ir,;'. 



THE AGRICULTURAL NEWS. 



Ma\ 10, 1913. 



FUNGUS NOTES. 



RED ROT FUNGUS AND THE SUGAR- 

 CANE IN THE WEST INDIES. 

 Paht III. 



In the last issue of the Agricultural X^ws an account 

 ■was given of inoculation experiments with the red rot fungus 

 {Volletotricliuiii fakatum) carried out by South and I »uiilop 

 in St. Kitts. In the present, and final article on the 

 subject, will be presented the results obtained by these 

 investigators from subsequent experiments in Karbados. 



It may be remembered that in the St. Kitts experi- 

 ments, the different -series ol inoculations were made on 

 White Transparent, and the fungus appeared not to be an 

 active wound parasite on the growing cane. There was, 

 however, some evidence to show that infected cuttings of 

 this variety might occasionally perpetuate the disease, 

 though the most generally observed effect was a falling 

 oH' in vigour and appearance of the young .shoots growing 

 irom the infected cuttings without any definite sign of 

 C. falcatiitti in the shoots The following work, carried out 

 in Barbados, was designed to investigate the behaviour of 

 the fungus in infected cuttings in a more complete manner. 



l;.\I»Kl;l.'MENTS IN BAl:l!.\I10S. 



l'"our lots of forty cuttings were obtained from healthy 

 jjlants lielonging, respectively, to the following varieties: 

 B.147, J'>.376, Bourbon and White Transj)arent About half 

 of each lot were top cuttings, the remainder being stem 

 •uttings, later referred to as 'bottoms'. Before treatment, the 

 forty cuttings of each series were {wired as regards size to 

 ensure the control plants being strictly comiiaralile. Treat- 

 ment consisted first in a thorough washing to remove mealy- 

 bugs and dirt; the planting material was then sterilized for 

 five minutes in corrosive sublimate (1 in 1,000), dried in 

 the sun, and finally the ends were tarred, with the object 

 of preventing subsequent infection in the soil. Twenty 

 cuttings of each variety were then inoculated in the 

 mycoiogical laboratory of the Imperial Department of 

 Agriculture, the methods employed being the .same as those 

 used in I he case of series A in the St. Kitts experiments, 

 except that mycelium was used from a culture four days old 

 and sterile wet cotton wool was bound over the needle 

 •wounds. Before planting out, notes were made as to the size 

 of each cutting, and any which were found to be slightly split 

 in the exposed tissue at each end were retarred. The 

 cuttings were planted horizontally in thoroughly moist well- 

 tilled garden soil adjoining the laboratory 



In carrying out the experiments comparative observations 

 •were recorded with a view to obtaining information on the 

 following points: — 



(1) External and internal changes in the inoculated and 

 controls before the appearance of the shoots above the ground. 



(2) Effect of the fungus, and of 'tops' and 'bottoms' and 

 size of cuttings on rate of germination (i.e. the first appear 

 ance of the shoots above the ground). 



(3) Extent of infection after germination. 



(4) Effect of inoculation on the development of the 

 young canes, particularly as regards whether tlie fungus can 

 8pread from stool to shoot. 



It will be convenient to present the results in the order 

 of the aliove arrangement. 



UEjl'LT.s. 



(Jne week after planting there were dug two pairs of 

 cuttinga of each one <>( the four varieties. Light showers 



had fallen during the week and the soil was in a goodl 

 damp condition, having a midday temperature of 100°E. at. 

 a depth of 3 inches. 



As regards external characters, there was very little- 

 variation to be seea between the different sets of material 

 planted. The cutting was generally swollen with the central 

 bud more developed than the remaining two at either end. 

 The root system had developed from the underneath surface 

 only, the roots being about iinch in length and more or- 

 les.s confined to the two lower nodes. 



On removing the tape the controls of all four varieties 

 showed either no djicoloration, or else a slight blackening 

 around the puncture; but in the inoculated canes there was 

 a streak in the rind about j-inch wide by A- to :,'■ inch long 

 of a red or reddish-brown colour, sometimes accompanied by 

 shrinkage and wrinkling. 



On splitting open the cuttings in the plane of the 

 needle wound a brick red discoloration was found extending, 

 in the case of one of the inoculated Bouibon cuttings, 

 through the entire internode; in most of the inoculated 

 cuttings of the other varieties the discoloratioji was less, 

 measuring about 1 { by ,';, inch. Cultures were made from, 

 all these discoloured ti.ssues and C. talcaium was obtained in 

 every case, thus providing conclusive evidence of succe.-sfuE 

 inoculation. In the controls (and in the inoculated cuttings 

 too) there was some grey and red discoloration in the toi>. 

 and bottom internodes, although partly the effect of tair 

 absorption, bacteria were isolated from the red tissue and 

 a pink Fusariuni from the grey. Tarring is therefore not 

 sufficient to prevent infection at the cut ends, though it is 

 probably the splitting that enables bacteria and fungus, 

 saprophytes to enter. 



Turning to the second series of observations on the rate 

 of germination, it will be convenient to consider first any 

 differences between the controls and inoculated cuttings. 

 Stated shortly, it was found that in the Bourbon series of 

 shoots, six controls came through before the corresponding 

 inoculated; in the case of B.376, four inoculated came through 

 before the corresponding controls; in White Transparent two 

 inoculated came above the ground before the controls to these;, 

 and in B. 147, on? inoculated appeared before its control. 

 The remainder either appeared at the same time or did not 

 germinate at all As regards total germination up to six 

 weeks after planting, the following are the numbers of .shoots 

 that appeared: I!. 147, ten control shoots, ten inoculated 

 shoots; B.376, twenty-four controls, twenty-four inoculated: 

 White Transi)arent, twenty four controls, twenty-five inocu- 

 lated; Bourbon, twenty controls, seventeen inoculated. 



The above figures point to the inability of the fungus 

 to check germination except in the case of the Bourbon 

 cane. 



In connexion with the effect of 'top' and 'bottom' and 

 size of cutting upon germination, the following observations 

 were made. Tlie pairs of very small cuttings (i e. the 

 cuttings with three nodes close together) germinatecl 

 earliest, particularly in the case of B.376, which in general 

 was the variety quickest to germinate; an exception appeared 

 however, in the case of White Transparent, of which the very 

 largest cuttings came up tirst. In the other three varieties, 

 the small stem cuttings germinated before the large top- 

 cuttings. 



The next point to be considered is the extent of infec- 

 tion after germination. 



Two pairs of cuttings in each series were dug six weeks 

 after planting Dufing the previous month the weather had 

 been rather dry with a few slight >howers. The soil wa£^ 



