17t 



THE AGRICULTURAL NEWS. 



May 24, 1913. 



FUNG'JS NOTES. 



A DISEASE OF SISAL HEMP. 



For some years specimeLS of diseased Agave have been 

 observed in India, the irjury being in most cases confined to 

 the leaves of the plant, or. which are produced small circular 

 patL-hes that eventually turn black in colour, and become 

 sui rounded by small erumpent nodules. A similar condition 

 has been noted in fleriiiiin East Africa, where sisal hemp i.s 

 extensively cultivated, and formerly in this country it was 

 thought that the condition was induced by excessive isolation, 

 aini.e it was found possible to produce the blackening by 

 exposure to high temperatures such as frequently occur at 

 midday in that Colony. 



While it is not disputed that excessive isolation, 

 especially when the rays of the sun are concentrated through 

 drops of water, may produce burnt and discoloured patches of 

 the leaf, yet recent work by Shaw, in India (published in 

 the Agricultural Jovrnal or India for .January, 1913) has 

 demonstrated that in that country, the disease is due to the 

 attacks of a parasitic fungus. 



The name of the fungus is ColleMrichum Agaves. 



In the inoculation experiments which were made with 

 the object of definitely ascertaining the parasitic nature of 

 the organism, wound infections had two effects according to 

 whether the host succumbed or resisted the disease. In the 

 first case ihe whole leaf turns yellow, the change in colour 

 spreading from the seat of infection. As the disease advances, 

 the yellow colour changes to black, and small black acervuli 

 (fruit bodies) of CoUetotrichum are produced and, in most 

 cases the acervuli are distributed in concentric rings. The 

 whole leaf becomes shrunken and dry, the cuticle being thrown 

 into a series of ridges and furrow.^. 



If the host plant resists the attack of the fungus the 

 pri'tress of the disease is much slower In this case the 

 damage is confined to the leaf immediately around the source 

 •of infection. Acer\ uli are produced in concentric rings as 

 in the more extensively diseased specimens. The hyphae 

 eventually bur.st through the epidermis (skin) as a mass of 

 conidiophores bearing spores. In those cases where the 

 diseased portion of the leaf is restricted to a small area 

 surrounding the seat of infection, a section through the 

 junction of the diseased and healthy tissue shows a layer of 

 cork cells across which the hyphae do not penetrate. 



Other infections made by laying pieces of agar culture 

 upon the uninjured upper surface were not successful, 

 indicating that Colletotrichutit Agaivs is a wound parasite, 

 which is not surprising considering the thickness of the 

 cuticle of the Agave leaf 



It is net unusual to find longitudinal cracks in the 

 leaves of Agaves especially after a period of hot dry weather; 

 such bleaks in the superficial tissues would afford a ready 

 means of infection from wind borne spores. Collecting and 

 burning diseased leaves, the prevention of accidental injury 

 to the leaves, and spraying with Bonleux mixture, are 

 methods which are recommended in India, as likely to be 

 efficacious in checking the disease. 



The fungus may occur in the West Indies, but .so far 

 it appears not to have been noted or described. 



possible that they may be of value, for certain diseases, in the 

 ^^'est Indies:- - 



'The polysulphides of calcium, barium, andzinc with sodium 

 have shown an etticacy equal or superior to that of Bordeaux 

 mixture in controlling A'.i-o'/.«<».< (!■ t'onintiis and other fungus 

 diseases of peach and apple . They have also been used with 

 success against Oidium of rose, oak, and euonymus, against 

 Kxo/iasidiuiii a:alf.(i', etc. These polysulphides and combina- 

 tions thereof with Bordeaux mixture, acetate of copper, and 

 nitrate of silver, are recommended as efficacious also against 

 Peronospora and Oidium of the grape. The polysulphides of 

 barium and zinc with sodium, are said to show a stimulating 

 action on vegetation, especially that of peaches, and to be 

 harmless to both leaves and flowers, whereas those of calcium 

 are fatal to the foliage of the peach'. 



A New Group of Fungicides. —The following 



note, taken frcni the K •piriiu'mt St'i'inn R-'rotii, Vol. .X.WII, 

 No. 9, deals with chemical solutions that have recently been 

 found u.ieful for .spriying diseased placts in Italy. It is 



THE PREPARATION OF PLANTATION 

 PARA RUBBER. 



A lengthy paper on the above subject embodying the 

 re.'.ults of some twenty-seven series of experiments eomi-rises 

 Btdleliii No. 17 of the Departmejit of Agriculture, Federated 

 Malay States The author is B. J. Eaton, Agricultural 

 Chemist on the staff of that Department, and the infor- 

 mation presented in the publication should be of very cousin- 

 erable practical value to those interested in Para ruober and 

 its preparation In the present article the results obtained 

 are briefiy abstracted. 



Dealing first with the minimum ijuantity required of 

 each one of the principal acids and salts to effect complete 

 coagulation of a normal or average latex containing about 

 30 per cent, of dry rubber, the writer presents figures which, 

 disagree with those obtained previously by Parkin. Thirty one 

 coagulants were tried, and the mininium quantity required 

 was generally smaller than formerly supposed, in several 

 cases, particularly as regards the common acids (acetic, 

 sulphuric, etc.) very much smaller than those advocated 

 by Parkin. 



In connexion with the maximum amount of coagulant 

 required, Eaton states that there is no maximum figure for 

 either acetic or any other coagulant, that the process of coagu- 

 lation — except when an excess of the agent is added — depends- 

 on a time factor, and that complete coagulation with the 

 minimum quantity of coagulant is not usually effected under 

 three to five hours. This result is claimed to negative Cross- 

 ley's figures The author explains ihe changes on a dilutioD 

 and adsorption basis. 



The third series of experiments concerned the choice o{ 

 a coagulant, and the most interesting refult obtained in this 

 direction, was the indication that an excellent coagulant is 

 to be found in sulphuric acid. If used with care, this acid 

 is superior in some of its effects, and more economicaf 

 than the commonly employed acetic acid ifany coagulants 

 affect the colour of the rubber. For instance, tannic acid 

 causes excessive darkening or o.xidation: hydrofluoric acid, 

 on the other hand, produces a light-coloured rubber. 



The experiments to ascertain the effect of dilution with 

 water, which follow, proved that if an average latex (contaio- 

 ing about 30 per cent, of dry rubber) is diluted with water 

 beyoiid a certain limit, no coagulation occurs with the mini- 

 mum amounts of coagulant already referred to. This maxi- 

 mum limit is usually about two volumes of water to one 

 volume of pure latex. The rubber was found to be much 

 softei and weaker from the dilute solutions, the quality being- 

 in direct correspondence with the dilution. The addition of 

 water to the cups is not recommended. 



