foliar application of T 8: T 2 + Foliar Nano ZnO @ 150 ppm ha -1 at 30 and 60 DAT and next highest plant height was recorded by the treatment which received T 7: T 2 + Foliar Nano ZnO @ 100 ppm ha -1 at 30 and 60 DAT.

Significantly the lowest plant height (93.36 cm) was with T 1: Absolute control (water spray). With the change in Zn application method from soil to foliar, plant height increased which might be attributed to greater photosynthetic activity and chlorophyll synthesis due to Zn fertilization that resulted in better vegetative growth. Similarly significant increase in plant height was recorded by Kumar et al. (2021) [19] .

Number of Tillers per Plant

The data pertaining to number of tillers per plant is furnished in Table 1. Аmong different combinаtion of conventionаl аnd foliаr fertilizаtion of nаno fertilizers, the treаtment thаt received T 8: T 2 + Foliar Nano ZnO @ 150 ppm ha -1 at 30 and 60 DAT recorded significаntly higher number of tillers per plant (4.42) followed by the treаtment which received T 7: T 2 + Foliar Nano ZnO @ 100 ppm ha -1 at 30 and 60 DAT (3.58), the lowest number of tillers per hill was recorded by T 1 Absolute control (2.02) The significаnt increment in the number of tillers m -2 with the foliаr аpplicаtion of nаno fertilizers wаs due to the fаct thаt nаno fertilizers instigаted the аctivity of nitrаte reductаse, chloroplаst (Hong et аl., 2005) [15] and аntioxidаnt enzyme system (Nekrаsovа et аl., 2011) [24] which might be the possible mechаnisms thаt enhаnced the growth аnd resulted in higher number of tillers. These findings were in аccordаnce with the findings of Rаthnаyаkа et аl. (2018) [31]

Leaf Area

The leaf area of a plant represents its source size, which was closely related to grain yield. The data regarding Leaf area is presented in Table 1 At Harvest highest leaf area (1002.67 cm 2 plant -1 ) was noticed by T 8 i.e. T 2 + Foliar Nano ZnO @ 150 ppm ha -1 at 30 and 60 DAT followed by T 7 i.e T 2 + Foliar Nano ZnO @ 100 ppm ha -1 at 30 and 60 DAT (871.89 cm 2 plant -1 ). The lowest leaf area was recorded by T 1 i.e. control (586.98 cm 2 plant -1 ). The leaf area differed according to zinc application in different concentrations and the increased leaf area was ascribed to foliar application of Nano zinc oxide at 30 and 60 DAT which might have helped in fast absorption of zinc through leaf and further helped in enhancement of cell division, elongation and photosynthetic activity.

SCMR (SPAD chlorophyll meter reading)

The data on SCMR is presented in Table 1. At harvest, treatment T8: T2 + Foliar Nano ZnO @ 150 ppm ha -1 at 30 and 60 DAT showed highest (SCMR 34.60). Whereas the lowest SCMR was noticed in control (T 1 ) (25.80) followed by T 3: T 2 + Soil application ZnSO 4 .7H 2 O @ 50 kg/ha (at sowing). Zinc is being a co-factor in numerous enzymes which might have helped in the synthesis of more chlorophyll pigments in leaves. Nano ZnO promoted seed germination, seedling vigor, early flowering and higher chlorophyll content in leaf. The probable reason might be because Zn may facilitate the uptake of essential nutrients by plants. Adequate nutrient availability can enhance chlorophyll synthesis and improve overall plant health, contributing to increased SPAD values. similar findings were reported by Zhang et al. (2021) [44] .

Days to 50% Flowering

The data on days to 50 percent flowering in Finger millet was recorded and furnished in the Table 1. There was a significant difference in the days taken for 50% flowering due to treatments effect of application of nano zinc oxide The shorter number of days taken for 50% flowering observed in treatment T 8 (T 2 + Foliar Nano ZnO @ 150 ppm ha -1 at 30 and 60 DAT) (57.66) followed by the treatment T 7 (T 2 + Foliar Nano ZnO @ 100 ppm ha -1 at 30 and 60 DAT) (59.01). However, a greater number of days taken for 50 percent flowering was recorded in control (T 1 ). Among the Nano zinc application treatments, significant differences in days to 50 percent flowering were observed. The treatment T 8: T 2 + Foliar Nano ZnO @ 150 ppm ha -1 at 30 and 60 DAT recorded significantly least number of days to 50 percent flowering (57.66) and followed by T 7: T 2 + Foliar Nano ZnO @ 100 ppm ha -1 at 30 and 60 DAT (59.01) and T 5: (T 3 + T 4 + T 5 ) (60.14). However, control (T 1 ) had recorded more number of days (68.09) compared to other treatments. The application of Nano zinc oxide appears to have positively impacted the plant's physiology and biochemical pathways, thereby facilitating more efficient floral development. The specific mechanisms through which Nano zinc oxide operates to expedite flowering might involve its role in enhancing various physiological processes, including hormone regulation, nutrient uptake, and cellular signalling. These processes collectively contribute to the acceleration of floral initiation and development. Similar results were also reported by (Mohanasundar et al., 2021) [23] in Finger millet. Prasad et al. (2012) [28] concluded that nano ZnO promoted seed germination, seedling vigor, early flowering and higher chlorophyll content in leaf. They also observed beneficial effects of NPs in enhancing plant growth, development and yield in peanut at lower doses, but at higher concentrations ZnO NPs were detrimental just as the bulk nutrients.

The crop production was determined by crop growth rate which indicates the dry matter accumulated per unit land per unit time (Watson et al., 1952) [43] . Grain yield was found to have a strong relationship with LAI, LAD, and CGR. The CGR of Finger millet was computed from 20 DAT to harvest at 20 days Interval and furnished in Table 1. The data revealed that CGR increased till 60 DAT and further decreased gradually till harvest due to declined leaf area in all the treatments. At all stages of crop development, the CGR differed among the zinc application treatments (except at 60 to harvest). At 60 DAT to harvest, T 8: T 2 + Foliar Nano ZnO @ 150 ppm ha -1 at 30 and 60 DAT recorded significantly higher CGR (28.24 g m -2 d-1 ). Whereas, the lowest CGR was recorded by (T 1 ) control (12.56 g m -2 d-1 ). The increased CGR was ascribed to increased leaf area index, light interception, photosynthetic rate and dry matter production. From the highest value, CGR reduced till maturity stage due to reduced number of leaves (Nicknejad et al., 2009) [25] . These findings are similar with Seyedsharifi and Khorramdel (2015) [35] The observed increase in Crop Growth Rate (CGR) can be attributed to several interrelated factors that likely resulted from the application of zinc. This includes the enhancement in the activity of carbonic anhydrase, along with improvements in plant height, Leaf Area Index (LAI), and Leaf Area Duration (LAD). Collectively, these factors likely contributed to a more efficient process of photosynthesis, which was facilitated by the application of zinc. This phenomenon aligns with findings reported by Sharath (2016) [36] .

Yield attributes of finger millet Number of Productive Tillers per Plant

Number of productive tillers per plant is one of the most condemnatory yield components. More the number of fruitful tillers better will be the yield. The data on number of productive tillers per plant influenced by zinc application was recorded at harvest and presented in Table 2.

More number of productive tillers per plant was noticed in the treatment T 8 . This was because of zinc as a constituent of various metalloenzymes might have controlled the senescence of leaves and contributed towards increase in the number of tillers (Barak and Helmke, 1993) [7] . However, the difference was non-significant between them and similar results were obtained by Patel et al. (2019) [26] . The increased productive tillers per plant might also be due to formation of more photosynthates which helped in production of more tillers and growth under zinc fortification treatments duly supported by more green leaves (Verma and Neue, 1984) [40] . The increased tiller production might be due to more zinc uptake and translocation owing to

International Journal of Advanced Biochemistry Research https://www.biochemjournal.com zinc fertilization and further helped in enhancement of photosynthetic rate. These results were homogeneity with the results reported by (Ravikiran and Reddy, 2004) [32] . The experimental data revealed that, there was significant difference among the zinc application treatments. The treatment T 8: T 2 + Foliar Nano ZnO @ 150 ppm ha -1 at 30 and 60 DAT recorded more number of productive tillers per plant (3.63) followed by T 7: T 2 + Foliar Nano ZnO @ 100 ppm ha -1 at 30 and 60 DAT (3.41) and T 9: T 2 + Foliar Nano ZnO @ 200 ppm ha -1 at 30 and 60 DAT recorded (2.39) which was on par with T 10: T 2 + Foliar Nano ZnO @ 250 ppm ha -1 at 30 and 60 DAT (2.53). However, the lowest number of productive tillers per plant was recorded by control (T 1 ) (1.83). Similar results were obtained by Ramaiyan et al. (2023). The more number of productive tillers per plant might be ascribed to optimum supply of zinc which might have increased the uptake and availability of other essential nutrients. This resulted in improvement of plant metabolic process and improved the crop growth. When nаno-ureа wаs аpplied, it increаsed the nutrient uptаke through the stomаtаl openings аnd nutrient trаnslocаtion within the plаnt. This increаsed nutrient uptаke resulted in increаsed cell division, meristemаtic аctivity аnd cell elongаtion stimulаtion, producing more productive tillers plаnt -1 . The number of effective tillers produced is а good indicаtor аs it is the mаjor yield determinаnt. Аccording to Benzon et аl. (2015) [8] , the number of reproductive tillers in rice wаs significаntly аffected by аpplying conventionаl fertilizer in combinаtion with nаno fertilizer аnd аlso enhаnced аvаilаbility of nutrients by eаsy penetrаtion of nаno fertilizers through stomаtа of leаves viа gаs uptаke. Similаr results were reveаled by (Аbdel-Аziz et аl., 2018) [1] (Jаssim et аl., 2019) [16] .

Data on 1000 grain weight is presented in Table 2. 1000 grain weight is an important indicator for prediction of yield (Deivasigamani and Swaminathan, 2018) [11] . It is also a very important measure of seed quality, which is effective on sprouting, seed potential, seedling growth and plant performance (Afshari et al., 2011) [2] . This quality depends on the size of embryo and reserved nutrient quantity used for sprouting and growth (Ebadi and Hisoriev, 2011) [12] (Cao et al., 2011) [9] . Maximum weight of 1000 seeds observed in treatment T 8 while the minimum weight was recorded in treatment T 1 .

The increase in1000-grain weight may be due to the reason that nano fertilizers promote the plant to absorb the water of soil and nutrients, then the photosynthesis is improved. The higher 1000 grain weight could be due to complete utilization of starch towards more seed set and developing grains. Rahaman et al. (2011) reported that the application of zinc might have helped in execution of zinc in various metabolic processes which are involved in the production of healthy grains. Similar results were also obtained by (Gouis, 1992) [20] . Data on zinc application treatments revealed that, there was difference in 1000 grain weight was maximum in T 8 i.e. T 2 + Foliar Nano ZnO @ 150 ppm ha -1 at 30 and 60 DAT (3.13g) and was followed by T 7 i.e. T 2 + Foliar Nano ZnO @ 100 ppm ha -1 at 30 and 60 DAT (3.10g) and T 5 i.e. (T 2 + T 3 + T 4 ) (2.95 g) followed by T 4: T 2 + Foliar ZnSO 4 .7H 2 O @ 0.2% at 30 and 60 DAT (2.86 g) Whereas, the lowest 1000 grain weight was seen in control (T 1 ) (2.01g). Results are in accordance with (Mohanasundar et al., 2021) [23] . The grain development in Zn-applied treatments largely increased, possibly as a result of increased levels of IAA and proteins which might have enhanced the plant growth by increased photosynthetic translocation. Further, this might be due to the fact that Zn is an active ingredient in enzymes involved in energy metabolism pathway of plants.

It also plays a major role in photosynthesis and is a structural constituent of many intermediaries in photosynthesis and carbohydrate metabolism. Similar findings were also obtained by (Chowdary and Patra, 2019) [10] . NPs could up-regulate the expression of aquaporin genes, thus facilitating water and H 2 O 2 diffusion Meanwhile, elevated ROS, especially H 2 O 2 observed in nano-primed seeds during germination could act as signal molecules for stimulating germination process. Additionally, NPs penetrated into seeds, could possibly interact with αamylase enzyme or act as nano catalyst. Thereby enhancing seed starch degradation for seed germination and seedling growth (Mahakkam et al., 2016) [22] .

Grain Yield

The data revealed that, all the treatments recorded significantly higher grain yield over control (T 1 ). However, T 8 i.e.T 2 + foliar of Foliar Nano ZnO @ 150 ppm ha -1 at 30 and 60 DAT was recorded highest grain yield (2438 kg ha - 1 ), followed by T 7 i.e. T 2 + foliar Nano ZnO @ 100 ppm ha -1 at 30 and 60 DAT (2281kg ha -1 ). Whereas, the lowest grain yield (1453 kg ha -1 ) was shown by control (T 1 ) i.e. without fertilizers and manures followed by T 2 i.e. NPK and FYM (1664 kg ha -1 )

The increment in the grain yield was also attributed to the improved physiology of plants with the added Zn which consequently involved in the efficiency of different enzymes, synthesis of chlorophyll and IAA and improved the nitrate assimilation in plant system. Further it was also observed that ZnO NPs enhanced chlorophyll synthesis in leaves by affecting the activities of glutamyl-tRNA reductase and protoporphyrinogen oxidase (Siddiqui et al., 2019) leading to higher grain yields and better rice qualities of ZnO NPs treatments (Zhang et al., 2021) [44] .

Straw Yield the treatment T 8: T 2 + Foliar Nano ZnO @ 150 ppm ha -1 at 30 and 60 DAT recorded highest straw yield (4941 kg ha -1 ) followed by T 7 i.e. T 2 + Foliar Nano ZnO @ 100 ppm ha -1 at 30 and 60 DAT with straw yield of (4763 kg ha -1 ). The highest straw yield might be attributed to continuous availability of macro and micro which might have enhanced the plant height, leaf area, total dry matter. Similar results were obtained by Arulmozhiselvan et al. (2013) [4] . Among the zinc application treatments, the data revealed that, there was significant difference in grain zinc content. The higher zinc (34.96 mg kg -1 ) content was noticed in T 8: T 2 + Foliar Nano ZnO @ 150 ppm ha -1 at 30 and 60 DAT, followed by T 7 i.e. T 2 + Foliar Nano ZnO @ 100 ppm ha -1 at 30 and 60 DAT (32.41 mg kg -1 ). However, the lowest zinc (14.82 mg kg -1 ) content was noticed in control (T 1 ) and by T 6: T 2 + Foliar Nano ZnO @ 50 ppm ha -1 at 30 and 60 DAT (19.34 mg kg -1 ). Similar results were obtained by (Kumar et al., 2021) [18] . Thе probablе rеason might bе bеcausе of thе high uptakе and translocation еfficiеncy of nano zinc oxidе than bulk zinc form. Similarly, increased grain zinc content might be ascribed to the increased absorption through foliar spray of zinc and further translocated to the grain rapidly without any fixation losses. Bala (2018) found that foliar application of nano-zinc oxide in rice cv. PR-121 and Basmati-1509 enhanced grain zinc content. Lin and Xing (2008) also found that ZnO nanoparticles wеrе primarily adsorbеd onto thе cеll surfacе and thеn thеir uptakе is followеd furthеr quickly and еfficiеntly translocatеd to thе sink. The increased quality parameters with zinc application might also be due to higher zinc assimilation in plants compared to control. Similar results were also obtained by Stalin et al. (2011) [37] and also were in agreement with Prasad et al. (2012) [28] wherein the accumulation of zinc in the kernels of peanut was high with the use of nanoscale zinc oxide particles. [43] . Similar results were also obtained by (Vijaykumar et al., 2020) [41] . The increased protein content with zinc application during present study was in agreement with the hypothesis that protein represents a sink for zinc in the grain. Further, zinc fertilization might have enhanced the zinc availability to the plants, and which played pivotal role in protein synthesis. A thinkable reason for the improvement in quality and yield due to foliar applied Zn might be phloem mobile and could be easily translocated into the developing grains. Further, Zn was believed to be essential for RNA synthesis which in turn, helped in protein synthesis (Zuchi et al., 2012) [45] . The application of nano-Zn fertilizer can increase Zn mobility in phloem, increasing its bioavailability in the endosperm and contributing to protein synthesis and other biochemical traits of crop plants (Rossi et al., 2019) [33] (Ahmad et al., 2020) [3] Table 4: Effect of different sources of zinc on Protein content in grains of Finger millet.

Treatments

Protein content in grains (%) T1: Absolute control (Water spray) 5.84 T2: RDF (Recc NPK + FYM) 7.13 T3: T2 + Soil application ZnSO4.7H2O @ 50 kg/ha (at sowing) 7.49 T4: T2 + Foliar ZnSO4.7H2O @ 0.2% at 30 and 60 DAT 8.14 T5:(T2 + T3 + T4) 7.82 T6: T2 + Foliar Nano ZnO @ 50 ppm ha -1 at 30 and 60 DAT 6.81 T7: T2 + Foliar Nano ZnO @ 100 ppm ha -1 at 30 and 60 DAT 8.58 T8: T2 + Foliar Nano ZnO @ 150 ppm ha -1 at 30 and 60 DAT 8.92 T9: T2 + Foliar Nano ZnO @ 200 ppm ha -1 at 30 and 60 DAT 6.54 T10: T2 + Foliar Nano ZnO @ 250 ppm ha -1 at 30 and 60 DAT 6.36 SE m± 0.095 CD 5% 0.283 2882.81 T3: T2 + Soil application ZnSO4.7H2O @ 50 kg/ha (at sowing) 2879.54 T4: T2 + Foliar ZnSO4.7H2O @ 0.2% at 30 and 60 DAT 3181.17 T5:(T2 + T3 + T4) 3219.33 T6: T2 + Foliar Nano ZnO @ 50 ppm ha -1 at 30 and 60 DAT 3243.29 T7: T2 + Foliar Nano ZnO @ 100 ppm ha -1 at 30 and 60 DAT 3582.64 T8: T2 + Foliar Nano ZnO @ 150 ppm ha -1 at 30 and 60 DAT 3343.92 T9: T2 + Foliar Nano ZnO @ 200 ppm ha -1 at 30 and 60 DAT 3282.73 T10: T2 + Foliar Nano ZnO @ 250 ppm ha -1 at 30 and 60 DAT 3152.97 SE m± 210.12 CD 5% NS

Conclusion

Nano-zinc oxide at the concentration of 150 ppm showed the best results and caused maximum increase in plant height, No. of. Tillers, SCMR, Grain yield and Straw yield compared to the control and zinc Sulphate treatment. Further indicates that the use of ZnO-NPs as a nano fertilizer for crops grown in Zn deficient soils will improve crop yield, food quality and address malnutrition, globally.

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