bluuebunny/crossref_metadata_2025 huggingface dataset:
Soil Variables Associated with Sudden Death Syndrome in Soybean Fields in Iowa
Authors: Scherm H. , Yang X. B. , Lundeen P.
Published: May 2007

Sudden death syndrome, caused by Fusarium solani f. sp. glycines, has increased in prevalence in soybean production regions in the North-Central United States. Little is known about soil factors and environmental conditions that influence disease severity in this pathosystem. We studied associations between biological, chemical, and physical soil variables and severity of foliar symptoms of sudden death syndrome in nine commercial soybean fields in Iowa during 1995 and 1996. Disease was patchy in all fields, and soil samples were collected in each field along a transect that ran from a symptomless area through a diseased area. There were 25 sampling stops along each transect, separated by distances of 1.5 to 2.5 m. At each stop, soil samples were collected and soil strength, soil moisture, and foliar disease severity (at plant growth stage R6) were measured. Soil samples were assayed for population densities of F. solani f. sp. glycines, cysts of the soybean cyst nematode (Heterodera glycines), and for chemical variables (soluble salts, pH, organic matter, cation exchange capacity, and concentrations of P, K, Ca, Mg, Mn, and Fe). Cross-correlation analyses were carried out to test for associations between soil variables and disease severity in individual fields, while discriminant analysis was used to assess the effects of soil variables across all fields. Disease severity showed consistent associations with F. solani f. sp. glycines populations (strong effect) and H. glycines cyst counts (minor effect). Available K was identified as a possible disease-enhancing factor, but the magnitude of its effect was dependent on the overall K-concentrations in the fields. For example, as the median K-concentration increased, the correlation between K and disease decreased. None of the other soil variables showed consistent associations with disease. The results suggest that localized presence or absence of F. solani f. sp. glycines is the chief reason for the patchiness of sudden death syndrome in affected fields. Thus, manipulation of soil nutrient status or fertility level appears to have limited potential for reducing disease in the high-yield soybean production environment of Iowa. Instead, producers should focus on preventing the establishment or reducing populations of F. solani f. sp. glycines and H. glycines in their fields.
Effect of Phosphite on Tomato and Pepper Plants and on Susceptibility of Pepper to Phytophthora Root and Crown Rot in Hydroponic Culture
Authors: Förster H. , Adaskaveg J. E. , Kim D. H. , Stanghellini M. E.
Published: May 2007

Tomato and pepper plants were grown hydroponically in a greenhouse using phosphate or technical and commercial formulations of phosphite as sources of phosphorus nutrition to determine the effects on plant development and susceptibility to Phytophthora root and crown rot. Phosphite-treated tomato and pepper plants were deficient of phosphate and developed phosphorus-deficiency symptoms. Growth of plants (leaf area and leaf, stem, and root dry weights) that were fertilized with phosphite was significantly (P < 0.05) reduced compared with phosphate-fertilized plants. In Phytophthora capsici–inoculated pepper plants, incidence of Phytophthora crown rot was significantly reduced in phosphite-treated plants compared with no phosphorus or phosphate-treated plants. Incidence of crown rot in pepper plants treated with 1 mM phosphate plus 0.3 mM phosphite was intermediate between plants treated with only phosphite (1 mM or 0.1 mM) and plants treated with phosphate (1 mM).
Rust Disease of Oregano and Sweet Marjoram in California
Authors: Koike S. T. , Subbarao K. V. , Roelfs A. P. , Hennen J. F. , Tjosvold S. A.
Published: May 2007

In 1996 and 1997, a rust disease was detected on commercial, fieldgrown oregano (Origanum vulgare) and sweet marjoram (Origanum majorana) in coastal California. Symptoms on both plants were similar and mostly consisted of small (2 to 5 mm in diameter), circular, brown, necrotic leaf spots that developed cinnamon brown pustules in the center of the spot or in concentric groups on the spot periphery. Pustules sometimes developed without spots. On sweet marjoram, leaf spots were sometimes surrounded by a chlorotic halo. Teliospores were not detected on either host. Ellipsoidal urediniospores measured 22 to 25 μm by 19 to 22μm and contained 2 to 3 germ pores in an equatorial configuration. The rust was identified as Puccinia menthae. Pathogenicity was tested by depositing urediniospores onto leaves of healthy plants and then incubating plants in a humidity chamber for 48 h. Urediniospores from oregano infected Italian (Origanum× majoricum), Sicilian (Origanum × marjorana), trailing (O. prostrata), and Greek (O. heracleoticum) oregano, and sweet marjoram. Urediniospores from sweet marjoram infected sweet marjoram and the one oregano tested, Italian oregano. With all inoculations, both symptoms and fungal fruiting bodies were similar to those observed in the field. Neither the oregano nor the sweet marjoram isolates infected spearmint (Mentha spicata), which is consistent with previous studies (1,2). This is the first report of a rust disease of oregano and sweet marjoram in California. Rust significantly reduced the quality and yield of both crops.

References: (1) J. T. Fletcher. Trans. Br. Mycol. Soc. 46:345, 1963. (2) M. Wilson and D. M. Henderson. 1966. British Rust Fungi, Cambridge University Press, Cambridge.
Peronospora sparsaon CultivatedRubus arcticusand Its Detection by PCR Based on ITS Sequences
Authors: Lindqvist Hannele , Koponen Hilkka , Valkonen Jari P. T.
Published: May 2007

In 1994 to 1996, large yield losses were reported in cultivated arctic bramble (Rubus arcticus) due to berries drying in the middle of the growing season in the entire cultivation area (62° to 66° N) in Finland. Interveinal, angular, purple-red lesions on leaves are associated with the dryberry disease. Cultivations of arctic bramble were inspected in 1995 and 1996, and 69 plant samples and 137 rootstocks were collected and examined for fungi in the laboratory. Perono-spora sparsa was the species most commonly found in all types of samples tested, but Fusarium avenaceum, Cylindrocarpon destructans, and Botrytis cinerea also were detected. P. sparsa was shown to overwinter in the underground parts of arctic bramble. Laboratory tests showed that the two main cultivars of arctic bramble (Pima and Mespi) were susceptible to P. sparsa. Sequences of the internal transcribed spacer (ITS) regions 1 and 2 of the rDNA genes were determined in four and six isolates, respectively, of P. sparsa, and little sequence variability was detected. The corresponding ITS regions of arctic bramble, the above mentioned fungi, a Phoma sp. previously isolated from arctic bramble, and Phytophthora cactorum isolated from strawberry were also determined and compared with the corresponding sequences of P. sparsa. Subsequently, two pairs of primers were designed to the ITS regions that could be used to detect either P. sparsa and Phytophthora cactorum, or only P. sparsa, respectively, by polymerase chain reaction (PCR) using two different types of thermal cyclers (“heated block” Mini Cycler and “hot air flow” Rapid Cycler).
Epidemic Development of Bacterial Blight on Rice Carrying Resistance Genes Xa-4, Xa-7, and Xa-10
Authors: Oña I. , Cruz C. M. Vera , Nelson Rebecca J. , Leach Jan E. , Mew T. W.
Published: May 2007

Epidemic development of bacterial blight caused by Xanthomonas oryzae pv. oryzae on three near-isogenic lines (IRBB lines) carrying bacterial blight resistance genes Xa-4 (IRBB4), Xa-7 (IRBB7), and Xa-10 (IRBB10) was studied in two farmers' fields located in Calauan and Mabi-tac, Phillipines, during 1993, 1994, and 1995. The plots were planted continuously during dry and wet seasons, with disease assessments done during the wet seasons, when weather was conducive to bacterial blight development. Disease incidence (number of hills infected) and severity (diseased leaf area) were assessed and area under the disease progress curve (AUDPC) values were computed. Mean disease incidence and severity in Calauan (AUDPC = 3,241.5 and 716.7, respectively) were significantly higher than in Mabitac (AUDPC = 2,431.2 and 558.0, respectively). In Calauan, AUDPC values for disease incidence and severity on IRBB4, IRBB10, and IR24 did not differ significantly during the three years of testing. In Mabitac, the AUDPC values for disease incidence and severity were not significantly different among IRBB4, IRBB10, and IR24 in 1993 and in 1995. However, in 1994, disease incidence (AUDPC = 3,037.7) and severity (AUDPC = 891.0) on IRBB4 were significantly lower than on IRBB10 and IR24. Bacterial blight was lowest on IRBB7 at both sites and throughout 1993 to 1995, indicating that this genotype is effective in suppressing the disease even with the presence of an indigenous virulent population of X. oryzae pv. oryzae.
Role of Flag Leaf and Spike Emergence Stage on the Incidence of Karnal Bunt in Wheat
Authors: Kumar J. , Nagarajan S.
Published: May 2007

Removal of the flag leaf of wheat, earlier hypothesized to act as a site where secondary sporidia of Tilletia indica multiply and conjugate, reduced the severity of Karnal bunt. Evidence reported here suggests that sporidia reach the flag leaf from the soil by splashing, multiply on the surface of the flag leaf, and move with rain water or dew into the boot of the flag leaf to cause infection of the spikelets. Plants in growth stage 49 (first awns visible) were more vulnerable to infection by secondary sporidia than were plants at other growth stages. At growth stage 49, the flag leaf lamina was fully opened, compared with its preceding stages, which had tubular and closed lamina. Also, leaf posture of the flag leaf at growth stage 49 is erect and thus may facilitate movement of sporidial inoculum into the boot. Upon completion of stage 49, the flag leaf becomes droopy, leading to lesser inoculum movement into the emerging spike. Thus, maximum success can be achieved in artificial creation of Karnal bunt by inoculating with secondary sporidia before onset of growth stage 49. Genotypes whose maturity avoids coincidence of this critical stage of spike emergence with periods of weather favorable for infection by T. indica may be selected for resistance breeding.
First Report of Diaporthe phaseolorum var. meridionalis on Soybean Seeds from Ghana
Authors: Asante S. N. A. , Wolffhechel H. , Neergaard E. de
Published: May 2007

Fifty-nine soybean samples (Glycine max) of various varieties, grown in various agro-ecological zones of Ghana, and harvested in 1995 and 1996, were collected during May through June 1996 and sent to Denmark for analysis. Seed samples were analyzed by the blotter method: seeds were placed on three layers of moistened blotter paper in petri dishes, 10 seeds per dish, 200 or 400 seeds per sample. The seeds were incubated for 7 days at 22 ± 2°C, exposed to alternating cycles of 12 h NUV-light and 12 h darkness. Subsequently, they were analyzed microscopically for fungal infection. Phomopsis spp. were detected in 68% of the samples, at infection levels ranging from 0.25 to 21.0% (mean 3.4%). One to five isolates of Phomopsis spp. were selected at random and cultured on potato dextrose agar acidified to pH 4.5 with 90% lactic acid (APDA) for identification to species. Isolates were cultured on APDA, with and without sterile soybean stem pieces, under either NUV-light/darkness or artificial daylight/darkness cycles. Of 103 isolates, 101 isolates produced only pycnidia and were identified as P. longicolla T. W. Hobbs based on the production of aggregated pycnidia with prominent beaks (2). Seventy-seven of these isolates produced only alpha conidia whereas 24 isolates produced both alpha and beta conidia, which differs from the description by Hobbs et al. (2). Two isolates from one seed sample produced perithecia but no pycnidia. Perithecia were evenly scattered in the colony, 200 to 350 × 250 to 400 μm, and had a beak of 900 to 1500 μm. Apical beak width was 60 to 110 μm, basal beak width 70 to 120 μm. Asci were 25.0 to 37.5 × 5.0 to 7.5 μm. Ascospores were two-celled, biguttulate in each cell, and 10.0 to 12.5 × 2.5 to 4.0 μm. Based on the description by Fernández and Hanlin (1), these isolates were identified as Diaporthe phaseolorum (Cooke & Ellis) Sacc. var. meridionalis Fernández (DPM), the causal agent of southern stem canker of soybean, which has not previously been reported from any African country. Ten 14-day-old soybean seedlings were inoculated with an isolate identified as DPM by the toothpick method (3) and two seedlings inoculated with sterile toothpicks served as controls. Local expanding lesions formed after 1 week on all plants at the point of inoculation with DPM; 2 weeks after inoculation, the pathogen was reisolated from all lesions by plating stem pieces, surface sterilized in 1% NaOCl, on APDA. In control plants no lesions were seen and no mycelial growth occurred from stem pieces plated on APDA.

References: (1) F. A. Fernández and R. T. Hanlin. Mycologia 88:425, 1996. (2) T. W. Hobbs et al. Mycologia 77:535, 1985. (3) B. L. Keeling. Phytopathology 72:807, 1982.
Banana Streak Badnavirus and Cucumber Mosaic Cucumovirus in Farmers' Fields in Zanzibar
Authors: Vuylsteke D. R. , Hughes J. d'A. , Rajab K.
Published: May 2007

Symptoms resembling those of viral leaf streak disease, caused by banana streak badnavirus (BSV), were observed in May 1998 on two banana (Musa spp.) landraces grown from farmer-collected propagules in a farmer's field at Kiboje Uchukuni, Zanzibar. Those showing symptoms were “French plantain” cv. Mzuzu and “Cavendish” banana cv. Mtwike. Leaf symptoms were expressed as chlorotic streaks and blotches. Leaf samples were indexed by immunosorbent electron microscopy with BSV and cucumber mosaic cucumovirus (CMV) antibodies, using partially purified preparations (2). The two landraces tested positive for BSV, corroborating the occurrence of BSV in Zanzibar. In addition, cv. Mtwike was found to be coinfected with CMV. No other viruslike particles were seen by electron microscopy. Although BSV has been reported in Zanzibar (1), it was only from symptoms in the Musa field genebank at Kizimbani Research Station. BSV has been found in many Musa collections worldwide, particularly in the widely grown cv. Mysore. This report confirms the presence of BSV in farmers' fields and is also the first report of CMV infecting banana in Zanzibar.

References: (1) A. J. Dabek and J. M. Waller. Trop. Pest Management 36:157, 1990. (2) M. Diekmann and C. A. J. Putter. Musa spp. FAO/IPGRI Technical Guidelines for the Safe Movement of Germplasm No. 15. FAO/IPGRI, Rome, Italy, 1996.
First Report of Colletotrichum gloeosporioides on Russian-thistle
Authors: Schwarczinger I. , Vajna L. , Bruckart W. L.
Published: May 2007

A pathogen identified as Colletotrichum gloeosporioides (Penz.) Penz. & Sacc. in Penz. was isolated from foliar and stem lesions on Russian-thistle (Salsola tragus Torner ex L.) collected in Bugac, Hungary, in 1996. Symptoms on leaves and stems began as discrete, sunken, 2- to 10-mm-diameter chlorotic spots, followed by formation of circular buff-colored lesions that eventually coalesced, desiccated, and caused plant tissue death above the lesions. Lesions that occurred near ground level usually killed the plant. Salmon-colored spore masses developed in setose acervuli in the center of the necrotic lesions. Conidia were hyaline, one-celled, falcate to nearly straight, and measured 15 to 25 × 5 to 6 μm. The teleomorph stage of the pathogen (Glomerella cingulata (Stoneman) Spauld. & H. Schrenk) was not observed in the field or on inoculated plants. These morphological characteristics of the isolate were consistent with the description of C. gloeosporioides (1). Pathogenicity was proved by completing Koch's postulates in Hungary and the U.S. Inoculation with conidial suspension (106 conidia per ml) sprayed on S. tragus plants in the greenhouse at the three- to four-leaf stage caused severe necrosis and wilting within 6 days and plant death in 2 weeks. Symptoms did not appear on control plants inoculated with sterile, distilled water. Inoculation test was repeated on 6-week-old plants and at the stage of flowering. All treated plants were killed at both stages within 4 weeks. Because of high virulence and host specificity of this isolate of C. gloeosporioides in preliminary pathogenicity tests it is being evaluated for use as a mycoherbicide for Russian-thistle control in the U.S. This is the first report of C. gloeosporioides causing anthracnose on S. tragus.

Reference: (1) B. C. Sutton. Pages 1–27 in: Colletotrichum Biology, Pathology and Control. J. A. Bailei and M. J. Jeger, eds. CAB Int., Wallingford, UK, 1992.
Transmission of Alternaria brassicicola to Cabbage by Flea Beetles (Phyllotreta cruciferae)
Authors: Dillard H. R. , Cobb A. C. , Lamboy J. S.
Published: May 2007

In 1995 and 1996, flea beetles (Phyllotreta cruciferae) were observed in the field feeding on cabbage plants that were infected with Alternaria brassicicola. Flea beetles were captured in glass vials, etherized, and placed on agar media for isolation of A. brassicicola. In 1995, A. brassicicola was isolated from 13 out of 69 (18.8%) flea beetles in the first test and 38 out of 132 (28.8%) in the second test. In 1996, flea beetles were collected nine times during the growing season, and the isolation frequency increased from 0 to 77% as the crop approached maturity. In another study, flea beetles were collected from a field of A. brassicicola-infected cabbage, enclosed in plastic bags containing potted healthy cabbage plants, and then placed on a shaded greenhouse bench for 6 days. Alternaria leaf spot developed on plants that were infested with the contaminated flea beetles. Feces obtained from flea beetles that fed on cabbage infected with A. brassicicola contained intact and broken conidia of A. brassicicola and undigested pieces of cabbage leaf. The conidia were viable after passing through the flea beetles, as evidenced by their germination on the glass slides used for collecting the feces. Conidia of A. brassicicola were observed by scanning electron microscopy on all parts of flea beetle bodies, including wings, mouthparts, antennae, and legs.
Effects of Fruit and Pollen Exudates on Growth of Botrytis cinerea and Infection of Plum and Nectarine Fruit
Authors: Fourie J. F. , Holz G.
Published: May 2007

Sugars in exudates from Harry Pickstone plum and Sunlite nectarine fruit and from pollen of weeds commonly found in orchards were determined by gas-liquid chromatography, and their effect on the development of Botrytis cinerea was determined in vitro and in vivo. Fructose, glucose, and sorbitol were the only sugars detected in exudates of immature fruit. They occurred at low concentrations, but their concentration generally increased as fruit ripened. Sucrose was first detected during maturation. In nectarine, an increase in sugar concentration, especially sucrose, was pronounced during the period of rapid cell enlargement, which occurred approximately 2 weeks before harvest. Absorbance readings of culture media amended with sugar indicated that the hexose sugars (fructose and glucose) and sucrose did not markedly influence growth of B. cinerea at concentrations below 0.22 and 0.12 mM, respectively. The hexose sugars caused a steady increase in growth when supplied at concentrations in excess of 0.44 mM, and sucrose caused a steady increase in growth at 0.23 mM. The stimulatory effect of fruit exudates on growth of B. cinerea on glass slides coincided with the period of rapid sugar release from the fruit and the shift in susceptibility to decay. Only fructose (1.72 mM) and glucose (0.72 mM) were detected in nectarine pollen exudates. Pollen exudates from weeds stimulated fungal growth and significantly increased the aggressiveness of the pathogen on plum and nectarine fruit when added to conidia during the last 4 weeks prior to the picking-ripe stage. The study showed that changes in the composition of nectarine and plum fruit exudates may contribute to the late-season susceptibility of these fruit to B. cinerea infection.
Specific Detection of Potato Virus A in Dormant Tubers by Reverse-Transcription Polymerase Chain Reaction
Authors: Singh Rudra P. , Singh Mathuresh
Published: May 2007

A reverse-transcription polymerase chain reaction (RT-PCR) protocol was developed for the detection of potato virus A (PVA) in dormant tubers. A 255-bp amplified product was produced using a primer pair from the P1 gene of the PVA genome. The 255-bp product was detected in nucleic acids from leaves, tubers, and purified virions and was specific to PVA as determined by Southern blot tests and detection by a PVA-specific probe. When presented with seven potato virus/strain nucleic acids and a viroid, singly and in mixed infections, the primer pair did not amplify any products. Its specificity to PVA was further demonstrated by RT-PCR detection of PVA from the known mixtures of PVA and potato virus Y samples. PVA was detected in foliage nucleic acids at a dilution of 1:1024–1:4096 and tuber nucleic acids at 1:256–1:1024. It was uniformly present in various parts of the potato tuber. PVA was detected in composite tuber samples containing a ratio of infected to healthy sap of 1:29 and was readily detected in tubers of several cultivars or breeding lines, in dormant as well as in sprouting tubers stored at 20–25°C for 4 months.
Binucleate Rhizoctonia on Tobacco in Zimbabwe
Authors: Masuka A. J.
Published: May 2007

Rhizoctonia solani Kühn (teleomorph Thanatephorus cucumeris (A. B. Frank) Donk) anastomosis groups AG 4 and AG 3 cause, respectively, widespread stem rot and leaf spot diseases of tobacco in Zimbabwe (2). Stem rot leads to substantial field losses, necessitating routine chemical and biological control (1). A recent increase in reports on Rhizoctonia-induced damping-off in tobacco seedlings and lodging of mature field plants prompted detailed studies on the causal pathogen. Nuclear fluorescence microscopy studies of 83 isolates from diseased tobacco revealed the presence of binucleate isolates. The isolates were collected in 1981 (1 isolate), 1990 (1 isolate), 1996 (3 isolates), and 1997 (1 isolate) and caused damping-off in seedlings (2 isolates) and stem rot and lodging in field tobacco (4 isolates). We confirmed that all binucleate isolates contained only two nuclei per cell. There was variability in the number of nuclei among the multinucleate stem rot (mean 4.2, SE 0.265) and leaf spot (mean 7.5, SE 0.259) isolates. Two tested binucleate Rhizoctonia isolates were pathogenic to 7-week-old tobacco seedlings (cv. Kutsaga 35) in a greenhouse experiment, laid out as a randomized complete block design. Uninoculated healthy plants served as control. Based on a disease rating scale of 1 to 5 (1 = no disease and 5 = >50% stem damage), overall disease incidence was 88.9% 5 days after inoculation with macerated mycelium at the rate of 3.60 × 105 CFU per seedling, applied around the stem base. Over 50% of inoculated seedlings were rated in disease categories 4 and 5. Binucleate Rhizoctonia were consistently isolated from infected plants. A country-wide survey is being conducted to determine the incidence, distribution and severity of diseases caused by binucleate Rhizoctonia on tobacco in Zimbabwe.

References: (1) J. S. Cole and Z. Zvenyika. Plant Pathol. 37:271, 1988. (2) S. I. Mpofu and A. M. Julian. J. Phytopathol. 140: 367, 1994.
First Report of Cephaleuros virescens in Arkansas and Its Occurrence on Cultivated Blackberry in Arkansas and Louisiana
Authors: Holcomb G. E. , Vann S. R. , Buckley J. B.
Published: May 2007

Blackberry (Rubus sp.) cane samples (cultivar Navaho) showing disease symptoms were collected from a commercial grower in Texarkana, AR, and sent for diagnosis to the plant disease clinic in Lonoke in June, 1997. Cane symptoms consisted of stem cracking, tissue discoloration beneath the bark, and the presence of an orange, velvetlike growth that was identified as sporangiophores and sporangia of the parasitic green alga Cephaleuros virescens Kunze. Zoospores were released when sporangia were placed in water drops. The alga was isolated from infected canes on potato dextrose agar, but pathogenicity tests were not attempted because pathogenicity has never been demonstrated successfully, nor have zoospores been produced in culture. C. virescens also was found infecting cultivated blackberry at the Louisiana Calhoun Research Station, where it occurred more commonly on thornless than on thorned type cultivars. This parasitic alga occurs commonly along the U.S. Gulf Coast and has been recorded on 287 plant species and cultivars, including 80 that are subject to stem infections (1,2). The occurrence of C. virescens in Arkansas extends its known northernmost range from 32.5°N to 33.5°N in the U.S. This is the first report on the occurrence of C. virescens in Arkansas and the first report of its occurrence on cultivated, commercially grown blackberry.

References: (1) G. E. Holcomb. Plant Dis. 70:1080, 1986. (2) R. B. Marlatt and S. A. Alfieri, Jr. Plant Dis. 65:520, 1981.
Soybean Genotypes Resistant to Phytophthora sojae and Compensation for Yield Losses of Susceptible Isolines
Authors: Wilcox J. R. , St. Martin S. K.
Published: May 2007

Two isolines, with different alleles for resistance to Phytophthora sojae, of the soybean cultivars, Beeson, Century, and Williams were grown in replicated tests to assess yield losses attributable to this pathogen. Isolines susceptible to prevalent races of the pathogen had black seed coats as a marker trait; isolines resistant to prevalent races of the pathogen had yellow seed coats. Included in the tests were blends composed of equal numbers of seed of the two isolines for each cultivar. Tests were conducted at three locations in Indiana and one location in Ohio for three years. In six environments, where Phytophthora root and stem rot damaged soybean, isolines susceptible to prevalent races of the pathogen produced seed yields from 65 to 93% of the yields of isolines resistant to these races. In four of these environments, isoline blends produced yields equal to those of the resistant isoline. In two environments, where susceptible isolines averaged 65 and 69% of the yield of the resistant isoline; the blends averaged 89 and 83% of the yield of the resistant isoline. Where the pathogen reduced yields of susceptible isolines, yellow seeds of the isoline resistant to prevalent races of the pathogen contributed from 10 to 33% more seed than would be expected if resistant and susceptible isolines contributed equally to seed yield. The data demonstrate that plants of the resistant isoline were compensating for reduced productivity of the susceptible plants in the blend.
Characterization of Halo Blight Races on Dry Beans in South Africa
Authors: Fourie D.
Published: May 2007

Isolates of the halo blight pathogen Pseudomonas syringae pv. phaseolicola were collected in the bean-producing areas in South Africa from 1991 to 1996. Of the 1,128 isolates collected, 967 were identified as P. syringae pv. phaseolicola. The majority of these isolates were obtained from a wide range of Phaseolus vulgaris cultivars, and the rest from P. coccineus and P. lunatus. Two hundred fifty-five isolates, representative of all the localities and cultivars sampled, were categorized into different races according to their reaction on a set of differential cultivars. Seven races (1, 2, 4, 6, 7, 8, and 9) were identified, with race 8 the most prevalent. Races 1, 2, 6, and 8 were widely distributed through the whole production area, while races 4, 7, and 9 were restricted to one or two localities.
Seed Transmission of Indian Peanut Clump Virus (IPCV) in Peanut and Millets
Authors: Reddy A. S. , Hobbs H. A. , Delfosse P. , Murthy A. K. , Reddy D. V. R.
Published: May 2007

An enzyme-linked immunosorbent assay (ELISA) procedure was developed to test peanut seed for Indian peanut clump virus (IPCV). A double antibody sandwich form of ELISA detected the Hyderabad isolate (IPCV-H) in seed of peanut. Correlation was established between the results from ELISA performed on cotyledons of peanut seed and grow-out tests. Seed transmission in the field-infected peanut plants ranged from 3.5 to 17%, depending on the genotype. The transmission frequency was 48 to 55% in seed collected from plants infected through seed. Because testae of all seed contained viral antigen, their removal was essential for the determination of frequency of seed transmission. Apparently the virus present only in cotyledons and embryo contributed to the seed transmission. For the first time, IPCV-H was shown to be seed transmitted in finger millet (Eleusine coracana), foxtail millet (Setaria italica), and pearl millet (Pennisetum glaucum) at frequencies of 5.2, 9.7, and 0.9%, respectively. Seed transmission was not observed in sorghum (Sorghum bicolor). Significance of seed transmission in millet crops is discussed.
Occurrence of Turnip Yellow Mosaic Virus on Oriental Cruciferous Vegetables in Southern Ontario, Canada
Authors: Stobbs L. W. , Cerkauskas R. F. , Lowery T. , VanDriel L.
Published: May 2007

Turnip yellow mosaic virus (TYMV) has been reported throughout Europe, New Zealand, and Australia. In 1994, this virus was identified in two field plantings of Bok Choi and one planting of Pak Choi (Brassica campestris Chinensis group var. communis) in Durham and Haldimand-Norfolk counties, respectively. In early October, approximately 25% of the plants were infected at each site. Both the striped flea beetle (Phyllotreta striolata (F.)) and the crucifer flea beetle (P. Cruciferae(Goeze)), reported vectors of the virus (1), were present at each site. Infected plants exhibited bright yellow to yellow-green mosaic mottling and often showed chlorotic lesions on the lower leaves. Vein clearing was also seen on several plants. Plants were often coinfected with turnip mosaic virus. Four symptomatic plants were taken from each field site for testing. Spherical virus particles (28 nm) were identified as TYMV by electron microscopy following post-antibody decoration and enzyme-linked immunosorbent assay with the TYMV Agdia test kit. Symptoms were reproduced on both Bok and Pak Choi by mechanical inoculation into healthy plants. Extended host range susceptibility tests with 14 differential hosts were consistent with those reported in the VIDE database (1). This virus, in the presence of the flea beetle vectors, may pose a threat to susceptible traditional cruciferous vegetables grown extensively in this area.

Reference: (1) A. A Brunt et al., eds. Plant Viruses Online: Descriptions and Lists from the VIDE Database. Version: 16th January 1997.
First Report of Moroccan Watermelon Mosaic Potyvirus in Zucchini in Italy
Authors: Roggero P. , Dellavalle G. , Lisa V. , Stravato V. M.
Published: May 2007

Unusual symptoms were observed in summer 1997 in field zucchini of several cultivars grown in central Italy. Symptoms included reduction in growth, severe mosaic, blistering and deformation of leaves, and malformation on fruits. Plants gave negative results in enzyme-linked immunosorbent assay (ELISA) for cucumber mosaic cucumovirus, squash mosaic comovirus, papaya ringspot, zucchini yellow fleck, zucchini yellow mosaic, and watermelon mosaic 2 potyviruses. Positive reactions were obtained in ELISA with a monoclonal antibody that reacts with many potyviruses (from J. Vetten, Braunschweig) and with polyclonal antibodies (Sanofi, France) to Moroccan watermelon mosaic potyvirus (MWMV). Field symptoms were reproduced in zucchini cvs. Genovese and Striato d'Italia by mechanical inoculation of samples from symptomatic field plants. Chenopodium amaranticolor, C. quinoa, and Gomphrena globosa gave local lesions, while Citrullus lanatus cv. Crimson Sweet, Cucumis melo cv. Top Mark, C. metuliferus, C. sativus cvs. Marketer, MM76, and Sweet Slice, and Cucurbita maxima reacted with systemic mosaic. C. melo cv. Doublon formed necrotic local lesions followed by systemic necrosis. No infection occurred in Nicotiana benthamiana, N. clevelandii, N. glutinosa, Phaseolus vulgaris cv. Black Turtle, Pisum sativum cv. Alaska, tobacco White Burley, and Vigna unguiculata. These data are in agreement with the known host range of MWMV. MWMV is a tentative species in the genus potyvirus, widely present in Africa and occasionally found in Spain (1,2). Further spread of this virus in the Mediterranean area will create new problems for commercial cucurbit production and breeding, and for diagnosis.

References: (1) E. Kabelka and R. Grumet. Euphytica 95:237, 1997. (2) N. M. McKern et al. Arch. Virol. 131:467, 1993.
Influence of Low Oxygen Levels in Aeroponics Chambers on Eucalypt Roots Infected withPhytophthora cinnamomi
Authors: Burgess Treena , McComb Jen , Hardy Giles , Colquhoun Ian
Published: May 2007

Aeroponics root chambers were designed to evaluate the influence of low oxygen on disease development in clones of Eucalyptus marginata susceptible or resistant to infection by Phytophthora cinnamomi. Actively growing 7-month-old clones of E. marginata were transferred into the aeroponics chambers, into which a nutrient solution was delivered in a fine spray, providing optimal conditions for root growth. Prior to inoculation by zoospores of P. cinnamomi under normal oxygen, the roots were exposed to four treatments: (i) normal oxygen, approximately 8 mg of O2liter-1; (ii) 6 days of hypoxia, 2 mg of O2liter-1; (iii) anoxic acclimatization 2 days at 2 mg of O2liter-1, 2 days at 1 mg of O2liter-1, 2 days at 0.5 mg of O2liter-1, 2 days at 2 mg of O2liter-1, and 6 h at <0.05 mg of O2liter-1; and (iv) 6 h of anoxia, <0.05 mg of O2liter-1. Root extension during hypoxia was greatly reduced. Lesion development was least for roots exposed to hypoxia and greatest for roots exposed to anoxia for 6 h, suggesting increased resistance of E. marginata to P. cinnamomi following hypoxia.
Behavior of a Wild-Type and Two Mutant Strains of Colletotrichum gloeosporioides f. sp. aeschynomene on Northern Jointvetch in the Field
Authors: Luo Y. , TeBeest D. O.
Published: May 2007

The fungus Colletotrichum gloeosporioides f. sp. aeschynomene causes an anthracnose on Aeschynomene virginica and has been used as a biological control agent to control this weed in the United States. The population dynamics of a wild-type strain (3-1-3) and two mutant strains of 3-1-3 of C. gloeosporioides f. sp. aeschynomene, a benomyl-resistant strain (B21) and nitrate-nonutilizing strain (Nit A), were studied in field tests on northern jointvetch in 1994 and 1995 to determine how the strains interacted on infected plants under field conditions. Plants were co-inoculated with strains 3-1-3 and B21, strains 3-1-3 and Nit A, and strains 3-1-3, B21, and Nit A at equal and unequal initial proportions. Plants were grown and maintained under flooded conditions in small wading pools. In co-inoculation of plants with 3-1-3 and B21 from equal initial proportions, the population of 3-1-3 increased slightly until it reached a proportion of 60 to 70%, whereas the population density of B21 reached 30 to 40% at the end of growing season. From unequal initial proportions, the population density of B21 decreased from 90 to about 50%, whereas the 3-1-3 increased from 10 to 50%. The population density of 3-1-3 increased from an equal initial proportion and was significantly greater than that of Nit A on every sampling time. From unequal initial proportions, the population density of 3-1-3 increased from 10 to 90%, whereas that of Nit A declined. In co-inoculation of plants with the three strains, the population density of 3-1-3 was significantly greater than those of the mutant strains at every sampling time. The proportions of mutant strains within the total population of C. gloeosporioides f. sp. aeschynomene on plants varied according to the test conditions and the number and types of strains co-inoculated.
Natural Occurrence of Microsphaera pulchra and Phyllactinia guttata on Two Cornus Species
Authors: Klein Leigh Ann , Windham Mark T. , Trigiano Robert N.
Published: May 2007

Powdery mildew has become a common foliar disease of Cornus florida and other dogwood species in the eastern United States during the last several years. This study was conducted to determine the identity of powdery mildew fungi on C. florida and C. amomum. Ascocarps of Microsphaera pulchra and Phyllactinia guttata occurred singly and together on both C. florida and C. amomum leaves. M. pulchra ascocarps occurred at a higher density than P. guttata ascocarps on C. florida leaves, whereas P. guttata ascocarps occurred more frequently than M. pulchra ascocarps on C. amomum leaves. Histological studies, however, did not provide supplementary data of infection by the powdery mildew species that occurred less frequently on the leaves of each dogwood species. M. pulchra did not penetrate the cells of C. amomum, and likewise P. guttata did not enter through stomata of C. florida leaves. The presence of ascocarps of both species was not the result of infection of the dogwoods by both pathogens. The ascocarps of M. pulchra probably became airborne and then settled on the C. amomum leaves. Similarly, the ascocarps of P. guttata landed on C. florida leaves. These results emphasize the importance of correct pathogen identification using several criteria such as ascocarp morphology, host-pathogen relationships, distribution of the pathogen, conidial morphology, and histology.
Aphanomyces euteiches Inoculum Potential: A Rolled-Towel Bioassay Suitable for Fine-Textured Soils
Authors: Williams-Woodward J. L. , Pfleger F. L. , Allmaras R. R. , Fritz V. A.
Published: May 2007

A sensitive measure of soil inoculum potential is needed to evaluate field management of common root rot (Aphanomyces euteiches) in peas (Pisum sativum). A modified rolled-towel (RT) bioassay had been proposed to measure soil inoculum potential in fine-textured soils used for pea production in Minnesota. Homogenized soil was used because organic debris containing the inoculum could not be separated by wet sieving. The poor precision prompted an evaluation of procedures to improve this modified RT bioassay. Seed treatment with a 5% solution of sodium hypochlorite before pea seed germination and plant isolation procedures during the RT bioassay preparation/incubation reduced seedborne contamination and seedling loss to less than 5%. Tests conducted with pasteurized soil that was artificially infested with oospores showed the region of the pea taproot 1 to 2 cm below the seed to be more susceptible to infection (33% compared with 15% infected seedlings) than the region 1 to 2 cm above the root tip. A soil volume of 1.0 cm3 increased inoculum potential compared with 0.5 cm3 applied to each seedling but did not influence the random error; the 40-seedling compared with the 20-seedling RT bioassay reduced random error from 18 to 12%. The modified RT bioassay conducted on soil that was artificially infested after steam treatment or without steam treatment showed superior performance when using 40 seedlings compared with 20 seedlings when evaluated for accuracy and precision. Multiple infection theory demonstrated more multiple infections in the RT bioassay with a 0.5 cm3 soil volume applied to each seedling, which shows that soil mass is a factor preventing a higher percentage of infected seedlings. These modifications to the RT bioassay improved the method enough to reduce the random error by one-half compared with using homogenized soil without the proposed modifications.
Characterization of Phytophthora infestans in Wisconsin from 1993 to 1995
Authors: Marshall-Farrar K. D. , McGrath M. , James R. V. , Stevenson W. R.
Published: May 2007

Late blight of potato (Solanum tuberosum), caused by Phytophthora infestans, recently reappeared in Wisconsin and was a significant production problem in 1994. P. infestans isolates collected in Wisconsin from 1993 to 1995 were characterized for the following traits: mating type, sensitivity to metalaxyl, and allozyme genotype for Glucose-6-phosphate isomerase (Gpi). Characterization of these isolates revealed that a new, more aggressive population (A2 mating type, metalaxyl resistant, and Gpi genotype 100/111/122) is displacing the old population (A1 mating type, metalaxyl sensitive, and Gpi genotype 86/100) in Wisconsin.
Isolation of Nectria galligena from Cankers on Sweet Birch
Authors: Anagnostakis Sandra L. , Ferrandino Francis J.
Published: May 2007

The fungus Nectria galligena infects many species of hardwood trees, causing “perennial canker,” “European canker,” or “target canker.” Cultures from ascospores produced in stromata on the cankers have confirmed the pathogen species, but the fungus has rarely been successfully isolated from inside the cankers. Concern for the sweet birch trees affected by this disease in Connecticut prompted us to try isolations, using a method successful in isolating chestnut tree pathogens. Small pieces of cankered bark were stabbed into Granny Smith apples and, after incubation in boxes in the laboratory, pure cultures of N. galligena were easily removed as the pathogen slowly grew out, unchallenged, into the tissue of the apples. This technique will now be used to sample the N. galligena population in the birch populations being studied.
Haustorial Function During Development of Cleistothecia in Blumeria graminis f. sp. tritici
Authors: Götz Monika , Boyle Christine
Published: May 2007

Cleistothecia of Blumeria graminis are a means of survival under adverse conditions as well as a means of sexual reproduction, and are produced by the generative mycelium at the end of the vegetation period. Vital stains and 14C-labeled sucrose were transported from the host (Triticum aestivum) through the haustoria into the generative mycelium. Translocation was intense during the early developmental stage of the generative mycelium. Colonies of later stages with macroscopically visible developing cleistothecia showed reduced staining and labeling. This correlated with an increase in the number as well as the degree of haustorial encasement and papillae formation. Detached mycelia of later developmental stages produced ripe cleistothecia containing ascospores of high germination rates in vitro, but early stages with microscopically small primordia only developed dark fruit bodies that did not produce ascospores. The data indicate that nutrition supply by the host is essential at the early stages of the generative mildew mycelium. The resulting metabolites are mainly stored within the hyphae. At later developmental stages, the generative mycelium progressively becomes more independent of nutrition supply by the host, providing its own metabolites for the growing fruit bodies.
Biological Species of Armillaria in Japan
Authors: Ota Y. , Matsushita N. , Nagasawa E. , Terashita T. , Fukuda K. , Suzuki K.
Published: May 2007

Pairing tests with isolates of Armillaria in culture were used to identify species of Armillaria and their distribution throughout Japan. The existence of 10 intersterile groups of Armillaria was determined by pairing haploid single spore isolates obtained from 20 basidiocarps from a wide geographic distribution in Japan. Two to four haploid tester isolates from each intersterile group were then paired to biological and morphological species with haploid tester isolates from Europe and North America identified in previous studies. Japanese haploid tester isolates were then paired with 190 haploid or diploid isolates and compatibility reactions were used to identify these to species. Of the 10 intersterile groups identified in Japan, 7 were authenticated as A. gallica, A. nabsnona, A. ostoyae, A. cepistipes, A. mellea, A. sinapina, or A. tabescens. Three of the groups were not compatible with any of the tester species. The distribution and host relationships of the Japanese biological species are also discussed.
Efficacy of Fungicide Treatments for Control of Common Rust and Northern Leaf Spot in Hybrid Corn Seed Production
Authors: Wegulo S. N. , Rivera-C J. M. , Martinson C. A. , Nutter F. W.
Published: May 2007

Field experiments were conducted during the 1992 and 1993 growing seasons in 13 commercial fields in Iowa to assess the efficacy of foliar applications of fungicides to seed corn for control of common rust, Puccinia sorghi, and northern leaf spot, Bipolaris zeicola. Chlorothalonil, mancozeb, and/or propiconazole sprays were initiated at growth stage (GS) 2.5, GS 4.0, or approximately 2 weeks before detasseling, and applications were repeated up to five times at various growth stages. The majority of fungicide treatments resulted in an increase in salable seed units (1 unit = 80,000 seeds) compared to untreated control treatments. The greatest increase in salable seed occurred in the large and medium seed size units. Although disease severity on the final assessment date in both years and standardized area under the disease progress curve in 1993 were significantly higher (P ≤ 0.05) in untreated control plots than in fungicide-treated plots in all experiments, the best disease control was provided by 5 applications of chlorothalonil or 2 to 4 applications of chlorothalonil, mancozeb, or propiconazole initiated on the first spray date.
Interplanting Wheat Is Not an Effective Postplant Management Tactic for Criconemella xenoplax in Peach Production
Authors: Nyczepir A. P. , Bertrand P. F. , Parker M. L. , Meyer J. R. , Zehr E. I.
Published: May 2007

In two orchard experiments, interplanting wheat (Triticum aestivum cv. Stacy) around either newly planted or 4-year-old well-established peach trees did not suppress (P ≤ 0.05) the population density of the ring nematode, Criconemella xenoplax, after 3 years. Furthermore, inter-planting wheat around newly planted trees reduced tree growth, perhaps the result of competition for water and (or) nutrients. Wheat root exudate was not as attractive to C. xenoplax as peach root exudate, but wheat root exudate did not repel the nematode either. Stacy wheat appeared to be more beneficial as a preplant rather than as a postplant ground cover management tool for suppressing the population density of C. xenoplax.