RESUMO
The pathogenicity of seven strains of Fusarium equiseti isolated from seabed soil was evaluated on different host plants showing pre and post emergence damage. Radial growth of 27 strains was measured on culture media previously adjusted to different osmotic potentials with either KCl or NaCl (-1.50 to -144.54 bars) at 15°, 25° and 35° C. Significant differences and interactive effects were observed in the response of mycelia to osmotic potential and temperature.
RESUMO
The pathogenicity of seven strains of Fusarium equiseti isolated from seabed soil was evaluated on different host plants showing pre and post emergence damage. Radial growth of 27 strains was measured on culture media previously adjusted to different osmotic potentials with either KCl or NaCl (-1.50 to - 144.54 bars) at 15º, 25º and 35º C. Significant differences and interactive effects were observed in the response of mycelia to osmotic potential and temperature.
RESUMO
Thirty-one soil samples from 14 different fields of Guatemala melon with vine decline symptoms were analyzed for the presence of organisms associated with the disease. With a soil-dilution plating method, only Macrophomina phaseolina was detected in five samples. With a melon bait plant technique, Olpidium bornovanus, often together with Melon necrotic spot virus (MNSV), was found in nearly all the samples, corresponding with all the fields studied. Other pathogens that were detected less frequently included Pythium aphanidermatum, Monosporascus cannonballus, and Rhizoctonia solani. Consequently, O. bornovanus and MNSV were uniquely associated with disease occurrence and thus are the most probable cause of melon vine decline in the fields studied.
RESUMO
Approximately 10,000 ha of melon (Cucumis melo L.), primarily cantaloupe and honeydew types, are grown in Honduras for export to U.S. markets. In 2004 and 2005, several soil surveys were conducted in areas with a history of vine decline. Twenty-nine soil samples from six farms were collected from the rhizosphere of wilted plants. Thirty-six melon plants were planted in a mixture of each rhizosphere sample and vermiculite (1:6 v/v). The plants were maintained in a growth chamber at 23 to 25°C with a 16-h photoperiod. The first symptoms, which appeared at the one- or two-true-leaf stage, were girdling of the lower stem, leaf chlorosis, and wilting. Affected plants exhibited necrotic crowns and roots and half of all plants died less than 3 days after wilting. Isolations from washed and dried crown and roots pieces from affected plants were placed on malt extract agar. Colonies were transferred to potato carrot agar and into dishes of sterile water and immature carnation petals to aid in the identification of recovered fungi. Nearly 500 isolates of Pythium species were cultured, and approximately 60% were identified as P. aphanidermatum (Edson) Fitzp. on the basis of their toruloid sporangia, aplerotic oospores, terminal and smooth oogonia, monoclinous sac-shaped antheridia (one to two per oogonium), and abundant appressoria. The pathogenicity of nine isolates was confirmed in a growth chamber. Ten plants of melon cv. Amarillo Canario, grown in sterilized vermiculite, were inoculated at the two- or three-true-leaf stage by drenching pots with 100 ml of a suspension of each isolate (103 CFU ml-1). Noninoculated plants served as controls. There were three replicates per isolate. Plants began to die 7 days after inoculation and the incidence of the affected plants reached an average of 70%. P. aphanidermatum causing decline of melon plants has been previously reported in hot and semi-arid areas in Israel and Spain (1,2). To our knowledge, this is the first report of P. aphanidermatum pathogenic to melon plants in Honduras. References: (1) S. Pivonia et al. Plant Dis. 81:1264, 1997. (2) J. Gómez Enfermedades del Melón en los Cultivos "Sin Suelo" de la Provincia de Almería. Junta de Andalucía, 1993.
RESUMO
During the winters of 2002 and 2003, a wilt occurred in melons cultivated on 1,500 ha in Colima State, Mexico. Yield losses reached 25% of final production, despite soil disinfestation with 60% methyl bromide and 40% chloropicrin. On the basis of the observation of plants with necrotic xylem, yellowing, and wilting of leaves, this disease was identified provisionally as Fusarium wilt. During February 2003, four soil samples from affected fields were plated onto a Fusarium-selective medium (1), which resulted in the detection of 2,260 ± 357, 179 ± 76, 668 ± 357, and 1,391 ± 256 CFU/g of F. oxysporum (3). Thirty-one randomly chosen isolates were used to inoculate differential cultivars of melon as described by Risser et al. (4). The cultivars were Amarillo Canario (susceptible to all races), Diana (resistant to races 0 and 2), Tango (resistant to races 0 and 1), and Vulcano (resistant to races 0, 1, and 2) (2). Ten plants of each cultivar, grown on sterilized vermiculite, were inoculated at the first true-leaf stage by drenching with 200 ml of a conidial suspension (1 × 105 CFU/ml) of each isolate. Noninoculated plants of each cultivar served as controls. Plants were maintained in a growth chamber with a 16-h photoperiod (18 × 103 lux) and temperatures at 23 to 25°C. Yellowing, wilt, and vascular discoloration symptoms developed on cvs. Amarillo Canario and Diana following inoculation with each of the 31 isolates, while noninoculated plants remained symptomless. F. oxysporum was consistently reisolated on potato dextrose agar from the affected plants. On the basis of the combination of affected cultivars, all isolates were identified as F. oxysporum f. sp. melonis race 1. To our knowledge, this is the first report of F. oxysporum f. sp. melonis race 1 in Colima State, Mexico. References: (1) H. Komada. Rev. Plant Prot. Res. 8:114, 1975. (2) J. Marín Rodríquez. Portagrano 2004. Vadmecum de Variedades Hortícolas. Agrobook, Spain. 2004. (3) P. E. Nelson et al. Fusarium Species: An Illustrated Manual for Identification. Pennsylvania State University Press, University Park, 1983. (4) G. Risser et al. Phytopathology 66:1105, 1976.