The effect of temperature on the phenotypic features and the maceration ability of <Emphasis Type="Italic">Dickeya solani</Emphasis> strains isolated in Finland,Israel and Poland

Pectinolytic bacteria from the genus Dickeya (former Erwinia chrysanthemi), belonging to Dickeya dianthicola and Dickeya solani species, are causative agents of blackleg and soft rot diseases in Europe. Recently, D. solani have been isolated most frequently from potato plants with the symptoms of blackleg and soft rot. D. solani strains were shown to cause more severe disease symptoms on potato plants than D. dianthicola especially at the higher temperature. They are also able to develop blackleg disease from lower inoculum levels. In the presented study we not only compared phenotypic features of fifteen D. solani strains isolated in countries having different climatic conditions, Poland, Finland and Israel, but also we examined three D. dianthicola strains. The comparison was performed to determine the influence of the strain origin and the temperature of incubation on the ability of the strains to macerate potato tissue and on their major virulence factors such as: pectinolytic, cellulolytic and proteolytic activities, siderophore production and motility. Polish D. solani strains showed higher activities of cell wall degrading enzymes than the Finnish and Israeli strains at all the tested temperatures: 18, 27, 37 °C. This observation is correlated with the higher ability of Polish D. solani strains to cause soft rot. In addition, D. solani strains exhibited higher activity of the above mentioned enzymes and caused more severe potato tuber maceration in laboratory tests than the tested D. dianthicola strains. The collected results indicate that although D. solani strains from different climatic conditions have identical Pulse Field Gel Electrophoresis (PFGE) profiles in addition to the same fingerprint profiles obtained by the repetitive sequence-based polymerase chain reaction (REP, ERIC and BOX repetitive sequences), they differ in the examined phenotypic features, especially in the activities of pectinolytic, cellulolytic and proteolytic enzymes and their capacity to macerate potato tuber tissue.     

Diversity of <Emphasis Type="Italic">Fusarium</Emphasis> species associated with root rot of sugar beet in China

Sugar beet is widely grown throughout the world and represents the second largest crop used to produce sugar. Root rot in sugar beet, caused by Fusarium, significantly reduces yield, juice purity, and sugar concentration. Here, 307 Fusarium isolates were collected from sugar beet roots exhibiting typical root rot symptoms in eight provinces or autonomous regions of China from 2009 to 2012. Based on morphological characteristics and sequence data of the internal transcribed spacer (ITS) region of ribosomal DNA (rDNA) and the translation elongation factor 1α (EF-1α), Fusarium oxysporum (38.4%) was identified as the most prevalent species, followed by F. solani (20.9%), and F. equiseti (18.9%). These three species were widely distributed in all eight of the provinces and autonomous regions. F. tricinctum (5.9%), F. brachygibbosum (4.6%), F. redolens (3.3%), F. proliferatum (3.3%), F. graminearum (2.3%), F. verticillioides (1.6%), F. nygamai (0.7%), and F. culmorum (0.3%) were less frequently obtained. Of the 307 Fusarium isolates, 117 representing different species and geographic locations were demonstrated to cause tip rot and vascular discoloration in sugar beet roots, with disease incidence ranging from 84.2 to 100.0% and disease index ranging from 41.94 to 75.83. This is the first detailed report of Fusarium species, in particular F. tricinctum, F. brachygibbosum, F. redolens, F. proliferatum, F. nygamai, and F. culmorum, causing sugar beet root rot in China.     

Characterization of <Emphasis Type="Italic">Dickeya</Emphasis> and <Emphasis Type="Italic">Pectobacterium</Emphasis> strains obtained from diseased potato plants in different climatic conditions of Norway and Poland

Soft rot and blackleg of potato caused by pectinolytic bacteria lead to severe economic losses in potato production worldwide. To investigate the species composition of bacteria causing soft rot and black leg of potato in Norway and Poland, bacteria were isolated from potato tubers and stems. Forty-one Norwegian strains and 42 Polish strains that formed cavities on pectate medium were selected for potato tuber maceration assays and sequencing of three housekeeping genes (dnaX, icdA and mdh) for species identification and phylogenetic analysis. The distribution of the species causing soft rot and blackleg in Norway and Poland differed: we have demonstrated that mainly P. atrosepticum and P. c. subsp. carotovorum are the causal agents of soft rot and blackleg of potatoes in Norway, while P. wasabiae was identified as one of the most important soft rot pathogens in Poland. In contrast to the other European countries, D. solani seem not to be a major pathogen of potato in Norway and Poland. The Norwegian and Polish P. c. subsp. carotovorum and P. wasabiae strains did not cluster with type strains of the respective species in the phylogenetic analysis, which underlines the taxonomic complexity of the genus Pectobacterium. No correlation between the country of origin and clustering of the strains was observed. All strains tested in this study were able to macerate potato tissue. The ability to macerate potato tissue was significantly greater for the P. c. subsp. carotovorum and Dickeya spp., compared to P. atrosepticum and P. wasabiae.     

Improved control of black rot of broccoli caused by <Emphasis Type="Italic">Xanthomonas campestris</Emphasis> pv. <Emphasis Type="Italic">campestris</Emphasis> using a bacteriophage and a nonpathogenic <Emphasis Type="Italic">Xanthomonas</Emphasis> sp. strain

We examined the potential for biological control of black rot of broccoli, caused by Xanthomonas campestris pv. campestris (Xcc), using nonpathogenic Xanthomonas sp. strain 11-100-01 (npX) mixed with bacteriophage XcpSFC211 (pXS). Inoculation of intact broccoli plants in greenhouse trials with either npX or pXS did not control black rot. After injured plant inoculation, however, npX alone or npX with pXS significantly controlled black rot. When a mixed suspension of npX with pXS was placed on a membrane filter, then washed with distilled water and air-dried, a substantial amount of pXS adsorbed to the surface of npX. In a field trial, broccoli plants were sprayed with a suspension of npX with pXS, then inoculated with Xcc. A meta-analysis of the results from five field trials showed an integrated risk ratio (IRR, the ratio of disease incidence in inoculated broccoli plants to the incidence in control plants) of 0.69 after treatment with only npX and 0.59 with npX with pXS, indicating that black rot incidence was significantly reduced by each treatment. The difference between these two treatments was also significant. IRR was 1.24 when comparing suppression by npX with pXS and that by basic copper sulfate wettable powder; thus, their control was comparable. The combination of npX with pXS improved the preventive effect against black rot. This is the first report describing that a nonpathogenic Xanthomonas sp. strain mixed with a bacteriophage effectively controlled black rot of broccoli in field trials.     

Conidial density of <Emphasis Type="Italic">Monilinia</Emphasis> spp. on peach fruit surfaces in relation to the incidences of latent infections and brown rot

To evaluate the effect of conidial density of Monilinia spp. on the fruit surface on the incidence of latent infection and brown rot in peaches, eleven field surveys were performed in commercial orchards located in Cataluña, Spain over four growing seasons from 2002 to 2005, and nine surveys were conducted to determine the sources of overwintered Monilinia spp. inoculum. There was a significant positive relationship (r?=?0.69) between the numbers of conidia of Monilinia spp. on the fruit surface and the incidence of latent infections, but not with brown rot at harvest. Although mummified fruit, twigs and pits have been identified as being able to carry the pathogen from year to year in peaches grown in Spanish orchards, no relationships between any of these sources and the numbers of conidia on the fruit surface, or incidence of latent infection or brown rot were found. The effect of temperature (T), solar radiation (SR), rainfall (R) and wind speed (WS) on the area under the number of conidia of Monilinia spp. curve (AUncC) on peach surfaces was analysed. Regression analysis revealed that T, SR, R, and WS could account for 99% of the total variation in the area of the AUncC on peach surfaces. Thus, in order to reduce the incidence of latent infection and brown rot it is essential not only to remove the sources of primary inoculum but also to reduce the number of Monilinia spp. conidia on the fruit surface. Furthermore, the sources of airborne conidia of Monilinia spp. should be taken into consideration in disease management programmes in Spain.     

Identity and pathogenicity of <Emphasis Type="Italic">Fusarium</Emphasis> species associated with crown rot on wheat (<Emphasis Type="Italic">Triticum</Emphasis> spp.) in Turkey

An extensive survey was carried out to collect Fusarium species colonizing the lower stems (crowns) of bread wheat (Triticum aestivum L.) and durum wheat (T. durum Desf.) from different wheat growing regions of Turkey in summer 2013. Samples were collected from 200 fields representing the major wheat cultivation areas in Turkey, and fungi were isolated from symptomatic crowns. The isolates were identified to species level by sequencing the translation elongation factor 1-alpha (TEF1-α) gene region using primers ef1 and ef2. A total of 339 isolates representing 17 Fusarium species were isolated. The isolates were identified as F. culmorum, F. pseudograminearum, F. graminearum, F. equiseti, F. acuminatum, F. brachygibbosum, F. hostae, F. redolens, F. avenaceum, F. oxysporum, F. torulosum, F. proliferatum, F. flocciferum, F. solani, F. incarnatum, F. tricinctum and F. reticulatum. Fusarium equiseti was the most commonly isolated species, accounting for 36% of the total Fusarium species isolated. Among the damaging species, F. culmorum was the predominant species being isolated from 13.6% of sites surveyed while F. pseudograminearum and F. graminearum were isolated only from 1% and 0.5% of surveyed sites, respectively. Six out of the 17 Fusarium species tested for pathogenicity caused crown rot with different levels of severity. Fusarium culmorum, F. pseudograminearum and F. graminearum caused severe crown rot disease on durum wheat. Fusarium avenaceum and F. hostae were weakly to moderately virulent. Fusarium redolens was weakly virulent. However, F. oxysporum, F. equiseti, F. solani, F. incarnatum, F. reticulatum, F. flocciferum, F. tricinctum, F. brachygibbosum, F. torulosum, F. acuminatum and F. proliferatum were non-pathogenic. The result of this study reveal the existence of a wide range of Fusarium species associated with crown rot of wheat in Turkey.     

Identification and community dynamics of fungi associated with root,crown, and foot rot of field pea in western Canada

Fungal and oomycete communities in symptomatic roots, crowns and lower stem tissues of field pea plants from sites across the Canadian prairies were characterized using plate culture and sequence-based identification. Symptomatic plants were sampled at the mid-flowering stage from a total of 21 fields in 2014 and 2015. Fungi and oomycete species were isolated on agar medium and grouped into operational taxonomic groups (OTU) based on their morphology. From the OTUs, 40 fungal and oomycete species were identified according to translation elongation factor-1 alpha or ITS sequences. Fusarium spp. accounted for more than 60 % of total isolations. The fungal communities were similar in roots and crowns, but differed from communities in lower stems. In 2014, the most prevalent fungi isolated from roots were F. avenaceum, F. solani and F. redolens, but F. solani was dominant in 2015. In crown tissues, F. avenaceum was most prevalent in 2014 but F. solani was more prevalent in 2015. Stem tissues were primarily colonized by Peyronellaea spp. (= Ascochyta / Phoma spp.) and Alternaria spp. in 2014, but there was a drastic decrease in Peyronellaea spp. in 2015. This study indicated that climate, primarily precipitation levels, and local edaphic characteristics may play a profound role in the structure of phytopathogen communities associated with the root and foot rot diseases complex of field pea on the Canadian prairies.     

Identification and characterization of pathogens associated with root rot of winter peas grown under organic management in Germany

Root rots are limiting factor for pea production worldwide. This disease is caused by a pathogen complex and the role of single pathogens is unclear. This study aimed at identifying pathogens involved in a root rot of organically grown field pea in Germany, and establishing their importance in the disease complex. The potential of yard waste compost to suppress the diseased was also studied. Average disease severity index was similar in 2010 and 2011 (DI of 4.56 to 4.59, respectively) but it increased in 2012 to DI 5.8. Peyronellaea pinodella was most frequently isolated pathogen, with isolation frequency from 86%, 73% and 86% in 2010, 2011 and 2012, respectively. In addition, Didymella pinodes, Fusarium solani f. sp. pisi, F. oxysporum f. sp. pisi and F. avenaceum were the main fungi recovered from pea roots. In pathogenicity test all of the tested pathogens caused weak symptoms on the pigmented winter variety EFB33 and moderate to severe symptoms on the white flowering summer variety Santana. F. avenaceum was the most aggressive pathogen on Santana with DI of 7.4 followed by P. pinodella with DI of 5.7. The high aggressiveness combined with the wide host range highlights the possibility of F. avenaceum emerging as potential risk for organic crop rotation. High levels of resistance of EFB33 against all pathogens shows the potential of this variety to serve as a resource in further research for identification and development of new sources of resistance against root rot diseases of pea.     

Soft rot disease alters soil characteristics and root-associated,culturable microbial community of <Emphasis Type="Italic">Amorphophallus konjac</Emphasis>

To elucidate how soft rot disease affects soil characteristics and root-associated, culturable microorganisms in Amorphophallus konjac stands, the responses of soil around roots of A. konjac with soft rot disease were investigated in stands with and without soft rot. Changes in the root-associated culturable microbial community and diversity were investigated by dilution plating. Soil characteristics were compared between stands using standard techniques. A. konjac with soft rot had higher concentrations of available soil P and K, NH₄–N, organic matter and water content and lower pH compared with plants without. The community composition of root-associated culturable microorganisms differed between stands with and without soft rot. The microbial community associated with soft rot in A. konjac was characterized by four types of abundant microorganisms (Fusarium solani, Fusarium oxysporum, Pseudomonas chlororaphis subsp. aureofaciens and Stenotrophomonas pavanii) and three types of less-abundant microorganisms (Rhizobium radiobacter, Bacillus thuringiensis and Streptomyces cellulosae), and a small number of Bacillus and Streptomyces species in the rhizosphere and rhizoplane soils. Particular microbial combinations were diametrically opposed between plants with and without soft rot. The richness and diversity of root-associated culturable microorganisms were higher in the stand without soft rot than in the stand with soft rot. A. konjac soft rot led to obvious differences in the diversity and community composition of root-associated culturable microorganisms and in soil characteristics.     

Decreased potassium fertilization is associated with increased pathogen growth and disease severity caused by <Emphasis Type="Italic">Acidovorax citrulli</Emphasis> in melon foliage

The gram-negative bacterium Acidovorax citrulli causes bacterial fruit blotch (BFB) disease of cucurbits, which represents a serious threat to melon and watermelon production worldwide. To date, there are no efficient means to manage the disease, and reliable resistance sources for cucurbit germplasm are lacking. Mineral nutrition markedly affects plant diseases. Recently, we reported that disease severity on melon foliage and A. citrulli growth in the leaf tissue were significantly influenced by the form of nitrogen supply. In the present study, we investigated the influence of potassium nutrition on BFB severity and A. citrulli establishment in the foliage of melon plants. Fertilization with relatively low concentrations of potassium increased these variables compared with higher potassium concentrations. Since establishment of A. citrulli during the growing season is assumed to increase the incidence of fruit infection, the fact that mineral nutrition influences BFB incidence in the plant foliage is of particular importance.     

Five plant families support natural sporulation of <Emphasis Type="Italic">Cronartium ribicola</Emphasis> and <Emphasis Type="Italic">C. flaccidum</Emphasis> in Finland

Fusarium is one of the most destructive fungal genera whose members cause many diseases on plants, animals, and humans. Moreover, many Fusarium species secrete mycotoxins (e.g. trichothecenes and fumonisins) that are toxic to humans and animals. Fusarium isolates from date palm trees showing disease symptoms, e.g. chlorosis, necrosis and whitening, were collected from seven regions across Saudi Arabia. After single-sporing, the fungal strains were morphologically characterized. To confirm the identity of morphologically characterized Fusarium strains, three nuclear loci, two partial genes of translation elongation factor 1 α (tef1α) and β-tubulin (tub2), and the rDNA-ITS region, were amplified and sequenced. Of the 70 Fusarium strains, 70 % were identified as F. proliferatum that were recovered from six regions across Saudi Arabia. Fusarium solani (13 %), as well as one strain each of the following species: F. brachygibbosum, F. oxysporum, and F. verticillioides were also recovered. In addition, five Fusarium-like strains were recognized as Sarocladium kiliense by DNA-based data. The preliminary in vitro pathogenicity results showed that F. proliferatum had the highest colonization abilities on date palm leaflets, followed by F. solani. Although F. oxysporum f. sp. albedinis is the most serious date palm pathogen, F. proliferatum and F. solani are becoming serious pathogens and efforts should be made to restrict and control them. In addition, the potential toxin risks of strains belonging to F. proliferatum should be evaluated.     

Pathogenicity and Fungicide Sensitivity of <Emphasis Type="Italic">Rhizoctonia solani</Emphasis> and <Emphasis Type="Italic">R. cerealis</Emphasis> Isolates

The Rhizoctonia solani species consists of multinucleate isolates that belong to anastomosis groups AG1–AG3 and differ in virulence and host affinity. R. cerealis is a binucleate species of anastomosis group AG-D which causes sharp eyespot, a common plant disease in Poland. Rhizoctonia spp. is a ubiquitous soil pathogen that poses a significant threat for global crop production due to the absence of effective crop protection products. The aim of this study was to determine the virulence of R. solani and R. cerealis isolates towards Beta vulgaris, Zea mays, Triticum spelta and T. aestivum seedlings, to confirm the presence of endopolygalacturonase genes pg1 and pg5 in the genomes of the tested isolates and to evaluate the tested isolates’ sensitivity to triazole, strobilurin, imidazole and carboxamide fungicides. All tested isolates infected B. vulgaris seedlings. but none of them were virulent against Z. mays plants. R. solani isolates AG4 PL and AG2-2IIIB PL were characterized by the highest virulence (average infestation score of 2.37 and 2.53 points on a scale of 0–3 points) against sugar beet seedlings. The prevalence of infections caused by most of the analysed isolates (in particular R. solani AG4 J—11.8, and R. cerealis RC2—0.78) was higher in spelt than in bread wheat. The virulence of the analysed isolates was not correlated with the presence of pg1 and pg5 genes. The efficacy of the tested fungicides in controlling Rhizoctonia spp. infections was estimated at 100% (propiconazole + cyproconazole), 98.8% (penthiopyrad), 95.4% (tebuconazole) and 78.3% (azoxystrobin).     

Occurrence and characterisation of <Emphasis Type="Italic">Rhizoctonia</Emphasis> species causing diseases of ornamental plants in Italy

During surveys conducted in 2010–2012 Rhizoctonia symptoms were observed on 30 ornamental species in different nurseries located in eastern Sicily (Southern Italy). Eighty-eight isolates of Rhizoctonia spp. were obtained from symptomatic leaves, roots and stems. Fifty-six of the isolates were binucleate and 32 were multinucleate Rhizoctonia. Characterisation of anastomosis groups (AGs) was performed using morphological characteristics and sequence analysis of the internal transcribed spacer of ribosomal DNA ( rDNA-ITS) region. Most isolates collected were Rhizoctonia solani AG-4 HG-I (35.2% of all isolates) and one isolate was AG-2-2 IIIB. The binucleate isolates belonged to AG-R (27.3%), AG-A (21.6%), AG-G (12.5%), AG-V (1.1%) and AG-Fb (1.1%). The pathogenicity of 38 representative isolates collected from each host was tested on seedlings or cuttings grown in a growth chamber. All R. solani AG-4 HG-I isolates, most of the binucleate AG-R, AG-A and AG-G and AG-V were pathogenic and reproduced symptoms identical to that observed in nurseries, while binucleate AG-Fb and R. solani AG-2-2 IIIB isolates were nonpathogenic. This is the first report of the occurrence of Rhizoctonia species on some ornamental plants and the first report of binucleate Rhizoctonia AG-R and AG-V in Europe.     

Identification of <Emphasis Type="Italic">Fusarium</Emphasis> species associated with soybean root rot in Sichuan Province,China

Soybean root rot is a worldwide soil-borne fungal disease threatening soybean production, causing large loss in yield and quality of soybean. Fusarium species are well recognized as the important causal agent of Fusarium root rot, which are often distinct with respect to various factors in different soybean-producing regions around the world. Recently, Fusarium root rot has been frequently reported in Sichuan Province of China, where is unique in its climate and diverse cropping patterns, but it is still unclear about the predominant Fusarium species and their pathogenicity on soybean. In this study, diseased soybean roots were collected from three regions of Sichuan Province during 2014–2015. Based on morphological characteristics and phylogenetic analysis of nucleotide sequences of the ribosomal internal transcribed spacer region and the translation elongation factor 1-α gene, 78 isolates of Fusarium were identified as nine distinct species. Pathogenicity tests showed that seven species of Fusarium were able to infect soybean, but differed in pathogenicity. F. oxysporum, F. equiseti and F. graminearum were the most aggressive species to soybean, whereas F. fujikuroi and F. verticillioides were not pathogenic to soybean. There was a strong positive correlation of the pathogenicity of Fusarium species with seedling emergence and fresh root weight. In addition, the diversity of Fusarium species varied among soybean-growing regions. To our knowledge, this report on population and pathogenicity of Fusarium species, in particular, F. graminearum, associated with soybean root rot in Sichuan Province of southwest China, will be helpful to provide effective control strategies for the disease.     

First report of leaf sheath rot of Welsh onion caused by nine taxa of <Emphasis Type="Italic">Rhizoctonia</Emphasis> spp. and characteristics of the pathogens

From 2007 to 2013, a disease of Welsh onion, causing leaf sheath rot and concomitant death of outer leaves was found in 20 fields in Hokkaido, Japan. We obtained 20 Rhizoctonia isolates from diseased tissues and identified them based on the number of nuclei, hyphal fusion reactions, and molecular techniques using specific PCR primers and sequence of the rDNA-ITS region. The 20 isolates consisted of 16 multinucleate and four binucleate isolates. Of the multinucleate isolates, five were found to be so far unknown and designated here as Rhizoctonia solani AG-4 hybrid subgroup between HG-I and HG-II. Others were identified as AG-1 IB (three isolates), AG-2-2 IIIB (two isolates), AG-4 HG-I (two isolates), AG-1 IC (one isolate), AG-2-1 (one isolate), AG-4 HG-II (one isolate) and AG-5 (one isolate). All four binucleate isolates were binucleate Rhizoctonia AG-U. Original symptoms were reproduced on all plants inoculated with these isolates. Thus, we revealed that as many as nine taxa of Rhizoctonia spp. were associated with the disease. This is the first report of leaf sheath rot of Welsh onion caused by Rhizoctonia spp.     

Response of sorghum stalk pathogens to <Emphasis Type="Italic">brown midrib</Emphasis> plants and soluble phenolic extracts from near isogenic lines

Sorghum [Sorghum bicolor (L.) Moench] has drawn attention as potential feedstock for lignocellulosic biofuels production, and reducing lignin is one way to increase conversion efficiency. Little research has been previously conducted to assess the response of reduced lignin sorghum lines to the Fusarium stalk rot pathogens Fusarium verticillioides and Fusarium proliferatum and the charcoal rot pathogen, Macrophomina phaseolina. Loss of function mutations in either the Brown midrib (Bmr) 6 or 12 gene that both encode a monolignol biosynthetic enzyme in the pathway that produces subunits of the lignin polymer, results in reduced lignin content. Near-isogenic bmr6, bmr12, and bmr6 bmr12 lines had previously been developed, which were shown to have significantly reduced lignin content and increased levels of soluble phenolics. In the current study, these lines in two backgrounds were shown to not be more susceptible to F. verticillioides, F. proliferatum and M. phaseolina inoculations, and some bmr lines exhibited increased resistance to F. proliferatum and M. phaseolina, compared to wild-type lines. When the Fusarium stalk rot pathogen, Fusarium thapsinum, was grown on methanol soluble stalk extracts from bmr6 and wild-type plants, it grew significantly faster on medium with bmr6 extract than on wild-type extract or controls. This result suggested that factors other than soluble phenolics from the extract, such as cell wall bound phenolics or inducible defense compounds, contributed to increased resistance observed in bmr6 plants.     

Increased susceptibility of potato to <Emphasis Type="Italic">Rhizoctonia</Emphasis> diseases in <Emphasis Type="Italic">Potato leafroll virus</Emphasis>-infected plants

In Hokkaido potato fields, tubers produced from the plants with leaf curl symptoms caused by potato leaf roll virus (PLRV) were noted to be more densely covered with Rhizoctonia sclerotia. This observation led us to hypothesize that potato infected with PLRV would have an increased susceptibility to Rhizoctonia solani. To test this hypothesis, in a pot experiment, we inoculated PLRV-infected mother tubers with Rhizoctonia. As a result, PLRV-infected plants produced significantly fewer and smaller tubers than virus-free plants did, suggesting that PLRV-infected plants are more susceptible than virus-free plants to R. solani. Virus-free seed tubers should thus be used to reduce Rhizoctonia diseases.     

Seed treatments enhance photosynthesis in maize seedlings by reducing infection with <Emphasis Type="Italic">Fusarium</Emphasis> spp. and consequent disease development in maize

Maize seed that was either treated with the fungicide Cruiser Extreme 250 ® (fludioxonil + azoxystrobin + mefenoxam + thiamethoxam) or not treated was planted at two Iowa locations in 2007. Root, mesocotyl and crown rot severity, incidence of Fusarium spp. colonisation and chlorophyll florescence (CF) were assessed at growth stages V2, V4 and V6, and stalk rot severity at R6. At both locations, seed treatment reduced disease severity and incidence of Fusarium spp. infection at all growth stages assessed. Measurements of CF decreased significantly with increased disease severity and incidence of Fusarium spp. at V2 and V4 at both locations, indicating that seedling disease negatively affected photosynthetic performance. Mesocotyl rot severity at V4 predicted crown rot severity at V6 at both locations, as well as crown rot at V6 and stalk rot at R6 at one location.     

Disease suppressive effects of resistance-inducing agents against red rot of sugarcane

Red rot caused by Colletotrichum falcatum is one of the most devastating fungal diseases of sugarcane in many tropical countries. In this study, the efficacy of various resistance-inducing agents was evaluated against red rot at two growth phases of sugarcane, i.e., the germination and grand growth phases, for four consecutive cropping seasons (2011–12 to 2014–15) under field conditions. Inducer candidates of both synthetic origin (benzothiadiazole [BTH], salicylic acid [SA], potassium silicate [PSi]) and biotic origin (Colletotrichum falcatum [Cf] elicitor and Reynoutria sachalinensis extract) were evaluated for their efficacy on a red rot susceptible sugarcane cultivar CoC 671. Inducer concentrations that showed significant reduction of red rot lesion length in leaf bioassays without exhibiting direct antifungal activity were used in the field trials. Overall, results of the four field trials indicated that application of BTH (125 μM) and Cf elicitor (60 μg glucose equivalent/ml) were most efficient in reducing disease incidence during the germination and establishment phases against soil-borne inoculum and suppressed disease severity in pathogen challenged cane stalks during the grand growth phase. In addition, other treatments also had significant effects on germination and stalk disease severity. Quantification of C. falcatum biomass in resistance inducer-treated canes by quantitative PCR (qPCR) substantiated the disease suppressive effect of BTH and Cf elicitor. Whereas all resistance inducers significantly increased the cane weight, only BTH and PSi significantly increased the juice quantity. Other juice quality parameters were generally not affected by the inducers.     

Antagonistic activity of <Emphasis Type="Italic">Trichoderma</Emphasis> spp. against <Emphasis Type="Italic">Scytalidium lignicola</Emphasis> CMM 1098 and antioxidant enzymatic activity in cassava

Trichoderma spp. are used as antagonists against different pathogens. Despite many possibilities of using Trichoderma as an antagonist, there are gaps in the knowledge of the interaction between Trichoderma, cassava and Scytalidium lignicola. This fungus causes cassava black root rot and is an inhabitant of the soil, so it is difficult to control. Antagonists may contribute to the possible induction of resistance of plants because, when exposed to such pathosystems, plants respond by producing antioxidative enzymes. The test for potential inhibition of growth of S. lignicola CMM 1098 in vitro was performed in potato-dextrose-agar with two Trichoderma strains T. harzianum URM3086 and T. aureoviride URM 5158. We evaluated the effect of the two selected Trichoderma to reduce the severity of cassava black root rot and shoots. Subsequently, the production of enzymes (ascorbate peroxidase, catalase, peroxidase and polyphenol oxidase) was evaluated in cassava plants. All two Trichoderma strains show an inhibition of the growth of S. lignicola CMM 1098. The most efficient was T. harzianum URM 3086, with 80.78% of mycelial growth inhibition. T. aureoviride URM 5158 was considered the best chitinase producer. All treatments were effective in reducing severity, especially treatments using Trichoderma. Cassava plants treated with T. aureoviride URM 5158 had the highest enzyme activity, especially peroxidase and ascorbate peroxidase. Trichoderma harzianum URM3086 and Trichoderma aureoviride URM 5158 were effective in reducing the severity of cassava black root rot caused by S. lignicola CMM 1098.