Mycoflora and vitamin content of sun-dried food condiments in Nigeria

The fungi most frequently isolated (of 20–100% incidence) from fresh okra, pepper fruits and melon seeds areBotryodiplodia theobromae, Rhizopus stolonifer, Trichoderma harzianum, Mucor mucedo andFusarium oxysporum. The major mycoflora of the fruits which had been sun-dried for twenty days are comprised ofAspergillus spp andPenicillium spp which initially had formed the minor components (of less than 20% incidence) of the colonising population. The effect of sun-drying on the fruits was a statistically significant (P=0.05) decrease in the riboflavin content and a generally small and non-significant decrease in the concentrations of thiamine, niacin, biotin and ascorbic acid. The effect of mouldiness during sun-drying was to further decrease the concentration of the vitamins.     

Occurrence and characterization of fungi and oomycetes transmitted via potting mixtures and organic manures

A study was conducted to investigate the most common fungal and oomycete pathogens introduced into farms in Oman via potting mixtures and organic manures. A total of 37 commercial types of potting mixtures (2 local and 35 imported from overseas), 4 commercial types of organic manures and 11 non-commercial types of organic manures were included in the study. Identification of the isolated species was based on morphological characteristics, except for the most common species which were further identified using sequences of the internal transcribed spacer region of the ribosomal DNA (ITS rDNA). Fusarium spp. (14%), Pythium aphanidermatum (3%), Alternaria spp. (5%), Helminthosporium spp. (5%) and Cladosporium spp. (3%) were recovered at different frequencies from samples of potting mixtures. Fusarium solani (40%) and Fusarium equiseti (47%) were recovered at high frequencies from samples of organic manures. Isolations from organic manures also yielded Pythium periplocum (7%), Rhizoctonia solani (7%), Fusarium lichenicola (7%), Helminthosporium spp. (27%) and Alternaria spp. (27%). Trichoderma spp., Penicillium spp., Aspergillus spp. and Rhizopus spp. were found to be common in samples of potting mixtures and organic manures. Investigating sensitivity to hymexazol among 9 isolates of F. equiseti and 13 isolates of F. solani revealed variations among different isolates. The EC₅₀ values ranged from 1 to over 1200 (avg. 192 μg ml⁻¹) for F. equiseti isolates and from 135 to 789 (avg. 324 μg ml⁻¹) for F. solani isolates, indicating presence of resistance to this important fungicide among some Fusarium isolates. This appears to be the first report of contamination with R. solani, P. periplocum, F. solani, F. equiseti and F. lichenicola of organic manures. This study appears to report for the first time F. lichenicola in Oman and appears to be the first report of occurrence of resistance to hymexazol among F. equiseti and F. solani isolates.     

Chemical composition and anti-fungal properties of the essential oils and crude extracts of Orthosiphon stamineus Benth

The hydrodistilled essential leaves and stems oils of Orthosiphon stamineus Benth were analysed by GC–MS/MS. Sixty nine compounds representing 97.6 and 97.4% of the total leaves and stems oils, respectively were identified, of which β-caryophyllene (24.0 and 35.1%), α-humulene (14.2 and 18.4%), β-elemene (11.1 and 8.5%), 1-octen-3-ol (8.2 and 7.0%), β-bourbonene (3.4 and 3.0%), β-pinene (2.1 and 1.7%), caryophyllene oxide (1.6 and 2.2%), camphene (1.6 and 1.3%) and limonene (1.2 and 1.1%) were the major compounds. Thus, the monoterpenes and sesquiterpenes were the predominant portions of the oils. Essential oils and methanol extract of O. stamineus and the derived fractions of hexane, chloroform, and ethyl acetate were tested for anti-fungal activity, which was determined by disc diffusion and minimum inhibitory concentration (MIC) determination methods. The oils, methanol extract and derived fractions of methanol extract displayed great potential of anti-fungal activity as a mycelial growth inhibitor against the tested phytopathogenic fungi such as Botrytis cinerea, Rhizoctonia solani, Fusarium solani, Colletotricum capsici and Phytophthora capsici, in the range of 49.3–70.3% and minimum inhibitory concentration ranging from 500 to 1000 μg/ml.     

Suppressiveness of steam-exploded biomass of Miscanthus sinensis var. giganteus against soil-borne plant pathogens

Commercial compost is a renewable resource widely used in horticulture as an organic amendment, though its suppression against soil-borne plant pathogens remains limited. Preliminary studies conducted on the disease suppression effect of the biomass waste obtained in a steam explosion plant demonstrated positive results. Steam-Exploded Biomass (SEB) of Miscanthus sinensis var. giganteus, a herbaceous perennial energy crop, is a multifunctional renewable energy resource, which could also be useful in crop protection to find valid alternative to the compost use in horticulture. The purpose of this work was to assess the suppressiveness of SEB against five plant pathogenic fungi that are important in many Italian horticultural cropping systems. Analyses of the microbial inhibitors (furfurals, organic acids and lignosulfonates) present in the SEB were performed by the High Performance Liquid Chromatography technique. Assessment of toxic effect of the furfurals present in the SEB (furfuraldehyde and 5-hydroxymethylfurfural), added to a growing medium at the different concentration ranges, was carried out in vitro on Phytophthora nicotianae, Pythium ultimum, Fusarium oxysporum f. sp. lactucae, F. oxysporum f. sp. melonis and Rhizoctonia solani. The suppressiveness of SEB, added to a potting soil used in horticulture at the different doses, was tested in vivo on tomato/P. nicotianae, cucumber/P. ultimum, lettuce/F. oxysporum f. sp. lactucae, melon/F. oxysporum f. sp. melonis and bean/R. solani. The results showed that furfuraldehyde, 5-hydroxymethylfurfural, lignosulfonates, acetic and formic acid were detected at a concentration of 2.93, 0.28, 4.12, 10.07 and 1.88 g/kg SEB, respectively. The P. nicotianae, P. ultimum and R. solani fungi were highly inhibited by the addition of 3.2 g/L furfuraldehyde and 0.48 g/L 5-hydroxymethylfurfural. Moreover, the inhibitory effect was found not adequate against F. oxysporum at the same concentrations. The SEB increased significantly the suppressiveness level of the peat substrate on P. ultimum in cucumber and R. solani in bean in all the trials. For P. nicotianae in tomato, the SEB addition showed a significant suppression at the 20 and 30% doses, but the change was not significant at the 10% dose. In case of F. oxysporum f. sp. lactucae in lettuce and F. oxysporum f. sp. melonis in melon, the SEB addition showed no suppressive effect with respect to compost in all the trials. In conclusion, the SEB could be used against some soil-borne fungal diseases in place of compost in the potting soil, and its suppressiveness could be related to the concentration of the microbial inhibitors produced during the processing of fresh biomass in the steam explosion plant.     

Effect of sample pretreatments on the storability of ground melon ‘egusi’—Colocynthis citrillus L.

In the maintenance of shelf-stability, nutritional and organoleptic properties of ground melon egusi—Colcynthis eitrullus L., vacuum-packaged samples were found to be better than unpackaged samples and samples treated with 0.2% butylated hydroxyanisole (BHA) and 0.02% BHA + 0.045% sodium metabisulphite. After 56 days at 35°C, stored samples showed significant differences (P 0.01) in chemical composition peroxide value (PV), fungal counts and organoleptic attributes. Lipid oxidation and, to a lesser extent, fungal deterioration were responsible for the spoilage of stored ground melon kernel. The dominant fungal flora isolated from stored samples were of the generaPenicillium, Botryodiplodia, Rhizopus andAspergillus.     

Improvement of the traditional method of ogiri production and identification of the micro-organisms associated with the fermentation process

Fermented products were developed from different proportions of melon (Citrullus vulgaris schrad) and groundnut (Arachis hypogea) seeds after a 96 hour fermentation period. Proximate analysis, carried out on both fermented and unfermented samples, indicated that only the total carbohydrate content was appreciably reduced by the fermentation process. Micro-organisms responsible for fermentation were identified by gram staining and lactophenol staining, as bacteria and fungi. Identified bacteria were of the Bacillus and Acinetobacter species while the fungi were yeasts, rhizopus and mucor. Samples containing 50–100% melon showed a decrease in pH with increasing fermentation period. Bacteria were largely responsible in samples containing up to 75% groundnuts. Sensory analysis of dried fermented products after fortification with salt, ascorbic acid and flour indicated that they were acceptable.     

A bioplastic-based seed coating improves seedling growth and reduces production of coated seed dust

Although recently introduced, film-coating of agronomic seeds is now widely accepted in modern agriculture as an effective technology for protecting germinating seeds and seedlings. These experiments explored the possibility of using a bioplastic-based formulation to film-coat corn (maize; Zea mays L.) and canola (Brassica napus L.) seeds, alone and in combination with synthetic pesticides and plant growth-promoting bacteria. The thin bioplastic coat did not affect percent germination or seedling growth. However, incorporating spores of the plant growth-promoting bacterium Bacillus subtilis QST 713 into the bioplastic matrix resulted in a greater elongation of corn and canola seedlings than that of seedlings from untreated seeds. Specifically, stems and roots of seedlings that germinated from corn seeds coated with bioplastic containing spores were 18.0% and 21.4% longer, respectively, than stems and roots from uncoated control seeds. In canola seeds, these values were 19.9% and 20.9% higher for stem and roots, respectively. Incorporating a neonicotinoid insecticide, imidacloprid, and a fungicide, pyraclostrobin, into bioplastic coatings, along with B. subtilis spores, provided results comparable to spores and bioplastic alone. Coated seeds were also evaluated for their potential to generate dust after abrasion testing, using a novel image-based method made possible because seed coatings are typically artificially colored. Abraded seed coat fragments are consequently easily detectable with conventional optical instruments. Corn and canola seeds coated with bioplastic released up to 86.1% and 97.6% less dust during abrasive handling than seeds coated with a commercial seed coating matrix measured by the optical approach described here.     

Etiology and characterization of cucumber vine decline in Oman

A long-term study was conducted between 2000 and 2009 to characterize the incidence, progress and causal agents of cucumber vine decline in Oman. A survey in 175 different greenhouses showed that disease incidence levels range from 0 to 50%, with the highest levels of mortality being in the hotter seasons. Detailed temporal disease increase data from 24 different greenhouses showed mortality progress consists of two phases. The first phase is characterized by attack of young seedlings (<3 weeks old), resulting in damping-off disease. The second phase was characterized by re-appearance of symptoms and plant death (vine decline) during the fruit setting period, 35-50 days after transplanting. Isolations from 148 declining adult cucumber plants yielded Pythium aphanidermatum (80%), Pythium spinosum (13%), Fusarium equiseti (12%), Fusarium solani (8%), Rhizoctonia solani (5%) and one isolate each of Trichoderma hamatum and Bionectria sp. P. aphanidermatum, P. spinosum, R. solani and F. solani were found to be pathogenic on cucumber, with P. aphanidermatum being the most aggressive. This appears to be the first report of association of P. spinosum with vine decline in greenhouse cucumbers and the first report of the high susceptibility of adult cucumber plants to vine decline during the initial period of fruit setting. In addition, this is the first report of association of R. solani and F. solani with declining adult cucumber plants in Oman and the first report of the occurrence of T. hamatum and Bionectria species in the country.     

Evaluation of the short term effect of nursery treatments with phosphite-based products,acibenzolar-S-methyl,pelleted Brassica carinata and biocontrol agents,against lettuce and cultivated rocket fusarium wilt under artificial inoculation and greenhouse conditions

Experimental trials have been carried out in order to evaluate the efficacy of preventative treatments based on plant defense activator products, biocontrol agents, a microbial complex with arbuscular mycorrhizal fungi, and Brassica carinata pellets against Fusarium oxysporum f. sp. lactucae race 1 on lettuce and Fusarium oxysporum f. sp. raphani on cultivated rocket under greenhouse conditions. These products were compared with fungicides known for their ability to induce host resistance (phosethyl-Al and acibenzolar-S-methyl), and with azoxystrobin. Three and four applications of the tested products were carried out on lettuce and rocket seedlings grown in nursery conditions. Treated and untreated plants were transplanted into soil infested with Fusarium wilt agents to obtain an average disease severity (DS) of 65.6–69.2 and of 56.9–62.1 on the untreated lettuce and rocket plants, respectively. The best Fusarium wilt biocontrol was obtained after four applications of Bacillus subtilis Qst713 and with the Glomas microbial complex (42 and 46.7%, efficacy, respectively). B. carinata pellets provided a consistent control when applied 14 days before the rocket and lettuce were transplanted into the infested soil. Acibenzolar-S-methyl, applied at 0.025 g/Liter, showed a DS reduction in F. oxysporum f. sp. lactucae from 36 to 61% and of F. oxysporum f. sp. raphani from 54 to 73%, thus showing statistically similar results to those of azoxystrobin, which was used as a reference (DS reduction from 59 to 65%). Although the Fusarium wilt control provided by such products was not complete in the present experimental conditions, these products can be considered interesting components for an integrated pest management of the Fusarium wilt of leafy vegetables, starting from nursey applications. Moreover, the tested BCAs could become potentially useful, especially for plant monocultures. This study has been produced new information on the effects of potassium phosphite, applied at the nursery level, on reducing lettuce and rocket fusarium wilt. An average efficacy of 69.5% was observed for lettuce, while an average efficacy of 65.2% was observed for cultivated rocket. The good fungicidal activity of the phosphite-based product, coupled with the positive effect on plant biomass, is of special interest.     

Anti-fungal action of bioconverted eicosapentaenoic acid (bEPA) against plant pathogens

Bioconverted eicosapentaenoic acid (bEPA), obtained from Pseudomonas aeruginosa PR3, was assessed for its in vitro and in vivo anti-fungal potential. Mycelial growth inhibition of the tested plant pathogens (Rhizoctonia solani, Botrytis cinerea, Fusarium oxysporum, Fusarium solani, Phyptophthora capsici, Sclerotinia sclerotiorum and Colletotrichum capsici) was measured in vitro. bEPA at the concentration of 5 μl/ml inhibited 52–60% fungal mycelial growth for all of the plant pathogens in vitro except S. sclerotiorum. Minimum inhibitory concentrations (MICs) of bEPA were found in the range of 250–500 μg/ml. Also, bEPA had a detrimental effect on spore germination for all the tested plant pathogens. Three plant pathogenic fungi (F. oxysporum, P. capsici and C. capsici) were subjected to an in vivo anti-fungal screening. bEPA at the initial concentration of 3000 μg/ml had a 100% anti-fungal effect against all of the tested plant pathogens. Concentrations of bEPA corresponding to 1500, 500 and 300 μg/ml were applied to the plants and revealed promising anti-fungal effects, supporting bEPA as a potential anti-fungal agent.     

Bioactive Indole Diketopiperazine Alkaloids from the Marine Endophytic Fungus Aspergillus sp. YJ191021

Six new prenylated indole diketopiperazine alkaloids, asperthrins A–F (1–6), along with eight known analogues (7–14), were isolated from the marine-derived endophytic fungus Aspergillus sp. YJ191021. Their planar structures and absolute configurations were elucidated by HR-ESI-MS, 1D/2D NMR data, and time-dependent density functional theory (TDDFT)/ECD calculation. The isolated compounds were assayed for their inhibition against three agricultural pathogenic fungi, four fish pathogenic bacteria, and two agricultural pathogenic bacteria. Compound 1 exhibited moderate antifungal and antibacterial activities against Vibrio anguillarum, Xanthomonas oryzae pv. Oryzicola, and Rhizoctonia solani with minimal inhibitory concentration (MIC) values of 8, 12.5, and 25 μg/mL, respectively. Furthermore, 1 displayed notable anti-inflammatory activity with IC₅₀ value of 1.46 ± 0.21 μM in Propionibacterium acnes induced human monocyte cell line (THP-1).     

Induction of hydrolytic enzymes and antifungal in vitro activity inS. tuberosum subsp.andigena after infection withFusarium solani f. sp.eumartii

Summary Fusarium solani (Mart.) Sacc. f. sp.eumartii (Carp.) Snyder & Hansen is the causative agent of two important types of disease in potato (Solanum tuberosum) plants: wilt in stems and leaves and dry rot in tubers. The aim of this work was to study the molecular response of the potato to fungal attack. Micropropagated plantlets were tested, using a biological assay to detect antifungal proteins. An inhibitory activity of spore germination was detected in protein fractions from infected plantlets 7 days after inoculation with the pathogen. In addition, β-1,3-glucanase activity (glucanase III) was measured in protein fractions with antifungal activity. Induction of hydrolytic enzymes and antifungal activity in infected plantlets ofSolanum tuberosum subp.andigena suggests that it could be a suitable source of resistance genes.     

Combining residues of herb crops with soil heating for control of soilborne pathogens in a controlled laboratory system

Plant residues from herb crops were examined as organic amendments for the control of soilborne pathogens with and without soil heating for a short exposure of 2 weeks. Residues of herbaceous plants of oregano, sage, rosemary, tarragon, bay, wild rocket, spearmint and thyme were incubated for 14 days in a controlled laboratory system which emulates soil solarization. Green cabbage residues were included for comparison. The tested pathogens included Fusarium oxysporum f. sp. radicis-lycopersici, Macrophomina phaseolina, Rhizoctonia solani and Meloidogyne javanica. Heating soil amended with herb residues, particularly tarragon, spearmint and wild rocket, resulted in high mortality of the tested pathogens. Volatile compounds which were generated in heated soils amended with wild rocket or tarragon showed significant toxicity to M. phaseolina and R. solani. Only oregano, thyme, bay, wild rocket and tarragon amendments were effective in pathogen control without heating. Incorporation of leaf and stem residues of thyme, sage, tarragon, rosemary or wild rocket in soil and exposure to solarization under field conditions resulted in 95-100% mortality of the tested pathogen. This study demonstrates that the residues from herb crop production can serve as organic amendments for the control of soilborne pathogens, especially when combined with heating or solarization.     

Comparative study of microorganisms and sensory attributes of condiments from the fermentation of different seeds

Seeds of African locust bean, melon, castor oil bean and soybean were processed and fermented for 3 days to produce local condiments in the laboratory with a method that simulated the traditional production process. Microorganisms associated with their fermentation and the organoleptic properties of the products were compared.Altogether, seven species of bacteria were involved in the fermentation. These included fiveBacillus spp. and one species each ofPseudomonas andStaphylococcus. Their occurrence vary between the seeds on the different days of fermentation. However,Bacillus spp. were present in all the seeds throughout the fermentation period. The sensory evaluation preference rating for the four products was highest for soybean condiment, followed by that made from locust bean. Melon condiment was the least preferred among the four products. Statistical analysis showed that there were significant differences (P0.05) among the four products for each of the four organoleptic properties evaluated by the judges and also for titratable acidity. Glutamic acid level of soybean condiment was highest (0.31%) among the four products with that of melon being the lowest (0.04%). These results could serve as useful indices for the development of starter culture and optimization of production process in commercializing the production of these local condiments.     

Resistance to gangrene (Phoma exigua var.foveata) and dry rot (Fusarium solani var.coeruleum) in potato tubers. 2. Evaluation of genotypic differences in pectin-bound magnesium and calcium for screening purposes

Summary The levels of incorporation of Mg and Ca into tuber cell walls and middle lamellae were compared with the intensity of attack byPhoma exigua var.foveata (P.e.f.) (gangrene) andFusarium solani var.coeruleum (F.s.c.) (dry rot) in six genotypes varying in their levels of resistance. The Mg:Ca ratio was higher in those genotypes more resistant toP.e.f., while the cation effect on attack byF.s.c was variable. Although genotype resistance may be improved by extra Mg bridges in the pectin structure the genotypic differences in susceptibilty to gangrene could not be explained by differences in Mg content assessed from alcohol-insoluble solids. Analyses of breeders' selections showed no general relationship between Mg or Ca contents and disease incidence. Therefore, genotypic differences in incorporation of these cations could not be used for screening for improved resistance.     

Antifungal activity of liquid waste obtained from the detoxification of steam-exploded plant biomass against plant pathogenic fungi

The antifungal activity of steam-exploded liquid waste (SELW) produced by the detoxification of steam-exploded biomass of Miscanthus sinensis, Arundo donax and wheat straw for 2nd generation industrial bioethanol production was studied against plant pathogenic fungi for the first time. Quantification of fermentation inhibitors (2-furaldehyde, 5-hydroxymethylfurfural, acetic and formic acid) was carried out by standard methods. Mycelial growth inhibition and conidial germination of eight fungal strains [Alternaria alternata, Botrytis cinerea, Colletotrichum acutatum, Cladosporium fulvum, Fusarium oxysporum f. sp. lycopersici (FOL), F. oxysporum f. sp. melonis (FOM), F. solani f. sp. pisi and Verticillium dahliae] were evaluated in vitro at different dilution rates (1:2, 1:4 and 1:8) for each SELW. Disease suppressiveness was assessed in vivo in eight horticultural pathosystems (A. alternata/tomato, B. cinerea/tomato, C. acutatum/strawberry, C. fulvum/tomato, FOL/tomato, FOM/melon, F. solani f. sp. pisi/pea and V. dahliae/eggplant) under greenhouse conditions. Pathogen suppression by each SELW, applied both in spray form on to tomato leaves and skins of tomato and strawberry, and by means of dipping method in watering suspensions on to seedling root systems of tomato, melon, pea and eggplant, was evaluated at dilution rates of 1:2, 1:4 and 1:8 using irrigation water during curative and preventive treatments. Investigations carried out in vitro showed that M. sinensis SELW was more suppressive than wheat straw SELW, and A. donax SELW was less suppressive than wheat straw SELW at the lowest dilution rates. Relationships between the concentration of 2-furaldehyde, acetic and formic acid present in SELWs and their antifungal effect were found. Moreover, B. cinerea, C. fulvum, V. dahliae, A. alternata, C. acutatum and F. solani f. sp. pisi were more effectively inhibited than FOL and FOM. Investigations performed in vivo showed that SELWs of M. sinensis and wheat straw can be diluted at a 1:2 rate and used for controlling six fungal diseases during preventive treatments. In particular, they can be used by dipping of the root systems during transplanting in the case of F. solani f. sp. pisi/pea and V. dahliae/eggplant; on the other hand, they can be nebulized on to the leaves and fruits before symptoms appearance in the case of A. alternata/tomato, B. cinerea/tomato, C. acutatum/strawberry and C. fulvum/tomato. This study is of particular interest because it points out how these SELWs could be employed in horticultural crop protection in Southern Italy, thereby making it possible to effectively combine industrial production of 2nd generation biofuels with sustainable horticulture under greenhouse conditions.     

Antifungal textile dyeing with<Emphasis Type="Italic">Mahonia napaulensis D.C.</Emphasis> leaves extract based on its antifungal activity

The antifungal activity of the methanolic extract ofMahonia napaulensis D.C. or Taming (local name) leaves was evaluated with four species of common pathogenic fungi e.g.Colletotrichum capsici (MTCC No. 2071),Leptosphaerulin trifoli (MTCC No. 2328),Alternaria brassicicola (MTCC No. 2102) andHelminthosporium solani (MTCC No. 2075). The present investigation also aims at developing an eco friendly natural antifungal finish from plant extract ofMahonia for textile application. The antifungal textile dyeing was also carried out with aqueous extract of stem and leaves ofMahonia and the dyed fabric was tested against fungal speciesTrichoderma for its antifungal activity in vitro.Mahonia extract showed substantial antifungal activity of 83.33% forLeptosphaerulin trifoli andAlternaria brassicicola by 80 ppm dose in 24 hours and 46% antifungal activity inMahonia dyed pieces in broth againstTrichoderma.     

Activities of essential oils from Asarum heterotropoides var. mandshuricum against five phytopathogens

Some secondary metabolites of plants function as antimicrobial products against phytopathogens and constitute an increasingly important class of pesticides. In the present study, the essential oil of Asarum heterotropoides var. mandshuricum was analyzed by GC/MS and its antimicrobial activity was evaluated against five phytopathogenic fungi. Major components of the oil were methyleugenol (59.42%), eucarvone (24.10%), 5-allyl-1,2,3-trimethoxybenzene (5.72%), and 3,7,7-trimethylbicyclo(4.1.0)hept-3-ene (4.93%). The essential oil and the most abundant component, methyleugenol, were separately assayed for inhibition of 5 pathogens: Alternaria humicola, Colletotrichum gloeosporioides, Rhizoctonia solani, Phytophthora cactorum and Fusarium solani. Both the oil and methyleugenol strongly inhibited the growth of the test pathogens (IC₅₀ values <0.42 μg ml⁻¹) except F. solani, with the best activity against P. cactorum (IC₅₀ values = 0.073 and 0.052 μg ml⁻¹, respectively). It is concluded that the essential oil of A. heterotropoides var. mandshuricum has a broad antiphytopathogenic spectrum, and that methyleugenol is largely responsible for the bioactivity of the oil. The mode of action of methyleugenol against P. cactorum is discussed based on changes in the mycelial ultrastructure.     

Effect of inoculum density and quantitative PCR-based detection of Rhizoctonia solani AG-2-1 and Fusarium avenaceum on canola

Canola seedling blight, caused by Rhizoctonia solani, and Fusarium spp., can result in large yield losses to canola (Brassica napus) at high inoculum pressure. The effect of inoculum density was studied by mixing different amounts of R. solani AG-2-1 and Fusarium avenaceum into a sterilized natural soil and soil-less mix (2:1, v:v) separately, and recording seedling emergence, damping-off and seedling height within ten days after seeding; root rot severity at 12 days after seeding and seed yield at harvest on canola cultivars ‘45H29’ and ‘73-77RR’. Root rot severity increased and emergence, plant height and seed yield decreased with increased inoculum density of both R. solani and F. avenaceum. For quantification of R. solani AG-2-1, a primer and TaqMan probe set (Rs21F/Rs21R/Rs21P) was designed based on the nuclear ribosomal internal transcribed spacer (ITS) region of R. solani AG-2-1. From a conventional PCR amplification, an 88-bp product was amplified from all isolates classified as AG-2-1 with the primers Rs21F and Rs21R. No product was amplified with DNA from isolates belonging to other anastomosis groups of R. solani, other pathogens or the host plant. By using quantitative PCR, DNA amounts as low as 100 fg of R. solani AG-2-1 were detected. The quantity of DNA from soil samples with different inoculum densities estimated using qPCR was highly correlated to the number of colony-forming units (cfu) obtained from the same soil samples for both R. solani AG-2-1 and F. avenaceum.     

Comparative susceptibility of some potato cultivars to dry rot caused byFusarium sulphureum andF. solani var.coeruleum

Summary The susceptibility of 15 potato cultivars to dry rot caused byFusarium sulphureum andf. solani var.coeruleum was examined over 8 years. Tubers were wounded, inoculated, incubated at 10°C for 7–8 weeks and the size of the rot assessed.F. sulphureum was the more aggressive species. There was little correlation between the rank order of susceptibility of the cultivars to the two pathogens, but a higly significant correlation between years. Two years' tests are deemed sufficient to assess susceptibility to both species.