A. Minuto

Alternatives to Methyl bromide in Strawberry Production in the United States of America and the Mediterranean Region

Methyl bromide (MB) is a broad-spectrum soil fumigant, which has been critical in strawberry production for forty years. Strawberry and other high-value cash crops benefit from pre-plant soil fumigation with MB and chloropicrin (Pic). Mixtures of these two fumigants work synergistically in controlling a wide range of plant pathogens and pests, including fungi, nematodes, insects, mites, rodents, weeds, and some bacteria. Methyl bromide was listed in 1993 by the Parties of the Montreal Protocol as an ozone-depleting compound. According to the Montreal Protocol, the import and manufacture of MB in the United States of America (USA) and other developed countries will be banned by 2005, after stepwise reductions in 1999, 2001, and 2003. Currently, there is no single registered alternative fumigant for all of the MB uses and there is a need for environmentally sound and economically feasible alternatives. The fumigants 1,3-dichloropropene (1,3-D) and Pic in combination with methyl isothiocyanate (MITC) generators have shown to be the most promising alternatives to methyl bromide for strawberry production. Studies with the experimental fumigants methyl iodide and propargyl bromide suggested that these compounds have higher reactivity than MB as stand-alone fumigants. This review evaluates the commercially available and experimental alternatives to MB soil fumigation for strawberry production based on relevant scientific publications, proceedings, and personal communications.

Evaluation of antagonistic strains of Fusarium spp. in the biological and integrated control of Fusarium wilt of cyclamen

Abstract The ability of antagonistic strains of Fusarium spp. to control Fusarium wilt of cyclamen caused by Fusarium oxysporum f. sp. cyclaminis was tested under glasshouse conditions over three years. Several antagonistic strains of F. oxysporum and one strain of F. moniliforme , applied alone or in mixtures, were able to decrease significantly ( p = 0.05) the incidence of Fusarium wilt. Biological control was consistent especially when the antagonists were applied both by mixing a chlamydospore talc preparation in the potting substrate (3 × 10 4 –5 × 10 5 CFU/ml of soil) two weeks before transplant and by dipping plant roots at transplant in a conidial suspension (1 × 10 7 –5 × 10 8 CFU/ml). The combination of the benzimidazole fungicide carbendazim and antagonistic Fusarium spp. generally increased the efficacy of control. Carbendazim (0.5 mg a.i./ml of substrate) proved most effective in reducing or delaying the appearance of Fusarium wilt symptoms when the dosage was split into two applications, one at transplant and one 2 months later. Sodium alginate and kaolin formulations of F. oxysporum antagonistic strain 251/2 were not effective in reducing Fusarium wilt on cyclamen, while the same strain applied as chlamydospores dispersed in talc or as conidial suspension controlled the pathogen. The findings are discussed with respect to the most effective application and formulation methods of biocontrol agents under commercial conditions.

Identification of Fusarium oxysporum f. sp. basilici Isolated from Soil, Basil Seed, and Plants by RAPD Analysis

Fifty-two isolates of Fusarium oxysporum, obtained from infected basil plants, seed, flower residues, and soil from different growing areas in Italy and Israel, were analyzed by random amplified polymorphic DNA-polymerase chain reaction (RAPD-PCR), coupled to a DNA extraction protocol from colonies grown on Fusarium-selective medium. In a pathogenicity assay, 35 isolates caused 32 to 92% disease on seedlings of the highly susceptible basil cultivar Fine verde, while 17 isolates were nonpathogenic on basil. Thirty of the F. oxysporum f. sp. basilici isolates obtained from soil or wilted plants gave identical amplification patterns using 31 different random primers. All tested primers allowed clear differentiation of F. oxysporum f. sp. basilici from representatives of other formae speciales and from nonpathogenic strains of F. oxysporum. RAPD profiles obtained from DNA of isolates extracted directly from cultures grown on Fusarium selective medium were identical to those obtained from DNA extracted from lyophilized mycelia.

Application of selected antagonistic strains against Phytophthora cryptogea on gerbera in closed soilless systems with disinfection by slow sand filtration

Abstract In two separate trials during 2000–2002, the efficacy of slow sand filtration and UV treatment in eliminating Phytophthora cryptogea propagules, artificially added in the recirculating nutrient solution, was evaluated with gerbera plants grown in closed soilless systems. A slow sand filtration technique was tested both alone and in combination with different antagonistic strains belonging to Fusarium spp. and Trichoderma spp., isolated from gerbera rhizosphere and applied into the soilless system. The dynamics of these fungi in the recirculating nutrient solution and in the sand filter was also investigated by plate counts on selective media. Slow sand filtration and UV treatment were both effective in reducing P. cryptogea root rot. However, slow sand filtration may be a more feasible disinfection method than UV because of lower costs of installation and maintenance and for its adaptability to a wide range of production systems. Moreover, this disinfection technique can be successfully combine with the application of antagonistic microorganisms.

Biological Control of Fusarium Wilts

The biocontrol activity of antagonistic Fusarium spp. against several formae speciales of Fusarium oxysporum, their survival in the soil and methods for strain characterization are described.

First report of downy mildew on basil (Ocimum basilicum) in Italy.

Sweet basil (Ocimum basilicum) is an economically important herb in several Mediterranean countries. Approximately 80 ha are grown annually in Italy for fresh and processed consumption. In 2003, a damaging foliar disease was observed in several greenhouses located in the Liguria Region of northern Italy. More that 50% of the plants were affected. Leaves of infected plants were initially slightly chlorotic, especially near the central vein. Within 2 to 3 days, a characteristic gray, furry growth was evident on the lower surface of infected leaves. These symptoms sometimes occurred on the top sides of leaves. Although the distribution of the disease was generally uniform, symptoms appeared first in a patchy pattern in the central part of the greenhouses where air temperature and relative humidity were highest. Where air circulation was apparently poor, bottom leaves were severely affected by the disease. Microscopic observations revealed conidiophores branching two to seven times. Conidiophores with a length of 250 to 500 μm (average 350 μm) ended with sterigmata bearing single conidia. Conidia measured 15 to 25 × 20 to 35 μm (average 22 × 28 μm) and were elliptical and grayish in mass. The pathogen was identified as a Peronospora sp. based on its morphological characteristics (3). Pathogenicity was confirmed by inoculating leaves of 40-day-old healthy plants with a conidial suspension (1 × 105 conidia per ml). Three containers containing 150 plants each of O. basilicum cv. Genovese gigante were used as replicates. Noninoculated plants served as controls. Inoculated and noninoculated plants were maintained in a growth chamber at 20°C (12 h of light per day) and 90 to 95% relative humidity. The pathogenicity test was carried out twice. After 6 days, typical symptoms of downy mildew developed on the inoculated plants and a Peronospora sp. was observed on the leaves. Noninoculated plants did not show symptoms. To our knowledge, this is the first report of a Peronospora sp. on basil in Italy. Peronospora sp. and P. lamii were previously reported on sweet basil in Uganda (1,2). References: (1) C. G. Hansford. Rev. Appl. Mycol. 12:421, 1933. (2) C. G. Hansford. Rev. Appl. Mycol. 17:345, 1938. (3) D. M. Spencer. The Downy Mildews. Academic Press, N.Y., 1978.

Effect of antagonistic Fusarium spp. and of different commercial biofungicide formulations on Fusarium wilt of basil (Ocimum basilicum L.)

Abstract The ability of antagonistic Fusarium spp. to control Fusarium wilt of basil caused by F. oxysporum f. sp. basilici was tested under glasshouse conditions from 1994 to 1996. Fusarium oxysporum antagonistic strain 251/2, a protoplast fusion-derived hybrid coded FI-11 and F. moniliforme strains TF4 and TF4 RB were able to decrease ( P = 0.05) the incidence of Fusarium wilt significantly. Biocontrol was consistent, especially when the antagonists were applied by mixing a talc preparation of propagules in the substrate (10 5 CFU/ml of substrate) 1–2 weeks before sowing or at sowing. Seed coating with the biocontrol strains (10 8 CFU/g of seed) did not generally provide sufficient disease containment, whereas the combination of substrate treatment and seed coating did not improve wilt control in comparison with substrate treatment alone. Two commercial formulations, based on antagonistic F. oxysporum strains and one containing the antagonistic strain K61 of Streptomyces griseoviridis , were generally not sufficiently effective at the tested dosages.

First Report of Downy Mildew Caused by Peronospora sp. on Basil (Ocimum basilicum) in France

Sweet basil (Ocimum basilicum) is an economically important herb in several Mediterranean countries. Approximately 30 ha are grown annually in France for fresh and processed consumption. During the spring and fall of 2004, a damaging foliar disease was observed in some crops near Saint Tropez in the French Riviera Region. More than 50% of plants were affected in an organically produced field-grown crop at an altitude of 250 m. Leaves of infected plants were initially slightly chlorotic, especially near the central vein. Within 2 to 3 days, a characteristic gray, furry growth was evident on the lower leaf surface and sometimes on the upper leaf surface. The appearance and severity of the disease was affected by overhead sprinkler irrigation. Basal leaves were severely affected. Microscopic observations revealed sporangiophores branching two to seven times. Sporangiophores, with a length of 250 to 500 μm (average 350 μm), ended with sterigmata bearing single sporangia. Sporangia measured 15 to 25 × 20 to 35 μm (average 22 × 28 μm), were elliptical and grayish in mass. The pathogen was identified as Peronospora sp. on the basis of its morphological characteristics (4). Pathogenicity was confirmed by inoculating leaves of 40-day-old healthy plants with a sporangial suspension (1 × 105 conidia/ml). Three containers with 150 plants each of O. basilicum cv Genovese gigante were used as replicates. Noninoculated plants served as controls. Plants were maintained in a growth chamber at 20°C (12 h of light per day) and 90 to 95% relative humidity. The pathogenicity test was carried out twice. After 6 days, typical symptoms of downy mildew developed on the inoculated plants, and Peronospora sp. was observed on the leaves. Noninoculated plants did not show symptoms. To our knowledge, this is the first report of Peronospora sp. on basil in France. Peronospora sp. was previously reported on sweet basil in Italy (1) and P. lamii on sweet basil in Uganda (3). Seed transmission (2) is suspected as the reason for recent outbreaks in Europe. References: (1) A. Garibaldi et al. Plant Dis. 88:312, 2004. (2) A. Garibaldi et al. Z. Pflanzenkr. Pflanzenschutz 111:465, 2004 (3) C. G. Hansford. Rev. Appl. Mycol. 12:421, 1933. (4) D. M. Spencer. The Downy Mildews. Academic Press, NY, 1981.

Verticillium Wilt Incited by Verticillium dahliae in Eggplant Grafted on Solanum torvum in Italy

Eggplant cultivars grafted on rootstocks resistant to root-knot nematodes (Meloidogyne spp.) are increasingly grown in Italy to reduce nematode infection. During the winter of 2003-2004, eggplants (cv Black Bell and Mirabell) grafted on the nematode-resistant rootstock Solanum torvum were observed with symptoms of a wilt disease in several greenhouses in Sicily (southern Italy). The vascular tissue in stems of affected plants appeared brown. These plants were stunted and developed yellow leaves with brown or black streaks in the vascular tissue. The wilt appeared in several greenhouses at a very low incidence (0.01 to 0.05%). Later, during the fall of 2004, disease incidence was approximately ten times greater in the same greenhouses on new crops. Verticillium dahliae was consistently and readily isolated from symptomatic vascular tissue of the rootstock (S. torvum) and the scion (cv Black bell) when cultured on potato dextrose agar (PDA) (1). Healthy, 50-day-old plants of S. torvum and eggplant (cv. Black Bell) were separately inoculated by root dip with a conidial suspension (1 × 107 CFU/ml) of two isolates of V. dahliae obtained from the rootstock and the scion of the infected grafted plants and with a known pathogenic isolate of V. dahliae from nongrafted eggplant. Noninoculated S. torvum and eggplant served as control treatments. Plants (30 per treatment) were grown in a glasshouse at temperatures ranging between 12 and 41°C (weekly average 15 to 36°C) and relative humidity ranging between 36 and 99% (weekly average 54 to 95%). The first wilt symptoms and vascular discoloration in the roots, crowns, and veins developed 26 and 21 days after inoculation on S. torvum and eggplant, respectively. Seventy-two days after inoculation, 20, 26, and 27% of S. torvum plants and 97, 100, and 87% of the eggplants showed symptoms caused by V. dahliae isolates obtained from the scion of diseased grafted plants, the rootstock of diseased grafted plants, and nongrafted eggplants, respectively. Noninoculated plants remained healthy. To our knowledge, this is the first report in Italy of Verticillium wilt on eggplant grafted on S. torvum rootstocks under commercial conditions. Use of eggplant grafted on the nematode-resistant rootstock of S. torvum presents an interesting opportunity to control the root-knot nematode but has to be carefully considered when dealing with soils severely infested by V. dahliae. Reference: (1) G. F. Pegg and B. L. Brady. Verticillium Wilts. CABI Publishing, Wallingford, UK, 2002.

Effectiveness of fumigants and grafting against tomato brown root rot caused byColletotrichum coccodes

In an attempt to find effective control measures againstColletotrichum coccodes, an emerging pathogen causing root rot on tomato in northern Italy, four experimental trials were carried out during the years 2005 and 2006 in Piedmont and Liguria in order to evaluate the effectiveness of the combination of different rootstocks (Beaufort F1, He Man F1, Maxifort) with various fumigants. In the presence of medium to high disease incidence, the best results were obtained by combining the use of a resistant tomato rootstock with soil fumigation with dimethyl disulfide at 40 or 80 gm−2 or metham sodium at 192 g m−2. Chloropicrin, applied at 20 g m−2, and the tested rootstocks alone, did not enable effective control of the pathogen. The need to monitor the appearance of new diseases and the resurgence of old ones is stressed.