i6o 



CHAPTER IX 



Argentina as Polvillo or Gangrena humida, and described by Spegazzini^s, 

 seems to be also this disease. 



Red Rot of the Stem. Colletotnchum falcatunfi^ (Went). — Setis nunc seriatis, nunc 

 in pseudo conceptaculum congregatis cuspidatis, 100-200 x 4, fuligineis, sursum palli- 

 doribus, conidiis falcatis, 25 X 4, hyalinis, ad basim setulorum, basidiis ovoideis 20 x 8, 

 hyalinis vel fuscis, suffultis. Hab. in culmis vivis. 



Fig. 56 shows the spores, and Plate XVII a photograph, of the diseased 

 cane, both after Lewton-Brain. This disease was first described by Went 

 in Java, and afterwards has been studied by Howard^' in the West Indies, 

 by Butler®^ in India, and by Lewton-Brain ^^ in Hawaii. It is a serious and 

 widespread disease, and is caused by the presence in the interior of the cane 

 of the causal organism. Unless the plant is seriously affected, no outward 

 sign of disease is observed. At a later stage the stalks become sickly and the 

 leaves die prematurely. On cutting open an infected stalk the manifestation 

 of the disease is shown by an unequally distributed red coloration, with 

 characteristic white spots in the centre, as indicated at X in Plate XVII. 

 This appearance serves to differentiate the disease from the red stripe of 

 sereh. In the white patches a mould is always present, while a few threads 

 of myceliirm are found in the red ones. In the vascular bundles brownish- 

 black patches also occur, connected with which is a mycelium flourishing 

 in the cells and walls of the bundles. 



If a piece of diseased cane be allowed to dry, black streaks appear, due 



to stromata, from each of which spring a 

 number of brownish-black straight hairs 

 measuring from 100 microns to 200 

 microns in length and 4 microns wide. 

 Among these hairs arise a number of sickle- 

 shaped conidia, measuring 25 microns by 

 5 microns. If the diseased cane be kept 

 in a damp place a white mycelium turning 

 to grey appears, forming, in a few days, 

 chlamy do-spores or resting spores. 



The lesion is entirely confined to the 

 parenchyma, and since the libro-vascular 

 bundles congregated near the rind are not 

 affected, the leaves can still communicate with the roots. 



Canes affected by this fungus afford a juice of lower sugar content and 

 purity than do sound canes. This effect was shown by Lewton-Brain 

 to be due to the presence of a sugar-inverting enzyme. 



Different varieties of canes exhibit veiy different degrees of susceptibility, 

 and Butler has observed that the reed-like canes of India are less liable 

 to attack than the thick ones. Otaheite cane is peculiarly susceptible. 



Originally the disease was considered to be a wound parasite, obtaining 

 entrance only after the protective rind had been injured by insects or by 

 other processes, such as high trashing. Butler has, however, shown that the 

 fungus may obtain entrance through the embryonic roots. He has also 

 observed the organism as parasitic on the leaves of the cane, and that cuttings 

 may be infected through the soil. 



This disease is specifically associated with the cane, and is not known to 

 occur on other plants. It has been reported from Java, India, the West 

 Indies and Hawaii, and may be regarded as cosmopolitan. 



Fig. 56 



