March 2, 1912 



THE GARDENERS' MAGAZINE. 



187 



A DISEASE OF SWEET 



PEAS, ETC 



We take the following- a^^coimt of Mr. G. 

 Massee's important investigations of the 

 ** streak " disease in sweet peas from the 

 Kew Bulletin " : 



A disease attacking- asters, sweet peas, and 

 various other cultivated plants, more espe- 

 cially during the seedling stage, caueed by 

 n minute parasitic fungus, Thielavia basicola, 

 /i)pf, has become so prevalent during recent 

 •ars, that in some localities their cultiva- 

 m has been practically abandoned. The re- 

 i])t at Kew of a considerable amount of 

 diseased material in a condition favourable 

 for investigation has led to the discovery of 

 the cause of the disease, and also of measures 

 whereby the danger can be prevented. 



Morpholog^y, Etc. 



The several very dissimilar forms consti- 

 t uting the life-cycle of Thielavia basicola, 

 Zopf, has led to much complication and 

 svnonymv. 



The mycelium first produced as the result 

 <j1 infection, permeat-es the tiseues and re- 

 mains slender and colourless. As a rule, the 

 host shows decided sig-ns of injury, or is 

 killed outright before the fungus commences 

 to produce its fruit on the surface of the in- 

 jured portions. When this stage has been 

 reached, if conditions are favourable, 

 branches of the mycelium grow outwards and 

 cover the surface of the diseased part with 

 a plexus of mj^celial branches, which soon 

 give origin to the first or Milowia form of 

 Iruit, which consists of simple or branched, 

 upright, septate branches, becoming gradu- 

 ally narrowed upwards, and remaining per- 

 fectly colourless. In due course the apical 

 portion of each erect branch becomes rup- 

 tured, and the contents grow out through 

 the torn apex as. a chain of spores which 

 i- adily separate from each other, and germi- 

 nate at once. This form of fruit is very 

 ephemeral, and is rarely seen in the field, 

 altliough in pure cultures it forms a si ow- 

 wfiite, mould-like stratum. It alone is re- 

 sponsible for the spread of the fungus in 

 tae torm of an epidemic durine the ^-arlv 

 stage of growth of the host-plant, but it doe's 

 not appear to be capable of infecting the 

 root of a mature plant. The sports retain 



]ZVT*T^- germination for a very limited 

 period ot time, not more than one month so 

 lai as my experience goes. I first met vith ■ 

 w i f «f Thielavia forming a delicate 



^ nte mould at the base of a dying plant of 



Si. at the time con- 



M.tl It as an entity and worthy of ^^eueric 



S.a.;,.;/"^.P"^^'"^^^ ^« Milowia'nixea. 

 tvn. " afterwards placed Milowia as the 



wl ch"l 'f'J:,*,^^^ Hyphomycetes 



Milowief ""'^r??^'"'^^ the nanfe of 



• i^P^^ spores or conidia are some- 



drical thin-walled, 

 ancal with truncate ends 

 l-2o X 4.6_ 



tlie'n!vcPl^"*''1'' '^^^ f™it disappears, 

 host S , ;"\.^^^^J-P«i externally Z the 



to a "secoi^^ '^^^^ ^r''''' '^"^ origin 

 the \ 1 ^"^^^'^ form of fruft. In fact 



ti!"- t'^et^with'^^-^"^^^ ^'^^^^ "^^^ 

 mycelium ; 



or second 



what 



cylin- 

 and average 



on the same branch of 

 m such instances the Torula 



the mvcelin? K """"r'^rr.^^ ^Pi'^^l Portion of 

 ^ompaSivil Morula spores are 



' " WaduallJ^ ? thm-walled and colourless, 

 'tSv "^^"^'"§^.to a dark brown and 

 uaily becoming quite opaque. The cell- 



gToTh ITt^^^^'^i in thickness 

 ' s u" °f the spore. When the 



^oinix.neut cell. T^'I ^'^^^ ^^^^ their 



' '^^"''h resemble discs of 



h.ckness, and are circular! ^r 

 ■ <le a U 1;;^ ^ polygonal, in outline. 



^■''^i^ying 



of maturity, but do .so readily after remain- 

 ing in a passive condition for some months. 

 This phase of the fungus is usually the only 

 one observed, unlet>s special watch is kept, 

 being rendered conspicuous by the copious 

 production of 6pore«, which often form black, 

 crust-like patches on the discard root and 

 collar of the host-plant. The spores vary 

 considerably in size, and may be straight or 

 curved, average 8ize 40-65 'x 12-2C) at the 

 widest part near the apex. Thi8 stage of 

 Tliielavia was first observed, in 1850, by 

 Berkeley and Broome, who con^sidered it an a 

 member of the genus Torula, and de^eriWd it 

 as T. basicola. It was found at the base of 

 rttems of peas, and of nemophila. Respect- 

 ing its propensitiees, the authors wrote as 

 follows : It is either destructive of the ])lant 

 on which it growls, or i^ developed on it in 

 consequence of previous disease." l-'roni an 

 economic standpoint, this is the most dan- 

 gerous phase of the fungus, a*> the resting 

 spores enable the parasite to tide over tliat 

 portion of the year when its ho8t-|>:aiit.N. 

 which are mostly annuals, are not in active 

 growth. These resting spores germinate 

 readily on dung, and produce the Milowia 

 and Torula forms of fruit on this matrix; 

 in fact, the fungus appear^ invariably to 

 commence life as a saprophyte, and when 

 conditions are favourable, as expretssed by 

 the presence of rootlets of seedlings, it as^- 

 sumes a parasitic habit ; otherwise it can 

 pass through all the phases of its life-cycle 

 as a saprophyte. In fact, the fungu^s at best 

 is but a very imperfect parasite, the vegeta- 

 tive mycelium first resulting from the ger- 

 mination of the sports being alone parasitic, 

 but its action is sufficient to cripple, il not 

 completely to kill, the host. The various 

 forms of fruit are then produced externally on 

 the host, which it has previously killed. I 

 have repeatedly observed the Torula follow 

 the Milowia stage, when the fungus was 

 growing on pea seedlings infected with 

 diseased portions of plants killed by the 

 fungus, and have also observed the same 

 sequence when a pure culture of Milowia 

 spores was need. 



Distribution. 



The fungus was first observed by Berkeley 

 in England in 1850. It has also been re- 

 corded from France, Germany, Italy, Russia, 

 the United States, and Cuba. It has proved 

 to be very destructive to cultivated crops 

 in Italy, Germany, and the United States, 

 and is probably much more widely distri- 

 buted in the soil than is generally suspected. 



Now that a simple and certain method for 

 determining its presence has been discovered 

 we are in a position to anticipate it and to 

 act accordingly, as the means necessary for 

 its arrest are practical, inexpensive, and eflPec- 

 tive. 



In England its distribution is certainly 

 widespread; seedling asters and sweet peas, 

 more especially, have been received at Kew 

 in large quantities from practically every 

 part of the country ; many weeds also suffer 

 from its presence. Excluding trees and wmidy 

 plants, the fungus appears to be practically 



omnivorous. 



It has 'been recorded as parasitic on plants 

 belonging to the following genera: Apium, 

 Aralia, Aster, Begonia, Beta. Hlysmus, Coch- 

 learia. Cyclamen, Daucus, Lathyrus, Lupinus, 

 Cypripedium, Xemophila, Nicotiaua, Onobry- 

 chis, Pisum, Scorzonera, Senecio, Trigonella, 

 Viola. In some instances the injury caused 

 by this fungus assumes serious proportions, 

 and the tobacco crop, both in Eur^^pe and in 

 the United States, has suffered to the 

 greatest extent. In this country the disease 

 has assumed the proportions of an epidemic 

 in the case of asters and peas; in fact, dur- 

 ing the past few years it has become practi- 

 cally impossible in certain districts to grow 

 asters, the seedlings being destroyed whole- 

 sale. Sweet peas also suffer to a very seri- 

 ous extent in many places, and culinary peas 

 to a less extent. 



Cultures of the Fungous. 



The conidia of the summer stage (Milowia) 

 germinate I'reely within twenty-four hours in 



water. As a rule, only one germ-tube is 

 produced from one end of the conidium. In 

 those instances where two germ-tubes are 

 produced, one from each end of a coni- 

 dium, one of the germ tut)os continues to 

 grow vigorously, the otlier remaining sJnall 

 and stunted, and eventually dying. The 

 conidia only retain their vitality for about 

 ten days, and no conidium was observed to 

 germinate after it had been liberated for 

 more than a fortnight. Germination is most 

 vigorous immediately after the conidia are 

 liberated, and the percentage of germination 

 decreases daily with the increasing age of 

 the conidia. As compared with a neutral 

 medium, the presence of a slight amount of 

 acidity in the nutrient solution favours ger- 

 mination and the development of mycelium, 

 wherea.s, on the other hand, a trace of 

 akalinity in the nutritive medium retards 

 germination and subsequent (rrowtli <>i the 

 mycelium. T]\o conidia alsiv u-erminate 

 i'reely on moist stable manure, covering the 

 surface within a week with the snow-white 

 tufts of the Milowia stage of the fungus, 

 which is followed by the black masses^ of 

 conidia forming the Torula stag^e. Tlie asci- 

 gerous condition was not observed. llie 

 fact that the fungus can produce its two 

 conidial phases as a i)ui'<^ sa])r(»]>liyte is a 

 point of great important*' from ;ni vt-onnmic 

 standpoint, and suggests thr iTn|i(>rtan(<' of 

 burning all diseased plants. ]t'>t ilioy slionid 

 by any chance find their way to the manure 

 heap, from whence the conidia of the Torula 

 stage of the fungus wwild eventually bo re- 

 turned to the land in a (■<»iHl;t ion favourable 

 Tor germination. By such unguis the wide- 

 s))r(v^d occurrence of the fungus may iirob- 

 ab1v be explained. 



Hie chlamydospores resultin<i: from ilie 

 breaking up of the Torula form of fruit do 

 not germinate until after a period of rest, 

 and serve to tide the funo-us over that 

 period when living host-plants are not 

 fortlicominq-. 



Chlamydospores obtained from aster seed- 

 I'ngs that had been dried for a year e^er- 

 minated in a very dilute solution of stable 

 manure, at the end of four davs, and another 

 batch of chlamydospores obtained fmm the 

 same source germinated on sterili--('n stable 

 manure, and produced the Milowia o> in 

 w'thin a week, followed bv the Torijla form. 

 Experiments prove that tli- ^li'ow n coni- 

 dial form constantly reproduces itsc'f; this 

 takes i^lafo so 1onof as flimatic coirlitions are 

 favourable for its development, and tho dis- 

 tribut'on of the funtru^ ^uace depends en- 

 t'rely on its Milowia conidial phase. 



(To be continued.) 



T.iTr»*»w^»«Ki»H,* Machines. 



fii everj gar- 

 Un and on 

 very estaie 

 me of tbese 

 'Four Oalifi ' 

 ra a c h i n *'8 

 re i di s - 

 persabJo. 



Will eprsy 

 he Fru it 

 frees, Lime- 

 *v a P h 1 h e 

 Stables Ken- 

 nels, O a t- 



b u i 1 d i n?e, 

 itc, ill a 

 fraction of 

 the time 

 ta k e n b v 



* 



brushes. 



C i» m p 1 e t e 

 C atalojcr n e 8 

 i.jf c-p ajiiitr 



and Lime- 

 w a 8 h i n J? 

 Mflf'hines X 

 Syrin fires free 



tioii to Solf 

 Manf u'tr8. . 



Rovall*attoiu" £3 18s. 6d. i 



FOUR OAKS SPRAYING MACHINE CO . 

 No. Sutton Coldfleld, Birming^ham. 



