U-2 



THE AORICULTUKAL NEWS. 



Apiul 20, 1913. 



FUNGUS NOTES. 



RED ROT FUNGUS AND THE SUGAR- 

 CANE IN THE WEST INDIES. 

 P.\ET II. 



The objects of the following investigation into the para- 

 sitology of the red rot fungus (Coll(totrichumfalcatum) were 

 explained in the last issue of the Agricultural Xews, and 

 a brief historical account of previous wurk on the same 

 subject was presented there. The position in regard to past 

 results wa.s summarized, and it was endeavoured to show 

 the complexity of the position and the somewhat contra- 

 dictory nature of the results that had been ol)tained. 



It is now intended to proceed with a descri[)tion of the 

 inoculation work of South and Dunlop, in St. Kitts and 

 Barl>ados, with a view to showing the extent to which 

 their results agree with those obtained already by other 

 investigators. 



The preliminary experiment.? were carried out in 

 St. Kitt.s, and it will be convenient, therefore, to deal with 

 these first. 



EXPEEIMENT.S IK ST. KITTS. 



The inoculations were made on fifty stools of White 

 Transparent cane, seven months old, growing strongly under 

 ordinary estate conditions (Series A to D.) Sixty healthy 

 cuttings of the same variety were employed in Series E. The 

 plan and methods adopted in the experiments were as 

 follows: — 



(1) C. fakatuiit (red rot fungus). 



. Series A Ten node.s and ten internodes inoculated bj- 

 needle pricks. Twenty controls similarly treated without 

 the fungus. Wounds protected with sterile budding tape. 



Series B. Pin pricks made in ten nodes, without any 

 fungus, and protected with sterile budding tape. Controls, no 

 budding tape 



Series C Twenty inoculations on leaf scars w'ith spores 

 suspended in drops of water. Twenty controls. 



Series D. 'J'wenty inoculations by means of spores 

 suspended in water sprayed in between the leaf sheaths and 

 stem Twenty controls. 



Each inoculation was made on a separate shoot. 



Series E Tiiirty cuttings inoculated as in Series A. 

 Thirty controls. 



(2) MeUmcnniur.i sacc/iari (rind fungus). 



Since this fungus is still regarded by some as the cause 

 of a specific rind disease, it was thought advisable to repeat 

 the above series with this organism as well. 



In connexion with the methods and conditions of inocu- 

 lation, the followin>: details may be noted. Before communi- 

 cating the fungus the surface of the cane was washed with 

 strong corrosive sublimate solution for one minute, then with 

 sterilized water and finally with alcohol. When the surface 

 had dried, the fungus was deposited or introduced, as the 

 case might be, with a sterile platinum loop or with a needle. 

 The budding tape was flamed in the field before each appli- 

 cation. 



The inoculating material consisted of j)ure cultures of 

 C. falcatuiii and .1/. snccluiri on sweet potato and sugarcane 

 slabs respectively, prepared in the mycological laboratory of 

 the Imperial Department of Agriculture at E.irbados. The 

 cultures were in a state of fructification and about a month 

 old. The germination capacity of the spores was tested in 

 hanging drops, and found to be satisfactory. In Series B, 

 a second inoculation was made in each case on the day 



following the first inoculation in order to maintain moist 

 conditions and abundance of spores. The different series of 

 inoculations were made within a few days of each other under 

 similar climatic conditions. The weather at the time of 

 inoculation was rather dry, but heavy rains were received 

 during the course of the experiments. 



UKSULT.-J. 



In order to ttace the development of the disease, two 

 inoculated and two control shoots of each series were cut and 

 examined every fortnight. The experiments therefore lasted 

 about three months. It may be at once stated generally, 

 thut in these experiments there was no further development 

 of the fungus alter about the first montii The extent of the 

 infection during this jieriod will be gathered from the follow- 

 ing observations. 



Series A {C. falcatum). Fifteen inoculated canes exhib- 

 ited the typical red and yellowish discoloration about 2cm. 

 each side of the wound, two canes (after one month) 

 had the entire internode discoloured red, with the charac- 

 teristic white centre. The nodes were not penetrated. 

 In general, the internodal infections took best. C. Jal- 

 rati'i/i was isolated Irom the two latter canes, but not 

 from the former fifteen. The remaining three inoculations 

 gave no results. Of the controls, twelve were not discol- 

 oured, except immediately along the course of the needle 

 wound. This was attributed in most cases to mechanical 

 injury and oxidation. Four of the controls were dis- 

 coloured as much as the inoculated canes but two 

 of these contained moth borer in the node under experi- 

 ment. No fungus could be isolated from these canes. 

 Amongst the canes that were reaped during the latter half 

 of the experiments were several in which the tapes had come 

 off. Immediately this was observed, Series B was instituted 

 to check the diagnostic value of the red discoloration. All 

 the uncovered wounds in this series showed after three weeks 

 nearly as much discoloration as the inoculated canes. There 

 was no discoloration in the controls in Series B. No fungus 

 could be i^olated from the uncovered wounds, and therefore, 

 the reddening was put down to oxidation and possibly to 

 yeasts and bacteria. In several of the inoculated canes 

 which might [iresumably be regarded as having been 

 infected, hyphae were seen to occur in the larger vessels, 

 and a comparison of sections of these specimens with sections 

 of a cane bearing fructifications ot C. Jnlcatiim made 

 it fairly evident that this fungus had at least been partly 

 the cause of the diseased condition in the inoculatsd canes 

 from which no fungus could be isolated. 



The conclusions to be drawn from the above results are 

 as follows: — 



(1) In most cases in Series A the fungus died early — 

 probably within the first two weeks after inoculation. In the 

 more susceptible canes, the fungus developeil quickly through- 

 out the entire internode but did not penetrate the joints 



(2) Not nuich reliance can be |,laced upon the symptom 

 of red discoloration for purposes of diagnosis, and, further, 

 red discoloration of the tissue tunnelled by moth borer does 

 not necessarily signify the presence of C- fakatum. 



(3) Under the conditions of the above experiments 

 C. falcatum did not show itself to be an active wound 

 parasite. One cause may have been the resistance offered by 

 the cane; or possibly the fungus may have become weakened 

 through cultivation. It is not improliable that the conditions 

 of moisture and jjarticularly of air-sup[)ly were unfavourable 

 fur the germination of the spores and mycelial growth. 



Turning now to the other .series of inoculations, it was 

 found that in the case of Series C and D, the fungus was in 



