62 



THE AGRICULTURAL NEWS. 



February 14, 1914. 



FUNGUS NOTES. 



SUGAR-OANE DISEASES IN INDIA. 



The results of further studies of the red rot of sugar-cane 

 in India caused by Colletotrichum falcatum are given by 

 E. J. Butler and Abdul Ha6z Khan in Vol. 6, No. 5, of the 

 Memoirs of the Depa)tiiient of Agriculture in India (Botanical 

 Series). Red rot is stated to be the most serious disease to 

 which sugar- cane is subject in that country. 



Experiments havo been carried out to test the trans- 

 mission of the disease by the use of infected cuttings, and 

 this subject is treated in detail in view of negative results 

 obtained by Edgerton in Louisiana, and by South and Dunlop 

 in the West Indies. The results of planting healthy and 

 diseased setts in alternate rows show a very much greater 

 proportion of infection in plants from the diseased cuttings, 

 and it was found possible to trace the course of the infection 

 up into the stem and to establish a direct connexion between 

 the mycelium in the cutting and that in the new shoot. 



The possibility of reducing the disease to negligible 

 proportions by means of sett selection is discussed in the 

 light of experience accumulated during the last ten years. 

 It is found that where the selected cuttings are taken from 

 a diseased crop the impossibility of detecting the existence 

 of the parasite in its early stages makes the method largelj' 

 ineffective. Once, however, a healthy stand of canes has 

 been secured by introducing cuttings from a healthy district, 

 it is found possible by rejecting cuttings from canes which 

 appear to be diseased, to prevent the increase of the disease 

 which would otherwisa occur. 



Other sources of infection are next considered. It was 

 found that cuttings are liable to infection from spores in 

 the soil or in the irrigation water. The form of the fungus 

 occurring on the leaves of the sugarcane was found to be 

 capable of producing the disease in the stems. The authors 

 have found little or no evidence that infection takes place 

 through holes made by insect borers nor was infection 

 through leaf scars found easy of production. On the other 

 hand, slightly damaged buds (eyes) were found to admit the 

 fungus readily, while the young adventitious roots were found 

 to be very easily infected even when sound and uninjured. 

 The feeding roots of the plant, temporarily uncovered and 

 sprinkled vrith a suspension of the spores, were found to be 

 susceptible. It is the conclusion of the authors that while 

 injuries to the stem are responsible for a certain amount of 

 infection, the commonest points of entry in new infections in 

 India are undoubtedly the shoot and root eyes at the nodes. 

 For the production of spores which may give rise to new 

 attacks or extend infection already existing, importance is 

 attached to the form occurring on the leaves. Spores from 

 both stems and leaves were found to be capable of infecting 

 uninjured leaves under favourable conditions, though infec- 

 tion takes place much more readily where slight wounds such 

 as are commonly made by insects occur. 



Although the upper portion of the cane ia richer in 

 glucosBj which favours the growth of the fungus in cultures, 

 it was found that it was not when planted more liable to 

 infection. Thus there is no objection from that point of 

 view to the planting of tops — a measure which may be found 

 advisable when healthy setts are required. 



A reference to Rind Disease raises the old question as 

 to the parasitism of Melancmiiuiu. sacc/iari, mention being 

 made of Lewton-Brain, Cobb, and Edgerton as having revert- 

 ed to the older view that this fungus is the active agent in the 

 disease. The present writer is not aware of the publication of 



any experimental results at all adequate to support this opinion 

 against the evidence which has accumulated in favour of the 

 view put forward by Went and Howard that ColletotricMim 

 _falcatum is the real cause. Since the cultivation of seedling 

 canes has become general in the West Indies, rind disease 

 has had little more than historic interest. In Barbados 

 where the affection known by that name was very severe, 

 Melancoiiiu-in ■'<acchari is still universally present on 

 damaged canes, the greater number of which have been severe- 

 ly weakened or killed outright by moth borer; while the 

 periodic attempts made by planters here and there to return 

 to their old love the Bourbon cane are regularly defeated by 

 Colletotricltum falcatuai, which is extremely rare on the 

 seedling varieties. Published evidence of this may be found 

 in the report of the Local Department of Agriculture, 

 Barbados 1910-11, page 46. 



The same authors in No. 6 of the same series describe 

 certain new sugarcane diseases met with in India. The first 

 is a wilt due to a fungus which receives the name of 

 Cephalosporium saccliai-i. It is very similar in its effects 

 to Colletotriciium falcatiun, and like that fungus produces 

 a reddening of the cane pith; but instead of bright red 

 patches and streaks broken by transversely expanded white 

 areas, there is a diffuse purple or dirty red colouration in 

 which brighter red vertical lines mark the position of the 

 bundles. The tendency of the colour to become muddy at 

 an early period is its most strongly marked character and 

 serves to distinguish the disease. In old cases the red 

 almost disappears, being replaced by an earthy brown. The 

 pith dries up and becomes hollow. 



Inoculation experiments showed that the fungus 

 cannot penetrate the unbroken rind of the internodes, but 

 the adventitious root eyes can be easily infected. It was 

 also found to be capable of entering through the planted 

 setts. Wound infection through borer holes is far more 

 common than with Colletotrichum. 



The disease is found over a large part of India and as 

 a rule seems to accompany red rot but may occur unmixed. 

 So far as has been observed, the infection is not virulent; 

 spread within the cane is gradual and communication from 

 one plant to another slow. 



It may be noted here that a Cephalosporium has been 

 noticed to occur in the West Indies on pieces cut with the 

 usual precautions from the interior of diseased canes. 



The second disease is known as collar rot and des- 

 cribed as due to a fungus of a new genus and species of the 

 Sphaerioidaceae. The symptoms outwardly resemble those 

 of red rot so far as the withering of the top is concerned 

 On splitting, the upper part is usually pithy and dry in the 

 centre. Lower down, the pith may be still juicy but has 

 a curious translucent watery appearance; still lower the 

 central portion may be brown while red streaks or patches 

 may often Vje seen, especially at the nodes. The roots 

 arising from the basal nodes are usually blackened and rotten 

 and the appearance suggests that the disease enters the base 

 of the stem from the roots. The pycnidia develop in the 

 internodes under the epidermis, which becomes raised up and 

 ruptured by the roughly conical deep portion of the fruit 

 body, which is hollowed out into one or several cavities. The 

 spores are variable but fall into two types, the first of 

 which ia bicellular and brown, the second filamentous and 

 hyaline, usually without septa. The amount of damag 

 caused by the disease is unknown. 



The third fungus described is named Ilelminthosporiiui 

 sacchari, and is a leaf spot very similar to, and possibly 

 identical with, Cercospora sacchari, Br. de Haan. 



