350 



THE AGRICULTURAL NEWS. 



October 25, 1913. 



FUNGUS NOTES. 



TOBACCO WILT DISEASE. 



C M. HutchinsoD, in lodia, has discovered that tbe 

 annually occurring wilt disease of tobacco plants in Bengal is 

 due to infection with a bacterium possessing characters similar 

 to those of B. solanw'afuiii, Smith, which induces a well- 

 known disease of tomatoes. 



SYMPTOMS. 



The symptoms are at first wilting of the plant followed 

 later Iiy the development of dark-brown streaks in the stems 

 and midribs of the leaves, vissible on the surface and found, 

 on cutting open the former, lo extend inwards to the pith and 

 spreading upwards from the point of infection, generally 

 about ground-level, to a distance depending upon the stage to 

 which the disease has advanced. 



ISOLATION OF THE CAUSATIVE ORGANISM, 



In endeavouring to obtain a pure culture of the causative 

 organism it was found that the method of flaming the infected 

 stem and cutting out externally uncontarainated blocks with 

 a red-hot knife was impracticable owing to the invasion of 

 foreign bacteria. To overcome this ditticulty, Hutchinson 

 employed a useful method in which the portion of removed 

 tissue was coated with wax previous to being penetrated by 

 the medium in which a bacterial growth was desired. A large 

 number of commonly occurring saprophytic forms were isolat- 

 ed, amongst which 11. jirodigiosHs was present — a matter of 

 interest since the investigator had failed up to that time to 

 find this species in any Bengal soil. As far as one can gather 

 from the paper, />'. solan'i.ctarum was not actually obtained in 

 pure culture, or at least not in sufficient quantity to provide 

 material for inoculation purposes. The infections had to be 

 made with cultures cdntaining a sufficient preponderance of 

 the pathogenic organism to serve as efficient sources for 

 inoculation. 



It is important to note that this requisite condition can 

 be determined chemically by means of litmus. This same 

 test is used in connexion with B. aolanaceanim on tomato 

 fruit: tests with litmus showed the juice of the inoculated 

 fruit to be strongly alkaline on the side next to the point of 

 inoculation, and acid on the opposite side. 



INOCILAIION EXTKRIMKNTS. 



Successful wound inoculation experiments were made 

 with cultures of high virulence, though no infections resulted 

 from applying to the soil water with Ijacteria in suspension, 

 unless some of the roots happened to be damaged Old 

 cultures appear to lose their virulence quickly. The virulence 

 f>f cultures was alsj reduced to a great extent by keeping, 

 though their parasitic habit was gradually regained by 

 passage through a fresh series of plants. 



From the appearance of the diseased tissue, one might 

 orcicarily suppose that the wilting of the plant was caused 

 by a blockage of the vessels with the nia.sses oftacteria. It 

 has been fairly conclusively shown, however, by means of 

 injections into a healthy plant, that the wilting phenomenon 

 is produced by the toxic aub.siances secreted by the bacteria. 



HELD TREATMENT. 



It is believed that the organism gains entrance through 

 mechanical injury: possibly on account of root damage at 

 the time of transplanting, or the organisms may obtain 

 entrance through tht- wounds caused by nomatoiles. 

 Hutchinson also suggests that the bacteria may gain entrance 

 through the lower leaf scars; for after the common practice 

 of removing the basal leaves, a certain amount of raw ti.ssue 



is exposed to infection previous to the formation of a cork 

 or a callus covering. 



Field practice should aim at the conservation of soil 

 moisture, and development of the root s}-stem, which serve 

 to produce better-grown and consequently more resistant 

 plants: hot weather ploughing, if effectively carried out, will 

 not only answer these two purposes but will aid in the 

 destruction of both the infecting organisms and the nema- 

 todes. Diseased plants should be burnt: not only the part 

 above the ground but that below also. Such manures as give 

 rise to an alkaline reaction in the soil should be avoided 

 as tending to produce a lower resistant power in the plant to 

 infection, and to increase the number of infecting organisms. 



THE STATE MYCOLOGIST IN THE 

 COLONIES. 



Under this heading. Nature (September 11, 1913) 

 reviews what is apparently a generally instructive handbook 

 of mycology, in spite of the fact that it deals with the 

 diseases of a single host plant, namely the potato, and in 

 a single country, namely Victoria. 



The author of the book. Dr. McAIpine, descril)esin detail 

 Phytopkthora iiifestans, Altermiria solxni, llhizoctonia, 

 Fusariuin solani, and £acillus solanaiearum. With regard to 

 these diseases, a number of highly interesting experiments 

 and observations are stated to lie reported. In the case of 

 Phi/tophl/iora intestatis, it is shown that sporangia can infect 

 the unbroken skin of healthy tubers: and that the mycelium 

 can remain living in a dried up tuber for more than four 

 months. Interesting diflerences are given in regard to 

 symptoms observed in Great Britain and in Australia, the 

 reason for these being attributed to the prevailing hotter 

 weather in Australia. A series of experiments is described, 

 which shows that the Fusarium of the potato and tomato 

 are transferable. 



The reviewer, however, takes exception to a well-known 

 type of statement which appears in the book, involving the 

 use of the word 'probably', often resorted to by biologists to 

 avoid admitting the absence of definite knowledge. Such 

 a type of statement is to be deprecated, according to the 

 reviewer; and although the criticism is just under certain 

 circumstances, it must be remembered that indefinite state- 

 ments of the kind referred to are really made to sound a note 

 of warning, and to indicate a subject which is undoubtedly 

 worth further investigation. They do more good than 

 harm, assuming, of course, that there exists a foundation 

 of scientific facts. 



DEPARTMENT NEWS. 



The Secretary of State tor the Colonies has been 

 pleased to appoint Mr. \V. Xowell, D.I.C., formerly 

 Assistant Superintendent of Agriculture, Barbados, to 

 the office of Mycologist on the St.ift' of the Imperial 

 Department. Mr. Xowell assumed his duties on the 

 20th instant. 



Mr. P. T. Saunders, M.R.C V.S., Veterinary Officer 

 to the Imperial Department of Agriculture, left 

 Barbados on Monday, October 20, 19l'S, by the K.:M.S. 

 'Druba' for Antigua, to investigate a skin disease of 

 cattle. 



