Effect of plant growth regulators and micronutrients on reproductive attributes of acid lime (Citrus aurantifolia Swingle) in hasta bahar cropping season H.K. Deshmukh*, D.H. Paithankar, P.K. Nimbolkar1, R.K. Dewangan and C. Awachare1 Department of Horticulture, P.G.I. Dr. Panjabrao Deshmukh Krishi Vidyapeeth Akola - 444104, Maharashtra, India *E-mail: hdeshmukh975@gmail.com ABSTRACT Plant growth regulators and micronutrients at various combinations [GA3 50ppm + Cycocel 1000ppm + KNO3 0.2% + Zn 0.3% + Boron 0.1%; GA3 50ppm + Cycocel 2000ppm + KNO3 0.2% + Zn 0.3% + Boron 0.1%; GA3 50ppm + Paclobutrazol 2.5g a.i./tree (soil application) + KNO3 0.2% + Zn 0.3% Boron 0.1%; GA3 50ppm + Paclobutrazol 3.5g a.i./tree (soil application) + KNO3 0.2% + Zn 0.3% + Boron 0.1%; GA3 50ppm + Paclobutrazol 1000ppm (foliar application) + KNO3 0.2% + Zn 0.3% + Boron 0.1%; and, GA3 50ppm + Paclobutrazol 2000ppm + KNO3 0.2% + Zn 0.3% + Boron 0.1%] were sprayed before flower emergence in acid lime. Minimum days taken to emergence of flower bud (39.57), duration of flowering (24.07), days to 50% fruit set (6.54) and days taken to fruit maturity (145.90) were observed with application of GA3 50ppm + Paclobutrazol 3.5g a.i./tree (soil application) + KNO3 0.2% + Zn 0.3% + Boron 0.1% (T5), whereas, fruit drop (5.92%) was minimum with GA3 50ppm + Cycocel 2000ppm + KNO3 0.2% + Zn 0.3% + Boron 0.1% (T3). Treatment T3 also increased the number of flowers per meter length of shoot (49.65) as well as fruit yield (8.90). Key words: Acid lime, growth regulators, nutrients, flower set, fruit set J. Hortl. Sci. Vol. 11(1):63-66, 2016 INTRODUCTION Acid lime (Citrus aurantifolia Swingle) belongs to the family Rutaceae. It originated in India and has a chromosome number of 2n=18. Among the various types of citrus fruits grown, acid lime occupies about 3.7 per cent of the total area under citrus in the country. The area under acid lime cultivation in Maharashtra alone is 49.30 hectares, with a production of 739.53MT and productivity of 15.0MT (Anon., 2013). Acid lime flowers thrice a year, i.e., in the months of January-February, June-July and September-October, under Vidharbha condition and these seasons are generally known as Ambia, Mrig and Hasta bahar, respectively. A bulk of the flowering occurs in Ambia bahar (60%), followed by Mrig bahar (30%) and Hasta bahar (10%). Hence, the market is glutted with Ambia bahar fruits, that are harvested in June-July, leading to the lowest price of the fruit during a year in this period. Hasta bahar flowering occurs in October-November, and the fruits are ready for harvest in March-May, which is predominately the off-season for acid lime fruits (Thirugananavel et al, 2007). In Vidharbha region, it is highly difficult to regulate bahar treatment during September-October due to the absence of sufficient rains. Here, manipulation of Hasta bahar flowering with the use of plant growth regulators and other chemicals can serve as an alternative to realize maximum yields during summer, which fetch 6 to 8 times the price of Ambia bahar, and 3-4 times the price of Mrig bahar season. Keeping the above in view, the present study was aimed at investigating the effect of different combinations of plant growth regulators and micronutrients on reproductive attributes in acid lime in the Hasta bahar season. MATERIAL AND METHODS A field experiment was conducted in Randomized Block Design (RBD), with three replications, during the year 2013-2014 at the acid lime orchard, College of Horticulture, Dr. Panjabrao Deshmukh Krishi Vidyapeeth, Akola, Maharashtra, situated at 307-457m above mean sea level, of 20.42°N latitude and 72.02°E longitude. Uniform- sized trees were selected, and the required dose of manures, fertilizers, irrigation and other plant protection measures 1Division of Fruit Crops, ICAR-Indian Institute of Horticultural Research, Hesaraghatta Lake Post, Bengaluru – 560089, Karnataka, India 64 were applied. Treatment combinations used included: T1 (Control), T2 (GA3 50ppm + Cycocel 1000ppm + KNO3 0.2% + Zn 0.3% + Boron 0.1%), T3 (GA3 50ppm + Cycocel 2000ppm + KNO3 0.2% + Zn 0.3% + Boron 0.1%), T4 [GA3 50ppm + Paclobutrazol 2.5g a.i./tree (soil application) + KNO3 0.2% + Zn 0.3% Boron 0.1%], T5 [GA3 50ppm + Paclobutrazol 3.5g a.i./tree (soil application) + KNO3 0.2% + Zn 0.3% + Boron 0.1%], T6 [GA3 50ppm + Paclobutrazol 1000ppm (foliar application) + KNO3 0.2% + Zn 0.3% + Boron 0.1%] and T7 [GA3 50ppm + Paclobutrazol 2000ppm + KNO3 0.2% + Zn 0.3% + Boron 0.1% (foliar application)]. In all the above treatments, water stress for one month was improved from 15th September to 15th October 2013. Spray of plant growth regulators and micronutrients was scheduled as: (i) GA3 was applied in the first fortnight of June, (ii) Cycocel and Paclobutrazol were sprayed at release of trees from water stress (i.e., 15th September), (iii) Spray of KNO3, zinc and boron 2 to 3 days prior to release of water stress (i.e., 15th October). Observations were recorded on days taken to emergence of flower-bud, number of flowers per meter length of shoot, duration of flowering, days required for 50% fruit set, fruit drop (%), days to fruit maturity, and yield (t/ha). RESULTS AND DISCUSSION Days required for emergence of flower-bud in acid lime was significantly influenced by plant growth regulators and micronutrients (Table 1). After imposition of the treatments, minimum number of days required for emergence of flower-bud (39.57) was observed in treatment T5 [GA3 50ppm + Paclobutrazol 3.5g a.i./tree (soil application) + KNO3 0.2% + Zn 0.3% + Boron 0.1%], which was significantly superior to all the other treatments. Maximum number of days taken for emergence of flower- bud (54.67) was seen in treatment T1. Similar results were obtained earlier in acid lime, treated with micronutrients and Paclobutrazol (Baskaran et al, 2010; Haribabu and Rajput 1982). Similarly, Khanduja et al (1974) observed in grape-vine, that zinc promoted nucleic acid synthesis, in turn influencing the formation of flower-bud primordia. Arora (1969) also observed earlier flowering in guava with application of zinc. It is clear from Table 1 that the number of flowers per meter length of shoot was significantly influenced by growth regulators and micronutrients in our study on acid lime. Maximum (49.65) number of flowers per meter length of shoot was observed in treatment T3 which was significantly superior to all the other treatments, followed by T5 (44.25) and T2 (42.63), which were at par with each other. The lowest number of flowers per meter length of shoot (21.40) was recorded in Control (T1). Duration of flowering in acid lime under various treatments in our study was found to be non-significant (Table 1). Kachru et al (1971) demonstrated that gibberellic acid inhibited flowering in mango, as, higher levels of GA3 are antagonistic to formation of flower primordial; high levels of endogenous auxins and low levels of endogenous gibberellin favour flower-bud initiation. Paclobutrazol and Cycocel are known inhibitors of gibberellin biosynthesis. Reduced levels of endogenous gibberellins resulting from action of these chemicals may favour early and profuse flowering in mango (Kurian and Iyer, 1993). Growth retardants (Paclobutrazol and Cycocel) have anti-gibberellin effect which, in turn, checks vegetative growth and promotes early flowering. Results depicted in Table 1 reveal that the Table 1. Effect of different concentrations/ combinations of GA3, Cycocel, KNO3, zinc, boron and Paclobutrazol on flowering parameters, fruit set, fruit drop and fruit maturity of acid lime (Citrus aurantifolia swingle). Treatment Days taken Flowers per Duration Days to Fruit Days Yield to emergence meter length of flowering 50% fruit drop taken kg/plant of flower bud of shoot set % to fruit maturity T1 54.67 21.40 31.33 11.05 12.36 (3.52) 164.50 11.64 T2 46.87 42.63 29.33 9.36 6.85 (2.62) 156.70 30.58 T3 44.56 49.65 27.67 8.40 5.92 (2.43) 154.40 32.29 T4 42.77 40.20 26.45 7.68 8.62 (2.94) 149.60 25.63 T5 39.57 44.25 24.07 6.54 7.96 (2.82) 145.90 31.12 T6 51.08 32.40 30.87 10.88 9.25 (3.04) 161.30 20.43 T7 49.12 36.40 30.45 9.48 9.03 (3.00) 157.70 24.41 ‘F’-test * * NS * * * * SE(m)± 1.44 1.00 1.56 0.51 0.25 2.88 0.66 CD (P=0.05) 4.46 3.08 4.82 1.59 0.80 8.89 2.04 NS = Non-significant; * Deshmukh et al J. Hortl. Sci. Vol. 11(1):63-66, 2016 65 number of days required for 50% fruit set in acid lime under various treatments was significantly influenced by plant growth regulators and micronutrients. Treatment T5 recorded minimum (6.54) number of days for 50% fruit-set, followed by T4 (7.68) and T3 (8.40), while, maximum number of days taken for 50% fruit-set was recorded in treatment T1 (11.05). Application of Cycocel and Paclobutrazol (known anti- gibberellins) cause effective translocation of carbohydrates besides causing a positive effect of cytokinins and auxins in conversion of vegetative buds to flower buds. Similar results were reported in lemon (Monselise et al, 1966), mango (Maiti et al, 1971) and ‘Eureka’ lemon (Nir et al, 1972). Greenburg et al (1993) observed higher fruiting in orange cv. ‘Shamouti’ on application of Paclobutrazol. Data depicted in Table 1 reveal that fruit drop in acid lime is significantly influenced by plant growth regulators and micronutrients. Minimum fruit drop was recorded in treatment T3 (5.92%), which was significantly superior to all the other treatments, followed by T2 (6.85%), T5 (7.96%) and T7 (9.03%). Treatment T1 (12.36%) showed maximum fruit drop. Haribabu and Rajput (1979) reported in kagzi lime that spraying zinc sulphate inhibited abscission, thereby reducing flower and fruit drop. The number of days required to fruit maturity in acid lime was found to be significantly influenced by plant growth regulators and micronutrients (Table 1). Significantly lower number of days (145.90) were required for fruit maturity in treatment T5, which was significantly superior to all the other treatments. Treatments T3 (154.40 days), T2 (156.70 days) and T7 (157.70 days) were at par with each other. However, treatment T1 (Control) took maximum number of days for fruit maturity (164.50). Paclobutrazol advances flowering, and ultimately results in early maturity of the fruits. Significantly high yield (8.90t/ha) was obtained in treatment T3, followed by T5 (8.62 t/ha), which was significantly superior to all the other treatments; minimum yield (3.22 t/ha) was seen in T1 (Control). Appropriate combinations and concentrations of growth regulators and micronutrients (GA3 50ppm+ Cycocel 2000ppm + KNO3 0.2% + Zinc 0.3% + Boron 0.1%, and utilization of these at the appropriate stage, along with water stress, is effective in regulation of Hasta bahar. This is achieved by maximizing the number of fruits and increasing fruit yield harvested during March-April when the demand is higher and prices are at an all-time high. Based on the above findings, appropriate combinations and concentrations of growth regulators, and, micronutrients, i.e., GA3 50ppm+Cycocel 2000ppm + KNO3 0.2% +Zinc 0.3% + Boron 0.1%, along with imposition of water stress, was found by us to be effective. This can be very well achieved by applying T3 and T5 for increasing fruit yield to be harvested during March - April. Thus, timely application of the treatments GA3 50ppm + Cycocel 2000ppm + KNO3 0.2% + Zn 0.3% + Boron 0.1% (T3), and, GA3 50ppm + Paclobutrazol 3.5g a.i./tree (soil application) + KNO3 0.2% + Zn 0.3% + Boron 0.1% (T5) promise higher returns to the acid lime grower. REFERENCES Anonymous. 2013. Area and Production of Citrus in India and Maharashtra. http//www.nhm.gov.in Arora, J.S. 1969. Nrutitional studies in mango and guava. Ph.D. thesis submitted to Banaras Hindu University, Varanasi, Uttar Pradesh, India Baskaran, A., Renuga, R. and Saraswathy, S. 2011. Advancement of flowering in acid lime by soil applied paclobutrazol. Madras Agri. J., 97:388-389 Greenburg, J.E., Goldschidt, E. and Goren, R. 1993. Potential and limitation of the use of PBZ in citrus orchard in Israel. Acta Hort., 329:58-61 Haribabu, R.S. and Rajput, C.B.S. 1982. Effet of zinc, 2, 4- D and GAç on flowering in kagzi lime. Punjab Hort. J., 22(3-4):140-144 Kachru, R.B., Susan, R.N. and Guam, E.K. 1971. Inhibition of ûowering in mango (Mangifera indica L.) by gibberellic acid. Hort. Sci., 6:140-141 Khanduja, S.D., Balasubramanyan, V.R. and Saraswat, J.B. Table 2. Details of treatments applied Treatment Treatment details T1 Control T2 GA3 50ppm + Cycocel 1000ppm + KNO3 (0.2%) + Zn (0.3%) + Boron (0.1%) T3 GA3 50ppm + Cycocel 2000ppm + KNO3 (0.2%) + Zn (0.3%) + Boron (0.1%) T4 GA3 50ppm +Paclobutrazol 2.5g a.i./tree (soil application) + KNO3 (0.2%) + Zn (0.3%) + Boron (0.1%) T5 GA3 50ppm + Paclobutrazol 3.5g a.i./tree (soil application) + KNO3 (0.2%) + Zn (0.3%) + Boron (0.1%) T6 GA3 50ppm + KNO3 (0.2%) + Zn (0.3%) + Boron (0.1%) + Paclobutrazol 1000ppm (foliar application) T7 GA3 50ppm + KNO3 (0.2%) + Zn (0.3%) + Boron (0.1%) + Paclobutrazol 2000ppm (foliar application) Effect of growth regulators and micronutrients in acid lime J. Hortl. Sci. Vol. 11(1):63-66, 2016 66 1974. Zinc improves fruit set in grapes. Indian Hort., 19(4):36 Kurian, R.M. and Iyer, C.P.A. 1993. 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