78 



THE AOKiUULTUllAL NEWS 



March 2, 1912. 



FUNGUS NOTES. 



THE RED ROT DISEASE OF THE SUGAR- 

 CANE IN LOUISIANA. 



A fairly complete account of tlie red rot disease of sugar- 

 cane, due to CoUetotrichuvi falcatmn, as it appears in Louisi- 

 ana, has lecently been prepaied by C. W. Edgerton, Plant 

 Pathologist at the Louisiana State LTniversitj', and has been 

 published in the Modern Sugar Planter for January 27 and 

 February 3 of this year. As some interesting points have 

 resulted from this work, it is thought that an account of it 

 may be of interest to West Indian readers, particularly as 

 there is most probably a close connexion between it and the 

 rind disease of these islands. 



.SYMPTOMS. In Louisiana the red rot disease at tacks both 

 the leaves and th& stems of the sugar-cane. Affected canes 

 frequently .show no symptoms of ill health on the outside; but 

 when they are split open, the internal tissues exhibit a bright 

 red discoloration, quite characteristic, and distinct from the 

 reddening produced by other injuries. Very frequently, the 

 centres of the red areas are occupied by white or whitish 

 spots, the strands of vascular tissue are discoloured red, and 

 may be surrounded by a red ground tissue. The attack on 

 the leaves usually commences as a red spot on the upper side 

 of the midrib. This extends in both directions along the 

 axis, and often becomes from 1 to 3 feet in length. The 

 centre of the spot dries, and becomes whitish in colour, and 

 ' is finally covered with the black fruiting pustules of the 

 fungus. Since the disease does not cause any external symp- 

 toms on the stems of the infected canes, the spots on the 

 leaves form a useful means of ascertaining whether or not 

 it is present in a field. Two points of difference be- 

 tween Edgerton 's description and that of the rind disease 

 given by Howard are worthy of note (A. Howard, Annals 

 of Botany, Vol. XVII, No. LXVI, p. 373). In the first place, 

 the brown discoloration of the rind, followed by shrinkage, 

 which are noticeable on the outside of canes infected by rind 

 disease, does not occur in the Louisiana disease; while Howard 

 also makes no mention of the occurrence of the red spots 

 on the leaves, though he describes the leaf symptoms in 

 some detail. 



INOCULATION E\PERIMENT.S AND PEOliRESS OF THE 



DISEASE. Edgerton made over 275 inoculations with pure 

 cultures of Colletotrichum faleatum, on stems of canes belong- 

 ing to the varieties D.74, D.9.5, purple and striped. The 

 inoculations were effected at needle punctures in the lower 

 joints. Only about six of the 27.'J canes failed to develop 

 the disease, while of the equal number of controls employed 

 about six showed the disease. This was probably due to 

 the difSculty of preventing accidental infection whenj:ed rot 

 is abundant in the field. In addition to proving conclusively 

 that the fungus can act as a wound parasite, these experi- 

 ments showed that D. 74 and D. 9.5 are more resistant to 

 the disease than the local types; while of the former D.74 

 appeared to be the more resistant. Further inoculations 

 were made with two species of Colletotrichum which resemble 

 C. falrafuiii so closely as to be indistinguishable under the 

 microscope or in pure cultures. The first of these is C. line- 

 ola commonly found on broom corn and Johnson grass 

 {Sorfjkuiii halepenfe), in the Southern States; the second is 

 C. cereals, that attacks wheat and other grasses in the North- 

 ern States. 



These inoculations did not yield any conclusive results, 

 though in a few cases indications of infection were obtained 

 with C. lineola. There is a possibility tliat the fungus on 



the sugar cane was originally the same as C. lineola, but has 

 become adapted to living on cane. Further work to deter- 

 mine this will be carried out. 



The first sign of infection is a reddening of the tissues 

 at the point of inoculation. The discoloration spreads in all 

 directions, but most rapidly along the stalk. The fungus 

 grows very rapidly in the vascular bundles, which it discol- 

 ours red. It passes up them from the infected internode 

 through the node into the internode above, and may extend, 

 in this way, through two to five joints during the season. 

 Red patches appear here and there in the ground tissue near 

 diseased vascular strands, as the fungus .grows out laterally 

 from the bundles into the parenchyma. Several weeks after 

 inoculation , the centres of the red patches dry out and show 

 the white spots characteristic of the advanced condition of 

 the disease. Infected stalks usually show little, if any, decrease 

 in size and cannot be distinguished from healthy stalks by an 

 examination of the exterior. Sometimes, when the stalk is 

 inoculated when very young, the fungus breaks through the 

 rind tissue which becomes dry and sunken, while fructifica- 

 tions of the fungus appear on its surface; at other times the 

 growth of the fungus may be so rapid as to kill young stalks 

 altogether. Apparently, the fungus cannot penetrate the 

 fully developed rind and fructifications do not form at the 

 nodes, as they usually do on canes attacked by Colletotrichum 

 falcatuin, in the West Indies. In his infection experiments 

 with C. falcatum, Howard (loc. cit.) usually obtained the 

 characteristic external symptoms observed in the case of the 

 West Indian rind disease. 



INFECTION IN THE FIELD. Carefully conducted field 

 observations showed that there is a possibility that the fun- 

 gus can enter previously undamaged canes at the node, where 

 the rind tissue is broken by the leaf traces and rootlets. 

 This was not definitely proved, as small wounds due to 

 minute insects may have been present. Howard was able to 

 produce successful inoculations by placing the fungus on the 

 leaf bases and on the broken surfaces produced when 

 the leaves were stripped oft". There is also a possibility that, 

 in Louisiana, the fungus penetrates the stem from the leaves, 

 entering along the leaf traces. By far the commonest means 

 of entry is, however, the tunnels made by the moth borer 

 {Diatraea saet-haralig). Not only do the tunnels aft'ord an 

 easy means of entry to the fungus, but the grubs serve to 

 disseminate the mycelium throughout the cane far more 

 thoroughly than this could be done by its own, unaided, 

 growth. Observations showed that over 50 per cent, of 

 canes attacked by moth borer are proliably also infected with 

 red rot. One other point was definitely established, namely 

 that the disease does not spread upwards into the young 

 growing shoots from previously infected cuttings. 



LCSSES FROM RED EOT DISEASE. A Certain amount of 

 loss is occasioned by the killing out of young shoots, and 

 even more by the injury to the leaves. The disease does not 

 appear to be as serious in its direct effects as is the local 

 rind disease, since shoots are rarel)' completely destroj-ed. 

 The two main sources of loss are, however, a bad stand due 

 to the failure to germinate evinced by infected cuttings, as 

 well as to the possibility that the disease can spread in the 

 soil from infected to healthy cuttings; and the loss of sucrose 

 and increase of glucose in the juice caused by the presence 

 of the fungus in the tissues. The fact that no selection of 

 cuttings is practised in Louisiana necessitates the planting of 

 a large number, and often results in a poor stand, partly due 

 to the presence of red rot in the canes cut up for planting. 

 Analyses of the juice of artificially infected canes showed 

 that not only is the juice from the infected internodes defi- 

 cient in sucro.se, but that the deficiency extends to the inter- 



