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THE AGRICULTURAL NEWS. 



November 22, 1913. 



FUNGUS NOTES. 



PINK DISEASE. 



^ fungus causing a pink incrustation on cacao trees 

 was described bj' Stockdale ( West Indian Bulletin, Vol. IX, 

 p. 17t<) as occurring in Dominica and St. Lucia; and South 

 {West Indian RnUetin, Vol. XII, p. 293) recorded its occur- 

 rence on pigeon pea {Cajanuii indiciis) in the latter island. 

 The fungus was identified at Kew as Corticium lilacino- 

 fvsniiii, B. it C. Some forms of the disease known as 

 thread blight have by various investigators also been 

 ascribed to unidentified species of Corticium. 



The closely similar pink disease of Hevea, tea, coflfee, 

 and a large number of other plants in Ceylon, Java and the 

 Straits Settlements lias loiig been the subject of investiga- 

 tion in the East. It is identified with Corticium satmon- 

 icohr, B. and Br., often referred to as C. Javanicuin, Zimra. 



The results of a detailed study of the disease in Java by 

 Dr. A Rant, published in the Hallttin of the Botanic Gar- 

 dens, Buitenzorg, Vol. IV, 1912, remove a great deal of con- 

 fusion and carry our knowledge of the disease very consid- 

 erabl}' forward. 



The disease is known by the Malayan name Djamoer 

 oepas, and has been recorded on hosts numbering 141 species 

 from 104 genera. Only two plants are mentioned as having 

 proved to be immune. The present investigation has been 

 mainly carried out with species of Cinchona. 



Three forms of the disease have been supposed and are 

 now proved to be due to the same fungus. In the typical 

 form, the twigs are covered with a thin, continuous, pick 

 incrustation, which later cracks in an irregular manner and 

 turns yellow. The second form consists of a silky web, and 

 is developed in damp situations. From the description it 

 seems closely analogous to one type of thread blight as 

 found in the West Indies. The third form takes the shape 

 of small pink cushions formed in cracks in the bark. 

 Further than this, a form which often accompanies pink 

 di.sease, and which had been regarded as a distinct fungus 

 under the name of Xeratr/r den-etus, Massee, has also been 

 proved to belong to the Corticium. It was first described 

 as a disease of coffee trees from Singapore. It begins at the 

 tips of the shoots and works backwards; the fructifications 

 burst through the epidermis as minute rounded white 

 pustules, which later change to an orange red colour and 

 a gelatinous consistency. 



Perhaps the most interesting part of Rant's work lies in 

 the experiments by means of which he investigated the 

 possible occurrence of biological species. One of the greatest 

 advances of modern mycology was made in the discovery 

 that certain fungi regarded as identical though growing on 

 different hosts were, in reality, so much specalized that they 

 could only infect the particular species on which they were 

 found. It is thus very important in a case where a fungus 

 such as the Corticium in question occurs in morphologically 

 identical forms on various host plants, to determine whether 

 cross infections from one host to the others can take place. 

 The results of the e.xperiments established: (a) that all the 

 examples of the fungus occurring in that neighbourhood 

 belong to one biologic species (with one exception); (b) that 

 80 far as it has been tested the genus Corticium contains no 

 biologic forms. The disease is thus shown to be transferable 

 from one host to another without regard to difference of 

 species, genus, or natural order. l''ven f lymnosperms, 

 (e.g. T/nija sp.) are liable to attack. A lower degree of 

 virulence appeared in expeiiments with material from other 

 districts. 



A considerable difference was found among individuals 

 of the same species in liability to the disease. It was dis- 

 covered that the principal factors influencing infection are the 

 humidity of the air, the water content of the susceptible 

 organs, and the amount of shade present. In laying out 

 plantations attention should be given to the first named 

 factor by having regard to the occurrence of fogs, and the 

 amount of the rainfall. Close planting should be avoided. 

 Insect attacks render plants more liable to the disease. The 

 author recommends as the principal direct method of dealing 

 with the disease, the cutting off and burning of the affected 

 parts, especially the twigs. Burying them is insufficient, 

 since they are liable to be brought to the surface again by 

 cultivation and are then capable of serving as sources of 

 infection. Fungicides are regarded as of little avail, owing 

 to the presence of hyphae in the wood which are unaffected 

 by their application. Carbolineum and Bordeaux mixture 

 were both tried with little apparent effect. It should be noted 

 here, that in a rev-iew of Itant's paper, Petch states that the 

 prevention of attacks on Hevea by this fungus has been very 

 successfully practised in Ceylon by means of sprayings with 

 Bordeaux mixture just before the mon.soon, the spores which 

 have collected on the twigs and l)ranches being killed as they 

 germinate in response to the rain. 



OOTTON DISEASES IN ST. CROIX. 



In the advance copy of the Report of the St. Croix 

 Department of Agriculture by Dr. Longfield Smith, Superin- 

 tendent of Agriculture, some particulars are given of two 

 important diseases of cotton found in that island. 



After mentioning angular leaf spot, round spot, cotton 

 rust and mildew, the report stites that a much more serious 

 disease than these is caused by a fungus attacking the 

 young and nearly mature bolls. 'The disease at first causes 

 a pink discoloration of the boll, which later becomes black. 

 If very young bolls are attacked they shrink up and remain 

 on the plant without opening. Older bolls open sometimes 

 at the tip only, and sometimes by a small slit in the middle 

 of the boll. The lint of such bolls is discoloured and 

 practically [spoiled?] and the seeds are also attacked and 

 spores are commonly found on them.' These spores were 

 examined by the late Mycologist of the Imperial Depart- 

 ment (Mr. F. W. South) who reported them to lielong to 

 a Macrosporium, possibly AI. m-gricaniuin, Atkinson, found 

 on cotton leaves in the United States. 



The .second dise;ise is one that was referred to in the 

 Report of the St. Croix Department for 1911-12, and is 

 descrilied as causing the young leaves to assume a blistered 

 and torn appearance, and the young Hower to drop off when 

 but the size of a pin's head. It occurs particularly where 

 plants are overcrowded, and is more prevalent on moist 

 soils. Iti severity is such that unle.ss the plant recovers it 

 is usually entirely sterile. 



Dr. Smith and the officers of his Department have been 

 unable to trace the diaetise to any insect or fungoid parasite, 

 and the present reviewer has examined preserved material 

 with the same result. Dr. Smith is of opinion that the points 

 of resemblance to a malady recently described in the U.S.A. 

 under the name of Tomosis or Leaf Cut (OF. Cook, Circular 

 No. 120, Bureau of Plant Industry, I'.S.D.A.) make it 

 probable that the St. Croii disease is the same. The con- 

 clusion reached in the American investigation was that 'leaf 

 cut is a disease only in a sense that frost bite, snow blindness 

 and other environmental injuries are to be considered as 

 diseases.' 



