Disease Of Sugar Beet Research Articles

New natural weed host Raphanus raphanistrum L. (Brassicaceae) for Beet necrotic yellow vein virus and its vector Polymyxa betae Keskin

Rhizomania is an important virus disease of sugar beet (Beta vulgaris) caused by Beet necrotic yellow vein virus (BNYVV). The virus is transmitted to the roots of host plants by the plasmodiophorid Polymyxa betae. During survey studies in September and October 2009, yellow vein banding symptoms were observed on wild radish (Raphanus raphanistrum) plants growing in spinach (Spinacia oleracea) fields with a history of rhizomania in Samsun Province in the Black Sea Region of Turkey. To verify possible alternative hosts for BNYVV and P. betae, R. raphanistrum and spinach plants and soil samples were collected. BNYVV was detected in the leaf samples of field-collected R. raphanistrum using the DAS-ELISA test. This result was confirmed by RT-PCR and the Raphanus isolate was determined to be from the type A strain based on restriction fragment length polymorphism analysis. The presence of P. betae cystosori was not detected in the roots of R. raphanistrum plants using a light microscopy technique, but some objects resembling sporogenic plasmodia of P. betae were observed in the infested root cells. To confirm this result, total RNA was extracted from the roots of these samples and tested by RT-PCR using Polymyxa-specific primers. In contrast to the microscopy method, all samples tested positive for P. betae using RT-PCR. Healthy seeds of R. raphanistrum were planted in plastic pots containing soil from the same fields infested with BNYVV and the seedlings showed similar symptoms to those growing in natural conditions. To our knowledge this is the first report of a BNYVV infection of R. raphanistrum under natural conditions.

Improvement of Lesion Phenotyping in Cercospora beticola-Sugar Beet Interaction by Hyperspectral Imaging.

Cercospora leaf spot (CLS) caused by Cercospora beticola is the most destructive leaf disease of sugar beet and may cause high losses in yield and quality. Breeding and cultivation of disease-resistant varieties is an important strategy to control this economically relevant plant disease. Reliable and robust resistance parameters are required to promote breeding progress. CLS lesions on five different sugar beet genotypes incubated under controlled conditions were analyzed for phenotypic differences related to field resistance to C. beticola. Lesions of CLS were rated by classical quantitative and qualitative methods in combination with noninvasive hyperspectral imaging. Calculating the ratio of lesion center to lesion margin, four CLS phenotypes were identified that vary in size and spatial composition. Lesions could be differentiated into subareas based on their spectral characteristics in the range of 400 to 900 nm. Sugar beet genotypes with lower disease severity typically had lesions with smaller centers compared with highly susceptible genotypes. Accordingly, the number of conidia per diseased leaf area on resistant plants was lower. The assessment of lesion phenotypes by hyperspectral imaging with regard to sporulation may be an appropriate method to identify subtle differences in disease resistance. The spectral and spatial analysis of the lesions has the potential to improve the screening process in breeding for CLS resistance.

Diversity and Activity of Lysobacter Species from Disease Suppressive Soils.

The genus Lysobacter includes several species that produce a range of extracellular enzymes and other metabolites with activity against bacteria, fungi, oomycetes, and nematodes. Lysobacter species were found to be more abundant in soil suppressive against the fungal root pathogen Rhizoctonia solani, but their actual role in disease suppression is still unclear. Here, the antifungal and plant growth-promoting activities of 18 Lysobacter strains, including 11 strains from Rhizoctonia-suppressive soils, were studied both in vitro and in vivo. Based on 16S rRNA sequencing, the Lysobacter strains from the Rhizoctonia-suppressive soil belonged to the four species Lysobacter antibioticus, Lysobacter capsici, Lysobacter enzymogenes, and Lysobacter gummosus. Most strains showed strong in vitro activity against R. solani and several other pathogens, including Pythium ultimum, Aspergillus niger, Fusarium oxysporum, and Xanthomonas campestris. When the Lysobacter strains were introduced into soil, however, no significant and consistent suppression of R. solani damping-off disease of sugar beet and cauliflower was observed. Subsequent bioassays further revealed that none of the Lysobacter strains was able to promote growth of sugar beet, cauliflower, onion, and Arabidopsis thaliana, either directly or via volatile compounds. The lack of in vivo activity is most likely attributed to poor colonization of the rhizosphere by the introduced Lysobacter strains. In conclusion, our results demonstrated that Lysobacter species have strong antagonistic activities against a range of pathogens, making them an important source for putative new enzymes and antimicrobial compounds. However, their potential role in R. solani disease suppressive soil could not be confirmed. In-depth omics'–based analyses will be needed to shed more light on the potential contribution of Lysobacter species to the collective activities of microbial consortia in disease suppressive soils.

Mid-Infrared (MIR) and Near-Infrared (NIR) Detection of Rhizoctonia solani AG 2-2 IIIB on Barley-Based Artificial Inoculum.

The amount of Rhizoctonia solani in the soil and how much must be present to cause disease in sugar beet (Beta vulgaris L.) is relatively unknown. This is mostly because of the usually low inoculum densities found naturally in soil and the low sensitivity of traditional serial dilution assays. We investigated the usefulness of Fourier transform mid-infrared (MIR) and near-infrared (NIR) spectroscopic properties in identifying the artificial colonization of barley grains with R. solani AG 2-2 IIIB and in detecting R. solani populations in plant tissues and inoculants. The objectives of this study were to compare the ability of traditional plating assays to NIR and MIR spectroscopies to identify R. solani in different-size fractions of colonized ground barley (used as an artificial inoculum) and to differentiate colonized from non-inoculated barley. We found that NIR and MIR spectroscopies were sensitive in resolving different barley particle sizes, with particles that were <0.25 and 0.25-0.5 mm having different spectral properties than coarser particles. Moreover, we found that barley colonized with R. solani had different MIR spectral properties than the non-inoculated samples for the larger fractions (0.5-1.0, 1.0-2.0, and >2.0 mm) of the ground barley. This colonization was confirmed using traditional plating assays. Comparisons with the spectra from pure fungal cultures and non-inoculated barley suggest that the MIR spectrum of colonized barley is different because of the consumption of C substrates by the fungus rather than because of the presence of fungal bands in the spectra of the colonized samples. We found that MIR was better than NIR spectroscopy in differentiating the colonized from the control samples.

Transcriptome Analysis of Beta macrocarpa and Identification of Differentially Expressed Transcripts in Response to Beet Necrotic Yellow Vein Virus Infection.

BackgroundRhizomania is one of the most devastating diseases of sugar beet. It is caused by Beet necrotic yellow vein virus (BNYVV) transmitted by the obligate root-infecting parasite Polymyxa betae. Beta macrocarpa, a wild beet species widely used as a systemic host in the laboratory, can be rub-inoculated with BNYVV to avoid variation associated with the presence of the vector P. betae. To better understand disease and resistance between beets and BNYVV, we characterized the transcriptome of B. macrocarpa and analyzed global gene expression of B. macrocarpa in response to BNYVV infection using the Illumina sequencing platform.ResultsThe overall de novo assembly of cDNA sequence data generated 75,917 unigenes, with an average length of 1054 bp. Based on a BLASTX search (E-value ≤ 10−5) against the non-redundant (NR, NCBI) protein, Swiss-Prot, the Gene Ontology (GO), Clusters of Orthologous Groups of proteins (COG) and Kyoto Encyclopedia of Genes and Genomes (KEGG) databases, there were 39,372 unigenes annotated. In addition, 4,834 simple sequence repeats (SSRs) were also predicted, which could serve as a foundation for various applications in beet breeding. Furthermore, comparative analysis of the two transcriptomes revealed that 261 genes were differentially expressed in infected compared to control plants, including 128 up- and 133 down-regulated genes. GO analysis showed that the changes in the differently expressed genes were mainly enrichment in response to biotic stimulus and primary metabolic process.ConclusionOur results not only provide a rich genomic resource for beets, but also benefit research into the molecular mechanisms of beet- BNYV Vinteraction.

Evaluation of Rhizoctonia zeae as a potential biological control option for fungal root diseases of sugar beet

AbstractSeveral common root diseases routinely damage sugar beet in Nebraska and other production areas of the Central High Plains, and it is becoming more common to find fields infested simultaneously with multiple pathogens. Owing to the shortage of available fungicides for economic management of soilborne diseases, alternative techniques such as biological control are increasingly being sought for disease management. Over the last several years, unidentified, sterile fungi have been isolated in conjunction with pathogens from infected sugar beet roots and seedlings. At least two promising isolates have been identified from in vitro assays that inhibit the radial growth of multiple sugar beet root pathogens, including Rhizoctonia solani, Fusarium oxysporum f. sp. betae, Phoma betae and Pythium aphanidermatum. Based on morphological and molecular characterisation, two isolates, ‘Hall’ and ‘R47’, were putatively identified as Rhizoctonia zeae. In vitro pathogenicity testing indicated that these isolates were not pathogens of sugar beet. Both isolates were compared with the well‐established biological control fungus Laetisaria arvalis and tested as potential treatments in a field naturally infested with multiple sugar beet root diseases. Data indicated that these fungi provided some level of protection against a complex of soilborne diseases and suggest that these isolates could have a potential fit in an integrative management strategy for several sugar beet root diseases.

Stemphylium sp., the cause of yellow leaf spot disease in sugar beet (Beta vulgaris L.) in the Netherlands

During the summer of 2007, a distinctive type of yellow leaf spot was observed for the first time in sugar beet (Beta vulgaris L.) in the Netherlands. In the following years a rapid spread over all regions of the Netherlands was reported. The infestation appears in June-August on the leaves of sugar beet and starts with small, irregular, yellow spots. Subsequently the yellow spots become necrotic from the centre of the lesion outward, with the tissue becoming brown (or brownish). The spots spread over the leaves and infest all the leaves of the plant. Due to the loss of leaves the size of the canopy declines and yield loss occurs. Research was conducted to identify the causal agent. Climate room trials with isolates obtained from infested sugar beet leaves showed that Stemphylium sp. was able to infest leaves of healthy growing sugar beet plants with brown spots, similar to the necrotic spots seen in the field. From the leaf spots in the climate room trials, Stemphylium sp. was re-isolated, according to Koch’s postulates. Thus, it was confirmed that this Stemphylium sp. is a primary pathogen for sugar beet. In field trials of fungicide efficacy a sugar yield loss of up to 42 % (a financial yield loss of 51 %) was found. Field trials show that it is hard to control this Stemphylium sp. with the fungicides registered for sugar beet in the Netherlands and efficacy of control of Stemphylium sp. differs between fungicides with active ingredients belonging to the same chemical class. In addition to sugar beet, potato (Solanum tuberosum L.), white mustard (Sinapsis alba L.), red beet (Beta vulgaris L.), spinach (Spinacia oleracea L.) and fat hen (Chenopodium album L.) were identified as hosts in an assay of plants grown and inoculated in climate rooms.

First Report of Beet necrotic yellow vein virus on Red Table Beet in Brazil.

Beet necrotic yellow vein virus (BNYVV) is an economically important pathogen of sugar beet (Beta vulgaris var. saccharifera) in several European, and Asian countries and in the United States (3). The virus is transmitted by the soil-inhabiting plasmodiophorid Polymyxa betae and causes the rhizomania disease of sugar beet. In November 2012, plants of B. vulgaris subsp. vulgaris cv. Boro (red table beet) exhibiting mainly severe characteristic root symptom of rhizomania were found in a commercial field located in the municipality of São José do Rio Pardo, State of São Paulo, Brazil. No characteristic virus-inducing foliar symptom was observed on diseased plants. The incidence of diseased plants was around 70% in the two visited crops. As the hairy root symptom is indicative of infection by BNYVV, the present study aimed to detect and identify this virus associated with the diseased plants. Preliminary leaf dip analysis by transmission electron microscopy revealed the presence of very few benyvirus-like particles. Total RNA was extracted from roots of three symptomatic plants and one asymptomatic plant according to Toth et al. (3). One-step reverse-transcription-polymerase chain reaction (RT-PCR) was performed as described by Morris et al. (2) with primers that amplify part of the coat protein gene at RNA2. The initial assumption that the hairy root symptom was associated with BNYVV infection was confirmed by the amplification of a fragment of ~500 bp from all three symptomatic samples. No amplicon was obtained from the asymptomatic control plant. Amplicons were directly sequenced, and the consensus nucleotide and deduced amino acid sequences showed 100% identity. The nucleotide sequence for one amplicon (Accession No. KM433683) was compared with other sequences deposited in GenBank. The nucleotide (468 nt) and deduced amino acid (156 aa) sequences shared 93 to 100 and 97 to 99% identity, respectively with the corresponding nucleotide and amino acid sequences for other isolates of type A of BNYVV. The virus was transmitted to three of 10 red table beet plants inoculated with contaminated soil, and infection was confirmed by nested RT-PCR, as described by Morris et al. (1), and nucleotide sequencing. This is the first report on the occurrence of BNYVV in Brazil, which certainly will affect the yield of red table beet in the producing region. Therefore, mapping of the occurrence of BNYVV in red table beet-producing areas in Brazil for containment of the spread of the virus is urgent. In the meantime, precautions should be taken to control the movement of contaminated soil and beet roots, carrots, or any vegetable grown on infested land that might introduce the virus to still virus-free regions.

Przyczyny odporności izolatów Cercospora beticola (chwościk buraka) na strobiluryny w Wielkopolsce

Leaf spot caused by Cercospora beticola is one of the most serious diseases of sugar beet. Various fungicide groups are used to control this disease and among them also strobilurin based products. The aim of the study was to analyze the causes of strobilurin resistance of C. beticola isolates collected in Wielkopolska region. The strobilurin inhibits mitochondrial respiratory processes and mutations occurring in the cytochrome b gene (cytb) are the most important reason of C. beticola strobilurin resistance. An increasing activity of an alternative oxidase (AOX) also plays an important role in resistance occurring in C. beticola isolates. The sequence of cytochrome b gene of C. beticola isolates were analyzed. Mutations G143 and F129L – the main determinants of strobilurin resistance were no found. However, an increased strobilurin resistance level of the isolates is caused by higher activity of alternative oxidase, which replaces the function of cytochrome b in the respiratory pathway. Chwościk wywoływany przez Cercospora beticola należy do najpoważniejszych chorób buraka cukrowego. Do ochrony upraw buraka wykorzystywane są fungicydy z różnych grup chemicznych, także strobiluryny, które hamują procesy oddechowe zachodzące w mitochondriach. Mutacje pojawiające się w genie cytochromu b (cytb) są najważniejszą przyczyną nabywania odporności na strobiluryny przez izolaty C. beticola. Wśród pozostałych przyczyn odporności wymienia się wzrost aktywności alternatywnej oksydazy. Celem badań była analiza przyczyn podwyższonej odporności na piraklostrobinę izolatów C. beticola zbieranych na terenie Wielkopolski. W badanym fragmencie genu cytochromu b izolatów C. beticola nie stwierdzono mutacji G143A oraz F129L, które wymieniane są wśród podstawowych czynników warunkujących odporność na strobiluryny. Zwiększona odporność badanych izolatów spowodowana jest wzmożoną aktywnością alternatywnej oksydazy, zastępującej funkcję cytochromu b w szlaku oddechowym.

Phytoplasmas associated with yellow wilt disease of sugar beet in Chile

Due to the sporadic occurrence of yellow wilt of sugar beet disease throughout the last three years, a survey was carried out in two regions where the Chilean sugar beet production is concentrated. The tuf and 16S rRNA genes were used for phytoplasma detection and identification. Virtual restriction fragment length polymorphism analyses, cloning, and sequencing identified the presence of a phytoplasma belonging to the ribosomal subgroup 16SrIII-J.

Rhizoctonia cerealis anastomosis group GAG-1, the common pathogen of wheat, barley and sugar beet

Isuluies of &lt;i&gt;Rhizoctonia cerealis&lt;/i&gt; anastomosis group GAG-1 were obtained from sharp eyespot lesions on wheat and on barley culms and from diseased sugar beet seedlings. Isolates of &lt;i&gt;R. cerealis&lt;/i&gt; were collected from a fields with crop rotation experiments: sugar beet-spring wheat-winter barley. In pathogenicity tests isolates of &lt;i&gt;R. cerealis&lt;/i&gt; from sugar beet seedlings and from sharp eyespot lesions on wheat and barley were pathogenic to these crops. Isolates of &lt;i&gt;R. cerealis&lt;/i&gt; from sharp eyespot lesions on wheat and barley caused severe damping-ofTof sugar beet. Isolates of &lt;i&gt;R. cerealis&lt;/i&gt; from sugar beet seedlings also caused symptoms of sharp eyespot on wheat and barley. None of the wheat and barley isolates of &lt;i&gt;R. cerealis&lt;/i&gt; tested caused root-rot on wheat or barley seedlings. Isolates of &lt;i&gt;R. cerealis&lt;/i&gt; obtained from diseased plants of wheat, barley and sugar beet were similar in morphology of cultures and anastomosed with GAG-1 tester isolate. The relatinoship between anastomosis. colony characters, growth rate, hyphal diameter and pathogenicity of AG-4. AG-2-2 and AG-5 isolates obtained together with &lt;i&gt;R. cerealis&lt;/i&gt; from diseased plants were also investigated.

Biological control of Polymyxa betae, fungal vector of rhizomania disease of sugar beets in greenhouse conditions

Abstract: Rhizomania is one of the most important diseases of sugar beet around the world – including in Iran. The disease causes a severe decrease in sugar yield and is a limiting factor in sugar beet cultivation. Control of the disease is very difficult due to the long-term survival of its fungal vector (Polymyxa betae) in the soil. In this study, we investigated the effects of antagonistic fungal isolates on the population of the resting structure (cystosorus) of P. betae, under greenhouse conditions. Antagonistic fungi, including Trichoderma harzianum and Talaromyces flavus, were isolated from soil samples collected from sugar beet infested fields in the Semnan Province of Iran. In the next step, their inocula were prepared through reproduction on rice bran. For evaluation of the efficacy of antagonists in greenhouse conditions, a split plot trial was conducted and performed. The main factor was three different methods of application of T. flavus as the soil treatment, seed treatment, and a combination of both methods. The sub-factor was the use of different fungal isolates. To determine the cystosorus population of the fungal vector, seedling roots in all treatments were stained with lactic acid and fuchsine (lactofushine), 60 days after sowing. The number of cystosorus in one gram of root was counted using a light microscope and hemocytometer. At the end of the study, average root weight in different treatments was also measured to select and introduce the best treatments in regard to their effects on root weight. According to the results, the number of cystosorus in 1 g of root was different in various treatments and those treatments containing TF-Su-M-1, TF-Su-M-2, TH-Su-M-1, and TH-Su-M-2 used as a soil application method were more effective in the reduction of the cystosorus population and root weight increase. Among the above-mentioned treatments, maximum reduction of cystosori population and the increase in root weight were observed in TH-Su-M-1 and TF-Su-M-2 through the soil application method.

Characterization of Fusarium secorum, a new species causing Fusarium yellowing decline of sugar beet in north central USA

This study characterized a novel sugar beet (Beta vulgaris L.) pathogen from the Red River Valley in north central USA, which was formally named Fusarium secorum. Molecular phylogenetic analyses of three loci (translation elongation factor1α, calmodulin, mitochondrial small subunit) and phenotypic data strongly supported the inclusion of F. secorum in the Fusarium fujikuroi species complex (FFSC). Phylogenetic analyses identified F. secorum as a sister taxon of F. acutatum and a member of the African subclade of the FFSC. Fusarium secorum produced circinate hyphae sometimes bearing microconidia and abundant corkscrew-shaped hyphae in culture. To assess mycotoxin production potential, 45 typical secondary metabolites were tested in F. secorum rice cultures, but only beauvericin was produced in detectable amounts by each isolate. Results of pathogenicity experiments revealed that F. secorum isolates are able to induce half- and full-leaf yellowing foliar symptoms and vascular necrosis in roots and petioles of sugar beet. Inoculation with F. acutatum did not result in any disease symptoms. The sugar beet disease caused by F. secorum is named Fusarium yellowing decline. Since Fusarium yellowing decline incidence has been increasing in the Red River Valley, disease management options are discussed.

Growth analysis of rhizomania infected and healthy sugar beet

Viral disease of rhizomania is one of the most important diseases of sugar beet all over the world. The disease significantly has reduced the yield and quality of sugar beet, and has imposed high economic loss to farmers. Long-term breeding programs to introduce tolerant cultivars are the only chance of avoiding further yield losses. This study tried to measure and analyze the growth of shoots and roots of rhizomania-tolerant and -susceptible sugar beet with the aim of providing information for modeling of the rhizomania effects on the growth of sugar beet. Growth indices were used for analyzing, quantification, and time-course of sugar beet growth under infested and non-infested soils conditions. A 2-year experiment was conducted using four sugar beet cultivars in 2010 and 2011 in Mashhad, Iran. The results of this study showed that under infested soils, root dry matter and leaf area index of the susceptible cultivars in comparison to tolerant cultivars were lower by 57 and 24%, respectively. In addition, crop growth rate and net assimilation rate of susceptible cultivars were affected by rhizomania and were lower than in tolerant cultivars. On non-infested soil, the difference between dry matter and growth indices of susceptible and tolerant sugar beet cultivars was not significant. Rhizomania decreased green area and photosynthesis capacity and led to lower growth rate and dry matter production. Our study quantified the growth of rhizomania-infested sugar beet plants in comparison with non-infested plants and provided information to be used for modeling of the rhizomania effects on the growth of sugar beet.

Beet curly top: America's first serious disease of sugar beets

Beet curly top: America's first serious disease of sugar beets

Photosynthetic Efficiency Promotion of Sugar Beet by Formulation of Trichoderma and Control of Some Sugar Beet Disease Seedling

Four isolates of Fusarium sambucinum (Fuckel ) (isolates 1,2,3,4)and four isolates of Fusarium solani ( Mart.) Sacc . (isolates5, 6, 7, 8)were isolated from different localities of sugar beet in Assiut Government .The tested isolated were pathogenic to sugar beet oskarpoly variety causing damping off and root rot. Isolates 2 and5 had the highest pathogen city to sugar beet isolates 3 and 8 had the lowest pathogen city pathogen city. Trichoderma viride have been used for their potential antagonism for controlling Fusarium sp damping off and root rot disease of sugar beet. In vitro studies showed that the culture filtrate of Trichoderma viride significantly decreased the growth of the tested isolates of both Fusarium sambucinum and Fusarium solani Treating the soil with formulation of Trichoderma viride before planting decreased damping off and root rot of sugar beet compared with untreated and untreated soil with formulation of Trichoderma viride under greenhouse conditions during growing seasons 2010and 2011.Chlorophyll a chlorophyll b and total chlorophyll carotenoids decreased when treatment the infested soil with either Fusarium sambucinum or Fusarium solani compared with untreated and untreated soil with formulation of Trichoderma viride.

Odporność na fungicydy izolatów Cercospora beticola pochodzących z terenu Wielkopolski

Leaf spot caused by Cercospora beticola is one of the most serious disease of sugar beet. For the disease control benzimidazole, triazole, strobilurine, morpholine and pyrimidine fungicides have been used. The aim of the study was to evaluate the resistance level of C. beticola isolates collected in Wielkopolska region to selected fungicides. Most of the tested isolates were resistant to carbendazim and thiophanate-methyl, and only a few of the isolates were sensitive to benzimidazoles. Most of the tested isolates were sensitive to the other tested fungicides. However, several isolates resistant to triazoles and piraclostrobin were identified. Chwościk wywoływany przez Cercospora beticola należy do najważniejszych chorób buraka cukrowego. Do ochrony upraw buraka wykorzystywane są fungicydy zawierające związki z grup benzimidazoli, triazoli, strobiluryn, morfolin i pirymidyn. Celem badań była ocena odporności izolatów C. beticola zbieranych na terenie Wielkopolski na wybrane fungicydy. Większość badanych izolatów C. beticola była odporna na karbendazym i tiofanat metylu, jedynie kilkanaście spośród badanych izolatów było wrażliwych na benzimidazole. Większość badanych izolatów była wrażliwa na pozostałe z badanych fungicydów. Wśród badanych izolatów zidentyfikowane zostały także szczepy odporne na triazole i piraklostrobinę.

Progeny derived from Thanatephorus cucumeris (Rhizoctonia solani) AG-2-2 IV isolates on sugar beet foliage show more clonal diversity in somatic compatibility grouping than those from roots and petioles

Twenty-nine isolates of Thanatephorus cucumeris (Rhizoctonia solani) AG-2-2 IV were collected from the roots, petioles, and leaves of diseased sugar beets in Hokkaido, Japan. We examined the genetic variation of the field isolates using somatic compatibility grouping of progeny (cultured isolates derived from induced basidiospores) based on analysis of hyphal anastomosis reactions (i.e., hyphal perfect fusion) and inter-simple sequence repeats (ISSRs). The number of somatic compatibility groups (SCGs) of single basidiospore isolates was strongly correlated with the host plant tissue from which the parental isolates were obtained. Parental isolates from roots and petioles tended to be genetically heterogeneous and generated plural SCGs, whereas isolates (except for two non-self-anastomosing isolates) from leaves tended to be homogeneous and generated a single SCG. Heterogeneous sibling basidiospore isolates yielded homogeneous progeny within a few generations. These findings were supported by the results of ISSR analysis, which showed that the homogeneous isolates generated progeny with the same genotype, whereas heterogeneous isolates generated progeny with different genotypes. However, like SCGs, ISSR genotypes of heterogeneous progeny tended to be homogeneous within two or three generations. Additionally, we examined clonal diversity during the basidiospore infection process over a 2-year period. A heterogeneous isolate generated a large number of progeny SCGs, thereby increasing clonal diversity. In contrast, progeny SCGs were almost all the same in a homogeneous isolate plot with a few exceptions. These results indicate that infection of T. cucumeris basidiospores play a role in the clonal diversity of AG-2-2 IV isolates, as indicated by progeny SCGs in the field.

First Evidence of a Binucleate Rhizoctonia as the Causal Agent of Dry Rot Canker of Sugar Beet in Nebraska.

Sugar beet (Beta vulgaris L.) is the primary source of domestic sucrose in the United States. In 2011, a sugar beet field in Morrill County, NE, was noted with wilting and yellowing symptoms suggestive of Rhizoctonia root and crown rot (RRCR), an important disease of sugar beet primarily caused by Rhizoctonia solani anastomosis group 2-2 (4). While the foliar symptoms were consistent with RRCR, the symptoms on the root were not. Root symptoms consisted of localized, dry, sunken lesions covering brown spongy tissue penetrating deeply into taproots. The surface tissues of the cankers distinctively produced a series of concentric circles. These root symptoms are inconsistent with RRCR, but are suggestive of a rarely occurring disease known as dry rot canker (DRC). DRC was first identified from Utah in 1921 (1), and assumed at the time to be caused by an uncharacterized strain of R. solani. It has since been sporadically but empirically noted from most western sugar beet growing states (4), but little is known about the pathogen or disease due to its infrequent appearances. To investigate the etiology of this disease, necrotic lesion borders were excised from diseased taproots, surface disinfested in 1% (v/v) sodium hypochlorite for 90 s, rinsed with distilled water for 90 s, and after drying on sterile tissue paper, placed on half-strength potato dextrose agar (½PDA) and incubated at 25 to 27°C. After 24 to 36 h, Rhizoctonia-like fungal growth was readily observed emerging from tissue pieces. Resulting colonies were tan to light brown. The ITS region of the rDNA was amplified from 4 isolates obtained from 4 distinct lesions and roots using the ITS1 and ITS4 primers (3) with standard PCR conditions, and sequenced (GenBank KC842197 to KC842200). The ITS regions were 100% identical between the 4 isolates and 96% (E-value = 0.0) identical to binucleate Rhizoctonia and Ceratobasidium sp. AG-F (e.g., JF519832, FR734295, JF705217). Hyphal cells were observed to be binucleate after staining 48-h-old cultures with lactophenol blue. Therefore, these isolates were identified to be a binucleate Rhizoctonia group AG-F based on morphological and molecular characteristics. Although distinct from DRC, a similar phenomenon has been recently reported from China implicating binucleate Rhizoctonia species with seedling disease in sugar beets (2). To determine pathogenicity of DRC isolates, 1- and 2-month-old sugar beet plants grown in 10 cm pots (5 plants per pot with 4 replications per isolate) were inoculated with all 4 isolates by placing 3 mycelial plugs (8 mm diameter) taken from the leading edge of ½PDA plates onto the soil surface of each pot. PDA plugs were utilized as controls. After ~3 weeks, root lesions resembling DRC were observed and isolates were recovered and identified from diseased plants as described above. No symptoms developed on control plants. To our knowledge, this is the first formally confirmed report of DRC on sugar beets in more than 75 years from the Western Hemisphere. The original investigator suspected that the isolates he found inducing this disease were different from typical R. solani isolates based on different symptoms (1). Our results, based on different symptoms but also with distinct molecular, biological, and pathogenicity traits, validate those suspicions while also fulfilling Koch's postulates with binucleate Rhizoctonia AG-F pathogenic to sugar beet that is distinct from the more common R. solani.

A New Integrated Pest Management (IPM) Model for Cercospora Leaf Spot of Sugar Beets in the Po Valley, Italy

Cercospora leaf spot (CLS), caused by the fungus Cercospora beticola, is the most economically important foliar disease of sugar beets in Italy. It can be controlled with the integrated use of resistant varieties, crop practices and foliar fungicides. Environmental conditions strongly influence the activity of C. beticola in the field; they can be used to guide fungicide applications once the relationships are understood. To assist growers in application of foliar fungicides for CLS control, a predictive model, developed at the University of Minnesota and North Dakota State Universities, was evaluated under Italian conditions. The model was designed to predict the time when the infection by C. beticola was initiated based on hourly temperature and relative humidity data. CLS control is currently based on treatments scheduled using a “calendar” programme. This system recommends to start fungicide applications on a fixed date and continue regularly every 18–20 days. Three years of field trial evaluation of the CLS prediction model at several experimental sites, compared with the calendar programme, has resulted in a savings of 1.5 fungicide treatments (corresponding to 130 €/ha) without a significant loss of yield. To control CLS, multiple applications of the same fungicide during a growing season are unfortunately common. This practice provides the target fungus a suitable condition to evolve resistance. Sensitivity assays of C. beticola to DMI and QoI fungicides were carried out on CLS isolates collected in 2009 and 2010 in Northern Italy by the University of Bologna and North Dakota State University, respectively. CLS isolates were tested sensitivity to tetraconazole, difenoconazole, pyraclostrobin and trifloxystrobin using radial growth and spore germination assays. All samples collected in 2009 showed EC50 values for QoI ranging from 0.0008 to 0.2195 μg/ml. The percentage of isolates collected in 2010 with EC50 values >1 for tetraconazole was 44 %, for difenoconazole 84 %, for pyraclostrobin 27 % and for trifloxystrobin 34 %. For isolates with EC50 values >1 μg/ml, the range of EC50 values (μg/ml) for tetraconazole was 3.4–70.0, for difenoconazole 2.0–69.5, for pyraclostrobin 1.5–43.6, and for trifloxystrobin 3.8–77.1, respectively.