Biological Control of Groundnut Late Leaf Spot and Rust by Seed and Foliar Applications of a Powder Formulation of Pseudomonas fluorescens

Glasshouse and field trials were conducted to determine the efficacy of a talc-based powder formulation of Pseudomonas fluorescens strain Pf1 in controlling groundnut leaf spot ( Cercosporidium personatum ) and rust ( Puccinia arachidis ). Seed treatment with the talc-based powder formulation of the bacterium alone effectively reduced the severity of leaf spot and rust. When the treated seeds were sown in soil, the antagonist moved to the rhizosphere and multiplied well in it. Foliar application with the powder formulation effectively controlled the groundnut leaf spot and rust. P. fluorescens multiplied well in the phyllosphere after foliar application of powder formulation. Combined application of the P. fluorescens formulation to seed and foliage effectively controlled leaf spot and rust, and increased the pod yield in greenhouse and field tests.     

国槐DNA导入花生D5代性状遗传变异的分析

利用花粉管通道技术对国槐DNA导入花生栽培品种79266,D2代变异株98D010－7经连续自交,D3代获得9个株系,61个株行,641个单株,观察D5代群体内每个单株的开花型、株型、主茎高、第一对侧枝长、分枝数及单株结果数等主要农艺性状的表现型。结果表明：（1）79266和98D010－7均为连续开花型,D5代出现了交替开花型变异株,占总株数4．37％,开花型分离株行占16．39％;（2）79266株型直立,98D010－7株型葡匐,D5代表现型有直立,葡匐和半葡匐3种类型,分别占34．95％、14．04％和51．09％;表现分离的株行占73．77％;（3）株高和第一对侧枝长与79266相比显著降低;（4）单档分枝数与受体平均值相近,只有1个株系分枝数显著少于受体79266,其它8个株系差异不显著;（5）D5代群体有3个株系的单株结果数显著大于受体79266的单株结果数。     

Use of Rhizobacteria in the Control of Root Rot–Root Knot Disease Complex of Mungbean

Thirty-two isolates of Pseudomonas aeruginosa and a Bacillus subtilis strain were isolated from rhizosphere and rhizoplane of four wild and 15 cultivated plants. Biocontrol and growth-promoting potentials of the bacterial isolates were tested under laboratory, greenhouse and field conditions. The bacterial isolates not only exhibited nematicidal activity by killing the second stage larvae of Meloidogyne javanica to a varying degree but also produced inhibition zones by inhibiting the radial growth of Macrophomina phaseolina, Fusarium solani and Rhizoctonia solani . Strain IE-2 and IE-6 of P. aeruginosa also lysed the fungal mycelium. P. aeruginosa and B. subtilis used as seed dressing or as soil drench significantly suppressed root rot–root knot infection and nematode population densities under greenhouse and field conditions and thereby enhanced plant growth and yield in mungbean.     

一种利用生理指标评价玉米弯孢菌叶斑病抗性的方法

本试验以4种不同抗性的玉米自交系幼苗为材料,比较了新月弯孢菌毒素浓度和处理时间对玉米主要防御酶系苯丙氨酸解氨酶（PAL）、过氧化酶（POD）和超氧化物歧化酶（SOD）比活力的影响。结果表明：在不同毒素浓度和胁迫时间下,PAL、POD和SOD比活力与品种抗病性的相关程度不一致。稀释200倍的毒素溶液处理玉米幼苗12h时,PAL比活力与抗病性呈极显著线性正相关,POD比活力与抗病性呈曲线正相关,SOD比活力与玉米抗病性呈极显著线性负相关。因此,可利用稀释200倍的新月弯孢菌毒素溶液处理12h时测得的玉米幼苗PAL、POD及SOD比活力估算玉米自交系弯孢菌叶斑病的抗性水平。     

Foliar Application of Fungal Biocontrol Agents for the Control of White Mold of Dry Bean Caused by Sclerotinia sclerotiorum

Field experiments were conducted during 1992–1994 to evaluate the effectiveness of five indigenous fungi for control of white mold (Sclerotinia sclerotiorum) of dry bean (Phaseolus vulgaris). The five fungi consisted of one antagonist, Epicoccum purpurascens, and four mycoparasites, Coniothyrium minitans, Talaromyces flavus, Trichothecium roseum, and Trichoderma virens. Spore suspensions of each fungus were sprayed onto bean plants two or three times during the early bloom to midbloom period. Incidence of white mold of dry bean was significantly reduced by all biocontrol agents. C. minitans and E. purpurascens, the most effective agents, reduced the proportion of plants infected by an average of 56 and 43%, respectively (P < 0.001). C. minitans was the only biocontrol agent recovered consistently from sclerotia and diseased seed present in harvested samples. It was recovered at similar frequencies in samples from all treatments. Of the sclerotia of S. sclerotiorum collected from harvested seed, 59% were infected by C. minitans in 1993 and 20% were infected by C. minitans in 1994. In three additional trials in 1994, comparing C. minitans with the fungicide benomyl, the fungus was not effective in any of the experiments, whereas benomyl reduced disease incidence relative to the control in one trial. The study suggests that, among the five indigenous fungi, C. minitans is the most promising agent for control of white mold of dry bean under Canadian prairie conditions.     

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.     

Suppression of Meloidogyne arenaria Race 1 by Soil Application of Endospores of Pasteuria penetrans

The potential of Pasteuria penetrans for suppressing Meloidogyne arenaria race 1 on peanut (Arachis hypogaea) was tested over a 2-year period in a field microplot experiment. Endospores of P. penetrans were mass-produced on M. arenaria race 1 infecting tomato plants. Endospores were inoculated in the first year only at rates of 0, 1,000, 3,000, 10,000, and 100,000 endospores/g of soil, respectively, into the top 20 cm of microplots that were previously infested with M. arenaria race 1. One peanut seedling was planted in each microplot. In the first year, root gall indices and pod galls per microplot were significantly reduced by 60% and 95% for 100,000 endospores/g of soil, and 20% and 65% for 10,000 endospores/g of soil, respectively. Final densities of second-stage juveniles (J2) in soil were not significantly different among the treatments. The number of endospores attached to J2 and percentage of J2 with attached endospores significantly increased with increasing endospore inoculation levels. Pasteuria penetrans significantly reduced the densities of J2 that overwintered. In the second year, root and pod gall indices, respectively, were significantly reduced by 81% and 90% for 100,000 endospores/g of soil, and by 61% and 82% of 10,000 endospores/g of soil. Pod yields were significantly increased by 94% for 100,000 and by 57% for 10,000 endospores/g of soil, respectively. The effect of P. penetrans on final densities of J2 in soil was not significant. Regression analyses verified the role of P. penetrans in the suppression of M. arenaria. The minimum number of endospores required for significantly suppressing M. arenaria race 1 on peanut was 10,000 endospores/g of soil.