INTRODUCTION Custard apple belongs to the family Annonaceae which has 46 genera and around 500 to 600 species, most of them found in the Tropics. Of the several species of Annona, at least five are available in India and yield edible fruit. These are: custard apple (Annona squamosa L.), cherimoya (Annona cherimola Mill.), soursop (Annona muricata L.), ‘Ramphal’ (Annona reticulata L.) and atemoya (Annona atemola Hort.). Custard apple has been performing well under dryland conditions where other crops do not. The tree is small, more or less shrub-like, shedding leaves in winter. The flowers are borne on current season’s growth (newly emerging young shoots). Flowers are bisexual and distinctly protogynous (Sampath and Jalikop, 2000). Pruning and defoliation are essential components for inducing off-season flowering while aiming at quality and quantity of fruits. In custard apple, fruiting occurs on the current season’s growth. With this in view, the present investigation was conducted to test the effect of different pruning intensities in combination with chemical defoliation on induction of off- season cropping in custard apple cv. Balanagar. MATERIAL AND METHODS The experiment was laid out in the experimental orchard of custard apple at ICAR - Indian Institute of Induction of off-season flowering in custard apple (Annona squamosa L.) cv. Balanagar G.M. Vinay and R. Chithiraichelvan1 Collage of Horticulture, Bengaluru University of Horticultural science, Bagalkot - 587 123, India E-mail: vingeegmvegs@gmail.com ABSTRACT Pruning and defoliation are essential operations for inducing off-season flowering and fruiting to yield better quality and quantity of fruits in custard apple. Trees were subjected to two levels of pruning (25% and 50%) combined with use of chemical defoliants (urea 5%, Ethrel 2000ppm, potassium iodide 1%, or ortho-phosphoric acid 1%) besides the Control, with each treatment replicated thrice. Early initiation of flowering and better vegetative growth was seen in pruned (25%) and defoliated trees than in the Control or other treatments. Maximum off-season yield (10.33kg/ plant) was obtained in T4 (25% pruning, combined with 5% urea spray as defoliant) and T6 (25% pruning, combined with 1% potassium iodide-spray as defoliant). Findings of this investigation helped standardize pruning and defoliation practices on a scientific basis for off-season production of custard apple fruits. Key words: Pruning, defoliation, off-season, custard apple, urea Horticultural Research, Bengaluru, during 2013-2014. Eleven-year-old trees of cv. Balanagar showing uniform vigour were selected for the study. Randomized Complete Block Design (RCBD) was followed, with two levels (25% and 50%) of pruning intensity combined with defoliating chemicals (urea 5%, Ethrel 2000ppm, potassium iodide 1%, ortho-phosphoric acid 1%) with Control. Each treatment was replicated thrice. Number of shoots that emerged (secondary and tertiary shoots were counted), length of the emerged shoots (from the point of emergence to the tip, in cm), number of flowering shoots, number of flowers per shoot, and number of flowers per plant were noted at monthly interval; days taken to first flower, duration of flowering, days taken to fruit-set from onset of pruning, average number of fruits per tree, and fruit yield (kg/tree) were recorded. RESULTS AND DISCUSSION Growth attributes Pruning, when performed appropriately, provides the tree with a proper shape and size. It also enables essential operations for custard apple for enhancing production of quality fruits. Significant differences among treatments at different dates of observations for number of shoots that emerged were observed (Table 1). Maximum number of shoots emerged at 30, 60 and 90 days in treatment T4 (66.0, 1Division of Fruit Crops, ICAR-Indian Institute of Horticultural Research, Hesaraghatta Lake Post, Bengaluru-560089, India J. Hortl. Sci. Vol. 10(1):13-17, 2015 14 86.00 and 125.67, respectively), which was on par with T5, T6, T8, T7, T2 and T10, and, no branches were seen in T1 (Control- no pruning and no chemical spray). This could be due to greater availability of leaf area on shoots from 25% pruning compared to 50% pruning. Further, as T4 is a combination (25% pruning + spray of 5% urea), more numerous shoots may have been induced, resulting in greater leaf area, consequently increased photosynthetic activity. The present findings are in line with Pandey et al (1998) who reported maximum number of shoots under 25% pruning in ber. At 120 days from treatment, T1 (198.0) was found to be highly significant relative to other treatments; minimum shoot number was seen in treatments T11, T9, T10 and T8. This could be attributed to the fact that Control trees were neither pruned nor sprayed with chemicals, and, sprouting occurred as a natural consequence of leaf shedding and production of new growth from all the buds, 120 days after treatment-imposition in the other trees. Bajwa et al (1986) found significantly high total number of shoots in unpruned ber trees. Lal and Prasad (1971) also found unpruned ber trees as producing more shoots compared to the pruned trees. Data on length of shoot (Table 1) indicate significant differences among treatments, at monthly intervals. At 30 days of observation, maximum shoot length was seen in T3 (6.3) and T2 (5.5), at 60 days in T11 (13.57), T3 (12.93) and T8 (12.67), at 90 days in T3 (25.23), and, at 120 days in T5 (30.74) which was on par with T10, T3, T11 and T9. Minimum shoot length was observed in T1 (5.60). No shoots emerged in Control T1 at 30, 60 or 90 days. Longest shoots were observed in the lightly pruned (25%) trees during initial stages of growth, in severely pruned (50%) trees at the end of growth period, and shortest shoots were seen in unpruned trees, throughout the growth period. Similar results were obtained by Dhaliwal et al (2014) in kinnow, and by Trevor and Steven (2009) in custard apple. Yield attributes Significant differences were noticed for number of flowering shoots per tree at monthly intervals (Table 2). At 30 days, maximum flower number was found in treatment T4 (46.0), at 60 days in T11 (74.67), at 90 days in T2 (85.0), and was on par with T5, T6, T8, T10, T2, T11, T7, T3 and T9. No shoots or flowers emerged in Control T1 at 30, 60 or 90 days. These findings are in agreement with Guimond et al (1998) who found pruning in cherry trees to influence number of flowering shoots. Similar results were reported by Braswell and Spiers (2005) and Lord et al (1979). At 120 days, T1 (148.33) was more significant than the other treatments and the least number of flowers were seen in T3 (120.33), which was on par with T7, T8, T9 and T2. Control trees showed maximum number of flowering shoots at this stage, because, it was the main season for flowering in custard apple under Bengaluru conditions. Flowering period in treated trees ended at 120 days, as, the trees had started flowering early in the season, and, all the differentiated buds had bloomed. Similar results were reported by Mohamed and Fawzi (2010) in custard apple, and by Bruno and Evelyn (2001) in cherimoya. At 30 days, higher number of flowers per shoot appeared in T3, T7 and T8 (6.67); at 60 days, most number of flowers were found in T10 (6.67), and at 90 days in T4 (6.33), which was on par with the other treatments, excepting T1 and T9 (4.67). At 120 days, more flowers per shoot were found in T1 (12.67), followed by T5 (7.00); the least number was seen in T2 (5.00) and other treatments (Table 2). More Table 1. Effect of various pruning levels and defoliants on shoot emergence and shoot length Treatment Number of shoots emerging per tree Length of emerged shoots (cm) (days after pruning) (days after pruning) 30 60 90 120 30 60 90 120 T 1 Control (no pruning, no chemicals) 0.00 0.00 0.00 198.00 0.00 0.00 0.00 5.60 T 2 25% pruning (no chemicals) 61.00 81.00 121.00 176.00 5.50 9.53 18.03 27.30 T 3 50% pruning (no chemicals) 59.00 79.00 118.67 165.33 6.30 12.93 25.23 29.57 T 4 25% pruning + Urea 5% 66.00 86.00 125.67 175.00 4.10 9.23 23.67 29.20 T 5 25% pruning + Ethrel 2000ppm 64.67 83.33 123.67 171.33 5.23 10.13 21.00 30.74 T 6 25% pruning + Potassium iodide 1% 64.00 82.67 123.33 168.67 4.53 12.03 24.30 29.20 T 7 25% pruning + Ortho-phosphoric acid 1% 61.33 83.33 123.00 166.33 4.57 12.10 23.83 27.23 T 8 50% pruning + Urea 5% 63.00 83.00 121.67 162.33 5.33 12.67 23.83 26.30 T 9 50% pruning + Ethrel 2000ppm 60.67 80.00 119.33 160.67 3.53 13.20 23.27 29.27 T 1 0 50% pruning + Potassium iodide 1% 61.33 81.67 122.00 162.00 4.03 12.20 24.53 30.50 T 1 1 50% pruning + Ortho-phosphoric acid 1% 60.33 78.67 117.00 157.00 4.57 13.57 23.73 29.43 SEm± 1.637 1.436 1.558 1.842 0.311 0.330 0.683 0.519 CD (*P=0.05) 4.830* 4.237* 4.957* 5.433* 0.918* 0.974* 2.015* 1.532* J. Hortl. Sci. Vol. 10(1):13-17, 2015 Vinay and Chithiraichelvan 15 flowers per shoot were observed in pruned trees than in unpruned trees, as light-pruning removes apical dominance, resulting in bud-break from the lower portion of the shoot. These findings are in agreement with George and Nissen (1987) in custard apple. However, at 120 days, number of flowers per shoot in T1 was more because of presence of more number of shoots at the time, naturally resulting in the highest number of flowers in unpruned trees. Similar results were obtained by Trevor and Steven (2009) in custard apple, and by Dhaliwal et al (2014) in kinnow. Kahn et al (2001) found an increase in the number of flowers per shoot after pruning in cherimoya. As for number of flowers per tree (Table 3), at 30 days of treatment, more flowers per tree were observed in treatment T8 (280.67), at 60 days in T11 (504.33), at 90 days in T4 (526.00), and at 120 days in T1 (989.0). Due to a higher number of flowering shoots, and more flowers per shoot in these treatments, the number of flowers per tree was high too. Similar results reported by Kahn et al (2001) revealed that pruning increased the number of flowers per tree in cherimoya and so did Trevor and Steven (2012) in atemoya. All the pruning treatments together with defoliation gave better results as for early initiation of flowering. Significant difference was seen between pruning-with- defoliation, and unpruned trees (Table 4). Minimum number of days taken for emergence of the first flower were seen in T8 (22.6), while longest time taken for the appearance of first flower was seen in Control T1 (95.3) (Table 4). By pruning, apical dominance could be arrested thus, directing the movement of photosynthates to the lateral buds, thereby aiding flower initiation. Similar results were reported by Trevor and Steven (2012) in atemoya, and by Laura and Julian (2008 and 2009) in cherimoya. Table 4 shows longer duration of flowering as observed in pruned defoliated tress than in Control trees; T8 (130.0) showed the longest duration, followed by the other Table 3. Effect of various pruning levels and defoliants on number of flowers Treatment Number of flowers per tree (days after pruning) 30 days 60 days 90 days 120 days T 1 Control 0.00 0.00 0.00 989.00 (no pruning, no chemicals) T 2 25% pruning 232.33 309.00 422.67 617.67 (no chemicals) T 3 50% pruning 216.67 277.33 438.33 762.67 (no chemicals) T 4 25% pruning + 230.67 368.00 526.00 623.33 Urea 5% T 5 25% pruning + 241.67 311.33 474.00 863.33 Ethrel 2000ppm T 6 25% pruning + 261.00 347.33 494.00 744.33 Potassium iodide 1% T 7 25% pruning + 269.00 305.00 410.67 724.67 Ortho-phosphoric acid 1% T 8 50% pruning + 280.67 289.33 411.00 732.00 Urea 5% T 9 50% pruning + 254.67 344.67 372.67 737.67 Ethrel 2000ppm T 1 0 50% pruning + 219.33 422.00 403.00 773.33 Potassium iodide 1% T 1 1 50% pruning + 241.67 504.33 436.00 810.67 Ortho-phosphoric acid 1% SEm± 27.339 61.357 42.946 63.950 CD (P=0.05) 80.642* 180.98* 126.67* 188.62* Table 2. Effect of various pruning levels and defoliants on number of flowering shoots and number of flowers Treatment Number of flowering shoots per tree Number of flowers per shoot (days after pruning) (days after pruning) 30 60 90 120 30 60 90 120 T 1 Control (no pruning, no chemicals) 0.00 0.00 0.00 148.33 0.00 0.00 0.00 12.67 T 2 25% pruning (no chemicals) 41.00 61.67 85.00 123.33 5.67 5.00 5.00 5.00 T 3 50% pruning (no chemicals) 32.33 59.67 82.33 120.33 6.67 4.67 5.33 6.33 T 4 25% pruning + Urea 5% 46.00 64.67 83.00 124.33 5.00 5.67 6.33 5.00 T 5 25% pruning + Ethrel 2000ppm 44.67 62.00 83.67 123.33 5.33 5.00 5.67 7.00 T 6 25% pruning + Potassium iodide 1% 43.67 65.00 82.33 124.00 6.00 5.33 6.00 6.00 T 7 25% pruning + Ortho-phosphoric acid 1% 40.33 61.00 81.67 121.00 6.67 5.00 5.00 6.00 T 8 50% pruning + Urea 5% 42.00 62.00 82.67 122.33 6.67 4.67 5.00 6.00 T 9 50% pruning + Ethrel 2000ppm 40.00 61.00 79.67 122.67 6.33 5.67 4.67 6.00 T 1 0 50% pruning + Potassium iodide 1% 41.33 63.00 81.00 129.00 5.33 6.67 5.00 6.00 T 1 1 50% pruning + Ortho-phosphoric acid 1% 40.67 74.67 81.67 128.00 6.00 5.33 5.33 6.33 SEm± 2.140 9.798 1.409 1.830 0.526 0.469 0.536 0.521 CD (P=0.05) 6.313* 28.90* 4.157* 5.398* 1.551* 1.384* 1.582* 1.537* J. Hortl. Sci. Vol. 10(1):13-17, 2015 Induction of off-season flowering in custard apple 16 treatments. This could be attributed to the fact that treated trees flowered earlier and continued to flower into the normal season. Minimum duration of flowering was seen in Control T1 (73.00) where trees flowered in the normal season only. Similar results were reported by Trevor and Steven (2012) in atemoya, and by George and Nissen (1987) in custard apple. Minimum number of days taken to fruit-set seen in treatment T11 (109.0) was on par with the other treated trees. Control T1 (156.0) took longer to set fruit (Table 4), as photosynthate pruning increases photosynthate translocation to flower buds causing them to fruit earlier than in the Control. These findings are in accordance with that of Naira and Moieza (2014) and Lal et al (2000) in guava. Average number of fruits per tree differed significantly among treatments. Pruning regimes, including defoliation, increased the mean number of fruits per tree over Control (Table 4). More fruits were seen in T4 (41.33) and T6 (41.33), whereas, fewest fruits were seen in T1 (30.0). Pruning along with defoliation appears to have resulted in increase in new growth, culminating in higher translocation of photosynthates from the leaves to the shoots. Our results are in agreement with findings of Farre et al (2000) and Kahn et al (2001) in cherimoya. Data presented in Table 4 reveal significant difference between treatments. Pruning at 25% produced higher yield than 50% pruning or that in unpruned trees. Pruning operation removed apical dominance, released lateral buds from correlative inhibition, and, changed the tree form and construction. This, in turn, enhanced flower-bud initiation in lateral buds, leading to increased yield. Maximum yield was obtained in T4 (10.33) and T6 (10.33), as more number of Table 4. Effect of various pruning levels and defoliants on reproductive growth and yield Treatment Days taken to Duration of Time taken for Average no. of Fruit yield/tree first flower flowering (days) fruit-set (days) fruits per tree (estimated) (kg) T 1 Control (no pruning, no chemicals) 95.3 73.00 156.00 32.00 8.00 T 2 25% pruning (no chemicals) 26.6 121.67 121.00 37.33 9.33 T 3 50% pruning (no chemicals) 24.6 123.00 117.67 30.00 7.50 T 4 25% pruning + Urea 5% 25.3 127.33 116.67 41.33 10.33 T 5 25% pruning + Ethrel 2000ppm 26.3 128.00 114.00 39.33 9.83 T 6 25% pruning + Potassium iodide 1% 26.6 129.00 111.67 41.33 10.33 T 7 25% pruning + Ortho-phosphoric acid 1% 25.6 129.00 112.33 40.33 10.08 T 8 50% pruning + Urea 5% 22.6 130.00 110.00 37.67 9.42 T 9 50% pruning + Ethrel 2000ppm 24.3 129.33 111.67 37.00 9.25 T 1 0 50% pruning + Potassium iodide 1% 24 126.33 110.67 38.33 9.58 T 1 1 50% pruning + Ortho-phosphoric acid 1% 23.6 127.67 109.00 36.67 9.17 SEm± 0.686 1.210 1.367 1.214 0.303 CD (P=0.05) 2.023* 3.56* 4.302* 3.583* 0.895* fruits were borne on the tree. Similar results were reported by Mohamed et al (2011) in plum, and by Demirtas et al (2010) in apricot. Minimum fruit yield was recorded in T3 (7.50) and T1 (8.0 which may be attributed to 50% pruning in T3, resulting in reduced tree-size and available photosynthates. Mohamed and Fawzi (2010) reported a similar phenomenon in Annona. The regular in season crop of Annona under Bengaluru conditions coincides with the South-West monsoon that is August; therefore, quality of the fruit is affected due to rains. The present investigation on induction of off-season flowering through pruning and chemical defoliants resulted in achieving off-season flowering and fruiting (in June) in cv. Balanagar. As Annona fruits are not available in the market during this period, growers will be able to get better market price and profits. In our findings, maximum off-season yield was obtained in T4 (25% pruning, combined with 5% urea as spray) and T6 (25% pruning, combined with 1% potassium iodide as spray). Our findings have helped standardize the cultural practices required on a scientific basis for off-season production of Annona fruits. REFERENCES Bajwa, G.S., Sandhu, H.S. and Bal, J.S. 1986. Effect of pruning severity on growth and bearing of ber. Indian J. Hort., 43:203-206 Braswell, J. and Spiers, H.J.M. 2005. Effect of pruning on blueberry (Vaccinium ashei). Acta Hort., 574:37- 38 Bruno, R.M. and Evelyn, D.V. 2001. Effect of summer pruning and bark girdling on cherimoya var. Concha Lisa. Agri. Tech., 61:215-220 Demirtas, M.N., Bolat, I., Ercisli, S., Ikinci, A., Olmez, H.A., Sachin, M., Altindag, M. and Celik, M. 2010. The J. Hortl. Sci. Vol. 10(1):13-17, 2015 Vinay and Chithiraichelvan 17 effects of different pruning treatments on the growth, fruit quality and yield of ‘Hacihaliloglu’ apricot. Acta Sci., 9:183-192 Dhaliwal, H.S., Banke, A.K., Sharma, L.K. and Bali, S.K. 2014. Impact of pruning practices on shoot growth and bud production in kinnow (Citrus reticulata Blanco.) plants. J. Exptl. Biol. Agril. Sci., 1:507- 513 Farre, J.M., Hermoso, J.M., Guriado, E. and Garcia, T.J. 2000. Techniques of cherimoya cultivation in Spain. Procs. First International Symposium on Cherimoya, Ecuador. C.F. Hort. Abstr., 70:3040 George, A.P. and Nissen, N.C. 1987. Effect of cincturing, defoliation and summer pruning on growth and flowering of custard apple (Annona cherimola x Annonas squamosa) in subtropical Queensland. Australian J. Exptl. Agri., 27:915-18 Guimond, C.M., Lang, G. and Andrews, P.K. 1998. Timing and severity of summer pruning affects flower initiation and shoot re-growth in sweet cherry. Hortl. Sci., 33:647-649 Kahn, T.L., Adams, C.J. and Arpaia, M.L. 2001. Effect of pruning and nitrogen fertilization on cherimoya (Annona cherimola Mill.). Sci. Hort., 64:25-30 Lal, H. and Prasad, A. 1971. Pruning in ber (Zizyphus mauritiana Lamk.): Effect on vegetative growth. Punjab Hort. J., 11:143-146 Lal, S. Tiwari, J.P. and Misra, K.K. 2000. Effect of plant spacing and pruning intensity on fruit yield and quality of guava. Prog. Hort., 32:20-25 Laura Soler and Julian Cuevas. 2008. Development of a new technique to produce winter cherimoyas. Hort. Tech., 18:24-28 Laura Soler and Julian Cuevas. 2009. Early flower initiation allows ample manipulation of flowering time in cherimoya (Annona cherimola Mill.). Sci. Hort., 121:327–332 Lord, W.J., Greene, D.W. and Damon, R.A. 1979. Flowering of young apple trees following summer pruning. J. Amer. Soc. Hortl. Sci., 104:540-44 Mohamed Elham and Fawzi. 2010. Effect of pruning, defoliation and nitrogen fertilization on growth, fruit set and quality of Abdel-Razik Annona cultivar. Nat. Sci., 8:281-287 Mohamed, S.M., Fayed, T.A., El-Shrief, H.M. and Mokhtar, O.S. 2011. Effect of heading, cut levels, bending and NAA on spurs formation, yield and fruit quality of Sun Gold plum cultivar. J. Hortl. Sci. Ornamen. Pl., 3:232-243 Naira, A. and Moieza, A. 2014. Summer pruning in fruit crops. African. J. Agril. Res., 9:206-210 Pandey, R.C., Pathak, R.A. and Singh, I.S. 1998. Effect of pruning intensity on vegetative and reproductive growth in ber (Ziziphus mauritiana). Indian J. Hort., 55:306-313 Sampath, K.P. and Jalikop, S.H. 2000. Cross-compatibility among Annona species. Indian J. Hort., 57:309- 313 Trevor Olesen and Steven. 2009. Branch development in custard apple (Cherimoya Annona cherimola Miller X Sugar apple Annona squamosa L.) in relation to tip-pruning and flowering, including effects on production. Trees, 23:855–862 Trevor Olesen and Steven. 2012. Effects of defoliation on flower development in atemoya custard apple (Annona cherimola Mill X A. squamosa L.) and implications for flower-development modelling. Australian J. Bot., 60:160–164 (MS Received 01 July 2014, Revised 15 May 2015, Accepted 28 May 2015) J. Hortl. Sci. Vol. 10(1):13-17, 2015 Induction of off-season flowering in custard apple