94 FROGHOPPER BLIGHT OF SUGAR-CANE. 



On the outside of sheaths infested with this fungus is found a closely- 

 felted granular surfaced fungus in which numerous spores are produced 

 (Plate X). Two closelj' similar species of this type have been described 

 as Otlontia Sarxhari and 0. saccharicola. It is the opinion of Nowell, 

 Johnston and Stevenson that this is the fruiting or spore pi-oducing 

 stage of the previous feathery Himantia fungus. From my own 

 experience in the field I can testify to the constant association of the 

 two forms, often in such close proximity as to leave almost no doubt as 

 to their identity. On Plate X a few strands of the Himantia type will 

 be seen near the top where the surface sheath has been removed 

 exposing the fungus that has developed in the darkness. 



DISCUSSION AND SYMPTOMS. 



The recognition in the field of these two types of fimgus is a com- 

 paratively easy matter, but the determination of the amount of damage 

 done is extremely difficult. The fungi are " facultative parasites," that 

 is to say they can exist quite readily on dead and decaying matter 

 (suprophytically) but under certain conditions they become parasitic, 

 in^■ade the still living tissue and destroy it. "When parasitic, these 

 fungi grow in the roots and root-stock of the canes, cause the death and 

 decay of the smaller roots and the staining of the tissue of the larger 

 roots and root-stock. 



A cane with its roots damaged by such an attack ceases to grow, 

 and even in moist weather shows symptoms of a shortage of water. 

 The leaves curl inwards at the edges and wilt and become paler in 

 colour. The internodes of the upper part of the cane do not elongate, 

 the leaves remain crowded together, and adventitious roots are thrown 

 out at the base of the cane underneath the matted leaf sheaths in an 

 attempt to obtain the required moisture. If conditions remain favour- 

 able to the fungus these small roots become in turn infected and the 

 stool may die out completely. 



Only rarely does the infection spread above ground to any extent 

 inside the cane and commonly when conditions become favomable 

 quite healthy shoots are put out by diseased root-stocks. 



The disease may attack a few isolated stools in a field, or the greater 

 part of a field, but outside Ti'inidad it does not appear to destroy such 

 large areas as is found to be the case with the blight in this island. 



The conditions which determine the extent of parasitism of the 

 fungus are not well understood. The amount of ^■isible fungus present 

 in the fields is no measure of the amount of damage. The injury always 

 shows most severely in dry weather, particularly when this occurs at an 

 unusual time of the year. Thus it is more conspicuous after severe dry 

 spells in September to November in Trinidad than in the normal 

 dry season. 



The dis-ease is known in all the chief sugar-growing districts of the 

 world (W. Indies, Louisiana, Java, Hawaii, Queensland, S. Africa etc.) 

 and it is usually found that any condition which adversely affects the 

 vitality of the cane will reduce its resistance to the fungus. Thus 

 previous insect or fungus injury, starvation due to poor soil, heavy 

 badly-aerated or waterlogged soil, and also aciditj' due to injudicious use 

 of chemical fertilizers in soils deficient in lime, are all found to increase 

 the damage done by these species of fungi. 



There is great need of more critical experiments on this subject. 

 Johnstone and Hai'tman (1919) have studied the influence of soil acidity, 

 moisture and soil temperatures on a fungus Thielavia basicola which 



