Multiplication ofPseudomonas solanacearum in resistant potato plants and the establishment of latent infections

When 1-mo-old plants of a wilt-resistant clone ofSolanum phureja (1386.15) were stem-inoculated with three strains ofPseudomonas solanacearum (K60, S123, and S206), the bacteria multiplied rapidly at the point of inoculation and then moved in the vascular system to other parts of the stem. Resistant plants showed a remarkable ability to support relatively high populations of the bacterium in the absence of disease symptoms. Although multiplication in this resistant clone was substantially less than in susceptible Russet Burbank potato plants, large numbers of bacteria (up to 624 × 10⁴ cells of K60 per 5-cm stem segment) reached the base of the stem of plants maintained at high temperature (28°C) for 20 days after stem inoculation. From the base of the stem, the bacteria moved rapidly into the roots and tubers. Strains ofP. solanacearum differed in their ability to cause latent tuber infection in different resistant potato clones. When 11S.phureja ×S. tuberosum hybrids were stem-inoculated, maintained at 28°C for 3 wk and then grown to maturity at 20°C., most of the clones yielded tubers infected by one or more strains. The race 1 strain (K60) was the most infectious; 53.8% of all tubers harvested from all plants inoculated with this isolate carried latent infections. Because one clone (BR 53.1) never yielded infected tubers, there appear to be genetic factors which may be useful in breeding programs aimed at eliminating latent tuber infection.     

Factors affecting early screening of tomatoes for monogenic and polygenic resistance to Fusarium wilt

Tomatoes (cv. Bari-RVF-SMD) monogenically (I gene) resistant to Fusarium wilt (Fusarium oxysporum f.sp. lycopersici) were not affected by inoculum dilutions (10¹, 10³ and 10⁶ conidia/ml), temperature regimes (22°C and 26°C) and plant age (two and four leaves), whereas the phenotypic expression of susceptible and polygenically resistant tomatoes (cvs Rutgers and Marglobe) was conditioned by these factors. Rutgers tomatoes were found to possess a higher level of resistance than Marglobe. Early screening (33 days after inoculation) of resistant Rutgers plants could be made on plants inoculated at the two-leaf stage with an inoculum dilution of 10³ conidia/ml and grown at 22°C or 26°C. Thirty-three days after inoculation, Marglobe tomatoes inoculated at the two- and four-leaf stages with inoculum dilutions of 10³ and 10⁶ conidia/ml and grown at 22°C or 26°C proved to be susceptible. The following first-order interactions were found to be statistically significant: cultivar × inoculum dilution, cultivar × temperature, cultivar × plant age, inoculum dilution × temperature and inoculum dilution × plant age.     

Resistance toPseudomonas solanacearum in potato: Infectivity titrations in relation to multiplication and spread of the pathogen

When several wilt-resistant potato clones were tested against a highly virulent strain from Mexico (No. 276) by standard stem inoculation methods, only one clone ofSolanum phureja was resistant. When different inoculum concentrations were introduced quantitatively for infectivity titrations, however, different levels of resistance were clearly defined among clones previously rated as susceptible. Linear regression was used to estimate the ED₅₀ values (dosage required to wilt 50% of the population) for each of seven clones. These values ranged from 3 and 100 colony-forming units (CFU) for Katahdin and Russet Burbank, respectively, to 2.1 x 10⁶ CFU for S.phureja clone 1386.15. The distribution of bacteria in stems of Russet Burbank plants inoculated with the compatible strains 276 and K-60 and the incompatible strains B1 and S-210 was very different. In all cases, incompatible bacteria were not detected 10 cm above the inoculation point in the stem, even by 12 days after inoculation, whereas compatible strains multiplied rapidly at this site by 6 days. At the inoculation site and at sites immediately adjacent to it, however, incompatible bacteria attained populations that only differed by one order of magnitude from those of compatible bacteria. Similar results were obtained when a resistant clone (MS 118.24) was inoculated with the virulent strain K-60. Thus, resistance was characterized both by reduced acropetal spread and by tolerance to large numbers of the bacterium.     

Two Bacillus amyloliquefaciens strains isolated using the competitive tomato root enrichment method and their effects on suppressing Ralstonia solanacearum and promoting tomato plant growth

Two tomato root colonizing strains, Bacillus amyloliquefacien CM-2 and T-5, were isolated after the enrichment procedure on the roots of tomato seedlings, and evaluated for their antagonistic activities against pathogenic Ralstonia solanacearum (RS) in vitro. Three inoculation methods were used to test their biocontrol efficacy and growth promotion effects in greenhouse based on their colonization ability in rhizosphere soil. Both CM-2 and T-5 strains showed strong biocontrol and growth promotion effects on tomato seedlings. The best biocontrol efficacy was obtained by treating both seedlings and soils with the biocontrol agents. In comparison to the control, the disease incidence was reduced by 70.1 and 79.4% for CM-2 and T-5, respectively. The numbers of colony-forming units of RS in rhizosphere soil were significantly (P < 0.05) decreased as compared to the control. The density of both strains in the rhizosphere soils remained at a high level (≥10⁷ CFU/g) during a five-week period. Both strains were recovered from the interior of the stems and roots of plants. They showed positive reactions for ammoina, indole acetic acid and siderophores production, and phosphate solubilizing activity. Our data proved the potential of isolated strains for the biocontrol of tomato bacterial wilt.     

Evaluation of an avirulent strain ofPseudomonas solanacearum for biological control of bacterial wilt of potato

An avirulent strain ofPseudomonas solanacearum, B82, was tested for its ability to protect the potato cultivar, Ontario, from bacterial wilt caused by virulent strains of this bacterium. Strain B82 was not antagonistic to 124 virulent strains ofP. solanacearum and was not bacteriocinogenic. When potato seedpieces were soaked for 5 hr in suspensions of B82 (10⁸ to 10⁹ cfu/ml), reduction in disease severity (up to 50%) was noted in some experiments. The treated plants, grown in the greenhouse or growth room for 4–5 wk, were challenged by stem inoculation, soil drenching, or root-to-root infection with virulent strains (276 or Br5) of the bacterium. Protection was not obtained consistently, however, and much of the variability could be attributed to differences in ambient temperature and light conditions in the greenhouse between experiments. In general, high ambient temperatures and/or reduced sunlight resulted in no protection. Protection appeared to depend on the ability of strain B82 to multiply in the vascular system in the crown region and to colonize the rhizosphere of treated plants. Soil temperatures above 24 C affected the ability of strain B82 to survive in the rhizosphere. The close dependence of protection on environmental conditions suggests that this method of control may not be practical under field conditions.     

Winter cover crops influence Amaranthus palmeri establishment

Winter cover crops were evaluated for their effect on Amaranthus palmeri establishment and growth in cotton production. Cover crops examined included rye and four winter legumes: narrow-leaf lupine, crimson clover, Austrian winter pea, and cahaba vetch. Each legume was evaluated alone and in a mixture with rye. Cover crop biomass in monoculture was greatest for rye and lupine (>6750 kg ha⁻¹), while clover, pea, and vetch were less and ranged from 2810 to 4610 kg ha⁻¹. Cover crop biomass was more than doubled when rye was mixed with clover or vetch relative to the legume monoculture. In early-June, A. palmeri densities were 46 seedlings m⁻² in the non-disturbed areas between cotton rows in the fallow, while populations were <4 seedlings m⁻² with rolled vetch or pea and 18 and 29 seedlings m⁻² in rolled clover and lupine. Rye and legume mixtures reduced A. palmeri densities to <3 seedlings m⁻², while rye monocultures had 8 seedlings m⁻². There were no differences in A. palmeri densities (≥144 plants m⁻²) in the cotton row among cover crop treatments. By late-June, rye and winter pea controlled A. palmeri in the row middle >80% relative to the non-cover crop fallow treatment, while control from clover, vetch and lupine ranged from 64 to 70%. The relationship between A. palmeri control in between cotton rows and cover crop biomass was described by a log-logistic regression model with 4530 kg ha⁻¹ providing median weed control (Bio₅₀); predicted A. palmeri control was 25, 50, and 75% from 2950, 4900, and 8600 kg ha⁻¹ cover crop biomass, respectively. However, A. palmeri plants in the cotton rows prevented yield production in the absence of herbicides. Where A. palmeri was controlled with herbicides, the highest yields occurred following rye, with lower yields following lupin/rye mixture and treatments including pea. Management of herbicide resistant weed species requires diverse management tactics; this may include high-biomass cover crops to reduce weed establishment between crop rows. However, greater research effort is needed to devise weed management options for the crop row that do not rely exclusively on the diminishing array of herbicide tools.     

A simple and efficient method to assess susceptibility of potato to stem rot byErwinia carotovora subspecies

Limited development of blackleg resistant potato cultivars has been ascribed to the lack of an effective and reliable test for large scale blackleg resistance screening. A method using leaf petioles was developed for assessing susceptibility of potato stems to blackleg pathogens (Erwinia carotovora subspeciesatroseptica andE. c. subspeciescarotovora). Fifty grams of sterile autoclaved silica sand in Magenta jars (GA-7 vessel, Magenta Corp., Chicago, Illinois) was drenched with bacterial suspension, (17 ml, 2.6 × 10 to 2.6 × 10⁷ cfu/ml) and freshly cut petioles from 5 to 6 week-old plants were inserted to about 5 mm into the sand. The Magenta jars with lids closed were kept on a laboratory bench (20 ±2 C, 16 hours light). The arrangement provided near ideal post-inoculation incubation environment of high humidity for pathogen multiplication and rot development in the petioles. Length of rot was recorded 72 hours after inoculation. Linear regression of rot development on inoculum concentration had R² ≥ 0.80. The petioles inoculated and incubated by this method produced measurable rot lesions with a bacterial concentration as low as 2.6 × 10⁴ cfu/ml and differentiated between the resistant cultivar Russet Burbank and the susceptible cultivar Sangre at all the inoculum concentrations used. Furthermore, susceptibility ranking of five cultivars obtained by this method agreed in general with their reported field reactions. The method is simple and sensitive, and could be used for large scale screening for stem rot resistance in wildSolanum species and early generation breeding populations.     

An <Emphasis Type="Italic">In Vitro</Emphasis> Assay Method for Resistance to Bacterial Wilt (<Emphasis Type="Italic">Ralstonia solanacearum</Emphasis>) in Potato

To develop an in vitro assay method for bacterial wilt resistance in potato, resistant and susceptible standard genotypes were grown in vitro, and different conditions of inoculation with Ralstonia solanacearum phylotype I/biovar 4 were examined. The optimal condition was the inoculation of 6–8 leaf stage plants with a bacterial concentration of 10² CFU ml^?1 and an incubation temperature of 28 °C. Evaluation of stem wilting was more reliable than that of leaf wilting. Using this method, nine genotypes with different resistance levels in the field were evaluated. Lower disease indices were obtained for genotypes with high resistance levels in the field, suggesting that this assay is useful for evaluating bacterial wilt resistance in a controlled environment.     

Infection and decontamination of citrus canker-inoculated leaf surfaces

Citrus canker (Xanthomonas citri subsp. citri, Xcc) is now considered endemic in Florida and continues to spread. Various surfaces, including plant material, personnel and equipment can become contaminated. Decontamination is practiced in both disease-endemic and disease-free areas to reduce the risk of bacterial spread by man or machinery. We used grapefruit leaf surfaces to explore the efficacy of a commonly used personnel sprayer system applying a quaternary amine decontaminant. In three experiments, plants in flush (leaves ¾ expanded) were inoculated (∼10⁵ CFU ml⁻¹). Immediately after inoculation, plants were passed through the sprayers 0, 1, 2, 3, or 6 times. Leaves were sampled at 0.5, 10 and 20 min after decontamination and tested for viable Xcc by dilution plating. There was a large and rapid decline in the quantity of live bacteria with one pass through the decontamination sprayer (>80% decrease in CFU ml⁻¹), and multiple sprays (2-6) resulted in up to 100% mortality of surface Xcc. Presumably more thorough coverage with multiple sprays killed remnant bacteria, although the first spray invariably caused the highest proportion of population mortality. The effect of the decontaminant spray was immediate (within 0.5 min only 3-11% of surface bacteria survived, and by 20 min <1-3% survived). Based on these results, use of a personnel sprayer with a quaternary amine compound is highly effective for reducing surface inoculum. A single spray kills a high proportion of the population, but multiple sprays increase mortality of Xcc. All the Xcc-inoculated plants subsequently developed symptoms of citrus canker. No significant difference in incidence or severity of grapefruit leaf infection was detected among decontamination treatments or compared to the untreated control. This finding indicates that infection occurred at, or very soon after, inoculation, and that Xcc was in protected sites inside the leaf before exposure to the decontaminant spray.     

Evidence of <Emphasis Type="Italic">Potato virus Y</Emphasis> Spread through Post-Emergence Management Practices in Commercial Potato Fields

Potato virus Y (PVY) transmission was studied in six commercial potato fields in 2015 and 2016 in New Brunswick, Canada. Plants emerged from PVY-positive tubers, or PVY-free plants that were artificially inoculated with PVY shortly after emergence, were used as PVY inoculum plants in the study. In all trials, equal numbers of PVY inoculum plants from each of three strains common in the region, PVY^O, PVY^N:O and PVY^NTN, were used. PVY inoculated into tractor-traffic rows showed 2 to 7 times as much PVY spread to previously virus-free plants by the end of the season (up to 48.5% in one tractor row, compared to a maximum of 16.3% in a distant control row unaffected by tractor traffic). Evidence supporting a hypothesis that tractor traffic enhances PVY transmission through aphid disturbance was observed by PVY spread in both directions along the rows, not biased in the direction of tractor travel, and that the ratio of spread of the three strains was nearly indentical in control and tractor rows. However, the lack of spread to immediately adjacent rows, and statistically significant spatial pattern matching the circumference of tractor wheels specific to each field support the hypothesis that direct mechanical transmission of wounded plant sap could also be a factor in the enhanced PVY transmission.     

Evaluation of a mass inoculation method of potatoes withPseudomonas solanacearum

Wounding of potato stems by the application of clean sand at a 45° angle at 550 kPa pressure followed by a spray-mist ofPseudomonas solanacearum proved to be the most reliable method of rapidly inoculating a large quantity of potato plants to incite bacterial wilt in the field. The technique was 100% efficient (320/320) and it was estimated that 10,000 plants/hr could be inoculated by using this method. Because of its hygroscopic nature, sand coated withP. solanacearum created too many mechanical problems to be of practical value for field use even though the amount of wilt after 21 days was not significantly different from that of the best treatment. In addition, viability of inoculum as a bacterial suspension in water was greater than as coated sand.     

Effect of inoculum dose and preparation,strain variation,and plant growth conditions on the eggplant assay for bacterial ring rot

Quantitative differences among strains ofCorynebacterium sepedonicum (Spieck. and Kotth.) Skapt. and Burkh. (=Clavibacter michiganense subsp.sepedonicum) were distinguished in eggplant (Solanum melongena L. ‘Black Beauty’) bioassays with a simple leaf axil inoculation technique. Latent period of infection (time from inoculation to first appearance of symptoms) varied inversely with inoculum dose. Latent period of infection varied significantly among strains ofC. sepedonicum. Symptoms developed more rapidly in plants grown under controlled conditions in a growth chamber than those grown in a greenhouse. Plants treated with inoculum prepared from broth cultures exhibited symptoms more rapidly than those treated with inoculum grown on agar.     

Row spacing and weed control timing affect yield of aerobic rice

Field experiments were conducted during the wet season of 2009 and dry season of 2010 to determine the effects of row spacing and timing of weed control on weed growth and yield of aerobic rice. Ten weed management treatments were used to identify critical periods of weed competition with aerobic rice grown in three different row spacings (15-cm, 30-cm, and as paired rows 10-20-10-cm). Dominant weed species during both growing seasons were Rottboellia cochinchinensis, Digitaria ciliaris, Echinochloa colona, and Eleusine indica. Rice grown in 30-cm rows had greater weed biomass and less grain yield than in 15-cm and 10-20-10-cm rows; weed growth and grain yields were similar between 15-cm and 10-20-10-cm rows. Rice yields in the wet season ranged from 170 kg ha⁻¹ where weeds were not controlled throughout the crop duration to 2940 kg ha⁻¹ in weed-free treatment, indicating a 94% yield loss with uncontrolled weed growth. Similarly in the dry season, plots with no weed control (140 kg ha⁻¹) compared to weed-free plots (3640 kg ha⁻¹) indicate a 96% yield loss with no weed control. Gompertz and logistic equations were fitted to yield data resulting from increasing durations of weed control and weed interference, respectively. Critical periods for weed control in the wet season, to obtain 95% of a weed-free yield, were estimated as between 18 and 52 days after sowing (DAS) for crops in rows at 15-cm, 20-51 DAS at 10-20-10-cm, and 15-58 DAS at 30-cm. These intervals in the dry season were 17-56 DAS for crops in rows at 15-cm and 17-60 DAS at 10-20-10-cm and 15-64 DAS at 30-cm. Durations of the critical periods in the wet season were 31 days at 10-20-10-cm, 34 days at 15-cm and 43 days at 30-cm, while in the dry season, these were 43 days at 10-20-10-cm, 39 days at 15-cm and 49 days at 30-cm. In both seasons, crops in the wider spacing (30-cm) were vulnerable to weed competition for the longest period. The information gained from this study suggests that the aerobic rice yields better in 15-cm rows and 10-20-10-cm arrangements than in 30-cm rows and there is very little benefit of weed control beyond 8 weeks after sowing.     

The expression of resistance to the white potato cyst nematode (Globodera pallida) by individual potato seedlings under different inoculation treatments

Summary The resistance toGlobodera pallida of individual potato seedlings from three progenies derived fromSolanum tuberosum ssp.andigena CPC 2802 was assessed using three inoculation treatments. Plants grown from tubers from the seedlings were used to reassess resistance. All the seedling test inoculation treatments over-estimated the proportion of clones classified as resistant compared to the results from tuber-grown plants. However, the mean relative resistance of progenies estimated by both tests showed good agreement, and it is suggested that seedlings are best used for assessing the resistance of progenies of crosses to identify promising combinations rather than individual clones.     

Survival of south african strains of biovar 2 and biovar 3 ofPseudomonas solanacearum in the roots and stems of weeds

Summary South African strains of biovar 2 and biovar 3 ofPseudomonas solanacearum were compared for their ability to survive in the roots and stems of ten weed species. After artificial inoculation with a biovar 2 strain none of the weed species developed wilt symptoms, but the pathogen was isolated from one species,Physalis angulata L. Using inoculum of a biovar 3 strain, two of the weed species developed wilt symptoms (Datura stramonium L.,Solanum nigrum L.), and the pathogen was isolated from four species,Eragrostis curvula, Amaranthus hybridus L.,Datura stramonium L. andSolanum nigrum.     

Latent infection of potato tubers byPseudomonas solanacearum

Strains ofPseudomonas solanacearum differed in their ability to infect tubers of different resistant potato clones grown in infested soil. When eight resistant clones (Solanum phureja orS.phureja ×S. tuberosum hybrids) were grown at 24–28°C in soil infested with a race 1 or a race 3 strain of the bacterium, relatively few plants had wilt symptoms at harvest, but 26.7% and 9.2% of the tubers harvested from plants infected with the race 1 and race 3 strains, respectively, carried latent infections. Some infected clones never yielded diseased tubers, however. The development of symptoms above ground was not correlated with the incidence of tuber infection in any particular clone. No tuber infection occurred in tolerant or resistant clones grown in infested soil at cool (12–22°C) temperatures. Tubers were inoculated directly in an attempt to evaluate the ability of bacteria to multiply in these tissues at different temperatures. Highly virulent strains ofP. solanacearum survived in susceptible tubers in higher numbers and for longer periods than in resistant ones. Low temperature (4°C) had a deleterious effect on survival of the bacterium in tubers, but did not completely eliminate the pathogen even after 40 days.     

Use of field-integrated information in GIS-based maps to evaluate Moko disease (Ralstonia solanacearum) in banana growing farms in Colombia

Ralstonia solanacearum (formerly Pseudomonas solanacearum) causes large losses in more than 200 different cultivated plant species. Banana and plantain “Moko” disease is caused by R. solanacearum race 2. Moko disease may cause 100% loss if prompt control measures are not applied. Although a number of investigations have been carried out, many ecological and epidemiological aspects of R. solanacearum race 2 are still unknown, particularly in the tropics. Bacteria dispersion occurs by infested tools, soil, water, insects, domestic animals and agricultural labourers. Alternative hosts have been described which may contribute to inoculum availability in crop fields. In banana crops, cable-ways are routinely used to transport fruit and materials inside plantations. In most humid tropical areas, drainage channels are made to evacuate excess soil water. It is thought that agricultural activities associated with drainage channels and cable-ways may play a role in bacteria dispersion but individual contributions have not yet been quantified. In this work we have used field-integrated information in geographical information systems (GIS)-based maps to evaluate Moko presence in the Urabá region of Colombia, during three different time periods. A previously described risk index (RI) and losses throughout the three periods were quantified. A regression model was developed to quantify the relationship between infested area and distance from every Moko focus to the nearest cable-way and drainage channels. Farms were grouped into four different profiles according to the RI. Parameters calculated using the regression model showed that 76% of Moko foci detected during the three time periods were associated with cable-ways used for transport of fruit and consumables. This finding has important implications for disease management since bacteria spread in these ways may be prevented by simple measures taken inside plantations.     

Biological control of southern stem rot caused by Sclerotium rolfsii using Trichoderma harzianum and arbuscular mycorrhizal fungi on Jerusalem artichoke (Helianthus tuberosus L.)

Efficacy of Trichoderma harzianum and the arbuscular mycorrhizal fungus (AMF) Glomus clarum for suppression of southern stem rot caused by Sclerotium rolfsii in Jerusalem artichoke was investigated in Thailand under greenhouse conditions. Experimental factors included two Jerusalem artichoke genotypes (HEL 246 and JA 37), two levels of T. harzianum and G. clarum (inoculated and blank). The biological control agents were added to the potting medium immediately before seedlings of Jerusalem artichoke were transplanted into it; 20 days later, seedlings were inoculated with S. rolfsii by placing infested sorghum seeds at the base of the stem. The combination of cv. HEL 246 with addition of both G. clarum and T. harzianum had the lowest disease incidence (30%) and required the longest time to permanent wilt (11 days after inoculation). Inoculation of cv. JA 37 and HEL 246 with G. clarum alone gave better control of the disease than did inoculation with T. harzianum alone. The results are the first published report of biological control of S. rolfsii on Jerusalem artichoke.     

Genetics and mapping of resistance to spore inoculum and culture filtrate of Phaeosphaeria nodorum in spring wheat line ND 735

Stagonospora nodorum blotch (SNB), caused by Phaeosphaeria nodorum, is one of the most devastating foliar diseases on wheat (Triticum aestivum L.) in the northern Great Plains of North America. This study was conducted, under controlled environmental conditions, to elucidate the genetics and map the resistance to SNB caused by spore inoculum and culture filtrate of P. nodorum isolate Sn2000. A hard red spring wheat population was developed from a cross between the susceptible cultivar Steele-ND and the resistant line ND 735 for this study. Two-leaf seedlings of the parents, F₁ and F₂ generations, and F_2:6 recombinant-inbred lines (RILs) were inoculated with spore suspensions while independent two week old seedlings of segregating generations were infiltrated with culture filtrate. Disease reaction was assessed 8 days after inoculation based on a lesion-type scale while plants were evaluated for culture filtrate response four days after infiltration for the presence or absence of necrosis. Genetic analysis revealed that a single recessive gene, Tsn1, in ND 735 confers resistance to both spore suspension and culture filtrate of P. nodorum isolate Sn2000. Mapping analysis using Diversity Arrays Technology (DArT) and simple sequence repeat (SSR) markers indicates the gene, Tsn1, is located on the long arm of chromosome 5B and is flanked by the DArt markers wPt-8285 and wPt-3049 at a distance of 7.0 cM and 2.9 cM, respectively. This gene also controls resistance to tan spot caused by Pyrenophora tritici-repentis race 2. Results of this study reveal that wheat-P. nodorum interaction follows the toxin model of gene-for-gene hypothesis. Additionally, the finding of single gene control in the line ND 735 for both tan spot and SNB enhances the utility of the line ND 735 in wheat breeding program as a source of multiple disease resistance.     

Biological control of fusarium dry rot of potato tubers under commercial storage conditions

Lack of effective chemicals impedes control of Fusarium dry rot of stored potato tubers destined for processed and table stock use. Biological control of dry rot incited byGibberella pulicaris (anamorph=Fusarium sambucinum) has been demonstrated in laboratory studies but not in commercial storage environments. Several Gram-negative bacterial strains that were efficacious and amenable to production in liquid culture in laboratory studies were selected for pilot studies in Idaho and for bin trials at commercial storage houses in Idaho and North Dakota. In the first year of pilot studies,Pseudomonas fluorescens S22:T:04 (≈1 x 10⁸ cfu/ml) decreased dry rot caused byG. pulicaris by 19% when coinoculated with the pathogen compared to controls and to the fungicide thiabendazole (TBZ) applied at label rates. In second year pilot studies,P. fluorescens P22:Y:05 andEnterobacter cloacae S11:T:07 (≈4 x 10⁸ cfu/ml) reduced the severity of disease incited byG. pulicaris (25% and 17% average disease decrease, respectively) when antagonists were applied after pathogen inoculum. Treatment effects on dry rot that developed from inoculation withNectria haematococca (anamorph=Fusariumsolani var.coeruleum) were variable and influenced by interactions between antagonists, a wetting agent, and TBZ. In commercial storage bin trials,E. cloacae S11:T:07 reduced naturally occurring levels of dry rot by an average of 21% compared to 14% for TBZ, demonstrating that this antagonist was effective when produced using a liquid culture medium and methodology that approximates commercial practices for producing biomass.