Roberta Roberti

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.

Activities of Aureobasidium pullulans cell filtrates against Monilinia laxa of peaches

The Aureobasidium pullulans L1 and L8 strains are known as efficient biocontrol agents against several postharvest fungal pathogens. In order to better understand the mechanism of action underneath the antifungal activity of L1 and L8 strains, yeast cell filtrates grown at different times were evaluated in vivo against Monilinia laxa on peach. Lesion diameters on peach fruit were reduced by L1 and L8 culture filtrates of 42.5% and 67% respectively. The ability of these filtrates to inhibit M. laxa conidia germination and germ tube elongation was studied by in vitro assays. The results showed a 70% reduction of conidia germination for both strains while for germ tube elongation, it was 52% and 41% for L1 and L8 culture filtrates respectively. Finally, the activity of cell wall hydrolytic enzymes such as chitinase and glucanase in cell filtrates was analysed and the expression of genes encoding these activities was quantified during yeast growth. From 24h onward, both culture filtrates contained β,1-3,glucanase and. chitinase activities, the most pronounced of which was N-β-acetylglucosaminidase. Gene expression level encoding for these enzymes in L1 and L8 varied according to the strain. These results indicate that L1 and L8 strains culture filtrates retain the yeast antagonistic activity and suggest that the production of hydrolytic enzymes plays an important role in this activity.

Physiological responses of grapevines to biodynamic management

A 3-year (2011–2013) field trial was carried out in a mature vineyard ( Vitis vinifera L., cv. Sangiovese), planted in 2003, to assess physiological responses of grapevines to biodynamic management. Starting in 2007, the vineyard was managed with organic production protocols in accordance with EC Regulations (834/2007). In 2008, the vineyard (2 ha) was divided in two large plots, with each plot having similar soil physico-chemical properties. One of the plots was managed with organic protocols per EC Regulations and the other with biodynamic practices, consisting of spray application of preparations 500, 500 K, fladen and 501. During the 2011–2013 season, the biodynamic preparations were used at least twice per year, with the exception of 501 that was applied only once in 2013. Concentration of hormones and mineral elements in biodynamic preparations were determined. Biodynamically managed vines showed lower stomatal conductance in all years and lower leaf water potential in 2012. Leaf photosynthetic activity was not influenced by cultivation method. Biodynamic management led to an increase in leaf enzymatic activities of endochitinase (EC 3.2.1.14), exochitinase (β -N- acetylhexosaminidase, EC 3.2.1.52 and chitin 1,4-β-chitobiosidase) and β-1,3-glucanase (EC 3.2.1.39), which are typically correlated with plant biotic and abiotic stresses and associated with induced plant resistance. Year effects were observed with 1,3-β-glucanase, whose activity in 2012 was 4.1-fold higher than in 2013. Disease incidence and grape yields were not different between organic and biodynamic treatments. This study provided a strong indication of a stimulation of natural defense compounds in grapes grown under biodynamic cultivation, but subsequent effects on plant protection and productivity require further evaluation.

Studies on the potential role of root exudates in the interaction between musk melon roots and Fusarium oxysporum f. sp. melonis

The interactions of resistant (Bingo, Giusto, Sweetness) and susceptible (Cantalupo di Charantais, Harper, Retato degli Ortolani) muskmelon cultivars with Fusarium oxysporum f. sp. melonis races 0, 1, 2 (FOM0, FOM1, FOM2) were studied through the effects of root exudates (REs), released by 14 and 21 days old hydroponic plantlets, on the percentage of germinated conidia. REs caused a moderate promotion or inhibition of conidial germination or did not cause any effect. The observed patterns mostly depended on pathogen race, plant cultivar and plant age: among the races, only FOM2 conidial germination was reduced by almost all REs but never totally; among the cultivars, none affected FOM0 conidial germination at any plant age. FOM1 conidial germination was either not affected or enhanced, depending on plant age. REs from Bingo and Retato degli Ortolani were also tested for their effects on FOM2 hyphal growth, number and length of germ hyphae and for root callose deposition after FOM2 challenge. Inhibitory effects of REs on the formation of germ hyphae by conidia of FOM2 were not noted. In case of the macroconidia the number increased. The length of germ hyphae was increased in both macro and microconidia and more pronounced with REs from cultivar Bingo. REs from Bingo and Retato degli Ortolani enhanced hyphal growth of FOM2. Fluorescence microscopy showed that FOM2 infection of roots caused callose deposition in root cortical cells in the resistant cultivar Bingo, but not in the susceptible Retato degli Ortolani. In conclusion, under our experimental conditions, REs appeared to be only partially involved in plant-pathogen interaction, whereas callose deposition in the roots of the resistant cultivar Bingo was elicited after inoculation with FOM2.

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.

Use of algae in strawberry management

In agriculture, extracts from algae are used for their stimulant effects on plant vigor and productivity but little is known on their effect against fungal pathogens. However, the recent EU restriction on synthetic pesticides made the management of fungal plant pathogens difficult and greatly stimulated the research of alternative solutions to chemicals. Applications of extracts from algae can help limit disease spread in several crops and the development effective alternatives to chemical treatment in crop protection and nutrition management. In particular, for strawberry, the management of a number of serious diseases in open field and greenhouse in soil or soilless cultivation has become difficult due to recent restrictions in agrochemical use and the lack of effective alternatives. This review provides an overview of the most recent findings on the potential use of extracts of algae for strawberry management, concerning both their biostimulant effects and antifungal properties against pathogens. The existing reports on this topic show the strong potential of algae extracts application on plants both as biostimulants and bioprotectants against fungal pathogens. Further investigation is needed to fully uncover the interesting and exploitable antifungal properties of extracts from algae and to clarify the mechanism of action of extracts and singular components against pathogens.