Characterization of a <Emphasis Type="Italic">Pseudomonas fluorescens</Emphasis> strain from tomato rhizosphere and its use for integrated management of tomato damping-off

A highly antagonistic Pseudomonas fluorescens strain was isolated from tomato rhizosphere and characterized for its in vitro and in vivo biocontrol potential against Pythium aphanidermatum. The identified Pseudomonas fluorescens strain (PfT-8) was capable of producing high levels of chitinase, β-1,3-glucanase, cellulase, fungitoxic metabolites and siderophores. Seven different carrier formulations including a talc-based powder, lignite-based powder, peat-based powder, lignite + fly ash-based powder, wettable powder, bentonite-paste and polyethylene glycol (PEG) paste were prepared utilizing PfT-8. Shelf life was evaluated for up to 6 months of storage at ambient room temperature (28 °C). Biocontrol efficacy of formulations was studied under greenhouse and field conditions. The formulations were stable up to at least 2 months of storage at ambient room temperature. Among the formulations, peat, lignite, lignite+fly-ash and bentonite paste based formulations maintained higher propagule number than others and also showed greater biocontrol potential. However, propagule number gradually decreased with time. Several organic amendments including farm yard manure (FYM), leaf-compost, poultry manure, press mud, vermi-compost and neem cake were incorporated into soil to study their influence on P. fluorescens colonization in the rhizosphere and on potential disease control. Soil incorporation of organic amendments and specifically poultry manure and FYM, significantly reduced damping-off incidence and also augmented the rhizosphere population of the marked␣P.␣fluorescens strain that was resistant to streptomycin and rifampicin. An integrated␣approach of damping-off management employing dual inoculation of PfT-8 in seed and soil coupled with soil application of organic amendments including poultry manure or␣FYM was evaluated under field conditions. Under these conditions, damping-off incidence substantially reduced by up to 90% and further the healthy plant stand, plant biomass and plant rhizosphere population of P. fluorescens increased significantly.     

Integration of Pythium nunn and Trichoderma harzianum isolate T-95 for the biological control of Pythium damping-off of cucumber

Two biological control agents, Pythium nunn and Trichoderma harzianum isolate T-95, were combined to reduce Pythium damping-off of cucumber in greenhouse experiments lasting 3–4 weeks. T. harzianum T-95, a rhizosphere competent mutant, was applied to seeds and P. nunn was applied to pasteurized and raw soils naturally and artificially infested with Pythium ultimum. Some treatments were also amended with bean leaves to enhance the activity of P. nunn. The biological control of Pythium damping-off was evaluated in a Colorado soil (Nunn sandy loam) and an Oregon soil mix, which were replanted twice after 2 and 3 months. Interactions between P. nunn and T-95 were detected in the Colorado but not the Oregon soil. No consistent evidence of antagonism between P. nunn and T. harzianum was seen, and significant interactions were detected in the Colorado, but not the Oregon soil. In the first planting of some treatments, the combination of P. nunn and T. harzianum gave greater control of damping-off than either applied alone. P. nunn was most effective in soils that were pasteurized or amended with bean leaves. T. harzianum controlled Pythium damping-off in the Colorado, but not the Oregon soil. In both soils, disease declined over time in treatments amended with bean leaves but without P. nunn or T. harzianum added. This suppression was greater in the Colorado soil, which contained an indigenous population of P. nunn. This work demonstrates that two compatible biological control agents can be combined to give additional control of a soil-borne plant pathogen.     

Control of Pythium damping-off of sugar beet by seed treatment with crop straw powders and a biocontrol agent

Seed treatment with non-sterilized powdered straws from 39 crops was tested for the control of Pythium damping-off of sugar beet. Four straws, including flax, coriander, pea, and lentil were effective in controlling the disease in soil artificially infested with Pythium sp. “group G.” Sterilizing flax and pea straws eliminated the efficacy of these straws. Wheat straw powder coated on sugar beet seeds increased the incidence of Pythium damping-off but this effect was reversed by the co-inoculation of wheat straws with the biocontrol agent Pseudomonas fluorescens 708. Coating sugar beet seeds with P. fluorescens 708 and flax or pea straws also increased the efficiency of the bacterial strain for the control of Pythium damping-off. Pea straws and to a lesser extent lentil straws produced volatile substances that affected mycelial growth of Pythium sp. “group G” on potato dextrose agar in Petri plates when the straws were mixed with water and left to ferment for two days. Fermentation of pea straws led to the accumulation of volatile ammonia, which was produced by the reduction of the large amount of nitrate stored in the straw. Reduction of nitrate and therefore the release of volatile ammonia did not occur in sterilized pea straws. However, fermenting sterile pea straws with bacteria from different genera restored nitrate reduction and the release of volatile ammonia, suggesting that microorganisms associated with pea straws are responsible for the conversion of nitrate into volatile ammonia which in turn control Pythium damping-off disease in sugar beet.     

Biocontrol of <Emphasis Type="Italic">Pythium</Emphasis> damping-off in cucumber by arbuscular mycorrhiza-associated bacteria from the genus <Emphasis Type="Italic">Paenibacillus</Emphasis>

The Pythium biocontrol features of 17 Paenibacillus strains, all previously isolated from the rhizosphere, hyphosphere or bulk soil from mycorrhizal and non-mycorrhizal cucumber plants, were examined using a cucumber seedling emergence bioassay. Thirteen strains – four strains of Paenibacillus polymyxa, eight strains of P. macerans and one strain of Paenibacillus sp. – significantly increased the percentage of seedling emergence of seeds inoculated with agar plugs of Pythium aphanidermatum FC42. Overall, the efficacy of Pythium biocontrol did not seem to differ between isolates of Paenibacillus originating from either mycorrhizal or non-mycorrhizal systems. No strains significantly reduced the damping-off incidence caused by the aggressive isolate Pythium sp. B5. Two strains of P. macerans not only reduced the incidence of pre-emergence damping-off by 73%, but they also counteracted the plant growth-depressing effect of P. aphanidermatum FC42, so that 68–82% of the emerged seedlings remained healthy 7 days after sowing. Two strains of P. macerans and one strain of P. polymyxa also significantly increased the percentage of seedling emergence following inoculation with approximately 10⁵ zoospores of P. aphanidermatum FC42. There was no significant difference between the dry weight of three selected bacteria-inoculated and -uninoculated plants in the absence of Pythium; however, the dry weight of bacteria-inoculated plants was significantly higher than that of the uninoculated control plants with bacteria in the presence of P. aphanidermatum FC42.     

Field evaluation of plant growth-promoting Rhizobacteria amended transplant mixes and soil solarization for tomato and pepper production in Florida

Field trials were performed in Florida to evaluate tomato and pepper transplants amended with formulations of several plant growth-promoting rhizobacteria (PGPR) in a production system that included soil solarization. Transplants grown in five different formulations of PGPR were planted into plots treated by soil solarization, MeBr fumigation, or untreated soil. Treatments were assessed for incidence of several naturally occurring tomato and pepper pathogens including root-knot nematode (Meloidogyne incognita) and species of Pythium, Phytophthora, and Fusarium. Highly significant increases in tomato and pepper transplant growth occurred in response to most formulations of PGPR tested. Transplant vigor and survival in the field were improved by PGPR treatments in both tomato and pepper. Diseases of tomato caused by root-knot nematodes, Fusarium, Phytophthora, and Pythium were not affected by PGPR treatments. PGPR formulation LS261 reduced numbers of root-knot nematode galls on pepper while pepper root condition was improved with formulations LS213, LS256 and LS261. Individual PGPR strains affected the number of Pythium colonies isolated from pepper roots, but did not affect isolation of Pythium from tomato roots. Greater numbers of colonies of Pythium were isolated from pepper roots in the MeBr treatment and fewest in the solarization treatment. Numbers of colony forming units of Fusarium were significantly higher in the untreated soil than in MeBr fumigated or solarized soil with no effect of PGPR on isolation of Fusarium from either crop. Incidence of wilt symptoms on tomato was significantly lower in MeBr treated plots and highest in the untreated plots. Yield of extra large tomato fruit and total yield increased with PGPR formulation LS256. Yield of pepper was increased with formulations LS255 and LS256. Solarization combined with LS256 on pepper produced yields comparable to MeBr.     

Biological control of seedling blight of wheat caused by Fusarium graminearum with beneficial rhizosphere microorganisms

Fusarium graminearum is associated with the cereal damping-off complex which reduces germination, seedling stand and yield. Fifty-two bacterial strains and six Trichoderma spp. isolated from the wheat rhizosphere were evaluated for biocontrol of seedling blight of wheat caused by F. graminearum. Their potential as biocontrol agents was tested in vitro and in the greenhouse. Isolates varied in their ability to inhibit the mycelial growth of F. graminearum in agar plate bioassays by 0–79%. This parameter was not related with biocontrol efficacy of in vivo assays. In greenhouse trials, all isolates were initially evaluated for reducing disease on wheat cultivars Klein Centauro (moderately resistant to F. graminearum) and Pro INTA Oasis (susceptible) planted in sterilized soil artificially infested with the pathogen. Among the 25 bacteria and six fungal isolates that exhibited a pronounced suppressive effect, the most efficient 10 for both cultivars were further assayed on eight cultivars (Buck Candil, Buck Catriel, Buck Chambergo, Buck Poncho, Buck Topacio, Klein Cacique, Klein Centauro and Pro INTA Oasis) potted in cultivated–inoculated soil. Three weeks after sowing, plant stand, percentage of diseased emerging seedlings, plant height and dry weight were evaluated. Among the antagonists only Stenotrophomonas maltophilia was significantly better than the control for the average of the eight cultivars for plant stand, height and dry weight. Stenotrophomonas maltophilia also caused a non-significant decrease in the percentage of diseased plants. Three strains of Bacillus cereus and one isolate of Trichoderma harzianum gave also a good control in some cultivars. The ability of these isolates to affect the infection of wheat seedlings by F. graminearum may be of potential value in field trials.     

Risk assessment for engineered bacteria used in biocontrol of fungal disease in agricultural crops

A plant growth promoting rhizobacterium (PGPR)Pseudomonas fluorescens SBW25 (WT) protects a number of crop plant species from damping-off caused by Pythium ultimum. A genetically modified, phenazine-1-carboxylic acid (PCA) producing variant, 23.10, carries on its chromosome a single copy of phzABCDEFG, under the control of the P tac constitutive promoter. The genetically modified biological control agent (GM-BCA), 23.10, has improved biocontrol activity when compared to wild type SBW25, and can effectively suppress Pythium spp. present at up to 100 times normal field infestations. GM-BCA inocula establish high population densities which persist well in the phytosphere of several crop plants including pea, wheat and sugar beet, effectively suppressed infection and promoted increase in total plant biomass. It also has an improved spectrum of activity over other plant phytopathogens such as Fusarium spp. Gaeumannomyces graminis var. tritici, Phytophtora cinnamomi and Rhizoctonia solani. However in developing BCAs and in particular GMBCAs it is important to determine whether their use has any adverse effect in the environment. Any observed changes following inoculation with wild type BCA or GM BCA in microbial diversity (bacteria and fungi) were negligible when assessed by either quantitive selective plate count methods (CFU/g) or culture independent molecular assays (SSU rRNA based PCR-DGGE). Rhizosphere community diversity profiles (DGGE) in infected plants in the presence of inocula were highly similar to disease free systems. Histological assessment of the impact of inocula on established functional mycorrhizae associations were conducted on cores collected from an established field margin grassland pasture. No adverse impact on mycorrhizal colonization and root infection were recorded after addition of WT or GM-BCA bacterial inocula as a soil drench. This approach and the related culturable and culture independent methods have recorded only a minor, transient perturbation to microbial communities, but as far as we are aware this is the first direct demonstration that a functional, AFC producing GMM also has only a transient impact on mycorrhizal associations in established plant communities. In all instances studied the plant species, plant stage of development and disease, damping-off, had a greater impact on changes in rhizosphere diversity than the presence of an introduced GM bacterial inocula.     

Integration of soil solarization with chemical, biological and cultural control for the management of soilborne diseases of vegetables

The long-term effectiveness of soil solarization integrated with (integration of pest management [IPM]) a biological control agent (Trichoderma virens), chemical fungicide (pentachloronitrobenzene [PCNB]), organic amendment (chicken litter) or physical method (black agriplastic mulch) to reduce southern blight (Sclerotium rolfsii) and southern root-knot diseases (Meloidogyne incognita) were evaluated on vegetable production. Results showed that the long-term effectiveness of IPM plus soil solarization reduced soilborne diseases of vegetables more than two years following the termination of solarization. These disease management strategies in 1991 and 1992, following soil solarization in 1990, reduced the numbers of sclerotia in the soil, and the number of plants killed by southern blight and root-knot of tomatoes, compared to nonsolarized bare soil treatment. The integration of a reduced dosage level of PCNB or T. virens in field plots, reduced southern blight of tomatoes by 100% and 71%, respectively, in solarized soil, compared to nonsolarized bare soil two years following soil solarization. PCNB effectively controlled southern blight in nonsolarized bare soil both years. All solarized treatments, except PCNB plus solarized soil increased tomato yields compared to nonsolarized bare soil plots. In the second study (1992) following soil solarization in 1991, the effectiveness of solarized bare soil, and nonsolarized bare soil mulched with black agriplastic film, with or without Reemay spunbounded polyester row cover, were effective in reducing root-knot of tomatoes as indicated by the root-knot gall index. Following a one year fallow period in 1994 three years following soil solarization, the root-knot gall index for severity of tomato roots grown in solarized bare soil, nonsolarized bare soil, black agriplastic mulched bare nonsolarized soil and black agriplastic mulched solarized bare soil, were 1.0, 3.0, 3.0 and 2.0, respectively, on a 0–5 scale, where 0=0% and 5=100% root-knot galled. In the third study 1992 and 1993, different dosage levels of chicken litter were used to amend soil artificially infested with sclerotia of S. rolfsii at different depths following solarization, decreased the number of viable sclerotia by 85–100%. All solarized treatments and nonsolarized bare soil amended with 18.8 MT/ha of chicken litter, were effective in controlling southern root-knot damage, and postharvest storage root rots of sweetpotato storage roots (Fusarium root rot [Fusarium solani] and Java black rot [Diplodia tubericola]). Our study showed that all soil solarization treatments, and soils amended with chicken litter, stimulated a shift in the soil microbial population dynamics. Rhizobacteria of Bacillus spp. and fluorescent pseudomonads increased significantly in the rhizosphere, rhizoplane, and interior root tissues of tomatoes and sweetpoatoes, grown in solarized soil compared to nonsolarized soil. These microorganisms may have contributed to the increased growth response of vegetables and some were probably suppressive to soilborne diseases     

Chemical,physical and biological control of carrot seedling diseases

In naturally infested soil containingPythium ultimum, P. acanthicum andPhytophthora megasperma, onlyP. ultimum was associated with root rot and damped-off seedlings. Damping-off was promoted by low soil temperatures and by flooding. Seedling stands were markedly reduced when seed was pre-incubated in soil at 12°C but not at 25°C or 35°C. Dusting carrot seed with metalaxyl significantly increased seedling stands in the field at rates from 1.5–6 g kg⁻¹ seed and in both flooded and unflooded, naturally infested soil at 3.15 g kg⁻¹. In greenhouse experiments using artifically infested soil,P. ultimum andP. paroecandrum caused damping-off of carrot seedlings andRhizoctonia solani reduced root and shoot weights.R. solani caused damping-off in nutrient-enriched soil.P. acanthicum andP. megasperma were not pathogenic to seedlings, although both fungi colonized roots. Soil populations of allPythium spp., particularlyP. ultimum, increased during growth of seedlings and population growth ofP. megasperma was promoted by periodic flooding. Infestation of soil withP. acanthicum did not reduce damping-off of carrot seedlings byP. ultimum orP. paroecandrum, but significantly increased root and shoot weights and decreased root colonization byR. solani P. acanthicum has potential as a biocontrol agent againstR. solani.     

Colonization behaviour of Pseudomonas fluorescens and Sinorhizobium meliloti in the alfalfa (Medicago sativa) rhizosphere

The colonization ability of Pseudomonas fluorescens F113rif in alfalfa rhizosphere and its interactions with the alfalfa microsymbiont Sinorhizobium meliloti EFB1 has been analyzed. Both strains efficiently colonize the alfalfa rhizosphere in gnotobiotic systems and soil microcosms. Colonization dynamics of F113rif on alfalfa were similar to other plant systems previously studied but it is displaced by S. meliloti EFB1, lowering its population by one order of magnitude in co-inoculation experiments. GFP tagged strains used to study the colonization patterns by both strains indicated that P. fluorescens F113rif did not colonize root hairs while S. meliloti EFB1 extensively colonized this niche. Inoculation of F113rif had a deleterious effect on plants grown in gnotobiotic systems, possibly because of the production of HCN and the high populations reached in these systems. This effect was reversed by co-inoculation. Pseudomonas fluorescens F113 derivatives with biocontrol and bioremediation abilities have been developed in recent years. The results obtained support the possibility of using this bacterium in conjunction with alfalfa for biocontrol or rhizoremediation technologies.     

Enhancing the biocontrol efficacy of Pseudomonas fluorescens F113 by altering the regulation and production of 2,4-diacetylphloroglucinol

Pseudomonas fluorescens F113 is an effective biocontrol agent against Pythium ultimum, the causative agent of damping-off of sugarbeet seedlings. Biocontrol is mediated via the production of the anti-fungal metabolite 2,4-diacetylphloroglucinol (Phl). A genetic approach was used to further enhance the biocontrol ability of F113. Two genetically modified (GM) strains, P. fluorescens F113Rif (pCU8.3) and P. fluorescens F113Rif (pCUP9), were developed for enhanced Phl production and assessed for biocontrol efficacy and impact on sugarbeet in microcosm experiments. The multicopy plasmid pCU8.3 contains the biosynthetic genes (phlA, C, B and D) and the putative permease gene (phlE) of F113 cloned into the rhizosphere stable plasmid pME6010, independent of external promoters. The plasmid pCUP9 consists of the Phl biosynthetic genes cloned downstream of the constitutive Plac promoter in pBBR1MCS. Introduction of pCU8.3 and pCUP9 into P. fluorescens F113 significantly altered the kinetics of Phl biosynthesis when grown in SA medium. A significant and substantial increase in Phl production by the GM strains was observed in the early logarithmic phase and stationary phase of growth compared with the wild-type strain. In microcosm, the two Phl overproducing strains proved to be as effective at controlling damping-off disease as the proprietary fungicide treatment, indicating the potential of genetic modification for plant disease control.     

Effect of soil solarization on corn stalk rot

Seven weeks solarization of irrigated soil raised its temperature by 11.5°C over non-solarized soil at 10 cm depth and effectively controlled weeds (98.5%), stalk borer (8.9%) and stalk rot disease (69.1%) in corn. Solarization also reduced symptoms of Fusarium moniliforme and Macrophomina phaseolina significantly by 64.2% and 78.4%, respectively, and completely controlled M. phaseolina in corn cultivars, viz. Pool-10, Shaheen and Gauher. Whereas symptoms of F. moniliforme were observed in these cultivars, Fusarium graminearum was not observed except in two cultivars, Shaheen and Akbar. Growth of crop planted in solarized plots was better and it yielded almost one to three times more grains in cultivars under test. Soil analysis immediately following solarization revealed that essential elements were readily available in simpler forms, which may have increased pest resistance and reduced stalk breakage.     

Quorum-sensing system influences root colonization and biological control ability in Pseudomonas fluorescens 2P24

Pseudomonas fluorescens 2P24 is a biocontrol agent isolated from a wheat take-all decline soil in China. This strain produces several antifungal compounds, such as 2,4-diacetylphloroglucinol (2,4-DAPG), hydrogen cyanide and siderophore(s). Our recent work revealed that strain 2P24 employs a quorum-sensing system to regulate its biocontrol activity. In this study, we identified a quorum-sensing system consisting of PcoR and PcoI of the LuxR–LuxI family from strain 2P24. Deletion of pcoI from 2P24 abolishes the production of the quorum-sensing signals, but does not detectably affect the production of antifungal metabolites. However, the mutant is significantly defective in biofilm formation, colonization on wheat rhizosphere and biocontrol ability against wheat take-all, whilst complementation of pcoI restores the biocontrol activity to the wild-type level. Our data indicate that quorum sensing is involved in regulation of biocontrol activity in P. fluorescens 2P24.     

Rhizotron studies on Zea mays L. to evaluate biocontrol activity of Bacillus subtilis

The effect of Bacillus as a biocontrol agent against some root-rot fungi was tested using maize (Zea mays L.) in rhizotrons placed in a growth chamber with relative humidity 60% with a 12 h photoperiod and day and night temperatures of 24 and 18°C respectively. Rhizoctonia solani Kühn caused pre-emergence damping-off in the untreated maize seeds showing weak and soft roots as observed through the perspex rhizotrons. Image analysis was used to quantify the effects of Bacillus treatment on seedlings infected with Pythium sp. Bacillus B77 and B81 were most effective in the control of the pathogen, R. solani which achieved a biocontrol activity of 24 and 35% respectively with regard to shoot dry biomass while B81 achieved 48% biocontrol with reference to root dry biomass. There was no effect on the root area. For root dry biomass, B81, B69, B11 and B77 showed higher biocontrol activity in comparison to the control. Pythium sp. caused pre- and post emergence damping- off in the untreated seeds. Root rot of the maize seedlings caused by Pythium sp. was slightly controlled by Bacillus B69 and B81 which achieved biocontrol activity of 18 and 11% respectively. For the biocontrol of Fusarium solani, Bacillus B77, B69, B81 achieved biocontrol activity of 50, 48 and 33% respectively with reference to root dry biomass.     

Enhancing biological control of basal stem rot disease (<Emphasis Type="Italic">Ganoderma boninense</Emphasis>) in oil palm plantations

Basal Stem Rot (BSR) disease caused by Ganoderma boninense is the most destructive disease in oil palm, especially in Indonesia and Malaysia. The available control measures for BSR disease such as cultural practices and mechanical and chemical treatment have not proved satisfactory due to the fact that Ganoderma has various resting stages such as melanised mycelium, basidiospores and pseudosclerotia. Alternative control measures to overcome the Ganoderma problem are focused on the use of biological control agents and planting resistant material. Present studies conducted at Indonesian Oil Palm Research Institute (IOPRI) are focused on enhancing the use of biological control agents for Ganoderma. These activities include screening biological agents from the oil palm rhizosphere in order to evaluate their effectiveness as biological agents in glasshouse and field trials, testing their antagonistic activities in large scale experiments and eradicating potential disease inoculum with biological agents. Several promising biological agents have been isolated, mainly Trichoderma harzianum, T. viride, Gliocladium viride, Pseudomonas fluorescens, and Bacillus sp. A glasshouse and field trial for Ganoderma control indicated that treatment with T. harzianum and G. viride was superior to Bacillus sp. A large scale trial showed that the disease incidence was lower in a field treated with biological agents than in untreated fields. In a short term programme, research activities at IOPRI are currently focusing on selecting fungi that can completely degrade plant material in order to eradicate inoculum. Digging holes around the palm bole and adding empty fruit bunches have been investigated as ways to stimulate biological agents.     

Effect of <Emphasis Type="Italic">Trichoderma</Emphasis> spp. isolates for biological control of tan spot of wheat caused by <Emphasis Type="Italic">Pyrenophora tritici-repentis</Emphasis> under field conditions in Argentina

Trichoderma spp. have been used as biocontrol agents to protect plants against foliar diseases in several crops, but information from field assays is scarce. In the present work, experiments were carried out to determine the effect of six isolates of Trichoderma harzianum and one isolate of T. koningii on the incidence and severity of tan spot, caused by Pyrenophora tritici-repentis (anamorph: Drechslera tritici-repentis) under field conditions. Significant differences between years, wheat cultivars and treatments were found. In 2003, two of the isolates assayed (T5, T7) showed the best performance against the disease applied as seed treatments or sprayed onto wheat leaves at different stages. The application of six of the treatments on wheat plants significantly reduced disease severity by 16 to 35% in comparison with the control. Disease control provided by isolate T7 was similar to that provided by the fungicide treatment (56% reduction). This is the first report on the efficacy of Trichoderma spp. against tan spot under field conditions in Argentina.     

Beneficial microorganism survival on seed, roots and in rhizosphere soil following application to seed during drum priming

Priming is a technique used to improve seedling establishment of direct-seeded crops such as onion and carrot, resulting in a quick and uniform emergence. This work investigated the application of four selected beneficial microorganisms (Pseudomonas chlororaphis MA342, Pseudomonas fluorescens CHA0, Clonostachys rosea IK726d11 and Trichoderma harzianum T22) to onion and carrot seed during drum priming, and their subsequent survival and establishment in the rhizosphere once the seed was planted. Different application rates of fungi (7 log₁₀ cfu g⁻¹ dry seed) and bacteria (6 log₁₀ cfu g⁻¹ dry seed) were required on onion to achieve the end target of 5 log₁₀ cfu g⁻¹ dry seed, whereas a lower rate (5 log₁₀ cfu g⁻¹ dry seed for both bacteria and fungi) was successful on carrot. Microorganism-treated seed was planted in soil in the glasshouse and root and rhizosphere soil samples were taken at 2, 4 and 8 weeks post-planting. All seed-applied microorganisms were recovered throughout the experiment, although differences in the survival patterns were seen. The bacterial isolates declined in number over time, with P. fluorescens CHA0 showing better overall survival than P. chlororaphis MA342, particularly on the roots and in the rhizosphere soil of carrot. In contrast to the bacteria, the fungal isolate C. rosea IK726d11 showed good survival on both onion and carrot, and increased significantly in number throughout the 8-week period. Trichoderma harzianum T22 remained relatively constant in number throughout the experiment, but showed better survival on carrot than onion roots. Similar results were found in three different soil-types.     

Involvement of endogenous gibberellins in the regulation of increased tomato shoot growth in solarized soil

Environmental factors often affect plant growth bymodifying the levels of endogenous gibberellins (GAs).In this study, the involvement of GAs in theregulation of enhanced shoot growth in tomato (Lycopersicon esculentum Mill.) plants grown in soiltreated by solarization (a soil disinfestation method)was investigated. Seedlings at the cotyledonary stagewere transplanted into either solarized or untreatedcontrol soil. Plants in both soils grew free of anydisease symptoms. As soon as four days after planting,seedlings in solarized soil had a higher dry weightcompared to the control. Throughout most of theexperimental period of 18 days, leaf weight ratio washigher in the solarized vs. the control soil. Treatingshoot tips of control plants with 0.1 mg^.L^-1GA₃ resulted in enhanced leaf and stem growth,thus reaching values similar to those of plants grownin solarized soil. The opposite effect was obtained bytreating plants grown in solarized soil with1 mg^.L^-1 uniconazole, a GA biosynthesisinhibitor. Quantitative GC-MS analyses revealed thatGA₁ content in one and two-weeks old transplantsgrown in various solarized soils was up to 1.8 fold,and that GA₃ content in two-weeks old plants wasup to five fold the values in the control. Theseincreases were linearly correlated with the increasein leaf dry weight. It was concluded that theincreased quantities of GA₁, and eventuallyGA₃, play a role in the increased growth oftomato shoots in solarized soil as early as seven daysafter transplanting.deceased     

Analogous wheat root rhizosphere microbial successions in field and greenhouse trials in the presence of biocontrol agents Paenibacillus peoriae SP9 and Streptomyces fulvissimus FU14

Two Pythium-infested soils were used to compare the wheat root and rhizosphere soil microbial communities from plants grown in the field or in greenhouse trials and their stability in the presence of biocontrol agents. Bacteria showed the highest diversity at early stages of wheat growth in both field and greenhouse trials, while fungal diversity increased later on, at 12 weeks of the crop cycle. The microbial communities were stable in roots and rhizosphere samples across both soil types used in this study. Such stability was also observed irrespective of the cultivation system (field or greenhouse) or addition of biocontrol coatings to wheat seeds to control Pythium disease (in this study soil infected with Pythium sp. clade F was tested). In greenhouse plant roots, Archaeorhizomyces, Debaryomyces, Delftia, and unclassified Pseudeurotiaceae were significantly reduced when compared to plant roots obtained from the field trials. Some operational taxonomic units (OTUs) represented genetic determinants clearly transmitted vertically by seed endophytes (specific OTUs were found in plant roots) and the plant microbiota was enriched over time by OTUs from the rhizosphere soil. This study provided key information regarding the microbial communities associated with wheat roots and rhizosphere soils at different stages of plant growth and the role that Paenibacillus and Streptomyces strains play as biocontrol agents in supporting plant growth in infested soils.     

Biological and Integrated Control of Botrytis Bunch Rot of Grape UsingTrichodermaspp.

Field trials were carried out in upstate New York in 1990, 1992, 1993, and 1994 and in Chile in 1992–1993 and 1993–1994 in order to evaluate the ability of various strains ofTrichodermaspp. to control bunch rot of grape, to assess the compatibility and possible additive effects of selected biocontrol fungi and dicarboximide fungicides, and to determine factors affecting biocontrol efficacy. In 1990, three strains ofTrichodermaspp. were evaluated for their biocontrol ability, and all provided significant control ofBotrytis cinerea.As few as two late applications of the biocontrol fungi were nearly as effective as up to five applications throughout bloom and fruit development. Trials in New York in 1992 and in Chile in 1992–1993 indicated thatTrichoderma harzianumcould replace some applications of iprodione or vinclozolin with little reduction in efficacy. In New York in 1993, we found that applications ofT. harzianumat bloom and early fruit development followed by a tank-mix application ofT. harzianumand half rates of iprodione gave extremely effective control of bunch rot. In 1994, less effective control was obtained than in earlier years. Addition of a nutritive adhesive (Pelgel, a mixture of carboxymethyl cellulose and gum arabic) applied with the biocontrol agent tended to improve results. Thus, biological control of bunch rot of grape withT. harzianumcan be an effective method of management of this disease.