( l.llt HOOT OK CRl't'IFERS 



97 



I)is|HTsal l>y tlif (hmp; of livostoi'k fid with dis- 

 «';isfd roots is wry i-oimiion. 'VUv s])orts rciiiaiii alive 

 diiriiiii passaiTf tliroiia:li tlu- dijivstive tract, and if 

 animals wliicli liavc lucn fed on distascd i-rucifers 

 are let out to i)asturf, the spores are disseminated in 

 the dropi)ings. Gihbs (,'31) found that the s])ores 

 may remain viable in fresh cattle droppinjjs for at 

 least fifteen weeks. They also remain alive for long 

 periods of time in dung piles around stables, and it 

 has long been known that the a])plieation of sueh 

 maiuire to virgin soil introduces the parasite. 'I rans- 

 port of infected soil on farm implements, laborer's, 

 lior.se's and livestock feet. etc.. is also ettcctive in 

 spreading the disease. 



Numerous wild cruciferous plants are suscejitiblc 

 to club root, as has been shown by Halsted ('96-'99), 

 Ravn ('08), Cunningham ('12), Ssaeharoff ('16), 

 Nauuiova ('26). Gibbs ('32). Rochlin ('33). Jaraa- 

 lianen ('3() ) and others, and these hosts often harbor 

 and peri)etuate the disease in the absence of culti- 

 vated crueifers. Sueh wild infected hosts have been 

 found in grass pastures, wayside ditches, river beds, 

 gardens, and cultivated fields, and their presence on 

 infected soil reduces the effectiveness of crop rota- 

 tion in club root control. 



Environmental Factors 



The degree of infection, development and severity 

 of club root depends to a large extent on environ- 

 mental factors, but the manner and extent to which 

 each factor operates are not clearly understood. The 

 disease is connnonly believed to be favored by wet, 

 poorly-drained, acid soils and temperatures slightly 

 higher tlian those optimum for host root development, 

 but reports to the contrary have often been made. 

 Motte ('33). for instance, reported that club root is 

 most prevalent in light soils and during the dry sea- 

 son in Denmark. 



As to spore germination, many workers have found 

 it occurs mostly abundantly in acid media. Bremer 

 ('23. '2i. '26). however, reported that H-ion con- 

 centration is not the sole determining factor. He 

 found that strong alkalinity inhibits germination of 

 the sjjores without killing them and that germina- 

 tion occurs over a j)H range of .5.1- to 7.-5 but not at 

 pH 8.0. Honig ('31), on the other hand, reported 

 that sijores germinate as well in alkaline as in acid 

 solutions: all of which indicates that other little- 

 known soil factors operating in combination are 

 equallv as ini]>ortant as H-ion concentration. 



Most workers liave. nonetheless, found a fairly 

 close correlation between incidence of infection and 

 pH range (^Nlassee, '96; Christensen, Harder and 

 Ravn, 11 : Ravn, '12-13; Hiltner and Korff. '16; 

 Neger. 17; Atkins, '22; Bremer, '2J-'28; Lindfors, 

 '2i. '2.5 : Naumov, '2.5 ; Ludwigs, '2.5 ; Riehni, '25 ; 

 Tessenow, '26; Cileisberg, '26; Chupp, '28; Briinnle, 

 '28; Martin. '28 : Blunck. '29; SchafTnit and Meyer. 

 *30; Beaumont and Staniland, '33; Wilson. '3Ketc.). 

 I.indfors ('24) observed a marked decline in per- 



centage of infection with an increase in soil alkalin- 

 ity. In .1 pH range of 7.1 to 7. .5, 8.5 ))er cent of the 

 plants were diseased while .'it ])H 7.8 to 8.0, all 

 plants remained healthy. Naumov ('2.5) found that 

 infection occurs most rc;i<lily ;it pH fi.O to 6. .5 with 

 the optimum near neutrality, .litliougii infection of 

 seedlings took j)lace within a range of 5.7 to 8. K In 

 a more intensive study of the problem in 1927 he fur- 

 ther found that percentage of infection is not con- 

 sistently correl.-ited with tlic \)\l r.inge. as is shown 

 bi'low : 



300pnis. BaOs per 100 cc. soil pi I. (i.S Infection (1.00% 

 100 •' pi 1.7.3 " 0.00% 



(10 ■• ' ]ni.i.2 " 0.0070 



SO •• ' " pH.(i.9 " 11.30% 



1,; •• " " " " " pH.7.* " 20.90% 



Blunck ('29) likewise found infection occurring at 

 1)H. 8.8. Further inconsistencies in the literature on 

 the effects of raising the pH value is shown by the 

 reports of Martin ('28). Schaffnit and Meyer (30), 

 \\'ilson ('3rt). and others that club root can be effec- 

 tively controlled or serious loss prevented by adjust- 

 ing the pH of the soil to 7.1' and above. Chupp ('28) 

 ;ilso reported that infection does not ordinarily occur 

 in soils with pH ranges above 7.2 to 7.4. 



In 1930 Wellman made a survey of 116 club root 

 infested fields in Wisconsin and found a pH range of 

 3.0 to 7.8. In Lithuania. Vilkaitis ('33) found the 

 range to extend from kO to 7.6. By the addition of 

 certain chemicals to the soil Wellman modified the 

 pH value experimentally and found that raising the 

 H-ion concentration did not consistently inhibit the 

 disease as is shown below : 



).H value Ca(OH)2 CaCO.'s K^COs 



7.1 Diseased Diseased Diseased 



7.2 " 



7.3 Healthy " 



7.4 Diseased ■ 



7.5 Healthy " 



7.6 " " Diseased 



7.T " 



7.8 Diseased 



7.9 Healthy 



8.0 Healthy 



8.1 " Diseased 



ft is to be partic\ilarly noted that addition of suffi- 

 cient amounts of K^jCO:. to bring the (iH up to 8.1 did 

 not inhibit the disease. In thoroughly infested fields 

 treated with lime Wellman further found that 3 per 

 cent of cabbages were destroyed at pH 8.1, and 54 

 per cent and 49 per cent destroyed at pH 6.7 and 7. .5 

 respectively. Wellman accordingly concluded from 

 his tx])eriments that club root occurs in such a wide 

 pH range that to consider H-ion concentration alone 

 as an important factor in the occurrence of the dis- 

 ease is highly questionable. 



Since that time other workers have also shown that 

 club root may occur in a high ])H environment. Beau- 

 mont and Staniland ('33) reported that while infec- 

 tion is most common in acid soils, swedes and broc- 



