Dormant Mycelium Research Articles

Prvi nalaz teleomorfnog stadijuma prouzrokovača sive pegavosti lista i klasa pšenice Leptosphaeria nodorum u Srbiji

Parastagonospora nodorum (teleomorph Leptosphaeria nodorum) is the causal agent of septoria nodorum blotch (SNB). It was first discovered on wheat in 1845. and is common in regions with relatively high or periodically high rainfall. P. nodorum causes symptoms on all above-ground parts of the plant, including leaves, stems, glumes, and awns. The pathogen overwinters on wheat crop residues in the form of pseudothecia and pycnidia. Ascospores released from pseudothecia typically serve as the primary source of inoculum, but conidia released from pycnidia on crop residues can also infect seedlings. Additionally, the fungus is known to survive on seeds in the form of dormant mycelium, making infected seeds a potential source of primary infection. During the 2022/2023 growing season, precipitation totals in April (63.9 mm) and May (124.8 mm) exceeded seventeen-year averages, creating conditions conducive to occurence of SNB. Microscopic examination of lesions on leaves of wheat variety revealed the presence of the sexual stage (L. nodorum) for the first time in Serbia. The asexual stage (P. nodorum) was observed on infected ears of different varieties. This study highlights the need for more attention in monitoring conditions that could lead to outbreak SNB in wheat production areas in Serbia.

Quantification and conceptual validation of the inoculum potential of Sclerotinia sclerotiorum in soybean and bean seeds

Abstract: The fungus Sclerotinia sclerotiorum, the causal agent of white mold, is widespread throughout the world. The disease is considered to be one of the major diseases of soybean and bean crops in Brazil. The pathogen S. sclerotiorum is spread by soybean and bean seeds both in the form of sclerotia and dormant mycelium inside the seeds. The objective of this work was to evaluate the relationship between different potentials of S. sclerotiorum in soybean and bean seeds and the performance of these seeds, as well as to verify the localization and quantification of the inoculum of the pathogen in the seeds inoculated by Real-time PCR (qPCR), validating the term inoculum potential. Soybean and bean seeds were inoculated with the fungus by the osmotic conditioning method based on the exposure of the seeds to the fungus for periods of 24 h, 48 h, 72 h, and 96 h. Molecular analysis was carried out by means of qPCR in whole seeds and dissected in the integument, cotyledon and embryonic axis. The results showed that the effects of S. sclerotiorum on seed germination and vigor were progressive and proportional to the increases in inoculum potentials, since there was more severe damage to the seeds and consequently to the emerged plants at the highest potential (P96). The inoculum of the pathogen was found in all parts of the evaluated seeds, even at its lowest inoculum potential (P24), with an increasing DNA concentration, and the integument obtained a greater amount of DNA than the embryo, in comparison.

Sporangiospore Viability and Oospore Production in the Spinach Downy Mildew Pathogen, Peronospora effusa.

Downy mildew of spinach, caused by the obligate pathogen Peronospora effusa, remains the most important constraint in the major spinach production areas in the United States. This disease can potentially be initiated by asexual sporangiospores via "green bridges", sexually derived oospores from seed or soil, or dormant mycelium. However, the relative importance of the various types of primary inoculum is not well known. The ability of P. effusa sporangiospores to withstand abiotic stress, such as desiccation, and remain viable during short- and long-distance dispersal and the ability of oospores to germinate and infect seedlings remain unclear. Thus, the primary objectives of this research were to evaluate the impact of desiccation on sporangiospore survival and infection efficiency and examine occurrence, production, and germination of oospores. Results indicate that desiccation significantly reduces sporangiospore viability as well as infection potential. Leaf wetness duration of 4 h was needed for disease establishment by spinach downy mildew sporangiospores. Oospores were observed in leaves of numerous commercial spinach cultivars grown in California in 2018 and Arizona in 2019. Frequency of occurrence varied between the two states-years. The presence of opposite mating types in spinach production areas in the United States was demonstrated by pairing isolates in controlled crosses and producing oospores on detached leaves as well as intact plants. Information from the study of variables that affect sporangiospore viability and oospore production will help in improving our understanding of the epidemiology of this important pathogen, which has implications for management of spinach downy mildew.

Response of tomato seedlings inoculated with mycorrhizal fungi on the photosynthetic activity, growth, and health status of plants after infection with the fungus Colletotrichum coccodes

The aim of this study was to estimate the effect of mycorrhizal fungi (MF) on the photosynthetic activity, growth, and health status of tomato seedlings (‘Pelikan F<sub>1</sub>’) infected with the pathogenic fungus <em>Colletotrichum coccodes</em>. A commercial mycorrhizal inoculum (Mycoflor, Poland) containing spores and dormant mycelium of MF was used in the experiment. It was carried out in a growth chamber where 1-week-old seedlings were inoculated with 3 mL of mycorrhizal inoculum applied into the soil. Three-week old mycorrhized and nonmycorrhized tomato seedlings were infected with the pathogenic fungus. Seedlings planted in sterile horticultural soil without the mycorrhizal inoculum constituted an absolute control. The growth, disease index, and photosynthetic activity of the plants were measured after 4 weeks. There was no significant effect of the mycorrhiza on the photosynthetic parameters analyzed. However, it was noted that the mycorrhized and pathogen-infected seedlings had higher maximum quantum yield of PSII (F<sub>v</sub>/F<sub>m</sub>), higher effective quantum yield (Y) and more favorable photochemical (qP) and nonphotochemical fluorescence quenching (qN) coefficients than did the pathogen-infected seedlings. The experiment showed that the mycorrhizal commercial inoculum had varied effects on the health status of tomato seedlings depending on the pathogenic fungus isolate. Mycorrhiza did not have a significant effect on the length of roots and stems, whereas the roots inoculated with MF were better developed than those infected with the pathogenic fungus. It can be assumed also that not only the pathogen but also the mycorrhiza is a stress factor towards the seedlings and affects the growth performance parameters mentioned above.

Inhibitory influence of biocontrol agents, plant oils and an inorganic salt on Mycosphaerella fijiensis and Cordana musae, the causal pathogen of black sigatoka and leaf spot of banana

The search for alternatives to chemical treatments to control the causal pathogens of black sigatoka and Cordana leaf spot in banana was studied in vitro. We examined the effect of biocontrol agents, plant oils, and an inorganic salt on the mycelium growth ofMycosphaerella fijiensis and Cordana musae for 10 weeks. Trichoderma harzianumDGA01 and Bacillus amyloliquefaciens DG14 inhibited the development of M. fijiensisthroughout the duration of observation while Serenade ASO (Bacillus subtilis 1.34% EC) gave total control for six weeks. Piper betel oil (2.5% EC), garlic oil (15% EC), capsicum oil (20% EC) were not successful in killing dormant mycelium but do cause significant delay in development of M. fijiensis by 37, 9, and 43%, respectively. Potassium bicarbonate (14% EC) restricted the growth of M. fijiensis by 43%. Meanwhile, T. harzianum DGA01, B. amyloliquefaciens DG14, and Serenade ASO sustained total control of mycelium development of C. musae in 10 weeks while piper betel oil had only limited the mycelium growth by 60%, garlic oil and capsicum oil by 20%, and potassium bicarbonate by 28%. Key words: Banana, biocontrol agent, inorganic salt, plant oil, black sigatoka, Cordana leaf spo

Detection of Ustilago nuda (Jensen) Rostrup in winter barley seed

Barley is one of the most important cereals grown in our agroecological conditions. The causal agent of loose smut on barley Ustilago nuda (Jensen) Rostrup occurs frequently as varieties susceptible to this pathogen are present in the production. Disease symptoms are manifested on barley head (spike). Parasite is transmitted by seed (seedborne) and stays in the embryo tissue of the infected kernel as dormant mycelium. Recommended method for detection of U. nuda is given by ISTA Rules (method 7-013). In tests, nine samples (weighing 120 g each) of naturally infected barley seed (about 1000 seeds, depending on the absolute mass of seed) were examined, observed and described using a Zeiss microscope with sub stage illumination with magnification range x 40 or higher. Mycelium of the fungus approximately 3 μ thick, golden brown in colour was detected and visible without a stain. The percentage of infected embryos in the examined samples of barley seeds ranged from 0.8% to 5.2%.

The Role of White Mold‐Infected White Bean (Phaseolus vulgaris L.) Seeds in the Dissemination of Sclerotinia sclerotiorum (Lib.) de Bary

Abstract Sclerotinia sclerotiorum survived in infected seeds of white beans as dormant mycelium in testa and cotyledons. The rate of survival averaged 85 to 89% and did not change appreciably over a 3‐year period. When the infected bean seeds were sown in soil or sand, 88 to 100% failed to germinate. The seeds that failed to germinate, depending on the severity of seed infection, were rotted by S. sclerotiorum. In place of each seed, 3 to 6 sclerotia were formed. A low percentage of these sclerotia germinated carpogenically with or without preconditioning, (2.5 and 11.5% respectively). Myceliogenic germination of sclerotia with and without preconditioning was 35.5% and 70.5% on water agar and 81.0% and 93.0% on glucose agar, respectively. Both, preconditioning and nonpreconditioned sclerotia which were scattered on soil surface could germinate myceliogenically and infect bean leaves by contact. It is therefore, concluded that dormant mycelia in the infected seeds play an important role notonly in dissemination of the fungus but also in epidemiology of the disease.

Phaeoisariopsis griseola . [Descriptions of Fungi and Bacteria

Abstract A description is provided for Phaeoisariopsis griseola . Information is included on the disease caused by the organism, its transmission, geographical distribution, and hosts. HOSTS: Members of the Leguminosae including Desmodium cephalotus, D. gangeticum, D. pulchellum, Dolichos lablab, Phaseolus acutifolius, P. angularis, P. calcaratus, P. coccineus, P. lunatus, P. mungo, P. vulgaris , and also Hibiscus esculentus [Abelmoschus esculentus] (Malvaceae). DISEASE: Angular leaf spot of beans, including development of pod lesions. GEOGRAPHICAL DISTRIBUTION: Africa (Angola, Congo, Ethiopia, Ghana, Ivory Coast, Kenya, Malagasy Republic, Malawi, Mauritius, Mozambique, Nigeria, Reunion, Senegal, Sierra Leone, Somalia, South Africa (Natal), Sudan, Tanzania, Uganda, Zambia, Zimbabwe), Asia (Bhutan, China (Xunnan, Jiangsu, Guangxi), India (Kerala, Mysore, Tamil Nadu, Uttar Pradesh), Indonesia (Irian Jaya), Iran, Israel, Japan, Korea, Laos, Malaysia (West, Sabah, Sarawak), Nepal, Philippines, Taiwan, Thailand, Turkey, U.S.S.R. (Caucasus, Republic of Georgia, Krasnodar)), Australasia & Oceania (Australia (NSW, Qd, Vic.), Fiji, Hawaii, New Caledonia, New Zealand, Norfolk Island, Solomon Islands, Papua New Guinea), Europe (Bulgaria, Greece, Irish Republic, Italy, Netherlands, Poland, Portugal, Rumania, Sardinia, Spain, Switzerland, Yugoslavia), North America (Mexico, U.S.A. (Connecticut, Delaware, Florida, Georgia, ME, MD, Maine, North Carolina, New Hampshire, New York, Oklahoma, South Carolina, Texas, Virginia, Wisconsin)), Central America & West Indies (Antilles, Cuba, Dominican Republic, Guatemala, Haiti, Jamaica, Nicaragua, Panama, Puerto Rico, Salvador, Trinidad & Tobago), South America & Southern Atlantic (Argentina, Brazil (Minas Gerais), Colombia, Paraguay, Peru, St Helena, Surinam, Venezuela). TRANSMISSION: From plant litter from previous years crop (57, 2704); Only a small number (< 2%) of seeds from a diseased crop were infected (60, 4739); Epidemiology (64, 3238). Conidia in plant debris remain viable for 8 months in the field whereas dormant mycelium in the seeds remains viable for > 1 year (60, 2314).

Summer and winter survival of Puccinia Recondita and infection by soilborne urediniospores

Emerging wheat seedlings readily trapped urediniospores of Puccinia recondita from soil or host plant debris. Soilborne spores survived simulated summer temp, of 34/22 °C day/night for up to 22 d on moist soil, 13 d on dry soil and 4–7 d when covered with a 5 mm layer of soil. Trapped spores survived 8 d on dry leaves at 34/22°. Spores in pustules on excised leaves placed on soil during simulated summer (30–33°) conditions survived up to 15 d. Spores floating on flood waters were able to cause infection when brought in contact with partially submerged host leaves. Dormant mycelium survived all conditions that host tissue was capable of surviving. Changes from 21 to +1, 0 or −1° caused host tissues to remain chlorotic and, in some cases, dormant mycelium was able to sporulate, but reduction to −4° caused host tissues to become necrotic, prohibiting sporulation.

Epidemiological aspects of Didymella bryoniae, the cause of stem and fruit rot of cucumber

The survival ofDidymella bryoniae and the incidence of ascospores in glasshouses, outdoors and under controlled conditions were studied. The fungus was able to overwinter in the open as dormant mycelium. Dry and undecomposed crop residues remained a source of infection for more than one year. Moisture and a minimum temperature between 5 and 10°C were needed for fructification. For ascospore release a high relative humidity was not sufficient, the substrate had to be moist during a short period. Ascospores could be trapped throughout day and night both outdoors and in glasshouses, but there was a marked peak during a period of 3 h in the evening. Both on days with and without rain about the same numbers of ascospores were trapped from crop residues in the open. Ascospore release was favoured by watering the plants in the glasshouse. Under controlled conditions the release of ascospores was determined by humidity and not by light or darkness.

Peronospora sparsa . [Descriptions of Fungi and Bacteria

Abstract A description is provided for Peronospora sparsa . Information is included on the disease caused by the organism, its transmission, geographical distribution, and hosts. HOSTS: Cultivated roses and the following species, Rosa californica, R. centifolia, R. canina, R. chinensis, R. rubiginosa . DISEASE: Downy mildew of rose. Bright red to purple or, less frequently, brown spots develop on the leaves which fall very readily especially if the bushes are shaken gently. A non-parasitic defoliation of unknown origin termed a 'false mildew' has been reported from France (Tramier, 1962). The necrotic spots formed on the leaves are similar at a certain stage to those caused by P. sparsa . Conidiophores and conidia develop on the under surface of the downy mildew spots in high relative humidity. In Europe their production is sparse but in California it is reported as copious (Baker, 1953). In heavy infections stems and flowers (both calyx and petals) become diseased and badly infected and young stems often die back. Flowers and flower buds can be retarded and malformed by the pathogen without visible damage to the leaves (53, 3523). GEOGRAPHICAL DISTRIBUTION: Africa (Egypt, Morocco, S. Africa, Zimbabwe); Asia (Brunei, Iran, Israel, Japan, Mauritius, Philippines); Australasia (Australia, New Zealand); Europe (Austria, Britain (incl. Jersey), Bulgaria, Czechoslovakia, Estonia, France, Germany, Greece, Iceland, Italy, Latvia, Netherlands, Portugal, Poland, Romania, Sweden, Switzerland, Yugoslavia, USSR); N. America (Canada, USA); S. America (Argentina, Brazil). TRANSMISSION: As dormant mycelium in cuttings and plants. It is reported that mycelium can overwinter within infected stems both from warmer countries such as Australia (57, 2154) and Brazil (19, 98) and also from Northern Europe (53, 3523). The role of oospores in disease transmission is less certain. They have been found in leaves and stems (Baker, 1953; Fraymouth, 1956) and flowers (Cuboni, 1888) but their occurrence seems to be sporadic and they do not appear to be of great importance in carrying over the pathogen. The possibility that the disease may be seed borne was suggested by a worker in Poland (7, 325). In 1926 downy mildew was discovered in a commercial nursery near Lublin on one-year-old seedlings of Rosa canina . The seedlings had been raised from seed imported from Vienna and the inference was that the disease came with the seed especially as all seedlings of local origin were healthy. Peronospora sparsa is not listed as a seed pathogen by Neergaard (1977).

Sclerospora graminicola in pearl millet seeds and its transmission

Sclerospora graminicola (Sacc.) Schroet. inoculum may be present in pearl millet seed either as oospores externally or in the form of dormant mycelium internally. Oospore inoculum was detected by using the washing method, and mycelial infection by the modified embryo count procedure. Fifty-nine seed samples out of ninety-three obtained from different sources were found contaminated with oospores whose viability was checked by the tetrazolium test. Percentage of viable spores ranged from 5.5 to 20.2. Forty-three samples showed mycelial infection of 0.1–7.5 Per cent in various parts of the seed. Seeds from healthy-looking plants are not necessarily pathogen-free. Transmission was obtained from a two-year-old seed sample contaminated with oospores and from mycelium. The significance of the results with particular reference to survival of inocula, development of epidemics and quarantine implications in international movement of germplasm are discussed.

Infection of seed of subterranean clover and allied species by species of Fusarium

Fusarium avenaceurn (Corda ex Fr.) Sacc. was shown for the first time to be carried in the hilum of subterranean clover (Trifolium Subterraneum L.) seed. Scanning electron microscopy and thin-section techniques showed that the fungus occurred only as dormant mycelium in parenchyma cells of funicle scar tissue. It emerged from these tissues after a 12 h incubation at 24�C and in 48 h penetrated internal parts of the seed through the hilum fissure. After 21 days on moist blotting paper, seedlings grown from infected seed developed lesions on their roots similar to those of root-rot of subterranean clover in the field. Fusarium spp. were also detected in the hilum of seeds of white (T. repens L.) and strawberry (T. fragiferum L.) clover and barrel medic (M. truncatula L.). It was demonstrated experimentally that all parts of the burr, incl~tding the funicle, became infected with F. avenaceuni when subterranean clover plants grown from healthy seed in pasteurized soil buried their burrs in soil inoculated with the fungus. Use of optical brighteners failed to trace seed infection because the compounds, although absorbed by the pathogen in culture, were not translocated.

Venturia saliciperda . [Descriptions of Fungi and Bacteria

Abstract A description is provided for Venturia saliciperda . Information is included on the disease caused by the organism, its transmission, geographical distribution, and hosts. HOST: On Salix spp. DISEASE: Willow scab. GEOGRAPHICAL DISTRIBUTION: Canada, Europe, USA. TRANSMISSION: By air-borne conidia. The fungus overwinters by dormant mycelium in pustules on twigs and releases air-borne conidia in spring which infect young growth. Secondary infection may occur by conidia dispersed during summer.

Leptosphaeria maculans . [Descriptions of Fungi and Bacteria

Abstract A description is provided for Leptosphaeria maculans . Information is included on the disease caused by the organism, its transmission, geographical distribution, and hosts. HOSTS: On Brassica spp. ; Brassica oleracea, B. rapa and B. napobrassica and other Cruciferae . DISEASE: Variously known as canker, dry rot and black leg, mainly of Brassica oleracea, B. rapa and B. napobrassica . Several cruciferous genera are attacked. The first symptoms are seen on seedlings as pale lesions on the stem, cotyledons and first true leaves. These become greyish with the pycnidia developing in their centres. On older plants in the field lesions on the leaves and other above-ground parts often have purplish margins. The stem, root and bulb are attacked causing necrotic, girdling cankers and transverse splits; severe infection of stem or root leads to wilt or the plant toppling over. Pycnidia develop abundantly on all infected areas. The perfect state has been reported from Australia, Canada, England and the Republic of Ireland (44, 65; 45, 1568; 48, 51). GEOGRAPHICAL DISTRIBUTION: Widespread but mostly in temperate regions (CMI Map 73 ed. 3, 1969). Records not yet mapped are: Australia (NT), Brazil, Costa Rica, Salvador, USSR (Ukraine). TRANSMISSION: The seed is invaded, dormant mycelium forming beneath the seed coat (11: 489; 19: 58). A recent survey in Denmark (48, 2641) showed seed of B. oleracea var. capitata to be most frequently infected and a longevity of 3 yr 8 months reported. From New Zealand a longevity of 14 months was found (39: 200). Seed treatment for control of conidial infection has led to the recognition that the disease may also be introduced by air-borne ascospores from host debris (42: 62; 49, 1822; 50, 2027). A persistence of 3 yr in soil organic matter can occur (9: 218; 29: 448).

Ustilago nuda . [Descriptions of Fungi and Bacteria

Abstract A description is provided for Ustilago nuda . Information is included on the disease caused by the organism, its transmission, geographical distribution, and hosts. HOSTS: On species of Agropyron, Hordeum, Lolium, Secale and Triticum . DISEASES: Loose smut of wheat, barley, oats and rye, characterized by the complete destruction of the spikelets of affected heads. Infected seed may be reduced in size and lighter. GEOGRAPHICAL DISTRIBUTION: World-wide (CMI Map 368, ed. 2, 1969). TRANSMISSION: By air-borne spores from smutted spikes to healthy flowers up to 150 m from a point source (19: 334; 44, 2114a) and by seed-borne dormant mycelium in the embryo, chiefly the scutellum (40: 41). Infection is favoured by frequent light showers but heavy rainfall reduces infection by washing spores into the ground (42: 193; 49, 1322). Spores are normally short-lived but many remain viable after 12-13 yr storage at -2-0<Degrees>C (34: 591).

Sphaerotheca macularis . [Descriptions of Fungi and Bacteria

Abstract A description is provided for Sphaerotheca macularis . Information is included on the disease caused by the organism, its transmission, geographical distribution, and hosts. HOSTS: On Humulus lupulus and many other plants, e.g. Fragaria vesca , especially in the Rosaceae (Junell, 1967; Blumer, 1967; Dennis, 1960). The fungus usually occurs in the conidial state on leaves and stems, sometimes also on sepals and fruits. DISEASE: Hop and strawberry mildew. Mostly infecting nursery plants. GEOGRAPHICAL DISTRIBUTION: World wide on Fragaria spp. and Humulus spp. TRANSMISSION: New infection in spring (usually May) comes from dormant mycelium in the leaves (41: 161; 45: 1443).

Studies on Tolyposporium Ehrenbergii the Cause of Long Smut of Sorghum in Egypt (U.A.R.)

The fungus Tolyposporium ehrenbergii infects its host by means of a dormant mycelium in the grain, spores lying in the soil, or air-borne sporidia. This study refutes the long-accepted belief that ...

Studies on Tolyposporium ehrenbergii the Cause of Long Smut of Sorghum in Egypt (U.A.R.)

SUMMARYThe fungus Tolyposporium ehrenbergii infects its host by means of a dormant mycelium in the grain, spores lying in the soil, or air-borne sporidia. This study refutes the long-accepted belief that long smut infection of sorghum in nature results only from air-borne sporidia. This is probably the first report of a dormant mycelium in T. ehrenbergii.

OBSERVATIONS ON CEREAL EMBRYOS IN RELATION TO THE "EMBRYO TEST" FOR LOOSE SMUTS

The embryos of wheat, barley, oats, and rye may be distinguished readily by differences in the shape of the scutella and by the relative sizes of the root initials. Photomicrographs of transverse sections of a wheat embryo show that the embryonic leaves within the coleoptile are arranged alternately, the first one facing towards the scutellum. Their edges are curled around the growing point and meet on the opposite side of the cavity in the coleoptile. A structure, referred to as a "pad", covers the side of the embryo facing the endosperm.Abnormalities found in whole barley embryos include the dormant mycelium of loose smut which appears as brown threads mainly in the surface tissues of the scutellum. Frost, occurring during the later development of the kernel, causes a stunting of the embryo, particularly of the coleoptile, and the production of small particles of yellowish-brown pigment in the tissues of the embryo. Other abnormalities are figured and discussed.