3^6 



THE AGRICULTURAL NEWS, 



No\KMBER 16, 191 S. 



PLANT DISEASES. 



<>t 



A SCHEME OF CLASSIFICATION FOR 

 PARASITIC PLANT DISEASES. 



In K [iar>T by V. L. Siemens {A'o/iuiii>i/ G<iu//. , \ol. 

 C3 No. 4) the need, which will be generally admitted, for a 

 classification of plant diseases, with reference to the nature of 

 the parasitism involved, is pointed out. and the following 

 Ireful scheme is suggested to this end:^— 



I The parasite living in ilie sap or in cavities or parts 

 iieviid of living protoplasm: — 



(a' Wilt diseas^e, due to mechanical stoppage ot 

 • vascular bundles by parasites, e.g. B. solaiia- 

 (eariim. 

 (b: Diseases caused bs disintegration of xylem 

 structures, e.g. various wood rots. Hydi'inn, 

 Femes, etc- 

 II. The parasite for the moat part of its life dniwitig it> 

 aiatriraent from host cells that are still living; — 



(a Endocellular parasites — the strictest lyp 



parasite, e.g. Syiuhylrium. 

 (b Diseases due to parasites which draw their 

 nutriment from living cells by haustoria (endo- 

 cellular haustorial parasitism,) e.g. Peroiios- 

 poia, Cyf/opus. 

 (e! Diseases affecting only live epidermal cells 



(epidermitis), e.g. Etysiphaks 

 (d Diseases in which the parasite grows between 

 ,the living host-cells; absorption is by the inter- 

 cellular mycelium Ontercellular myco.-is), e.g. 

 ste. 



■i.seases in which the hf^ist tissue is displaced 

 replaced by fungous masses (mycosclerosis), 

 - «-. Claviceps and the smuts. 

 (f; The .tumourlike diseases, e.g. I'seudomonin 

 tiimcfiuieiii. 

 III. The parasite living Within host-cells or tissues 

 vhich have recently been killed or partly disorganized by it;— 

 (a; Di.-'eases in which the dominant feature is 

 death of the host-cells before they are actually 

 iovadec] by the parasite (necrosis). According 

 to the part involved we may recognize; — 

 ii) Cortical necrosis, in which tjje cortex chiefly is 



involved, e.g. Sphaeropsh. 

 (ii Parenchymal necrosis, in which the paren- 

 chyma is afftcted, including the greater 

 number of the soft roots, eg. Rlih<p,iy 

 Peniii Ilium. 

 (u Macular necrosis, in which necrosis is limited 

 :o spoti- chiefly oceurring on leave.s. (M this 

 there are tw4 types, according to whether 

 there i.-* absci-ssion or not. Examples of the 

 former are Cyliiidrof/'oiium and Maissonio. 

 <A ''i^ latter, P'.r'vifi'ipfzizn and Siptoria- 



banana and itsdisi'afi.*, the greater portion of which is devoted 

 to the Panama disease This disease is caused by a fungus 

 {hum rill III tii/i,iift). and has caused severe loss lo growers of 

 bananas in Cuba, espt'cially in the case of two highly valued 

 varieties known as 'Slanzano' and 'Johnston'. Kntire planta- 

 tion> of froui lO.OOd to 20.(KI0 plants have been destroyed 

 by tlie progress of the disease. Many planters have given up 

 the cultivation ot thfpse two varietie>, .■substituting fiT them 

 another which goes by the name of '.Macho'. 



TH2 PANAMA DISEASE OF BANANAS IN 



CUBA." 



(,[ , . ■ '.-r. PItnt fathologi»t. 1 )epartinent ot 



Agricultur ^ article to the''jVi77V/« ik 



A'r'in,:!!' for August 1911?. on the 



The first symptoms of the disease are the yellowing 

 and withering of the leaves. The bunch of fryit becomes 

 twisted or aborted, or at least the fruits become .small and 

 dry. The stem of vigorous plants attacked splits longitudin- 

 ally from the nut.^idi- inwards. The suckers remain green 

 until the}' luo begin to show .symptoms of the diseas-e, and are 

 unablt lo produ(;t .i healthy bunch of fruit. Successivt- 

 generationa of plants are in every case sm-aller and smaller. 



Transverse .sections of a diseaserl .stem show that tin- 

 tibro vascular tissues are affected with ,i yellow dis2<iloralion, 

 changing to red and brown, which at length turns almost 

 bliick. .\ transverse section of a dist';ised root stock .shows 

 the central portion much discoloured, owing to the pre.-ence 

 of the disease-producing organism wLii-.h traverses it. 



There are few healthy roots, and these are lo be found 

 chiefly towards tlu^ surface of the .soil, taking their origin 

 from the u[)per [lart of the rootstock. The only varieties of 

 banana badly attacked in Cuba by this disease are tlie .M»n- 

 zano and the .Johnstot.. ('>n the other liand, there are sevenU . 

 varieties which Dr -fohnston says may be considered for the 

 present as inimune. A similiar fungus however attacks these 

 very varieties in I'aiiHura, and apparently the same fungus 

 attacks other <>f tlie-c varieties in Porto Hico. The advice i.s 

 given that in place of the Johnston r)anana in tho.se distiicts 

 where the disease occurs, one of the immune^ varieties should 

 be planted. 



Many investigitions have been undertaken in the hope 

 of discovering effii-tivc remedies again.st this disease Chemi- 

 cal fertilizers have been applied to plants attacked, obtaining 

 in some cases a vigorous growth but without conquering the 

 disease. 



Chemicals have Ivtsen injected into the steni of the plant 

 attacked without apparent results. Ili-idthy plants from a 

 district fn^e ol the disease have been brought intri aa 

 infected district and. they have contracted' the disease. 

 Diseased plants have been carried to spots free (-f the disease 

 without any benefit resulting from such transplantations. 

 Other crops have been cultivated lor three years in field." 

 where the disease e.\i«ted, and when replanted with bananas 

 the disease has broken out afresh. The eimtrol of this 

 disease is certainly ,i great problem for I he Cuban I tepart- 

 inent rif Plant Pathology. I'p to the present, only partial 

 results in the line of. preventive measures have been 

 obtained by destroying the infected plants, disinfecting , 

 all instruments used in their cultivalion, preventing the 

 tran.'sport of earth or plants frcnn infected fields, and forbid- 

 ding the transport cyfr plants from an infected region te 

 another where the disease may not exist. 



Diseosed plants ought to be cut down. The steins 

 should be cut in [lieces and burnt with thi- foliage as 

 completely as possible; the remainder ought to hive a cover- 

 ing of quicklime. It ia to be hoppd th it elfectual remedial 

 meisures for r(.inb«ting this disease may soon be found. 



