Inoculum Rate Research Articles

Influence of carbon dioxide, inoculum rate, amount and mixing of casing soil on Agaricus blazei fruiting bodies yield

Influence of carbon dioxide concentration during compost and casing soil overgrowth, inoculum rate, casing soil depth and mixing on Agaricus blazei fruiting bodies yield was determined. Compost composed of chicken manure and wheat straw which is used for commercial button mushrooms cultivation in Slovenia showed to be appropriate for A. blazei fruiting bodies production. Out of the parameters tested in our experiments, casing soil depth and inoculum rate had the biggest positive effect on fruiting bodies production. For A. blazei fruiting bodies production higher rates of inoculum and at least 8.5 kg of commercial casing soil per square meter of compost surface should be used. Higher carbon dioxide concentrations shoved to be beneficial for attaining higher yields of A. blazei fruiting bodies.

Transcriptome analysis of Arabidopsis roots treated with signaling compounds: a focus on signal transduction, metabolic regulation and secretion

Gene expression in response to signaling molecules has been well studied in the leaves of the model plant species Arabidopsis thaliana. However, knowledge of gene expression and metabolic regulation at the root level is limited. Here, the signaling compounds salicylic acid (SA), methyl jasmonate (MeJA) and nitric oxide (NO) were applied exogenously to induce various defense responses in roots, and their effect was studied using a combination of genomic, molecular and biochemical approaches. Genes involved in defense signaling/activation, cellular redox state, metabolism, transcription factors and membrane transport were altered in expression following treatment with SA, MeJA and NO. In addition, it was found that SA-, MeJA- and NO-elicited roots increased the root exudation of phytochemicals compared with the roots of nontreated control plants. Transport systems likely to be involved in the root exudation of phytochemicals, including the MATE, ABC, MFS, amino acid, sugar and inorganic solute transporters, showed altered expression profiles in response to treatments. Overall, significant differences were found in the signaling compound-elicited expression profiles of genes in roots vs those in leaves. These differences could be correlated to the underground nature of roots and their exposure to higher microbial inoculum rates under natural conditions.

Influence of carbon dioxide, inoculum rate, amount and mixing of casing soil on Agaricus blazei fruiting bodies yield

Influence of carbon dioxide concentration during compost and casing soil overgrowth, inoculum rate, casing soil depth and mixing on Agaricus blazei fruiting bodies yield was determined. Compost composed of chicken manure and wheat straw which is used for commercial button mushrooms cultivation in Slovenia showed to be appropriate for A. blazei fruiting bodies production. Out of the parameters tested in our experiments, casing soil depth and inoculum rate had the biggest positive effect on fruiting bodies production. For A. blazei fruiting bodies production higher rates of inoculum and at least 8.5 kg of commercial casing soil per square meter of compost surface should be used. Higher carbon dioxide concentrations shoved to be beneficial for attaining higher yields of A. blazei fruiting bodies.

Dual application of beneficial microorganisms to seed during drum priming

Dual application of beneficial microorganisms to carrot and onion seed during drum priming was demonstrated for the first time. Combinations of one bacterial ( Pseudomonas chlororaphis MA342 or Pseudomonas fluorescens CHA0) and one fungal isolate ( Clonostachys rosea IK726d11 or Trichoderma harzianum T22) were tested for compatibility when applied simultaneously to seed. On carrot seed, all microorganisms proliferated during the priming process, whereas on onion seed the fungal isolates declined in number. Different inoculum rates were required for carrot and onion seed to achieve the target rate of at least 5 log 10 cfu g −1 dry seed at the end of the priming process. Glasshouse experiments showed that the microorganisms applied in combination to the seed survived on roots and in rhizosphere soil for 8 weeks, with similar survival patterns seen irrespective of whether the microorganisms were applied to seed singly or in combination. C. rosea IK726d11 in combination with the bacteria actively colonised the onion and carrot roots and rhizosphere better than T. harzianum T22 in similar combinations. Initial dose rates on the seed significantly affected the numbers of microorganisms recovered from the rhizosphere.

Effect of water activity and temperature on growth of ochratoxigenic strains of Aspergillus carbonarius isolated from Argentinean dried vine fruits

Aspergillus carbonarius is an ochratoxin A (OTA) producing fungus, predominantly responsible for the production of this mycotoxin in grapes, wine and dried vine fruits. The objective of this study was to determine the in vitro effects of water activity ( a w, 0.80–0.95) and temperature (15–35 °C) on lag phase extension and radial growth rate of a cocktail inoculum of four strains of A. carbonarius. The maximum growth rate was observed at 0.95 a w and 30 °C (17.46 mm day − 1 ). In general, growth rates increased with the increment of a w. No growth was observed at a w below 0.85. For all a w levels tested the highest growth rate was detected at 30 °C. At 15 °C growth only occurred at the higher a w levels evaluated (0.925 and 0.95) at a growth rate of 3.82 and 5.57 mm day − 1 respectively. The shortest lag phase (0.26 days) was found at 0.925 a w and 35 °C. At marginal conditions of a w and temperature the lag phases increased, being the highest registered at 20 °C and 0.89 a w (33.7 days). The pattern of effects of environmental factors on growth was similar among Argentinean A. carbonarius strains and those from several European countries, Israel and Australia.

Production and Characterization of Amylases by Aspergillus niger under Solid State Fermentation Using Agro Industrials Products

The use of agro industrials products cassava starch and sugar cane bagasse present a great potential as substrate and support, respectively, showing low production costs for amylases production under solid-state fermentation by Aspergillus niger LPB 28. The effect of various factors was examined and some variables were optimized to ?-amylase and amyloglucosidase production. Inoculum rate in different concentrations (105, 106, 107 and 108 spores/g of cassava starch) were used to inoculate the solid substrate for the SSF. The material was supplemented with nitrogen sources; calcium source and micronutrients solution. The ratios of cassava starch to sugar cane bagasse (1/1; 1.5/1; 1/1.5; 1/2; 2/1; 1/3; 3/1) were tested and the initial moisture content varying 80, 85 and 90%. Cultivation was carried out at temperatures 25, 30 and 35ºC for 48, 60 and 72 h. Study of influence of pH initial in SSF was conduced in pH 4.0, 5.0, 6.0, 7.0 and 8.0. Statistical analysis was carried out using the software STATISTICA 5.1 (StatSoft, Tulsa, OK, USA). A 32 complete factorial design (2 factors, 3 levels and 9 experiments) was used to study the effect of the factors in ?-amylase and amyloglucosidase production. The results showed cassava starch and sugar cane bagasse at the ratios of 2/1 was the best for optimum production of ?-amylase and amyloglucosidase. The maximum yield (?-amylase 1732.95 U/g of cassava starch and amyloglucosidase 2044.94 U/g of cassava starch) was achieved with optimized process parameters such as incubation period (60 hours), moisture level was 90%, inoculation rate (105 spores/g of dried material), pH 4.0 and fermentation temperature (30ºC). The nitrogen source (KNO3) also enhanced the ?-amylase and amyloglucosidase activities. In kinetic characterization of enzymes the Michaelis-Menten constant KM and maximum velocity Vmax (KM 10.84 g/l, Vmax 3.42 g/l) for ?-amylase and KM 11.32 g/l and Vmax 5.18 g/l for amyloglucosidase.

Growth response of tomato (<i>Lycopersicum esculentum</i> Mill) inoculated with <i>Azotobacter croococcum</i> in an alfisol

The performance of Azotobacter croococcum Beijerinck in enhancing growth and fruit production of tomato (Lycopersicum esculentum Mill) was investigated in 3 greenhouse experiments and a field study. The first experiment assessed the appropriate method of inoculation while the 2 nd study determined the relationship between increases in the volume of inoculum and the yield parameters. Experiment 3 investigated the required number of doses needed for optimum yield.. The field study attempted to validate positive responses obtained in the greenhouse. Seedling inoculation and urea application at 2 weeks after transplanting (WAT) led to increases ranging from 50% to over 160% in all the parameters assessed when compared with the un-inoculated and unfertilized control. The observed increases started from 6WAT. Soil and seed inoculation did not significantly (p=0.05) impact positively on the height, stem girth as well as the number of fruits of the test crop when compared with the control. There was a positive correlation between increase in inoculum rates and plant height and girth with the regression coefficient (r 2 ) ranging from 0.74 to 0.96. Application of 2-3 doses of 50mls of the inoculum to the seedling enhanced plant height and stem girth especially from 6WAT. Application of 2 doses at 2weeks interval gave about 10% increase in the number of fruits over the 2 dose-application. In the field, no significant (p=0.05) differences were obtained in plant growth and yield when either the Azotobacter inoculum or urea was used. Each of the treatments however, increased the growth and fruit yield of tomato when compared with the control. Nitrogen fertilization promoted growth and yield of tomato. The use of Azotobacter croococcum inoculum was an effective biological management option in tomato fertilization programme. Keywords : Azotobacter croococcum , growth, tomato, urea Moor Journal of Agricultural Research Vol. 5(1) 2004: 13-18

New Method for Screening Cowpea Germ Plasm for Resistance to Cucumber mosaic virus.

Utilizing the Cucumber mosaic virus(CMV)-resistant cowpea germ plasm line, GC-86L-98, a new method of screening for resistance in the greenhouse followed by field screening was developed. A uniform source of CMV inoculum (freeze-dried infected cowpea tissue) was diluted to provide an infection rate in GC-86L-98 similar to that observed under field conditions. Plants of test lines were mechanically inoculated with this standard inoculum rate and assessed under greenhouse conditions. Lines considered equivalent in infection percentage with GC-86L-98 were then evaluated in field tests. Test line plants were exposed to virus from susceptible cultivar Coronet when plants were at the first or second trifoliolate leaf stage, and then leaf samples were assayed by direct antigen coating-enzyme-linked immunosorbent assay. Lines with infection percentages similar to or lower than the resistant control were considered resistant. A new line (PI 441917) with CMV resistance and several lines with Blackeye cowpea mosaic virus resistance were found. Newly discovered CMV-resistant lines will help to control the serious cowpea stunt disease caused by synergism of the two viruses.

Effects of Nocturnal Soil Temperatures and Meloidogyne incognita Densities on Cotton Seedling Growth and the Interaction with Thielaviopsis basicola

Controlled studies were conducted to evaluate the effects of soil temperatures typical of field conditions during the first 6 weeks of the growing season in Arkansas and different population densities of Meloidogyne incognita on damage to cotton (Gossypium hirsutum) seedlings associated with the interaction between M. incognita and Thielaviopsis basicola. Treatments consisted of varying nocturnal temperatures that approximated the temperatures that occurred during the 2001, 2002, and 2003 growing seasons in southeastern Arkansas. Nocturnal temperatures in the study were as follows: high, the first week at 15°C, followed by 3 weeks at 17°C, 1 week at 21°C, and 1 week at 17°C (approximating the 2002 season); medium, 3 weeks at 15°C and 3 weeks at 19°C (approximating the 2003 season); and low, 1 week at 15°C, 1 week at 13°C, 2 weeks at 17°C, 1 week at 15°C, and 1 week at 17°C (approximating the 2001 season). Pathogen population densities were either 0 or 100 chlamydospores of T. basicola per gram of soil and 0, 2,000, 4,000, or 8,000 eggs of M. incognita per 500 cm3of soil. Plant height and fresh top weight increased with an increase in nocturnal temperature across treatments. There were significant reductions in plant growth and development with T. basicola, but not with M. incognita, at these nocturnal temperatures, but decreased plant height and weight were seen where both pathogens were present in comparison with either pathogen alone. Trends of increased disease associated with T. basicola were observed with increasing inoculum rates of M. incognita, indicating that the interaction between T. basicola and M. incognita occurs even at soil temperatures below the minimum temperature reported as necessary for damage from M. incognita.

Effect of combined applications of Metarhizium anisopliae (Metsch.) Sorokin (Deuteromycotina: Hyphomycetes) strain CIAT 224 and different dosages of imidacloprid on the subterranean burrower bug Cyrtomenus bergi Froeschner (Hemiptera: Cydnidae)

Abstract The effects of combined applications of higher and lower dosages of imidacloprid (Confidor 350 SC) and Metarhizium anisopliae (Metsch.) Sorokin (strain CIAT 224) at different inoculum rates on the mortality of fourth instar nymphs of Cyrtomenus bergi Froeschner (Hem.: Cydnidae) were evaluated under laboratory and greenhouse conditions. Initially, the in vitro effects of three different concentrations of Confidor 350 SC or one concentration of its blank formulation on the vegetative growth of M. anisopliae were studied. In all tests on potato dextrose agar (PDA), significantly greater colony sizes than in the untreated control were recorded when M. anisopliae was cultured in the PDA medium amended with the insecticide and/or its blank formulation. Subsequently, C. bergi nymphal mortality was assessed in sand bioassays. A significantly higher C. bergi nymphal mortality was recorded in all experiments when M. anisopliae was applied in combination with imidacloprid compared to the fungus alone, and a synergistic interaction between the two agents was found throughout the entire experiments. Applications of M. anisopliae (1E+07 conidia/g sand) in combination with 1.05 μg imidacloprid/g sand resulted in 88.1% of C. bergi nymphal mortality compared to 39.5% when the fungus was applied alone at the same dosage, 20 days after application. The lower dosage of imidacloprid not only enhanced the efficacy of the pathogen but also lead to a reduced quantity of inoculum needed to cause high levels of nymphal mortality. 81.2% mortality was recorded 25 days after application of 1E+06 conidia/g sand and a lower dosage of imidacloprid, which was not significantly different to the mortality achieved using 1E+05 conidia/g sand and the same lower dosage. Interactions between M. anisopliae and imidacloprid were predominantly additive at low dosages of the fungus and synergistic at dosages greater than 1E+06 conidia/g sand. Combined applications of M. anisopliae and a lower dosage of imidacloprid also resulted in high mortality of C. bergi nymphs when the treatment was applied to a native Colombian soil under greenhouse conditions. Fifteen days after application, the interaction between M. anisopliae and imidacloprid was synergistic, and 30 days after the application of the treatments nymphal mortalities of 88.3 and 85% were recorded in sterile and non-sterile soil, respectively, compared to 70.8 and 41.7% in the two soil types following a sole application of M. anisopliae .

Cylindrocarpon didymum— a root pathogen of subterranean clover in the lower south-west of Western Australia

The pathogenicity ofCylindrocarpon didymum towards roots of subterranean clover (Trifolium subterraneum) at four inoculum rates (0.5, 1.0, 2.0, 5.0% w/w) under three temperature regimes (15/10, 18/13, 21/16°C) and the ability ofC. didymum to produce the mycotoxin brefeldin Ain vitro was determined.C. didymum infected and damaged tap and lateral roots of subterranean clover and reduced plant dry weights, particularly when sufficiently high levels of inoculum were present. Most disease occurred at the cooler temperature regime of 15/10°C, a temperature regime that would closely approximate field soil temperatures in the lower south-west of Western Australia during the winter months.C. didymum produced brefeldin Ain vitro and the frequently observed, stunted appearance of affected tap and lateral roots was possibly as a consequence of production of brefeldin A in the root tissue by this pathogen. This is the first published report ofC. didymum as a root pathogen of subterranean clover.

Survival of Lactobacillus acidophilus LA-5 and Bifidobacterium bifidum BB-02 in white-brined cheese

The viability of probiotic cultures used as adjunct cultures including Bifidobacterium bifidum BB-02 and Lactobacillus acidophilus LA-5 in white-brined cheese was investigated. The microbiological and biochemical properties of cheeses were assessed throughout 90 days of storage. Two inoculum rates for probiotic starters (2.5% and 5.0%, v/v, corresponding to (1.0–1.3)×109 cfu/g and (2.0–2.1)×109 cfu/g, respectively) were compared with the control cheese. Results obtained showed that a higher inoculum rate resulted in faster proteolysis. The cheese inoculated with 5% probiotic strains had higher water-soluble nitrogen, non-protein nitrogen, proteose-peptone nitrogen and tyrosine values than the other experimental cheeses. At the end of storage, the cheese supplemented with 5% probiotic culture had a ripening coefficient of 28.3%, followed by 2.5% probiotic strains containing the sample being 24.9%, and the control being 23.6%, respectively. It was also found that the colony counts of both probiotic microorganisms declined during storage. After 90 days of storage, the number of probiotic colonies were still around the threshold for a minimum probiotic effect (106 cfu/g).

Use of response surface methodology for optimizing process parameters for the production of α-amylase by Aspergillus oryzae

Optimization of three parameters (incubation temperature, initial substrate moisture and inoculum size) was attempted by using a Box–Behnken design under the response surface methodology for the optimal production of α-amylase by Aspergillus oryzae NRRL 6270 in solid-state fermentation (SSF). Spent brewing grains (SBG) was used as sole carbon source. The experimental data was fitted into a polynomial model for the yield of enzyme and an optimum level was arrived at which nutrient supplements were optimized. A Plackett–Burman design was employed to screen nineteen nutrient components for their influence on α-amylase production by the fungal culture. Three components (soybean meal, calcium chloride and magnesium sulphate) were selected based on their positive influence on enzyme formation. A Box–Behnken design was employed to optimize their composition, which showed that an incubation temperature of 30 °C, an initial moisture of 70% and an inoculum rate of 1×10 7 spores/g dry substrate were the best conditions to produce α-amylase with A. oryzae NRRL 6270 on SBG. Under optimized conditions of SSF, about 20% increase in enzyme yield was observed.

Media and Fermentation Processes for the Rapid Production of High Concentrations of Stable Blastospores of the Bioinsecticidal Fungus Paecilomyces fumosoroseus

In shake flask and fermentor studies, various media components and culture inocula were tested to improve P. fumosoroseus spore production rates, yield and stability. To evaluate inoculum potential and inoculum scale-up for fermentor studies, conidia and liquid culture-produced spores of various strains of P. fumosoroseus were compared as inoculum. Inoculation of liquid cultures with blastospores at concentrations of at least 1×106 spores mL−1 resulted in the rapid production of high concentrations of blastospores (∼1×109 spores mL−1, 48 h fermentation time) for all strains tested. The rapid germination rate of blastospores (90% after 6 h incubation) compared to conidia (>90% after 16 h incubation) and the use of higher inoculum rates reduced the fermentation time from 96 to 48 h for maximal spore yields. A comparison of various complex nitrogen sources showed that liquid media supplemented with acid hydrolyzed casein or yeast extract supported the production of high concentrations of blastospores that were significantly more desiccation-tolerant (79-82% survival after drying) when compared to blastospores produced in media supplemented with other nitrogen sources (12-50% survival after drying). For rapid spore production, requirements for trace metals and vitamin supplementation were dependent on the type of hydrolyzed casein used in the medium. Fermentor studies with two strains of P. fumosoroseus showed that high concentrations (1.3-1.8×109 spores mL−1) of desiccation-tolerant blastospores could be produced in 48-h fermentations. These studies have demonstrated that the infective spores of various strains of the fungal bioinsecticide Paecilomyces fumosoroseus can be rapidly produced using deep-tank, liquid culture fermentation techniques.

Inoculum Rate Influences Selection for Field Resistance to Soybean Sudden Death Syndrome in the Greenhouse

Effective selection of field resistance to soybean sudden death syndrome (SDS) caused by Fusarium solani (Mart.) Sacc. f. sp. glycines (Fsg) (Roy, 1997), measured by disease index (DX), requires multiple environments. Current greenhouse assays reduce genotype × environment interactions, but fail to predict field resistance. Our objective was to compare selection for field resistance to SDS in the greenhouse among recombinant inbred lines (RILs) inoculated with Fsg at three rates. Thirty soybean [Glycine max (L.) Merr.] RILs with characterized field resistance to SDS were evaluated in the greenhouse for scorch severity at three inoculum rates in four experiments. Ten cultivars with characterized field resistance were compared using disease severity (DS) readings from one experiment at one inoculum rate. The heritability of DS among RILs in the greenhouse was 46% at the low, 66% at the moderate, and 37% at the high inoculum rates. Reduced inoculum rates in the greenhouse (3500 to 5000 spores cm−3 plant growth medium) provided DS values that explained ≈65% of variation in the field Using a Fsg inoculum rate of 5000 spores cm−3 plant growth medium and greenhouse midparent DS as criterion for selection, the number of lines potentially resistant to SDS within a segregating population could be reduced by 53%. Errors caused ≈10% of field resistant lines to be eliminated. Among unrelated soybean cultivars, greenhouse DS values from an inoculum rate of 4000 spores cm−3 plant growth medium explained 81 and 73% of variations in field DS and DX, respectively. Therefore, the method is an effective tool for inheritance studies and cultivar evaluation for SDS.

Inoculation of containerized Pinus pinea L. seedlings with seven ectomycorrhizal fungi

Containerized Pinus pinea L. seedlings are commonly used for reforestation in the Mediterranean area. While there is an increasing knowledge of the potential ectomycorrhizal fungi associated with Pinus pinea, few studies exist of inoculation techniques with selected ectomycorrhizal fungi. We tested seven ectomycorrhizal fungi for their effectiveness with containerized Pinus pinea seedlings. Hebeloma crustuliniforme, Laccaria laccata and Pisolithus tinctorius were applied as vegetative inocula while Melanogaster ambiguus, Pisolithus tinctorius, Rhizopogon luteolus, Rhizopogon roseolus and Scleroderma verrucosum were tested as spore inocula. The inoculum of each fungus was tested at several application rates. Among the fungi tested as vegetative inocula, the highest percentages of ectomycorrhizas were obtained with H. crustuliniforme at all rates tested. The ectomycorrhizas formed by L. laccata varied from 11% to 40% depending on the inoculum rate applied. Vegetative inoculum of Pisolithus tinctorius was only effective at the highest inoculum rates and gave mycorrhization percentages around 60%. Pisolithus tinctorius applied as a spore inoculum formed ectomycorrhizas at a frequency of about 50% at the effective inoculum rates. The rest of the fungi applied as spore inocula produced more than 50% of ectomycorrhizas at the effective spore concentrations. These included the highest percentages of ectomycorrhizas (>80%) obtained with both Rhizopogon species. Differences in growth due to inoculation with the different fungi were not detected and in some cases inoculation even reduced the total biomass accumulated by seedlings. All seedlings reached a size suitable for transplantation.

Varied rates of mycorrhizal inoculum on growth and nutrient acquisition by barley grown with drought stress

Effectiveness of arbuscular mycorrhizal fungi (AMF) is crucial for maximum plant growth and acquisition of mineral nutrients under drought. The objective of this research was to determine effects of varied rates of AMF inoculum on plant growth and acquisition of phosphorus (P), zinc (Zn), copper (Cu), and manganese (Mn) by barley (Hordeum vulgare L. cv. SLB‐6) grown with and without drought stress (WS and nonWS). Plants inoculated with four inoculum rates [control (M0), 120 (M1), 240 (M2), and360 (M3) spores per 100 g dry soil] of Glomus mosseae were grown in a low P silty clay (Typic Xerochrept) soil (pH=8.0) mix in a greenhouse for 45 days. Root AMF colonization increased as inoculum rate increased in plants grown with WS and nonWS. Leaf area and shoot and root dry matter (DM) increased as inoculum rate increased up to M2 regardless of soil moisture. Shoot concentrations of P, Cu, and Mn were generally higher for mycorrhizal (AMF) than for nonmycorrhizal (nonAMF) plants grown with both WS and nonWS. Shoot contents of P, Zn, Cu, and Mn were higher for AMF than for nonAMF plants grown with nonWS, and shoot contents of P were higher for AMF than for nonAMF plants with WS. For plants grown with WS and nonWS, contents of P, Zn, Cu, and Mn were generally higher for plants inoculated with M2 compared to other rates of inoculum. The results of this study indicated that plant responses to root colonization with AMF were dependent on AMF rate and soil moisture. Based on enhancements in plant DM and mineral acquisition traits, M2 inoculum was the most effective rate of inoculation for this AMF isolate.

Effect of Inoculum Rate of Biological Control Agents on Preharvest Aflatoxin Contamination of Peanuts

Studies were conducted during 1994 and 1995 in the environmental control plot facility at the National Peanut Research Laboratory to determine the effect of different inoculum rates of biological control agents on preharvest aflatoxin contamination of Florunner peanuts. Biocontrol agents were nontoxigenic color mutants ofAspergillus flavusandAspergillus parasiticusthat were grown on rice for use as soil inoculum. Three replicate plots (4.0 × 5.5 m) were treated with 0, 2, 10, and 50 g/m of row (0, 20, 100, and 500 lb/acre, respectively) of an equal mixture of the color mutant-infested rice in 1994, and the same plots were retreated in 1995. Aflatoxin concentrations were determined by high performance liquid chromatographic analysis of all peanuts. Treatment means for total kernels in 1994 were 337.6, 73.7, 34.8, and 33.3 ppb for the 0, 2, 10, and 50 g/m treatments, respectively. Regression analysis indicated a trend toward lower aflatoxin concentrations with increasing rates of inoculum (R2= 0.40;P< 0.05). For the same repeated treatments in 1995 aflatoxin concentrations in total kernels averaged 718.3, 184.4, 35.9, and 0.4 ppb. Regression analysis revealed a stronger relationship between inoculum rate and aflatoxin concentrations (R2= 0.66;P< 0.05) in the second year of treatment. Compared with untreated controls, the 2, 10, and 50 g/m treatments produced respective reductions in aflatoxin of 74.3, 95.0, and 99.9% in the second year. The data indicated not only a treatment-related effect, but also that a higher degree of control might be achieved when plots or fields are retreated with biocontrol agents in subsequent years.

Seed Treatment Using Pre-infiltration and Biocontrol Agents to Reduce Damping-off of Corn Caused by Species of Pythium and Fusarium.

Bioassays were conducted in a greenhouse at 18°C to determine the effectiveness of a seed treatment used in combination with biocontrol agents for the reduction of corn damping-off caused by species of Pythium and Fusarium. Corn seeds were infiltrated with tap water, drained, air-dried, and then coated with biomass of an antagonistic fungus, Gliocladium virens isolate Gl-3, or an antagonistic bacterium, Burkholderia cepacia isolates Bc-B or Bc-1, or a combination of Gl-3 with each of the bacterial isolates. A nonsterile field soil was infested with a combination of pathogens: Pythium ultimum, P. arrhenomanes, and Fusarium graminearum at 2 inoculum rates (1× and 4×). Pre-infiltration enhanced (P ≤ 0.05) disease control with most treatments at both inoculum rates. Treatments with biocontrol agents alone or in combination, as well as the fungicide captan, effectively reduced the disease at a pathogen inoculum rate of 1×, resulting in greater (P ≤ 0.05) seedling stands, plant height, and fresh weight, and lower (P ≤ 0.05) root rot severity compared with untreated seeds in infested soil. At a pathogen inoculum rate of 4×, stands were lower (P ≤ 0.01) and root-rot severity was higher (P ≤ 0.01) compared to those at 1× for all treatments. Nevertheless, coating seeds with all biocontrol agents (alone or in combination), except with Bc-1 alone, reduced disease (P ≤ 0.05) compared to untreated seeds in infested soil. At both inoculum rates of 1× and 4×, coating seeds with Gl-3 + Bc-B was more effective (P ≤ 0.05) in disease control than any other treatment, resulting in stands, growth rate (plant height and fresh weight), and root rot severity similar to plants from untreated seeds in noninfested soil. In addition, when the exudate from a 2-h infiltration of corn seed was added to the seeds during seed coating, seedling stand was often lower and root rot severity was often higher than those from infiltrated seeds (P ≤ 0.05). These results indicated that the infiltration process removed certain exudates, including nutrients and/or stimulants (not detected in this study) that might be utilized by pathogens to initiate seed infection. A thin-layer chromatography (TLC) profile of the exudates showed the presence of eight amino acids and three major carbohydrates.

Striga hermonthica Seed Inoculum Rate Effects on Maize Hybrid Tolerance and Susceptibility Expression

A parasitic plant, Striga hermonthica (Del.) Benth., infests millions of hectares of arable land in sub‐Saharan Africa, and it threatens production of major cereal crops including maize (Zea mays L.). Erratic natural infestation is considered a major constraint to assess host plant resistance to the parasite. The objective of this study was to evaluate the effects of different S. hermonthica seed inoculum rates on a tolerant and a susceptible maize genotype. Individual maize plants of the tolerant (8322‐13) and the susceptible maize hybrid (8338‐1) were inoculated with six rates of germinable Striga seeds: 750, 1500, 2250, 3000, 3750, and 4500. Uninfested plots served as the control. The experiment was conducted at two locations, Mokwa (two seasons) and Abuja (one season), in Nigeria. Increasing Striga inoculum level increased Striga emergence and the amount of damage to the host plant, plant height, and grain yield of the host crop. The tolerant hybrid showed less host plant damage (P &lt; 0.01) and that fewer S. hermonthica plants emerged (P &lt; 0.05) than the susceptible hybrid. Among the four traits studied, host plant damages core was most correlated with grain yield (r = −0.65**). Average grain yield of the tolerant hybrid, 8322‐13, was 97% higher than that of the susceptible hybrid, 8338‐1, across the six inocolum rates. The tolerant hybrid produced similar grain yields under all levels of the inoculum; the yield reductions ranged from 27% (2250 seeds) to 35% (4500 seeds), while the yield reduction of the susceptible hybrid ranged from 43% (750 seeds) to 74% (3750 seeds). Based on the results this study, we conclude that host plant tolerance is the key element for stabilizing crop yield under S. hermonthica infestation.