Soybean cultivar reactions to soybean stem canker caused by Diaporthe phaseolorum var. caulivora and pathogenic variation among isolates.

used in this study to detect the presence of Keeling, B. L. 1985. Soybean cultivar reactions to soybean stem canker caused by Diaporthe a very virulent strain of the fungus if one phaseolorum var. caulivora and pathogenic variation among isolates. Plant Disease 69:132-133. were among those selected. Cultivar Bragg was used as an indicator of the Twelve isolates of Diaporthe phaseolorum var. caulivora that cause stem canker disease of relative virulence of the isolates tested. soybeans (Glycine max) were compared for their relative virulence on field-grown plants of the soybean cultivars Tracy, Bragg, and J77-339. A wide range of virulence was measured among Bragg was chosen because previous isolates. The most virulent caused lesions with a mean length up to 61.9 cm at 60 days after research (1) has shown that this cultivaris inoculation; the least virulent caused lesions averaging 20.7 cm at 60 days. Differences in virulence moderately susceptible to the disease but of the pathogen are believed to contribute to observed variation in severity of the disease at different that canker development is slow enough locations. Fifteen soybean cultivars resistant to stem canker disease were identified. to allow measurements of canker enlargement. Preparation of inoculum. Flat toothStem canker disease of soybeans symptomatic of stem canker disease (2). picks were boiled for 30 min in each of (Glycine max (L.) Merr.) caused by Diseased plants were collected by the three changes of water, dried, and placed Diaporthe phaseolorum (Cke. & Ell.) author or sent to him by W. Moore or W. in 150-ml vials with 25 ml of potatoSacc. var. caulivora (Athow & Caldwell) Jordan, Mississippi State University, and dextrose broth. The broth-saturated (Dpc) (3) was first recognized in L. Young, Jackson, TN. The isolate from toothpicks were sterilized in the vials by Mississippi in 1975 (1). In retrospect, this Ohio was provided by A. F. Schmittautoclaving for 15 min at 120 C. After disease is believed to have been present in henner, Wooster. All isolates were from cooling, they were inoculated with the state for several years before 1975, but plants grown in 1981 and their sources are mycelium of appropriate Dpc isolates its prevalence was low and did not attract listed in Table 1. To recover the pathogen and incubated at 21 C for 15 days before attention. The disease was first observed from diseased plants, stem sections taken use (1). in the northeastern and east central from the margin of a canker were surfaceInoculation technique. A modification portions of the state but has now been disinfected in 1% sodium hypochlorite of the toothpick inoculation method was observed in most areas of the state where for 1 min, rinsed in sterile water, and used (1). The cultivars used in this study soybeans are grown. plated on acidified potato-dextrose agar were seeded in sandy loam soil on 1 June Disease severity has varied greatly at (PDA). After incubation for 3 days at 21 1982 and inoculated on 1 July by making different locations. This variation may be C, hyphal tips were transferred to PDA a hole through the soybean stem about 10 the result of variation in environmental slants for maintenance. cm above the soil with a dissecting needle conditions, especially the degree of Cultivars used. Soybean cultivars and inserting a toothpick infested with drought stress, or variation in the Tracy and Bragg and the breeding line the pathogen into the hole. The inserted virulence of the pathogen at different J77-339 were inoculated to determine the toothpick was not protected with a locations. Isolates of the pathogen relative virulence of Dpc isolates. J77-339 sealing compound. Twenty plants of recovered from diseased plants growing is very susceptible to stem canker disease Tracy, Bragg, and J77-339 were inoculated in different areas were tested for and was used as an indicator to using each Dpc isolate in each of three differences in pathogenic virulence, demonstrate development of the disease. replicates. Uninfested toothpicks were Measured differences in virulence among 12 isolates are presented in this report. Fifteen cultivars with resistance to the Table 1. Response of Bragg soybeans 60 days after inoculation with isolates of the stem canker stem canker disease are identified. pathogen Diaporthe phaseolorum var. caulivora from different locations MATERIALS AND METHODS Plants with Isolates tested. All isolates of the Source of isolate Lntoflesion s1c Pilants pathogen (Table 1) (except the one from Isolate Cultivar Location (cm) (%) (%) Oi)wrisltdfo sobaplns 81-6 Bedford Carroll County, MS 61.9 aZ 9.8 a 21.0 b 8 1-75 Bragg Grenada County, MS 54.9 ab 19.8 bc 8.7 bc Contribution of USDA, ARS, Soybean Production 8 1-82 J77-339 Lee County, MS 53.2 ab 13.5 ab 48.8 a Research, in cooperation with the Mississippi 8 1-102 Bedford Madison County, TN 45.2 abc 35.5 de 0.0 c Agricultural and Forestry Experiment Station, 81-73 Bedford Grenada County, MS 40.1 bcd 23.1 cd 0.0 c Stoneville 38776. D-209 J77-339 Lee County, MS 35.0 bcd 37.5 de 9.2 bc 8 1-77 Unknown Yalobusha County, MS 27.0 cd 34.9 de 5.3 bc Accepted for publication 20 July 1984. 81-7 Bedford Carroll County, MS 26.4 cd 46.2 ef 17.3 bc ___________________ 81-11 Bedford Carroll County, MS 22.5 d 58.7 fg 0.0 c The publication costs of this article were defrayed in part 8 1-70 Ransom Noxubee County, MS 22.4 d 61.7 g 1.6 c by page charge payment. This article must therefore be 81-65 Bedford Madison County, MS 20.7 d 62.3 g 0.0 c hereby marked "advertisement" in accordance with 18 U.S.C. § 1734 solely to indicate this tact. D0048M1 Unknown Ohio 1.0 e 100.0 h 0.0 c Control ..... 0.5 e 100.0 h 0.0 c This article is in the public domain and not copyrightable. It may be freely reprinted with cus~ Data are the means of three replicates (20 plants per replicate); lesion data are from living plants tomary crediting of the source. The American only. Means not followed by the same letter are significantly different (P =0.05) according to Phytopathological Society, 1985. Waller-Duncan's multiple range test. 132 Plant Disease/Vol. 69 No. 2 inserted into control plants. by isolate 81-65. Table 2. Disease reactions of soybean cultivars Measurement of virulence of isolates. The relative virulence of isolates was to inoculation with isolate D-209 of the stem Stems of inoculated plants were split with also reflected in the percentage of plants canker pathogen Diaporthephaseolorum var. a very sharp roofing hatchet 60 days after with stem lesions 10cm or shorter and the caulivora in field plots' inoculation. The extent of internal lesion percentage of plants killed (Table 1). The Maturity Lesion length development was measured from the data indicate that differences in disease Matup Lilg point of inoculation toward the top of the severity at different locations may be Cultivar group (mm) plant. The number of dead diseased caused by a variation in virulence of the Luthy V 14 (10-20) plants was also recorded, pathogen. A striking difference was also Virginia V 16 (10-20) Test for sources of resistance. A search measured between isolates from the same Hayseed VI 3 (2-5) Laredo 2 1 3) was made among soybean cultivars location. Isolates 81-6, 81-7, and 81-11 Rose Non-pop VI 2(1-3) maintained in the germ plasm collection were recovered from Bedford soybean FC 31745 Vi 3 (2-5) at Stoneville, MS, for additional sources plants growing only a few meters apart in Clemson VII 9 (8-10) of resistance to stem canker in 1983. a field in Carroll County, MS. Isolate 81-6 CNS VIlI 3 (1-5) Twenty-six selected cultivars were was one of the most virulent isolates Pluto VII 23 (20-30) inoculated with a virulent isolate of the tested, whereas 81-7 and 81-11 were Tanner VII 12(10-15) pathogen recovered from a diseased J77among the least virulent (Table 1). Arisoy VIII 13 (10-15) 339 plant growing at Verona, MS, and Besides differences in virulence of the Avoyelles VIII 2 (1-3) rated for their response as described pathogen at different locations and Mamloxi VIII 3 (2-5) before. Twenty plants of each tested differences in environmental conditions Dorman VIII 3 (1-5) cultivar were inoculated, that may influence disease development, Tracy-M VIII 2 (1-5) results of this research indicate that the a Planted on 2 June, inoculated on 7 July, data severity of the disease is also affected by recorded on 14 September 1983. RESULTS AND DISCUSSION the resistance of the cultivar. In a search bLesion length is mean of 20 plants; figures in Cultivar J77-339 was very susceptible for additional sources of resistance in parentheses represent the range of lesion to all Dpc isolates tested except the one 1983, 16 cultivars developed very small lengths for cultivar. from Ohio. Ninety-two to 100% of all lesions when artificially inoculated in inoculated J77-339 plants were dead 60 field plots (Table 2). The resistance of susceptible, with most inoculated plants days after inoculation. The isolate from Tracy-M and CNS has been reported (1) dead within 60 days of inoculation. Ohio was not virulent to J77-339 and and they were included in this test as plants inoculated with this isolate did not resistant controls. These resistant LITERATURE CITED differ from the controls. None of the cultivars may be very important in future 1. Keeling, B. L. 1982. A seedling test for resistance isolates caused disease symptoms in breeding programs for stem canker to soybean stem canker caused by Diaporthe phaseolorum var. caulivora. Phytopathology Tracy plants. A wide range in virulence resistance. In addition to the resistant 72:807-809. was measured among isolates of Dpc cultivars listed in Table 2, cultivars 2. Sinclair, J. B., ed. 1982. Compendium of Soybean when disease development in Bragg was Hollybrook, Bedford, Ogden, Tanner, Diseases. American Phytopathological Society, measured (Table 1). Lesion length varied and Seminole and the breeding lines J77St. Paul, MN. 104 pp. significantl