Genetic diversity of <Emphasis Type="Italic">Ralstonia solanacearum</Emphasis> strains from Mexico associated with Moko disease

The aim of this study was to develop and validate a standard area diagram set (SADs) to assess the severity of peach rust, caused by Tranzschelia discolor. The proposed SADs includes ten images of leaves with a range of severity (0.1, 0.5, 1.0, 2.0, 5.0, 10, 15, 20, 25 and 30%). The SADs was validated by 14 raters who had no experience in plant disease severity estimation. In the first step of the validation, the raters made severity estimates of 50 leaves with a range of rust severity without using SADs. In the second step, the same raters estimated severity of rust on the same 50 leaves using the SADs to aid estimation. Lin’s concordance correlation analysis showed that both precision and accuracy improved when the raters used the SADs compared to the assessments made without SADs. Accuracy, as measured by the coefficient of bias (C _b ) improved from 0.70 to 0.98, without and with SADs, respectively, and precision measured by the correlation coefficient (r) improved from 0.85 to 0.90, without and with SADs, respectively. Overall agreement, measured by Lin’s concordance correlation coefficient (ρ _c ), improved from 0.59 to 0.88 without and with SADs, respectively. Furthermore, estimates were more reliable when using SADs: the coefficient of determination (R²) was 0.60 without and 0.73 with SADs; and the intra-class correlation coefficient (ρ) was 0.72 without, and 0.86 with SADs. Thus, the use of SADs improved the precision, accuracy and reliability of visual estimates of severity of peach rust.     

Development and validation of a standard area diagram set to aid assessment of severity of loquat scab on fruit

A standard area diagram set (SAD) to aid visual assessment of loquat scab (caused by Fusicladium eriobotryae) severity on fruit was developed and evaluated for improving accuracy, precision and reliability of visual estimates. The SAD set contains eight black and white diagrams of diseased fruit with severity values from 2 % to 98 %. To evaluate the SADs, a group of 20 raters (comprising 10 ‘experienced’ and 10 ‘inexperienced’ raters) assessed the same set of 50 images three times, the first without SADs and the second and third using the SADs as an aid. Only for the group of inexperienced raters did SADs significantly improve accuracy (bias correction factor, C _b?=?0.93 without SADs and 0.98 with SADs), precision (correlation coefficient, r?=?0.88 without SADs and r?=?0.96 with SADs) and overall agreement (Lin’s concordance correlation coefficient, ρ _c?=?0.82 without SADs and ρc with SADs = 0.95) of the estimates. Accuracy and precision of the estimates by inexperienced raters were significantly higher than those obtained by the experienced raters, especially for the second assessment with SADs. Inter-rater reliability was improved when SADs were used by inexperienced raters, whereas a high degree of intra-rater reliability was obtained by both experienced and inexperienced raters when using SADs. The SADs developed in this study were useful for obtaining more accurate, precise and reliable assessments of loquat scab for inexperienced raters, and should be used as an aid for assessing scab in epidemiological studies or monitoring for decision-making purposes.     

Development and validation of a standard area diagram set to assess blast severity on wheat leaves

This study aimed to develop and validate a standard area diagram set (SADS) to quantify the severity of blast, caused by Pyricularia oryzae, on wheat leaves. The SADs has ten levels: 0.1, 1, 5, 10, 22, 32, 42, 52, 62 and 72 % blast severity. To validate the SADs, 12 inexperienced raters estimated disease severity on 50 images of leaves from cultivars BR-18 (susceptible) and BRS-229 (partially resistant). Blast severity was first estimated without the use of the SADs on 50 leaves with a range of blast severity. The same raters evaluated the same 50 leaves using the SADs as an aid. The SADs improved accuracy (coefficient of bias, C _b ?=?0.88 and 0.99, without and with SADs, respectively) and agreement (Lin’s concordance correlation coefficient, ρ _c ?=?0.84 and 0.96 without and with SADs, respectively) of the estimates of severity. The absolute error was (-) 52 % without the SADs and (-) 24 % when using SADs as an aid. Severity estimates were more reliable when using SADs (R²?=?0.87 unaided and R²?=?0.92 with SAD). The SADs proposed in this study will improve accuracy and reliability of estimates of blast severity on wheat leaves.     

Development and validation of a set of standard area diagrams to estimate severity of potato early blight

Standard area diagrams (SADs) to assess the severity of potato early blight (Alternaria grandis) on leaves of potato (Solanum tuberosum L.) were developed and validated. The proposed SADs include images of leaves with 10 distinct disease severities (0.1, 1, 3, 5, 10, 20, 40, 60, 80 and 100 %). The SADs were validated by 12 raters who had no previous experience in evaluating plant disease. Lin’s concordance correlation analysis of estimated vs. actual disease severity (based on image analysis) showed that precision and accuracy improved for most raters using the SADs, compared to assessments made without the SADs. The SADs improved accuracy (coefficient of bias, C _b ?=?0.97 and 0.99, without and with SADs, respectively) and agreement (Lin’s concordance correlation coefficient, ρ _c ?=?0.91 and 0.98 without and with SADs, respectively) of the estimates of severity. Severity estimates were more reliable when using SADs (coefficient of determination, R ² ?=?0.80 unaided and R ² ?=?0.95 with SADs, and the intra-class correlation ρ?=?0.86 without SADs and ρ?=?0.97 using the SADs). The SADs improved raters’ ability to accurately, precisely and reliably estimate potato early blight severity, and as such can be used to assess severity for several purposes, including breeding for resistance, fungicide screening, and pathotype characterization.     

Development and validation of standard area diagrams to aid assessment of pecan scab symptoms on fruit

Pecan scab (Fusicladium effusum) causes losses of pecan nutmeat yield and quality in the southeastern United States. Disease assessment relies on visual rating, which can be inaccurate and imprecise, with poor inter‐rater reliability. A standard area diagram (SAD) set for pecan scab on fruit valves was developed. A set of 40 images of diseased fruit valves with known severity was assessed twice by 23 raters. The first assessment was conducted without SADs, and the second assessment was made using the SADs as an aid. SADs improved rater accuracy (correction factor, C_b = 0·86 and 0·97, without and with SADs, respectively) and agreement (Lin’s concordance correlation coefficient, ρ_c = 0·79 and 0·89 without and with SADs, respectively) with true values. SADs improved inter‐rater reliability (intra‐class correlation coefficient, ρ = 0·77 and 0·96 without and with SADs, respectively). The least accurate and precise raters without SADs improved more using SADs compared to the most accurate and precise raters. Experienced raters had significantly higher accuracy and precision compared to inexperienced raters, but only when unaided by the SAD set. There was no significant difference in time to assess images without SADs, but experienced raters using SADs were faster compared to inexperienced raters. There was a slight tendency for faster raters to assess more slowly, and slower raters to assess faster when using SADs. SADs improve rater estimates of pecan scab severity on fruit, and this SAD set should be useful for assessment where greater precision, accuracy and inter‐rater reliability are required.     

Characterization of <Emphasis Type="Italic">Fusarium oxysporum</Emphasis> f. sp. <Emphasis Type="Italic">melongenae</Emphasis> isolates from Turkey with ISSR markers and DNA sequence analyses

Fusarium oxysporum f. sp. melongenae (Fomg), causal agent of Fusarium wilt of eggplant, is a serious pathogen in open fields and greenhouses. Inter-simple sequence repeat (ISSR) banding profiles, sequence analyses of inter-transcribed-spacer (ITS), translation elongation factor 1-alpha (TEF-1α), and actin (actA) DNA regions were employed in this study to determine genetic diversity and population structure of Fomg isolates obtained from Turkey. For ISSR study, (ACTG)₅, (GACAC)₃, (GACA)₄, (GATA)₄, HVH(TG)₇ and (CA)₈RG primers were selected from a set of 16. Discriminative ability of the primers revealed with various indices including polymorphic information content (PIC), and mean PIC value was calculated as 0.26. The ISSR data revealed 31 loci belonging to 202 Fomg isolates and 14 of them were found to be polymorphic. The isolates on neighbor joining ISSR tree were grouped into two major clusters which separated Fomg and outgroup isolates. Population structure was investigated based on bayesian modeling and results indicated five subpopulations (K = 5, ?K = 205.42). Mean genetic and geographical distances among sampling locations revealed only a weak and insignificant correlation (r = 0.583, P = 0.06). Phylogenetic analyses were carried out with ITS, TEF-1α and actA DNA regions with a selected subset of 30 Fomg, along with one non-host and one outgroup isolates. Since ITS region were not able to provide a meaningful separation, TEF-1α and actA sequences of each organism were concatenated individually to build a dendrogram. The clustering tree successfully separated the Fomg, non-host and outgroup isolates in which all Fomg were located on the same branch, forming a monophyletic group in the dendrogram.     

TaqMan PCR assay for detection and quantification of <Emphasis Type="Italic">Stagonosporopsis tanaceti</Emphasis> in pyrethrum seed and seedlings

Pyrethrum seed has an important role in the transmission of Stagonosporopsis tanaceti, the cause of ray blight disease of pyrethrum. A TaqMan probe based polymerase chain reaction (PCR) assay was developed to quantify the level of S. tanaceti inocula in pyrethrum seed and seedlings. Primer pair (St_qF3, St_qR2) was designed based on the intergenic spacer (IGS) region of S. tanaceti, which produced a 125 bp amplicon specific to S. tanaceti. TaqMan PCR assay using St_qF3, St_qR2 and a probe St_qP was highly specific against the genomic DNA of S. tanaceti, but did not amplify DNA of 14 related Stagonosporopsis species or other foliar pathogens of pyrethrum. The sensitivity limit of this assay was measured using the cycle threshold (C_t) value which ranged from 17.59 for 10 nanograms (ng) to 36.34 for 100 femtograms (fg) genomic DNA of S. tanaceti. There was a significant negative correlation (r = ?0.999, P < 0.001) between the C_t value and the percent of S. tanaceti infected seed. In addition, this TaqMan PCR assay detected latent infection within seedlings. This assay could be applied to test commercial seed and seedlings before deciding on the appropriate management practices.     

Morphological and biochemical basis of resistance in okra to cotton jassid, <Emphasis Type="Italic">Amrasca biguttula biguttula</Emphasis> (Ishida)

Fifteen okra germplasm entries viz. accessions: IC0506027, IC0506118 and EC0306728; Abelmoschus spp.: Abelmoschus tuberculatus, Abelmoschus moschatus, Abelmoschus angulosus, Abelmoschus tetraphyllus, Abelmoschus manihot and Abelmoschus caillei; genotypes: POL-6 and POL-7; and four cultivated varieties: Punjab 8, Punjab Padmini, Punjab 7 and Pusa Sawani were screened against jassid, Amrasca biguttula biguttula (Ishida) in field at Vegetable Research Farm, Department of Vegetable Science, Punjab Agricultural University, Ludhiana, India during Kharif 2015. Different morphological and biochemical parameters of leaves of the selected entries were also studied. The correlation between jassid nymphal population and mid vein hair density, total phenols and tannins was negative and significant (r = ?0.67, ?0.83, ?0.75, respectively); negative and non-significant for hair length, angle of insertion of hair, total sugars and silica (r = ?0.40, ?0.49, ?0.63 and ?0.59, respectively) and positive and highly significant for lacination index, reducing sugars and lignins (r = 0.82, 0.95 and 0.90, respectively). Abelmoschus spp. Abelmoschus tetraphyllus, Abelmoschus angulosus and Abelmoschus moschatus were found to be field resistant on the basis of significantly lower pooled jassid nymphal population (1.56–1.99), jassid injury index (1.16–1.27) and susceptibility index (2.70–2.92). High degree of resistance in Abelmoschus tetraphyllus, Abelmoschus angulosus and Abelmoschus moschatus was found to be associated with high hair density (4.75–7.50), longer hair (1285.00–1513.20 μm), more erect hair (83.40–95.20°), broad leaves, high total sugars (15.21–18.36 mg/g), total phenols (1.52–1.58 mg/g), tannins (26.12–31.48 mg/g) and silica (32.66–33.17 mg/g) and low levels of reducing sugars (2.50–3.39 mg/g). Abelmoschus tuberculatus, A. manihot, IC0506027 and EC0306728 were found moderately field resistant with variable levels of morphological and biochemical parameters. High hair density, broad leaves, moderate levels of total sugars, reducing sugars, total phenols, tannins and silica seems to be associated with moderate levels of resistance in these entries. The variable levels of above mentioned parameters in moderately resistant entries also indicate that a single factor is not responsible for resistance but combination of different factors may be conferring resistance to jassid.     

Genetic structure of <Emphasis Type="Italic">Pyrenophora teres</Emphasis> f. <Emphasis Type="Italic">teres</Emphasis> and <Emphasis Type="Italic">P. teres</Emphasis> f. <Emphasis Type="Italic">maculata</Emphasis> populations from western Canada

Infection by Pyrenophora teres f. teres (Ptt) or P. teres f. maculata (Ptm), the causal agents of the net and spot forms of net blotch of barley, respectively, can result in significant yield losses. The genetic structure of a collection of 128 Ptt and 92 Ptm isolates from the western Canadian provinces of Alberta (55 Ptt, 27 Ptm), Saskatchewan (58 Ptt, 46 Ptm) and Manitoba (15 Ptt, 19 Ptm) were analyzed by simple sequence repeat (SSR) marker analysis. Thirteen SSR loci were examined and found to be polymorphic within both Ptt and Ptm populations. In total, 110 distinct alleles were identified, with 19 of these shared between Ptt and Ptm, 75 specific to Ptt, and 16 specific to Ptm. Genotypic diversity was relatively high, with a clonal fraction of approximately 10 % within Ptt and Ptm populations. Significant genetic differentiation (PhiPT = 0.230, P = 0.001) was found among all populations; 77 % of genetic variation occurred within populations and 23 % between populations. Lower, but still significant genetic differentiation (PhiPT = 0.038, P = 0.001) was detected in Ptt, with 96 % of genetic variation occurring within populations. No significant genetic differentiation (PhiPT = 0.010, P = 0.177) was observed among Ptm populations. Isolates clustered in two distinct groups conforming to Ptt or Ptm, with no intermediate cluster. The high number of haplotypes observed, combined with an equal mating type ratio for both forms of the fungus, suggests that P. teres goes through regular cycles of sexual recombination in western Canada.     

Attempts to eradicate graft-transmissible infections through somatic embryogenesis in <Emphasis Type="Italic">Citrus</Emphasis> ssp. and analysis of genetic stability of regenerated plants

Ability to detect Pseudocercospora macadamiae infection in macadamia husk at least four months before symptoms become visible will aid the development of disease control measures. This study examined the distinctness of P. macadamiae within the phylogenetic lineages of the genus Pseudocercospora. In addition, we developed two quantitative PCR (qPCR) assays, as rapid diagnostic tools, for early detection and quantification of P. macadamiae in planta. Phylogenetic analysis of concatenated sequences of four gene loci (large subunits, internal transcribed spacer (ITS), translation elongation factor 1-alpha (TEF-1α) and actin of 47 P. macadamiae isolates showed that P. macadamiae is a distinct species in the genus Pseudocercospora. P. macadamiae isolates were partitioned into subunits in the cluster but the grouping of the isolates was regardless of location. Nucleotide diversity (0.02) and the coefficient of genetic differentiation (0.07) were low in the P. macadamiae population. Two qPCR primer sets, based on ITS (PMI) and TEF-1α (PME) were designed that consistently amplified P. macadamiae in fungal cultures (Ct = 16.93 ± 0.11 and Ct = 21.20 ± 0.11, respectively) and in planta (Ct = 32.36 ± 0.28 and Ct = 38.07 ± 1.20, respectively). The PMI primers also detected species in the genus Pseudocercospora, while PME was more specific and robust for quantification of P. macadamiae. Both primer sets detected P. macadamiae in asymptomatic tissue samples and strongly differentiated various stages of disease progression, which revealed approximately 10-fold increase in fungal biomass between each consecutive stage of symptom development.     

Rice response to simultaneous bacterial blight and drought stress during compatible and incompatible interactions

Plant response to one type of stress can be affected by simultaneous exposure to a second stress, for example when abiotic and biotic stresses occur together. Ten rice genotypes comprising those with bacterial blight (BB) resistance (R) genes, drought quantitative trait loci (QTLs) plus a BB R gene, and BB susceptible genotypes, were subjected to mild and moderate drought stress and plants were inoculated with two Xoo strains (PXO99 and PXO145) to simulate the challenges rice crops face under simultaneous stress of drought and BB. Plant height and dry shoot biomass were significantly reduced by drought stress treatments. The BB disease lesion lengths varied according to rice genotypes and PXO99 Xoo multiplication and spread in planta was higher compared to that of PXO145, which generally decreased under mild drought stress. Rice genotype IRBB7 (Xa7) showed less Xoo spread and a reduced Xoo multiplication under drought stress compared to the well-watered control with PXO145. In contrast, in genotypes with a different BB R gene and/or drought QTLs [IRBB4 (Xa4), IR87705–6-9-B (Xa4 + qDYT _2.2 ), IR87707–445-B-B-B (Xa4 + qDYT _2.2  + qDYT _4.1 ) and IR87707–446-B-B-B (Xa4 + qDYT _2.2  + qDYT _4.1 )], Xoo multiplication and spread in planta was higher with drought stress. This study has shown that drought stress affected rice response to the BB pathogen and the response varied according to the rice genotype. It is concluded that evaluating rice varieties under combined abiotic and biotic stresses will be the best strategy to determine biotic stress resistance durability under climate change.     

Infection of <Emphasis Type="Italic">Sorghum bicolor</Emphasis>, selected grass species and <Emphasis Type="Italic">Zea mays</Emphasis> by G<Emphasis Type="Italic">loeocercospora sorghi</Emphasis>, causal pathogen of zonate leaf spot

Zonate leaf spot (Gloeocercospora sorghi) is a common disease in Sorghum bicolor producing areas of the U.S., but little is known about its biology, virulence and severity on S. bicolor, Zea mays, and related crop grassweeds. Greenhouse studies were conducted to determine and compare the virulence and severity of G. sorghi on 10 commercially available sorghum hybrids, four Z. mays hybrids and selected grassweed species including Sorghum bicolor (grain sorghum and shattercane biotypes) and Sorghum halepense (Johnsongrass), two of the most problematic arable weeds. Plants from the respective species were inoculated with a local G. sorghi isolate and maintained in a dew-chamber at 24 °C for 24 h and then incubated under greenhouse conditions for 4 weeks. Plants were observed for lesion expression and rated using a modified Horsfall-Barrett scale (0–10). The first symptoms of infection were visible within 24 h following inoculation on shattercane and S. bicolor hybrids. Symptoms consisted of small, non-diagnostic purple lesions on the leaves. Results showed that S. bicolor, S. halepense and shattercane were susceptible to G. sorghi. All other species tested in this study were not infected. More particularly, disease severity, increased from a rating of 3 to 10 on sorghum and from 2 to 7 on S. halepense between 2 and 23 days after inoculation, respectively. However, disease severity on shattercane increased rapidly from 3.5 to 10 between 2 and 8 days after inoculation, respectively. Among the sorghum hybrids tested, FFR-322 appeared to be the most resistant to G. sorghi while Pioneer 83G66 appeared to be the most susceptible. Z. mays hybrids were not infected by the fungus used in this study. G. sorghi could be used effectively to manage shattercane and S. halepense infestations occurring in Z. mays and S. bicolor fields consisting of specific G. sorghi-resistant hybrids.     

Rapid diagnosis of soybean anthracnose caused by <Emphasis Type="Italic">Colletotrichum truncatum</Emphasis> using a loop-mediated isothermal amplification (LAMP) assay

A loop-mediated isothermal amplification (LAMP) assay that directly detects Colletotrichum truncatum in diseased soybean tissues is described, thus allowing rapid diagnosis of soybean anthracnose. Using the target gene Rpb1 (that codes for the large subunit of RNA polymerase II), we designed and screened a set of species-specific primers allowing amplification at 62 °C over 70 min. After addition of SYBR Green I to the LAMP reaction products, a yellow-green color (visible to the unaided eye) developed only in the presence of C. truncatum. The detection limit of the LAMP assay was 100 pg (per μL genomic DNA). The Rpb1-Ct-LAMP assay has been successfully used to diagnose soybean anthracnose in field samples collected from Jiangsu, Anhui and Hubei provinces of China, and to detect C. truncatum in soybean seeds from farmers’ markets. Our results show that the Rpb1-Ct-LAMP assay is a useful and convenient method for detecting C. truncatum, and thus for diagnosis of soybean anthracnose.     

Environmental and inoculum effects on epidemiology of bacterial spot disease of stone fruits and development of a disease forecasting system

Bacterial spot disease of stone fruits, caused by Xanthomonas arboricola pv. pruni, is of high economic importance in the major stone-fruit-producing areas worldwide. A better understanding of disease epidemiology can be valuable in developing disease management strategies. The effects of weather variables (temperature and wet/dry period) on epiphytic growth of X. arboricola pv. pruni on Prunus leaves were analyzed, and the relationship between inoculum density and temperature on disease development was determined and modeled. The information generated in this study, performed under controlled environmental conditions, will be useful to develop a forecasting system for X. arboricola pv. pruni. Optimal temperature for growth of epiphytic populations ranged from 20 to 30 °C under leaf wetness. In contrast, multiplication of epiphytic populations was not only interrupted under low relative humidity (RH) (< 40%) at 25 °C, but also resulted in cell inactivation, with only 0.001% initial cells recovered after 72 h incubation. A significant effect of inoculum density on disease severity was observed and 10⁶ CFU/ml was determined as the minimal infective dose for X. arboricola pv. pruni on Prunus. Infections occurred at temperatures from 15 to 35 °C, but incubation at 25 and 30 °C gave the shortest incubation periods (7.7 and 5.9 days respectively). A model for predicting disease symptom development was generated and successfully evaluated, based on the relationship between disease severity and the accumulated heat expressed in cumulative degree day (CDD). Incubation periods of 150, 175 and 280 CDD were required for 5, 10 and 50% of disease severity, respectively.     

Insecticidal activity of plant-derived extracts against different economically important pest insects

With the aim of selecting potential botanical insecticides, seven plant extracts (Daphne mucronata (Family: Thymelaeaceae), Tagetes minuta (Asteraceae), Calotropis procera (Apocynaceae), Boenninghausenia albiflora (Rutaceae), Eucalyptus sideroxylon (Myrtaceae), Cinnamomum camphora (Lauraceae) and Isodon rugosus (Lamiaceae)) were screened for their toxic effects against four important agricultural pest insects, each representing a separate insect order; pea aphids of Acyrthosiphon pisum (Hemiptera), fruit flies of Drosophila melanogaster (Diptera), red flour beetles of Tribolium castaneum (Coleoptera), and armyworms of Spodoptera exigua (Lepidoptera). Aphids were the most susceptible insect with 100% mortality observed after 24 h for all the plant extracts tested. Further bioassays with lower concentrations of the plant extracts against aphids, revealed the extracts from I. rugosus (LC₅₀ 36 ppm and LC₉₀ 102 ppm) and D. mucronata (LC₅₀ 126 ppm and LC₉₀ 198 ppm) to be the most toxic to aphids. These most active plant extracts were further fractionated into different solvent fractions on polarity basis and their insecticidal activity evaluated. While all the fractions showed considerable mortality in aphids, the most active was the butanol fraction from I. rugosus with an LC₅₀ of 18 ppm and LC₉₀ of 48 ppm. Considering that high mortality was observed in aphids within 24 h of exposure to a very low concentration of the butanol fraction from I. rugosus, we believe this could be exploited and further developed as a potential plant-based insecticide against sucking insect pests, such as aphids.     

Sensitivity of <Emphasis Type="Italic">Cochliobolus heterostrophus</Emphasis> to three demethylation inhibitor fungicides,propiconazole, diniconazole and prochloraz,and their efficacy against southern corn leaf blight in Fujian Province,China

Southern corn leaf blight (SCLB) caused by Cochliobolus heterostrophus is a fungal disease that impacts production of corn in China. Fungicides have been the main strategy to manage SCLB. In this study, 276 isolates of C. heterostrophus from seven locations in Fujian Province of China were tested for sensitivity to three demethylation inhibitor (DMI) fungicides. The results indicated that most of the isolates of C. heterostrophus tested were exceptionally sensitive to the three DMI fungicides. Correlation analysis revealed positive association between propiconazole and diniconazole (r?=?0.8145, P?<?0.0001), propiconazole and prochloraz (r?=?0.6190, P?<?0.0001), and diniconazole and prochloraz (r?=?0.5784, P?<?0.0001). However, there was no cross-resistance between these three DMI fungicides and the other six fungicides tested, which included carbendazol, chlorothalonil, mancozeb, iprodione, fluazinam, and pyraclostrobin. In a preventive pot experiment, one spray of 25% propiconazole emulsifiable concentrate (EC) with 250 μg active ingredient (a.i.) mL^?1 applied 12 and 24 h before inoculation at the seedling (V6) stage reduced severity of SCLB by 85.60–89.21%. Nevertheless, the curative activity of propiconazole was much weaker (P?<?0.05) than its preventive efficacy. In greenhouse pot assays, one dose of propiconazole at 250 μg a.i. mL^?1 was the most efficacious for controlling SCLB at the seedling and tasseling (VT) stages of corn, decreasing severity by 80.31%–84.85%, which was higher (P?<?0.05) compared to diniconazole, prochloraz, and other reference fungicides. Therefore, propiconazole appears to be very effective in reducing SCLB and should be applied as a preventive rather than therapeutic fungicide. Our findings provide essential information on the evolution of DMI resistance in C. heterostrophus in Fujian Province of China and may serve as a guide for early resistance monitoring in the future.     

Chitinolytic <Emphasis Type="Italic">Streptomyces griseorubens</Emphasis> E44G enhances the biocontrol efficacy against <Emphasis Type="Italic">Fusarium</Emphasis> wilt disease of tomato

Streptomyces griseorubens E44G is a chitinolytic bacterium isolated from cultivated soil in Saudi Arabia (a hot, arid climatic region). In vitro, antifungal potential of S. griseorubens E44G was assessed against the phytopathogenic fungus, Fusarium oxysporum f. sp. lycopersici (the causative agent of the Fusarium wilt disease of tomato). An inhibition zone of 24 mm was recorded. The chitinolytic activity of S. griseorubens E44G was proved when the colloidal chitin agar plate method was used. A thermostable chitinase enzyme of 45 kDa molecular weight was purified using gel filtration chromatography. The optimum activity was obtained at 60 °C and pH 5.5. The purified enzyme has shown a very pronounced activity against the phytopathogenic fungus, F. oxysporum. The molecular characterization of the chitinase gene indicated that it consists of 1218 bp encoding 407 amino acids. The phylogentic analysis based on the nucleotide DNA sequence and the deduced amino acids sequence showed high similarity percentages with other chitinases isolated from different Streptomyces species. In the field evaluation, application of both S. griseorubens E44G treatments significantly increased all tested growth and yield parameters and decreased the disease severity compared with the infected-untreated tomato plants suggesting potential as a biocontrol agent.     

Disease development and mycotoxin production by the <Emphasis Type="Italic">Fusarium graminearum</Emphasis> species complex associated with South African maize and wheat

Fungal species comprising the Fusarium graminearum species complex (FGSC) may cause disease in maize and wheat. Host preference within the FGSC has been suggested, in particular F. boothii towards maize ears. Therefore, the disease development and mycotoxin production of five FGSC species in maize and wheat grain was determined. Eighteen isolates representing F. acaciae-mearnsii, F. boothii, F. cortaderiae, F. graminearum and F. meridionale were used. Each isolate was inoculated on maize ears and wheat heads to determine host preferences. Disease severity and disease incidence was measured for maize and wheat, respectively. Fungal colonisation and mycotoxins, deoxynivalenol (DON), nivalenol and zearalenone, was also quantified. Isolates differed significantly (P < 0.05) in their ability to produce symptoms on maize ears, however, no significant differences between FGSC species were determined. Similarly, significant differences (P < 0.05) between isolates but not between FGSC species in disease incidence on wheat were determined. The isolates also differed significantly (P < 0.05) in their ability to colonise maize and wheat grain. No significant differences in fungal colonisation, among the five FGSC species, were determined in field grown maize. However, under greenhouse conditions, F. boothii was the most successful coloniser of maize grain (P < 0.05). In wheat, F. graminearum colonised the grain more successfully and produced significantly more (P < 0.05) DON than the other species. Fusarium boothii isolates were the best colonisers and mycotoxin producers in maize, and F. graminearum isolates in wheat. The selective advantage of F. boothii to cause disease on maize was supported in this study.     

Long-term dynamics of causative agents of stem base diseases in winter wheat and reaction of Czech <Emphasis Type="Italic">Oculimacula</Emphasis> spp. and <Emphasis Type="Italic">Microdochium</Emphasis> spp<Emphasis Type="Italic">.</Emphasis> populations to prochloraz

Trichoderma aggressivum is an aggressive contaminant mould in the cultivation of Agaricus bisporus leading to severe reductions in mushroom yields. Production of fully colonised A. bisporus substrate in Europe is commonly carried out in large tunnels (Phase III), after which the substrate undergoes several bulk handling (mixing) operations before ending up on shelves in mushroom growing facilities. The work presented here studied the effect of Trichoderma aggressivum inoculum, substrate mixing and supplementation on Agaricus bisporus yields and evaluated four methods to detect T. aggressivum in bulk handled substrate. Inoculum dilution level was shown to correlate well with mushroom yield (P < 0.0001) with reductions of 2–6 % at the most dilute level (10^?4) and 60–100 % at the most concentrated level (10^?1), depending on the experiment. Supplementation, with or without T. aggressivum, had no significant effect on mushroom yield (P ≥ 0.85) but a high degree of substrate mixing was shown to significantly increase (P < 0.0001) T. aggressivum-associated crop losses. Four T. aggressivum detection methods were evaluated and a quantitative polymerase chain reaction (qPCR) method gave the most consistent and least variable results. Cycle threshold (CT) values ranged from 24 to 40, depending on the experiment and the inoculum dilution level, and false negatives (CT = 40) were reported on one occasion with the most dilute samples. The results indicate that Phase III mushroom substrate is vulnerable to infection by T. aggressivum when the fully colonised substrate is broken up and mixed during bulk handling operations, identifying a previously unidentified risk for Phase III substrate producers.     

Rutin promoted resistance of tomato against <Emphasis Type="Italic">Xanthomonas perforans</Emphasis>

Xanthomonas perforans is the causal agent of bacterial spot, one of the most devastating diseases of tomato that results in considerable yield losses worldwide. Rutin, as a polyphenolic substance, was used to induce resistance in tomato against X. perforans. Rutin at concentration of 2 mM had ability to reduce the disease severity of bacterial spot. On the other hand, 2 mM rutin had no antibacterial activity in vitro. Expression profiling of pathogenesis-related gene 5 (PR-5), Phenylalanine ammonia-lyase (PAL) and lipoxygenase (LOX) was probed during the enhanced resistance by rutin. Pretreatment with rutin (rutin/ X. perforans) led to induction of PR-5, PAL and LOX compared to controls (water/ X. perforans). Our results suggest that rutin-induced resistance against X. perforans in tomato might be mediated through stimulation of some defense genes such as PR-5, PAL and LOX.