Gloria Innocenti

Antagonistic activity of xylotrophic mushrooms against pathogenic fungi of cereals in dual culture

The antagonistic activity of 17 species of xylotrophic Basidiomycotina (Coriolus versicolor, Flammulina velutipes, Ganoderma lucidum, Hypholoma fasciculare, H. sublateritium, Kuhneromyces mutabilis, Lentinula edodes, Lentinus tigrinus, Pholiota alnicola, Ph. aurivella, Ph. destruens, Pleurotus ostreatus, P. cornucopiae, Polyporus squamosus, P. subarcularius, P. varius and Schizophyllum commune) against 4 fungi (Bipolaris sorokiniana, Fusarium culmorum, Gaeumannomyces graminis var. tritici and Rhizoctonia cerealis), responsible for foot and root diseases of winter cereals, were tested in dual-culture experiments on potato-dextrose agar. Almost all tested mushroom species markedly inhibited mycelial growth of the four phytopathogenic fungi, antagonistic activity of P. ostreatus, H. fasciculare, G. lucidum, L. tigrinus and S. commune being particularly strong. Inhibiting activity mainly comprised two reactions: deadlock, consisting in mutual inhibition at a distance or at mycelial contact, and replacement, consisting in initial deadlock followed by partial or complete overgrowth.

Effects of Collembola on plant-pathogenic fungus interactions in simple experimental systems

Abstract Take-all and brown foot rot, caused respectively by Gaeumannomyces graminis var. tritici and Fusarium culmorum, are two important components of the foot and root fungal disease complex of winter cereals world-wide. These fungi persist in soil and in crop debris in the same layer of agricultural soil as Collembola, a well represented taxon of soil animals. Previous in vitro tests showed that these fungi grown on agarised medium were readily consumed by springtails. In a simplified experimental system with wheat plants and the pathogenic fungi grown on millet and wheat kernels, the severity of disease was significantly reduced by collembolan feeding activity.

Functional relationships between Collembola and plant pathogenic fungi of agricultural soils

Summary The interactions between the collembolan Mesaphorura krausbaueri and four soilborne plant pathogenic fungi all living in the same layer of agricultural soil were studied under laboratory conditions. Mycelia of Gaeumannomyces graminis var. tritici, Fusarium culmorum and Rhizoctonia cerealis were palatable to Collembola and were a food source adequate for reproduction. Hyphae of Bipolaris sorokiniana were toxic and repellent for M. krausbaueri , but its conidia were eaten and proved to be a sufficient diet for reproduction. The four fungi fed had a different impact on the life processes of M. krausbaueri. Depending on the species of fungus, the animals produced significantly different numbers of eggs and had different life spans. In particular, animals fed with G. graminis var. tritici showed early maturation, early burst in egg production, early loss of fertility and early death. The different nutritional values of the four fungi pathogen for cereals might have a different influence on the life strategy of Collembola in the field. Thus, since these fungi usually coexist in agricultural soils, though in different percentages, this influence might also affect the capacity of different fungi to attack the plant and thus modulate the appearance of disease.

Efficacy of microorganisms antagonistic to Rhizoctonia cerealis and their cell wall degrading enzymatic activities

The effect of Trichoderma atroviride, T. harzianum, T. longibrachiatum, Clonostachys rosea and Bacillus subtilis isolates applied to wheat seeds against Rhizoctonia cerealis disease of seedlings was investigated under controlled greenhouse conditions. Most Trichoderma isolates significantly reduced the incidence of disease compared with the infected control. Bacillus subtilis was also effective against sharp eyespot, although less active than Trichoderma spp. Interactions between the antagonistic microorganisms and the cereal pathogenic fungus in dual culture experiments on agar growth medium were also studied. Almost all tested antagonists showed competitive activity against R. cerealis: inhibition of its mycelial growth and hyphal interaction. The production of extracellular beta-N-acetylhexosaminidase, chitin 1,4-beta-chitobiosidase, glucan 1,3-beta-glucosidase and protease activity by the tested microorganisms in the presence of cell walls of R. cerealis was then determined. All isolates showed glucosaminidase and chitobiosidase activity. They also produced glucosidase activity, except B. subtilis, whereas only C. rosea, B. subtilis and one isolate of T. harzianum showed detectable levels of protease activity.

Soil-borne plant pathogenic fungi in relation to some collembolan species under laboratory conditions

Interactions between springtails (Onychiurus armatus, O. tuberculatus, Folsomia candida) and plant pathogenic fungi (Gaeumannomyces graminis var. tritici, Fusarium culmorum, Bipolaris sorokiniana and Rhizoctonia cerealis) living in the same soil layer were investigated under laboratory conditions. The fungi are responsible for the foot and root disease complex of winter cereals and can cause serious reduction in yield. Since these species coexist in agricultural soils, feeding preference tests were performed in such a way that the springtails were allowed to interact simultaneously with all the tested fungi. O. armatus, O. tuberculatus and F. candida fed on the mycelia of G. graminis var. tritici, F. culmorum and R. cerealis: in the first hours of the trials individuals of all springtail species distributed themselves among the colonies, though moving from one to the other. Subsequently F. culmorum mycelium became the preferred food of all species tested; however, the other two fungi continued to be consumed. Mycelia of G. graminis var. tritici, F. culmorum and R. cerealis were shown to be an adequate food source for reproduction of Folsomia candida. Bipolaris sorokiniana mycelium had both repellent and lethal effects on F. candida and O. armatus, whereas this fungus was lethal, although not repellent, for O. tuberculatus. Long-term experiments on F. candida indicate that conidia of B. sorokiniana were eaten and proved to be a sufficient diet for reproduction.

An environmentally sustainable approach for the management of Phaeoacremonium minimum, the main agent of wood diseases in Actinidia deliciosa

Among the fungi associated with the kiwi wood diseases, the vascular pathogen Phaeoacremonium minimum can infect plants already at nursery stage, without any external symptoms. At the moment, there are not effective control strategies. The effect of soil treatments applicable in organic agriculture was evaluated in two-years experiments on potted kiwi plants artificially inoculated with P. minimum. The soil treatments were based on commercial formulations of iron chelate, silicon, neem paste, Trichoderma afroharzianum strain T22, and cover cropping with selected perennial Poaceae. Cover cropping and iron chelate treatments enhanced the iron availability for the plants and significantly reduced wood necrosis caused by the pathogen. Both treatments also produced an increase of hairy root proliferation, so the plants were able to better cope with stress conditions. Laboratory assays showed the role of iron on the pathogen growth and its pathogenesis enzyme activities.

Epidemiological Investigations Shed Light on the Ecological Role of the Endophyte Phomopsis quercina in Mediterranean Oak Forests

Findings of a study extending over a number of years on some key aspects of the biology and ecology of Phomopsis quercina in Mediterranean oak forests are reported. The main biometric parameters and physiological requirements of this significant endophytic fungus were determined in the laboratory. The microorganism was also studied in the field to explore its lifestyle in natural oak stands. The isolation frequencies of the fungus in various oak species were also related to the vitality of the trees (healthy or declining) and this showed that the fungus is involved in the widespread phenomenon of oak decline. In planta studies have proved the pathogenic activity of P. quercina in oak, and have found that it remains latent for a long time in the inner wood of oaks, but may turn into an aggressive and harmful coloniser of the tree if this is weakened by some stress factors. An important part of the study concerns an examination of the antagonism that some other endophytes, which colonise the same oak tissues and organs as P. quercina, display against this fungus. The increasing presence and abundance of P. quercina in declining (and especially drought-stressed) oaks suggests that climate change is having a significant role in destabilising the precarious balance between the host tree and the fungus, to the benefit of the latter. Lastly, some practical suggestions are offered on ways to counter the epidemic spread of this latent pathogen.