Vol. III. No. 46. 



THE AGKICULTUEAL NEWS. 



23 



LECTURES TO PLANTERS AT BARBADOS. 



Tlie following i.s a .suinmary of Mr. Lew ton-Brain s 

 third lecture on Sugar-cane diseases : — 



The root disease of the sugar-caiie has 2>rolia!>ly caused 

 more damage, during tlie past few years, than all other sugar- 

 cane diseases together. It ajipears to attack eijually well all 

 varieties of cane at present in cultivation and yields to no 

 fungicidal treatment. The fungus attacks ratoons more 

 frequently than it does plant canes. The leaves first show 

 signs (jf the disease ; instead of a dozen or so broad, bright 

 green leaves, we get them drying u}) much earlier than they 

 shouUl do. The drying up takes place first at the tip and 

 edges of the leaves and gradually spreads until the whole 

 leaf is dry and withered. The younger leaves, before they 

 even begin to turn yellow, do not open out as they shouUl 

 do ; they remain partially rolled up. Evidently the plant 

 is suffering from the lack of water. The leaves farthest from 

 the main axis, and first the parts of them which are farthest 

 removed, are drying up and dying, while the younger leaves 

 which are still receiving a certain amount of water roll up 

 to reduce the water lost by the process of transiiiration. 



The old dry leaf-sheaths, which in a healthy plant are 

 thrown off leaving the base of the stem clean, remain attached 

 and require considerable force to remove them. On 

 examination we find that they are all matted together, by 

 a clean looking, white felt which is the mycelium of the 

 fungus Marasmius. The matted leaf bases have a characteristic 

 musty smell. The roots normally spring from the nodes, burst 

 through the leaf bases and then grow down into the soil. 

 Either these do not develop at all or their growth ceases when 

 they are about | or i inch long. 



The canes attacketl l:>y the root fungus are usually 

 considerably dwarfed in comparison with others in the same 

 field ; not only are fewer leaves developed, but the stems are 

 much thinner and drier and usually shorter than normal 

 canes. Again the diseased canes are very easily uprooted, the 

 slightest pull being sufficient to remove the stool. 



Finally from the bases of the stools or from the roots 

 arise the fruits of the fungus. These are small, white or 

 yellowish toadstools, and we usually find them in groups. 

 They are rarely to be found exceiit in wet weather, and the 

 best time to look for them is in the early morninii before the 

 sun has dried them up. These fruits bear the spores. 



Under natural conditions the spores are shed at the base 

 of the cane plant and are thence carried away either by wind 

 or insects. Each spore is capable, if conditions be favourable, 

 of infecting a cane plant with root disease. If one of 

 these spores be carried by the wind and get on a cane 

 plant, it will, in all probability, fall on one of the leaf- 

 sheaths and will lodge somewhere between the sheath and 

 the stem. The chances are that the spore will germinate and 

 soon give rise to a mycelium, which at first grows in, and 

 obtains its nourishment from, the dead and dying tissues of the 

 leaf-sheaths. It passes from one of these to another and by 

 its dense matted habit of growth, binds them altogether into 

 a uuisty smelling mass. In a similar way the fungus spreads 

 to any dead or dying part of the plant above or below ground. 



The mycelium then proceeds to attack the growing 

 region of the root which is composed of a number of very 

 delicate thin-walled cells, full of protoplasm. The fungus 

 does no other damage and attacks no other part of 

 the plant ; it simply enters the tissues of the gi-owing 

 points and destroys them. This is the cause of the dark 

 colour of the root-tips which I mentioned as one of the 

 symptoms of root disease. But this is quite enough to affect 

 seriously the growth and nourishment of the cane. 



As roots die away and are not replaced by others, the 

 water and mineral salts from the soil are absorbed in 

 gradually decreasing quantities, consequently the leaves are 

 unable to manufacture so much of the sugar and proteid 

 substances, which are required for use during growth. 



The first sign of the disease is due to the cutting off of 

 a jiart of the water supply. The effect on the plant is the 

 same as that of excessive drought. The leaves under these 

 conditions roll uji in order to lessen the loss of water by 

 transpiration, and with plants infected with root disease 

 this condition becomes more or less permanent. This 

 prevents them from taking in the full amount of gases from the 

 air. In this way the food supplies of the plant are attacked 

 at both end.s, at the roots and the leaves, and this at a time, 

 it must be remembered, when the plant requires more food 

 than usual in order to replace the roots which are being 

 killed off by the fungus. 



The fungus has now established itself on its host. The 

 latter gradually becomes weaker and weaker, owing to the 

 process of slow starvation. The stunted habit of the plant 

 is due to its inability to form new organs, owing to lack of 

 nourishment ; while the ease with which the plant is 

 uprooted is due to the non-development of roots, which are 

 the anchoring as well as the absorbing organs of the plant. 



Later on in the year, usually during the wet season, the 

 fungus proceeds to reproduce itself. This it does by putting 

 out the small toadstools, on which the spores are borne. 

 The toadstools usually grow out near the ground, either 

 from dead roots or from the trash at the base of the stem. 



The cane does not of course always succumb to the 

 attack of the fungus in this manner. The fungus will 

 establish itself, as before, on the old leaf-sheaths and other 

 dead parts and be ready to attack the roots. But a plant 

 cane growing vigorously and under favourable conditions 

 will be able to form new roots so abundantly and so fast 

 that the attack of the fungus produces little effect on it. 

 The same thing of course may happen after the fungus has 

 commenced to do damage, if the conditions change and 

 become such as favour root development. 



The fungus is also .spread by the mycelium travelling 

 underground. Any old cane stump or piece of trash is a 

 sufficient source of nourishment for the mycelium. If then 

 any infected stump is brought near a growing cane, the 

 mycelium passes from one to another. 



We must, in every possible way, increase the vigour of 

 the canes. A cane growing vigorously is not likely to be 

 damaged, seriously, by the root fungus. The soil should 

 therefore be cultivated as thoroughly as possible, so as to 

 give the roots the best chance of developing, and at the 

 same time to weaken the fungus. When only a small patch 

 in a field is attacked and the disease is noticed in time, this 

 area should be isolated from the rest of the field to prevent 

 the fungus spreading by its mycelium underground. This 

 can be done by digging a trench around the area. 



Then we have the disposal of infected material. All 

 cane stumps infested with the Marasmius myceliiun should, 

 if possible, be burnt, otherwise they may be mixed with lime 

 and buried, but not in a cane field. Trash from infested 

 fields should not be used in cane fields, nor should it be 

 made into i)en manure which is to be applied to canes. It 

 may be used on land which is to be planted in cotton or in 

 any other crop which is not liable to root disease. 



Again land which has borne a badly attacked crop of 

 canes should not be planted in cane till the fungus has laeen 

 starved out. Cotton offers itself as a remunerative crop, 

 which might be grown in rotation with sugar-cane. 



