and Magazine of the Ceylon Agricultural Society. 



587 



A ROOT DISEASE OF PARA 

 RUBBER TREES. 



By W J Gallagher, m.a., Government 

 Mycologist, F.M.S. 



A fungus, which attacks the roots of Para 

 Rubber trees with fatal results, appears from 

 the number of communications received by the 

 Department of Agriculture to be fairly common 

 at present over this Peniusuia. It is doubtful if 

 there is an estate free from it, as its presence, 

 even when it has killed trees, often remains 

 unsuspected. 



The disease is seldom distributed over an 

 entire estate, but is confined to limited areas in 

 which at first a tree here and there is attacked. 

 Half-a-dozen or more vacancies may often be seen 

 together when, owing to a misconception of the 

 cause of death or for other reasons, no preven- 

 tive measures were taken on the death of the 

 first tree. The trees succumbed one after an- 

 other aft the disease spread. The "supplies'' 

 were failures too ; planted in a soil full of 

 threads of the fungus they were soon 

 attacked by it and either never " struck ',' 

 or died shortly after doing so. On these infected 

 areas the mortality is often as high as thirty 

 trees per acre, but for a whole estate the yearly 

 average is probably not a tree per acre. 1 have 

 seen only one particularly bad instance , in 400 

 acres of trees 24 years old, 



ABOUT FIVE PER CENT HAD DIED, 



and two dead trees were never adjacent. The 

 incidence is heaviest on peaty soils, and where 

 there has been a bad burn. The disease occurs 

 among trees of from fifteen to thirty months old. 

 I have not noticed it on trees older than two-and- 

 a-half years. Nursery plants of a few months 

 old may be attacked, and will quickly succumb 

 if a source of infection is at hand. 



Symptoms. 



The disease is not discovered, as a rule, until 

 the tree is dead. The first symptoms are some- 

 what as follows: — The leaves of a healthy-looking 

 tree suddenly became brown, first round the 

 edge and specially at the tips, and the entire 

 leaf soon loses its natural colour : this is 

 a sign that something has interfered with the 

 water supply to the parts above ground ; it is 

 due to the "ringirjg 1 ' of the tap root by the 

 fungus. Little or no latex will How in response 

 to a wound in the stem. Occasionally the leaves 

 fall off, but generally before this happens the 

 tree is blown down. Sometimes a healthy-looking 

 tree falls over, the leaves remain greon, and the 

 plant apparently continues to grow. If the roots 

 are examined all will be found to be dead except 

 one or two lateral roots which still supply the 

 necessary nourishment ; and it is only a question 

 of days or at most weeks until these are k'lled. 



Owing to the destruction of some of the lateral 

 roots by the parasite a tree frequently loses 

 its firm hold in the soil and is shaken about by 

 the wind causing a cup-shaped depression 

 round the collar. This may go on for many days 

 before the tree shows any other signs of the 

 disease, but it is a pretty sure indication of the 

 presence of root disease, and the "shuck" tree, 

 as planters term it, should be treated hh 



infected and incurable. The following ex- 

 tracts taken at random from letters sent into 

 the Department from different districts give an 

 idea of the unformity of the symptoms as 

 observed by planters: — 



A. " The first signs are the leaves turning a metallic 

 colour, drooping, and then falling off. It does not show 

 until the tr e * are practically dead, the high lands seem as 

 subject to it as the valleys or Hats, estate virgin jungle." 



B. "The diseased plants are scattered over the estate, 

 but in one instance four or live were together. The leaves 

 generally become a rusty colour from the bottom upwards, 

 there is no Inclination to topple over except where white 

 auts have eaten the roots, ground well drained, plants from 

 one-and-a half to two years old, estate virgin jungle." 



(J "In sporadic instances over the planted area well- 

 nurtured trees (mostly eighteen months old) have suddenly 

 died back, ten cases on300 acres in the last six months; 

 this in itself is not serious, but one has to look to the 

 futuie, especially as fungus seems to be the cause." 



D "On this estate there is somewhat heavy mortality 

 among trees of 20-30 months old, the disease is especially 

 rapid as noted abore ground, trees appear ' shuck ;' leaves 

 crumple and in the course of a day or two fall off, sick- 

 njss attacks not in isolated cases but in clumps of adjacent 

 trees. The tap root seems to be first attacked. The 

 neighbouring estate in same lie of country seems to be 

 free of the disease." 



B " About a dozen have died out on. 26 acres, each root 

 has a white thready growth on it, virgin jungle, other 

 trees healthy looking, those that have died nave beea in 

 different parts of the land." 



F. " I send some of the dead troes. They were sixteen 

 months old audgrewou Sit well drained land, the trees 

 were together, but neighbouring plants lookquite healthy." 



When a tree, which has been killed by this 

 root disease, is pulled up, the cause of death is 

 at once apparent. In many places there is a 

 cobweb like felt of whitish fungus, but in parts 

 the fungus threads {mycelia) are closoly aggre- 

 gated in straw-coloured strands, like stout cord, 

 stretching somewhat irregularly over the surface 

 of the root. 



If incisions are made in the tap root and stem, 

 a discoloration of the wood will be observed in 

 the former, but in the latter except occasionally 

 for a little way above the collar. 



Method of Attack. 



Some planters maintain that the tap root is 

 first attacked. Considering the method of 

 planting and for various reasons this seems 

 unlikely ; as far as I have seen the lateral roots, 

 and only those near the surface, are the first 

 to suffer. The deeper lateral roots, or at least 

 their extreme ends, are mostly free from fungal 

 threads even when the tap root is already 

 covered with them. Often the tap and lateral 

 roots over one side only have been choked by 

 the mycelia, the lateral roots on the other side 

 being free. In such cases the side on which the 

 diseased roots lie is always next a jungle stump. 

 Oti different occasions 1 hare traced the myce- 

 lia along lateral roots to decaying jungle stumps. 

 It may be taken as pretty certain that these 

 stumps and logs are the original source of 

 trouble. It is mostly impossible to identify 

 them, but on more than one occasion 1 have 

 found Meranti (Shorea sp.) and Merbau (Ajzelia 

 palembanica) offenders. "The lateral roots of the 

 para tree spread so fast that in a year or little 

 more all jungle stumps are in contact with them. 

 But a root may be attacked before reaching an 

 infected stump as the fungal threads can travel 

 for some distance through the soil. 



The only occasions on which I found nursery 

 plants attacked was when the nursery had 

 been badly cleared and old stumps had 

 been left in it. In many of these nurseries tha 



