148 



THE AGKICULTURAL NEWS. 



May 19. 1917. 



SEED SELECTION IN THE CULTIVATION 

 OP HEVEA RUBBER. 



The attention of Messrs. Clayton Beadle, and H. T. 

 Stevens, was recently drawn by the Director of the 

 Royal Botanic Gardens, Kew, to the probable importance 

 of seed selection in the cultivation of Hevea hrosilieiuis. 

 He pointed out the large increase in the yield of alkaloids 

 from cinchona bark which has been obtained as the 

 result of seed selection, and suggested that important 

 results might similarly be obtained in the cultivation 

 of Hei'ea brasilienns. 



In .June last they addressed a letter on this subject 

 to the British Rubber Growers' Association, which has 

 been submitted to Messrs. Morgan, Mar.sden and Reeve, 

 the Association's resident scientific officers in the East. 

 Below is given the substance of their original letter, 

 together with a digest of tlie views of the Association's 

 Experts, reproduced from the Keiv Bulletin (No. 1 of 

 1917):— 



In the cultivation of cinchona the yield of quinine from 

 the baik ba.s been raised from about 3 per cent, to 7 per cent, 

 or more as the re.sult of planting from the seed of trees whose 

 bark yielded a high percentage of alkaloids. Can a similar 

 method of seed .selection be applied to increase the yield of 

 rubber? 



Tie matter, however, iti not so simple in the case of Para 

 rubber as in the case of cinchona. In the latter, the analysis 

 of the bark reveals the percentage of alkaloid.", but in the case 

 of Para rubber it would be neces.sary to keep daily records of 

 theyield.sot individual trees over some considerable period 

 before it could be said with certainty whether the trees were 

 good or poor milkers. Work of this nature would liave to be 

 undertaken as a preliminary to seed selection, as there seems 

 to be some doubt as to how far trees fluctuate in their yields 

 over relatively long periods. We were informed by one planter 

 of experience that a tree which was yielding poorly might be 

 yielding well in a few months time, and similarly, trees which 

 appeared to be yielding large quantities of latex might, in the 

 course of a few months, be found to be yielding quite .small 

 quantities. We have not had an opportunity of obtaining 

 figures over a sufficiently long period. 



Having ascertained definitely that trees vary in yield, 

 it will then be necessary to devise means for selecting seeds 

 from good milkers and avoiding those from poor milkers. This 

 matter is more difficult in the case of a rubber tree than in the 

 case of cinchona. The cinchona produces a large number of 

 small steds, and consequently there is no difficulty in obtaining 

 ample seed from a few trees, sufficient for planting up large 

 areas. The bark gives a good yield of alkaloids when the 

 tree is four years old, and although the percentage yield 

 increases slowly over the next few years, the increase is 

 small and regular, .so that an examination of the bark of 

 four-year-old trees is sufficient to determine their value as 

 producers of alkaloids. On the other hand, Hevea produces 

 a relatively small number of large seeds. Moreover, the 

 bursting of the capsule by which these seeds become scattered 

 makes it practically impossible to collect seeds from any 

 particular tree*. There is al^o the question of cross-fertili- 

 zation, as, even if the seeds be taken from good milkers, 

 they may have been pollinated from trees which are poor 

 milkers. 



The points which require elucidation are: — 



1 . To ascertain if trees can be classified as good 

 and poor milkers. 



♦This difficulty might be overcome l)y cutting otf sce(K 

 bearing bnnches just l)efnre the seed is fully ripe. 



2. To ascertain which trees are good milkers. 



3. To collect seeds from particular trees. 



4. To avoid cross-fertilization between good and 

 poor milkers. 



5. Assuming that both male and female elements 

 be derived from good milkers, there would probably 

 be poor milkers among the ancestry. This would 

 produce throw-back.s, which might necessitate selection 

 over another generation. 



The necessary procedure would appear to be either: 



(a) To plant up a small area surrounded by jungle so 

 as to isolate the trees in the area from those of the planta- 

 tion, or: — 



{h) To select a small area on an estate which is separate 

 from other parts of the estate, and proceed to keep a record 

 of the daily yields of the dry rubber from the trees of this 

 area. As it becomes apparent that certain of these trees are 

 poor milkers, they should be cut out until eventually the 

 trees on this area consist of good milkers only. 



If, as under (a), the trees have to be planted up on 

 a fresh area, it will be seven or eight years before the poor 

 milkers can be eradicated. If, however, an area already 

 planted up should be found sufficiently isolated from the 

 main part of the plantation to |)revent the possibility of 

 cross-fertilization, a couple of years would probably suffice to 

 ascertain which are the poor milkers and to cut them out. 



The seeds now produced in this area will be entirely 

 from good milkers. They will produce trees, the majority of 

 which will be good milkers, although a few of them, in 

 accordance with (.5), may be throw-backs, and conse.iue'ntly 

 poor milkers. However, the seeds from this area should be 

 a vast improvement on seeds collected at random on an estate 

 Having carried the procedure so far, it would be well worth 

 while to make a further selection by jilanting up a new area 

 separated by a broad jungle belt from other Hevea trees and 

 agam to proceed regularly to record the vields, eventually 

 cutting out the poor milkers that will probably be found 

 among them. In this manner seeds will be available which 

 should produce practically nothing but good milkers. 



There is, perhaps, an alternati\e to the first part of the 

 procedure we hive outlined, Jiamelv. the propagation of 

 trees by means of cuttings. This is possible, and^if found 

 practicable, the small area to be planted up for seed 

 production could be furnished with good milkers yrown 

 directly from cuttings from the best nulkers on the planta- 

 tion. 1 



The preliminary work carried out to distingnish between 

 eood and poor milkers may residt by some simpler means 

 being discovered by which either may be recognized The 

 investigation would be well worth undertaking from this 

 point of view alone, as it would be of much benefit by 

 enabling poor milkers to be cut out in the process of 

 thinning out. 



It should also be noted that deterioration in latex yields 

 from newly-planted areas as compared with older areas is not 

 only possible but, regarded from some standpoints even 

 probable. Thus, it is found that the cinchona trees' which 

 yield the smallest proportion of alkaloids from their bark 

 produce abundance of seed, while exactly those trees which 

 give the higest percentage of alkaloids are .shy of fruitinir 

 If It 18 pcssible to draw the parallel conclusion in the case of 

 rubber trees, it follows that the present method of seed selec- 

 tion must re.sult in a gradual deterioration of the rubber 

 yielding capacity of the tree for, by taking the seeds at 

 random, a larger proportion of seeds from the prolific fruit, 

 ing trees will be obtained, and these trees are just those which 

 may be the poorest milkers. 



