Annals of the Sri Lanka Department of Agriculture. 2008.10:245-253.
IDENTIFICATION OF SUITABLE ROOT STOCKS FOR SOURSOP (Annona muricata) AND THEIR IMPACT ON YIELD PARAMETERS M.K. THANTIRIGE, C.K.D. WELLALA and M.S. KARUNARATNA Fruit Crops Research and Development Centre, Horana
ABSTRACT Soursop (A. muricata) is one of the better known fruits of high nutritive value, in Sri Lanka. This fruit has large potential for further development mainly by selection of productive cultivars. For the conservation of selected material, efficient propagation techniques need to be developed. Hence, the objective of this study was to select congenial root stock species which are capable of developing favourable characteristics of early fruiting and dwarf fruit canopy structure. Seven Annonaceous members, A. reticulata, A. squamosa, A. glabra, A. purpurea, and Rollinia mucosa along with A. muricata (as the control) were tested for their suitability as root stocks for soursop. Except for A. squamosa, the other species showed successful graft take and high survival after field planting. Grafts on A. purpurea developed densely while Rollinia mucosa had short plants. Although these plants flowered, no fruits were formed. Grafts on A. reticulata and A. muricata were moderately tall. All grafts and seed plants of soursop initiated fruits at the age of 15±0.69 to 22±1.58 months after field establishment. No significant difference was found in the yield produced by grafts of soursop and that of seed plants, giving a mean value of 0.84±0.12 and 0.75±0.10 t/ha during the 1st fruiting year and, 0.68±0.38 and 0.70±0.24 t/ha in the 2 nd year, respectively. Thus, in germplasm conservation programmes, soursop can be multiplied by using its own root stock and the root stock of other species such as A. reticulata. In addition to grafting, plants raised from seeds can also be used to propagate soursop, since bearing habits of seed plants are similar to that of grafts. KEYWORDS: Annona muricata, Germplasm, Grafting, Root stock, Soursop.
INTRODUCTION The soursop (Annona muricata L.) which originated in Central and South America, has a distribution throughout the lowland tropics. The fruit is known to be nutritious and is popular for its therapeutic values. The sweet, mildly acidic and aromatic fruit can also be successfully frozen and processed into drinks and various desserts (Morton, 1987). In Sri Lanka, soursop (katu anoda) is mostly confined to back yard gardens, and needs attention to improve its productivity and quality. With the objectives of identification and conservation of the existing variation of soursop, a survey was initiated under the SLUSA Germplasm Development Project in 2001. Results revealed that there are marked differences in sweetness and productivity of fruits grown in different regions of the wet zone (Anon., 2007). Among these, cultivars with promising characteristics could be selected for improvement. In order to transfer such characteristics to the
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production population, an efficient mode of propagation of plants needs to be developed.
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Soursop is primarily propagated by seeds, while clonal propagation, bud and shoot grafting are also practiced using seedlings of the scion species. Different budding methods (shield, patch and modified forkert) and grafting methods (splice, whip and tongue, cleft and crown) can be employed for Annonas with success varying from 53-100 % (Venkataratnam, 1965 and Campbell, 1970). By clonal propagation of different species of the genus, plants of specific characteristics such as high yielding ability with early bearing and plants of a dwarf nature can be produced (Rathore, 1990). Several researchers have tested different root stocks with soursop. Nakasone and Paull (1998) and Dassanayaka et al. (1993) reported that A. glabra (pond apple or wel anoda) is compatible with soursop, for ill drained soil conditions. Soursop on A. reticulate (bullockâ€™s heart or wali anoda), A. squamosa (sugar apple or seeni anoda) and A. montana (mountain soursop) have shown compatibility (Iglesias and Sanchez, 1985). Thus, root stock and scion compatibility has significant influence on imparting desirable characteristics of the root stock. As such, studies were undertaken at the Fruit Crops Research and Development Centre, Horana during 2004-2007 to identify a compatible root stock in order to develop an efficient method of propagation to multiply the selected germplasm. MATERIALS AND METHODS Experiment l - Evaluation of the success of patch budding and wedge grafting techniques on soursop grafted on five species of Annona and Rollinia mucosa Seeds of A. reticulata, A. squamosa, A. glabra, A. purpurea, A. muricata (as the control) and Rollinia mucosa were collected and raised as root stocks. The experiment was conducted in a Completely Randomized Block Design with 4 replications. Ten uniformly grown seedlings 5-7 months old, and 10-12 months old were taken per treatment for wedging and patching respectively. When stock plants attained a height of 20-30 cm and a diameter of 0.5-0.7 cm, they were wedge grafted at a stem height of 8-10 cm of the root stock plant. A uniform set of 6-8 cm long scion shoots of similar diameter to that of the stock plant were taken from 4 selected mother plants of soursop. Grafts were enclosed in a 100 gauge opaque polythene bag (sealed) with the bottom tied to serve as a single propagator. Plants were uncovered at 21 days after grafting. For patch bud grafting, diameter 0.8-1.0 cm were used obtain to bud patches from the same soursop mother plant. The percentage of graft take was recorded at 3 months after grafting and log transformation was done.
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Experiment II - Evaluation of growth and yield performances of grafted soursop on six different root stocks Five months old patch bud grafted plants on compatible root stocks obtained from the experiment I, along with similar aged soursop seedling plants were field planted to evaluate growth, development and fruiting ability. The experiment was arranged in a Randomized Complete Block Design having 4 replicates and 2 plants per treatment. Growth parameters such as plant height and crown spread were recorded at the fruit set. The time taken for fruit initiation, number of flowers formed at weekly intervals, number and weight of fruits produced during first two fruiting years were also collected as yield characteristics. Percentage data was log transformed. All the data were subjected to ANOVA using M-STAT package and mean separation was carried out by using the new DMRT. RESULTS AND DISCUSSION Success of propagation techniques Out of the two propagation techniques tested for soursop on 6 different root stocks, it was observed that except for A. glabra, all others responded well to both patch and wedge methods. The success rate of wedge and patch grafting was shown to be 71.3±7.5 and 68.8±7.0 %, respectively (Table 1). Soursop grafted on to A. glabra recorded the lowest success rate of graft take (5±0.48%) in wedge grafting whereas, a high rate of success (80±6.3%) was recorded in patch grafting. A. glabra which is a vigorously growing wild plant, may not be compatible when tender apical shoots are used in wedging. In contrast to wedge grafting, a piece of bark containing a bud taken from a 12-months old shoot at similar maturity stage may have contributed for the higher rate of bud take success in patch budding. As such, for propagation of soursop on A. glabra, only bud grafting could be adopted. Similar results have been obtained by Bourke (1976), where graft take on A. glabra was not much successful and the surviving grafts died subsequently. This further confirms the unsuitability of shoot (wedge) grafting of soursop on to A. glabra. For A. squamosa, A. reticulata, Rollinia mucosa, A. purpurea and A. muricata, both bud and shoot grafting could be employed whereas grafts on A. squamosa died three months after field planting. Similar findings have been obtained by Singh (1992), Coronel (1994), Popenoe (1974) and Iglesias and Sanchez (1985).
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For wedging, relatively young stock plants which were 5-7 months old were utilized, while for budding 10-12 months aged plants were taken. When comparing the two methods, though wedging needs an additional portion of scion material, it offers an efficient mode of propagation. Also the time taken to raise stock plants is relatively low compared with patching. Even though there was no significant difference in the success rate of these two methods tested in the present experiment, Duarte et al. (1974) stated that side whip and cleft methods of grafting are superior to budding in percentage take and subsequent growth. In contrast to this, Rathore (1990) reported that in A. cherimola (cherimoya), there was no difference in percentage success and subsequent growth in budding and grafting. Table 1. Success of patch and wedge grafting of soursop on 5 different Annona spp. and Rollinia mucosa. Root stock spp.
% graft take (at 3 months after grafting) Patch budding*
A. reticulata 70.5±4.1 A. squamosa 67.5±7.9 A. glabra 80.0±6.3 A. purpurea 67.5±14.1 A. muricata (control) 75.0±4.8 Rollinia mucosa 67.5±7.9 Mean 71.30±7.5 CV (%) 3.28 *- not significant at p=0.05. Mean in each column significantly different (p< 0.05).
% patch bud graft survival (at 3 months after planting) 100 0 80 100 100 100
82.5a±7.9 87.5a±10.4 5.0b±0.48 77.5a±7.9 85.0a±10.7 75.0a±4.8 68.8±7.0 19.98 followed by the same letter are not
Compatibility of root stocks Out of the 6 species of Annona and Rollinia mucosa tested as root stocks for soursop, except for A. squamosa, all others showed satisfactory graft survival of 80-100% at 3 months after planting (Table 1). All surviving grafts on A. squamosa developed leaf yellowing symptoms, followed by retarded growth and death. At three months after planting, no single plant survived indicating its incompatibility with A. muricata. It was also reported that dwarfing potential of A. squamosa, was vulnerable to Pseudomonas solanacearum (George and Nissen, 1986). Many root stocks have been tried for soursop with varying success. Morton (1967) reported that A. reticulata, A. glabra and also soursop itself performed well with soursop. Findings of the current experiment on the basis of graft take indicated that in addition to A. glabra, which showed poor survival with
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wedge grafting, A. reticulata and A. muricata, Rollina mucosa and A. purpurea showed satisfactory growth performances of grafts. Growth and yield performances Evaluation of vegetative growth dimensions of 5 members of Annonaceous showed that grafts on Rollinia mucosa had a significantly short plant height with well spread open tree canopy structure (Table 2). Although they flowered, no fruit set was observed in any of the 2 fruiting seasons. Iglesias and Sanchez (1985) and Sanewski (1991) reported that though certain species of Rollinia were congenial, some exhibited significant incompatibilities with soursop. The particular species Rollinia mucosa, used as root stock in this experiment was unsuccessful in fruit formation. Similarly, grafts developed on A. purpurea, a wild species grew as a dense tree canopy (Table 2). This resulted in no fruit formation though it flowered. Although, this species of Annona shows a prolific bearing habit, so far no work has been done to test the suitability as a root stock for any of the Annona species. Therefore, the possibility of using it on A. reticulata and A. squamosa to impart its bearing characteristics needs to be focused, as these are shy bearers. Table 2. Mean age at first fruiting and fruit set percentage of grafted soursop on different root stock and seed plants. Root Stock
Plant height (m) 2.56a±0.13 2.48a±0.06 1.50b±0.21 2.93a±0.17 2.54a±0.15
Crown diameter (m) 1.06b±0.09 1.27ab±0.11 1.55a±0.11 1.30ab±0.10 1.36ab±0.12
Time taken for fruit initiation (months)* 15±0.69 22.3±1.58 0 15.3±0.74 21.6±1.82
A. reticulata A. glabra Rollinia mucosa A. muricata A.muricata (seedling plants) A. purpurea 2.67a±0.18 0.84c±0.12 0 CV (%) 14.78 20.63 10.99 Mean of 8 plants. *- not significant at p=0.05. Mean in each column followed by the same letter are not significantly different (p< 0.05).
Grafts on A. muricata and A. glabra including plants raised from seeds grew with similar crown spread and similar plant heights, and set fruit at 15-22 months after establishment (Table 3). Grafts on A. reticulata had less crown spread and similar plant height compared to the above three and also fruit sets. No significant difference in time taken for first bearing was shown in soursop seed plants and grafts on these three species (Table 2). In soursop, fruit set is considerably low (22-29%), which may be due to lack of insect pollinators.
SUITABLE ROOT STOCKS FOR SOURSOP 251 Table 3. Vegetative growth and yield parameters of soursop (A. muricata) grafted on to 6 different root stocks at 12 months after planting during the first 2 fruiting years. Root stock species
% fruit set
First year Number 3.75±0.79
Yield (t/ha) Second year Weight Number 0.62b±0.14 6.0a±0.67
A. muricata 26.88a±4.1 3.25±0.79 0.84a±0.12 5.0a±1.17 0.688a±0.38 (control) A. muricata 21.67a±2.4 3.00±0.67 0.75ab±0.10 5.5a±1.07 0.695a±0.24 seed plants. CV (%) 10.57 20.13 24.91 18.57 24.89 Mean of 8 plants. . Mean in each column followed by the same letter are not significantly different (p< 0.05).
Poor fruit set is a common problem found in soursop due to absence of insect pollinators (George and Nissen, 1988). Morton, (1987) also reported that soursop is a poor bearer, the usual harvest being 12-24 fruits per tree per year with low initial yields. Significantly higher plant spread was observed on soursop grown on soursop than that of seed plants; however, no significant difference in plant height was found between these two types (Table 2). However, the yield produced by plants on A. glabra was significantly the lowest compared to the other root stocks used in both fruiting seasons (Table 3). This may be due to the fact that it is a wild species highly adapted to the ill drained soil conditions. Therefore, when grown in up land where well drained soils are found, it may not be conducive for growth and survival. This may have resulted in low yields in soursop grafted on to A. glabra showing its low compatibility for high lands. Similar findings of its partial compatibility for soursop were reported by Singh (1992), Coronel (1994), Popenoe (1974) and Iglesias and Sanchez (1985). Contrary to this, Sanewaki (1991), Nakasone and Paull (1998) indicated that A. glabra is compatible with soursop, without mentioning the soil conditions. Dassanayake et al. (1993) showed its suitability for water logged soils. However, present results indicated its partial compatibility with soursop growing on highlands. Out of all species, soursop on soursop and its seed plants produced the highest yield of 0.84±0.12 and 0.75±0.10 t/ha, respectively
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during the first year of fruiting with no significant difference in the yield among plants (Table 3). Similarly, no significant variation was found in number of fruits developed by soursop on A. glabra, A. reticulata and A. muricata and seedling soursop, giving a mean value of 2.5-3.75 fruits and 5-6 fruits in the first and second years, respectively. Similarly no significant variation was shown in the yield of soursop on A. reticulata and that of seed plants in the first year. During the second year of bearing, no significant difference was shown in the yields of soursop on soursop, A. reticulata and seed plants giving a mean yield as shown in the Table 3. This indicated the similar capabilities of soursop on its own root stocks, A. reticulata and seed plants of soursop in fruit formation. Mowry et al. (1941) showed that A. reticulata provides a vigourous root stock and enhances longevity of soursop. Furthermore, A. reticulata (bullockâ€™s heart) is grown in both humid and semiarid climates (Popenoe, 1974). Soursop is the most tropical tree (Popenoe, 1974 and Nakasone and Paull, 1998) and is found mainly the moist regions. Therefore, adaptability of soursop on A. reticulata for semi-arid or dry zone in Sri Lanka is good where as inability of soursop to perform well has to be investigated. This offers an added advantage of A. reticulata. Moreover, it is reported by Popenoe, (1974) and Pinto, (2005) that it adapts well to unfavorable soil conditions, with pH ranging 5-8. Due to this reason, it is shown to be a good root stock for soursop. According to the findings of the experiment, among seven root stocks tested only A. reticulata and its own root stock A. muricata were congenial to soursop. It has been shown that though soursop itself is the best root stock for soursop, grafting on to A. reticulata is usually successful, which is consistent with findings of the current experiment (Morton, 1987). In addition to shoot grafting, plants raised from seeds can also be used to multiply soursop as seed plants which had taken 22 months for 1 st fruiting, similar to that of grafts. Moreover, no significant variation was observed in the fruit yield in seed plants and grafts. In seed propagation, less skilled labour is required, which is an additional advantage over budding and grafting. Findings of Bourke (1976), confirmed these results that fruit initiation of seed plants occurred in the 2nd year. George and Nissen (1987 b) also stated that seedlings take 2-4 yrs. for initial bearing and are genetically uniform. Pinto, (2005) reported that though grafted soursop grows rapidly, the time taken for first bearing is similar to that of seed plants, which is in conformity with the findings of the current experiment. They further stated that seed plants are generally true to type.
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CONCLUSIONS A. reticulata and A. muricata (soursop) were found to be compatible root stocks for both wedge and patch grafting of soursop with over 70% success. A. glabra showed moderate compatibility for highlands using patch bud grafting with 80% success and moderate yielding ability. A. purpurea and Rollinia mucosa were found totally incompatible with soursop. Seed plants of soursop and that of grafts on soursop and A. reticulata initiated fruits by 15-22 months after establishment and produced a mean initial yield of 0.75±0.10, 0.84±0.12 and 0.62±0.14 t/ha during the first fruiting year and 0.70±0.24, 0.69±.0.24 and 0.77±0.15 t/ha in the second year, respectively. There was no significant difference either in time taken for first bearing or total yield. Therefore, promising accessions of soursop can efficiently be propagated by means of seeds or vegetative propagation. Less skilled labour requirement and easy propagation are the added advantages in seed prorogation over clonal propagation. REFERENCES Anon., 2007. Sri Lanka/ USDA Germplasm Development Programme, Annual report Sri Lanka. 110-112p. Bourke, D.O.D. 1976. Annona spp. In The Propagation of Tropical Fruit Trees, Eds. R.J. Garner and S.A. Chaudhri. Pp 223-248. Commonwealth Bureau of Horticulture and Plantation Crops, East Mailing, Maidstone, Kent. Campbell, C.W. 1970. In Proceedings of the 83rd Annual Meeting of Fla. State Horticulture Society, Miami, 83: 353-356. Coronel, R.E. 1994. “Atis” In Promising Fruits of the Philippines, Eds. R.E. Coronel, J.C. Zuno and R.C. Sotto. Pp 1-18. College of Agriculture, University the Phillippines, Los Banos, Laguna, the Phillippines. Dassanayake, E.M., M.K. Thantirige and W.G.S. Perera. 1993. Top working of pond apple (A. glabra). Krushi 13: 3-4. Duarte, O.J., Villagacia and R. Franciosi. 1974. The effect of different treatments on propagation of cherimoya. The Tropical Region of American Social Horticultural Science 18: 41-48. George, A.P. and R.J. Nissen. 1986. “Custard apple” Biennial Report. Maroochy Horticulture Research Station 4:46-68. George, A.P. and R.J. Nissen. 1987b. The effects of day/night temperatures on growth and dry matter production of custard apple. Scientia Horticulturae 31:269-274. George, A.P. and R.J. Nissen. 1988. The effects of temperature, vapor pressure deficit and soil moisture stress on growth, flowering and fruit set of custard apple (atemoya), ‘African Pride’. Scientia Horticulturae 34:183-191.
254 THANTIRIGE et al. Iglesias, A.A. and L.A. Sanchez. 1985. Propagation of soursop, Annona muricata L. by grafting on different annonaceous root stocks. Acta Agron 35: 53-58. Morton, J.F. 1967. The soursop, or ‘guanabana’ (Annona muricata L.). Fla. State Horticulture Society 79:355-366. Morton, J.F. 1987. Fruits of warm climates. J.F. Morton Publisher, Miami Florida USA. 7580 p. Mowry H.L.R. Toy and H.S. Wolfe. 1941. Miscellaneous tropical and sub tropical Florida fruits. Agriculture Extension Service, Gainesville, Florida Bulletin 109: 1121. Nakasone, H.Y. and R.E. Paull. 1998. Annons. In Tropical Fruits, Eds. H.Y Nakasone and R.E. Paull. Pp 45-75. CAB International, London U.K. Pinto, A.C. de Q. 2005. Agronomy. In Annona. Eds. A. Hughes, C.R. Clement, N. Haq, R.W. Smith and J.T. Williams. Pp 71-84. International Centre for Underutilized Crops, University of Southampton, Southampton, SO 171 BJ, UK. Popenoe, W. 1974. The Annonaceous Fruits-The Soursop. Manual of tropical and sub tropical fruits. Hafner Press, Division of Macmillan Publishing Co, Inc. New York, Collier - Macmillan Publishers, London. 182-186 p. Rathore, D.S. 1990. Custard Apples. In Fruits: Tropical and Sub Tropical Naya Prokash, Eds. T.K. Bose and S.K. Mitra. Pp 449-66. 206, Bidhan Sarani, Calcutta. Sanewski, G.M. 1991. Custard apple. Cultivation and Crop Protection. Information Series Q 190031, Queensland Department of Primary Industry. Brisbane. Singh, S.P. 1992. Fruit crops for wasteland. Scientific Publisher, Jodhpur, India. 42 p. Venkataratnam, L. 1965. The custard apple and allied fruits. Farmer’s Bulletin No. 29, p44. Indian Council of Agricultural Research.