Morphology, development and evolution of stromata/sclerotia and macroconidia of the Sclerotiniaceae

Willetts, H. J.

doi:10.1017/s0953756297003559

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“…It is expressed by four main types of sclerotia (compact bodies of aggregated hyphae), which are loose, terminal, lateral-chained and lateral-simple. These types are represented mainly, but not solely, by Rhizoctonia solani, Sclerotinia sclerotiorum, Sclerotium rolfsii and Sclerotinia minor, respectively (Chet et al, 1967(Chet et al, , 1969Chet & Henis, 1975;Le Tourneau, 1979;Willetts, 1971Willetts, , 1978Willetts, , 1997Willetts & Wong, 1980). These fungi are of great agricultural interest because they cause stem-rot diseases in a wide variety of economically important agricultural crops.…”

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Superoxide radical induces sclerotial differentiation in filamentous phytopathogenic fungi: a superoxide dismutase mimetics study

Papapostolou

Georgiou

2010

Microbiology

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This study shows that the superoxide radical (O 2˙" ), a direct indicator of oxidative stress, is involved in the differentiation of the phytopathogenic filamentous fungi Rhizoctonia solani, Sclerotinia sclerotiorum, Sclerotium rolfsii and Sclerotinia minor, shown by using superoxide dismutase (SOD) mimetics to decrease their sclerotial differentiation. The production rate of O 2˙" and SOD levels in these fungi, as expected, were significantly lowered by the SOD mimetics, with concomitant decrease of the indirect indicator of oxidative stress, lipid peroxidation. INTRODUCTIONSclerotial differentiation is a primitive form of differentiation exhibited by certain phytopathogenic filamentous fungi. It is expressed by four main types of sclerotia (compact bodies of aggregated hyphae), which are loose, terminal, lateral-chained and lateral-simple. These types are represented mainly, but not solely, by Rhizoctonia solani, Sclerotinia sclerotiorum, Sclerotium rolfsii and Sclerotinia minor, respectively (Chet et al., 1967(Chet et al., , 1969Chet & Henis, 1975;Le Tourneau, 1979;Willetts, 1971Willetts, , 1978Willetts, , 1997Willetts & Wong, 1980). These fungi are of great agricultural interest because they cause stem-rot diseases in a wide variety of economically important agricultural crops. Therefore, elucidating the mechanisms of sclerotium biogenesis of these fungi may lead to the development of non-toxic ways to combat plant diseases, which could be used as alternatives to the traditional toxic fungicides. Moreover, understanding sclerotial differentiation is very important because it will help to understand more complex forms of differentiation in other organisms as well as whether their mechanisms share common biochemical pathways.It has been proposed that sclerotial differentiation is related to high oxidative stress (Georgiou, 1997), based on the finding that sclerotium biogenesis in S. rolfsii was accompanied by the accumulation of high levels of lipid peroxidation products. This finding has been supported by other studies that developed into a theory of oxidative stress as an inducer of sclerotial metamorphosis (Georgiou et al., 2006). Specifically, hydroxyl radical scavengers, vitamin C and b-carotene (both also acting as endogenous fungal antioxidants), decreased sclerotial differentiation in S. rolfsii, S. minor, S. sclerotiorum and R. solani. In more recent studies, we demonstrated a strong relationship between the thiol redox state of these fungi and their sclerotial differentiation (Patsoukis & Georgiou, 2007a, b, 2008a. Specifically, in R. solani, S. rolfsii and S. minor, there was a decrease in the total amount of reduced thiols during transformation of the undifferentiated mycelium into sclerotium, which, for S. sclerotiorum was accompanied by an increase in the total oxidized components. Moreover, the antioxidant thiol redox state modulator N-acetylcysteine inhibited sclerotial differentiation in S. rolfsii, R. solani and S. sclerotiorum.Until now, our studies have associated only indirect indicators ...

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Superoxide radical induces sclerotial differentiation in filamentous phytopathogenic fungi: a superoxide dismutase mimetics study

Papapostolou

Georgiou

2010

Microbiology

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“…However, the sclerotial formation of the Botrytis isolates and the absence of sporulation when incubated in the dark, may lead to misidentification. Yet, sclerotial characteristics should be sufficient to distinct between the two genera (Willetts 1997), but when having less experience or in case of doubt, SDS-PAGE can be an easy tool to distinguish between Sclerotinia spp. and B. cinerea.…”

Section: Discussionmentioning

confidence: 99%

“…Sclerotia of B. cinerea are planoconvex and attached to the substrate, whereas the tuberoid sclerotia of Sclerotinia spp. are formed free of the substrate (Willetts 1997).…”

Section: Pathogen Isolationmentioning

confidence: 99%

Characterisation of fungal pathogens causing basal rot of lettuce in Belgian greenhouses

et al. 2008

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Basal rot is a common disease in lettuce greenhouses. A 3-year study on the diversity of pathogens associated with basal rot in Belgium was carried out. A total of 150 isolates were collected originating from 56 greenhouses. Four pathogens appeared to be involved. Rhizoctonia solani was found to be the causal agent at 23 locations, Sclerotinia spp. at 14, Botrytis cinerea at 17 and Pythium spp. at seven. The isolates of R. solani were further characterised to anastomosis groups and subgroups using morphological characteristics, pectic zymogram and PCR-RFLP. Five anastomosis groups could be distinguished: AG1-1B, AG4 HGI, AG10, AG2-1, AG2-1 Nt and AG3, with isolates of AG4 HGI and AG1-1B being the most prevalent and the most aggressive. Sclerotinia sclerotiorum was found at 13 locations, while S. minor was found at only one location. Based on ITS-sequencing Pythium isolates were assigned to three different species. At 20A degrees C, isolates of all pathogens were able to cause lesions on detached lettuce leaves, except isolates of R. solani AG3 and AG2-1 Nt. A correlation could be found between the occurrence of the pathogens and the growing season. Botrytis cinerea was the most common pathogen in winter, whereas R. solani was most frequently isolated in summer. Sclerotinia spp. and Pythium spp. were isolated in spring, summer and autumn. The information obtained in this study will be most useful in the development of an alternative control strategy for causal agents of basal rot

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“…The effect of light on sclerotium production was found to be complex and dependent on the growth medium. Light is not required for either the induction or maturation of sclerotia, but continuous irradiation of developing cultures with either white light or black light induces an endogenous rhythm whereby sclerotia are formed every 48 h. When exposed to alternating light/dark regimes mycelium that formed in the light does not mature sclerotia, but dark-formed mycelium does, even if it is subsequently exposed to light.Key Words glucose concentration; light; sclerotium-forming fungi; vitamins.Sclerotium-forming fungi are of great interest: firstly, because many such species are important plant pathogens (Willetts, 1978;Cooke, 1983;Willetts, 1997); and secondly, because these fungi can be used to study factors involved in controlling the transformation of normal vegetative hyphae into different physical and physiological forms (Cooke, 1983). Sclerotia are asexual, usually spherical bodies consisting of pseudoparenchymatous aggregations of hyphae, and in most cases they are resistant to unfavourable environmental conditions (Willetts, 1971).…”

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“…) de Bary (reviewed by Chet and Henis, 1975;Cooke, 1983;Willetts, 1978). As fungal sclerotia have probably evolved from a variety of asexual or sexual reproductive structures (Willetts, 1997;Willetts and Bullock, 1992), it is difficult to generalize concerning the conditions that might favour sclerotium production. In a more recent study of this fungus by Bowerman and Goos (1991 ), the effect on growth by physiological factors such as nutrition, temperature, and light were investigated, but not all problems were resolved.…”

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Factors influencing the production of sclerotia in the wild rice (Zizania aquatica) pathogen Sclerotium hydrophilum

Hausner

Reid

1999

Mycoscience

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Sclerotium hydrophilum was shown to be auxoheterotrophic for thiamine, with the addition of this vitamin being required for the induction of sclerotia on defined media, but riboflavin and pyridoxine also have a positive effect. In the absence of thiamine, an increase in glucose concentration lead to a decrease in the yield of sclerotia; however, the addition of thiamine negated this inhibition and, instead, as the glucose concentration increased a higher proportion of sclerotial initials matured. Overall it was found that thiamine, specifically the pyrimidine component of thiamine, is crucial for initiating sclerotium production, while glucose stimulates maturation. The effect of light on sclerotium production was found to be complex and dependent on the growth medium. Light is not required for either the induction or maturation of sclerotia, but continuous irradiation of developing cultures with either white light or black light induces an endogenous rhythm whereby sclerotia are formed every 48 h. When exposed to alternating light/dark regimes mycelium that formed in the light does not mature sclerotia, but dark-formed mycelium does, even if it is subsequently exposed to light.Key Words glucose concentration; light; sclerotium-forming fungi; vitamins.Sclerotium-forming fungi are of great interest: firstly, because many such species are important plant pathogens (Willetts, 1978;Cooke, 1983;Willetts, 1997); and secondly, because these fungi can be used to study factors involved in controlling the transformation of normal vegetative hyphae into different physical and physiological forms (Cooke, 1983). Sclerotia are asexual, usually spherical bodies consisting of pseudoparenchymatous aggregations of hyphae, and in most cases they are resistant to unfavourable environmental conditions (Willetts, 1971). Thus sclerotia are of great importance in the life cycle strategies of the organisms which produce them. Although the importance of sclerotia in the survival and dissemination of such fungi has long been recognized, the processes involved in their induction are still poorly understood (Georgiou, 1997).Under field conditions Sclerotium hydrophilum Sacc.has been implicated in both sheath and stem rots of Zizania aquatica L. (Punter et al., 1984). It has also been reported on Oryza sativa L. (Qu, 1972), Nymphaea odorata Aiton (Johnson et al., 1976; Bowerman and Goos, 1991), Myriophyllum spicatum L. (Lekic, 1971), and a wide range of both tropical and temperate macrophytes (reviewed in Punter et al., 1984). It has been suggested that it might be a potential candidate for biological control of undesirable aquatic plants: e.g., M.spicatum (Lekic, 1971 ).There is no published record that this fungus Present address: University of Calgary, Department of Biological Sciences, Calgary, Alberta, T2N 1N4, Canada (E-mail: hausner(~ucalgary.ca).produces an asexual or sexual spore state in culture or on its hosts, but it does produce small, black sclerotia on the vegetative mycelium on both agar and natural substrates. These scleroti...

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Morphology, development and evolution of stromata/sclerotia and macroconidia of the Sclerotiniaceae

Cited by 50 publications

References 64 publications

Superoxide radical induces sclerotial differentiation in filamentous phytopathogenic fungi: a superoxide dismutase mimetics study

Superoxide radical induces sclerotial differentiation in filamentous phytopathogenic fungi: a superoxide dismutase mimetics study

Characterisation of fungal pathogens causing basal rot of lettuce in Belgian greenhouses

Factors influencing the production of sclerotia in the wild rice (Zizania aquatica) pathogen Sclerotium hydrophilum

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