Possible contributions of volatile-producing bacteria to soil fungistasis

Soil fungistasis can adversely affect the germination and growth of most fungal species in the field. Among the inhibitors, volatiles of microbial origins are potentially very important. In this study, we investigated the frequency and identity of bacteria producing fungistatic volatiles. Among the 1018 bacterial isolates tested, 328 were found to produce antifungal volatiles that could inhibit spore germination and mycelial growth of two nematicidal fungi Paecilomyces lilacinus and Pochonia chlamydosporia. A phylogenetic analysis based on restriction fragment length polymorphism (RFLP) and 16S rDNA sequence placed the 328 bacteria in five groups: Alcaligenaceae, Bacillales, Micrococcaceae, Rhizobiaceae and Xanthomonadaceae. Volatile compounds of 39 bacterial isolates were identified by gas chromatography/mass spectrum (GC/MS). Tests with commercially available antifungal compounds suggested that seven volatile compounds of bacterial origins (acetamide, benzaldehyde, benzothiazole, 1-butanamine, methanamine, phenylacetaldehyde and 1-decene) likely play important roles in soil fungistasis.     

Soil volatile fungistasis and volatile fungistatic compounds

Fungistasis is a widespread phenomenon that can be mediated by soil microorganisms and volatile organic compounds (VOCs). The relationship between soil microorganisms and VOCs is still unclear, however, and many fungistatic compounds remain to be identified. We assessed the effects of soils (soil direct fungistasis) and VOCs produced by natural soils (soil volatile fungistasis) on the spore germination of several fungi. Both strong soil direct fungistasis and soil volatile fungistasis were observed in a wide range of soils. Soil fungistasis and VOC fungistasis were significantly correlated (P<0.001). The volatile fungistatic activity of soils stopped after autoclaving. Some VOCs were identified by using solid-phase microextraction-gas chromatography/mass spectrum. VOC composition and in vitro antagonism of relatively pure commercial compounds also were measured. Some VOCs, trimethylamine, 3-methyl-2-pentanone, dimethyl disulfide, methyl pyrazine, 2,5-dimethyl-pyrazine, benzaldehyde, N,N-dimethyloctylamine and nonadecane, were produced by various fungistatic soils. Moreover, antifungal activity test of above VOCs showed that trimethylamine, benzaldehyde, and N,N-dimethyloctylamine have strong antifungal activity even at low levels (4-12 mg l⁻¹).     

Suppression of damping-off of cucumber caused by Pythium ultimum with live cells and extracts of Serratia marcescens N4-5

Environmentally friendly control measures are needed for the soil-borne pathogen, Pythium ultimum. This pathogen can cause severe losses to field- and greenhouse-grown cucumber and other cucurbits. Live cells and ethanol extracts of cultures of the bacterium Serratia marcescens N4-5 provided significant suppression of damping-off of cucumber caused by P. ultimum when applied as a seed treatment. Live cells of this bacterium also suppressed damping-off caused by P. ultimum on cantaloupe, muskmelon, and pumpkin. Culture filtrates from strain N4-5 contained chitinase and protease activities while ethanol extracts contained the antibiotic prodigiosin, the surfactant serrawettin W1, and possibly other unidentified surfactants. Production of prodigiosin and serrawettin W1 was temperature-dependent, both compounds being detected in extracts from N4-5 grown at 28 °C but not in extracts from N4-5 grown at 37 °C. Ethanol extracts from strain N4-5 grown at 28 °C inhibited germination of sporangia and mycelial growth by P. ultimum in in vitro experiments. There was no in vitro inhibition of P. ultimum associated with ethanol extracts of strain N4-5 grown at 37 °C. Prodigiosin, purified from two consecutive thin-layer chromatography runs using different solvent systems, inhibited germination of sporangia and mycelial growth of P. ultimum. Another unidentified compound(s) also inhibited germination of sporangia but did not inhibit mycelial growth. There was no in vitro inhibition associated with serrawettin W1. These results demonstrate that live cells and cell-free extracts of S. marcescens N4-5 are effective for suppression of damping-off of cucumber caused by P. ultimum possibly due in part to the production of the antibiotic prodigiosin.     

Antifungal activity of strawberry fruit volatile compounds against Colletotrichum acutatum

Eight volatile products characterizing strawberry aroma, which is generated from the oxidative degradation of linoleic and linolenic acids by a lipoxygenase (LOX) pathway, were examined because of their antifungal activity against Colletotrichum acutatum, one of the causal agents of strawberry anthracnose. In this study, the effects of aldehydes, alcohols, and esters on mycelial growth and conidia development were evaluated. (E)-Hex-2-enal was found to be the best inhibitor of mycelial growth [MID (minimum inhibitory doses)=33.65 microL L(-1)] and of spore germination (MID=6.76 microL L(-1)), while hexyl acetate was the least effective of all volatile compounds tested (MID=6441.89 microL L(-1) for mycelial growth and MID=1351.35 microL L(-1) for spore germination). Furthermore, the antifungal activity of (E)-hex-2-enal on susceptibility of strawberry fruits to C. acutatum was also confirmed. The presence of these molecules in jars containing strawberry fruits inoculated with a suspension of spores inhibited the fungus growth and prevented the appearance of symptoms. Moreover, a study of the effects of (E)-hex-2-enal on conidial cells of C. acutatum was evaluated by transmission electron microscopy. This volatile compound altered the structures of the cell wall and plasma membrane, causing disorganization and lysis of organelles and, eventually, cell death.     

Effect of soybean lipoxygenase on volatile generation and inhibition of Aspergillus flavus mycelial growth

Volatiles generated from lipoxygenase (LOX) normal and LOX deficient soybean (Glycine max) varieties with and without added lipase inhibited Aspergillus flavus mycelial growth and aflatoxin production. Soybean volatiles were analyzed using a solid phase microextraction (SPME) method combined with gas chromatography-mass spectrometry (GC-MS). Twenty-one compounds, including 11 aldehydes, three alcohols, four ketones, one furan, one alkane, and one alkene were detected in the LOX normal soybean line. However, only nine volatile compounds were observed in the LOX deficient soybean variety. The antifungal aldehydes hexanal and (E)-2-hexenal were observed in both LOX normal and LOX deficient lines and were detected at significantly higher amounts in soybean homogenate with added lipase. These aldehydes may be formed through alternate pathways, other than the LOX pathway, and may account for the inhibition of A. flavus growth observed. Other volatiles detected, particularly the ketones and alcohols, may contribute to the antifungal activity observed in both LOX normal and LOX deficient soybean lines. These results suggest that other factors, other than LOX activity, may better explain why soybeans are generally not as severely affected by A. flavus and aflatoxin contamination as other oilseed crops.     

Broad-spectrum antifungal metabolites produced by the soil bacterium Serratia plymuthica A 153

Chlorinated macrolides, haterumalide NA, B and NE, and a new haterumalide X, were produced by the soil bacterium Serratia plymuthica. Haterumalides NA, B and NE caused complete suppression of apothecial formation in sclerotia of Sclerotinia sclerotiorum at a concentration of 0.5 μg ml⁻¹. Ascospore germination of this fungus was inhibited in the concentration range 0.8-3.0 μg ml⁻¹. Haterumalides NA, B and NE prevented spore germination of several other filamentous fungi as well as Oomycetes at concentrations ranging from 0.4 to 40 μg ml⁻¹, but did not show any effect against the yeast Candida albicans. Inhibition data could not be collected for haterumalide X due to its rapid conversion to haterumalide NA. The bacterium also produced two other antifungal metabolites: pyrrolnitrin and 1-acetyl-7-chloro-1-H-indole, which in contrast to the haterumalides, did not inhibit the apothecial formation on sclerotia. Pyrrolnitrin, and haterumalide NA, B and NE effectively inhibited spore germination of tested filamentous fungi at concentrations ranging from 0.06 to 50 μg ml⁻¹, whereas 1-acetyl-7-chloro-1-H-indole inhibited spore germination only at concentrations above 50 μg ml⁻¹. The minimal inhibitory concentrations of the respective compounds needed for total inhibition of spore germination varied for the fungal species tested.     

Time and burial depth influencing the viability and bacterial colonization of sclerotia of Sclerotinia sclerotiorum

Sclerotia are the primary over wintering inoculum of Sclerotinia sclerotiorum (Lib.) de Bary. The effects of tillage on the primary inoculum are not well understood. The purpose of this research was to study sclerotial viability over time and between burial depths in soil, to identify bacteria colonizing and degrading the sclerotia, and determine whether these bacteria may be utilized as biological control agents. Correlation analysis indicated that a significant negative relationship existed between sclerotial viability and elapsed temporal factors (R²=−0.68, P<0.0001), and depth of burial (R²=−0.58, P<0.0001). After twelve months, sclerotia on the soil surface had the highest viability (57.5%), followed by those at the 5 cm depth (12.5%), and only 2.5% of those placed at the 10 cm depth remained viable. A significant negative relationship between sclerotial viability and bacterial populations also existed (R²=−0.60, P<0.0001). Two hundred and sixty-eight bacteria were isolated from sclerotia, 29 of which showed strong in vitro antagonism to the mycelial growth of S. sclerotiorum. Biodiversity of the inhibitory bacterial isolates was minimal on sclerotia from the soil surface and within all depths sampled at three months (i.e. in January). All burial depths within the April and July sampling dates produced bacterial diversities that were distinct from each other.     

Evaluation of different Coniothyrium minitans inoculum sources and application rates on apothecial production and infection of Sclerotinia sclerotiorum sclerotia

The effects of three Coniothyrium minitans isolates (Conio, IVT1 and Contans^®), applied to soil as conidial suspensions or as maizemeal-perlite (MP) inocula (Conio), on apothecial production and infection of Sclerotinia sclerotiorum sclerotia were assessed in two soil pot bioassays and two novel box bioassays in the glasshouse at different times of the year. C. minitans isolate Conio applied as either MP or ground MP at full rate (10⁶-10⁷ cfu cm⁻³ soil) consistently decreased the carpogenic germination, recovery and viability of sclerotia and increased C. minitans infection of the sclerotia of S. sclerotiorum by in comparison with either MP or conidial suspension treatments applied at lower rates (10³-10⁴ cfu cm⁻³ soil). Additionally, when applied at the same rate, MP inoculum of C. minitans was consistently more effective at reducing carpogenic germination than a conidial suspension. The effect of MP and ground MP at full rate on carpogenic germination was expressed relatively early as those sclerotia recovered before apothecia appeared on the soil surface already had reduced numbers of apothecial initials. In general, there were few differences between the isolates of C. minitans applied as conidial suspensions. Box bioassays carried out at different times of the year indicated that temperature and soil moisture influenced both apothecial production and mycoparasitism. Inoculum concentration of C. minitans and time of application appear to be important factors in reducting apothecial production by S. sclerotiorum.     

草莓叶主要挥发性物质的测定及其对草莓球腔菌的抑菌效果

为探究草莓叶片中挥发性物质对草莓球腔菌的抑菌作用,本研究测定了草莓叶片中主要挥发性物质,并以草莓球腔菌为处理对象,研究草莓叶片主要挥发性物质对其孢子萌发、菌丝生长以及线粒体膜电位的影响。结果表明,草莓叶片挥发性物质中的萜类化合物主要组分为芳樟醇、桃金娘烯醇,C6醛类化合物主要组分为己醛、2-己烯醛、反式-2-己烯醛、顺式-3-己烯醛等。当芳樟醇、桃金娘烯醇浓度为50 μL·L^-1,己醛浓度为5 μL·L^-1, 反式-2-己烯醛浓度为0.5 μL·L^-1,顺式-3-己烯醛浓度为5 μL·L^-1 熏蒸处理草莓球腔菌时,能显著抑制病原菌孢子的萌发和菌丝生长,并能使病原菌线粒体膜电位下降,从而抑制草莓球腔菌的生长且对草莓叶片无明显损伤。研究表明利用适宜浓度的芳樟醇、桃金娘烯醇、己醛、反式-2-己烯醛、顺式-3-己烯醛熏蒸处理,能够有效抑制草莓球腔菌的生长。本研究为研制新型天然植物病害抑菌剂提供了依据。     

Control of apothecia of Sclerotinia sclerotiorum by soil amendment with S-H mixture or Perlka in bean, canola and wheat fields

Ascospores of Sclerotinia sclerotiorum produced from apothecia are the primary source of inoculum for causing diseases such as white mold of common bean, pod rot of pea, stem blight of canola and head rot of sunflower and safflower in the Canadian prairies. A field study was conducted for 4 years to determine efficacy of control of production of apothecia from carpogenically germinated sclerotia of S. sclerotiorum by soil amendment with Perlka^® (calcium cyanamide) and S-H mixture (a formulated compound). Results of the 4-year experiments showed that amendment of soil with Perlka^® at low (30 g/m²) or high (60 g/m²) rate was effective in reducing carpogenic germination of sclerotia and production of apothecia under the canopy of host crops (common bean and canola) and a non-host crop (wheat). In the experiments of 1988, for example, the numbers of apothecia produced in the treatments of Perlka^®-low rate (30 g/m²), Perlka^®-high rate (60 g/m²) and untreated control were 42, 46, and 182 apothecia/plot (m²), respectively, for bean; 89, 42, and 318 apothecia/plot (m²), respectively, for canola; and 146, 143, and 412 apothecia/plot (m²), respectively, for wheat. However, soil amendment of S-H mixture at low (30 g/m²) or high (60 g/m²) rate was ineffective in reducing carpogenic germination of sclerotia and production of apothecia for all the 4 years of testing in all three crops. The ineffectiveness of S-H mixture and the practicality of Perlka^® for control of Sclerotinia diseases of crops grown under Canadian prairie conditions are discussed.     

Interactions between Sclerotium rolfsii and Trichoderma spp: Relationship between antagonism and disease control

Ten isolates of Trichoderma spp were examined for their ability to antagonize growth and to parasitize mycelium of Sclerotium rolfsii (Sr-1) on agar media, to inhibit germination of sclerotia of S. rolfsii on natural soil plates and to sporulate on the sclerotia, and to protect bean seedlings against the pathogen in the greenhouse. A high negative correlation (r = ?0.844) was observed between plant stand in the greenhouse and sclerotial germination on soil plates but not with antagonism on agar plates. Three isolates of T. harzianum (Th-7, Th-20, WT-6) and one of T. hamatum (TRI-4) were especially effective in reducing sclerotial germination and controlling disease in the greenhouse. Three isolates of Trichoderma spp (WT-6, TMP, and TRI-4), effective in reducing sclerotial germination of isolate Sr-1, also prevented sclerotial germination in four out of five additional S. rolfsii isolates studied.     

Experimental complexities in evaluating the allelopathic activities in laboratory bioassays: A case study

Soil is the major player in deciding allelopathic activities. A study was designed to examine experimental complexities in determining the allelopathic behavior of soil amended with water-soluble leachates from Chenopodium murale. Chenopodium murale interferes with the growth and establishment of crop seedlings. The present study examined the role of water-soluble organic substances, if any, in the shoot growth suppression of rice (Oryza sativa L.). Rice seeds were grown on C. murale leaf leachate-amended soil to investigate the phytotoxic effects of C. murale leachates. Any modification of C. murale phytotoxic activities was studied through using abiotic soil, activated charcoal and nitrogen (N) fertilization. Chemical and microbiological analysis of C. murale-amended soil was made to evaluate the role of soil components in C. murale phytotoxicity. Significant inhibition in the shoot growth of rice was observed when abiotic or biotic soil was amended with full-strength leaf leachate (T1) of C. murale compared to unamended soils. The inhibitory effect of T1 is maintained when rice seeds were placed on T1-amended soil after 0, 24 or 48 h; however, the inhibitory effects were eliminated when seeds were placed on amended soil after 72, 96 h or 1 wk of incubating soil with T1. Activated charcoal (1, 2 or 4 g) could not eliminate the inhibitory effects of T1-amended soil to the shoot length of rice. The phytotoxic effects of T1-amended soil to the shoot length of rice, however, were largely eliminated after the addition of N fertilization. Interference of C. murale leaf leachate to rice shoot growth could be due to number of effects that could be misconstrued as allelopathy effects.     

Suppression of Sclerotinia sclerotiorum apothecial formation by the soil bacterium Serratia plymuthica: identification of a chlorinated macrolide as one of the causal agents

A selection of soil bacteria was screened for their ability to interfere with carpogenic germination of Sclerotinia sclerotiorum. Nine out of 300 bacterial isolates were found to significantly suppress apothecial formation. One of these isolates, identified as a strain of Serratia plymuthica, was highly effective in inducing complete suppression of apothecial formation at high concentrations, and also strongly inhibited the germination of ascospores as well as hyphal growth of S. sclerotiorum. A bioassay-guided purification procedure starting with the cell-free supernatant of the bacterial culture led to the identification of a chlorinated macrolide as an active compound able to induce the observed inhibition. Spectroscopic data showed the compound to be identical to haterumalide A. The data presented show the ability of this compound to inhibit apothecial formation and ascospore germination. Other possible mechanisms involved in inhibition of apothecial formation and mycelial and hyphal growth of S. sclerotiorum by the same isolate are discussed. The relevance of our observations to natural systems will be the subject of further research.     

Evaluation and identification of potential organic nematicidal volatiles from soil bacteria

Naturally occurring volatile compounds with nematicidal activities (NAs) are of significant economical importance in agriculture and forestry. In this study, volatile organic compounds (VOCs) produced by 200 isolates of soil bacterial were evaluated in in vitro experiments. Our results identified that among the 200 bacterial isolates, 149 (74.5%) and 165 (82.5%) exhibited a greater than 20% NA against the free-living nematode Panagrellus redivivus and the pinewood nematode Bursaphelenchus xylophilus, respectively. Among them, 22 isolates showed 100% NA against P. redivivus and seven isolates showed 100% NA against B. xylophilus. When exposed to nematicidal volatiles, nematodes gradually reduced their movements within 1-12 h after treatment, and most stopped moving completely after 24 h. Our analysis indicated significant variation in nematicidal capability of the VOCs not only among bacterial species but also among isolates of the same species. Volatiles of representative isolates were extracted using solid-phase micro-extraction (SPME) and their structures identified using gas chromatography-mass spectrometry (GC-MS). The detected so volatile compounds included alcohols, aldehydes, ketones, alkenes and ethers. Of the 20 VOCs with strong NA (?80%), nine (phenol, 2-octanol, benzaldehyde, benzeneacetaldehyde, decanal, 2-nonanone, 2-undecanone, cyclohexene and dimethyl disulfide) displayed 100% NA to both model nematodes. Furthermore, five compounds (terpineol, benzeneethanol, propanone, phenyl ethanone and nonane) showed different NA to B. xylophilus (75-100%) and P. redivivus (17.02-100%).     

Prolonged compost curing reduces suppression of Sclerotium rolfsii

Composts have long been recognized to facilitate biological control of soil borne plant pathogens. Composts can introduce biocontrol agents into growth media and serve as a food base for their establishment and activity. Mature biosolids compost (a blend of sewage sludge and yard waste) was found to be suppressive to germination of the sclerotia of S. rolfsii on compost plates and also suppresses the disease development in bean plants (Phaseolus vulgaris L.). Microscopic observations revealed that sclerotia placed on suppressive compost were attacked by mycoparasites. However, prolonged curing of compost negated this phenomenon. This research was aimed to study the changes in chemical and biological properties occurring during prolonged curing and their relation to compost suppressiveness. Correlations were found between the decrease and subsequent loss of suppression of sclerotia germination and the decrease in basal respiration, dissolved organic carbon (DOC) and concentrations, and the increase in concentration and specific UV absorbance. A shift of both bacterial and Ascomycetes populations as a consequence of curing was observed. Interactions between micro-organisms and their chemical environment are discussed.     

Soil and compost humic fractions regulate the response of Sclerotinia sclerotiorum to exogenously added allelochemical compounds

Allelochemical compounds released by plants to signal their presence and needs interact in soils with very important macromolecules, such as humic acids (HAs), which are able to modulate the ultimate effects on target organisms. Most of the available studies on plants and microorganisms report the effects of allelochemicals or those of humic fractions, separately. In this study, we investigated the combined activity of these two types of compounds on the soil-resident fungus Sclerotinia sclerotiorum. Thus, ferulic acid (FA), caffeic acid (CA), benzoic acid (BA), salicylic acid (SA), gallic acid (GA) and phthalic acid (PA), exogenously applied to the fungal growth medium, were tested both alone and in combination with a soil HA (SHA) and a compost HA (CHA). The two HAs were also tested alone on the fungus. When the allelochemicals were applied alone, only FA, BA and SA evidenced a significant inhibition of mycelial growth, whereas FA, BA and CA increased the number of sclerotia formed. The two HAs alone reduced the early growth of the fungus and markedly stimulated sclerotia formation. A significant attenuation or, in some cases, suppression of the allelochemical effect on mycelial growth was caused by the coexistence in the medium of the allelochemical and each HA, especially CHA. Moreover, in general, the combinations of HA-allelochemical significantly stimulated sclerotia formation, with respect to the sole allelochemical, but decreased it with respect to HA alone. Thus, investigations on the response of fungi to plant-released allelochemicals should not exclude interactive aspects of these compounds with ubiquitous coexisting humic macromolecules.     

Crude extract of Astragalus mongholicus root inhibits crop seed germination and soil nitrifying activity

Astragalus mongholicus has been of medicinal use within the traditional Chinese system for centuries. However, little information is available on its allelopathic effects on other crop plants and soil biochemical properties. Field experiment showed that the extracted residues of A. mongholicus root inhibited seed germination of wheat. Inhibition of seed germination was further confirmed in laboratory using the same crude extract. When the crude extract was applied to soil at various rates and incubated for 30 days, soil urease activity and denitrifying enzyme activity were significantly increased while soil nitrification rate was significantly decreased at 10% amendment rate as compared to the control. Soil respiration rate was significantly increased by the crude extract when measured at the start of incubation but returned to basal levels after 30 days of incubation. The crude extract supplemented to NB medium significantly decreased the colony numbers of Agrobacterium tumefaciens C58, Paraccocus denitrificans and soil bacteria. The stimulating effects of crude extract observed in the amended soil was attributed to the easily-available carbohydrates in the extract, which might served as external energy sources for heterotrophic microbial activities. It was concluded that A. mongholicus contained some compounds that inhibited seed germination, soil nitrification and bacterial growth in general. Possible links between allelochemicals responsible for the inhibitory effects observed in the present study and the medically bioactive compounds are discussed based on information reported in other fields. Further work is needed to specify and verify the allelochemicals produced by this herbal plant.     

Variation in oxalic acid production and mycelial compatibility within field populations of Sclerotinia sclerotiorum

This study was aimed at detecting mycelial compatibility groups and variations in oxalic acid production in Sclerotinia sclerotiorum. For this purpose, 121 isolates of this plant pathogen recovered from lettuce, soybean and sunflower field crops, and grouped in 46 MCGs were tested for their ability to release oxalic acid and other organic acids to the medium. Oxalic acid production on liquid media was measured spectrophotometrically and release of organic acids was estimated by isolate abilities to discolour solid media amended with bromophenol blue. There were significant differences among MCGs in both oxalic acid and organic acids releasing, ranging the mean production of oxalic acid between 18 and 110 μg oxalic acid mg⁻¹ dry wt. When isolates were grouped by their hosts, those obtained from soybean presented the highest release of oxalic acid (71 μg oxalic acid mg⁻¹ dry wt), while those from sunflower showed the highest release of other acids to the medium. Solid medium discoloration was not correlated with oxalic acid concentration in liquid medium (Spearman R=−0.085; P=0.126).     

Saprophytic growth of Rhizoctonia solani Kühn AG2-1 (ZG5) in soil amended with fresh green manures affects the severity of damping-off in canola

Plants of the Brassicaceae contain glucosinolates, the hydrolysis products of which inhibit the growth of many soil-borne fungi that cause plant disease. However, amending soil with green manures of these plants gives inconsistent control of several soil-borne diseases, including those caused by Rhizoctonia solani. To identify factors that contribute to this inconsistency we investigated, in the laboratory and in pot experiments in the glasshouse, the saprophytic behaviour of R. solani AG2-1 (ZG5) in a sandy soil amended with various green manures. Fresh material from either Brassica napus var. Karoo, B. napus B1, B. napus B2, B. nigra, Diplotaxis tenuifolia (a brassicaceous weed) and the non-Brassicaceae species, oat (Avena sativa) or lupin (Lupinus angustifolius) was used at 10 or 100 g of fresh material kg⁻¹ of dry soil in Lancelin sand. At 100 g kg⁻¹ the volatiles of all green manures reduced the hyphal growth of R. solani, except for B. napus B1. D. tenuifolia at 100 g kg⁻¹ inhibited the growth and sclerotial formation of R. solani. Most green manures at 10 g kg⁻¹, and at 40% water holding capacity, stimulated the growth of R. solani for up to 3 months and increased the activity of other microbes. R. solani infected the brassicaceous plants when growing and colonized the residues mixed with soil at 10 g kg⁻¹. This inoculum increased the severity of damping-off in canola, by 27%. Disease was particularly severe when the green manure species, except D. tenuifolia and oat, were grown in situ and residues returned to the pot from which they came, before sowing canola. There is a potential hazard in applying green manures of Brassica species as their residues can, under certain conditions, support the saprophytic activity of R. solani which increases damping-off in canola sown in the amended soils.     

Effect of Germination on Flavor Volatiles of Cooked Brown Rice

The effect of germination on flavor volatiles of cooked brown rice among three different rice cultivars was investigated using the headspace solid‐phase microextraction method combined with gas chromatography‐mass spectrometry. The results showed that some flavor compounds varied significantly throughout the germination process and others did not show distinct changes. The amount of total volatiles, most lipid‐oxidation products, and phenolic compounds decreased in the initial stage of germination but increased significantly at a later stage. The amounts of ethanol and ethyl acetate increased significantly in the initial stage of germination and maintained almost the same levels during further germination. The amount of dimethyl sulfide increased significantly during germination; it showed the most significant change among all volatile compounds.