S66 



THE AGRICULTURAL NEWS. 



November 9, 1912, 



FUNGUS NOTES. 



ILIAU-A CANE DISEASE OF HAWAII. 



An interesting account of an endemic cane disease 

 known for some time in Hawaii is published in Bulletin 

 No. 11, Pathological and Physiological Series of the Experi- 

 ment Station of the Hawaiian Sugar Planters' Association, by 

 H. L. Lyon. The disease appears to be limited to the 

 island mentioned, but some account of it may be of interest 

 in case it should appear locally at any time. It was first 

 described by Cobb in Bulletin 5 of the series already referred 

 to; but he failed to recognize its true cause or to appreciate 

 its economic importance, and Lyon's account is the first to 

 deal with it fully, i 



SYMPTOMS. The disease is essentially one aflecting the 

 leaf sheaths, and the major portion of the damage 

 caused by it is inflicted on the young shoots just emerging 

 from the ground. The name Iliau meani 'tight skin', and 

 describes the most conspicuous symptom of the disease which 

 is the cementing of the leaf sheaths into a tight, firm jacket 

 about the stem. This encloses the growing tip so effectively 

 that its elongation is prevented and it is eventually strangled. 

 The leaf sheaths killed by the fungus causing the disease are 

 always pinkish brown in colour, while the infected rind of 

 such canes as have produced any stem is bluish grey. These 

 colours are very constant and afford a means of diagnosing 

 the disease. 



Since the young shoots are the parts principally affected, 

 the greatest damage is naturally caused in fields of young 

 cane; while it has been observed that plant canes are always 

 attacked more severely than are ratoons. The development 

 of the fungus is favoured by cool, damp weather which checks 

 the growth of the cane, and the amount of harm done varies 

 according to the incidence and continuation of such weather. 

 If it begins when the shoots are young and endures for 

 some time, the fungus, which is always prese nt in cane fields in 

 Hawaii, obtains a good hold and may destroy nearly all the 

 shoots in a stool. Moreover, it is also natural that the disease 

 should be more severe on fields at a high elevation or with 

 a northerly aspect than on those lying low and facing south. 

 Shoots weakened by any other cause than those already 

 mentioned are also more liable to the disease than are healthy 

 shoots. Usually under normal conditions in Hawaii a certain 

 number of shoots grow away from the fungus and only the 

 later secondary shoots are killed. Their death, when they 

 are only about 10 inches long, does not give a field any very 

 diseased appearance, especially as the main shoots are 

 healthy, and the presence of the disease may l)e hardly 

 manifest except inasmuch as it causes a poor initial stand of 

 cane. At the same time the damage inflicted is considerable. 

 Only when the primary shoots are killed out by the disease 

 does it become conspicuous, and on!}' then is it usually noted 

 on the plantations. 



The fungus generally commences its attack on the leaf 

 sheaths of young shoots at a point below the surface of the soil. 

 It then progresses upwards and inwards from leaf sheath to leaf 

 sheath, and finally into the stem. The fungus thus penetrates 

 the compact roll of j'oung leaf sheaths surrounding the 

 growing point and cements them together in a firm jacket; 

 consequently the growing point is killed, often long before 

 the mycelium of the fungus has reached it. Frequently, the 

 stems of young shoots severely attacked are found, when the 

 shoots are split open, to be variously twisted and doubled in 

 their attempts to elongate. Sometimes the bending of the 

 stem splits the leaf sheaths longitudinally and a loop of stem 



is forced through. The fungus can penetrate the stem,, 

 which it enters usually by way of the leaf bases, but it can 

 attack directly where the tissues are soft. Hardening of the 

 stem tissues checks the progress of the mycelium. 



Often if a young infected shoot elongates rapidlj' before 

 the fungus has had time to cement the leaf sheaths into aa 

 entirely closed jacket, very little harm is done to it, beyond 

 the destruction of a few basal leaf sheaths and perhaps the 

 scarring of one or two of the bottom internodes. Very 

 rarely, badly attacked shoots recover and make good growth 

 above the point of infestation, but such are liable to break 

 at the base owing to the damage caused to the lower joint.Oj, 

 one or two of which are always shrivelled and blackened. 



The disease is due to a fungus present almost universally 

 in the soils of the Hawaiian fields and the extent of the 

 damage due to it depends as already stated largely on condi- 

 tions that tend to check the growth of the cane. Thus the 

 harm inflicted varies in a manner very similar to that caused 

 by the root disease due to Marasmius saochari in these 

 islands, and the lines of treatment of the two are also similar, 

 as will appear below. Part of the damage actually caused 

 by iliau in preventing the formation of a good stand by the 

 destruction of secondary shoots was formerly attributed t» 

 the Ithyphallus said to cause root disease in Hawaii (see 

 Aiiriadfural Neics, Vols. VIII, p. 315; IX, 159). 



THK CADSATIVE FUNGUS. In one stage, this is aa 

 undescribed species of Melanconium very similar in certaim 

 of its gross characters to Melanconium sacchari, but differing 

 materially in the size and shape of its spores and in other 

 characters. Moreover its complete or ascus-bearing fructifica- 

 tions have been found on the outermost leaf sheaths of dead 

 or very badly diseased canes. These belong to the genus 

 Onomonia, and as the species is undescribed it has been, 

 cilled Gnomonia iliau. 



The fungus produces a white cottony mycelium, which 

 under suitable conditions of cultivation gives rise to cups ic; 

 which are formed spherical black masses of Melanconium spores. 

 These spores are dark coloured under the microscope and are 

 filled with dense granules; usually, they are one-celled but occa- 

 sionally they may be divided into two by a cross wall. la 

 nature they are formed between the leaf sheaths of the 

 cane or on the stem itself, where it is enveloped by 

 leaf sheaths, but not on the outside of the sheaths. 

 They are thus rarely disseminated liy wind, but are more 

 usually liberated and dispersed by water, since when the 

 compact mass of leaves is wetted, the individual sheaths fall 

 apart and the spores are set free This usually occurs in 

 the field when the diseased or dead stems are lying on or ia 

 the soil. Another fact which suggests that the spores are 

 usually water-borne is that they will not germinate readily 

 in water. The Melanconium spores, and the mycelium on 

 the leaf sheaths are, therefore, probably the means by whicb 

 infection usually occurs, since it commences below the surface 

 of the soil. The spores of the CTUomonia stage, however, 

 being produced on the outside of the sheaths, are probably, 

 wind-borne, and serve to extend the area of the disease. 



EE.MEDIAL MEASURES. The most perfect means of control 

 would be to obtain an entirely resistant variety Oi cane; such 

 is, however, not yet known. The standard Hawaiian canes- 

 appear to be all equallj' susceptible, but the Demerarat 

 seedlings grown there have proved partly resistant. 



The only measures at present known for controlling- 

 iliau are preventive. Since the Melanconium spores and the 

 mycelium are rapidly killed by sunlight, good preparatory- 

 cultivation, resulting in a frequent stirring of the soil and the 

 exposure of much of the spores and mycelium, is beneficial itt 



