14 



THE AQRICULTUKAL NEWS. 



Jaxuaey 12, IK 1 8. 



PLANT DISEASES. 



THE DISSEMINATION OF PARASITIC 

 FUNGI. 



In a paper on the dissemination of parasitic fungi and 

 international legislation relating thereto (Afenaiirs of t/u 

 Deimrtm-'nt '•/ Agriculture hi India, Vol. IX, Xo. 1) Dr. E .1. 

 Butler, Imperial Mycologist, discusses a subject of very 

 general interest to agriculturists. For the detailed examples 

 ■with which the discussion is illustrated reference must be 

 made to the original paper; the following summary will 

 show the nature of the conclusions reached. 



Fungi depend for their spread upon the transfer of 

 either spores, which in their nature are analogous to the 

 Eeeds of flowering plants, or of their vegetative part, the 

 mycelium. The former are small and often form a dry dust, 

 and are quite common!}' long-lived, resistant bodies. They 

 are thus capable of transmission for long distances in a large 

 variety of ways. Air-currents, streams, and animals of all 

 kinds from insects to man afford obvious agencies for their 

 disjjersal. 



The mycelium is mainly liable to be transmitted only 

 with the plants or their parts on which it occurs, in .some 

 cases on living material only (which may include seeds\ in 

 others on dead parts such as wood, stems, or leaves. In 

 a few cases the mycelium of plant parasites may be trans- 

 mitted in dry or moist soil. 



In considering transfers from one place to another when 

 natural barriers — seas, mountain ranges, or regions of widely 

 differing climate — intervene, the natural means are practically 

 reduced to two: winds and migratory animals, (chiefly birds, 

 and in a few cases insects). While these are possible means, 

 consideration of the evidence does not suggest that they 

 have much importance over any but short distances. 

 The positive and negative evidence of the distribution 

 of all the best-known diseases points to the conclusion 

 that their introduction to new countries depends on the 

 interchange of growing plants, of seeds, and perhaps, to 

 a lesser extent, of fruit and vegetables. The agencies 

 most conspicuous in this respect are Departments of 

 Agriculture^ Botanic and Experiment Stations, and com- 

 mercial nurserymen and seed de.ilers. (The criticism often 

 heard of the activities in this direction of the first- and 

 eecondnamed institutions may be met to some e.vtent by 

 pointing out that as a rule they are the only agents fully 

 aware of the dangers involved and in a position to take the 

 necessary precautions.) 



Probably at no period in the history of the world has 

 the movement of plants of economic worth, to and from 

 distant countries, been carried on so extensively as at the 

 present day. The time taken in transit ha- been continually 

 shortened since the introduction of steam, and whether the 

 parasite is best fitted to travel as spores or as mycelium, few 

 |>art8 of the world are now remote enough to prevent the 

 great majority of the fungi that cause disease from being 

 introduced with their host plants in a living condition. 



Diseases, once they arc present in a countrj'. can 

 ordinarily make use of the methods of cfmtinnous 

 spread which are mostly uncontrollable. There have 

 been attempts in the past, and several are in priigress at 

 the present moment, to exterminate newly intrfiduced parasites 

 in various parts of the world. It is doubtful if any have 

 succeeded, while some are known to have failed completely. 

 The action taken to be effective niu-t be such a- to keep the 

 disease from getting a footing in the country. For this 

 purpose it is iinportant to know from what part of the world 

 diseases dangerous to the crops of any particular country 



are likely to come and what diseases exist in each area which 

 could be imported and might prove injurious. In order to 

 be as secure as possible against the introduction of exotic 

 diseases there seems to be no alternative at present but to 

 consider each important economic plant separately, and 

 examine the records of the parasites that attack it in various 

 countries. Difficulties arise from the imperfections of our 

 knowledge regarding even the best-organized countries, and 

 the almost entire ab-sence of information regarding others. 

 There is also the unfortunate circumstance illustrated by 

 some of the most notorious diseases, that a parasite which 

 is relatively harmless in one country may be extremely- 

 destructive in another. No amount of organization will 

 remove this difficulty. 



In February 1914 an International I'hytopathoiogical 

 Conference was held at Fiome and agreed u|ion a L'onveniion 

 the object of which was to control the inter state circulation 

 of horticultural produce. The application of the Conventioa 

 has been largely suspended as a result of the war. 



It is proposed to control the interchange of living 

 plants, cuttings, grafts, flowering bulbs and cut flowers 

 with certain exceptions. Each State undertakes to set up 

 a Government service of Phytopathology, the duties of 

 which will be to supervise nurseries and inspect consignments 

 intended for export, No such material will be admitted 

 without a certificate that its sanitary condition is satisfactory. 

 and (where requLied) that it is free from certain specified 

 diseases. Each adhering country will prepare a list of che 

 diseases against which it wishes to guard itself. Common 

 diseases already widely distributed must not be included, and 

 the diseases mentioned must be those of an eindemic character, 

 very harmful, and easily disseminated by living plants or their 

 parts. The Convention does not apply to seeds or to edible 

 root crops, fruits and vegetables, or field produce. JJving 

 plants for scientific study in authorized institutions are also 

 exempted. From non-adhering countries imports may not 

 be acceiited unless certified by 'competent otticial agents.' 



Dr. liutler points out that these rules, while representing 

 the maximum of c(.ntrol that could be agreed upon, and 

 presenting numerous difficulties in their application to special 

 circumstances, will fall very far short of ensuring complete 

 security. The stipulation that only very harmful diseases 

 may be listed leaves out of account the variation in virulence 

 already referred to, and for that reason the rules could not 

 have hindered the original transmission of parasites which 

 have turned out to be extremely destructive in fresh countries. 

 The exemptions referred to each leave a large loophole for the 

 introduction of disease. There is however no reason why any 

 particular country that so desires should not further protect 

 itself, and the international machinery once it is established 

 will no doubt cpiickly be improved upon. 



The position of the West In<lies with regard to thes& 

 questions is in many respects a special one. Their agricul- 

 tural territory is divided by broad chii.nncls of the .sea into 

 relatively small areas, each concerned with but a small number 

 of staple crops, and the existence in each island of an agricul- 

 tural department makes it feasible for a clo.se control to be 

 maintained over introductions. But these circumstance 

 though tliev make protection possible, do not in themselves 

 ensure it 



So far as it can he ensured it depends on the mainten- 

 ance of an up-to date .service of information, on the restriction 

 of introductions to responsible agencies, and their reduction 

 to the minimum consistent with real re<|uirement.s, and above 

 all on the vigilance with which the order- made are adminis- 

 tered. As regards imports, local regulations have in most 

 cases already gone well beyond the scope of the Convention. 



W.N 



