Spontaneous mutability and colony morphology of Gibberella baccata

1986 ◽  
Vol 28 (6) ◽  
pp. 932-941 ◽  
Author(s):  
E. B. Lawrence ◽  
Paul E. Nelson ◽  
T. A. Toussoun
Keyword(s):  
Genetic Basis ◽  
Aerial Mycelium ◽  
Morphological Type ◽  
Colony Morphology ◽  
Fusarium Lateritium ◽  
Original Culture ◽  
Mutator Activity ◽  
Unknown Factor ◽  
Spontaneous Mutability ◽  
Colony Color

Cultural instability is a common phenomenon in the genus Fusarium. As with other species, Gibberella baccata (Fusarium lateritium) contains cultures that are less morphologically stable than others. When grown on certain media, such as potato dextrose agar, these cultures produce areas of aberrant growth (mutant patches) after 6 weeks. Single conidial cultures from these patches produce colonies different from the original culture and from each other in growth rate, colony color, aerial mycelium production, and pionnote production. Random ascospore analyses of crosses of the original morphological type to the mutant types showed there had been a one gene change in each case. Mutant patch forming and nonforming isolates of Gibberella baccata were crossed in all possible combinations, and the progeny were rated for ability to produce mutant patches. Broad sense heritability estimates for inheritance of mutant patch formation were high (60.0 to 95.9%), strongly indicating a genetic basis with a limited number of genes involved. The mutator activity of these genes appeared to be conditional and mutant patch development was dependent on the presence of some unknown factor in certain media rich in carbohydrates and other compounds.Key words: Gibberella baccata, Fusarium lateritium, colony morphology, spontaneous mutability, cultural instability.

scholarly journals Peripheral Pathways in the Food-Intake Control towards the Adipose-Intestinal Missing Link

2013 ◽  
Vol 2013 ◽  
pp. 1-12 ◽  
Author(s):  
Hugo Mendieta Zerón ◽  
Ma. Victoria Domínguez García ◽  
María del Socorro Camarillo Romero ◽  
Miriam V. Flores-Merino
Keyword(s):  
Diabetes Mellitus ◽  
Genetic Basis ◽  
Physiological State ◽  
Hormone Secretion ◽  
Gut Hormones ◽  
Diabetic Patients ◽  
Early Presentation ◽  
Gut Hormone ◽  
Unknown Factor

In the physiological state a multitude of gut hormones are released into the circulation at the same time depending on the quality and quantity of the diet. These hormones interact with receptors at various points in the “gut-brain axis” to affect short-term and intermediate-term feelings of hunger and satiety. The combined effects of macronutrients on the predominant gut hormone secretion are still poorly understood. Besides, adipokines form an important part of an “adipoinsular axis” dysregulation which may contribute toβ-cell failure and hence to type 2 diabetes mellitus (T2DM). Even more, gestational diabetes mellitus (GDM) and T2DM seem to share a genetic basis. In susceptible individuals, chronic exaggerated stimulation of the proximal gut with fat and carbohydrates may induce overproduction of an unknown factor that causes impairment of incretin production and/or action, leading to insufficient or untimely production of insulin, so that glucose intolerance develops. The bypass of the duodenum and jejunum might avoid a putative hormone overproduction in the proximal foregut in diabetic patients that might counteract the action of insulin, while the early presentation of undigested or incompletely digested food to the ileum may anticipate the production of hormones such as GLP1, further improving insulin action.

Genetics of Gibberella fujikuroi. 1. Inheritance of certain cultural traits

1983 ◽  
Vol 25 (2) ◽  
pp. 93-96 ◽  
Author(s):  
Gurmel S. Sidhu
Keyword(s):  
Growth Rate ◽  
Colony Growth ◽  
Infection Process ◽  
Colony Morphology ◽  
Gibberella Fujikuroi ◽  
Crop Species ◽  
Colony Color ◽  
Conidial Stage ◽  
Cultural Traits ◽  
Pathogenic Variability

Gibberella fujikuroi (conidial stage Fusarium moniliforme) is a pathogen of many crop species. It exhibits a tremendous cultural and pathogenic variability in the field through sexual and parasexual cycles. This report investigates the inheritance of mating type, colony color, colony morphology, and colony growth rate. The tetrad and random ascospore analysis of variants of these traits, obtained from nature and through mutagenesis, confirm that they are controlled by single nuclear genes. The genes for colony morphology and colony growth rate were linked whereas other genes show independent assortment. These traits can be used as genetic markers in the infection process of this fungus.

scholarly journals Genetic Basis for Conversion of Rough-to-Smooth Colony Morphology in Actinobacillus actinomycetemcomitans

2005 ◽  
Vol 73 (6) ◽  
pp. 3749-3753 ◽  
Author(s):  
Ying Wang ◽  
Amy Liu ◽  
Casey Chen
Keyword(s):  
Promoter Region ◽  
Genetic Basis ◽  
Actinobacillus Actinomycetemcomitans ◽  
Expression Level ◽  
Colony Morphology ◽  
Wild Type ◽  
Wild Type Promoter

ABSTRACT The basis of the rough-to-smooth conversion of Actinobacillus actinomycetemcomitans was examined. Smooth variants often contained mutations at the flp promoter region. Replacing the mutated flp promoter with the wild-type promoter restored the rough phenotype. The expression level of the flp promoter was ∼100-fold lower in smooth than in rough strains. Mutations of the flp promoter are a cause of the rough-to-smooth conversion.

scholarly journals First report of Leaf Wilt caused by Fusarium proliferatum and F. brachygibbosum on Date Palm (Phoenix dactylifera) in Tunisia

Plant Disease ◽  
2020 ◽  
Author(s):  
Ahmed Namsi ◽  
Amal Rabaoui ◽  
Mario Masiello ◽  
Antonio Moretti ◽  
Ahmed Othmani ◽  
...  
Keyword(s):  
Date Palm ◽  
Elongation Factor ◽  
Aerial Mycelium ◽  
Phoenix Dactylifera ◽  
Fusarium Proliferatum ◽  
Morphological Identification ◽  
First Report ◽  
Leaf Yellowing ◽  
Colony Color

Since 2017, a new leaf wilt syndrome was observed in plantations of date palm in Tunisia. Its incidence increases sharply from year to year, especially in ‘Deglet Nour’ trees, aged between 5 and 15 years. In severe cases, the large number of dried leaves per tree can lead to complete cessation of date production. Symptoms appear on one or more leaves in the center of the crown. Whitening and drying start at the top of the leaflets and proceed to their base, while the midrib remains green. Then the whole leaf dies. Small white-creamy leaflet fragments and roots were collected from five different regions in the Djerid Oases. They were disinfected with diluted bleach (0,8 % NaOCl) and ethanol (80%) (each 2 min), rinsed with sterile distilled water, dried and finally plated in Petri dishes containing Potato Dextrose Agar (PDA) amended with 50mg/l neomycin. After incubation for 7 days at 25ºC±2, emerging fungal colonies were single-spored by serial dilution. They were transferred to PDA, Carnation Leaf Agar (CLA) and Spezieller Nahrstoffarmer Agar (SNA) for morphological identification. Based on the colony color on PDA, conidial morphology and phialide structures on CLA and/or SNA, of the 85 Fusarium isolates, around 90% were identified as F. proliferatum and around 10% as F. brachygibbosum (Leslie and Summerell, 2006). Fusarium proliferatum colonies rapidly developed white aerial mycelium that became purple in old cultures. Microconidia were abundant in the aerial mycelium and formed chains of variable length, on monophialides and polyphialids, a characteristic that distinguishes F. proliferatum from F. verticilloides. Less often, they were observed in false heads. Chlamydospores were absent. On CLA, microconidia were mostly 2 × 15 µm in size, a large number of sickle shaped macroconidia (2 × 25 µm) had one septum, some were larger (2 × 50 µm) with 3 septa and tips at both ends. Molecular identification was carried out based on elongation factor (EF-1α) gene sequencing. The region between the EF1 and EF2 primers (O’Donnell et al., 1998) was amplified and the sequences were compared to Fusarium reference sequences (GenBank). The sequences of the isolates Fus 1953 (539 bp), Fus 1962 (618 bp), and Fus 1965 (605 bp) shared respectively 100%, 99.51% and 99.51% homology with that of F. proliferatum JF740713.1 and were deposited in GenBank with the following accession numbers: MT630418, MT630419, and MT630420, respectively. The sequences of isolates 7F, 28F, Fus 1955 and Fus 1956 shared 100 % homology with that of F. brachygibbosum (GQ505418.1) while those of Fus 1955 and Fus 1956 showed 99.02 and 98.91 % identity, respectively, with F. brachygibbosum JX118981.1. The sequences of 7F (535 bp), 28F (535 bp), Fus 1955 (608 bp), and Fus 1956 (647 bp) were deposited in GenBank with the following accession numbers: MT630409, MT630410, MT630411, and MT630412, respectively. Two ml suspension of 106 conidia / ml of each isolate was sprayed separately or in combinations on in vitro cloned ‘Deglet Nour’ plants, placed in a greenhouse at 28°±2 °C and 70% R.H.. Isolates of F. proliferatum led to dryness and wilting leaflets after 3 weeks. Fusarium brachygibbosum only induced mild leaf yellowing, while in combination they were more virulent. Fungal isolates of both species were re-isolated and their identity confirmed to be the same of those isolated from leaflets infected in the open field, confirming Koch’s postulates. Control plants lacked symptoms. Fusarium proliferatum is known as date palm pathogen in many countries (Saleh et al. 2017), however, to our knowledge, this is the first report of F. proliferatum and also F. brachygibbosum causing Leaf Wilt symptoms on P. dactylifera in Tunisia.

scholarly journals Stem Canker of Giant Dogwood (Cornus controversa) Caused by Fusarium lateritium in Korea

Plant Disease ◽  
2013 ◽  
Vol 97 (10) ◽  
pp. 1378-1378 ◽  
Author(s):  
H. Y. Yun ◽  
Y. W. Lee ◽  
Y. H. Kim
Keyword(s):  
Basal Cell ◽  
Apical Cell ◽  
Aerial Mycelium ◽  
Stem Canker ◽  
Peat Moss ◽  
Fungal Culture ◽  
Sequence Identity ◽  
Fusarium Lateritium ◽  
Colony Surface ◽  
Cornus Controversa

In May 2012, a stem canker was observed on a ~20-year-old giant dogwood (Cornus controversa) in Suwon, Gyeonggi Province, South Korea, which consisted of necrotic lesions on stem bark with orange sporodochial fruiting bodies. A single fungal colony was obtained from hyphal tips that were grown out of affected tissues plated on potato dextrose agar (PDA) acidified with 0.1% lactic acid after surface sterilization with 1.0% NaOCl for 30 s and 70% ethanol for 30 s, and incubated at 25°C for 7 days in the dark. The fungal isolate was grown on PDA and carnation leaf agar (CLA) to examine its mycological characteristics. The fungal colonies grown on PDA at 25°C for 7 days had diameters of 31 to 36 mm, with the colony surface sparsely cottony or with little or no aerial mycelium, very pale brown to pink, becoming progressively lighter toward the center; the colony reverse was pinkish-white to reddish-yellow, producing very few hyaline microconidia that were ellipsoidal, mostly 1-celled, and 15.4 to 22.8 × 4.1 to 4.8 μm. It produced hyaline macroconidia that were slightly curved, frequently 3 septate, a hooked or beaked apical cell and a foot-shaped or notched basal cell, 28.0 to 35.5 × 4.0 to 5.5 μm, borne on pink sporodochia. On CLA, the colony surface was lighter toward the center with no or sparse aerial mycelium, growing to 33 to 43 mm diameter at 25°C for 7 days. Microconidia were ellipsoidal, mostly 1-celled, and 9.2 to 17.5 × 2 to 2.5 μm on CLA. Macroconidia were produced on pink sporodochia near or on carnation leaf pieces, falcate to almost straight or slightly curved, frequently 5 to 7 septate, with a hooked or beaked apical cell and a foot-shaped or notched basal cell, and 45.5 to 59 × 5.5 to 6.5 μm. Chlamydospores were rare or absent. Based on these morphological characters, the isolate was identified as Fusarium lateritium (1,2). Sequences of the internal transcribed spacer (ITS) rDNA region of the fungus (GenBank Accession No. KC453998) amplified using primers ITS1/ITS4 had 100% sequence identity to F. lateritium (JN198452). The DNA sequences of translation elongation factor-1α (EF-1α) amplified using primers EF1/EF2 (KC453997) also had 100% sequence identity to F. lateritium (AY707172 and AY707156). The culture was deposited in the Korean Collection for Type Cultures (KCTC 46029). Pathogenicity tests were conducted using 1-year-old giant dogwood seedlings grown for 3 weeks before inoculation in a 1:1:1 mixture of peat moss, perlite, and sand in 10” × 10” × 12” plastic pots. The stems of three seedlings were inoculated with the mycelial plugs from the edge of the fungal culture on PDA grown at 25°C for 7 days, which were placed on three barkless cuts per stem and sealed with Parafilm that was removed 3 weeks later. Canker symptoms on the inoculated seedlings developed after 30 days of incubation at 25 to 32°C and relative humidity of 50 to 60% in a glasshouse, from which the same fungus was isolated. Non-inoculated control seedlings showed no canker development. To our knowledge, this is the first report of stem canker on giant dogwood caused by F. lateritium in Korea and also the family Cornaceae as new host for the fungus. References: (1) D. M. Geiser et al. Mycologia 97:191, 2005. (2) J. F. Leslie and B. A. Summerall. The Fusarium Laboratory Manual. Blackwell Publishing. Ames, Iowa, 2006.

High-density genetic mapping identifies the genetic basis of a natural colony morphology mutant in the root rot pathogen Armillaria ostoyae

2017 ◽  
Vol 108 ◽  
pp. 44-54 ◽  
Author(s):  
Renate Heinzelmann ◽  
Daniel Croll ◽  
Stefan Zoller ◽  
György Sipos ◽  
Martin Münsterkötter ◽  
...  
Keyword(s):  
Genetic Mapping ◽  
Root Rot ◽  
Genetic Basis ◽  
High Density ◽  
Colony Morphology ◽  
Armillaria Ostoyae

scholarly journals First Report of Diaporthe foeniculina Associated with Grapevine Trunk Diseases on Vitis vinifera in Cyprus

Plant Disease ◽  
2021 ◽  
Author(s):  
Georgios Makris ◽  
Solonas Solonos ◽  
Marios Christodoulou ◽  
Loukas Kanetis
Keyword(s):  
Aerial Mycelium ◽  
Its Region ◽  
First Record ◽  
Colony Morphology ◽  
Sweet Chestnut ◽  
Grapevine Trunk Diseases ◽  
Near Ultraviolet ◽  
Bt Genes ◽  
Light Darkness ◽  
Trunk Diseases

In June 2017, three vineyards were surveyed in the regions of Droushia (30-year-old, cv Mavro), Ineia (50-year-old, cv Xynisteri), and Lemona (15-year-old, cv Carignan) at the province of Paphos, Cyprus, with dieback incidence of 22%, 32%, and 14%, respectively. More specifically, affected grapevines exhibited severe dieback symptoms in spur and cordon positions, related to perennial cankers and internal brown discoloration. Thirty symptomatic samples, were surface-sterilized (95% ethanol) and wood chips were plated on potato dextrose agar (PDA), amended with streptomycin (500 μg/ml) at 25 °C for 3-5 days. Based on colony morphology (white to creamy color, with sparse aerial mycelium) and conidia production, nine Diaporthe-like isolates were obtained. For species identification, the internal transcribed spacer (ITS) region and β-tubulin (BT) genes were amplified using the primer pairs ITS1/ITS4 and Bt2a/Bt2b, respectively (Úrbez-Torres et al. 2008). Sequences of the isolates P101b, P114c, and P289a revealed >99.8% homology to NCBI voucher specimens of Diaporthe foeniculina (Sacc.) Udayanga & Castl. (ITS: CBS111553, MH050434; ΒΤ: KY511368, KF778966), and were deposited in the GeneBank (ITS: MT735646, MT737289, MT737287; BT: MT903969, MT903970, MT903971). Thus, 8.3% of the collected isolates (3 of 36) were identified as D. foeniculina, while the rest Diaporthe-like isolates were identified as D. ampelina. D. foeniculina isolates were also transferred on 2% water agar with sterile pine needles under a 12h/12h near-ultraviolet, light/darkness regime, at 25 °C, to induce sporulation (Guarnaccia and Crous 2017). Two weeks later, microscopic observations revealed dark brown to black, globose to sub-globose, ostiolate pycnidia (n = 30) 291 to 897 μm (595 ± 173) x 192 to 655 μm (364 ± 113) containing hyaline, unbranched conidiophores, bearing alpha‐ and beta‐conidia in the form of yellowish cirri. Alpha-conidia were aseptate, hyaline, ovate to ellipsoidal, ranging (n=100) from 5.6 to 9.9 μm (7.5 ± 0.8) x 1.9 to 3.3 μm (2.7 ± 0.3). Beta-conidia were abundant, aseptate, hyaline, filiform, slightly curved (n = 100) from 22.4 to 35.3 μm (28.1 ± 2.5) x 1.2 to 2.3 μm (1.6 ± 0.2) (Udayanga et al. 2014). Pathogenicity tests were conducted with isolates P101b and P289a under greenhouse conditions (24-32 ⁰C, 70% RH). Ten 1-year-old rooted canes cv Mavro were inoculated with 4 mm mycelium plugs from actively growing cultures into wounds made by drilling between two internodes at the middle of the trunk. The same number of cuttings were inoculated with sterile PDA plugs, sealed with Vaseline, and wrapped with parafilm, serving as controls. Seven months later, all inoculated cuttings developed brownish wood discolorations (average 39 ± 13 mm), similar to naturally infected plants. No symptoms were observed in the controls. Successful re-isolations were made only from the inoculated cuttings and confirmed by colony morphology. Previously, D. foeniculina (as D. neotheicola) has been reported as grapevine wood saprophyte (Úrbez-Torres et al. 2014). It has also been reported to cause shoot canker and dieback in numerous hosts, including almond, avocado, citrus, and sweet chestnut (Annesi et al. 2016; Guarnaccia and Crous 2017; Diogo et al. 2010; Mathioudakis et al. 2020). This is the first record of D. foeniculina associated with grapevine trunk diseases (GTDs) in Cyprus. However, its relative importance as the causal agent of GTDs remains to be further investigated.

scholarly journals Isolation and Identification of the Fungus Colletotrichum cordylinicola Causing Anthracnose Disease on Cordyline fruticosa in Florida

HortScience ◽  
2014 ◽  
Vol 49 (7) ◽  
pp. 911-916 ◽  
Author(s):  
Kalpana Sharma ◽  
Erica Goss ◽  
Ariena H.C. van Bruggen
Keyword(s):  
Regression Line ◽  
Aerial Mycelium ◽  
The United States ◽  
Isolation And Identification ◽  
Disease Progress ◽  
Progress Curve ◽  
Latently Infected ◽  
Cordyline Fruticosa ◽  
Mean Size ◽  
Colony Color

Imported Hawaiian Ti Cordyline plants (Cordyline fruticosa) ‘Tipsy Pink’ with anthracnose symptoms were found in Gainesville, FL, in 2013. A Colletotrichum spp. was isolated from symptomatic Cordyline plants and Koch’s postulates were fulfilled. The colony color on acidified potato dextrose agar (PDA) was orange with slight shades of pink and light gray aerial mycelium. Sclerotia and setae were absent. Conidia were one-celled, hyaline, guttulate, and cylindrical with round ends. The mean size of the conidia was 14.7 × 5.0 μm and ranged from 12.5 to 17.5 × 3.8 to 7.5 μm. Polymerase chain reaction (PCR) was performed on the internal transcribed space (ITS) and 28S rDNA regions of the isolate, and the sequences were compared with those of Colletotrichum spp. in GenBank. Sequence analysis indicated that the isolate belonged to C. cordylinicola. This is the first report of C. cordylinicola on C. fruticosa in Florida and the United States. Anthracnose symptoms developed on healthy-looking, latently infected Hawaiian Ti plants within 2 to 3 months, and 34% to 44% of the non-inoculated plants became diseased in 3 months. Reactions of several Dracaena and Cordyline species and varieties including Hawaiian Ti to C. cordylinicola were assessed. Several Dracaena and Cordyline species and varieties including Hawaiian Ti exhibited a differential response when inoculated with C. cordylinicola, but none of them was resistant. Hawaiian Ti was the most and lucky bamboo (Dracaena sanderiana) the least susceptible [area under the disease progress curve (AUDPC) = 71 vs. 10 cm2·d–1] to C. cordylinicola. The slope of the log-transformed disease progress regression line was steepest on Hawaiian Ti and D. marginata variety ‘Colorama’ plants, intermediate on varieties ‘Tarzan’ and ‘Magenta’, and least on lucky bamboo [slope = 0.046, 0.044, 0.036, and 0.034 vs. 0.020 log(cm2 + 1)/d, respectively, with a mean se of 0.0006].

scholarly journals First Report of Twig Canker of Hazelnut Caused by Fusarium lateritium in Italy

Plant Disease ◽  
2005 ◽  
Vol 89 (1) ◽  
pp. 106-106 ◽  
Author(s):  
A. Belisario ◽  
M. Maccaroni ◽  
A. Coramusi
Keyword(s):  
Fusarium Species ◽  
Robinia Pseudoacacia ◽  
Aerial Mycelium ◽  
Early Summer ◽  
Pyrus Pyrifolia ◽  
Sophora Japonica ◽  
Lazio Region ◽  
First Report ◽  
Fusarium Lateritium ◽  
Pure Cultures

Cultivation of hazelnut (Corylus avellana L.) has considerable economic potential in Italy, in particular, in the northern Lazio Region. Since early summer of 2000, cankered twigs have been observed on hazelnut trees that were severely affected by gray necrosis, which is a disease complex causing fruit drop (1). In subsequent years, sunken areas were observed on 1-year-old shoots from late April through May. The resulting cankers had reddish brown margins and the death of the cambium in the infected area and produced an L-shaped malformation of twigs. Girdling of the twig by the canker resulted in death of the foliage. Yellow-to-orange sporodochia were evident on cankers by early June. Isolations were made from the margins of young cankers from 20 twigs collected from 10 trees. Tissue pieces were plated onto potato dextrose agar (PDA) after surface disinfection with 1% sodium hypochlorite. Slow-growing, cream-to-reddish brown colonies with sparse aerial mycelium emerged from 80% of diseased tissue pieces within 10 days of incubation at 20 to 22°C. Conidial production was induced by keeping pure cultures at 22 to 25°C under natural light but out of direct sunlight. Within 1 month, sporodochia bearing ellipsoidal, spindle-shaped, commonly 1 to 3 septate macroconidia developed. Intercalary chlamydospores were often present in chains. Single conidia were subcultured on carnation leaf agar (CLA). On the basis of morphological and cultural characteristics, the fungus was identified as Fusarium lateritium Nees. (2). Pathogenicity tests were conducted outdoors on the current year's shoots of hazelnut trees with four isolates derived from single conidia of F. lateritium. Inocula used were either mycelial plugs cut from the margin of actively growing cultures or small (10 × 10 mm) pieces of sterile cheesecloth soaked in 1 × 106 conidia per ml suspension. The mycelial plugs were placed under the bark, while the soaked cheesecloth pieces were wrapped around an area that had been wounded by gently scraping off a length of the bark (approximately 10 mm) with a sterile needle. All the inoculations were wrapped with Parafilm to prevent desiccation. Six inoculations per isolate were performed. In a similar manner, controls were inoculated with agar plugs or water only. After 3 months, the length and width of each canker were measured. For both inoculation methods, cankers were similar to those observed in nature and averaged 20.6 × 5 mm, while the controls did not show any symptoms. F. lateritium was consistently reisolated from the canker margins of the inoculated shoots. To our knowledge, this is the first report of F. lateritium causing twig cankers on hazelnut. The fungus has been reported to cause cankers on several tree species, including Malus domestica (apple), Morus spp. (mulberry), Sophora japonica (Japanese pagoda tree), Robinia pseudoacacia (black locust), Citrus spp., and Pyrus pyrifolia (Asian pear). References: (1) A. Belisario et al. Inf. Agrario 59(6):71, 2003. (2) P. E. Nelson et al. Fusarium Species: An Illustrated Manual for Identification. Pennsylvania State University, University Park, 1983.

scholarly journals First Report of Fusarium armeniacum Causing Seed Rot and Root Rot on Soybean (Glycine max) in the United States

Plant Disease ◽  
2012 ◽  
Vol 96 (11) ◽  
pp. 1693-1693 ◽  
Author(s):  
M. L. Ellis ◽  
M. M. Díaz Arias ◽  
L. F. Leandro ◽  
G. P. Munkvold
Keyword(s):  
United States ◽  
Root Rot ◽  
Aerial Mycelium ◽  
The United States ◽  
Root Tissue ◽  
Colony Morphology ◽  
Ordinal Scale ◽  
First Report ◽  
Seed Rot ◽  
Slow Growing

In a survey for Fusarium root rot, soybean plants were sampled from eight counties across Iowa in 2008 to 2009. Fusarium isolates were recovered from surface-sterilized symptomatic and asymptomatic root tissue by culturing on peptone PCNB agar (2). Single-spore isolates were transferred to carnation leaf agar (CLA) and potato dextrose agar (PDA) for morphological identification; 11 isolates were identified as F. armeniacum (Forbes, Windels, and Burgess) Burgess and Summerell (previously F. acuminatum ssp. armeniacum) (2). Colonies on PDA produced white aerial mycelium, red to apricot pigment in agar, and bright orange sporodochia in the center of the culture. Some isolates produced a pionnotal form of slow-growing colonies with little aerial mycelium and abundant orange sporodochia. On CLA, macroconidia in orange sporodochia on carnation leaves and chlamydospores formed abundantly, but microconidia were absent (2). Species identity for the 11 isolates was confirmed by sequencing of the elongation factor gene (EF1-α) using ef1 and ef2 primers (4) (reference sequences deposited in GenBank JX101763 and JX101764). Pathogenicity of seven F. armeniacum isolates was tested using surface-sterilized soybean seed, cv. AG2403, in a petri dish assay with 3-day-old cultures on 2% water agar (1). Germination, seed rot, and lesion development were scored 7 dai using an ordinal scale (1). The experiment was a completely randomized design (CRD), had three replicate plates per isolate, and was conducted twice. All seven isolates were pathogenic on soybean, though variation in aggressiveness was observed among isolates (P < 0.0001) related to colony morphology on PDA. Seed germination was 0 to 40% when inoculated with four isolates showing white fluffy aerial mycelium on PDA. Seedlings were severely stunted with dark brown lesions covering a majority of the root system. When inoculated with three isolates showing the pionnotal form of slow-growing mycelium, germination was 70 to 100%, with few small brown lesions (~5 to 10 mm) on the roots. Noninoculated controls showed 100% germination and no symptoms. Pathogenicity was also tested in a growth chamber assay at 18°C using autoclaved soil mixed with an infested sand-cornmeal inoculum (3). Data for dry root and shoot weights and root rot severity (visually scored on a % scale) were collected at 6 weeks. The CRD experiment had five replications (single plant in a cone containing 150 ml infested soil), and was conducted twice. Root symptoms and similar variation in aggressiveness among isolates (based on colony morphology) was observed in inoculated plants. Isolates differed significantly for effects on root weight (P = 0.0125), shoot weight (P = 0.0035), and root rot severity (P = 0.0158). F. armeniacum was reisolated from infected root tissue, but not from noninoculated controls. Recovered isolates maintained their original colony morphology. F. armeniacum was previously reported in Minnesota on symptomless corn (2), but it has not been reported on soybean and its pathogenicity has not been established on any crop. To our knowledge, this is the first report of F. armeniacum as a pathogen on soybean in the United States. References: (1) K. E. Broders et al. Plant Dis. 91:727, 2007. (2) J. F. Leslie and B. A. Summerell. The Fusarium Laboratory Manual. Blackwell Publishing, Oxford, UK, 2006. (3) G. P. Munkvold and J. K. O'Mara. Plant Dis. 86:143, 2002. (4) K. O'Donnell et al. Proc. Natl. Acad. Sci. 95:2044, 1998.

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