Iowa State University Capstones, Theses and Retrospective Theses and Dissertations Dissertations 1958 Effects of antibiotics on control of angular leaf spot of cotton Paul Franklin Street Iowa State College Follow this and additional works at:https://lib.dr.iastate.edu/rtd Part of theBotany Commons Recommended Citation Street, Paul Franklin, "Effects of antibiotics on control of angular leaf spot of cotton " (1958).Retrospective Theses and Dissertations. 1676. https://lib.dr.iastate.edu/rtd/1676 This Dissertation is brought to you for free and open access by the Iowa State University Capstones, Theses and Dissertations at Iowa State University Digital Repository. It has been accepted for inclusion in Retrospective Theses and Dissertations by an authorized administrator of Iowa State University Digital Repository. For more information, please [email protected]. EFFECTS OF ANTIBIOTICS ON CONTROL OF ANGULAR LEAF SPOT OF COTTON by Paul Franklin Street A Dissertation Submitted to the Graduate Faculty in Partial Fulfillment of The Requirements for the Degree of DOCTOR OF PHILOSOPHY Major Subject: Plant Pathology Approved: Signature was redacted for privacy. In Cha e of Major Wo: Signature was redacted for privacy. Head of Major Departmi Signature was redacted for privacy. De n of Graduate College Iowa State College Ames, Iowa 1958 ii TABLE OF CONTENTS Page INTRODUCTION 1 REVIEW OF PERTINENT LITERATURE 4 METHODS AND MATERIALS 6 Field Studies 6 Greenhouse Studies 13 RESULTS 32 Field Studies 32 Greenhouse Studies 33 DISCUSSION 56 SUMMARY AND CONCLUSIONS 59 LITERATURE CITED 61 ACKNOWLEDGMENTS 6.4 APPENDIX: RAW DATA 65 1 INTRODUCTION The disease of cotton known as angular leaf spot and bacterial blight has been recognized as one of the three most important diseases of this valuable crop (Chester, 1950). It was first discovered by Atkinson in 1891 and the causal agent was proven to be Xanthomonas malvacearum (E.F.S.) Dow. by Erwin F. Smith in 1901. The bacteria are seed bourne (Edgerton, 1912a) and infect the cotyledon during germination (Tennyson, 1936), caus­ ing water-soaked lesions which produce an exudate. The bacteria from the exudate are disseminated by wind blown rain (Faulwetter, 1919) to sur­ rounding plants where entrance is gained through stomates (Figure la). Leaf tissues are affected first between the veins and the lesions assume a shape which gives rise to the name "angular leaf spot" (Figure lb). When the bacteria enter petioles or stems dark brown lesions develop which are described as the "black arm" phase (Edgerton, 1912a). Infection of the boll results in depressed water-soaked lesions which develop into the "boll rot" phase (Edgerton, 1912a). Losses due to this disease are difficult to determine sincet he host plants will usually have two and sometimes all three of the disease phases at one time. Disease appraisal methods should include losses from all three forms of the disease( Chester, 1950). Two avenues of approach are available for studies on the control of this disease: (1) Breeding for resistance (Bird, 1954)> and (2) Using chemicals as protectant and eradicants. The present study is concerned with the second approach. Control of wildfire, a bacterial disease of tobacco,w ith foliar Figure la. Bacteria in substomatal spaces of cotton cotyledon (Photograph by Dr. J. E. Sass) » Figure lb. Lesions cm mature cotton leaf typical of angular leaf spot 3 applications of 200 ppm. of the antibiotic, Streptomycin, (Heggested and Clayton, 1954) suggested similar results might be obtained if a group of antibiotics were applied to cotton plants exposed to infection by the angular leaf spot bacterium. Experiments I to IV reported herein are attempts to carry out this suggestion. Control of numerous plant diseases has been achieved with chemicals applied to the seeds prior to planting. Since angular leaf spot of cotton is caused by a seed bourne bacterium, the present study is concerned with attempts (Experiments V and VI) to find chemicals effective on seeds as protectants for increasing stands of seedlings and in seeds as eradicants for decreasing the amount of cotyledonary infection from the bacteria in­ side the seeds. 4 REVIEW OF PERTINENT LITERATURE Bacterial blight of cotton caused by Xanthomonas malvacearum (E.F.S.) Dawson was first reported by Atkinson (1891). Water soaked lesions, typical of bacterial diseases, develop between veins and veinlets of leaves giving rise to the common name, angular leaf spot. That the le­ sions are teeming with bacteria was shown by Atkinson who after unsuccess­ ful attempts to reinoculate the host and produce the disease concluded the condition was a physiological disorder with the bacteria acting as second­ ary parasites (Atkinson, 1892). This conclusion was questioned (Earle, 1899) and proven incorrect (Smith, 1901) when inoculations of leaves and bolls resulted in typical lesions. The causal organism is a short, rod- shaped, non-spore forming, actively motile bacterium capable of producing quantities of slime (Smith, 1901). Invasion of petioles and stems results in the "blackarm" stage of the disease and invasion of the bolls results in the "boll rot" stage (Edgerton, 1912a). Infected bolls are subject to invasion by numerous filamentous fungi (Edgerton, 1912b; Ray, 1942). The bacteria adhere to the lint( Edgerton, 1912a) and enter the seed through the basal cap (Tennyson, 1936). They have been found in the resin canals and the cotyledonary tissue (Archibald, 1927) Infected plants are € the source of inoculum in the field and the bacteria are spread to sur­ rounding plants chiefly by wind blown rain (Faulwetter, 1917, 1919) but can be spread by irrigation water (King and Parker, 1949; Shields, 1957). Insects have little if any effect in dissemination of the angular leaf spot organism (Faulwetter, 1917). When the bacteria reach the host they enter uninjured epidermis of leaves and bolls and produce lesions in 9 to 5 16 days (Edgerton, 1912b). Natural resistance is the only known control (Bird, 1954-) but the disease can be reduced by acid delinking the seeds (Massey, 1927; Ludwig, 1922; Bain, 1939). No reports are known of the use of antibiotics on cotton as a foliage protectant. The use of antibiotics on other plants has shown the absorp­ tion into the leaf (Daines, 1956; Anderson and Nienow, 1947)a nd the dif­ fusion of an antibiotic was demonstrated on pear and apple tissue (Dunegan and Wilson, 1956). The systemic action of streptomycin is probably more important than surface protection in the field (Williams and Lockwood, 1956). Antibiotics, while offering protection against a bacterial disease, may also produce injury to plants. Streptomycin "inserted" in young Elberta peach tree trunks caused chlorotic leaves (Dunegan and Wilson, 1956). Garden vegetables, celery and radish, were susceptible to injury by streptomycin but recovered rapidly (Marlett, 1956). Gall formation was not suppressed when antibiotics were applied to highbush blueberries but severe defoliation and reduction of yield resulted (Zuckerman,1 957). The use of fungicides as a seed protectant is recommended for cotton (Presley, 1954; Shields, 1957). Mycostatin, when used as a postharvest protectant in peach decay tests, gave no data from which conclusions could be drawn but indications were that some reduction had been attained (Dimarco and Davis, 1957a). In a postharvest treatment of strawberries with Mycostatin, the treated berries had only 4 percent moldy fruit while the checks, hydrocooled and dry, had 31 and 37 percent, respectively (Dimarco and Davis, 1957b). 6 METHODS AICS MATERIALS Field Studies Experiment I Field studies conducted during the summers of 1954- through 1957 were performed in Northeast Texas. These studies were conducted in order to determine the effectiveness of antibiotic sprays as a means of control of angular leaf spot of cotton, Xanthomonas malvacearum. The land for the field plots in 1954- was furnished by EastT exas State College on the college farm. The soil was a sandy loam which had been used for several years in the grass adaptations plots. This land had not been fertilized. The plot- was bordered by pasture on three sides with a small grain field on the fourth side. Since no farm machines were available,t he bedding was done by hand with a rake and a hoe. The beds were in rows with thirty-eight inch cen­ ters. The cotton varieties selected were Deltapine,^ because of its toler- 2 ance to the angular leaf spot disease,a nd Rowden, because of its com­ plete susceptibility to angular leaf spot. The fuzzy seeds were planted by hand in a furrow approximately two inches deep. The varieties were planted in alternating rows, the seeds were covered, and thes oil was packed along the top of the bed, a common practice in this area. ^Deltapine seeds furnished by Mr, Dow Porter, Superintendent of the Cotton Experiment Station, Greenville, Texas. Ttowden seeds furnished by the HurleyR owden Custom Ginning Co., Cooper, Texas. 7 The bacterial inoculum, a composite of races 1 and 2,"*" was maintained 2 s cai potato-carrot dextrose agar (PCDA). The organisms grown on PCDA , incubated at 30°G. for 4-8 hours, were streaked on sterile petri plates of the same medium and incubated as above. A suspension of the bacteria was made by flooding the cultures with sterile distilled water. A sterile inoculation needle was used to remove the growth from the surface of the agar and place it in suspension. The growth from one plate of each race was suspended in one-half gallon of sterile distilled water, immediately before inoculation to reduce the possible rupture of the bacterialc ells due to osmosis. Solutions of each of the five antibiotics, PenicillinS ulphate, 3 Streptomycin, Aureomycin, Terramycin, and Neomycin were prepared by weighing the sale on a microbalance in 250 mg. quantities and adding to 500 ml. of sterile distilled water to producea 500 parts per million (ppm.) dilution. The rates of 5 ppm. and 10 ppm. were obtained by dilu­ tion of the concentrated solution. Pure cultures of 2. malvacearunu races 1 and 2 and formula for PCDA furnished through the courtesy of Dr. L. S. Bird, Pathologist, Texas A & M College, College Station, Texas. 2 PCDA. Diced potatoes 200 gm., diced carrots 50 gm., dextrose 20 gm., magnesium sulphate 0.3 gm., calcium carbonate 0.2 gm.,a gar 25 gm. Add strained broth extracts of potatoes and carrots to magnesium and cal­ cium salts, and dextrose dissolved in water. Add mixture to dissolved agar and make up to one liter. 3 Chemicals furnished by the Research Laboratories of Merck and Co., Inc., Rahway, N. J.