V; 5"" at . " ,.‘-‘~~' i w‘ cazitehw “ ‘ELIE ' j ;_._ Air.‘ l‘ "A Ni») »— A63-1 1 28-8.000-Ll 80 TEXAS AGRICULTURAL EXPERIMENT STATION A. B. CONNER, DIRECTOR COLLEGE STATION, BRAZOS COUNTY. TEXAS BULLETIN NO. 389 NOVEMBER, 1928 DIVISION OF PLANT PATHOLOGY AND PHYSIOLOGY Relation 0f Cotton Root Rot and Fusarium Wilt to the Acidity and Alkalinity of the Soil AGRICULTURAL AND MECHANICAL COLLEGE OF TEXAS‘ T. O. WALTON, President K’ .-1 ,. n, J <9;-T:L.¢,.a {fig STATION STAFFT ADMINISTRATION: A CoNNER. M. S., Director R. E. KARPER, M. S., Vice-Director J. M. SCHAEDEL, Secretary M. P. HoLLEMAN, JR., Chief Clerk J. K. FRANcKLow. Assistant Chief Clerk CHESTER HIGGS, Executive Assistant C. . NEBLETPE, Technical Assistant CHEMISTRY: " G. S. FRAPs, Ph. D., Chief; State Chemist S. E. AsBURY, M. S., Assistant Chemist E. C. CARLYLE, B. S., Chemist WALDO H WALKER, Assistant Chemist VELMA GRAHAM, Assistant Chemist O. S. OSGOOD, M. S., Assistant Chemist T. L. OGIER, B S , Assistant Chemist J. G. EvANs, Assistant Chemist - ATRAN J STERGES, B. S., Assistant Chemist G. S. CRENSHAW, A. B., Assistant Chemist JEANNE M. FuEGAs. Assistant Chemist HANs PLATENIUS, M. Sc.. Assistant Chemist HORTICULTURE: HAMILTON P TRAuE, Ph. D , Chief H. NEss, M. S., Berry Breeder RANGE ANIMAL HUSBANDRY: J. JoNEs, A M., Chief; Sheep and Goat Investigations J. L. LUSH, Ph D., Animal Husbandman; Breeding Investigations STANLEY P DAVIS, Wool Grader ENTOMOLOGY: F. L. THOMAS, Ph. D., Chief; State Entomologist H. J. REINEARD, B. S., Entomologist R. K. FLETcnER, M. A., Entomologist W. L. OWEN, JR., M. S., Entomologist FRANK M. HULL, M. S., Entomologist J. C. GAiNEs. JR., M. S., Entomologist C. J. TODD, B S., Entomologist F. F. BIBEy, B. S., Entomologist S. E. McGREcoR, JR., Acting Chief Foulbrood Inspector * i 0110 MAcKENsEN, Foulbrood Inspector AGRONOMY: ' E. B. REvNoLDs. M. S., Chief R. E. KARPER. M. S., Agronomist; Grain Sor- hum Research P. IVIANGELSDORF, Sc. D., Agronomist; in charge of Corn and Small Grain Investi- ations D. . KrLLoucn, M. S., Agronomist; Cotton Breedin H. E REA, S., Agronomist; Cotton Root Rot Investigations W. E. FLINT, B. S., Agronomist PUBLICATIONS: A. D. JAcKsoN, Chief SUBSTATIONS N N o. 1, Beeville, Bee County: R. A. HALL, B S.. Superintendent o. 2, Troup, Smith County: P. R. JOHNSON, B. S., Act. Superintendent No. 3, Angleton, Brazoria County: R. H STANsEL, M. S., Superintendent No. 4, Beaumont, Jetferson County: R. H. WYcnE, B. S., Superintendent No. 5, Temple, Bell County: HENRY DUNLAVY, M. S., Superintendent B. F. DANA, M. S., Plant Pathologist H. E. REA, B S., Agronomist; Cotton Root Rot Investigations SiuoN E. WoLFF, M. S., Botanist; Cotton Root Rot Investigations No. 6, Denton, Denton County: P. B. DUNKLE, B. S., Superintendent No. 7, S" ur, Dickens County: R. E. icKsoN, B. S., Superintendent W. E. FLINT, B. S., Agronomist No. 8, Lubbock, Lubbock County: D. L. JoNEs, Superintendent FRANK GAINEs, Irrigationist and Forest Nurseryman No. 9, Balmorhea, Reeves County: J. J. BAYLEs, B. S., Superintendent Teachers in the School of Agriculture Carrying Cooperative Projects on the Station: . ADRiANcE, M. S., Associate Professor of Horticulture 4W6 W VPV. BILSING, Ph. D., Professor of Entomology "F! “FLU TA: of November 1, 1928. I "J. N. TATE, B. S., Assistant; _**O. G. BABCOCK, B. S . LEE, Ph. D., Professor of Marketing and Finance SCOATES, A. E., Professor of Agricultural Engineering _ P. Surrn, M. S., Associate Professor of Agricultural Engineering . H. WILLIAMS, Ph. D., Professor of Animal Husbandry . K. MAcKEv, M. S., Associate Professor of Animal Husbandry . S. MocFoRD, M. S., Associate Professor of Agronomy *Dean, School of Veterinary Medicine. "In cooperation with U. S. Department of Agriculture. '*"In cooperation with the School of Agriculture. VETERINARY SCIENCE: *M FRANCIS, D. V. M., Chief H. SCHMIDT, D. V. M., Veterinarian F. E . CARROLL, D. V. M., Veterinarian PLANT PATHOLOGY AND PHYSIOLOG J J. TAUBENHAUS, Ph. D., ie 7i W. N. EzEKIEL, Ph. D., Plant Pathologist w Laboratory Technician '* W. J. BACH, M. S., Plant Pathologist _ J. PAUL LUsK, S. M., Plant Pathologist B. F. DANA, M. S., Plant Pathologist FARM AND RANCH ECONOMICS: L. P. GABBARD, M. S.. Chie _' W. E. PAuLsoN, Ph. D., Marketing Rese -' Specialist y BoNNEN, M. S., Farm Management, - Research Specialist " L CORY, M. S., Grazing Research Bot - J. F. CRisw ELL, B. S., Assistant; Farm Recoi‘ and Accounts - '" Ranch Reco f‘ and Accounts RURAL HOME RESEARCH: _ JEssiE WHITACRE, Ph. D., Chief _ a MAmE GRIMES, M. S., Textile and Cloth - \ _ Specialist . i EMIlA E. SuuNER, M. S., Nutrition Special .~ SOIL SURVEY: * **W. T. CARTER, B. S., Chie E. H. TEMPLIN, B. S., Soi Surveyor T. C. RErrcR, B. S., Soil Surveyor L. G. RAcsDALE, B. S., Soil Surveyor BOTANY: _ _ H. NEss, M. S., Chief SIMON E. WOLFF, M. S., Botanist SWINE HUSBANDRY: FRED HALE, M. S., Chief DAIRY HUSBANDRY: I O C. COPELAND, B. S., Dairy Husbandman POULTRY HUSBANDRYL '> R. M. SHERWOOD, M. S., Chie ***AGRICULTURAL ENGINEERING: MAIN STATION FARM: G. . McNEss, Superintendent APICULTURE San Antonio): _H. B. PARKs, . S., Chief A. H. ALEx, B. S., Queen Breeder FEED CONTROL SERVICE: F. D. FULLER, M. S., Chief . D. PEARcE, Secretary . HH RoGERs, Feed Inspector . L. o . W000, Feed Inspector KIRKLAND, B. S., Feed Inspector . . D. NORTHCUTI‘, JR. B. S., Feed Inspector SIDNEY D. REvNoLDs, R., Feed Inspector . P. A. MooRE, Feed Inspector No. l0, Feeding and Breeding Station, near Colle e Station, Brazos County: i . R. M. KERwooD, M. S., Animal Husbandg man in Charge of Farm_ i L. J. McCALL, Farm Superintendent No. l1, Nacogdoches, Nacogdoches County: H. F. MoRRis, M. S., Superintendent "No. 12, Chillicothe, Hardeman County: J. R. UINBY, B. S., Superintendent _ * "J. C. TEPHENS, M. A., Junior Agronomist '_. No. l4, Sonora, Sutton-Edwards Counties: i W. H. DAuERQN, B. S., Superintendent E. A. TUNNICLIFF, D. V. M., M. S., Veterinarian ‘_ V. L. CoRY, M. S., Grazing Research Botanid ~‘ Collaborating - Entomologist O. L. CARPENTER, Shepherd No. 15, Weslaco, Hidalgo County: W. H. FRIEND, B. S., Superintendent _ SHERMAN W. CLARK, B. S. Entomologist W. J. BACH, M. S., Plant Pathologist No. l6, Iowa Park, Wichita County: E. J. W1LsoN. B. S., Superintendent _ J. PAUL LUsK S. M., Plant Pathologist SYNOPSIS Root rot of cotton, caused by the fungus PHYMATOTRI- CHUM OMNIVORUM, is the most destructive disease of cotton in Texas. It is especially serious in the “black lands,” where the heavy soils usually contain much lime. The present study was planned to determine whether the distribution of the disease in Texas is actually correlated with dilferences in the acidity or alkalinity of the soil. Laboratory studies of the growth of the fungus on culture media showed that it grew best at about the neutral point, pH 7 .0, and that it would not grow so well in more acid or in more alkaline media. Cotton fields in 16 counties of Texas were examined, and the acidity or alkalinity of the soil studied in relation to the pres- ence of cotton root rot and also of Fusarium wilt. Root rot was found in acid soils (pH 5.5—6.4) as well as in neutral (pH 6.5—7.4) and alkaline soils (pH 7.5—-9.0). However, in‘ the alkaline and neutral soils the percentage of fields in which the disease was present was twice that in the acid soils, and root rot was also much more destructive in these fields than when it was found in acid soils. Fusarium wilt, on the con- trary, was much more common on the acid soils. Hence it is probable that the differences in the distribution of these two important cotton diseases can be explained as due in part to differences in soil acidity. CONTENTS PAGE l: Synopsis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .- . 3' Historical . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 Growth of Phymatotrichum Omnivorum as Afiected by the Hydro- I gen Ion Concentration of Artificial Media . . . . . . . . . . . . . . . . . . .. 6 Root Rot and Fusarium Wilt as Afiected by the Soil Reaction. . . . . 8 Hydrogen Ion Concentration of the Soil and the Presence of 1: Root Rot and Wilt . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 9'; Hydrogen Ion Concentration and the Severity of Root Rot. . . . 11 Basicity of the Soil and the Presence of Root Rot and Fusarium Wilt . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13 Soil Reaction and the Distribution of Root Rot in Individual y» Fields . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 14 Reaction at Different Soil Depths, and Root Rot . . . . . . . . . . .. 15' i; Discussion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 16 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17 Literature Cited . . . . . . . . . . ._ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18 ' ,...J..itZ(;i.l3 or .. BULLETIN NO. 389 NOVEMBER, 1928 RELATION OF COTTON ROOT ROT AND FUSARIUM WILT TO THE ACIDITY AND ALKALINITY OF THE SOIL J. J. TAUBENHAUS, WALTER N. EZEKIEL, AND D. T. KILLOUGH* The relation of acidity and alkalinity of the soil to the growth of plant pathogens and to the destructiveness of plant diseases induced by them has been extensively investigated during recent years. With certain diseases, such as potato scab, this relation has ofiered means of practical control in the field. Two distinct aspects are included in such studies: first, the influence of the acidity of the soil and of arti- ficial culture media on the growth of the pathogen; and second, the pos- sibility of utilizing such information for practical control measures under field conditions. _ l The intensity of the acidity or alkalinity of the soil as well as of solutions is measured chemically by determining the hydrogen ion con- centration, which is expressed in units known as pH values. Neutrality is represented by pH '7 .0; the acidity becomes more intense as pH values become lower than 7.0 g and the alkalinity becomes more intense as pH values become higher than 7.0. A pH of 5.0 is ten times as acid as one of 6.0; similarly pH 4.0 is ten times as acid as pH 5.0. The present work has-been chiefly to determine the relation of the hydrogen ion concentration to the growth of Phymatotricltum omni- vorum (Shear) Duggar, the fungus which causes root rot of cotton and many other plants. Studies were made under laboratory condi- tions to determine the pH range of the organism in pure culture. A field survey was then conducted in which cotton fields in different parts of Texas were examined and soil samples collected. The pH and basicity of these samples were determined and studied in relation to the occurrence of root rot and also of Fusarium wilt in the fields. Experiments are now under way to find out whether the root rot disease may be controlled by changing the acidity or alkalinity of the soil to certain degrees harmful to the causal organism but without effect on the host.‘ The results of this work will appear in later pub- lications. . HISTORICAL Only a few of the many studies relating plant diseases with the hydrogen ion concentration of substrata need be mentioned. Gillespie and Hurst ('7) and Martin (9) found a definite relation between the ‘The writers Wish to acknowledge their indebtedness to Dr. G. S. Fraps for his advice and criticism during the progress of this work and his supervision v ,of the chemical phases of it; to Mr. E. C. Carlyle for making the pH and basicity determinations of the soil samples; and to Mr. W. T. Carter and Dr. L. J. Pessin for assistance in the collection of some soil samples. 6 BULLETIN NO. 389, TEXAS AGRICULTURAL EXPERIMENT STATION hydrogen ion concentration of the soil and the prevalence of po _ scab in the field. Potato scab was seldom found on acid soils with‘. pH of 5.2 or less, whereas it was common on less acid soils. As a i" sult of these studies, the New Jersey Agricultural Experiment Stati is now recommending for New Jersey soils the application of eulph’ for the control of potato scab. In working with tobacco blight q terium solanacearum) Arrhenius (2) found that the causal organi is serious only in acid soils, and is seldom of any consequence in neu or in alkaline soils. Similarly, the work of Johnson and Hartman (87 and of Anderson et al. (1) has shown that black root rot of tobacco a unimportant in an acid soil of pH 5.6, but increases in seriousness wi corresponding increases of soil alkalinity. Chupp (3) has shown I-'_ with club root of cabbage, the disease is most virulent in soil with ' . pH value of 6.0, while infection practically ceases at a pH of 7.2 to 7. Progressive cabbage growers have for many years controlled club if p by the application of lime to the soil. Scott (11) found that Fusariu - Zycopersici, the organism that causes tomato wilt, grew best in cul I f,- media of pH 4.5 to 5.5, and suggested that soil of appropriate alkalini might aid in controlling the disease. I There appears to be no information in the literature on the relatio‘ of cotton root rot to acidity of the soil or of culture media. With r gard to cotton wilt, caused by Fusarium vasinfectum Atk., more is kno i‘ Neal (10) found recently that this fungus grew better in culture me at pH 3.0 to 5.5 than in more nearly neutral or alkaline media, with thy maximum growth in a strongly acid solution at pH 3.5. Fahmy however, working with the Fusarium wilt in Egypt, found it abund -j_i in experimental plots in which the soil was slightly alkaline, between. 7.5 and 8.5, and mentions also that the disease was more destructive heavy soil than in the lighter, sandy soils. ' GROWTH OF PHYMATOTRICHUM OMNIVORUM AS AFFECTEDBY- THE HYDROGEN ION CONCENTRATION OF ARTIFICIAL MEDIA l Methods ' A pure culture of Phymatotrichum ominivorum was isolated from a; cotton plant, recently wilted by root rot, from a field of Houston clay soil at Substation No. 5 near Temple. The organism was grown in 200 c.c. Erlenmeyer flasks, in oatmeali broth made of 10 grams of ordinary oatmeal and one liter of distilled‘ water autoclaved 30 minutes at 10 pounds pressure, strained, and ster- ilized for 20 minutes at 15 pounds pressure. Amounts of acid or alkali previously determined as necessary to provide media of the desired pH were placed in 30 c.c. test tubes and sterilized separately for 15 minutes > at 15 pounds pressure. Under aseptic conditions in the culture room, “ the contents of these test tubes were poured into Erlenmeyer flasks each of which contained 100 c.c. of oatmeal broth also previously autoclaved. f, With a sterilized pipette, 20 c.c. samples were then withdrawn from each j RELATION OF COTTON ROOT ROT TO ACIDITY AND ALKALINITY OF SOIL 7 flask and stored in sterile tubes for hydrogen ion determination. The following day each flask was inoculated with small pieces of 10-day-old iiculture of Phymatotrichum omnivorum from oatmeal agar. Three flasks awere used for each strength oi": acid or alkali. h. 7 The test tubes containing the treated media t0 be used for pH deter- fmination were allowed to stand for 24 hours to permit the liquid to ibecome as clear as possible. Determinations of pH values were then jmade colorimetrically by the Gillespie (6) drop-ratio method. Growth Growth. Good Moderate Fair Poor Tr ac. e l l I I None _ 4.0 5.0 6.0- 7.0 8.0 9.0 pH i Figure 1.—_Re1ation of the growth of Phymatoirichum omnivorum in artificial culture to e hydrogen ion concentration of the nutrient solution. ‘in the flasks was recorded after 6 weeks, and 20 c.c. of the clear portion f the media from each flask were then withdrawn by a sterile pipette 1 a final pH determination. Changes from the original acidity were iind to be negligible. a Results ries, sulphuric acid in another, and acetic acid in a third. Sodium ydroxide was used for the single series with alkaline solutions. Growth q Acid media were secured by the addition of hydrochloric acid in one 8 BULLETIN NO. 389, TEXAS AGRICULTURAL EXPERIMENT STATION was almost precisely the same at the same pH readings with the three acids, and they will accordingly be considered together. The combined results, which are thus also nearly the same as those for each of the series, are shown graphically in Fig. 1. Phymartotriclzzam ommlvorum made its best growth at neutrality, pH i 7.0. Growth was still nearly as good at pH 7.7, at 6.5, and at 6.0. At 5.9 and at 8.0 growth was definitely checked as compared to that in the neutral medium; and at 4.1 on the acid side of neutrality and 8.9 on the alkaline side growth was completely inhibited. Since three different acids were employed and the same results se- cured, it is apparent that the prevention of growth of the root rot fungus at 4.1 was due to the hydrogen ion concentration rather than to the specific toxic effect of the other ions. In the alkaline range growth may have been prevented by specific toxic action by the sodium hydroxide as well as by the increasing alkalinity. ROOT ROT AND FUSARIUM WILT AS AFFECTED BY THE SOIL REACTION The work above had shown the relation of the growth of Phyma- totrichum omniivorum in artificial culture to the pH of the solutions used as substrata. It was deemed desirable to determine further whether the presence or absence of root rot under actual field conditions might be explained by accompanying difierences in the pH of the soil. Accord- ingly, a large number of fields were examined during May to October, 1925, and August to October, 1926, in 16 counties of the State. The survey included regions in which the disease was widespread, others in which it occurred in less abundance, and also some soil_types in which root rot had never been found. Cotton wilt (caused by Fmarium vasirv- i fectum Atk.) occurs in some of the fields included and the occurrence of this disease has also been studied with relation to the soil. One hundred and seventy-six composite soil samples were collected. The method used was to take the upper 3 inches of soil from a dozen points throughout each field, mix thoroughly together, and select a rep- resentative portion of this composite as the sample for analysis. Usually only one sample was used for each field. In a few cases separate sam- ples were obtained from the part of a field in which root rot was present and from the part in which it was absent. The pH and basicity determinations (Fraps, 5, p. 12) of the soil were made by the Division of Chemistry of the Texas Agricultural Experi- ment Station. Determinations of pH were made colorimetrically. The basicity was determined by treating 10 gm. soil samples with 100 c.c. of 0.2 N nitric acid, filtering, and titrating with 0.1 N sodium hydroxide. The results are expressed as the percentage of basicity of the soils as calcium carbonate. It is to be noted that by the method of determina- tion values above 10 per cent are not obtained, and this value in the tables therefore includes more basic soils. a 4.“... 4.&IL" ' .2 we RELATION 0F COTTON RooT ROT To ACIDITY AND ALKALINITY OF SOIL 9 Hydrogen Ion Concentration 0f the Soil and the Presence 0f Root Rot and Wilt The data for the hydrogen ion concentration as related to the presence of root rot and Wilt are given graphically in Figs. 2 and 3. In each case, the total number of fields in which the disease occurs is shown by the lower, black region of the chart. Even in these charts, without sum- mation or averaging, a definite relation of the occurrence of root rot and Number o fields 15 — 1O O pH 5.0 5.5 6.0 6.5 7.0 7.5 8.0 8.5 9.0 pH (Acid soils) (Neutral soils) (Alkaline soils) Figure 2.—Hydrogen ion concentration of the 176 soil samples, and the occurrence of root rot. The total number of samples with a given pH is shown by the upper line, and the number . from fields with root rot by the lower, black portion. Number of fields 15+ 1O o I H J pH 5.0 5.5 6.0 6.5 7.0 7.5 8.0 8.5 9.0 pH (Acid soils) (Neutral soils) (Alkaline soils) Figure _3.—Hydrogen ion concentration of the 176 soil samples, and the occurrence of Fu- sarium wilt. The total number o_f samples with a given pH is shown by the upper line, and the number from fields with Fusarium wilt by the lower, black portion. 10 BULLETIN NO. 389, TEXAS AGRICULTURAL EXPERIMENT STATION Fusarium wilt to the pH of the soil is apparent. noted that most of the root rot cases seem to fall to the righthor to the alkaline, side of neutrality, pH 7.0. With wilt, on the other hand i (Fig. 3), the preponderance of cases‘ is to the left, in the more acid soils. This relation is more evident when the results are combined as in Table 1. Going down the columns of this table, that is, from acid to alkaline soils, the percentage of fields in which root rot was found stead- ily increases, while the percentage of fields in which Fusarium wilt oc- curred becomes steadily less. These percentages are shown graphically 1n Fig. 4. Table 1.—Re1ation of the hydrogen ion concentration of the soil of cotton fields to the presence o root rot and Fusarium wilt. Number of fields with Percentage of fields with Number pH of fields Fusarium Fusarium Root rot wilt Root rot wilt 5 . 5-—5 .9 . . . . . . . . . . . . . 19 12 32 63 6 .0—6 .4 . . . . . . . . . . . . . 28 10 14 36 50 6 . 5—6 . 9 . . . . . . . . . . . . . 40 21 7 53 18 7 .0-—-7 .4 . . . . . . . . . . . . . 48 32 ' 4 67 8 7 .5—7 .9 . . . . . . . . . . . . . 38 26 1 68 3 8 .0--8 .4 . . . . . . . . . . . . . 2 2 0 *100 *0 8 .5——8 .9 . . . . . . . . . . . . . 1 1 0 T100 1'0 *Note that this percentage is based on only two fields. TNote that this percentage is based on only one field. Table 2.——Summary of the relation of the hydrogen ion concentration of the soil of cotton elds to the presence of root rot and Fusarium wilt. Soil neutral Soil acid or nearly Soil alkaline Total (pH 5.5-6.4) neutral (pH 7.5-9.0) (pH 6.5-7.4) All fields in the survey . . . . . . . . . . . . . . . . . 176 47 88 41 Number of fields with: oot rot . . . . . . . . . . . . . . . . . . . . . . . . . . 98 16 53 29 Fusarium wilt . . . . . . . . . . . . . . . . . . . . . 38 26 11 1 Percentage of fields with: Root rot . . . . . . . . . . . . . . . . . . . . . . . . . . 56 34 60 71 Fusarium wilt . . . . . . . . . . . . . . . . . . . . . 22 55 13 2 Root rot was found in the entire pH range of soils included in the survey. It occurred in one of the most acid fields (pH 5.5) and in the most alkaline one (pH 8.6). While the percentage of root rot in the neutral and alkaline soils (note Table 2) was twice that in the acid soils, yet root rot was found in more than a third of the fields with the more acid soils. There was not a sufiiciently wide range of pH dif- ferences in the soils surveyed to establish extreme limits for the occur- rence of root rot. Fusarium wilt occurred over a more limited part of the pH range of soils studied. N0 wilt was found in soils more alkaline than pH 7.7, and there were only four cases beyond 7.0. For the soils considered, In Fig. 2, it Wlll be RELATION OF COTTON ROOT ROT TO ACIDITY AND ALKALINITY OF SOIL 11 there i5 evidently a maximum pH limit between pH 7.5 and 8.0. The optimum and minimum for Wilt are probably below the range included in this mrvey. ‘Iydrogen Ion Concentration and the Severity of Root Rot‘ The results were tabulated above with regard only to the presence or absence of the disease in a given field and without regard to its severity there. When we consider the prevalence of root rot in the individual fields, a slightly different relation is evident. The one case in which root rot was found in a soil with pH of 5.5 (see Fig. 2) was in a field with only a trace of the disease present. There were five cases of root rot at pH 5.9. Three of these were recorded as only a trace. All five of the fields at 6.0 had only a trace of root rot. All of the five cases from 6.1 to 6.3 were recorded as a trace. It is only with a pH of 6.5 that the disease appears to have been found in destructive abundance. Though in one field of this pH only a trace of infection was found, and in another about 1 per cent was estimated, there was in a third field an estimated infection of 25 per cent. ' Thus while there was root rot in a total of 16 fields with soils more acid than pH 6.5, in 14 of these fields only a trace of the disease (usually less than 1 per cent) was present. Definite percentages of infection were not recorded for all of the fields in regions in which root rot is wide- spread, so that a complete summary of its abundance in the fields sur- veyed is not possible. However, of 10 fields with root rot, selected at random from those between pH 7.1 and 7.9, only two were recorded as “trace” or less than 1 per cent, five were between 10 and 20 per cent, i and the other three from 20 to 70 per cent. More precise comparison is to be desired here, yet it appears quite safe to conclude from the data at hand that root rot is not only of more frequent occurrence on soils of pH 7.0 to 8.0 than of pH 5.5 to 6.5, but also that it is more often of destructive abundance when it is present on neutral or alkaline soils than when it is present on acid soils. This conclusion agrees with years of field observations by the senior author and others who have been acquainted with the effects of the root rot disease in the alkaline “black lands” of Texas and in the more acid sandy soils. Basicity of the Soil and the Presence of Root Rot and Fusarium. Wilt The discussion above has been concerned with the relation of the de- gree of acidity or alkalinity of the soil to the distribution of the two diseases. The percentage of basicity is, on the other hand, not an in- dicator of the soil acidity but instead a measure of those basic constit- uents of the soil which are potential agents in affecting the present and future reaction of the soil. As such, one would expect the relation of the diseases to this criterion to be roughly similar to the relation to pH. This was found to be the case. Summaries of the data as related to basicity of the soil are given in Tables 3 and 4. The proportion of fields affected by root rot increases 12 BULLETIN NO. 389, TEXAS AGRICULTURAL EXPERIMENT STATICN with the basicity while Fusarium Wilt was found only in the less basic soil. As with the pH, the range for wilt is more definitely limited, at least for the fields of this survey, than was the range for root r01. Root 1 rot occurred throughout the range of soil basicities, while no "wilt was found in a soil more basic than 2.2 per cent, and only two casesiin more ‘g basic soils than 0.8 per cent. ‘ Percentages of fields in which root rot and Fusarium wilt occurred i’ are shown graphically in Fig. 5. Note that the sudden fall in the root L Percentage of fields affected 100 F" . Root. Rot. \ 20— I l V o; 5.0 6.0 1.0 8.0 9.0 p H Figure 4.—Occurrence of root rot and Fusarium wilt with regard to the hydrogen ion con- centration of the soil. (Data from Table 1.) 0 RELATION OF COTTON ROOT ROT TO ACIDITY AND ALKALINITY OF SOIL l3 rot curve at 8 per cent basicity is of little significance, since there was only a single field in this group and the “O” root rot for the group applies to that one field. Soil Reaction and the Distribution 0f Root Rot in» Individual Fields Root rot is often found only in particular areas in fields that are apparently of even soil type. Basicity and pH determinations fora few such fields are given in Table 5. It will be noted that the difierences in soil acidity between parts of the fields in which root rot was found Percenba e of fields affected I00 " 80 60 4O 2o f-Iusarium Wilt .0 2 4 8 8 l0 Percentage of soil basicity Figure 5.—Occurrence of root rot and Fusarium wilt with _regar_d to the basicity of_ the soil. Note that the drop 1n the root rot curve at 8 per cent basicity 1s not considered mgmficant sring? itavyas based on only one field (in which the SO11 was of that basicity). (Data from a e . 14 BULLETIN NO. 389, TEXAS AGRICULTURAL EXPERIMENT STATION Table 3.——Relation of the basicity of soils in cotton fields to the presence of root rot and Fusarium wilt. , » _ Number of fields with Percentage of fields with a Percentage of SO1l Number _ basicity of fields Fusarium Fusarium ; Root rot w' t Root rot wilt l 0.0— 0.4 . . . . . . . . . . . . .. 82 33 30 40 37 0.5——- 1 .4 . . . . . . . . . . . . . . 45 26 6 58 13 1 .5—— 2 .4 . . . . . . . . . . . . . . 12 " 9 2 75 17 2 .5—— 3 .4 . . . . . . . . . . . . . . 3 2 . 0 67 3 .5—— 4 .4 . . . . . . . . . . . . . . 6 4 0 67 0 4.5—- 5 .4 . . . . . . . . . . . . . . 3 2 O 67 0 5 .5— 6 .4 . . . . . . . . . . . . . . 1 1 0 *100 6 .5—- 7 .4 . . . . . . . . . . . . . . 1 1 0 *100 *0 7 .5—— 8 .4 . . . . . . . . . . . . . . 1 0 0 *0 *0 8.5—— 9.4 . . . . . . . . . . . . . . 2 2 0 T100 T0 9 .5—-10 .0 . . . . . . . . . . . . . . 20 18 0 90 *Note that this percentage is based on only one field. TNote that this percentage is based on only two fields. Table 4.-—Summary of the relation of the basicity of soils_in cotton fields to the presence of root rot and Fusarium wilt. Soil basicity Soil basicity Soil basicity Total (0—0.9) (1 .0—2.5) (2.5—10.0) All fields in the survey . . . . . . . . . . . . . . . 176 114 25 37 Number of fields with: Root rot . . . . . . . . . . . . . . . . . . . . . . . . 98 48 20 30 Fusarium ‘wilt . . . . . . . . . . . . . . . . . . . 38 36 2 0 Percentage of fields with: Root rot . . . . . . . . . . . . . . . . . . . . . . . . 56 42 80 81 Fusarium wilt . . . . . . . . . . . . . . . . . . . 22 32 8 0 and the parts in which it was absent are generally insignificant. Only in the second field, where a pH of 6.5 was found in the part with root rot as compared t0 6.9 for the other part, is the difference appreciably greater than the probable experimental error. In three of the five fields, the parts free from root rot apparently had the slightly more acid soils, while in the other two fields the reverse was the case. ..§ Further evidence on this point was obtained by a survey of the cotton fields on a single farm near College Station. The soil here was un- usually varied and a number of difierent types occurred even in a small field. Comparing different types of soil in a given field, it was noted that root rot did not occur in the more acid types, Susquehanna gravelly fine sandy loam and Susquehanna fine sandy loam, in which the pH of the surface soil was.6.5-'7.0; while it was found in the six other soil types that were at least slightly alkaline. To this extent, these results agree with comparisons between difierent farms and different regions. Distribution of the disease in a given soil type was, however, certainly not determined by the soil acidity alone. For example, in a field of Norfolk gravelly fine sand there was 80 per cent of root rot in part of the field where the surface soil was found to have a pH of '7 .3, and no root rot where the pH was 7.4. In some Kirvin fine sandy loam there RELATION OF COTTON ROOT ROT TO ACIDITY AND ALKALINITY OF SOIL 15 was 98 per cent loss in one part of the field, 1 per cent loss in another, and no loss in a third place; while the soil was of the same pH, 7.1, in the three places. Table 5.—Differences in soil acidity _within fields as related to the presence of root rot. (Five fields 1n four different counties.) pH of Soil Percentage of Soil Basicity Field In Areas Where In Areas Where In Areas Where In Areas Where Root Rot was Root Rot was Root Rot was Root Rot was Present Absent Present Absent A . . . . . . . . . . . . . . . . . . . . 7.7 7.6 0.8 0.6 B . . . . . . . . . . . . . . . . . . . . 6 . 5 6 .9 0 .2 0 . 1 C . . . . . . . . . . . . . . . . . . . . 7.3 7 .4 4.5 4.6 D . . . . . . . . . . . . . . . . . . . 7.5 7.6 3.3 3.8 E . . . . . . . . . . . . . . . . . . . 7 . 6 7 .4 1 . 9 3 .0 This is hardly surprising, for while soil acidity is a factor which can prevent the occurrence of root rot it is by no means the only one. Root rot may be checked to a certain extent by the acidity of surface soils more acid than about pH 6.5-7.0. But there are many other factors which may also prevent the occurrence or hinder the spread of the fungus even in soil of a favorable pH. We may mention here such factors as the effect of the prevalence of weed carriers on the success of hibernation, and the effect of soil moisture (12) on the spread of infec- tion. With different soil types the occurrence of root rot is apparently affected to a great enough extent by differences in the soil reaction for the result to be evident even though these local factors are also active. With the comparatively slight differences in soil reaction between parts of a field of even soil type, on the other hand, the effect of the acidity differences if present seems to be completely obscured. Reaction at Different Soil Depths, and Root Rot The survey from which most of the results above were secured in- cluded samples of the surface soil only. Are differences in acidity of lower depths in the soil also of importance in relation to the distribu- tion of root rot? An idea of the difierences in subsurface acidity, in soils with the same surface acidity, can be obtained from the following examples. Atten- tion was called above to a field of Kirvin fine sandy loam near College ' Station. Root rot was very destructive in part of this field, where the pH of the surface soil was 7.1, and practically absent in another part where the H was just the same. In the former case, however, the yellow sanffrom eight to twelve inches deep had a pH of 7.3 and the red clay below this of 7.1; while where root rot did not occur, the yellow sand at six to nine inches deep had a pH of 6.7 and the red clay sub- soil, 6.4. Compare, however, the distribution of root rot in the Norfolk gravelly fine sand. Root rot was abundant here in soil with a pH of 7.3, and 16 BULLETIN NO. 389, TEXAS AGRICULTURAL EXPERIMENT STATION absent at pH 7.4. And the yellow sand subsoils, beginning six inches below the surface, gave pH readings of 7.3 in the first place, and 7.5 in the second. While in the Kirvin loam the subsurface acidity might have been the deciding factor in the distribution of root rot, this could scarcely have been true in the Norfolk soil. Further study is planned to determine the effect of variations in sub- surface acidity on the occurrence of root rot. DISCUSSION It has been shown above that cotton root rot was more abundant and also more destructive in fields with neutral or alkaline soils than in fields with acid soils. Fusarium wilt, on the contrary, was found to be restricted to the more acid soils. With both diseases, these results secured from the field survey are in at least general accord with laboratory studies of the fungi causing the diseases. Phymatotrichum omnivorum was shown in the present paper to grow best in culture media adjusted to pH 7.0, or neutrality, and to be slightly inhibited in growth in only slightly acid media. In very acid media growth was completely inhibited. In the cultures growth was also less with slight alkalinity of the solution and ceased at a pH of 8.9. This is not in full agreement with the field results, since in the field root rot appeared to be more destructive in the more alkaline soils. The cause of this disagreement is perhaps the difference in the materials producing the alkalinity in the two cases, or the excretion by the roots of host plants of substances which produce pH conditions favorable for root rot even in soil that would otherwise be too alkaline. It should be noted that no fields were studied with soils as alkaline as pH 8.9, the point at which growth was prevented in artificial media. There is better agreement of the distribution of wilt in soils of various acidities with the laboratory results of Neal (10) with Fusarium easin- fectum. In culture, this fungus grew much better at pH 5.5 than at 6.0 or 6.5, with further diminution of growth in alkaline media. Similarly, almost all the cases of wilt in the field were in soils that were at least slightly acid. The distribution of wilt appears to be more sharply lim- ited on the alkaline side in the field than was the growth of the fungus in culture media. Soil Acidity and the. Distribution of Root Rot and Fusarium Wilt These results are of interest in connection with the present distribu- tion of the two diseases studied. Root rot has been widespread for years in the “black lands” and in other heavy soils of Texas but usually not in lighter soils. It is probable that this limitation of distribution was at least partly the result, either directly or indirectly, of the dif- ferences in the soil reaction. As will be discussed in a forthcoming bulletin on the distribution of root rot, root rot occurs also in Oklahoma, New Mexico, Arizona, and < an nuns-Ls.» RELATION OF COTTON ROOT ROT TO ACIDITY AND ALKALINITY OF SOIL 17 California, but has not been found in the other Southern States of the Cotton Belt, though climatic conditions are apparently favorable in many of them. The absence of root rot in these States may perhaps be explained by the acidity of the soils in these regions though absence of original infection may be the important factor. ' Fusarium wilt of cotton, in common with the Fusarium Wilts of many other plants, has been considered more destructive on sandy soils than on heavier soils. The present work furnishes an explanation of this observation in the fact that the lighter soils are generally acid and hence more suited to the disease. It should be mentioned that this relation is evidently quite at vari- ance with that of Fusarium wilt of cotton in Egypt, as studied by Fahmy (4, p. 55). Fahmy considers the Fusarium attacking cotton in Egypt to be distinct from the one common in this country, a conclusion which agrees with the fact that he finds wilt serious in plots with alka- line soil, pH 7.5 to 8.5, and occurring in the heavier soils. From this it would seem especially important to keep this Egyptian strain of the wilt; organism from ever being imported into the American cotton regions, since it might prove destructive in soils in which the American strain. has been of little importance. Soil Acidity and the Control of Root Rot Whether these results can be used as the basis for new methods of control in the field must be determined by further experiments. In this connection, it must be remembered that control of root rot by making the soil more acid, or control of Wilt by making the soil alkaline, may be a slow process. The factor of soil reaction probably influences the presence or absence of these two organisms in the soil; but it may do this, particularly in soils near the limiting acidities, not so much by immediate destruction of the organisms in soils of unfavorable acidity as by gradual decrease each year in the proportions of infective mate- rials that hibernate and are available in spring to start new spread of the diseases. ~ The fact that the two diseases, root rot and Fusarium wilt, occur respectively in alkaline and acid soils is to be considered in connection with such control measures. In fields in which both diseases occur, the addition of sulphur to make the soil'more acid as an attempt to control root rot might increase losses from wilt, and similarly the addition of lime to produce an alkalinity unfavorable to wilt would doubtless favor" increased loss from root rot. The most desirable soil acidity for such conditions would apparently be at about pH 6.5, considering only the- results of the present survey. SUMMARY A study of Phymatotriclaum omnivorum (Shear) Duggar, the fungus: causing root rot of cotton and many other plants, on artificial media. 18 BULLETIN NO. 389, TEXAS AGRICULTURAL EXPERIMENT STATION showed that its maximum growthwas at pH 7.0, and that its growth was completely inhibited at an acidity of pH 4.1 and at an alkalinity of pH 8.9. Cotton fields in sixteen counties of Texas were examined in a field I survey for cotton root rot and Fusarium wilt. Both the hydrogen ion concentration of the soil and the percentage of soil basicity were deter- mined from soil samples from each field. Root rot was found in 34 per cent of the fields with acid soils (pH 5.5-6.4), in 6O per cent of the fields with nearly neutral soils (pH 6.5- ‘ 7.4), and in 71 per cent of the fields with alkaline soils (pH 7.5-9.0). Moreover, even when root rot did occur in the acid soils it was seldom of much significance, while in the neutral or alkaline soils root rot when present usually caused losses ranging from 10 to 100 per cent. Fusarium wilt, on the other hand, occurred in 55 per cent of the fields with acid soils, in 13 per cent of the fields with nearly neutral soils, and in only 2 per cent of the fields with alkaline soils. Similarly, there was root rot in 42 per cent of the fields with a soil basicity of 0-0.9 per cent, in 80 per cent of fields with a basicity of 1.0-2.5 per cent, and in 81 per cent of fields with a basicity of 2.5-10.0 per cent, while Fusarium wilt was found in 32 per cent of the fields with the low basicity, in only 8 per cent of those of the second group, and in none of the fields with the most basic soils. The distribution of the root rot and Fusarium wilt diseases in the cotton fields of this survey was thus correlated, in general, with the dif- ferences in the reaction of the soil. Root rot was more abundant in the alkaline soils and in the neutral soils than in acid soils, while the Fusarium wilt was more common in the acid soils. It seems probable that the present limitations in the distribution of these diseases in the parts of Texas that were not included in this survey and in the other cotton States may also be associated with such differences in the reaction of the soil. In this connection a potential danger to American cotton is pointed out in the presence in Egypt of a strain of Fusarium wilt which attacks cotton on alkaline soils also. A few cases were studied in which root rot occurred only in particular areas in fields that were apparently of even soil type. It was found that the distribution of root rot in these fields was not associated with dif- ferences in the reaction of the soil. The disease is not necessarily pres- ent wherever soil conditions are favorable. LITERATURE CITED 1. Anderson, P. J ., Osmun, A. V., and Doran, W. L. Soil reaction to black root rot of tobacco. Mass. Agr. Expt. Sta. Bull. 2291118-133. 1926. 2. Arrhenius, O. A factor influencing the growth of tobacco- wilt disease. Meded. Deli. Proefstn. 1921. 3. Chupp, Charles. Club root in relation to soil alkalinity. Phyto- path. 18:301-306. 1928. H‘ 10. 11. 12L RELATION OF COTTON ROOT ROT TO ACIDITY AND ALKALINITY OF SOIL 19 Fahmy, Tewfik. The Fusarium disease of cotton (Wilt) and its control. Ministry of Agr., Egypt. Techn. and Sci. Service Bull. ‘74:1-_106. 1928. _ Fraps, G. S. The soils of Eastland, El Paso, Lubbock and San Saba counties. Texas Agr. Expt. Sta. Bull. 337z7-47. 19'26. Gillespie, L. J. Colorimetric determination of hydrogen ion con- centration Without buffer mixtures, With especial reference to soils. Soil Sci. 9:115-136. 1920. Gillespie, L. J ., and Hurst, L. A. Hydrogen ion concentration- soil type—c0mmon potato scab. Soil Sci. 6z2l9-236. 1918. Johnson, J ., and Hartman, R. E. Influence of soil environment on root rot of tobacco. Journ. Agr. Res. 17:41-86. 1919. Martin, W. H. The relation of sulphur to soil acidity and to the control of potato scab. Soil Sci. 9393-409. 1920. Neal, D. C. Cotton Wilt: a pathological and physiological investi- '" gation. Miss. Agr. Expt. Sta. Techn. Bull. 16 :3-51. 1928. Scott, I. T. The influence of hydrogen ion concentration on the growth of Fuqarium lycopersici and on tomato wilt. Mo. Agr. Expt. Sta. Res. Bull. 64z3-32. 1924. Taubenhaus, J. J ., and Dana, B. F. The influence of moisture and temperature on cotton root rot. Texas Agr. Expt. Sta. Bull. 38613-23. 1928. _. a? >€