Myceliogenic Germination Of Sclerotia Research Articles

Mycosynthesis of Silver Nanoparticles Using Screened Trichoderma Isolates and Their Antifungal Activity against Sclerotinia sclerotiorum.

To control the disease caused by Sclerotinia sclerotiorum, a total of 15 isolates of the Trichoderma species was screened for the biosynthesis of silver nanoparticles (AgNPs). Among them, the highest yield occurred in the synthesis of AgNPs using a cell-free aqueous filtrate of T.virens HZA14 producing gliotoxin. The synthetic AgNPs were charactered by SEM, EDS, TEM, XRD, and FTIR. Electron microscopy studies revealed that the size of AgNPs ranged from 5–50 nm and had spherical and oval shapes with smooth surfaces. Prepared AgNPs interacted with protein, carbohydrate and heterocyclic compound molecules, and especially, interaction patterns of AgNPs with the gliotoxin molecule were proposed. The antifungal activity assays demonstrated that percentage inhibition of the prepared AgNPs was 100, 93.8 and 100% against hyphal growth, sclerotial formation, and myceliogenic germination of sclerotia at a concentration of 200 μg/mL, respectively. The direct interaction between nanoparticles and fungal cells, including AgNPs’ contact, accumulation, lamellar fragment production and micropore or fissure formation on fungal cell walls, was revealed by SEM and EDS. These will extend our understanding of the mechanisms of AgNPs’ action for preventing diversified fungal disease.

Antagonism of Trichoderma-based biofungicides against Brazilian and North American isolates of Sclerotinia sclerotiorum and growth promotion of soybean

The antagonistic activity of Trichoderma asperellum (aerial conidia) and T. harzianum (microsclerotia) Pers. (1801) (Hypocreales: Hypocreaceae) was evaluated against six isolates of Sclerotinia sclerotiorum (Lib.) de Bary (Helotiales: Sclerotiniaceae) from Brazil and the USA and further assessed for their enhancement of soybean growth. The fungicide thiophanate-methyl was included as a standard in all experiments. In vitro assay revealed that thiophanate-methyl and Trichoderma spp. effectively suppressed carpogenic and myceliogenic germination of sclerotia. The S. sclerotiorum isolates from Brazil appeared to be less susceptible than those from the USA to both chemical and biological treatments. The in vivo seed coating test using thiophanate-methyl or Trichoderma spp. substantially improved seed germination and suppressed growth of all S. sclerotiorum isolates to varying degrees. Moreover, soybean biomass of shoots and roots, and root nodulation were increased by either thiophanate-methyl or Trichoderma species. Collectively, these results underline the antagonistic activity of Trichoderma spp. against S. sclerotiorum isolates, the importance of Trichoderma spp. to improve soybean growth, and the bioactivity of Trichoderma microsclerotia through seed coating.

Stem rot disease incidence on faba beans in an artificially infested field

Stem rot, a destructive fungal disease caused by Sclerotinia trifoliorum Eriksson, is a serious problem for many important crops including faba beans (Vicia faba L.). Field experiments were carried out for five consecutive years in northern Greece to study the period of infection of S. Trifoliorum and the disease incidence in faba beans grown in a field that was artificially infested by placing various numbers of fungal sclerotia into the soil during the sowing period. Disease severity was very low (< 4%) in all growing seasons, whereas a high percentage of infection (13.3 to 95.0%) was observed under controlled environment. Apothecial production in the field occurred from November to early January. Symptoms of fungal infection on faba bean plants were observed from early February to early April, with the most infection occurring during March. Faba bean plants were infected by mycelium, after myceliogenic germination of sclerotia, at the base of the stem close to the soil surface. Visible, water-soaked lesions appeared before flower initiation. Disease severity was not significantly correlated with monthly rainfall (r = 0.11) nor with mean monthly temperature (r = 0.15) over five growing seasons. The growth stage of plants and the absence of an energy source during ascospore release, as well as the mode of sclerotial germination (myceliogenic), may have been the critical factors responsible for the low disease severity in the field.

Effect of temperature during sclerotial formation, sclerotial dryness, and relative humidity on myceliogenic germination of sclerotia of Sclerotinia sclerotiorum

A study was conducted to determine the effect of sclerotial dryness, temperature during sclerotia formation, and relative humiditiy during incubation on myceliogenic germination of sclerotia of two isolates of Sclerotinia sclerotiorum (Lib.) De Bary. In the absence of exogenous nutrients, sclerotia germinated more readily at 100% RH than at 95% RH or lower. Desiccation of sclerotia is an important factor affecting myceliogenic germination and hyphal growth. At high humidity, either in an atmosphere with 100% RH or on moist sand, desiccant-dried sclerotia germinated readily and produced vigorous hyphal growth that often developed into colonies. On the other hand, fresh, untreated sclerotia germinated less readily and produced limited growth of hyphae that rarely developed into colonies. There was generally no effect of temperature at which sclerotia formed on germination. The incidence of seed rot and seedling wilt of sunflower was significantly (p &lt; 0.05) higher when desiccant-dried sclerotia were used as inoculum rather than fresh sclerotia.Key words: Sclerotinia sclerotionum, sclerotia, myceliogenic germination, sclerotinia wilt of sunflower, relative humidity.

Comparative studies on myceliogenic germination of tan sclerotia of Sclerotinia sclerotiorum and Sclerotium rolfsii

Tan-colored sclerotia of Sclerotium rolfsii and of an aberrant strain of Sclerotinia sclerotiorum that were freshly harvested from 5-week-old cultures on potato dextrose agar or stored at room temperature in paper bags for 4 weeks germinated myceliogenically on moist field soil without exogenous nutrients. A comparative study by time-lapse photomicroscopy revealed similarity in the mode of myceliogenic germination of sclerotia of the two species. The germination appeared to be of the hyphal type in both species and was characterized by the emergence of individual hyphae through the rind. There was no evidence of eruptive type of germination in any of the strains tested. Although several hyphae often emerged through the same spot of the rind, these hyphae emerged singly, and the time-lapse photomicrographs showed no evidence of eruptive germination. While most of the germinated sclerotia of S. rolfsii developed into colonies within 4 days of incubation on moist soil, the development of colonies from germinating sclerotia of S. sclerotiorum appeared to be slow, taking up to 28 days. Results of the inoculation studies showed that mycelia from the germinated sclerotia of S. rolfsii were able to infect and cause seed rot and damping-off of canola and alfalfa, which were planted near the soil surface at a distance of at least 15 mm from the sclerotium, without providing exogenous nutrients.

Effect of temperature on melanization and myceliogenic germination of sclerotia of Sclerotinia sclerotiorum

While sclerotia of the normal strain of Sclerotinia sclerotiorum produced on potato-dextrose agar at 7, 16, and 30 °C were black, the color of sclerotia of the aberrant strain was light brown, brown or tan, and dark brown or greyish black under 7, 16, and 30 °C, respectively. In the normal strain, deposition of melanin substance was heavy both on the surface and inside the cell walls of the rind of black sclerotia formed at 16 and 30 °C, but in sclerotia formed at 7 °C, many of the rind cells were unmelanized or partially melanized. In sclerotia from the aberrant strain, an electron-dense material, smaller than the melanin particles of the black sclerotia, was present in trace amounts or absent in light-brown sclerotia formed at 7 °C, but it was more abundant in dark-brown or greyish black sclerotia formed at 30 °C. Despite marked differences in color, sclerotia of the aberrant strain produced at the three temperatures were capable of undergoing myceliogenic germination on moist sand. It is concluded that temperature affects cell wall melanization during sclerotial morphogenesis, and that myceliogenic germination of sclerotia of S. sclerotiorum was affected by the black pigment but was unaffected by the color intensity of the brown pigment.

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.