Bacterial Wilt of Solanaceae Caused by Ralstonia solanacearum Race 1 Biovar 3 in Mali.

Ralstonia solanacearum (Smith) Yabuuchi et al. causes bacterial wilt worldwide on a wide range of plant species. In Mali, the disease is commonly found on potato (Solanum tuberosum L.), tomato (Lycopersicon esculentum var. esculentum L.), pepper (Capsicum annuum L.), eggplant (Solanum melongena L.), tobacco (Nicotiana tabacum L.), and peanut (Arachis hypogaea L.). Determination of race and biovar is critical for development of potato seed certification programs for management of the disease. Isolates (25) of R. solanacearum were obtained from wilting potato, pepper, eggplant, tobacco, and tomato plants collected from fields near Baguineda, Sonityeni, Sotuba, Sikasso, and Kolikoro. Isolations were made from bacterial streaming by dilution plating on triphenyl tetrazolium chloride medium (TZC) (2). Characteristic colonies were selected and identified by ELISA or Immunostrips (Pathoscreen Rs, Agdia Inc., Elkhart, IN). These isolates were used in host range studies and hypersensitivity (HR) tests on tobacco (cv. xanthi) (3) and tested for their ability to produce acids on Ayers basal media amended with disaccharide and hexose alcohol carbon sources (1). These isolates caused characteristic wilt 40 days postinoculation on greenhouse-grown tobacco (cv. Xanthi), peanut (cv. 4610), and tomato (cv. Roma VF) plants when stems of five plants of each host were syringe inoculated with 0.1 ml of a 1 × 109 CFU/ml of bacteria. Plants inoculated with sterile distilled water remained symptomless and R. solanacearum was reisolated from infected plants on TZC and identified with Immunostrips. All HR tests were negative. Infection of peanut, tobacco, and tomato and the results of the HR tests indicated that all isolates were Race 1 and no significant variation was noted between isolates. Acid was produced from the hexose alcohols: mannitol, sorbitol, and dulcitol; and the disaccharides: cellobiose, lactose, and maltose. This indicated that all isolates were biovar 3, the same as a known Race 1 strain from tobacco (MSU Plant Pathology teaching collection) (1). To assess relative distribution of R. solanacearum, 20 soil samples collected from potato fields in the vicinity of Baguineda, Kati, Koulikoro, and Sikasso were placed in pots (30 × 25 cm) under shade cloth at the IER Station in Sotuba and planted with 30-day-old tobacco plants. After 90 days, infected plants (35 to 100% infection) were found in all soils. Infected plants exhibited classical wilt symptoms and tested positive for R. solanacearum infections as confirmed by Immunostrip tests. Six of nine surface water samples taken near potato fields in Baguineda, Sikasso, Mopti, and Koulikoro tested positive for the presence of R. solanacearum by an Agdia Inc. enrichment kit and ELISA. A weed, Commelina forskalaei (Vahl), collected by Farako creek near Sikasso tested positive in the Immunostrip test even though no symptoms were obvious. No attempt was made to characterize the race, biovar, or phylotype of the soil, water, and weed isolates. To our knowledge, this is the first time that the race and biovar of R. solanacearum from Mali has been reported and the wide distribution of this pathogen in Malian soils and surface water has been demonstrated. It is significant that we did not detect Race 3 biovar 2, which is subject to quarantine and biosecurity regulations. References: (1) A. C. Hayward. J. Bacteriol. 27:265, 1964. (2) A. Kelman. Phytopathology 44:693, 1954. (3) J. Lozano and L. Sequeira. Phytopathology 60:833, 1970.

Comparison of Muscodor albus Volatiles with a Biorational Mixture for Control of Seedling Diseases of Sugar Beet and Root-Knot Nematode on Tomato.

A biorational synthetic mixture of organic components mimicking key antimicrobial gases produced by Muscodor albus was equivalent to the use of live M. albus for control of seedling diseases of sugar beet (Beta vulgaris) caused by Pythium ultimum, Rhizoctonia solani AG 2-2, and Aphanomyces cochlioides. The biorational mixture provided better control than the live M. albus formulation for control of root-knot nematode, Meloidogyne incognita, on tomato (Lycopersicon esculentum). The biorational mixture provided control of damping-off equal to a starch-based formulation of the live fungus for all three sugar beet pathogens, and significantly reduced the number of root-knot galls on tomato roots compared with a barley-based formulation. Rate studies with the biorational mixture showed that 2 and 0.75 µl/cm3 of soil were required to provide optimal control of Rhizoctonia and Pythium damping-off of sugar beet, respectively. Five microliters of biorational mixture per milliliter of water was required for 100% mortality in 24 h for Meloidogyne incognita in in vitro studies. In in vivo studies, 1.67 µl of the biorational mixture/cm3 of sand resulted in fewer root-knot galls than a Muscodor albus infested ground barley formulation applied at 5 g/liter of sand.

Beet Root-Rot Inducing Isolates of Fusarium oxysporum from Colorado and Montana.

A root-tip rot of sugar beet (Beta vulgaris L.) caused by Fusarium oxysporum Schlecht. emend. Snyd. & Hans. has been reported from Texas (2). This disease is typified by yellowing of the foliage, vascular discoloration, and a rot of the root tip. During 2002 and 2003, sugar beet samples from several fields in Colorado and Montana, some with tip rot symptoms, were received by the authors. Isolations were made from the root vascular tissue and tissue adjacent to the rot in Colorado and from the rot tissue in Montana. Isolates of Fusarium were obtained and identified as Fusarium oxysporum. At the ARS laboratory in Colorado, F. oxysporum isolates were tested for pathogenicity by dipping roots of 5-week-old sugar beet plants (FC716) in a suspension of 104 spores per ml for 8 min, 10 plants per isolate. One known isolate of F. oxysporum f. sp. betae that causes Fusarium yellows, Fob13, was used for comparison. For a negative control, plants were dipped in sterile water. Beets were planted in Cone-Tainers (3.8 cm in diameter × 21 cm) containing pasteurized potting mix. Plants were placed in a greenhouse at 24 to 27°C and fertilized with 15-30-15 fertilizer every 2 weeks to avoid chlorosis from nutrient deficiency. Plants were rated weekly for foliar symptoms for 6 weeks with a Fusarium yellows rating scale of 0 to 4, in which 0 = no disease and 4 = complete plant death (1). After the final rating, plants were removed from the soil and the taproot was examined for rot symptoms. Root segments were surface disinfested with 0.5% sodium hypochlorite and cultured on potato dextrose agar to confirm the presence of the pathogen. The experiment was done twice. Six of ten F. oxysporum isolates tested caused root vascular discoloration and foliar symptoms, including interveinal yellowing and wilting, of inoculated plants. A rot of the root tip was observed on the roots of plants inoculated with three of the six pathogenic isolates. Isolate Fob13 caused only vascular discoloration and foliar symptoms with no rot. Similar experiments were done in Montana with the exception that 3-week-old plants (cv. Monohikari) were used and planted in 10-cm plastic pots with five seedlings per pot. Inoculum levels were 105 spores per ml of F. oxysporum f. sp. betae (isolate 216C) or tip rot isolates (3 isolates), and the experiments were terminated 4 weeks after planting. The root rot isolates caused foliar symptoms, vascular discoloration, and root rot similar to that seen in the field, whereas isolate 216C caused only foliar wilt symptoms and vascular discoloration. Isolations from inoculated plants in Colorado and Montana resulted in F. oxysporum cultures similar to those used in inoculation. To our knowledge, this is the first report of F. oxysporum causing root rot of sugar beet outside of Texas. References: (1) L. E. Hanson and A. L. J. Hill. Sugarbeet Res. 41:163, 2004. (2) R. M. Harveson and C. M. Rush. Plant Dis. 82:1039, 1998.

The role of bacillus-based biological control agents in integrated pest management systems: plant diseases.

ABSTRACT Bacillus-based biological control agents (BCAs) have great potential in integrated pest management (IPM) systems; however, relatively little work has been published on integration with other IPM management tools. Unfortunately, most research has focused on BCAs as alternatives to synthetic chemical fungicides or bactericides and not as part of an integrated management system. IPM has had many definitions and this review will use the national coalition for IPM definition: "A sustainable approach to managing pests by combining biological, cultural, physical and chemical tools in a way that minimizes economic, health and environmental risks." This review will examine the integrated use of Bacillus-based BCAs with disease management tools, including resistant cultivars, fungicides or bactericides, or other BCAs. This integration is important because the consistency and degree of disease control by Bacillus-based BCAs is rarely equal to the control afforded by the best fungicides or bactericides. In theory, integration of several tools brings stability to disease management programs. Integration of BCAs with other disease management tools often provides broader crop adaptation and both more efficacious and consistent levels of disease control. This review will also discuss the use of Bacillus-based BCAs in fungicide resistance management. Work with Bacillus thuringiensis and insect pest management is the exception to the relative paucity of reports but will not be the focus of this review.

Mycofumigation with Muscodor albus and Muscodor roseus for Control of Seedling Diseases of Sugar Beet and Verticillium Wilt of Eggplant.

Mycofumigation is the use of antimicrobial volatiles produced by fungi such as Muscodor albusitalic and M. roseus for the control of other organisms. Sugar beet (Beta vulgaris L.) stand establishment was increased and disease severity decreased by mycofumigation with M. roseus and M. albus in autoclaved soil infested with Rhizoctonia solani, Pythium ultimum, or Aphanomyces cochlioides. Eggplant seedlings (Solanum melongena L.) transplanted into autoclaved soil infested with Verticillium dahliae and mycofumigated with M. albus and M. roseus had significantly less disease (P < 0.05) after 4 and 5 weeks compared with nonmycofumigated Verticillium-infested soil. The effect of formulation on efficacy of mycofumigation with M. roseus was tested using potato dextrose agar strips, alginate capsules, ground barley, pesta granules, and stabileze granules. The stabileze and ground barley formulations of M. roseus resulted in the best control of P. ultimum damping-off. The best control of A. cochlioides damping-off was with the stabileze formulation, and the stabileze, ground barley, and agar strip formulations provided similar control of R. solani damping-off. In soil infested with P. ultimum, mycofumigation with M. albus stabileze formulation resulted in stand establishment similar to that in the autoclaved soil. Mycofumigation was ineffective in controlling Fusarium wilt of sugar beet. Neither M. albus nor M. roseus affected sugar beet or eggplant growth or appearance except in the stabileze formulation, where stunting was noticed. Mycofumigation with M. albus and M. roseus shows promise for control of soilborne diseases caused by P. ultimum, A. cochlioides, R. solani, and V. dahliae.

Biological Control of Pseudomonas syringae pv. syringae, the Causal Agent of Basal Kernel Blight of Barley, by Antagonistic Pantoea agglomerans.

ABSTRACT Strains of Pantoea agglomerans (synanamorph Erwinia herbicola) suppressed the development of basal kernel blight of barley, caused by Pseudomonas syringae pv. syringae, when applied to heads prior to the Pseudomonas syringae pv. syringae infection window at the soft dough stage of kernel development. Field experiments in 1994 and 1995 revealed 45 to 74% kernel blight disease reduction, whereas glasshouse studies resulted in 50 to 100% disease control depending on the isolate used and barley cultivar screened. The efficacy of biocontrol strains was affected by time and rate of application. Percentage of kernels infected decreased significantly when P. agglomerans was applied before pathogen inoculation, but not when coinoculated. A single P. agglomerans application 3 days prior to the pathogen inoculation was sufficient to provide control since populations of about 10(7) CFU per kernel were established consistently, while Pseudomonas syringae pv. syringae populations dropped 100-fold to 2.0 x 10(4) CFU per kernel. An application to the flag leaf at EC 49 (before heading) also reduced kernel infection percentages significantly. Basal blight decreased with increasing concentrations (10(3) to 10(7) CFU/ml) of P. agglomerans, with 10(7) CFU/ml providing the best control. For long-term preservation and marketability, the survival of bacterial antagonists in several wettable powder formulations was tested. Over all formulations tested, the survival declined between 10- to >100-fold over a period of 1.5 years (r = -0.7; P = 0.000). Although not significant, storage of most formulations at 4 degrees C was better for viability (90 to 93% survival) than was storage at 22 degrees C (73 to 79%). However, long-term preservation had no adverse effect on biocontrol efficacy.

Role of plant pathology in integrated pest management.

Integrated Pest Management (IPM) is a paradigm that is widely adopted by all pest control disciplines but whose early definitions and philosophical basis belong to entomologists. Plant pathology research and extension work has historically emphasized integration of several control strategies and fits both historical and modern definitions of IPM. While the term IPM has been used only sparingly in the phytopathology literature, the integrated disease management strategies emphasized are now considered to be at the forefront of ecologically based or biointensive pest management. While IPM is broadly endorsed by crop protection disciplines, farmers, other agriculturalists, and consumers, the potential for Integrated Pest Management has not been fully realized. Most IPM programs reflect a package of tools and decision aids for individual crop insect, weed, nematode, and plant disease management. IPM programs that integrate all types of pests with the agroecosystem, crop growth and loss models still await the formation of interdisciplinary teams focusing on growers needs. Lack of funding for both discipline and interdisciplinary developmental research and implementation is responsible for the paucity of comprehensive IPM programs for the majority of the U.S. crop acreage. This review explores the origins and evolution of the IPM paradigm and reviews efforts to achieve the body of knowledge and implementation structure to achieve IPM's full potential.

Acute aflatoxicosis in feeder pigs, resulting from improper storage of corn.

Aflatoxicosis was diagnosed in 600 feeder pigs, of which 400 died, 150 were destroyed, and 50 were marketed. The pigs were exposed to 2,500 to 3,500 micrograms of aflatoxins/kg of feed. Drought-stressed damaged corn infected with Aspergillus flavus was stored under ambient conditions in a glass-lined silo, and this storage environment provided conditions that favored rapid fungal growth and mycotoxin production.

Effects of Temperature on Development of Heterodera glycines on Glycine max and Phaseolus vulgaris.

Soybean cyst nematode resistant 'Fayette' and susceptible 'Williams 79' soybeans (Glycine max) and resistant 'WIS (RRR) 36' and susceptible 'Eagle' snap beans (Phaseolus vulgaris) were used in determining the effects of host and temperature on the development, female production, sex ratios, and host response to Heterodera glycines. Temperatures were maintained constant at 16, 20, 24, 28, and 32 C using water-filled tanks. The most rapid development and greatest female production occurred between 20 and 28 C. The equation DS = 5(10)x(2)y(2) - 3(10)x(2)y - 2.8(10(3))x(2) - 1.94(10(2))y(2) + 0.4288x + 1.0220y - 12.7185, where DS = developmental stage, X = time, and Y = temperature, predicted the developmental stage of the nematode and accounted for 84% of the variation. Male : female ratios did not differ within this range and were generally less than one. At all temperatures the resistant soybean produced the greatest number of necrotic responses to H. glycines infection, followed by the resistant snap bean. The susceptible soybean and snap bean produced the fewest necrotic responses.