Incidence of bacterial blight of soybeans was observed from 1953 to 1959. During this period the disease was observed in 25 to 72 percent of the fields examined. A search was made for an improved source of blight resistance. A soybean introduction, P.I. 68708 was resistant to blight under natural conditions and when inoculated. It was also resistant to brown spot but was susceptible to race 8 of Peronospora manshurica as well as to Phytophthora rot. Yield, date of maturity, seed size, seed quality, and lodging resistance of the introduction were comparable to the same characters of the variety Blackhawk

Chamberlain, D. W.

Dunleavy, J. M.

Weber, C. R.

English

University of Northern Iowa

Proceedings of the Iowa Academy of ScienceVolume 67 | Annual Issue Article 191960A Source of Bacterial Blight Resistance ForSoybeansJ. M. DunleavyU.S. Department of AgricultureC. R. WeberU.S. Department of AgricultureD. W. ChamberlainU.S. Regional Soybean LaboratoryCopyright © Copyright 1960 by the Iowa Academy of Science, Inc.Follow this and additional works at: https://scholarworks.uni.edu/piasThis Research is brought to you for free and open access by UNI ScholarWorks. It has been accepted for inclusion in Proceedings of the Iowa Academyof Science by an authorized editor of UNI ScholarWorks. For more information, please contact scholarworks@uni.edu.Recommended CitationDunleavy, J. M.; Weber, C. R.; and Chamberlain, D. W. (1960) "A Source of Bacterial Blight Resistance For Soybeans," Proceedings ofthe Iowa Academy of Science: Vol. 67: No. 1 , Article 19.Available at: https://scholarworks.uni.edu/pias/vol67/iss1/19A Source of Bacterial Blight Resistance For Soybeans1 J. M. DUNLEAVY, C. R. WEBER2 and D. W. CHAMBERLAIN3 Abstract. Incidence of bacterial blight of soybeans was observed from 1953 to 1959. During this period the disease was observed in 25 to 72 percent of the fields examined. A search was made for an improved source of blight resistance. A soybean intro-duction, P.I. 68708 was resistant to blight under natural con-ditions and when inoculated. It was also resistant to brown spot but was susceptible to race 8 of Peronospora manshurica as well as to Phytophthora rot. Yield, date of maturity, seed size, seed quality, and lodging resistance of the introduction were compara-ble to the same characters of the variety Blackhawk. Bacterial blight is one of the most common diseases of soybeans in the Midwest, where it has been established for many years. It was observed by Heald (1906) in Nebraska as early as 1905 and was later reported in Connecticut by Clinton ( 1916) and in Nor th Carolina by Tisdale (1918). With the large, progressive increase in soybean acreage since 1942, bacterial blight has become wide-spread. The disease has been observed in Iowa for 20 years. The organism causing bacterial blight of soybeans, Pseudomonas glycinea Coerper, characteristically forms cream-white colonies tinged with brown on beef-peptone agar medium (Elliot, 1951). The bac-teria, if seed-borne, produce lesions on the cotyledons after seed germination. The bacteria spread to the upper leaves within a few weeks and produce small, translucent, watersoaked spots. As the lesions grow older there is often a halo of chlorotic tissue along their outer margins, and later they become necrotic. When the disease is severe, the lesions may coalesce and form irregular, necrotic spots surrounded by large, chlorotic areas of leaf tissue (Elliot, 1951; Johnson et al., 1954). Once the disease develops, there is no known practical means of controlling it. If the disease is not prevalent in an area, the best preventive measure is to plant disease-free seed (Elliot, 1951). This practice is frequently impractical because of the difficulty of tracing 1 Joint contribution from the Iowa Agricultural and Home Economics Ex-periment Station and Crops Research Division, Agricultural Research Service, U. S. Department of Agriculture. Journal Paper No. J-3826 of the Iowa Agricultural and Home Economics Experiment Station, Ames, Iowa. Project No. 1179. 2Plant Pathologist and Agronomist, respectively, Crops Research Division, U. S. Department of Agriculture, and Iowa Agricultural and Home Economics Experiment Station, Ames, Iowa. 3Plant Pathologist, U. S. Regional Soybean Laboratory, Urbana, Illinois. 120 1Dunleavy et al.: A Source of Bacterial Blight Resistance For SoybeansPublished by UNI ScholarWorks, 19601960] BACTERIAL BLIGHT RESISTANCE 121 the seed lot origin, and because seed is often combined from var-ious sources before it is sold. The need for bacterial blight resistant varieties of soybeans has long been recognized. Varietal variation in susceptibility to the disease was noticed by Woodworth and Brown (1920). More re-cently, the varieties Flambeau and Hawkeye have been recognized as being somewhat less susceptible than other northern varieties (Johnson et al., 1954). The principal deterrents to the develop-ment of truly resistant soybean varieties have been the lack of a source of high resistance and an inadequate understanding of the inheritance of disease .resistance. MATERIALS AND METHODS Disease resistance and agronomic characters were observed in field plots of 10-foot rows end-trimmed to 8 feet prior to harvest. Each variety or plant introduction was replicated four times. Lodging notes and plant height were recorded at maturity. Plant height was taken as the average length, in inches, from the ground to the tip of the stem. Chemical composition of seed was determined by the U. S. Regional Soybean Laboratory. Oil and protein con-tents of seed were obtained on a moisture-free basis. Field-grown plants were inoculated with the bacterial blight organ-ism. Inoculum was prepared by growing the bacterium in 4-liter flasks containing two liters of V-8 juice medium. The medium was prepared by adding the contents of one 12-ounce can of Campbell V-8 vegetable juices4 to 5 grams of dextrose and bringing the total volume to two liters with water. The medium was adjusted to pH 7 after sterilization. The bacteria were grown in the culture medium for 48 hours, and one part of inoculum' was diluted with 120 parts of water before use. Plants were sprayed with inoculum delivered from a motor-driven sprayer at a pressure of 80 pounds per square inch. They were inoculated when approximately six weeks of age, and disease ratings were recorded two weeks later. Seedling plants were evaluated for downy mildew (Peronospora manshurica (Naum.) Syd ex. Gaum.) and Phytophthora rot (Phy-tophthora so jae Kauf. & Gerd.) resistance in the greenhouse. They were rated for downy mildew 10 days after the seedlings had been inoculated. They were inoculated with a water suspension of conidia of the downy mildew fungus and held in a moist chamber overnight. Disease ratings were recorded for Phytophthora rot one week after 10-day-old seedlings had been inoculated with the fungus by inser-tion of mycelium into the hypocotyls. 4Mention of commercial products does not imply endorsement or recom-mendation over others of a similar nature not mentioned. 2Proceedings of the Iowa Academy of Science, Vol. 67 [1960], No. 1, Art. 19https://scholarworks.uni.edu/pias/vol67/iss1/19122 IOWA ACADEMY OF SCIENCE [Vol. 67 Plants were rated for bacterial blight, downy mildew, brown spot (Septoria glycines Hemmi) and Phytophthora rot on a scale ranging from 1 (immune) to 5 (completely susceptible). A rating of 2 indi-cated that a plant was resistant; 3, slightly susceptible; and 4, mod-erately susceptible. Observations and tests had revealed no evidence of resistance in any of the commonly grown soybean varieties. Accordingly, about 1,000 plant introductions from the collections maintained by the U. S. Regional Soybean Laboratory were evaluated for resistance to bacterial blight at Urbana, Illinois. Artificial inoculation, coupled with a heavy natural infection, provided ideal .conditions for bacterial blight development in the nursery. Almost all of the material was heavily infected, but several introductions were virtually free from infection. These plant introductions were observed under field con-ditions at Ames, Iowa, during the period 1957-1959. RESULTS Incidence of bacterial blight of soybeans in Iowa fields was ob-served closely during 1953-1959. Considerable variation in disease incidence with peaks of intensity in 1953 and 1957 was observed (Figure 1). The highest disease incidence was observed in 19 5 7, when bacterial blight was found in about three-fourths of 61 soy-bean fields located in 31 of Iowa's major soybean-producing counties. The lowest incidence was observed in 19 59, when the disease was present in only 2 5 percent of the fields observed. Prevalence of bacterial blight has created a decided need for a blight-resistant soybean variety possessing all the desirable agronomic attributes of improved susceptible varieties. An intensive screening of soybean lines believed to be resistant to bacterial blight was required. Eight soybean lines believed to be resistant were compared under field conditions in 1957. Although no line was immune to the dis-ease, several were resistant. A plant introduction, P.I. 68 7085 , was notably more resistant than the other lines. It was consistently more resistant to development of bacterial blight than Lincoln, a susceptible variety (Table 1). Heavy, natural bacterial blight in-fection was present in the soybean test plots in 1957 and 1958. In these years, P.I. 68708 showed only a few, small lesions, whereas Lincoln showed many lesions, some of which coalesced and formed large necrotic areas. Very little chlorosis was associated with the lesions on leaves of P.I. 68 708, but the heavily infected leaves of Lincoln plants were almost entirely chlorotic (Figure 2). P.I. 68708 showed no more infection when artificially inoculated with P. gly-5U. S. Department of Agriculture plant introduction number. 3Dunleavy et al.: A Source of Bacterial Blight Resistance For SoybeansPublished by UNI ScholarWorks, 19601960] BACTERIAL BLIGHT RESISTANCE 123 cinea under field conditions than when naturally infected, whereas inoculated Lincoln plants were consistently completely susceptible. Lincoln plants were rated only 4 in 1959 when there was less natural disease development. Plants of P .I. 68 708 showed no bacterial in-fection during the entire season and were rated 1. Table 1 Bacterial Blight Ratingl for P.I. 68708 and Lincoln Soybeans Naturally Infected with P. glycinea, Ames, Iowa, 1957-1959 Year 1957 1958 1959 P.I. 68708 2 2 1 lDisease rating ranges from 1 (immune) to 5 (completely susceptible) (f) 0 ...J 8 ~40 LL. LL. 0 30 w (.!) ~2 z w ~ 10 w 0. 1953 1954 1955 1956 1957 1958 YEARS 1959 Figure 1. Incidence of bacterial blight of soybeans in Iowa from 1953 to 1959. Lincoln 5 5 4 P.I. 68708 was compared with Blackhawk, Hawkeye, and Adams for disease resistance to race 8 of the downy mildew fungus, Phytoph-thora rot, and brown spot. When naturally infected under field con-ditions, the plant introduction was resistant to brown spot. It was slightly susceptible to Phytophthora rot and completely susceptible to race 8 of the downy mildew fungus when plants were inoculated in the greenhouse (Table 2). The introduction was not as resistant to Phytophthora rot as was Blackhawk, but it was more resistant 4Proceedings of the Iowa Academy of Science, Vol. 67 [1960], No. 1, Art. 19https://scholarworks.uni.edu/pias/vol67/iss1/19124 IOWA ACADEMY OF SCIENCE [Vol. 67 Figure 2. Left, an inoculated leaflet of P.I. 68708 soybeans with only a few small , chlorotic bacterial blight lesions at lower left; right, an inoculated leaflet of Lincoln soybeans with considerable chlorosis and numerous dark, necrotic bac~ terial blight lesions. than were Hawkeye and Adams. P.I. 68708 was evaluated for Phy-tophthora rot resistance in Ohio, where it was reported to have resistance when grown in a soybean field naturally infested with the fungus (A. 'F . Schmitthenner, personal communication, 1960) . Table 2 Downy Mildew, Phytophthora Rot, and Brown Spot Ratings! for P .I. 68708 Soybeans and Three Soybean Varieties, Ames, Iowa, 1959 Plant introduction or variety P .I. 68708 Blackhawk Hawkeye Adams Downy mildew2 (race 8) 5 5 5 5 Phytophthora 2 rot 3 2 4 4 lDisease rating ranges from 1 (immune) to 5 (completely susceptible) 2Plants inoculated under greenhouse conditions 8Natural infection under field conditions Brown spot3 2 3 5 4 In addition to having high resistance to bacterial blight, P .I. 68708 has several agronomic advantages over the other resistant lines ob-served. It matures early enough to be grown in most of the soybean-producing states in the northern portion of the United States and 5Dunleavy et al.: A Source of Bacterial Blight Resistance For SoybeansPublished by UNI ScholarWorks, 19601960] BACTERIAL BLIGHT RESISTANCE 125 in Ontario, Canada, for the purpose of varietal improvement. Its maturity date is between Blackhawk and Hawkye, which mature in Iowa during the last half of September (Table 3). The resistant plant introduction compared favorably in yield and chemical com-position with both Blackhawk and Hawkeye. One disadvantage of P .I. 68 708 was its short height. It was 29 inches high, whereas Blackhawk was 41 inches and Hawkeye was 45 inches high. Table 3 Comparison of Agronomic Characters of P.1. 68708 Soybeans With Those of Two Improved Soybean Varieties Grown at Ames, Iowa, in 1959 Plant Average Date of Plant introduction yield maturity height Chemical composition of seed or variety (bu.la.) (mo.-day) (in.) Oil % Protein % P.1. 68708 34.2 9/20 29 22.0 39.5 Blackhawk 35.1 9/19 41 22.1 40.4 Hawkeye 39.8 9/23 45 21.9 41.4 L.S.D. (5%) 4.2 Seeds of P.I. 68708 were brought to the United States from Har-bin, Kirin, Manchuria, in 1926. P.I. 68708 has purple flowers, gray pubescence, a yellow seed coat, and a buff hilum. Mostly 2-seeded pods were produced bearing seed of good quality, weighing 14.3 g/100 as compared with Blackhawk and Hawkeye seeds which weighed 15.8 g/100 and 18.1 g/100, respectively. Plants tended to grow very compact and erect, and pods were not susceptible to shattering. Because of its resistance to bacterial blight and brown spot, cou-pled with several desirable agronomic characteristics, P.I. 68708 is a good source of germplasm for incorporating bacterial blight re-sistance into northern soybean varieties. Literature Cited Clinton, G. P. 1916. Notes on plant diseases of Connecticut. Conn. Agr. Exp. Sta. Rept. 1915: 444-446. Elliot, Charlotte. 1951. Manual of Bacterial Plant Pathogens, second edition. Chronica Botanica Co., Waltham, Mass. Heald, F. D. 1906. Ann. Rept. Nebr. Agr. Exp. Sta. for 1905, 19: 71. Johnson, Howard W., Chamberlain, D. W., and Lehman, S. G. 1954. Dis-eases of soybeans and methods of control. U. S. Dept. Agric. Circular No. 931. Tisdale, W. H. 1918. Report of the division of plant pathology and bacteriol-ogy. Ann. Rept. No. Car. Agr. Exp. Sta., 1917-18: 59. Woodworth, C. M., and Brown, Florence Coerper. 1920. Studies on varietal resistance and susceptibility to bacterial blight of the soybean. Phytopath. 10: 68. 6Proceedings of the Iowa Academy of Science, Vol. 67 [1960], No. 1, Art. 19https://scholarworks.uni.edu/pias/vol67/iss1/19

A Source of Bacterial Blight Resistance For Soybeans

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A Source of Bacterial Blight Resistance For Soybeans

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