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A BANANA DISEASE.* 



Note by Dr. Axel Preyer. 



For about three years a peculiar disease has been spreading amongst 

 Bananas cultivated near Alexandria in Egypt. The first symtoms of 

 the disease are to be observed in a sudden check of growth, and soon 

 afterwards the leaf-points and the youngest central leaf become black 

 and die. The latter gets rotten, and numerous ants and other small 

 animals inhabit the upper part of the stem, jnd the putrefaction proceeds 

 downwards. The stem does not die immediately, but it is naturally 

 unfit to bear fruit. Very characteristic is the appearance of a great 

 many small, crippled leaves, instead of a few well-shaped large ones, 

 as is seen in the sound plant. 



A strongly infected stem dug out of the earth with roots was cut in 

 a longitudinal direction In the upper part, the youngest leaves were 

 all black and rotten ; the outer layers were white and seemed to her 

 sound, only the fourth and fifth layers were dark brown and saiurated 

 with a putrid liquid. The lower part of the stem and the root-stalk 

 showed no sign of disease. But on the roots themselves, especially on 

 the root-tips, one could observe small knobs, generally accompanied 

 by en excretion of a resinous substance. Sections of these knobs were 

 first examined under the microscope, and their contents were found to 

 be relatively large egg- sacs of a kind of pest belonging to the Nema- 

 todes. The eggs were in different stages of development ; even some 

 full-grown Nematodes, possessed with great mobility, had penetrated, 

 into the cellular texture of the root. On further investigation, and by 

 comparing infected with uninfected plants, the Nematodes may be 

 stated to be the cause of the Banana disease ; therefore the latter is 

 due to an infection of the roots. 



The Nematodes themselves are in shape long, thin, and cylindrical, 

 with around mouth-end and a fine sharp point at the oiher end, which 

 is strengthened by a thickening of the epidermis. The whole length 

 is 0.57 millimetre, the maximum diameter 0.014 mm. The pest 

 belongs to to the same genus Tylenchus, but its specific identification 

 has not yet been ascertained. This Nematode resembles very much 

 the Tylenchus acutocaudatus, Zn., which is the cause of a well-known 

 dangerous coffee disease in Java. 



As to the biology of the Banana Tylenchus, it is an interesting fact 

 that the pest not only lives in the roots but ascends with the watery 

 liquid streaming upward, and it is to be met with in great numbers 

 in the upper parts of the stem. I could not, however, find any egg- 

 sacs in these parts. 



The most important question with regard to the Banana disease is, 

 of course, how to suppress it. In this case the task is rather difficult, 

 because the Nematodes live free in the ground, and seem to have 

 spread over a great area near Alexandria. Experiments are going on 

 by manuring the Bananas with nitrates, and by isolating the planta- 

 tions by deep canals; but no results have as yet been obtained. In Java 



* Journal, R. Horticultural Society, England. 



