COBB'S DISEASE OF SUGAR-CANE. n 



There is no record of any cultures or inoculation experiments. 



In 1895 in an article on gumming of cane in the Annual Report of the Queensland 

 Department of Agriculture, Tryon states that the disease occurs in Queensland, and says 

 of Cobb's Bacillus vascularutn: "Personally I also have failed to produce the disease in 

 healthy plants by the method of inoculation with the pure culture of the bacillus." But 

 Tryon also says that Cobb says someone else in New South Wales, whose name is not 

 mentioned, has succeeded in inducing the disease by means of pure-culture inoculations. 



The writer of this abstract asked Dr. Cobb for details, but was unable to learn the 

 name of this experimenter, if such there was. 



Tryon studied this disease in the Burnett district and Wide-bay district (S. lat. 25 to 

 26), j. e., on the eastern coast of Australia, a few hundred miles north of the localities 

 examined by Cobb. 



His description of the signs of the disease on the foliage is in some respects confirmatory 

 of Cobb's. They are in many respects so strikingly like those obtained by the writer from 

 pure-culture inoculations that I quote in full, as follows: 



When the presence of the disease has been determined by the use of sets derived from a badly 

 "gummed" crop, some of them will fail after having emitted attenuated shoots, that fail to reach the 

 surface. Others will give rise to slender and weakly plants, which apparently struggle to survive, 

 whilst a few will develop foliage with the individual leaves narrower and more irregular in size than 

 if they were healthy, with the central ones yellow-green and more or less crinkled and contorted, 

 with, at times, the central leaves interlaced in a tangled mass. A few of these leaves, again, espe- 

 cially the inner ones, may exhibit bright rust-red streaks in their tissue, and this may constitute a 

 conspicuous feature. If any such plant is cut longitudinally through the point of growth, it will be 

 generally observed that the central shoot beyond where it joins the cane proper, instead of arising 

 in a straight, erect manner, is more or less bent and contorted, its upward tendency having been 

 apparently hindered. Moreover, the young cane itself, immediately below the shoot, will present 

 one or more cavities, each containing a semi-fluid tenacious pale brown substance. 



Should the "sets" be the progeny of a crop of cane affected but slightly by the disease, nothing 

 very abnormal may be noticed until the cane proper has commenced to form. Then, although the 

 bulk of the plants will appear well-grown and perfectly healthy, others, though at first fully devel- 

 oped, will evince the presence of the affection in varying degree. The first symptom in a plant of its 

 occurrence will then probably be afforded by a thin, pale longitudinal stripe arising in one of the outer 

 leaves, in which the green colouration being discharged may gradually be giving place to brown. If 

 this plant is divided by a longitudinal cut through its growing apex, nothing abnormal may yet be 

 recognized. A plant in which the disease has made further progress will exhibit brown stripes of 

 dead tissue one side of the central nerve, or along the margins of the outermost leaves, whilst on 

 two or three of the inner ones will ha\ r e appeared elongated rust-red streaks. If this plant be cut as 

 before, very marked changes will be noticed in the tissue immediately below the growing apex. 

 These are afforded by the presence of several cavities having ill-defined walls partly filled with an 

 odorous yellowish substance of the consistence of pus, as well as of spots where the external tissue 

 is becoming soft and brown to mark the site where subsequent ones may arise. These cavities occur 

 in the intervals between nodes, whilst the denser tissue of which these latter are composed may 

 exhibit in small number specks, or thread-like lines of a red colour. When still further advanced 

 we may have a strong, healthy-looking plant, with a stem measuring some 2 feet 6 inches in height 

 from the ground to where the green foliage commences. In this several of the outer leaves, and the 

 central ones as well, have longitudinal brown stripes or bands of dead tissue extending for the greater 

 part of their length ; and, as will be seen by a longitudinal cut, the joints or internodes immediately 

 below the apex, to a distance of from i to 2 inches, are quite hollowed out, and there is considerable 

 discolouration and softening of the tissue generally and incipient decay, both in them and in the nodes 

 also. In such a plant the central shoot, now almost dead, may readily be pulled out. * * * 



The disease may appear at any period in the growth of the cane, and even when it is fourteen 

 or more months old; but these late manifestations probably generally arise when the malady is of 

 spontaneous origin. * * * In the first instance the central leaves are quite normal in appearance, 

 and perfectly green and turgid, but the lateral leaves are marked by broad brown longitudinal bands 

 of dead tissue, the lowermost having evidently prematurely died. The eyes on that part of the stem 

 from which the leaves have naturally fallen have shot out, and the slender shoots thus formed are 

 already dead; the uppermost eyes, however, are still alive, and have not as yet sprouted. * * * 



