Control of Microdochium majus in winter wheat with botanicals – from laboratory to the field

The fungal pathogen Microdochium majus, causing snow mould, seedling blight and foot rot, results in severe yield losses in small grain cereals. There are few options to control this pathogen in organic production. In this study, aqueous extracts or botanical powders prepared from chamomile, meadowsweet, thyme and Chinese galls were tested in vitro against M. majus conidia germination and mycelial growth, respectively. Subsequently, three botanicals were chosen, applied as powders with different seed coating adhesives, and tested for their effect on the incidence of M. majus from naturally infected wheat seed lots and on seedling emergence from soil under controlled environmental conditions. Furthermore, seed treatments with warm water, a bacterial product or one chosen botanical were tested in a growth chamber and in a field experiment over three consecutive years. Of the botanicals tested, Chinese galls showed the highest efficacy in controlling M. majus, reducing conidia germination and mycelial growth by up to 97 and 100%, respectively, and reducing the incidence from infested seeds by up to 59%. In two growth chamber experiments, total seedling emergence increased by up to 30 and 59% compared with the control treatments following an application with Chinese galls. Under field conditions, yield increase through Chinese galls, the bacterial product and the warm water treatment was 19, 10 and 37% compared with the untreated control, respectively. This study demonstrates the potential of Chinese galls to control M. majus in wheat. Options for improved formulations or combinations of heat‐based treatments with Chinese galls are discussed.     

Effect of Dose Rate of Azoxystrobin and Metconazole on the Development of Fusarium Head Blight and the Accumulation of Deoxynivalenol (DON) in Wheat Grain

Glasshouse studies were undertaken to determine if fungicides used for the control of Fusarium head blight (FHB) result in elevated concentrations of the trichothecene mycotoxin, deoxynivalenol (DON) in harvested wheat grain. Metconazole and azoxystrobin, at double, full, half or quarter the manufacturer's recommended dose rate, were applied to ears of wheat (cv. Cadenza), artificially inoculated with conidia of either Fusarium culmorum or F. graminearum. Metconazole demonstrated high activity against both pathogens, reducing significantly the severity of FHB and the DON concentrations at each of the four dose rates tested when compared to untreated controls. Applications of azoxystrobin significantly reduced FHB and DON compared to unsprayed controls. However, their effectiveness was significantly less than that of metconazole and no dose rate response was observed. Quantification of the amount of trichothecene-producing Fusarium present in harvested grain was determined using a competitive PCR assay based on primers derived from the trichodiene synthase gene (Tri5). Simple linear regression analyses revealed strong relationships between the amount of trichothecene-producing Fusarium present in grain and the DON concentrations (r ²=0.72–0.97). It is concluded that fungicides, applied for the control of FHB, affect DON concentrations indirectly by influencing the amount of trichothecene-producing Fusarium species present in wheat grain. There was no evidence that fungicide applications directly increase the concentration of DON in grain.     

Induction of Systemic Acquired Resistance in Pepper Plants by Acibenzolar-S-methyl against Bacterial Spot Disease

The ability of acibenzolar-S-methyl to induce resistance in pepper plants against Xanthomonas campestris pv. vesicatoria was investigated in both growth chamber and open field conditions. Growth chamber experiments showed that acibenzolar-S-methyl (300M) treatment protects pepper plants systemically and locally against X. campestris pv. vesicatoria. Evidence for this was a reduction in the number and diameter of bacterial spots and bacterial growth in planta. Systemic protection was also exerted by the acibenzolar-S-methyl acid derivative, CGA 210007, which may be produced by hydrolysis in the plant. The efficacy of acibenzolar-S-methyl was also found in open field conditions, where both leaves and fruit were protected from the disease. The highest efficacy (about 67%) was obtained by spraying the plants 6–7 times every 8–12 days with a mixture of acibenzolar-S-methyl and copper hydroxide (2.5 + 40ghl^–1 active ingredient). Persistence and translocation data obtained from the growth chamber experiments revealed a persistence of acibenzolar-S-methyl lasting five days after treatment with rapid translocation and negligible levels of acid derivative formation. Since the protection exerted by acibenzolar-S-methyl against bacterial spot disease was observed when the inducer was completely degraded, it would appear to be due to SAR activation.     

Occurrence and Pathogenicity of Fusarium Species in Cereals in Finland1

Several Fusarium species occurred abundantly in spring cereal seed samples studied in 1966, 1968 and 1972 in Finland. A total of 17 species of Fusarium were isolated and identified. The most frequently isolated species were F. avenaceum (Fr.) Sacc., F. culmorum (W. G. Sm.) Sacc., F. poae (Peck) Wr. and F. tricinctum (Cda) Sacc. These species were found in more than 40% of the seed samples from 1972. The same 4 Fusarium species in addition to F. graminearum Schwabe were used in the pathogenicity test. Artificially inoculated spring wheat and barley seeds were grown in the field during the growing season of 1973. Of these 5 species F. culmorum was clearly the most pathogenic. This species significantly lowered the shooting percentage and the yield of both cereals. Foot rot assessment also revealed F. culmorum as the most damaging species. Natural soil-borne infection obviously increased the foot and root rot, and thus the soil-borne F. culmorum strongly affected all treatments. In the harvested seed F. poae dominated in all treatments, but F. culmorum still occurred most abundantly in the seed lot harvested from plots originally inoculated with this species.     

Effects of inoculum density,leaf wetness duration and nitrate concentration on the occurrence of lettuce leaf spot

In Ehime Prefecture, Japan, lettuce leaf spot (Septoria lactucae) caused huge losses in marketable lettuce yields. To explore potential measures to control disease outbreaks, the effects of inoculum density, leaf wetness duration and nitrate concentration on the development of leaf spot on lettuce (Lactuca sativa) were evaluated. Conidia were collected from diseased plants in an infested field by single-spore isolation and were used to inoculate potted lettuce plants with different conidial concentrations. Lesions developed on inoculated lettuce plants at inoculum concentrations from 10⁰ to 10⁶ conidia/ml. The disease was more severe when the inoculum exceeded 10² conidia/ml, and severity increased with increasing concentrations. Assessment of the relationship between disease development and the duration of postinoculation leaf wetness revealed that symptoms appeared when the inoculated plants remained wet for 12 h or longer. The number of lesions and total nitrogen content in the lettuce leaves both increased when nitrate was applied.     

Toxigenicity and pathogenicity of <Emphasis Type="Italic">Fusarium poae</Emphasis> and <Emphasis Type="Italic">Fusarium avenaceum</Emphasis> on wheat

In a field experiment between 2004 and 2006, 14 winter wheat varieties were inoculated with either a mixture of three isolates of F. poae or a mixture of three isolates of F. avenaceum. In a subsequent climate chamber experiment, the wheat variety Apogee was inoculated with individual single conidium isolates derived from the original poly conidium isolates used in the field. Disease symptoms on wheat heads were visually assessed, and the yield as well as the fungal incidence on harvested grains (field only) was determined. Furthermore, grains were analysed using LC-MS/MS to determine the content of Fusarium mycotoxins. In samples from field and climate chamber experiments, 60 to 4,860 μg kg⁻¹ nivalenol and 2,400 to 17,000 μg kg⁻¹ moniliformin were detected in grains infected with F. poae and F. avenaceum, respectively. Overall, isolate mixtures and individual isolates of F. avenaceum proved to be more pathogenic than those of F. poae, leading to a higher disease level, yield reductions up to 25%, and greater toxin contamination. For F. poae, all variables except for yield were strongly influenced by variety (field) and by isolate (climate chamber). For F. avenaceum, variety had a strong effect on all variables, but isolate effects on visual disease were not reflected in toxin production. Correlations between visual symptoms, fungal incidence, and toxin accumulation in grains are discussed.     

Passalora blight of anise (Pimpinella anisum) and its control in Turkey

Passalora blight of anise, caused byPassalora malkoffii (Bubák) U. Braun, is an important disease of anise in Turkey. The disease affects all the aboveground parts of plants including flower clusters. Infected seeds have dark, linear stromata. Detection of the pathogen on seeds was studied by the blotter method, agar method, washing test and sowing infected seeds in disease-free soils. The pathogen was recovered only by the washing test and to a limited extent by water agar + seed decoction agar. Sixteen of 24 seed samples from diseased regions were found to be infected. The pathogen was not detected by any other methods. However, several indigenous fungi,e.g. Alternaria alternata, were isolated, which may have prevented the growth of the pathogen. Seed washings of infected seed samples had typical spores of the pathogen up to 10⁶ conidia per gram of seed. Transmission of the pathogen was shown by sowing infected seeds in disease-free field soils in two locations where anise had not been grown previously. Azoxystrobin, chlorothalonil + carbendazim and flutriafol seed treatments at 0.04 g a.i. kg⁻¹ seed, 1.0 g + 4.5 g a.i. kg⁻¹ seed and 0.015 g a.i. kg⁻¹ seed reduced the disease by 92.5%, 89.6% and 36.2% in 2002 and by 78.9%, 75.8% and 41.2% in 2003, respectively. Three foliar applications of axosystrobin, chlorothalonil + carbendazim and flutriafol at the rates of 187.5 g a.i. ha⁻¹, 1500 g + 6750 g a.i. ha⁻¹ and 31.3 g a.i ha⁻¹ reduced disease incidence by 92.5%, 86.0% and 96.8% in 2002 and by 97.5%, 90.8% and 97.0% in 2003, respectively. http://www.phytoparasitica.org posting May 17, 2005.     

Biocontrol agents in combination with Moringa oleifera extract for integrated control of Sclerotium-caused cowpea damping-off and stem rot

Damping-off and stem rot disease-causing Sclerotium rolfsii has been reported as a destructive soil-borne pathogen of numerous crops, especially in the tropics and subtropics. Trials were conducted to test the efficacy of biocontrol agents alone or combined with Moringa oleifera leaf extracts for the control of the disease. In the laboratory, PDA was amended with Moringa leaf extract, and mycelial growth of S. rolfsii was measured. In the greenhouse and field, Trichoderma Kd 63, Trichoderma IITA 508 and Bacillus subtilis were evaluated as seed treatments, soil drench or sprinkle, separately or combined with Moringa leaf extracts. Percentage disease incidence, severity and control were recorded. In the laboratory, the higher the extract concentration the less the mycelial growth and no mycelial growth occurred on extract at 15 or 20 g leaves 10 ml⁻¹ water. In the greenhouse, the highest disease control was observed at a Moringa extract concentration of 15 kg leaves 10 l⁻¹ water (w/v). Seed treatments using Trichoderma Kd 63, and soil sprinkle using Trichoderma IITA 508 had a significantly (P = 0.05) higher effect on a disease incidence than Bacillus. Disease severity followed the same pattern. Moringa seed treatment combined with Trichoderma soil sprinkle resulted in significantly more than 94% and 70% disease control in the greenhouse and field, respectively, with significant yield increase in the field. This is the first report of Moringa leaf extract combined with Trichoderma as an integrated control for Sclerotium damping-off and stem rot of cowpea in the field.     

Genetic variation of aggressiveness in individual field populations ofFusarium graminearum andFusarium culmorum tested on young plants of winter rye

Fusarium graminearum andF. culmorum are capable of infecting winter cereals at all growth stages. From natural field epidemics of wheat head blight and rye foot rot, three fungal populations were collected with 21, 38 and 54 isolates, respectively; their aggressiveness was analyzed in comparison to collections ofF. graminearum (25 isolates) andF. culmorum (70 isolates) that represent a wide range of geographical locations and host species. All isolates were tested for aggressiveness on young plants of winter rye in the greenhouse and scored for disease severity on a 1–9 scale. Disease ratings of individual isolates ranged from 1.5 to 5.7 indicating quantitative variation of aggressiveness. Genotypic variance was highest in the twoFusarium collections. No substantial difference was found in the amount of genotypic variation betweenF. graminearum andF. culmorum. Individual field populations revealed 57–66% of the total genotypic variation of the collections. This implies a high degree of diversity of aggressiveness within single field populations ofF. graminearum andF. culmorum causing natural epidemics.     

Biological Control of Sclerotinia Diseases of Rapeseed by Aerial Applications of the Mycoparasite Coniothyrium minitans

Indoor and field experiments were conducted to evaluate the efficacy of applying the mycoparasite Coniothyrium minitans to the aerial parts of rapeseed plants at the flowering stage to control sclerotinia diseases caused by Sclerotinia sclerotiorum. Under controlled conditions, a petal inoculation technique was used to determine the effect of conidial suspensions of C. minitans on suppression of sclerotinia leaf blight. Results showed that C. minitans was effective in inhibiting infection initiated by ascospores of S. sclerotiorum on flower petals by restricting mycelial growth of the pathogen. Suppression of lesion development was related to the conidial concentration of C. minitans, with larger lesions at low concentration (5×10³conidia ml⁻¹), but smaller lesions at high concentration (5×10⁴ conidia ml⁻¹ or higher). When C. minitans-treated rapeseed leaves were inoculated with mycelia of S. sclerotiorum, C. minitans failed to prevent infection of leaves, but caused a significant reduction in number of sclerotia produced on the diseased leaves. No significant difference in efficacy was detected between the two isolates of C. minitans, LRC 2137 and Chy-1, on the two rapeseed cultivars, Westar (spring type) and Zhongyou 821 (winter type). Results of field trials showed a significant reduction of stem rot of rapeseed in four (1997, 1999, 2003 and 2004) out of five years by aerial application of C. minitans, compared with controls. No significant difference in suppressive efficacy was observed between the treatments of C. minitans (10⁶ conidia ml⁻¹), C. minitans (10⁶ conidia ml⁻¹) + benomyl (50 μg ml⁻¹) and benomyl (100 μg ml⁻¹) in 2003, and between the treatments of C. minitans (10⁶ conidia ml⁻¹), C. minitans (10⁶ conidia ml⁻¹) + vinclozolin (100 μg ml⁻¹) and vinclozolin (500 μg ml⁻¹) in 2004. Sclerotia of S. sclerotiorum collected from diseased plants in plots treated with C. minitans in 1999, 2000 and 2003, or with C. minitans + benomyl in 2003 were infected by C. minitans at frequencies ranging from 21.3 to 54.5%. This study concludes that aerial spraying of C. minitans is an effective method for controlling sclerotinia diseases of rapeseed.     

Effect of Fungicides on Fusarium Head Blight and Deoxynivalenol Content in Durum Wheat Grain

In 1998–99 and 1999–2000 six trials were conducted to evaluate the effect of fungicides on Fusarium head blight in the field, on infected kernels and deoxynivalenol (DON) concentration in grain. A single application of prochloraz, tebuconazole, epoxiconazole or bromuconazole, applied to durum wheat varieties at the manufacturer's recommended dose at the beginning of anthesis stage, provided good control of the disease when infective pressure in the field was low to medium, and when the main pathogens were F. graminearum and F. culmorum. Kresoxim-methyl showed a low efficacy at controlling the disease. Tebuconazole, prochloraz and bromuconazole were effective at controlling F. graminearum and F. culmorum, while kresoxim-methyl was not effective in reducing Fusarium infected kernels. DON concentration in grain of cultivars inoculated with F. graminearum and F. culmorum was high, averaging 4.2mgkg^–1 (untreated control). Tebuconazole, prochloraz and bromuconazole reduced DON concentration by 43%, while epoxiconazole was ineffective. DON concentration in kernels of naturally infected cultivars was 1.95mgkg^–1, a concentration which exceeds the 1mgkg^–1 maximum level of contamination allowed in the United States. Furthermore prochloraz, bromuconazole and tebuconazole applications, in the naturally inoculated trials, reduced DON concentration from 73% to 96%, while epoxiconazole showed the lowest effectiveness. Moreover, a positive linear correlation between Fusarium infected grains and the DON concentration was observed.     

Biopriming of Infected Carrot Seed with an Antagonist, Clonostachys rosea, Selected for Control of Seedborne Alternaria spp

ABSTRACT An ecological approach was used to select fungal antagonists effective against the seedborne pathogens Alternaria dauci and A. radicina on carrot. Twenty-five and 105 isolates originating from cereal and carrot habitats were screened against the pathogens in planta, respectively. Irrespective of isolate origin, fungal isolates belonging to Clonostachys rosea controlled pre- and postemergence death caused by A. dauci and A. radicina as effectively as the fungicide iprodione. Isolate IK726 of C. rosea was used in biopriming a seed lot with 29% A. radicina and 11% A. dauci (highly infected), and a seed lot with 4% A. radicina and 7% A. dauci (low infection). Seeds were primed with water alone (hydropriming) or with addition of C. rosea IK726 (biopriming). The occurrence of A. radicina and A. dauci increased twofold and fivefold, respectively, during 14 days hydropriming, irrespective of the initial infection level. On highly infected seed, biopriming reduced the incidence of A. radicina to <2.3% and that of A. dauci to <4.8% while the level of both pathogens was <0.5% on bioprimed seed with a low initial infection rate. In sand stand establishment tests, hydroprimed seeds had a lower healthy seedling stand than nonprimed seeds, mainly due to a high degree of postemergence seedling death. In contrast, biopriming resulted in a seedling stand that was better than that of both nonprimed and hydroprimed seeds. C. rosea IK726 multiplied fivefold to eightfold, and microscopic observations using C. rosea IK726 transformed with a green fluorescent protein (GFP) reporter gene showed that seeds were covered with a fine web of sporulating mycelium of C. rosea. The positive effect of biopriming on healthy seedling stand remained after 5 months of storage at 4 degrees C and IK726 survived at high numbers on these seed. In this study, we demonstrated that bio-priming with the biocontrol strain C. rosea IK726 facilitates priming of infected seeds without risking adverse effects on seedling establishment.     

Axenic culture and influence of wetness period and inoculum concentration on infection and development of cercospora blight ofHeliotropium europaeum

Cercospora heliotropii-bocconii is a fungal pathogen of the ephemeral annual weedHeliotropium europaeum. The effects of wetness period and inoculum concentration on disease severity were studied under controlled conditions. The fungus was grown on different artificial culture media and carrot juice agar with 5 g l^–1 yeast extract was found to be the most suitable medium for conidial production under artificial conditions. Abundant disease symptoms only occurred after 8 h of wetness at 20°C. The minimum incubation period before disease symptoms appeared was 8 days following a wetness period of at least 40 h. Inoculum concentration of 1×10⁴ conidia per ml killed plants in less than one month and reduced seed production by two thirds. These results suggest that this pathogen has the potential to reduce plant survival and seed bank replenishment of this annual weed species.     

New Media for Increasing Sporulation and Germination of Phaeoisariopsis Griseola Conidia

The slow growth rate of the fungus Phaeoisariopsis griseola and the availability of a homogeneous highly concentrated inoculum is an important constraint for pathogenicity or virulence studies, where plant inoculations are needed. Therefore, the purpose of this paper was to evaluate the effect of supplementing culture media with Amaranthus cruentus seed meal on fungal growth and sporulation of isolates of P. griseola belonging to the Mesoamerican and Andean groups. The amendment of PDA or V8 media with A. cruentus seed meal resulted in a considerable increase in the number of conidia and also in their capacity to germinate; this depended mostly on the stage of maturity of conidia. Mesoamerican and Andean isolates produced a different number of conidia when cultured in vitro. Furthermore, while in Mesoamerican isolates a second degree polynomial represented the relationship between number of conidia and amount of A. cruentus supplementation, in Andean isolates the relationship was linear. It seems that either one or several of the nutritional factors provided by A. cruentus contributed to the increased production of conidia and their development, resulting in faster development of the disease and an earlier appearance of symptoms. Therefore, for cultural studies, especially for inoculum production and for pathogenicity evaluations, supplementation of the media with A. cruentus seed meal proved to be a good alternative.     

Evaluation of non-chemical seed treatment methods for the control of Alternaria dauci and A. radicina on carrot seeds

The current study was initiated to evaluate the efficacy of physical methods (hot water, aerated steam, electron treatment) and agents of natural origin (resistance inducers, plant derived products, micro-organisms) as seed treatments of carrots for control of Alternaria dauci and A. radicina. Control of both Alternaria species by seed treatment with the resistance inducers was generally poor. Results were also not satisfactory with most of the formulated commercial micro-organism preparations. Based on the average of five field trials, one of these, BA 2552 (Pseudomonas chlororaphis), provided a low but significant increase in plant stand. Among the experimental micro-organisms, the best results were obtained with Pseudomonas sp. strain MF 416 and Clonostachys rosea strain IK726. A similar level of efficacy was provided by seed treatment with an emulsion (1%) of thyme oil in water. Good and consistent control was generally achieved with the physical methods aerated steam, hot water and electron treatment. Aerated steam treatment was, apart from the thiram-containing chemical standard, the best single treatment, and its performance may at least partially be due to extensive pre-testing, resulting in dosages optimally adapted to the respective seed lot. In some of the experiments the effect of the hot water treatment, which was tested at a fixed, not specifically adapted dosage, was significantly improved when combined with a Pseudomonas sp. MF 416 or C. rosea IK726 treatment. The results are discussed in relation to the outcome of experiments in which the same seed treatment methods and agents were tested in other seed-borne vegetable pathosystems.     

棉花内生真菌CEF-373菌株对棉花黄萎病的防效及其作用机理

为明确棉花内生真菌CEF-373菌株对棉花黄萎病的防效及其作用机理,利用圆盘滤膜法和平板对扣培养法测定菌株CEF-373对大丽轮枝菌Verticillium dahliae菌丝生长的抑制作用,测定其对棉花黄萎病的温室和田间防效,并通过活性氧含量及防御基因表达情况来分析其作用机理。结果表明,菌株CEF-373的挥发性代谢产物和非挥发性代谢产物对大丽轮枝菌菌丝的生长均有显著抑制作用,抑制率最高分别可达37.75%和100.00%。用1×107CFU/mL的菌株CEF-373分生孢子悬浮液灌根后,对棉花黄萎病的温室防效可达71.12%,用质量比为3%的菌株CEF-373固体菌剂拌土栽培后,对棉花黄萎病的温室防效可达62.74%,防治作用显著。菌株CEF-373的发酵液滴灌和微生物肥料处理40 d后,对棉花黄萎病的田间防效达到最大,分别为36.23%和27.71%,而在后期有所降低。菌株CEF-373可以诱导棉花叶片中细胞活性氧的爆发;且菌株CEF-373成功激活了苯丙氨酸解氨酶、过氧化物酶、多酚氧化酶、几丁质酶和病程相关蛋白基因PR10的表达,对大丽轮枝菌的侵染具有抵御作用。表明棉花内生真菌CEF-373菌株通过抑制大丽轮枝菌生长以及诱导寄主系统抗病性来有效防治棉花黄萎病,具有较好的生物防治应用前景。     

Studies on in vitro Growth and Pathogenicity of European Fusarium Fungi

The effect of temperature on the in vitro growth rates and pathogenicity of a European Fusarium collection consisting of isolates of Fusarium graminearum, F. culmorum, F. avenaceum, F. poae and Microdochium nivale was examined. Irrespective of geographic origin, the optimum temperature for the growth of F. graminearum, F. culmorum and F. poae was 25 °C, while that for F. avenaceum and M. nivale was 20 °C. In general, the growth rates of F. graminearum, F. culmorum and F. poae increased between 10 and 25 °C and those of F. avenaceum and M. nivale increased between 10 and 20 °C. Pathogenicity tests were carried out by examining the effect of the five species on the in vitro coleoptile growth rate of wheat seedlings (cv. Falstaff). Irrespective of geographic origin, the temperature at which F. avenaceum, F. culmorum and F. graminearum caused the greatest retardation in coleoptile growth ranges 20–25 °C (>89.3% reduction), whilst for F. poae and M. nivale it was 10–15 °C (>45.6% retardation), relative to uninoculated control seedlings. In general, F. culmorum and F. graminearum were the most pathogenic of the five species, causing at least a 69% reduction in coleoptile growth at 10, 15, 20 and 25 °C. General linear model analysis (GLIM) showed that species accounted for 51.3–63.4% of the variation in isolate growth and from 19.5% to 44.3% of the variation in in vitro pathogenicity. Country of origin contributed from 22.6% to 51.9% to growth rate variation and from 0.73% to 7.61% to pathogenicity variation. The only significant correlation between in vitro growth and pathogenicity was that observed for M. nivale at 15 °C (r = -0.803, P < 0.05).     

Use of sclerotia of<Emphasis Type="Italic">Sclerotinia sclerotiorum</Emphasis> for efficient production of conidia of<Emphasis Type="Italic">Coniothyrium minitans</Emphasis> in liquid culture

A study was conducted to determine the feasibility of using sclerotia ofSclerotinia sclerotiorum for producing conidia ofConiothyrium minitans in liquid culture. The medium (SST) was made of water containing 2.0, 1.5, 1.0 or 0.5% (w/v) ground sclerotia ofS. sclerotiorum and 100 μgl ⁻¹ thiamine hydrochloride (HCl). One ml of conidial suspension (2 × 10⁷ conidia ml⁻¹) ofC. minitans LRC 2534 was inoculated into 100 ml of SST medium or control (thiamine HCl in water) and incubated at 20 ± 2°C on a shaker at 200 rpm. Subsamples were removed periodically and examined under a compound microscope. Conidia in the SST media germinated within 24 h, developed into branched hyphae within 48 h, produced pycnidia after 3–4 days, and the pycnidia released mature conidia after 7 days. Production of conidia varied with the concentration of sclerotia in the SST medium. It was lower (3.6 × 10⁶ conidia ml⁻¹) at 0.5% but higher (1.2 × 10⁸ conidia ml⁻¹) at 2%. The new conidia were viable and the colonies developing from them showed the original morphological characteristics. It was concluded that using SST liquid medium as a substrate for mass production of conidia ofC. minitans has potential for use in commercial development of this mycoparasite as a biocontrol product. http:www.phytoparasitica.org posting Jan. 23, 2007.     

Impact of Foliar Diseases on Photosynthesis, Protein Content and Seed Yield of Alfalfa and Efficacy of Fungicide Application

Foliar pathogens attack alfalfa wherever the crop is grown, but their impact, especially on seed production, is poorly understood. In greenhouse trials, leaf spot injury caused by inoculation with various pathogens reduced the crude protein content of infected alfalfa leaves by 22% compared with a healthy control. There was a negative relationship between disease injury and the photosynthetic efficiency of alfalfa plants, as determined by measuring chlorophyll fluorescence in leaves from inoculated vs. non-inoculated seedlings. In field trials at two sites in Alberta from 2001 to 2003, inoculation with Phoma medicaginis increased disease incidence in four of six trials, Phoma sclerotioides increased incidence in four of five trials, and Leptosphaerulina trifolii and Stemphylium botryosum increased incidence in two of six trials. There was a trend for inoculation treatments to reduce seed yield, despite high levels of background infection by indigenous pathogens. The fungicides benomyl and propiconazole inhibited radial growth of Phoma spp. in vitro and reduced disease incidence in inoculated greenhouse experiments. In field trials, applications of benomyl and propiconazole reduced disease incidence, but did not always increase seed yield.     

Temporal dynamics of root and foliar severity of soybean sudden death syndrome at different inoculum densities

Temporal dynamics of soybean sudden death syndrome (SDS) root and foliar disease severity were studied in growth chamber experiments on susceptible plants exposed to different inoculum densities (0, 10⁰, 10¹, 10², and 10³ conidia g⁻¹ soil) of Fusarium virguliforme. The monomolecular model provided the best fit to describe the progress of root and foliar disease severity over time. Disease severity and area under disease progress curve (AUDPC) both increased in response to increasing inoculum density (P < 0.01), particularly for foliar symptoms. Rate of disease progress increased as inoculum densities increased for both root and foliar disease severities. The incubation period for root and foliar disease severity ranged from 9 to 18 and 15 to 25 days, respectively. Significant differences in root rot severity were most easily detected during the early stages of infection, whereas root rot and foliar severities were only weakly correlated when both were assessed simultaneously at later stages of disease development. Root rot severity assessments performed 15 to 20 days after inoculation (DAI) were most highly correlated (r > 0.9, P < 0.01) with foliar disease severity assessments performed 30 to 50 DAI. Root biomass was reduced by up to 67% at the three highest inoculum densities, indicating the aggressiveness that F. virguliforme possesses as a root rot pathogen on soybeans.