382 



THE AGRICULTURAL NEWS. 



NovisMBBR 25, 19n. 



FUNGUS NOTES. 



OBSERVATIONS ON ROOT DISEASES IN 

 THE WEST INDIES 

 PART II. 



In the preceding numlier of the Aijrkul/ural A'etrs^ an 

 article appeared dealing with the black root disease found on 

 several plants in Dominica, and probably also of common 

 occurrence in certain other islands of the Lesser Antilles. In 

 the present article, a description will be given of two other 

 forms of root disease, confined, as far as is known at present, 

 to lime trees in the island of Dominica. The investigations 

 are, however, of a recent character, and it is very probable 

 that one of these will be met with in other places. 



RED TtooT Di8E.\SE OF LIME TKEKs. This, as far as is yet 

 known, is found only on lime trees, in Dominica, and is due 

 to a species of Sphaerostilbe. It occurs sjwradically on the 

 roots of trees growing on estates in the interior of the island. 

 Although there is, so far, no evidence to show that it can 

 attack other host plants, yet it is worthy of mention that 

 a very similar fungus has been found in conjunction with 

 what was probably the black root disease on the roots of an 

 unidentified tree in St. Lucia. Furthermore, it .seems pro- 

 bable that it can live as a saphrophyte on decaying wood, as 

 can Sjihaerostilhe je/jeji.s, K. and Br., found by Fetch as an 

 occasional parasite on Ilrrea brasiliensis, and on arrowroot 

 in Ceylon. (The Physiology and Diseases of llevea In-aslli- 

 ensis, p. 192; and Circulars and Ai/n'cidfural Journal of t lie 

 Royal Botanic Ganhns, Ceylon, Vol. V, No. 8.) 



Trees attacked by this disease lose some of their leaves, 

 and the tips of their branches turn yellow. Eventually they 

 wilt and die, proliably somewhat rapidly, as in the case of the 

 black root disea.se. This point has not, however, been pro- 

 perly made out. On examining the roots, it is seen that 

 several of them are diseased, and that the damage inflicted 

 extends right up to the collar. The bark is brown in colour, 

 soft and rotten, and easily removed: while the surface of the 

 wcpod is also soft and damp, and of a redbrown tint. On 

 the ends of the main roots, near tlieir point of attachment to 

 the tree, round the collar, and in bad cases for some distance 

 up the stem, a smooth, red-brown sheet of fungus occurs 

 beneath the surface of the outer bark, closely adpresssed to 

 the wood. The dry outer bark falls away in places, and leaves 

 the .sheet of fungus ex))osed. 



The fungus produces a Stilbum form of lonidial fructi 

 fication, either near the soil level on the collar, or beneath 

 the soil in cavities between the principal roots. Each con- 

 sists of a short red stalk surmounted by a spherical head of 

 white si)ores. The whole is from 2 to I mm. in length. The 

 stalks were liorne upon red strands of the fungus in the cases 

 observed, and occurred in clusters, so that they were fairly 

 conspicuous in spile of the small size of the individual 

 fructifications. In one instance, minute, flask-shaped, bright- 

 red perithecia were found clustered on a red strand. They 

 were spherical below, with long, usually curved, necks and 



gave rise to bicellular ascospores, very light red-brown in 

 colour, constricted at the septum and somewhat acute at 

 either end. 



Thus this fungus, like the Jiosellina responsible for the 

 black root disease,' may spread by means of spores produced 

 above ground. At the same time, also, it can .spread 

 through the agency of long, narrow, red strands of mycelium 

 which grow through the soil. Since this is the case, the red 

 root disease can probably be easily controlled by the same 

 measures as are applicable to the black disease. These were 

 described at the end of Part I of this article. 



.STEM CANKER DISEASE OF Li.ME TREES. This is a pecu- 

 liar disease, found at present only under somewhat unfavour- 

 able conditions in Dominica, It is primarily a root disease, 

 though the name appearing above has been given to it on 

 account of one of its most easily distinguishable characters. 



Unlike the two diseases already described, which are 

 found only on trees four years old and upwards, the stem can- 

 ker disease occurs on trees of all ages from one and a half to 

 five years or more. The first symptom of the disease is a thin- 

 ning of the foliage, accompanied by the appearance of several 

 bare branches. At the same time the trees may take on a yel- 

 low colour, and thus have a very sickly apjjearance. They may 

 remain in this condition for three months to a year, or even 

 more; while those in bearing continue to produce fruits all 

 the time. Ultimately, however, all affected plants die. 



On examining the base of the stem of a sickly tree, an 

 open wound extending down to the wood and surrounded by 

 callus may be seen on one side, usuallj- near the ground. 

 This cankered patch may run either vertically or horizontally, 

 and varies in width from |inch to i-inch, and in length from 

 ^■inch to 2 inches. In more advanced cases, all the bark, 

 for a distance of from 3 to 12 inches above the ground level, 

 is cracked and split and has a peculiar scabby appearance. 

 This is due apparently to abnormal and irregular activity of 

 the caml>ium, which produces lumps and ridges of wood and 

 bark, that render the surface very rough and break up the 

 older cortex and outer bark. 



The roots show the presence of peculiar open splits in 

 the bark, each of which is usually not more than {-inch in 

 width, but extends for a considerable distance. These areas 

 are bordered by a vigorous callus, and it appears that in 

 some instances they are completely healed over. They fre- 

 quently occur at bends in the roots. In advanced cases of 

 the disease, the scabby appearance of the bark described 

 above extends to the roots also. 



The causes of the disease would appear to be physical 

 rather than fungoid. The pre.sence of a heavy clay soil, 

 difficult to drain adequately, combined with e.\i"isure to 

 strong winds at ci'rtain seasons of the year, would seem to 

 be factors that contribute largelj- to the production of this 

 unhealthy condition of the trees. Xo definite fungus has 

 been found as yet, generally, on diseased trees; though several 

 dirt'erent saprophytic species may be observed on dead or 

 (lying roots. .Moreover, there is no conclusive evidence of 

 the spread of the disease fron. tree to tree, in a manner 

 which would necessitate the presence of a parasitic fungus 

 upon affected plants, to account for it satisfactorily. 



The lines along which remedial measures should be 

 undertaken would appear to lie in the direction of providing 

 windbreaks and increasing as far as po.ssible the number and 

 depth of drains. 



It may be noted here that a somewhat similar disease 

 has been found on lime trees in Antigua and Montserrat. 

 In the latter island, however, diseased trees were characterized 

 by the alisenco of fibrous roots connected with their main 

 roots, and also exhibited peculiar strips of soft decaying bark 



