Studies On The Effect Of Micronutrients In Acid Lime ( Citrus aurantifolia Swingle) var. PKM-1

Acid lime ( Citurs aurantifolia Swingle) belongs to the family Rutaceae and widely grown in tropical and subtropical regions of India. India is the largest producer of acid lime in the world. In India, Maharashtra, Andhra Pradesh, Tamil Nadu, Gujarat, Rajasthan and Bihar are grown in larger area. In Tamil Nadu, commercially cultivated in Tirunelveli, Tenkasi, Turicorin, Dindigul, Madurai, Theni, Virudhunagar and Perambalur districts. Fruits are being used for preparation of pickles and beverages. They are rich in vitamin C, minerals and salts. Micronutrients such as Zinc, Iron and boron play a vital role in acid lime for growth and development. With this background, the present experiment on studies on the effect of micronutrients in acid lime var. PKM-1 was conducted at Citrus Research Station (TNAU), Sankarankovil during 2020-21 to study the effect of micronutrients on growth, yield and quality of acid lime. Foliar application was given twice in a season viz., the first spray was given during peak flowering stage and next spray during fruit set stage on selected five trees for each treatment at farmer’s field. The trial was laid out in a randomized block design (RBD) with thirteen treatments and replicated thrice. The treatments details are 0.5 % Ferrous sulphate (T 1 ), 1.0 % Ferrous sulphate (T 2 ), 0.5 % Zinc sulphate (T 3 ), 1.0 1.0 % Ferrous sulphate + 1.0 % Zinc sulphate + 1.0 % Copper sulphate + 1.0 % Manganese sulphate + 0.3 % borax (T 12 ) and control (T 13 ). Results revealed that T 12 recorded the highest values of growth and yield contributing traits such as plant height (5.50 m), number of fruits per plant (652.20), fruit weight (41.50 g), number of seeds (8.11) and yield per plant (15.87 kg/tree) and quality traits viz., TSS (6.48 o Brix), juice content (35.50 ml), ascorbic acid content (35.02 mg/100g), acidity (9.10 %) and B:C ratio (2.15) and followed by T 11 whereas the lowest values was observed in control (T 13 ).


INTRODUCTION
Acid lime (Citurs aurantifolia Swingle) is an important commercial species of citrus considered to be indigenous to India, and is extensively cultivated in many parts of India across tropical and subtropical regions. It is otherwise called as sour lime or Kagzi nimboo. India is the largest producer of acid lime in the world. The area and production of acid lime in India is about 305.0 thousand hectares and 3482.0 thousand MT, respectively (NHB, 2019). In Tamil Nadu, acid lime is cultivated in an area of about 9.88 thousand hectares which accounts for the production of 34.51 thousand MT. In India, Maharashtra, Andhra Pradesh, Assam, Tamil Nadu, Gujarat, Rajasthan, and Bihar are the leading states in acid lime cultivation. In Tamil Nadu, it is widely cultivated in Tirunelveli, Tenkasi, Turicorin, Dindigul, Madurai, Perambalur, Tiruchirapalli, Theni and Virudhunagar districts under rainfed and irrigated conditions. Fruits are being used for preparation of pickles, beverages and rich in citric acid, ascorbic acids, minerals and salts. Among the several factors responsible for reduction in yield and quality of acid lime, deficiency of soil micronutrients is the major hinder that cause significant loss in economic yield. Generally, acid lime is a micronutrient loving plant and hence, application of micronutrient considerably enhances the flowering and fruit quality. Micronutrients such as zinc, iron and boron plays a vital role in acid lime plants. Zinc is essential component of enzymes responsible for nitrogen metabolism, thereby resulting into increase in uptake of nitrogen by the plant. It has important role in starch metabolism, and acts as cofactor for many enzymes, affects photosynthesis reaction, nucleic acid metabolism (online first draft) and protein biosynthesis (Alloway, 2008). Iron plays an important role in the activation of chlorophyll and in the synthesis of many proteins such as different cytochrome, which participate in different functions in the plant metabolism (Al-Bamarny, et al. 2010;O' Neil and Ross, 2002). Nutrients play an important role in keeping up the growth, yield and quality of fruit crops through improving flowering, fruit set, fruit drop control, fruit shape and size etc. Nutritional deficiencies are closely associated with the poor plant growth and fruit set, heavy fruit drop, inferior quality of produce and also make the tree vulnerable to diseases, pests and other disorders (Vasure et al. 2018). With this background, the present experiment was undertaken to investigate the effect of different combinations of micronutrients on growth, fruit yield and quality of acid lime var. PKM-1.

MATERIALS AND METHODS
The present experiment on studies on the effect of micronutrients on growth, yield and quality of acid lime var. PKM-1 was conducted at farmers' field at Vannikonenthal, Sankarankovil block of Tirunelveli district, Tamil Nadu. The aim of the present study is to find out the suitable micronutrient combination for increasing flowering, yield and quality of acid lime fruits. The experiment was conducted during 2020 -2021. Seven years old trees of acid lime var. PKM-1 were selected at farmers' field for the experiment. Five trees were used for each replication. Trees were planted at a spacing of 6 x 6 m. Foliar application of micronutrients sprayed during September -October and March -April every year. Each treatment was imposed in five uniform trees. Spray was given twice in a season. The first spray was given during peak flowering stage (October) and next spray was given during fruit set stage (15 days after first spray). Micronutrients such as ferrous sulphate, copper sulphate, zinc sulphate, manganese sulphate and borax were prepared by dissolving in water and then the volume was made up. The experiment was laid out in a Randomized Block Design (RBD) with thirteen treatments and replicated thrice. The quality characters such as juice content of ten fruits from each treatment weighted and mean was calculated and expressed in per cent. TSS recorded by using hand Refractometer and expressed as o Brix. Ascorbic acid and acidity content were calculated by using AOAC (1975) method. The observations such as plant height, J. Curr. Crop Sci. Technol., 2022;https://doi.org/10.29321/MAJ.10.000663 (online first draft) number of fruits per plant, tree spreading, fruit girth, fruit circumference, fruit volume, fruit weight, yield per plant, B:C ratio, ascorbic acid content, acidity, TSS and fruit juice content were recorded and analysed statistically as per the methods suggested by Panse and Sukhatme (1967).

T1
-0.5 % Ferrous sulphate the semi permeability of cell wall which mobilizes more water into fruits thereby increasing size of fruits in kagzi lime (Babu et al. 1982). Singh and Kaur (2018) found that foliar application of borax @ 1.5 % increased fruit weight, fruit girth and yield per tree in Baramasi lemon under Punjab condition.
T12 treatment exhibited the highest yield per tree (15.87 kg/tree) followed by T11 (14.65 kg/tree) whereas the lowest yield was found in T13 (11.21 kg/tree). This might be due to foliar application of micronutrients increased the more fruit set, fruit retention and number of fruits per plant which leads to increased the yield per tree. The effect of micronutrients on quality traits are presented in The increased juice content due to application of micronutrients might be due to the role of zinc in plant metabolism. Zinc regulates the semi permeability of cell wall by J. Curr. Crop Sci. Technol., 2022;https://doi.org/10.29321/MAJ.10.000663 (online first draft) which more water was mobilized into the fruits, thereby increasing the percentage of juice. Increased in TSS with the application of micronutrients especially zinc might be due to increased photosynthetic activity and chlorophyll content of leaves which resulted in production of more TSS in fruit juice (Tagad et al. 2018). Singh and Rethy (1985) observed that application of different micronutrient and their combinations along with NAA improved the TSS and titrable acidity content of fruit juice in acid lime.
Regarding benefit cost ratio, T12 recorded the highest ratio of 2.15 followed by T11 (2.13) whereas the lowest B:C ratio was observed in control (T13) (1.90). This might be due to highest net profit, number of fruits per tree and yield per tree which enhanced the benefit cost ratio compared to the control.