Rubber Research Institute of Sri Lanka

IRRDB Seminar Paper

High field establishment rate, uniform growth, easy handling, low cost of production, undisturbed tap root system, etc. are some of the advantages of young buddings.

In young buddings, seedling plants grown in polybags are grafted with green buds at the age of 3-4 months. Bud grafting success of all RRIC clones recommended in groups I, II & III (i.e. RRIC 100, RRIC 102, RRIC 110, RRIC 117, RRIC 121, RRIC 130 and RRIC 133) and all PB clones recommended in group I, II, III & IV (i.e. PB 28/59, PB 217, PB 235 & PB 255) was 90 - 100%. The bud grafting success was neither dependent from the growth stage of the top most leaf whorl (immature or mature) nor the cut back time of the stock plant (either 2 weeks or 4 weeks).

The quality of stock plants and the budwood affected the budgrafting success as well as the growth of the grafted bud. Selection of early germinating seeds by using a germination bed proved to be essential to obtain buddable girth at 3-4 months of age. Further, correlation was found between the growth of stock plant and that of the scion. The length of the snag and the presence of leaves affected the sprouting time and the initial growth of the grafted bud. The incidence of taproot penetration could be reduced by placing two circles of gauge 500 polythene at the bottom of the bag prior to filling with soil.

Use of young buddings as a planting material should increase the productivity of plantations mainly by maintaining the correct stand together with uniform growth in the field while contributing toward reducing the immature phase. The clone of the budded plants can be identified at 2-3 leaf whorl stage and this will be an added advantage in young buddings when compared to bare root budded stumps.

Introduction

Young buddings have been widely accepted by the planters mainly because of their superior quality and low cost compared to other polybag planting materials. In fact, young budding is an improvement to green buddings where seedlings in polybags are grafted when they are about 3-4 months. This not only reduces the nursery time and thereby the cost, but is also acceptable under the climatic conditions and planting practices adopted in Sri Lanka. The main seed fall in Sri Lanka is around August. When stock nurseries are raised in August-September, they can be bud grafted in late December and cut back after one month allowing the grafted bud to grow for a period of 3-4 months until they are planted in the field during the main planting season in May-June.

Though green or brown budded polybag plants are recommended for a higher rate of field establishment and for a more uniform stand in the field, the technique still demands the use of a ground seedling nursery and a polybag nursery and requires a period of about 10-12 months to produce a two-whorl plant. In young budding, the ground nursery is totally eliminated and polybag plants with 2-3 leaf whorls and good root systems are produced in a shorter period.

Moreover, unlike other planting materials, almost all the inputs that usually go to raise the stock plant is diverted to scion growth in young buddings. Studies have been carried out by the scientists in the far-east to improve the quality of this planting material (Leong, et.al. 1985, Ong et.al.1989, Yoon et.al.1989, Seneviratne et.al. 1994, Seneviratne et.al. 1995).

In this paper various factors affecting the budgrafting success, scion growth etc. and the suitability of the planting materials to local conditions are discussed based on the results obtained at the RRISL during the past 5-6 years. Some parts of this paper have been published in the Journal of RRISL,1994.

MATERIALS AND METHODS

Seeds collected from mixed clonal areas were sown in germination beds and early germinated seeds were planted in polybags filled with soil. Top soil sieved with ½" sieve and mixed with rock phosphate @ 100 g/bag was used to fill the bags. Bags were arranged in single rows spacing 1½ feet between rows. Treatments were fully randomized and replication was 25-50.

The following treatments were tested;

a). Seedling types -Seedlings were harvested from the same germination bed at three different times,i.e., within the first two weeks, from the same germination bed but one month after the seed sow and 2½ months old seedlings from the same germination bed. They were planted in 15 x 33 cm size bags.

b). Polybags - 15 x 33 cm, 18 x 38 cm and 23 x 45 cm size bags were made from gauge 500, black, gusseted polythene were tested. Gauge 300 was also tested for 15 x 33 size. Bags were perforated prior to soil filling. In one experiment, two circles of gauge 500 black polythene were inserted in to the bag in order to see whether penetration of tap root could be reduced.

c). Clones - Bud grafting success of clones RRIC 100, RRIC 102, RRIC 110, RRIC 117, RRIC 121, RRIC 130 & RRIC 133, PB 28/59, PB 217, PB 235 & PB 255 was checked.

d). Growth stage of top flush of leaves - When the top most leaf whorl was either copper brown or apple green, it was considered as immature and when the same was dark green and fully expanded it was considered as mature.

e). Budwood types -Budwood was harvested from well maintained nurseries as well as overaged abandoned nurseries. Also, budwood from well maintained nurseries were stored for 24 and 48 h in polythene covers and kept under a shade in the nursery and used for grafting.

f). Bud type - Axillary buds and scale buds were harvested from 6-8 weeks old green shoots.

g). Snag - After bud grafting following snag types were tested.

I - 15 cm long snag + nicking

II - 15 cm + covered with black polythene.

III - 50 cm long snag + 3 leaves + nicking

IV - 50 cm long snag + nicking

V - 50 cm long snag + covered with black polythene

h). Cut back time - Zero, two and four weeks were tested with 15 cm long snag and 50 cm long snag with leaves.

i). Planting methods - Following three types were tested for field establishment and growth.

I - Bare root budded stumps (control)

II - Young buddings with graft placing union 2" below the ground Level.

III - Young buddings with graft union buring 6-8" below the ground level.

These treatments were repeated individually and in groups during three consecutive years. Data were analysed using SAS statistical program.

RESULTS

a). The effect of the quality of the seedlings on the growth.

The mean girth of the early germinates, late germinates and 2½ month old seedlings, after 3½ months of planting in bags, were 7.9 mm, 5.8 mm and 3.9 mm. Accordingly the % of buddable plants for the three types were 75%, 46% & 40% in the same order.

The effect of the growth of the seedling on the scion as measured by their diameter showed a good positive correlation (r=0.69463, p=0.0001) between the two at the time of field planting.

b). The effect of the bag size on seedling growth and the bud grafting success.

The diameter of the seedling plants at 10 weeks, at bud grafting and the budgrafting success of clones RRIC 100 & 121 are given in Table 1.

Bag size	Diameter (mm)		% Grafting Success
	at 10 weeks	at budgrating
15 x 33 cm	4.5 ± 0.62	5.6 ± 0.70	91.1
18 x 38 cm	4.5 ± 0.54	5.7 ± 0.48	95.3
23 x 45 cm	5.3 ± 0.71	6.1 ± 0.86	98.8

Table 1. The effect of bag size on seedling growth and bud grafting success.

The diameter of the stock plants and the number of leaf whorls increased with the increase of bag size. The differences between 15 x 33 and 18 x 38 was only 3% and also not significant. The differences in diameter & leaf whorls between 18 x 38 and 23 x 45 cm was significant though it was only 6%. Though the bud grafting success increased with the increase of the bag size the figures were not statistically significant (X² = 0.855).

The effect of the gauge of polythene of the bag - As far as the gauge of polythene is concerned, for both 15 x 33 cm and 18 x 38 cm size bags, gauge 300 polythene can also be used. But with 23 x 45 cm size bags, if the gauge is 300 the bag cannot be lifted or moved without damaging the brim.

The effect of the thicker base of the bag - When two circles of gauge 500 polythene were inserted in to the bag, the penetration of tap root could be reduced by 20% where the tap root was coiled at the bottom of the bag.

c). The effect of the clone on budgrafting success.

The budgrafting success of RRIC 100, RRIC 102, RRIC 110, RRIC 117, RRIC 121, RRIC 130, RRIC 133, PB 28/59, PB 217, PB 235 & PB 255 was in the range of 90 - 100% and the differences were not significant.

d).The effect of the growth stage of the top flush of leaves.

The effect of the growth stage of the top flush of leaves was not significant for bud grafting success. However, the grafting success was slightly higher when the top most leaf whorl was immature.

e). The effect of the quality of budwood

The bud grafting success of budwood harvested from different sources is shown in Table 3.

Source of budwood	% grafting success
Overaged nursery	60%
Well maintained nursery	100%
Well maintained nursery + 24 h storing	98%
Well maintained nursery + 48 h storing	98%

Table 3. Budgrafting success of budwood from different sources.

f). The effect of the bud type on grafting success and sprouting

The bud grafting success of the axillary and scale buds for clones RRIC 100 and RRIC 121 were 98% and 92% respectively. But the differences were not significant.

Though the initial sprouting is delayed with scale buds, 80% of the plants grafted with both bud types was sprouted within 2½ months.

g). The effect of snag treatment on sprouting and scion growth

Sprouting is faster with shorter snags. More than 70% has sprouted at about 15 days in treatments I & II. Though the treatments III, IV & V had similar size snag of about 50 cm, snags of treatment III contained leaves on them and showed the slowest sprouting. Though more than 75% of the plants with shorter snags sprouted at about 1 month of cut back, it was below 20% for longer snag and below 10% when long snags contend leaves.

As far as the growth of the scion shoots is concerned, both the diameter and the lengths of the scion shoots showed differences among treatments. Generally, the plants with long snags and leaves showed the highest diameter and length. Shorter snags showed better growth than those having long snags but no leaves.

h). The effect of the cut back time.

The cut back time had no influence on the percentage sprouting and number of successful plants, when the snag was long and with leaves. However, sprouting was not uniform and all three treatments showed a similar pattern, lasting for about 8 weeks. But, sprouting started earlier when the stock plants were cut at the time of bud grafting and this showed no adverse effect on the bud grafting success. Nevertheless, removing the stock plant either at 2 weeks or 4 weeks gave similar results.

With shorter snags removing the stock shoot at the time of bud grafting was a failure. Similar to long snags, cut back time of 2 weeks and 4 weeks showed a similar pattern of sprouting, but faster than with long snags.

i). The effect of the planting method.

As far as field establishment rate was concerned, 100% success rate was obtained with both shallow and deep planted young buddings, where as this was 95% for shallow planted bare roots despite the fact that the weather conditions were very favourable for about 1-2 months after planting.

The growth of young buddings are faster than that of bare root budded stumps. The differences in girth between the two treatments of young buddings was not significant but the girth of bare roots was significantly low (p = 0.001) from that of young buddings.

DISCUSSION

The influence of the rootstock on the growth of the scion has been studied (Buttery, 1961, Combe and Gerner, 1977) and accordingly various cultural practices are adopted to select vigorously growing seedlings. From the results obtained, the importance of using vigorous seedlings by selecting early germinates is very clear for the subsequent grown of the stock plant.

Though it is not surprising that bigger stocks are produced in larger bags, the difference in the diameter between the plants grown in small and medium size bags was very small. Also, the increase in seedling diameter was not proportionate to the capacity of the bags. The medium size bag was 60% bigger than the small bag and then the large bag was 90% bigger than the medium one and accordingly, large bag was 3 times bigger than the small bag. Apart from the cost of polythene, the higher quantity of soil is also a disadvantages with large size bags. For both 15 x 33 cm and 18 x 38 cm sizes, gauge 300 can also be used where the cost is reduced further.

Inserting polythene circles at the base reduced the incidence of penetration of the tap root yet the effect of coiled tap root on the subsequent growth is not known.

The clonal differences on bud grafting success was insignificant and when the budwood was harvested from properly maintained nurseries,and also if the stock plants are healthy, 100% bud grafting success could be obtained.

For normal brown and green budding, it is the normal practice to avoid grafting stock plants having an immature whorl for their peeling quality being poor which affects the bud grafting success. However, this was found to be immaterial for grafting young buddings and which is an advantage.

As far as the quality of budwood is concerned, the most important factor is to use them before desiccation. When the budsticks were sealed in a polythene bag and kept under a shade, bud grafting success was not affected even after 48 h.

When the bud sticks were harvested from badly managed nurseries the budgrafting success was significantly low. Though the results are not presented, this effect was different for different clones and for some clones it was as low as 50%.

The performances of scale and axillary buds was studied earlier also (Samaranayake & Gunaratne,1977) and the present finding is confirms with that the scale buds are slower than axillary buds in sprouting. However, use of axillary buds has the disadvantage of the requirement of removing leaves about 3 weeks prior to harvesting budwood. Also, early sprouting of axillary buds shows no advantage over scale buds as the growth of rubber occurs in flushes.

The effect of the snag seems to be the most important factor for the initial growth of the grafted bud. Longer snags with leaves attached show beneficiary effects for the growth of the grafted bud yet carry the disadvantages of nicking & delayed or uneven sprouting. Also, if the buds in long snags were not removed properly and timely, then the effect of the long snag on the scion was adverse as the food reserves in the stock is used by the stock shoots for their growth while the grafted bud remains dormant. Then the growth of the scion may be similar or sometimes poorer than that of short snags.

Covering the dormant buds with black polythene strips or similar device should be effective, but, however, in the present study, the results were not that encouraging due to various practical difficulties.

As the bud grafting success does not seem to be affected by the cut back time, removing the stock plant at the time of bud grafting can be practiced to advantage with long snags containing leaves, However, as the problem of nicking is associated with longer snags, the advantage of early sprouting may become less valuable, Therefore, if the nicking is acceptable this cut back at the time of bud grafting can be practiced to make sprouting early.

As far as the planting method is concerned, young buddings showed 100% field establishment either when they were planted as normal polybag plants or deep planted by buring about 6" - 8" stem. Elimination of the "elephant foot" formation, when they are deep planted, is also advantageous. The possible stock effect on the yield when the tapping panel reaches the ground level can also be minimized by adopting deep planting method.

However, the advantage of using young buddings than polybag plants is the well established root system of young buddings which helps in the continuous growth in the field specially under unfavourable weather and climatic conditions. Also, the cost of young budding is much less than that of a polybag plant. This is mainly due to less nursery time. Undisturbed tap root system of young buddings is also an advantage of young buddings, compared to polybag plants. High field establishment rate is also partially due to the well established root system. Uniform growth in the field is achieved mainly because of using selected plants and also due to less or no casualties in the field. Finally, the time schedule for varying of young buddings fits well with the local climatic conditions and our planting practices. In general, use of young buddings is one of the most effective ways towards increasing the productivity per unit land area.

ACKNOWLEDGEMENTS

The authors gratefully acknowledge the technical assistance of Mrs. G.A.S. Wijesekera, Miss. S.P. Withanage, Mr.L.L.P. Vitharana, Mr. H.P. Pieris of Plant science Department & Mr. S.M.A. Samarakoon of Polymer Chemistry Department. They are also thankful to Mr. W. Amaratunga of Plant Pathology Department for preparing photographs & slides and for Mrs. D.E. Jayawardena of Plant Science department for typing the manuscript.

REFERENCES

Buttery B R, 1961. Investigation into the relationship between stock and scion in budded trees of Hevea brasiliensis J.RRIM. 17(2): 46-76.

Combe J C, Gerner P, 1977. Effect of the stock family on the growth and production of grafted Hevea. J. RRISL. 54(1):83-92.

Leong, S K, Yoon, P K and P'ng,T C (1985). Use of young budding for improved Hevea cultivation Proc. Int. Rubber. Conf. Kuala Lumpur, 3, 555.

Ong, T S, Seh, W Y and Wong, C P (1989). Young budding - Commercial experience in a large plantation group. In Proc. Rubb. Growers Cong. Rubb. Res. Inst. Malaysia, 21 - 23.

Samaranayake, C and Gunaratne, R B (1977). The use of leaf buds and scale buds in the vegetative propagation of Hevea. Jl. Rubb. Res. Inst. Sri Lanka, 54 (1): 65-69.

Seneviratne P, Nugawela A and Samarakoon S M A (1995). The role of snag on the growth of scion in bud grafted plants of Hevea with special reference to young buddings. Jl. Rubb. Res. Inst. Sri Lanka 76, 21 - 35.

Yoon, P K, Leong, S K, Hch, W Y and Sim, B S (1989). Retention of Snag leaves in Young Budding. Proc Rubb. Growers Conf. Rubb. Res. Inst. Malaysia, 77-98.