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The effect of chitosan on the growth and morphology of Fusarium oxysporum f. sp. albedinis (Foa), the causal agent of Bayoud disease, and its ability to elicit a defence reaction against this fungus in date palm roots were investigated. Chitosan at 1 mg mlE-1 reduced the growth of Foa on potato dextrose agar medium by an average of 75%, while mycelial growth was totally inhibited in a liquid medium. When added to a solid medium, chitosan caused morphological changes in Foa mycelium. In addition, when injected into roots at three concentrations (0.1, 0.5 and 1 mg mlE-1), chitosan elicited peroxidase (PO) and polyphenoloxidase (PPO) activity and, particularly at the concentration of 1 mg mlE-1, increased the level of phenolic compounds. Concerning phenolics, chitosan led to an accumulation of non-constitutive hydroxycinnamic acid derivatives, known to be of great importance in date palm resistance to Bayoud. The accumulation of hydroxycinnamic acid derivatives was greater in cv BSTN than in cv JHL. Chitosan could be used to protect date palm against this vascular disease [Sono stati studiati l´effetto del chitosano sulla crescita e la morfologia di Fusarium oxysporum f. sp. albedinis (Foa), agente causale della malattia del Bayoud, e la sua capacità di provocare una reazione di difesa contro questo fungo nella palma da datteri. Il chitosano a 1 mg mlE-1 ha ridotto la crescita di Foa su un substrato agar-patata-destrosio del 75% in media, mentre in substrato liquido la crescita del micelio era inibita completamente. Aggiunto a un substrato solido, il chitosano ha determinato cambiamenti morfologici nel micelio di Foa. Inoltre, quando veniva iniettato nelle radici a tre concentrazioni (0,1, 0,5 e 1 mg mlE-1), il chitosano stimolava l´attività della perossidasi (PO) e della polifenolossidasi (PPO) e, in particolare alla concentrazione di 1 mg mlE-1, determinava un aumento del livello di composti fenolici. Riguardo ai composti fenolici, il chitosano portava a un accumulo di derivati non costitutivi dell´acido idrossicinnamico, noti per la loro importanza notevole nella resistenza della palma da datteri al Bayoud. L´accumulo di derivati dell´acido idrossicinnamico è risultato maggiore nella cv BSTN rispetto alla cv JHL. Il chitosano potrebbe essere utilizzato nella difesa della palma da datteri da questa malattia vascolare.]

One-year-old wood of grapevine cv Thompson Seedless, Grenache and Cabernet Sauvignon were pruned and the pruning wound immediately inoculated with a spore suspension (approximately 1 x 10E6 spores mlE-1 of water) of Phaeomoniella chlamydospora or Phaeoacremonium aleophilum. Based on the incidence of esca three years after inoculation, Thompson Seedless was rated as the most susceptible of the three cultivars. The results are consistent with the observed incidence of naturally-occurring esca in California vineyards on these three cultivars [Il legno di un anno di piante di vite delle cv Thompson Seedless, Grenache e Cabernet Sauvignon è stato potato e sulle ferite di potatura è stata immediatamente inoculata una sospensione di spore (circa 1 x 10E6 spore mlE-1 di acqua) di Phaeomoniella chlamydospora o Phaeoacremonium aleophilum. In base all´incidenza del mal dell´esca tre anni dopo l´inoculazione, Thompson Seedless è stata valutata la più suscettibile delle tre cultivar. I risultati sono in accordo con l´incidenza naturale del mal dell´esca nei vigneti californiani relativamente alle tre cultivar considerate.]

Using two cultivars (the susceptible ILC482 and the moderately resistant INRAT 87/1) of chickpea (Cicer arietinum), the antagonistic activities of 21 Rhizobium isolates were tested in vitro in dual culture, and in vivo under greenhouse and field conditions against Fusarium oxysporum f.sp. ciceris (Foc) race 0, the causal agent of Fusarium wilt of chickpea. In dual culture, 14 isolates inhibited the mycelial growth of the pathogen more than 30% and the most effective were Rh8, Rh11, Rh⊲6 and PchSOM, which inhibited fungal growth more than 50%. Among the 14 Rhizobium isolates tested for volatiles, cyanide production and phosphate solubilisation, 8 significantly inhibited fungal growth by producing volatiles, 6 were positive for cyanide production and only three were able to solubilise phosphate. Isolate Rh8 produced the highest levels of volatiles, giving more than 10.7% fungal inhibition, and was the only one positive for both cyanide production and phosphate solubilisation. Greenhouse experiments on the same 14 isolates revealed the effectiveness of five: PchDMS, Pch 121, Rh5, Rh17 and Pch43. These reduced the percentage of wilted plants in both susceptible and moderately resistant cultivars. These percentages ranged from 12.5 to 54.6% in the susceptible cultivar ILC482 and from 8.3 to 29.1% in the moderately resistant cultivar INRAT 87/1. The best disease control was achieved by isolate PchDMS. Despite its effectiveness in vitro, isolate Rh8 was ineffective under greenhouse conditions. Field experiments showed that none of the 14 Rhizobium isolates significantly reduced the percentage of wilted plants of the susceptible cultivar ILC482, although with the moderately resistant cultivar INRAT 87/1 eight of the isolates significantly reduced wilt incidence. Inoculation of seeds with these isolates reduced the percentage of diseased plants from more than 48.6% in infected control plants to less than 20.3% in plants inoculated with the bacteria and infected with the pathogen. The best protection against disease was obtained with isolates Pch43 and Rh4, which reduced the percentage of wilted plants to less than 8%. Besides their beneficial effects on disease control, our studies showed that rhizobia may improve plant growth and yield. These results indicate that Rhizobium isolates could be effective under commercial conditions in reducing the deleterious effects of Fusarium wilt.

Scanning electron microscopy of stems and roots of grapevine plants affected by Petri disease demonstrated that the obstruction of xylem vessels and reduction in the flow of xylem sap, two symptoms of this disease, were mainly caused by tylose forming in the vessels and, to a lesser extent, by accumulation of aggregates. Fungal hyphae were also found in the xylem. These hyphae propagated via the xylem and invaded other vessels or adjacent parenchymatic cells through the pit. Analysis of lignin peroxidase, manganese peroxidase and laccase activity (all of which are involved in lignin degradation) in different fungi isolated from Petri disease-infected grapevines showed that Phaeoacremonium aleophilum expressed low specific activity for manganese peroxidase and high specific activity for both lignin peroxidase and laccase, while Phaeomoniella chlamydospora showed no activity for any of these enzymes. All these enzyme activities were inhibited by the phenolic compounds in grapevine: p-coumaric acid, catechin, caffeic acid and tannins. The phenolic compounds also had a direct effect on fungal growth and sporulation. When 804 vines affected by Petri disease were treated with Brotomax (a product that stimulates synthesis of phenolic compounds), plants showed an increase of growth and a reduction of Petri disease symptoms. Any new shoot and root formed after Brotomax treatment did not show any sign of obstruction or tylose formation [La microscopia elettronica a scansione di fusti e radici di piante di vite affette dalla malattia di Petri ha dimostrato che l´ostruzione dei vasi xilematici e la riduzione del flusso della linfa grezza, due sintomi di questa malattia, erano determinate principalmente dalla formazione di tille nei vasi e, in minor misura, dall´accumulo di aggregati. Nello xilema sono state pure trovate ife fungine. Queste si propagavano attraverso lo xilema e invadevano altri vasi o cellule parenchimatiche adiacenti attraverso le punteggiature. L´analisi dell´attività della lignina perossidasi, della manganese perossidasi e della laccasi (enzimi coinvolti nella degradazione della lignina) in funghi diversi isolati da viti affette dalla malattia di Petri ha messo in evidenza che Phaeoacremonium aleophilum esprimeva bassa attività specifica per la manganese perossidasi ed elevata attività specifica per lignina perossidasi e laccasi, mentre Phaeomoniella chlamydospora non evidenziava attività per alcuno di questi enzimi. Tutte queste attività enzimatiche erano inibite dai composti fenolici nella vite: acido p-cumarico, catechina, acido caffeico e tannini. I composti fenolici presentavano pure un effetto diretto su crescita e sporulazione dei funghi. A seguito del trattamento con Brotomax (che stimola la sintesi di composti fenolici) di 804 viti affette dalla malattia di Petri, le piante hanno evidenziato aumento della crescita e riduzione dei sintomi della malattia di Petri. Ogni germoglio o radice formata dopo il trattamento con Brotomax non presentava alcun segno di ostruzione o formazione di tille.]

In order to study the Syrian pathotype diversity of Cochliobolus sativus, the causal agent of barley spot blotch disease, a survey was conducted using 31 isolates and 13 barley genotypes. Four pathotypes (pt 1-4) were identified, based on the lesion form and infection response of the genotype, with mean disease rating from 1.76 to 7.46. Pt 1 exhibited low virulence on all used genotypes, pts 2 and 3 were moderately virulent and pt 4 was highly virulent. The two most common pathotypes were pt 3 (35%) and pt 4 (42%). The barley genotype AECS 71 was highly resistant to all pathotypes suggesting the existence of a general resistance mechanism. This genotype may be recommended as a possible donor in breeding programmes. The information obtained from this study should facilitate deploying effective resistance to C. sativus in barley [Allo scopo di studiare la diversita' dei patotipi siriani di Cochliobolus sativus, agente causale dell'elmintosporiosi dell'orzo, e' stata effettuata un'indagine utilizzando 31 isolati e 13 genotipi di orzo. In base alla forma delle lesioni e alla risposta dei genotipi all'infezione, sono stati identificati quattro patotipi (pt 1-4), con una valutazione media della malattia da 1,76 a 7,46. Il pt1 ha manifestato una bassa virulenza su tutti i genotipi utilizzati, pt2 e pt3 erano moderatamente virulenti e pt4 e' risultato altamente virulento. I due patotipi piu' comuni erano pt3 (35%) e pt4 (42%). Il genotipo di orzo AECS 71 era altamente resistente a tutti i patotipi, facendo ipotizzare l'esistenza di un meccanismo generale di resistenza. Questo genotipo puo' essere suggerito come possibile donatore in programmi di miglioramento genetico. Le informazioni derivate da questo studio potrebbero facilitare il dispiegamento di una resistenza efficace nei confronti di C. sativus nell'orzo]

Salicylic acid (SA) plays a key role in establishing resistance to pathogens in many plants. To study the possible involvement of SA in the resistance of date palm (Phoenix dactylifera L.) to Fusarium oxysporum f. sp. albedinis (FOA), we investigated levels of phenolic compounds, known as indicators of resistance in the date palm/Fusarium pathosystem. After treatment with SA, the content of root soluble phenolics in F. oxysporum inoculated date palm seedlings was about 4 times higher in cv Bousthami noir and 6 times higher in cv Jihel than that in untreated plants showing disease symptoms. The largest increase was at a SA concentration of 50 micronM. SA treatment also enhanced the content of cell wall phenolics. In addition, inoculation of SA-treated roots of date palm with FOA (strain ZAG) resulted in a greater number of plants showing only limited hypersensitive reaction-like necrotic lesions. In contrast, SA-untreated plants normally showed spreading necrosis in response to fungus inoculation [L'acido salicilico (SA) gioca un ruolo chiave nell'attivazione della resistenza ai patogeni in molte piante. Per verificare il possibile coinvolgimento di SA nella resistenza della palma da datteri (Phoenix dactylifera L.) a Fusarium oxysporum f. sp. albedinis (FOA), abbiamo studiato i livelli dei composti fenolici, noti come indicatori di resistenza nel patosistema palma/Fusarium. A seguito del trattamento con SA, il contenuto di composti fenolici solubili nelle radici di palma da datteri inoculate con F. oxysporum e' risultato quattro volte piu' elevato nella cv Bousthami nera e sei volte piu' alto nella cv Jihel rispetto alle piante non trattate, che presentavano sintomi della malattia. L'incremento maggiore si e' avuto alla concentrazione di 50 micronM di SA. Il trattamento con SA determinava pure un aumento dei composti fenolici delle pareti cellulari. Inoltre, l'inoculazione delle radici trattate con SA con FOA (ceppo ZAG) si e' tradotto in un maggior numero di piante che presentavano solo lesioni necrotiche limitate, tipiche della reazione di ipersensibilita'. Al contrario, le piante non trattate con SA presentavano normalmente necrosi diffuse in risposta all'inoculazione del fungo]

Cross-inoculation experiments were carried out in southern Italy (Apulia) on grapevines cv. Italia and Matilde in order to study interactions among the white rot fungus Fomitiporia punctata (Fop) and two tracheiphilous hyphomycetes, Phaeoacremonium aleophilum (Pal) and Phaeomoniella chlamydospora (Pch), commonly associated with esca and brown wood-streaking of grapevine. In January 1999 the three fungi were inoculated through wounds on the trunks and spurs of cv. Italia, and branches and spurs of cv. Matilde. Pch, Pal and Fop were inoculated singly or in groups of two or three in all possible combinations. From the results so far obtained, the following conclusions can be drawn: 1. all three fungi are pathogenic; 2. inoculation of the above fungi on standing grapevines produces symptoms on trunks, shoots, leaves and berries that are reminiscent of those shown by esca-affected vines in the vineyard. In particular, symptoms in the wood (brown streaking, gummosis or \"black goo\", and wood decay or white rot), and on the leaves (various forms of chlorosis, reddening and necrosis, distortion of the lamina) and berries (black measles) were reproduced; 3. severity of internal symptoms, assessed as length of brown streaks and intensity of colour change of the infected wood, varied with the growth and interactions between the inoculated fungi; 4. the wood streaking which developed after inoculation with Pal or Pch on the spurs extended to the supporting shoot or branch, and even to the stem; 5. a non-synergistic, competitive association of the two hyphomycetes, and an inhibition of Fop growth by Pal was observed in planta. A similar marked antagonistic effect of Pal againsi Fop was previously shown to occur when examining interactions between the three fungi in vitro; 6. the wood discolouration caused by Fop was not hampered by Pch, but it is always limited by Pal; 7. on the basis of internal symptoms, grapevines cv. Italia were more susceptible to the esca fungi than grapevines cv. Matilde.

Twenty healthy cuttings each were inoculated artificially with Phaeomoniella chlamydospora Phaeoacremonium inflatipes and Phaeoacremonium aleophilum. After the formation of callus, they were planted in pots. Approximately one year after inoculation, disease occurrence was recorded as the length of brown vascular streaking from the base of plant toward the shoot tip. Discolored areas were cultured on potato dextrose agar amended with tetracycline hydrochloride (PDA-tet) and pathogens were re-isolated. Inoculation with Pa. chlamydospora showed that rootstocks 3309, 420A, 110R, 5C, Schwarzmann, St. George, and Salt Creek were least susceptible, while 99R, 39-16, Freedom, Riparia Gloire, 140Ru, 16-16 and 1103 were most susceptible. When inoculated with Pm. inflatipes, 16-16,3309, AXR1, Salt Creek, 110R, 5C, Freedom and 140Ru were least susceptible, while 420A, St. George, 161-49, and Harmony were most susceptible. Inoculation with Pm. aleophilum showed that 1103, 420A, Harmony, and Salt Creek were least susceptible, while 110R, SO4, 39-16 and 161-49 were most susceptible. The susceptibility of the rootstocks and the occurrence of vine decline in the field in California did not appear to be well correlated because 3309, 101-14, 5C, and 110R were always most susceptible. But these rootstocks are the most widely planted, and hence the natural occurrence of the disease is probably skewed towards these rootstocks. However, since no resistance was detected in our study, even though there was a wide range of susceptibility, the degree of rootstock susceptibility may not be such an important factor in disease expression under natural conditions.

In plants, the mechanism of RNA silencing has evolved to defend plants against viral infection as well as to regulate gene expression for growth and development. However, viruses counteract this antiviral defence by expressing silencing suppressor proteins, which are potent weapons in the 'arms' race between plants and invading viruses. These proteins efficiently inhibit RNA silencing by interacting with various steps of the different silencing pathways and these mechanisms of suppression are being unravelled progressively. Our better understanding the molecular bases of the induction and the suppression of RNA silencing dramatically improved our basic knowledge about intimate plant-virus interactions and also provide valuable tools to unravel the diversity, regulation and evolution of RNA-silencing pathways [Nelle piante il meccanismo di silenziamento dell'RNA si è evoluto per difendere le stesse dall'infezione virale, così come per regolare l'espressione genica per la crescita e lo sviluppo. Tuttavia, i virus contrastano questa difesa antivirale esprimendo proteine che agiscono da soppressori del silenziamento, che sono armi potenti nella competizione fra piante e virus infettanti. Queste proteine inibiscono efficientemente il silenziamento dell'RNA interagendo con vari passaggi dei percorsi di silenziamento e questi meccanismi di soppressione sono in via di progressivo chiarimento. La migliore comprensione delle basi molecolari dell'induzione e della soppressione del silenziamento dell'RNA ha migliorato sensibilmente le nostre conoscenze di base sulle interazioni intime pianta-virus e forniscono pure strumenti preziosi per chiarire la diversità, la regolazione e l'evoluzione dei meccanismi di silenziamento dell'RNA.]