Search

A monitoring was conducted in 35 commercial vineyards located in Piedmont (North-West Italy) in September 2018 to test the sensitivity of Botrytis cinerea populations to the fungicides that were commonly used in the past and at present: benzimidazoles, dicarboximides, anilinopyrimidines, phenylpyrroles, hydroxyanilides and SDHI fungicides. Sensitivity was tested by evaluating the spore germination on a medium amended with a discriminatory concentration of the different tested botryticides. Conidial suspensions were prepared from infected, randomly sampled bunches and used for the tests. In comparison with the years 2008–2014, the following trend was recorded: benzimidazole resistance was quite stable and was found in about 50% of the vineyards involved in the monitoring; dicarboximide resistance had disappeared in the tested samples, while the frequency of resistance to anilinopyrimidines had increased; the resistance to fenhexamid had decreased; in the case of boscalid, the presence of resistance was quite stable; no resistance to phenylpyrroles was found, although the high discriminatory dose used for fludioxonil cannot exclude the presence in the tested vineyards of low levels of resistance to this fungicide, typical of multidrug-resistant strains.

The efficacy of different fungicides, belonging to different chemical groups, was in vitro and in vivo tested in glasshouse trials against Allophoma tropica, the causal agent of a new leaf spot on lettuce. The in vitro trials showed that only a few fungicides were effective in inhibiting the mycelial growth of the four tested strains of A. tropica: the most effective fungicide, with the lowest ED50 and MIC values, was penconazole. Prochloraz, propiconazole, boscalid and fludioxonil showed low ED50 values, but high MIC values. The results from the in vivo trials showed that all the tested fungicides significantly reduced Phoma leaf spot incidence and severity, although differences were observed in the achieved disease pressure in the four trials. Generally, in the presence of an average disease severity in the untreated control, the best disease severity reduction (up to 90%) was provided 9 days after the application of fludioxonil, mancozeb, pyraclostrobin + boscalid, propiconazole and iprodione. Fludioxonil and iprodione showed a persistent effect (up to 90%) still being evident 12 days after the application. Generally, in the presence of a high disease severity in the untreated control, 9 days after the application of fludioxonil, mancozeb, iprodione and pyraclostrobin + boscalid provided a disease severity reduction up to 80%. Moreover, copper provided a disease severity reduction from 84 to 89%, applied as preventative treatment, resulting of special interest, particularly for crops grown under organic farming rules.

The susceptibility of nine Papaver species commonly grown for gardens, cut flowers and potted plants, to Fusarium wilt, caused by Fusarium oxysporum f. sp. papaveris, has been evaluated. The susceptibility of Chelidonium majus L. and Papaver rhoeas L., both belonging to Papaveraceae family and naturally present in Italian flora, was also tested. Plants were inoculated by dipping the roots into the conidial suspensions of each of five single-spore isolates of F. oxysporum f. sp. papaveris isolated from P. nudicaule grown in Italy. After appearance of the symptoms, the disease index (D.I.) was evaluated for each tested species that was successively assigned to one of the following susceptibility classes: R = resistant (D.I. 0–5); PR = partially resistant (D.I. 6–20); MS = moderately susceptible (D.I. 21–50); S = susceptible (D.I. 51–75); and HS = highly susceptible (D.I. 76–100). None of the tested species was found to be totally or partially resistant to F. oxysporum f. sp. papaveris. However, Papaver atlanticum (Ball) Cosson, P. dubium L., P. glaucum Boiss. and Hausskn., P. pseudocanescens Popov, P. nudicaule L., P. rupifragum Boiss. and Reuter and Papaver “Daneborg” were susceptible or highly susceptible to the pathogen, while P. trinifolium Boiss. and P. orientale L. showed an average susceptibility to the tested isolates. The susceptibility classes of Chelidonium majus L. and P. rhoeas L. ranged from moderately to highly susceptible. About the origin of F. oxysporum f. sp. papaveris, two hypotheses are discussed. The first hypothesis is related to the susceptibility of C. majus L. and P. rhoeas to F. oxysporum f. sp. papaveris. This fact indicates that this pathogen might have been present in the wild of Italy and that the wild species belonging to the Papaveraceae may be a potential sources of disease outbreaks. The second hypothesis is related to the climatic conditions of subpolar areas in which P. nudicaule is indigenous. Low temperatures might limit the appearance of plant symptoms caused by F. oxysporum, which is generally favored by elevated temperatures, such as those typical of glasshouse cultivation in Liguria region (north of Italy) where the pathogen was reported for the first time on P. nudicaule. The first hypothesis should be validated with further monitoring activities in order to isolate the pathogen on wild flora, whereas the second hypothesis should be confirmed with epidemiology tests.

The efficacy of dimethyl disulfide (DMDS) applied in pre-planting treatment by shank injection was investigated on the lettuce Fusarium oxysporum f.sp. lactucae (FOL) pathosystem in Northern Italy (Piedmont), in three experimental trials. DMDS was tested alone or in combination with metham sodium at 35.9 g/m2, on lettuce cultivars showing different levels of susceptibility to the pathogen. DMDS, at 60 g/m2, reduced FOL symptoms on the highly susceptible butterhead type of 70, 97 and 99%, and of 87, 97 and 100% on the moderately susceptible cultivar, respectively. DMDS at 30 and 40 g/m2 showed a only partial efficacy on both lettuce types used in naturally infested soil, with a disease reduction from 30.3 to 64.5%, significantly comparable with dazomet. The results provided by DMDS at 40 g/m2 plus metham sodium at 35.9 g/m2 were statistically similar to those obtained with DMDS alone at 60 g/m2, and better than those provided by dazomet alone. A positive effect on lettuce yield and weed control by DMDS, at the highest dosage tested and by DMDS plus metham sodium, was also observed.

The aim of the present work was to study if the level and reproducibility of suppressive properties of compost can be increased upon enrichment with biological control agents. A compost made from green waste, organic urban waste and urban sludge was inoculated with commercial formulations of Trich oderma and non-pathogenic Fusarium. The compost showed to be suppressive against some soil-borne pathogens, except R. solani, while such activity was lost after sterilisation. The suppressive effect of enriched compost was assessed in greenhouse trials on cucumber, tomato, bean and basil. The addition of T. harzianum T-22 at 4 g l-1 dosage was able to increase suppressiveness against R. solani of a 40% compost and 60% peat mix and to increase biomass of bean compared to a peat inoculated control. The same enrichment did not reduce suppressiveness of compost against P. ultimum and P. nicotianae, so its addition might be considered a good strategy to increase compost suppressiveness. Disease suppressiveness of sterilised compost was restored by the addition of T. viride TV1 (> 4 gl-1) in P. ultimum /cucumber and in P. nicotianae/tomato. This study represents a further step toward the development of a substrate able to control a wide range of soil-borne pathogens and in the use of fortified composts for controlling plant diseases.

The efficacy of the antagonistic yeasts Pseudozyma fusiformata AP6, Metschnikowia fructicola AP47 and Aureobasidium pullulans PL5 were investigated, in combination with hot water dipping (HWD), to control brown rot of peaches caused by Monilinia laxa. The effects on postharvest fruit quality were also evaluated under semi-commercial conditions. In potato dextrose broth, HWD at 50°C for more than 40 s or at 55-60°C for more than 10 s completely suppressed M. laxa spore germination and germ tube elongation. In fruits inoculated by wounding, HWD at 55°C for 50 s significantly reduced brown rot decay and maintained fruit quality. This treatment would be optimal for commercial application. The harvested fruits were dipped in HW at 55°C for 50 s, cooled to 1°C for 10 min, dipped in the selected yeast cell suspension (108 cells ml−1) for 60 s, and then stored at 1°C and 95% relative humidity (RH). After 21 days, the disease incidence was measured and the postharvest quality parameters of the fruits, including firmness, total soluble solids, ascorbic acid and titratable acidity, were measured. When used alone, the antagonists AP6, AP47 and PL5 reduced brown rot incidence on the peaches to 28.3%, 30.0% and 25.8%, respectively, compared with 74.2% for the untreated control. However, when applied together with HWD, AP6, AP47 and PL5 reduced brown rot incidences to 16.7%, 15.8% and 17.5%, respectively, while when HWD was used alone, disease incidence was 30.0%, suggesting that HWD greatly increased the effectiveness of the antagonists. In combination with HWD, the efficacies of AP6, AP47 and PL5 signifi-cantly increased from 61.8%, 59.6% and 65.2% to 77.5%, 78.7% and 76.4%, respectively, and they were similar to the efficacy of tebuconazole (77.5%). Analysis of postharvest quality indicated that none of the treatments damaged fruit quality. Our results showed that the three antagonists combined with HWD at 55°C for 50 s exhibited potential for commercial use, as an effective alternative to fungicides in controlling postharvest brown rot of peaches. This appears to be the first report on combined application of yeast strains M. fructicola or P. fusiformata with HWD to control M. laxa on peaches.

This study reports the effect of increased CO2 and temperature on powdery mildew (Erysiphe necatrix) of grapevine evaluated under controlled conditions. Grapevine potted plants, belonging to the cv Moscato and Barbera, were grown in phytotrons under four different simulated climatic conditions: standard CO2 concentration for the area (450 ppm) with standard (ranging from 22 to 26°C) and elevated temperature (4°C higher than standard), elevated CO2 (800 ppm) with standard and elevated temperature. Physiological responses of grapevine and pathogen development were studied. Results showed an increase of the chlorophyll content with higher temperatures and CO2 concentration, to which consequently corresponded an higher fluorescence index. Disease incidence did not significantly vary between cultivars. In conclusion, an increase in CO2 did not affect powdery mildew incidence, probably due to the increased photosynthetic activity of plants under such conditions.

Thirty-nine Trichoderma strains isolated from effective re-used substrates used in soilless systems and two commercial formulations (Trichoderma viride TV1 and Remedier WP) were tested against Pythium ultimum, the causal agent of cucumber damping-off, under greenhouse and growth chamber conditions. Trichoderma was applied to the soil or by root dipping. Plant growth promotion activity of the Trichoderma strains was also evaluated in absence of the pathogen. The best and most consistent results were obtained by applying Trichoderma to the soil, 7 days before soil infestation with the pathogen. Twelve out of 39 Trichoderma strains (FC 1, 2, 6, 7, 12, 19, 24, 38, 39, 69, 72 and 80) showed the best activity against P. ultimum and four of them provided a 95% efficacy. The activity of such strains resulted slightly better than that of the commercial formulation Remedier. Some of the best strains also showed a good growth promoting ability, as demonstrated by a positive effect on biomass produced. Therefore, the good biocontrol ability of Trichoderma was confirmed in strains isolated from soilless systems. Such biocontrol agents may play a role in the suppressiveness of substrates used for soilless cultivation.

Pythium blight is one of the most important turf grass diseases. During the past three years, the failure of fungicide treatments against the disease has been observed in several locations in Northern Italy. Twenty Pythium strains collected in nine locations were classified and tested in vitro for their sensitivity to three fungicides, including mefenoxam, fosetyl- aluminium, and propamocarb. Trials were carried out on an agar medium amended with 0, 0.1, 0.3, 1, 3, 10, 30, 100, 300 mg 1−1 of the active ingredient in each fungicide. Results showed that the different strains belonged to six different species, including P. graminicola, P. aphanidermatum, P. sulcatum, P. arrhenomanes, P. vanterpolii, and P. aristosporum. Among these species, P. sulcatum was never reported on turf grass. In addition, all strains showed reduced sensitivity to in vitro fungicide application.

The activity of two biofungicides based on Bacillus subtilis and Ampelomyces quisqualis alone and in combination with fungicides against Podosphaera xanthii on zucchini was tested in five experimental trials carried out under greenhouse conditions. The population of P. xanthii used throughout the work for artificial inoculation was able to cause slight infections on zucchini plants treated with the field dosages of azoxystrobin and penconazole. B. subtilis when combined with azoxystrobin against P. xanthii at the recommended field dosages provided better powdery mildew control than the two control measures alone. Such results were consistent throughout the different trials. A similar synergistic effect was shown by the combination of A. quisqualis with myclobutanil: however, in this case, more studies are necessary to confirm the consistency of that phenomenon. The results obtained in this study support the possibility of a synergistic effect among the biocontrol agent B. subtilis and QoI fungicides. Such interaction is very interesting because of the presence of resistance towards QoI in the populations of P. xanthii.

One-hundred and one microorganisms have been selected and tested for their antagonistic activity towards soil-borne plant pathogens from a compost originated from urban organic and yard wastes. Among them, twenty eight microorganisms, tested under laboratory conditions on tomato seedlings growing on perlite medium in Petri plates, controlled tomato wilt caused by Fusarium oxysporum f. sp. radicis-lycopersici. In a second round of trials, they were assessed under greenhouse condition on three pathosystems: Fusarium oxysporum f.sp. basilici on basil, Phytophthora nicotianae on tomato and Rhizoctonia solani on bean. The Fusarium strain K5 showed a disease control of 69% and an increase in biomass production of basil of 32% compared to inoculated control. In the case of tomato/P. nicotianae, the bacteria strain B17 showed a disease control of 82% and an increase of 216% of biomass production of tomato. Two microorganisms, E19 and P11 controlled root and stem rot caused by R. solani on bean and increased the biomass of bean up to 163%. None of the microorganisms was able to control all the soil-borne pathogens. Three Fusarium (K7, K9 and K11) and two Trichoderma (E28 and E36) isolates showed the best results and were tested in a third round of trials mixed together and at different dosages. Two Fusarium isolates, K7 and K9, were able to control F. oxysporum f. sp. basilici and confirmed they could be used in the future as commercial antagonists.

A new wilt of lamb’s lettuce (Valerianella olitoria) was detected in northern Italy in 2003 and the causal agent of the disease was identified as Fusarium oxysporum. Pathogenicity tests and vegetative compatibility analysis were carried out on different isolates of the fungus. The pathogenicity of six isolates was tested on radish (Raphanus sativus), wild (Diplotaxis tenuifolia) and cultivated (Eruca sativa) rocket, cabbage (Brassica oleracea var. sabauda), cauliflower (Brassica oleracea var. botrytis), Brussels sprout (Brassica oleracea var. gemmifera), broccoli (Brassica oleracea var. italica), and turnip (Brassica rapa var. rapa). The results indicated that isolates of F. oxysporum from lamb’s lettuce belong to the forma specialis conglutinans. Vegetative compatibility grouping analysis showed the presence of VCG 0101 pathogenic on lamb’s lettuce. Among the 12 isolates from lamb’s lettuce tested, 10 belongs to VCG 0101 and are classified as F. oxysporum f. sp. conglutinans, while two are self-incompatible.