Colletotrichum Coccodes Research Articles

Validation of Reliable Reference Genes for RT-qPCR Studies of Target Gene Expression in Colletotrichum camelliae During Spore Germination and Mycelial Growth and Interaction With Host Plants.

The tea plant [Camellia sinensis (L.) O. Kuntze] is one of the most important leaf crops, and it is widely used for the production of non-alcoholic beverages worldwide. Tea also has a long history of medicinal use. Colletotrichum camelliae Massee is one of the dominant fungal pathogens that infects tea leaves and causes severe tea anthracnose disease. To analyze the molecular biology of C. camelliae, the quantification of pathogen gene expression by the RT-qPCR method is necessary. Reliable RT-qPCR results require the use of stable reference genes for data normalization. However, suitable reference genes have not been reported in C. camelliae thus far. In this study, 12 candidate genes (i.e., CcSPAC6B12.04c, CcWDR83, Cchp11, Ccnew1, CcHplo, CcRNF5, CcHpcob, CcfaeB-2, CcYER010C, CcRNM1, CcUP18, and CcACT) were isolated from C. camelliae and assessed as potential reference genes. The expression stability of these genes in C. camelliae during spore germination and mycelial growth and interaction with host plants was first evaluated using several statistical algorithms, such as geNorm, NormFinder, and Bestkeeper. A web-based analysis program, Refinder, was then used to find the most suitable reference genes. Our results indicated that Cenew1, CcHplo, and CcSPAC6B12.04c were the most stable reference genes in C. camelliae under all conditions. Our work provided the most suitable reference genes for future studies performed to quantify the target gene expression levels of C. camelliae.

Synthesis and mode of action studies of novel {2-(3-R-1H-1,2,4-triazol-5-yl)phenyl}amines to combat pathogenic fungi.

Due to their high specificity and efficacy, triazoles have become versatile antifungals to treat fungal infections in human healthcare and to control phytopathogenic fungi in agriculture. However, azole resistance is an emerging problem affecting human health as well as food security. Here we describe the synthesis of 10 novel {2-(3-R-1H-1,2,4-triazol-5-yl)phenyl}amines. Their structure was ascertained by liquid chromatography-mass spectrometry, 1 H and 13 C NMR, and elemental analysis data. Applying an in vitro growth assay, these triazoles show moderate to significant antifungal activity against the opportunistic pathogen Aspergillus niger, 12 fungi (Fusarium oxysporum, Fusarium fujikuroi, Colletotrichum higginsianum, Gaeumannomyces graminis, Colletotrichum coccodes, Claviceps purpurea, Alternaria alternata, Mucor indicus, Fusarium graminearum, Verticillium lecanii, Botrytis cinerea, Penicillium digitatum) and three oomycetes (Phytophtora infestans GL-1, P. infestans 4/91; R+ and 4/91; R-) in the concentration range from 1 to 50 µg/ml (0.003-2.1 μM). Frontier molecular orbital energies were determined to predict their genotoxic potential. Molecular docking calculations taking into account six common fungal enzymes point to 14α-demethylase (CYP51) and N-myristoyltransferase as the most probable fungal targets. With respect to effectiveness, structure-activity calculations revealed the strong enhancing impact of adamantyl residues. The shown nonmutagenicity in the Salmonella reverse-mutagenicity assay and no violations of drug-likeness parameters suggest the good bioavailability and attractive ecotoxicological profile of the studied triazoles.

Optimization of Solid Fermentation Conditions of Bacillus subtilis 262XY2x and Its Control Effect on Colletotrichum coccodes

Optimization of Solid Fermentation Conditions of Bacillus subtilis 262XY2x and Its Control Effect on Colletotrichum coccodes

First Report of Black Dot Root Rot, Caused by Colletotrichum coccodes, on Tomato in Kentucky High Tunnels

As the most profitable vegetable crop grown in Kentucky (KY) high tunnels, tomato (Solanum lycopersicum L.) is often produced without crop rotation. In November 2016, ‘Mountain Fresh Plus’ tomato samples were received by the University of Kentucky Plant Disease Diagnostic Lab from Nelson County, KY. The high tunnel had an extended history of tomato production, and 100% of plants were affected. Common late-season symptoms of plant dieback and fruit decay were reported. Brown discoloration with dry, cracked cankers and microsclerotia were observed on primary and secondary sample roots, respectively. Symptomatic root sections (4 to 6 mm) were sterilized with 1% NaOCl and then placed on acidified potato dextrose agar (aPDA). Hyphal tips of the cultured fungus were aseptically transferred to fresh aPDA, and then mycelium was aseptically transferred to potato dextrose broth. DNA was extracted from 3-day-old broth culture (Li et al. 2008). Polymerase chain reaction (PCR) amplicons using ITS1/ITS4 (White et al. 1990) were generated, using protocols modified from Gardes and Bruns (1993) and Matsuda et al. (2005). Modifications included 35 total cycles, 30 s annealing step, and final extension for 10 min. Additional PCR products were amplified using partial actin (ACT; Prihastuti et al. 2009) and glyceraldehyde-3-phosphate dehydrogenase primers (GPDH; Berbee et al. 1999). ExoSap-IT (Affymetrix, Cleveland, OH) was used for PCR product cleanup, and then bidirectional Sanger sequence (Eurofin Genomics, Louisville, KY) was generated for each housekeeping gene. The internal transcribed spacer sequence was submitted to GenBank (MG544880) and matched 100% on identity and coverage with multiple Colletotrichum coccodes accessions, including KY364640. ACT and GPDH sequences were used in phylogenetic trees, which further supported identification as C. coccodes. The original isolate was grown on quarter-strength PDA at 23°C. Microsclerotia developed after 7 days within sparse, white mycelium. Conidia were dislodged from 4-week-old plates flooded with sterile deionized water using a sterile micropestle and then filtered through two layers of cheesecloth. Conidia were 18 to 22 μm long and 3 to 5 μm wide and were cylindrical, aseptate, and hyaline, with cylindrical conidiophores. Acervuli on tomato roots were circular with approximately 100-μm-long setae. Two-week-old ‘Sunstart’ tomatoes were used for Koch’s postulates. Eight plants were each drenched with 25 ml of 5 × 10⁵ conidia/ml (Vrisman et al. 2017). Eight plants drenched with 25 ml of sterile deionized water were noninoculated controls. After 11 weeks, root discoloration was observed, with black acervuli with setae visible on 50× magnified root surfaces; control plants were asymptomatic and lacked fungal growth. Symptomatic root cuttings were submerged in 0.6% NaOCl for 30 s and then plated on quarter-strength PDA. Mycelium was macroscopically visible after 1 week at ambient temperature. Microscopic examination indicated the fungus was morphologically indistinguishable from mycelium, conidiophores, and conidia of the original isolate, confirming Koch’s postulates. This experiment was repeated with the same results. Although C. coccodes and Pyrenochaeta lycopersici were recently reported to cause brown root rot complex in high tunnel tomato (Vrisman et al. 2017), P. lycopersici was not found here. This first report of black dot root rot in intensive high tunnel tomato production in KY reiterates the need for aggressive sanitation prior to disease development, because severe pathogen pressure in soil may necessitate relocation of the high tunnel.

Involvement of Colletotrichum coccodes causing atypical symptoms of potato tubers in Turkey

In 2015 and 2017, potato storages were surveyed for the prevalence of atypical potato tuber rots in Nevsehir and Isparta Provinces of Turkey. About 4–5 months after harvesting, 80% of the potatoes cv. Melody, that were stored at 4–5 °C and 65–75% relative humidity, were affected by the disease. The symptoms of the disease were similar to gangrene caused by Boeremia exigua var. foveata including superficial, dark lesions or dark brown, sunken lesions that have a sharp border with healthy tissue on tubers. A fungus was consistently isolated from necrotic tuber tissues. The pathogen was identified as Colletotrichum coccodes (Wallr.) Hughes based on morphological characteristics and the analysis of sequence of the internal transcribed spacer region of the rDNA. Pathogenicity was tested by tuber inoculation with mycelial agar discs. After 4–6 weeks, irregular and dark brown sunken lesions developed on potato tubers, while control tubers remained symptomless. This is the first report of C. coccodes that caused extraordinary symptoms on potato tubers in Turkey.

PCR DIAGNOSTICS OF COLLETOTRICHUM COCCODES IN POTATO LEAVES

Colletotrichum coccodes is a plant pathogenic fungus affecting different organs of potato, tomato, and some other plants. The leaf infection with C. coccodes may result in a rapid development of infection nidus and high losses caused by the infection of potato tubers during harvesting. Our study showed the presence of C. coccodes on potato leaves with dry necrotic lesions. The presence of a DNA region specific for C. coccodes was detected in DNA isolated from five potato leaf samples: one from the Northern Ossetia, one from the Kostroma region, and three from the Mari El Republic.

Antifungalna aktivnost eteričnih ulja i njihovih glavnih komponenti na rast micelija Colletotrichum coccodes

Antifungalna aktivnost eteričnih ulja i njihovih glavnih komponenti na rast micelija Colletotrichum coccodes

Differences in the Characteristics and Pathogenicity of Colletotrichum camelliae and C. fructicola Isolated From the Tea Plant [Camellia sinensis (L.) O. Kuntze

Colletotrichum, the causative agent of anthracnose, is an important pathogen that invades the tea plant (Camellia sinensis). In this study, 38 isolates were obtained from the diseased leaves of tea plants collected in different areas of Zhejiang Province, China. A combination of multigene (ITS, ACT, GAPDH, TUB2, CAL, and GS) and morphology analyses showed that the 38 strains belonged to two different species, namely, C. camelliae (CC), and C. fructicola (CF). Pathogenicity tests revealed that CC was more invasive than CF. In vitro inoculation experiments demonstrated that CC formed acervuli at 72 hpi and developed appressoria on wound edges, but CF did not develop these structures. Under treatment with catechins and caffeine, the growth inhibition rates of CF were remarkably higher than those of CC, indicating that the nonpathogenic species CF was more vulnerable to catechins and caffeine. Growth condition testing indicated that CF grew at a wide temperature range of 15–35°C and that the optimum temperature for CC growth was 25°C. Growth of both CC and CF did not differ between acidic and weakly alkaline environments (pH 5–8), but the growth of CC was significantly reduced at pH values of 9 and 10. Furthermore, the PacC/RIM101 gene, which associated with pathogenicity, was identified from CC and CF genomes, and its expression was suppressed in the hyphae of both species under pH value of 5 and 10, and much lower expression level was detected in CC than that in CF at pH 6. These results indicated that temperature has more important effect than pH for the growth of two Colletotrichum species. In conclusion, the inhibition by secondary metabolite is an important reason why the pathogenicity by CC and CF are different to tea plant, although the environmental factors including pH and temperature effect the growth of two Colletotrichum species.

Effect of plant extracts and emulsifiers on control of anthracnose (Colletotrichum coccodes) in persimmon trees

ABSTRACTThis study was conducted to determine suppression of the anthracnose fungus (Colletotrichum coccodes), causing disease in persimmon trees (Diospyros kaki Thunb), by (1) extracts from various parts of 45 plant species from 27 families obtained using different extraction methods, and (2) selected plant extracts and emulsifiers. Fermentation extracts of Torilis japonica roots and Portulaca oleracea, all above ground parts, as well as ethanol extracts of Rheum palmatum roots and Cinnamomum cassia barks were found to effectively suppress anthracnose, leading to 83%, or more, suppression by 10% plant extracts in laboratory tests. Additionally, anthracnose was suppressed by 100% by 3% brown rice vinegar, 3% powder soap, 5% loess sulphur, and by 5% natural emulsifier-B in a laboratory test. In the field trial with organically grown persimmon trees, treatments with plant extracts used on their own, resulted a reduction of anthracnose by 63% and 51% by 5% fermentation extract of T. japonica and 5% ethanol extract of R. palmatum, respectively, compared with a control. However, in treatments with combinations of plant extracts and emulsifiers, anthracnose was reduced by 79%, 67%, 63% and 56% when treated with 5% fermentation extract of T. japonica + natural emulsifier-B (1%), 5% fermentation extract of T. japonica + loess sulphur (1%), 5% ethanol extract of R. palmatum + natural emulsifier-B (1%), and 5% ethanol extract of R. palmatum + loess sulphur (1%), respectively, compared with the control. Thus, mixtures of plant extracts and emulsifiers may be used to control anthracnose in organic production systems.

Crinipellins A and I, Two Diterpenoids from the Basidiomycete Fungus Crinipellis rhizomaticola, as Potential Natural Fungicides.

In the course of screening for microbes with antifungal activity, we found that the culture filtrate of the IUM00035 isolate exhibited strong antifungal activity against Magnaporthe oryzae and Colletotrichum coccodes in planta. Based on the phylogenetic analysis with the ITS region, the IUM00035 isolate was identified as Crinipellis rhizomaticola. To identify antifungal compounds from the C. rhizomaticola IUM00035 isolate, the culture filtrate of the isolate was partitioned with ethyl acetate and n-butanol and, consequently, two active compounds were isolated from the ethyl acetate extract. The chemical structures of the isolated compounds were determined as crinipellin A (1) and a new crinipellin derivative, crinipellin I (2), by NMR spectral analyses and a comparison of their NMR and MS data with those reported in the literature. Crinipellin A (1) exhibited a wide range of antifungal activity in vitro against C. coccodes, M. oryzae, Botrytis cinerea, and Phytophthora infestans (MICs = 1, 8, 31, and 31 µg/mL, respectively). Furthermore, when plants were treated with crinipellin A (1) (500 µg/mL) prior to inoculation with fungal pathogens, crinipellin A (1) exhibited disease control values of 88%, 65%, and 60% compared with non-treatment control against tomato late blight, pepper anthracnose, and wheat leaf rust, respectively. In contrast to crinipellin A (1), crinipellin I (2) showed weak or no activity (MICs > 250 µg/mL). Taken together, our results show that the C. rhizomaticola IUM00035 isolate suppresses the development of plant fungal diseases, in part through the production of crinipellin A (1).

Biosynthesis, characterization and antimicrobial activities assessment of fabricated selenium nanoparticles using Pelargonium zonale leaf extract

AbstractThe present study focuses on the biogenic synthesis of selenium nanoparticles (Se NPs) usingPelargonium zonaleleaf extract under microwave irradiation. Response surface methodology was used to evaluate the effects of the synthesis parameters, namely amounts of the leaf extract (0.5–2.5 ml) and amounts of the 10 mmsodium selenite solutions (15–65 ml), at constant microwave heating (4 min), on the concentration and particle size of the fabricated Se NPs, optimize the synthesis conditions and verify the generated models and the procedures. The obtained results indicated that Se NPs with preferable attributes of mean particle size (50 nm), zeta potential (−24.6 mV), absorbance [34.6% absorbance units (a.u.)] and broad absorption peak (319 nm) were formed at the optimum synthesis conditions including amounts of 1.48 ml and 15 mlPelargoniumleaf extract and sodium selenite solution, respectively. The antibacterial activities of the synthesized Se NPs againstEscherichia coliandStaphylococcus aureusindicated that the created NPs had higher antibacterial activities toward the Gram-positive bacteria. Furthermore, the synthesized Se NPs indicated higher antifungal activities againstColletotrichum coccodesandPenicillium digitatum.

MORPHOLOGICAL IDENTITY AND POPULATION STRUCTURE OF HEMIBIOTROPHIC FUNGUS Colletotrichum coccodes COLONIZING PEPPER PLANTS

Colletotrichum coccodes (Wallr.) Hughes has been recognized as one of casual agents of anthracnose roots pepper in south-eastern Poland. During 2007–2012 the species was isolated from roots of sweet pepper (Capsicum annuum L.) cultivated in the field. The purpose of the study was morphological characterization and biotic activity of C. coccodes isolates. Five randomly chosen isolates from fungus population and one reference isolate obtained from Bank of Plant Pathogens and Investigation of their Biodiversity of IPP-NRI in Poznan in Poland were studied. The character of culture like growth rate, the colour of averse and reverse and the formation of morphological structures of the fungus such as acervuli, conidia, sclerotia were studied. Ultrastructural observations of morphological structures were made using light and scanning electron microscopy. Biotic activity of C. coccodes was conducted using the method of biotic series on PDA. Seven species of test fungi were used in the study: Alternaria alternata, Aureobasidium pullulans, Gibberella avenacea, G. intricans, Fusarium oxysporum, Penicillium aurantiogriseum, Trichoderma harzianum. The biotic activity test showed that C. coccodes is a weak competitor, and its development in the rhizosphere of sweet pepper may be limited by numerous antagonists.

Effects of different fractions of Rheum palmatum root extract and anthraquinone compounds on fungicidal, insecticidal, and herbicidal activities

This study was conducted to evaluate the suppression of Pyricularia oryzae, Colletotrichum coccodes, Rhizoctonia solani, Phytophthora capsici, and Botrytis cinerea, as well as the acaricidal activities against the two-spotted spider mite (Tetranychus urticae) and the weed control efficacy of solvent fractions of Pheum palmatum extract. In addition, we determined the inhibitory activities of the main bioactive substances of R. palmatum (aloe-emodin, emodin, chrysophanol, and physcion) against the aforementioned pathogens. The suppression rates of 5% ethylacetate and BuOH fractions against P. oryzae were 70 and 52%, respectively. However, the other fractions including hexane showed very little suppression of P. oryzae. Moreover, C. coccodes, B. cinerea, R. solani, and P. capsici were suppressed by 61, 47, 58, and 91% in response to treatment with the 5% ethylacetate fraction of R. palmatum, respectively, compared with the control. The ethylacetate and BuOH fractions were also confirmed in greenhouse trials of rice seedlings infected by P. oryzae. The ethylacetate and BuOH fractions of R. palmatum ethanol extract were shown to have the potential for control of powdery mildew (Sphaerotheca fuliginea causes) and weeds, but not to have acaricidal activities against the two-spotted spider mite. The suppression rates of P. oryzae and P. capsici increased with increasing concentrations of chrysophanol, emodin, aloe-emodin, and rhein, but these extracts had no effect on cucumber powdery mildew or two-spotted spider mites. The anthraquinone levels in the ethylacetate fraction were much higher than in the BuOH fraction. Thus, the higher suppression of P. oryzae and P. capsici of the ethylacetate fraction observed in this study may be related to higher levels of anthraquinone substances in the ethylacetate fraction than the BuOH fraction.

Evaluating Host Resistance to Limit Colletotrichum coccodes on Onion

Leaf and neck anthracnose is incited by Colletotrichum coccodes (Wallr.) Hughes, a new foliar disease of onion (Allium cepa L.) in Michigan that has been observed in the state since 2010. Symptoms include elliptical lesions on the leaves, necks, or both that appear bleached with a pale salmon to dark brown center. To develop an effective integrated disease management strategy, field studies were conducted in 2011 and 2012 to evaluate 16 commercial onion cultivars for their susceptibility to the pathogen. The incidence and severity of anthracnose were evaluated weekly following inoculation. Onion cultivars differed significantly in disease severity and incidence; differences between years were also observed. ‘Hendrix’ had the lowest disease severity, whereas ‘Highlander’ and ‘Candy’ exhibited severe onion leaf and neck anthracnose symptoms. Using less susceptible onion cultivars combined with effective fungicides against C. coccodes may limit crop losses for Michigan growers.

Vegetative compatibility groups in Colletotrichum coccodes from Turkey and their aggressiveness to potato

Black dot, caused by Colletotrichum coccodes, is a common disease of potato in Turkey, affecting tuber quality and yield. The objectives of the current study were to characterize vegetative compatibility groups (VCGs) of C. coccodes isolates from three regions in Turkey, and to assess the correlation between VCGs and aggressiveness of isolates on potato. A total of 147 C. coccodes isolates were recovered from plants showing typical black dot symptoms on stolons, roots and stems. The frequency of nitrate non‐utilizing (nit) nit1/nit3 and NitM phenotypes were 79% and 21%, respectively. Complementation between nit mutants of the isolates and eight European/Israeli EU/I‐VCG tester isolates was used to characterize the VCGs. Amongst the tested isolates, 33.3% were assigned to EU/I‐VCG6, 21.8% to EU/I‐VCG8, 15.7% to EU/I‐VCG4. EU/I‐VCG1, EU/I‐VCG3, EU/I‐VCG5 and EU/I‐VCG7 were classified at 1.4%, 3.4%, 4.8% and 5.4%, frequency, respectively. No isolate was assigned to EU/I‐VCG2 group, while 21 isolates (14.3%) were not assigned to any of the EU/I‐VCGs. The pathogenicity tests indicated significant differences in aggressiveness of the isolates with respect to sclerotia density on potato tissues. The highest densities of sclerotia on roots and crown were obtained with EU/I‐VCG6 isolates and the lowest with EU/I‐VCG1, EU/I‐VCG3 and EU/I‐VCG5 isolates. The results demonstrate that there is significant VCG diversity among C. coccodes isolates from potato plants in Turkey.

Discovery of Methyl (5 Z)-[2-(2,4,5-Trioxopyrrolidin-3-ylidene)-4-oxo-1,3-thiazolidin-5-ylidene]acetates as Antifungal Agents against Potato Diseases.

Synthesis, isomerism, and fungicidal activity against potato diseases of new (5 Z)-[2-(2,4,5-trioxopyrrolidin-3-ylidene)-4-oxo-1,3-thiazolidin-5-ylidene]acetate derivatives with 1,3-thiazolidine-4-one and pyrrolidine-2,3,5-trione moieties linked by an exocyclic C═C bond were described. Their structures were clearly confirmed by spectroscopic and spectrometric data (Fourier transform infrared spectroscopy, 1H and 13C nuclear magnetic resonance, and mass spectrometry), elemental analysis, and X-ray diffraction crystallography. A bioassay for antifungal activity in vitro against Phytophthora infestans, Fusariun solani, Alternaria solani, Rhizoctonia solani, and Colletotrichum coccodes demonstrated that 2,4,5-trioxopyrrolidin-1,3-thiazolidine derivatives exhibited a relatively broad spectrum of antifungal activity. One of the compounds showed considerable activity against all of the strains; in the case of F. solani, P. infestans, and A. solani, it possesses comparable or better fungicidal efficacy than the positive control Consento. Consequently, this compound is a promising fungicidal candidate for plant protection.

Tea plant SWEET transporters: expression profiling, sugar transport, and the involvement of CsSWEET16 in modifying cold tolerance in Arabidopsis.

Thirteen SWEET transporters were identified in Camellia sinensis and the cold-suppression gene CsSWEET16 contributed to sugar compartmentation across the vacuole and function in modifying cold tolerance in Arabidopsis. The sugars will eventually be exported transporters (SWEET) family of sugar transporters in plants is a recently identified protein family of sugar uniporters that contain seven transmembrane helices harbouring two MtN3 motifs. SWEETs play important roles in various biological processes, including plant responses to environmental stimuli. In this study, 13 SWEET transporters were identified in Camellia sinensis and were divided into four clades. Transcript abundances of CsSWEET genes were detected in various tissues. CsSWEET1a/1b/2a/2b/2c/3/9b/16/17 were expressed in all of the selected tissues, whereas the expression of CsSWEET5/7/9a/15 was not detected in some tissues, including those of mature leaves. Expression analysis of nine CsSWEET genes in leaves in response to abiotic stresses, natural cold acclimation and Colletotrichum camelliae infection revealed that eight CsSWEET genes responded to abiotic stress, while CsSWEET3 responded to C. camelliae infection. Functional analysis of 13 CsSWEET activities in yeast revealed that CsSWEET1a/1b/7/17 exhibit transport activity for glucose analogues and other types of hexose molecules. Further characterization of the cold-suppression gene CsSWEET16 revealed that this gene is localized in the vacuolar membrane. CsSWEET16 contributed to sugar compartmentation across the vacuole and function in modifying cold tolerance in Arabidopsis. Together, these findings demonstrate that CsSWEET genes play important roles in the response to abiotic and biotic stresses in tea plants and provide insights into the characteristics of SWEET genes in tea plants, which could serve as the basis for further functional identification of such genes.

Bioherbicidal enhancement and host range expansion of a mycoherbicidal fungus via formulation approaches

ABSTRACTEastern black nightshade (Solanum ptycanthum; EBN) is a problematic weed partly due to its tolerance or resistance to certain herbicides. We examined the effects of an invert emulsion (IE) on the host range and weed control efficacy of the fungus Colletotrichum coccodes (NRRL strain 15547) for biocontrol of EBN. Greenhouse tests demonstrated that several other solanaceous weeds were also infected and killed, and field tests revealed >90% EBN control and dry weight reduction in plants treated with the fungus-IE formulation. These results demonstrate that this IE formulation can promote the efficacy of this bioherbicidal pathogen.

Potato Black Dot – The Elusive Pathogen, Disease Development and Management

Black dot caused by Colletotrichum coccodes was initially considered a mild disease of potato, mainly infecting weakened plants. In the past two decades the fungus has been reported to infect roots and stems relatively early in the growing season, be prevalent on potato and in field soil in major potato production regions of the world, cause early death of foliage by itself and in association with other pathogens, reduce plant and root growth, and to reduce potato yields. Furthermore, the tuber phase of the disease is recognized as a major problem in that unsightly blemishes reduce value of fresh market potatoes. C. coccodes has been dubbed an elusive pathogen because infections are latent, disease symptoms on foliage are often non-descript and can be confused with other potential causes, disease effects on potato yield have not been consistent, and the disease is not satisfactorily managed. Sources of variation on yield likely arise from genetic variation within the pathogen population; the host population such as potato cultivar, maturity class, and plant organs infected; environmental variables; cultural and management practices such as timing of fungicide application; crop duration; post-harvest conditions; and interactions of C. coccodes with other microbes and with potato cultivars. Considerable research has been done on potato black dot during the last two decades, the scope of this paper is to define our current understanding on the disease and summarize disease management strategies.

Inoculation Method, Temperature, and Relative Humidity Affect Leaf and Neck Anthracnose, a New Onion Disease in Michigan

Leaf and neck anthracnose caused by Colletotrichum coccodes is a new disease of onion in Michigan. To test the effect of inoculation method, Prince onion seedlings were grown in the greenhouse and inoculated with either a conidial suspension of C. coccodes (alone or with an abrasive agent) or infested millet seed (dry or wet, 2 or 5 g). Foliar disease severity was greater when a conidial suspension (>39%) was used compared with infested millet seed (≤24.3%). Growth chamber studies were conducted using Infinity onion seedlings that were inoculated with a conidial suspension spray to determine the effects of temperature (15, 20, 25, or 30°C) and duration (0, 12, 24, 48, or 72 h) of high (95 ± 5%) relative humidity (RH) on disease severity (percentage of leaf area with C. coccodes lesions). Significant differences and interactions among temperature and RH were observed. The combination of high temperature (≥25°C) and extended (≥24 h) high RH resulted in >20% disease severity 28 days postinoculation. Results suggest that onion leaf and neck anthracnose symptoms are likely to be more severe when the environmental conditions are ≥25°C with ≥24 h of high RH.