First Report of Xanthomonas fragariae Causing Angular Leaf Spot on Strawberry Plants in México.

The state of Michoacán is the most important strawberry producer in México. During January 2007, field-grown strawberry plants cv. Aromas showing vein necrosis were observed in 3 ha in Zamora County, in fruit production fields. The average disease incidence in the field was 80%. Infected plants presented water-soaked lesions limited by veins on the lower leaf surfaces, which enlarged to form angular spots (1). Additionally, most affected plants presented severe necrosis in the main veins and reddish to necrotic lesions on the upper leaf surfaces. Gram-negative bacteria were consistently isolated from leaves with water-soaked lesions. Isolated bacteria produced mucoid, yellow colonies on YDC, grew on tween and nutrient agar (NA), but not on SX media. Strains produced non-fluorescent colonies on King's B media, were positive starch hydrolysis, negative esculin hydrolysis; and produced acid from fructose but not from arabinose, galactose, celobiose, and trehalose. Growth was inhibited by 2% NaCl (3). Indirect ELISA analysis (NEOGEN, Lansing, MI) was conducted using antibodies specific for Xanthomonas fragariae. Conventional PCR assay using the primer pairs 241A/241B was performed (2). The ELISA test was positive. The expected 300- and 550-bp bands were observed in the PCR analysis. The bacteria was identified as X. fragariae Kennedy and King. Pathogenicity tests were conducted twice in a greenhouse (24 ± 4°C) on a total of five strawberry cv. Aromas plants. The main vein of each of three leaves per plant were punctured using sterile needles. Pathogen inoculum was obtained from 6- to 8-day-old NA cultures. Bacteria were applied onto the wounds with a sterile cotton swab dipped into the bacterial suspension (105 CFU/ml). Inoculated plants were covered with plastic bags for 48 h. Symptoms resembling those seen in the field developed on all inoculated plants after 9 days. X. fragariae was re-isolated from the necrotic lesions and identified by PCR. Control plants were similarly inoculated with water but did not develop symptoms. To our knowledge, this is the first report of X. fragariae causing angular leaf spot in strawberry in Michoacán, México. References: (1) J. L. Maas, ed. Compendium of Strawberry Diseases. The American Phytopathological Society, St. Paul, MN, 1998. (2) M. R. Pooler et al. Appl. Environ. Microbiol. 62:3121, 1996. (3) N. W. Schaad et al. Laboratory Guide for Identification of Plant Pathogenic Bacteria. 3rd ed. The American Phytopathological Society, St. Paul, MN, 2001.

First Report of Geranium Rust (Puccinia pelargonii-zonalis) in the State of Michoacán, México.

Geranium is one of the most popular ornamental plants in México. In December 2012, rust symptoms were observed on leaves of common geranium (Pelargonium × hortorum L. H. Bailey) growing in pots in garden landscapes in Morelia, Michoacán. Dark brown pustules with chlorotic halos appeared on the lower leaf surface. A center pustule surrounded by one or more partial-to-complete concentric circles of smaller pustules was observed in each lesion. Urediniospores were globose or subglobose to ovoid, light brown, echinulated, thin-walled with two more or less conspicuous subequatorial pores, and 21 to 29 × 18 to 24 µm (25.5 × 22.8 µm average). Teliospores were not observed. Based on these characters, the rust was identified as Puccinia pelargonii-zonalis Doidge (1,2). Pathogenicity tests were conducted on three healthy P. × hortorum plants that were sprayed with water droplets containing urediniospores. The inoculated plants were covered with a plastic bag and placed in a screened house. The bags were removed after 24 h. Afterwards, the plants were maintained outside the screened house in full sun at ambient temperature (24 to 30°C in the day and 5 to 10°C at night). Initial symptoms were observed 15 to 17 days post inoculation. Symptoms appeared as small light yellow spots on the upper surface of mature leaves. Urediniospores production on the lower surface of the leaves was evident 22 to 25 days post inoculation. To our knowledge, this is the first report of P. pelargonii-zonalis in the state of Michoacán, México. Geranium rust has been previously reported only in the state of Guanajuato (2). References: (1) E. M. Doidge. Bothalia 2:1, 1926. (2) H. L. Gallegos and G. B. Cummings. Uredinales (royas) de México. Vol. 1. Culiacán, Sinaloa, México, SARH, 1981.

First Report of Powdery Mildew on Carrot Caused by Erysiphe heraclei in Michoacan, Mexico.

Carrot (Daucus carota L. subsp. sativus (Hoffm.) Arcang.) is planted as a home-grown vegetable in the central region of Michoacan, Mexico. Powdery mildew was observed on carrot plants cv. Nantesa at several locations near Morelia, Michoacan during March 2009. Affected plants had abundant, white, superficial conidia and mycelium on leaves and stems. All plants at each of five locations surveyed had powdery mildew symptoms with percent foliage coverage ranging from 50 to 80%. Mycelial growth was amphigenous, mainly on the upper leaf surface, covering the whole leaf and with irregular patches on inflorescences and stems. Hyphae were ectophytic with lobed appressoria. Conidiophores presented foot cells 22.5 to 35 (30) × 5.75 to 7 (6.3) µm followed by two cells, one shorter and one longer than the foot cell. Conidia were produced singly, most subcylindric to cylindric, lacked fibrosin bodies, and measured 31.2 to 42 (36.2) × 8.7 to 11.2 (10.5) µm. The teleomorph was not observed. Genomic DNA was extracted from infected leaves; sequences of the internal transcribed spacers (ITS) inclusive of 5.8S rDNA were amplified using previously described primers specific for Erysiphales (3). The ITS sequences shared 100% homology to Erysiphe heraclei specimen VPRI41227 from carrot in Australia (GenBank Accession No. EU371725). On the basis of the morphological characteristics observed and the ITS rDNA sequences, the pathogen was identified as E. heraclei DC. The ITS sequence was deposited in NCBI as Accession No. GU252368. Pathogenicity tests were conducted twice on a total of 10 healthy 8-week-old carrot plants cv. Nantesa. Infected plants were placed in close proximity to healthy plants and maintained in a greenhouse at 27 ± 5°C. Initial signs and symptoms were observed 3 weeks after inoculation and appeared as small, white colonies, which later coalesced and covered most of the foliage. Microscopic examination of the conidia and mycelial morphology matched the originally described pathogen, E. heraclei. Powdery mildew caused by this pathogen has been extensively reported on diverse species and genera of the Apiaceae in Europe and remains one of the most important diseases of carrot (2). The appearance of E. heraclei in diverse regions on a variety of umbelliferous crops indicates that formae speciales have spread, infecting different and specific hosts (1-3). Recently, E. heraclei has been reported on parsley in Puebla, Mexico (4). To our knowledge, this is the first report of E. heraclei causing powdery mildew on carrot in Michoacan, Mexico. This pathogen should be considered as a threat to commercial carrot crops in Mexico. Other crops in the Apiaceae may not be at risk in this area if this powdery mildew is specific for carrots. References: (1) B. J. Aegerter. Page 22 in: Compendium of Umbelliferous Crop Diseases. The American Phytopathological Society, St. Paul, MN, 2002. (2) U. Braun. The Powdery Mildew (Erysiphales) of Europe. Gustav Fischer-Verlag. Jena, Germany, 1995. (3) J. H. Cunnington et al. Australas. Plant Pathol. 32:421, 2003. (4) M. J. Yáñez-Morales et al. Schlechtendalia 19:47, 2009.

Root Rot of Hydroponically Grown Lettuce Caused by Phytophthora drechsleri in Mexico.

During March of 2008, bibb lettuce (Lactuca sativa L.) plants with severe wilting and root rot were observed in a commercial liquid-hydroponic greenhouse in Guanajuato, Mexico. By July of that year, the disease affected most plants in the facility. A Phytophthora sp. was consistently isolated from diseased roots on potato carrot agar. Several Phytophthora isolates were morphologically characterized. Sporulation was achieved by placing colonized disks of clarified V8 juice agar (V8A) into nonautoclaved soil extract (10 g avocado soil/1,000 ml distilled water, stirred for 3 h, and filtered). Sporangia were persistent, nonpapillate, and 40 to 58 µm long × 30 to 40 µm wide. External and internal proliferation was observed. Hyphal swellings were predominantly rounded. Oospores were not observed. The isolates grew on V8A at 35°C. Pathogenicity tests were conducted twice by utilizing a representative isolate (AC1) on bibb lettuce seedlings (10 replicates per experiment). Seeds were placed on sterile, water-soaked paper in petri dishes. After 10 days, each lettuce seedling was placed into a tube containing approximately 2 ml of sterile distilled water and 2,000 zoospores. Control plants were placed in tubes with water only. Plants were incubated for 7 days in a moist chamber at 25°C. Symptoms of wilting and root necrosis were observed 2 to 3 days after inoculation. All plants were dead 5 to 7 days after inoculation. A Phytophthora sp. was always isolated from the roots of inoculated plants. Control plants remained healthy. The pathogen was identified as Phytophthora drechsleri Tucker according to morphological characteristics. To confirm the identity of the pathogen, sequences of the internal transcribed spacers (ITS) were obtained from three representative isolates. The ITS sequences that were obtained shared 100% homology to several strains of P. dreschleri, including isolates from cucurbits (GenBank Accession No. AF228097). The ITS sequence was deposited in NCBI as Accession No. FJ790770. P. cryptogea and P. dreschleri have been reported as causing root rot on lettuce grown hydroponically in the United States and Korea (1,2). To our knowledge, this is the first report of P. drechsleri causing root rot on lettuce in Mexico. References: (1) H. J. Jee et al. Plant Pathol. J. 17:311, 2001. (2) A. R. Linde et al. Plant Dis. 74:1037, 1990.

A Novel Disease of Big-Leaf Mahogany Caused by Two Fusarium Species in Mexico.

Big-leaf mahogany (Swietenia macrophylla) is valued for its high-quality wood and use in urban landscapes in Mexico. During surveys of mango-producing areas in the central western region of Mexico, symptoms of malformation, the most important disease of mango in the area, were observed on big-leaf mahogany trees. The objectives of this research were to describe this new disease and determine its cause. Symptoms on big-leaf mahogany at four sites in Michoacán, Mexico resembled those of the vegetative phase of mango malformation, including compact, bunched growth of apical and lateral buds, with greatly shortened internodes and small leaves that curved back toward the supporting stem. Of 163 isolates that were recovered from symptomatic tissues, most were identified as Fusarium pseudocircinatum (n = 121) and F. mexicanum (n = 39) using molecular systematic data; two isolates represented unnamed phylospecies within the F. incarnatum-equiseti species complex (FIESC 20-d and FIESC 37-a) and another was in the F. solani species complex (FSSC 25-m). However, only F. mexicanum and F. pseudocircinatum induced malformation symptoms on 14-day-old seedlings of big-leaf mahogany. The results indicate that F. mexicanum and F. pseudocircinatum, previously reported in Mexico as causal agents of mango malformation disease, also affect big-leaf mahogany. This is the first report of this new disease and the first time that F. mexicanum was shown to affect a host other than mango.

First Report of Powdery Mildew on Greenhouse Tomatoes Caused by Oidium neolycopersici in Michoacan, Mexico.

During June and July of 2007, powdery mildew-infected tomato (Lycopersicum esculentum Mill. cv. Reserve) plants were observed in a commercial greenhouse with an open hydroponic system in Morelia County. Disease incidence increased from 0.5% to more than 90% in 1 month. Infected plants showed leaves with irregular areas of dense, white mycelium covering most of the upper surface. Microscopic analysis showed hyaline, septate hyphae with lobed appressoria. Conidia were ellipsoid to ovoid and 30 to 45 (38) µm × 15 to 20 (16) µm. Conidiophores were erect, 80 to 120 (103) µm, consisted of a foot cell 42 to 67 (56) µm, and two to three short cells. Conidia were produced singly. On the basis of the observed morphological characteristics, the fungus was identified as Oidium neolycopersici L. Kiss (1). Pathogenicity tests were conducted on fourth true-leaf tomato seedlings cv. Reserve under greenhouse conditions (22 ± 5°C). Inoculation was performed by transferring conidia from infected leaves to the leaves of uninfected tomato seedlings with a single-edged razor blade. Powdery mildew symptoms began to develop 7 days after inoculation. Symptoms and morphological characteristics were similar to those observed in the commercial greenhouse. Noninoculated plants remained healthy throughout the experiments. To our knowledge, this is the first report of O. neolycopersici causing powdery mildew on tomato in Michoacan, Mexico. This disease has been reported from Canada, Europe, Japan, the United States (2), and Venezuela (3) on greenhouse and field tomato crops. The observed high incidence and severe infection indicates that this disease may become an important problem in greenhouse tomatoes in Mexico. References: (1) L. Kiss et al. Mycol. Res. 105:684, 2001. (2) L. Kiss et al. Plant Dis. 89:491, 2005. (3) J. O. Montilla et al. Plant Dis. 91:910, 2007.

First Report of Haplotype I-b of Phytophthora infestans in Central Mexico.

Central Mexico is considered a center of genetic diversity for Phytophthora infestans on the basis of a range of genotypic and phenotypic characteristics (3). Surprisingly, while mitochondrial DNA (mtDNA) haplotypes I-a, II-a, and II-b have been reported from central Mexico, haplotype I-b has not been found in central Mexico (1). Therefore, a more extensive search for haplotypes was conducted in areas where sexual reproduction occurs. During the summer of 2003, leaflets of cvs. Rosita and Tollocan with a single lesion of late blight were collected in the area of Villarreal, located in Terrenate County in Tlaxcala, Mexico (170 km northeast of Mexico City). Fourteen P. infestans isolates were characterized for mtDNA haplotype, isozyme genotype (glucose 6- phosphate isomerase [Gpi] and peptidase [Pep]), and mating type. Isolation, mating type, and isozyme genotype were characterized following reported protocols (1,4). MtDNA haplotype was determined by amplifying and digesting the P2 and P4 regions and comparing amplicons to those of reference strains of known haplotype (1,2). Twelve isolates were mtDNA haplotype I-a and two were I-b. While the mtDNA I-b has been associated with the US-1 lineage (mating type: A1, Gpi: 86/100, Pep: 92/100), the genotypes for the Mexican isolates were A2, 86/100 Gpi, 100/100 Pep from cv. Rosita and A2, 86/100 Gpi, 92/100 Pep from cv. Tollocan. To our knowledge, this is the first report of the I-b mtDNA haplotype of P. infestans from central Mexico and it is now clear that all four haplotypes exist in Mexico. This finding therefore, stresses the importance of including a representative regional sampling of Mexican and Andean isolates in studies inferring the origin of this species. References: (1) W. G. Flier et al. Phytopathology 93:382, 2003. (2) G. W. Griffith and D. S. Shaw. Appl. Environ. Microbiol. 64:4007, 1998. (3) N. J. Grünwald and W. G. Flier. Ann. Rev. Phytopathol. 43:171, 2005. (4) N. J. Grünwald et al. Phytopathology 91:882, 2001.

First Report of Phytophthora capsici Causing Wilt on Hydropronically Grown Cucumber in Mexico.

During August 2005, wilted cucumber (Cucumis sativus cv. Tasty Green) plants were observed in a commercial greenhouse with a closed hydroponic system in the state of Mexico. Disease incidence was 50%. Diseased plants were detected 15 days after transplanting, when plants were overwatered. Yield was severely reduced when disease affected mature plants. Wilted plants showed basal stem lesions and root rot. Phytophthora capsici was consistently isolated from diseased tissue on corn meal agar (CMA) with tartaric acid. Oomycete identification was based on sporangial and gametangial characteristics (2). Sporangia produced on blocks of CMA at 25°C were spherical, broadly ellipsoid or obovoid with one papillae, and deciduous with a long pedicel (1). The isolates were heterothallic, and oogonia with amphigynous antheridia were observed in pairings with an A1 isolate of P. capsici, therefore, the isolates were determined to be an A2. Pathogenicity tests were conducted on 2-month-old cucumber seedlings under controlled conditions (25°C). Inoculation was performed by placing small pieces of agar with mycelium of 5- to 7-day-old cultures on the stem base and wrapping with Parafilm. Control plants were inoculated with CMA agar. No symptoms were observed on the control. Plants inoculated with the P. capsici isolated from the diseased cucumbers showed a basal stem lesion, followed by wilting and death 7 to 14 days after inoculation. The isolate was also pathogenic on tomato and eggplant that were grown at the same time in the commercial greenhouse sharing the nutrient solution. P. capsici sporangia were observed on the roots of both hosts. To our knowledge, this is the first report of P. capsici affecting cucumber in a hydroponics system in Mexico. References: (1) M. Aragaki and J. Y. Uchida. Mycologia 93:137, 2001. (2) D. C. Erwin and O. K. Ribeiro. Phytophthora Diseases Worldwide. The American Phytopathological Society. St. Paul MN, 1996.

First Report of Gladiolus Rust Caused by Uromyces transversalis in Michoacán, México.

During October 2005, rust lesions were observed on leaves of gladiolus (Gladiolus sp.) plants being grown for flower production in a 20-ha field in eastern Michoacán, México. Disease incidence was near 100% in the field. Five symptomatic plants were collected on 11 and 25 October 2005, from each of 10 farms for further examination. Uredinia were scattered, orange, elliptical to irregular, and arranged transversely across the leaf. The sori were covered by the epidermis initially and later were erumpent and pulverulent. Urediniospores were bright yellow gold, ovate to oblong, and measured 15 × 19 µm (average). The urediniospore wall was hyaline and minutely echinulate. Telia were scattered, dark brown, elliptical, arranged transversely across the leaf, and were covered by the epidermis. Teliospores were irregularly pyriform, ovate, irregular or angular, light to dark brown with a conical or truncate apex and measured 17 × 23 µm (average). The teliospore wall measured 1 µm (average) thick at the sides and 3 µm (average) thick at the apex. Pedicels were light yellow and measured as much as 60 × 3 µm (average). On the basis of these characters, the rust was identified as Uromyces transversalis (Thüm.) G. Winter (1). To our knowledge this is the first report of U. transversalis causing gladiolus rust in Michoacán, México. Originally reported from Africa, the disease has been reported from Argentina, Brazil, southern Europe, and Oceania (1). Gladiolus rust caused by Uromyces transversalis is a quarantine disease for Europe and the United States. There have been unpublished reports of interceptions of this rust on cut flowers of gladiolus going from México into the United States (1). References: (1) J. R. Hernández. Invasive Fungi. Gladiolus Rust. Systematic Botany and Mycology Laboratory, Online publication. ARS, USDA, 2004.

First Report of Ovulariopsis on Lupinus havardii.

In 1998 and 1999 a severe powdery mildew was observed in Las Cruces, NM, on Big Bend Bluebonnets (Lupinus havardii) grown in the greenhouse for cut flowers and vase life studies. An undescribed powdery mildew has been reported on L. havardii (2), but it has been observed only occasionally on leaves and has not cause a severe problem. The powdery mildew observed in Las Cruces began in March and caused severe infection from May through July. The disease spread rapidly due to movement of the pathogen during pruning operations and the close proximity of plants. Plants were heavily infected when no fungicide was applied. Plants were sprayed with the fungicide azoxystrobin, with best control obtained at 687 mg/liter of water. When an infected plant was used as a source of inoculum, disease spread rapidly to healthy plants placed around the infected plant. Infected leaves had chlorotic lesions that later became necrotic. Mycelia, conidiophores, and conidia of the pathogen were observed on leaves and occasionally on petioles and stems. Ellipsoid cylindrical-to-clavate conidia were hyaline, one-celled, and measured 49 to 68.1 µm × 12.2 to 14.7 µm. Conidia were produced on upright, simple conidiophores measuring 171 to 245 µm × 4.9 to 7.3 µm. Fibrosin bodies and cleistothecia were not found. The fungus was identified as an Ovulariopsis sp. (1). This is the first documented report of an Ovulariopsis sp. on L. havardii. References: (1) U. Braun. Beih. Nova Hedwigia 89:1, 1987. (2) W. A. Mackay and T. D. Davis. HortScience 33:348, 1998.

First Report of Pythium paroecandrum on Lupinus havardii.

Lupinus havardii Wats. (Big Bend Bluebonnet), a plant native to Texas, has been tested extensively for greenhouse production as a cutflower crop (1). Disease symptoms were observed on L. havardii plants grown in Las Cruces, NM, during two consecutive years. Plants were grown in Metro Mix 200 and watered by an automatic irrigation system every 3 days. During the growing season, which extended from September through February, 6% of mature plants (10-week-old plants) became chlorotic, wilted, and died. The first symptoms were observed during December 1998, when greenhouse temperatures were from 10 to 13°C. During the rest of the growing season, from February to July, only one plant became diseased, during May 1999, and the plant died within 1 week after greenhouse temperatures reached 20 to 25°C. Diseased plants were examined, and root, crown, and stem rot were found. Pythium paroecandrum Drechs. (2) was isolated routinely from infected tissues. Koch's postulates were fulfilled after plants were inoculated with oospores and mycelia of P. paroecandrum. Inoculum was applied next to the crown of 6-week-old plants in the form of water-agar plugs and a suspension that contained P. paroecandrum oospores and mycelia. Plants were maintained at 20 to 25°C. After 10 days, symptoms were similar to those previously observed, and the pathogen was reisolated from necrotic lesions observed on stems and crowns. Disease developed slower on 6-week-old plants (inoculated) than on 10-week-old plants (naturally infected). This is the first report of P. paroecandrum on L. havardii. References: (1) W. A. Mackay and T. D. Davis. HortScience 33:348, 1998. (2) A. J. Van der Plaats-Niterink. Monograph of the genus Pythium. Studies Mycol. 21:1, 1981.

First Report of Verticillium dahliae Causing Wilt on Solanum cardiophyllum and Solanum ehrenbergii.

Solanum cardiophyllum Lindl and Solanum ehrenbergii (Bitt) Rydb are wild edible potato plants found throughout central Mexico (2). These plants are not cultivated, but farmers collect tubers for their own consumption and to sell at local markets (2). Wilted plants were observed in experimental plots of these wild potatoes established near Chapingo, Mexico, during spring 1983. Initial symptoms included wilting and dark yellowing of lower leaves. As the disease advanced, all of the foliage became chlorotic and the plants wilted and eventually died. Disease incidence was 13.4% for S. ehrenbergii and 0.2% for S. cardiophyllum. Verticillium dahliae Kleb. was consistently isolated from the roots and lower stems of diseased plants of both Solanum species. The isolating procedure consisted of thoroughly rinsing roots and lower stems with tap water and cutting roots and stems into 3- to 6-cm sections that were placed in 10% bleach for 3 to 5 min. Bleach excess was removed with sterile paper, and the tissue sections were cut into smaller pieces (0.5 cm) and placed on potato dextrose agar (PDA) plates. Cultures of Verticillium produced numerous dark microsclerotia of various shapes and sizes (0.05 to 0.1 mm); erect, slender, hyaline, and branched conidiophores; and elliptical and hyaline, single-celled conidia characteristic of V. dahliae (1). Pathogenicity studies were conducted in a greenhouse on 2-month-old S. cardiophyllum and S. ehrenbergii plants grown from tubers. Inoculum was obtained from colonies growing on PDA for 10 days producing abundant conidia. Conidial suspensions were obtained by flooding the plate cultures with sterile distilled water, filtering the suspension with two layers of cheesecloth, and adjusting the inoculum to 1.0 × 106 conidia/ml (3). Ten ml of the conidial suspension were applied to each of four holes 5 cm deep and 3 to 5 cm next to the crown of each plant. Symptoms similar to those observed on field-grown plants were observed 15 days after inoculation, and V. dahliae was re-isolated from lower stems and roots. All inoculated plants were dead 4 weeks after inoculation. Water-inoculated plants remained healthy throughout the experiments. This is the first report of V. dahliae on S. cardiophyllum and S. ehrenbergii. References: (1) G. R. Dixon. Vegetable Crop Diseases. Avi Publishing, Westport, Connecticut. 1981. (2) J. Galindo. Naturaleza 13:175, 1982. (3) H. A. Melouk and C. E. Horner. Phytopathology 65:767, 1975.

Formation of Phytophthora infestans Oospores in Nature on Tubers in Central Mexico.

Oospore formation by Phytophthora infestans in nature has been detected on potato leaflets in central Mexico (1), but there are no reports of oospore formation on tubers. A severe late blight epidemic occurred in Calimaya, Mexico, in fields where potato cv. Alpha was planted during the summer of 2000. Yield was reduced despite numerous applications of fungicide. Four hundred potato tubers left in the field were collected from the upper 10 cm of soil and examined for late blight symptoms. Tubers with soft and dry rot symptoms were observed, but symptoms of pink rot (Phytophthora erythroseptica) were not found. Four percent of the tubers showed late blight symptoms. Sections of 10 tubers with late blight symptoms were air-dried for 2 weeks in the laboratory and homogenized with a mortar and pestle. Glycerol was added to the homogenized tissue and observed microscopically. Aplerotic oospores (10 to 15 oospores per tuber) with amphyginous antheridia typical of P. infestans were observed. P. mirabilis morphologically similar to P. infestans is present in the area but it does not infect potato tubers. The number of oospores observed in our tuber sample was much lower than the number reported on leaflets (>1,000 oospores per leaflet) in the Toluca Valley. Low numbers of oospores have been reported on tubers artificially inoculated with P. infestans under field conditions (2). Infected tubers left in the field may act as a source of primary inoculum. To our knowledge, this is the first report of oospores of P. infestans found on tubers in Mexico under natural field conditions. References: (1) M. E. Gallegly and J. Galindo. Phytopathology 48:274, 1958. (2) A. Levin et al. Phytopathology 91:579, 2001.

First Report of Pythium aphanidermatum Causing Crown and Stem Rot on Opuntia ficus-indica.

Opuntia ficus-indica (L.) Mill. (prickly pear cactus) is grown in semiarid regions of Baja California Sur (BCS), Mexico for human consumption and forage. Most of the produce is sold at local markets as a vegetable; however, there is an increasing demand from international markets. O. ficus-indica is propagated using individual cladodes, which are planted with half of the cladode covered with soil. Collapsed plants were observed in a commercial orchard near La Paz, BCS, during March 2000, and in an experimental plot at CIBNOR during August 2000. Disease incidence was 12% in the orchard and 27% at CIBNOR. The initial symptoms were soft, dark brown lesions on the cladode at the soil line. As the disease advanced, the lesions progressed along the soil line and to the upper part of the cladode. In some plants the infection reached upward to the next cladode. Root rot was observed in those cladode areas that were already rotting. Depending of the advance of the rot in the base cladode and the size of the plants, larger plants collapsed more rapidly than smaller plants, but eventually all plants with rot lesions collapsed. The organism consistently isolated from diseased cladodes of several varieties of O. ficus-indica produced inflated sporangia, intercalary antheridia, and oospores described for Pythium aphanidermatum Edson (Fitzp.) (2). To isolate the pathogen, cladodes with lesions were washed with detergent and brush, rinsed with tap water, and then the epidermis was covered with 95% ethanol and the ethanol burned. The epidermis was peeled away from the edge of the lesion and 1 square cm sections were aseptically removed. Tissue sections were plated out on potato-dextrose agar (PDA) plates. Pathogenicity studies were made twice in a greenhouse on a total of 16 potted O. ficus-indica plants with only one cladode. Inoculum was obtained from colonies growing on V8 agar for 7 days producing abundant oospores. Thirty milliliters of an oospore suspension (240 oospores per ml) and V8 agar plugs containing mycelia and oospores were applied next to the crown of the Opuntia plants. Initial symptoms were observed 2 days after inoculation and were similar to those observed on field-grown plants. All inoculated plants were dead 5 to 10 days after inoculation. P. aphanidermatum was re-isolated from diseased cladodes. Water-inoculated plants remained healthy throughout the experiments. P. aphanidermatum has been reported causing root rot in Opuntia sp. (1). This is the first report of P. aphanidermatum on O. ficus-indica. References: (1) S. A. Alfieri Jr. et al. Fl. Dept. Agric. Cons. Serv. Div. Plant Ind. Bull. 11 (rev.), 1984. (2) A. J. Van der Plaats-Niterink. Monograph of the genus Pythium. Studies Mycol. 21:1, 1981.

Buckeye Rot of Tomato Caused by Phytophthora capsici in Michoacan, Mexico.

The state of Michoacan is one of the main fresh pepper (Capsicum annuum L.) and tomato (Lycopersicon esculentum Mill.) producers in Mexico. During the last 5 years, pepper-producing areas in the state have become unproductive due to root-rotting pathogens, mainly Phytophthora capsici Leonian. Growers trying to overcome losses have increased tomato production in areas previously used for pepper production. Field-grown tomato plants with diseased green tomato fruits were observed in Tacambaro, Michoacan, during August 2002. Initially, brown-to-black lesions developed on fruits in contact with soil, followed by infection of the upper fruits in the raceme. Lesions enlarged and dark zonate "buckeye" bands were formed in the affected area. Diseased fruit turned mushy. Symptoms observed were similar to those described for buckeye rot of tomato (1). Diseased fruit were surface disinfested with 70% ethanol, cut into 0.5-cm slices, and incubated in a moist chamber to induce mycelial colonization. Isolation from mycelial tufts growing through the tomato slice was performed 3 days later, and mycelia was transferred to PARP selective medium (corn meal agar (CMA) plus ampicillin, pimaricin, rifampicin, and pentachloronitrobenzene). P. capsici was consistently isolated from diseased tomato fruits. Oomycete identification was based on sporangial and gametangial characteristics of cultures grown on CMA (1). Sporangia microscopically observed were spherical, broadly ellipsoid or obovoid with one papilla (occasionally two papillae), and deciduous with a long pedicel. Chlamydospores were not present (2). The isolates were heterothallic, and oogonia with amphigynous antheridia were observed in pairings with A1 and A2 isolates of P. capsici. Three isolates were A1 and two isolates were A2. To confirm pathogenicity, two experiments were performed using 20 healthy unwounded green tomatoes. One isolate of each mating type was tested. Isolates were grown for 5 days on CMA, and fruits were inoculated by placing P. capsici in contact with the fruit. Inoculated fruits were kept in a moist chamber at room temperature (17 to 20°C). Initial symptoms in the form of brown-to-black lesions appeared 24 h after inoculation. One week after inoculation, symptoms were similar to those observed in field-grown plants, and P. capsici was recovered from the margins of the diseased tissue. All inoculated fruits rotted. To our knowledge, this is the first report of P. capsici causing buckeye rot on tomato in Michoacan and of the presence of both mating types in the area. Reference: (1) D. C. Erwin and O. K. Ribeiro. Phytophthora Diseases Worldwide. The American Phytopathological Society. St. Paul MN, 1996. (2) M. Aragaki and J. Y. Uchida. Mycologia 93:137, 2001.

Soilborne Oospores of Phytophthora infestans in Central Mexico Survive Winter Fallow and Infect Potato Plants in the Field.

Survival and infectivity of oospores in soils naturally infested with P. infestans oospores were studied in central Mexico. Sporangia were selectively eliminated from soil samples to determine infectivity attributable to the presence of oospores. Selective elimination of sporangia was achieved by two cycles of wetting and drying the soil. Oospore concentration, viability, and infectivity varied among soils collected during the winter fallow in different locations of central Mexico. In some soils, oospores were infective regardless of the time at which they were collected during the winter fallow. However, oospore viability and infectivity decreased following 2 years of intercropping. The number of stem lesions and initial disease severity were significantly higher in soils with moderate (20 to 39 oospores g-1 soil) oospore infestation compared with soils with low (0 to 19 oospores g-1 soil) infestation. Our study confirms that oospores can survive winter fallow and serve as a source of primary inoculum in the central highlands of Mexico. Oospore survival appeared lower in the Toluca Valley soil, which may be an indication of soil suppressiveness.

Pythium aphanidermatum Causing Collar Rot on Papaya in Baja California Sur, Mexico.

Demand from international markets for organically grown papaya (Carica papaya L.) from Baja California Sur is increasing. Occasional rains during the summer of 2000 provided extra moisture to the soil in most papaya farms in the state. Collapsed plants of the Hawaiian type cv. Sunset were observed in 20 commercial orchards in Pescadero, Baja California Sur from July through September 2000. The average disease incidence per orchard was 2%, although there was one orchard with 25% of diseased plants. The initial symptoms were soft, watery lesions at the soil line. As collar rot progressed, foliage wilted. In plants with severe collar rotting, lesions girdled the stem, causing the foliage to be completely wilted and the plants to collapse. Root rot was not observed in plants with collar rot. To isolate the pathogen, 15-cm-long portions of the stem with rot lesions were excised, washed with soap and brush, and rinsed with tap water. Transverse sections of the stem were lightly sprayed with 95% ethanol, and the ethanol was ignited. The superficially burned tissue was removed aseptically, and 1-cm-square sections were cut from the remaining tissue. These sections were plated on potato dextrose agar. The fungus consistently isolated from disease stems grew optimally at 37°C, producing lobate sporangia, antheridia mostly intercalary, and aplerotic oospores characteristic of Pythium aphanidermatum (Edson) Fitzp. (3). Pathogenicity studies were conducted twice in a screened house on a total of 36 4 to 6 month-old Sunset papaya plants 85 to 100 cm tall. Two longitudinal wounds (0.5 cm long and 0.2 cm deep) were made on opposite sides at the base of the stem using sterile razor blades. Pathogen inoculum was obtained from 7-day-old V8 agar cultures. Thirty milliliters of an oospore suspension (200 oospores per ml) and V8 agar plugs containing mycelia and oospores were applied next to the crown of wounded and nonwounded plants. Initial symptoms were observed 3 days after inoculation and were similar to those observed on diseased plants in the field. Wounded, pathogen-inoculated plants were dead 6 days after inoculation. P. aphanidermatum was reisolated from diseased plants. Nonwounded pathogen-inoculated plants, wounded water-inoculated plants, and nonwounded water-inoculated plants remained healthy throughout the experiments. Pathogenicity experiments suggest that field grown papaya plants might be predisposed to infection by P. aphanidermatum due to mechanical damage to the base of the stem caused by abiotic factors such as wind driven sand. P. aphanidermatum has been reported to cause root rot in C. papaya in Tabasco, Mexico (2), and the United States (1). This is the first report of P. aphanidermatum causing collar rot on C. papaya in Baja California Sur. References: (1) Anonymous. 1960. Index of Plant Diseases in the United States. USDA. Handbook. No. 165. Washington, DC. (2) M. I. Saldaña et al. Rev. Mex. Fitopatol. 3:14, 1985. (3) A. J. Van der Plaats-Niterink. Studies Mycol. 21:1, 1981.

First Report of Blight on Ipomoea purpurea Caused by Phytophthora ipomoeae.

Several wild species of Ipomoea grow in the central highlands of Mexico. During the summer of 1999, in Metepec, Mexico, blighted leaves and petioles of Ipomoea purpurea were collected from diseased plants and placed in a moist chamber to induce sporulation. Sporangia that formed on the lesions were transferred with a piece of agar to selective rye agar medium (2). Phytophthora ipomoeae was consistently isolated. Species identification was based on sporangial and gametangial characteristics of five cultures grown on rye agar. Sporangia were mainly ellipsoid but occasionally ovoid, semipapillated, and deciduous with a short pedicel. All isolates were homothallic with smooth-walled and aplerotic oospores. Genotypic analysis for the allozymes Peptidase (Pep) and Glucose-6-phosphate isomerase (Gpi) indicated that all five isolates belonged to one genotype with alleles 78/78 (Pep) and 108/108 (Gpi). Morphological characteristics and the allozyme genotype correspond to the new, recently described species P. ipomoeae Flier & Grünwald (1) isolated from I. orizabensis (Pelletan) Ledeb. ex Steud. (I. tyrianthina) Lindl. and I. longepedunculata (Mart. & Gal.) Hemsl. Pathogenicity tests were carried out with leaves from greenhouse-grown I. purpurea plants. Detached leaves were inoculated with a suspension of 103 sporangia per ml and kept in a moist chamber at room temperature (17 ± 3°C). Lesions were observed between 7 and 15 days after inoculation and were characteristic of those observed in the field. The pathogen was reisolated from inoculated symptomatic tissue. To our knowledge, this is the first report of blight on I. purpurea caused by P. ipomoeae. References: (1) W. Flier et al. Mycol. Res. 106:848, 2002. (2) N. J. Grünwald et al. Phytopathology 91:882, 2001.

Pseudomonas corrugata Causing Pith Necrosis on Tomato Plants in Baja California Sur, México.

Fresh market tomato (Lycopersicon esculentum Mill.) cultivars are grown in field and greenhouse areas in Baja California Sur from October to June for international markets. During March and April 2001, field-grown tomato plants showing external necrotic stem lesions and hollowed necrotic pith were observed in a 50-ha field 30 km south of La Paz. The average disease incidence in the field was 3%. Most infected plants presented necrotic lesions in the main stem 20 to 30 cm above the soil line. A few plants also presented necrotic lesions in lateral branches. Transversally cut sections in the necrotic stem area showed rotting of the vascular system with hollow cavities, typical symptom of pith necrosis. To isolate the pathogen, 5-cm-long transverse portions of diseased stems were excised, washed with soap and brushed, and rinsed with tap water. The stem portions were soaked in 10% bleach for 2 min, blotted dry on sterile paper, and 1-cm2 sections were cut to include the margins of the necrotic pith. These sections were plated on nutrient agar and incubated at 28 to 30°C. Gram-negative, rod-shaped bacteria were consistently isolated from stems with pith necrosis. They were identified as Pseudomonas corrugata using Biolog analysis (carbon source utilization at 37°C), with a similarity index of 1.0. To confirm pathogenicity, experiments were conducted twice in a screenhouse on a total of 24 2-month-old tomato cv. Rutgers plants (50 to 60 cm tall). Bacteria were injected with a syringe into the stems above the point of lateral branching at two different sites, using 0.25 to 0.5 ml of a bacterial suspension (105 CFU/ml). Injection points were sealed after inoculation with a small amount of petroleum jelly. Necrotic lesions surrounding the point of injection were observed 10 days after inoculation. Four weeks after inoculation, plants showed necrotic pith symptoms similar to those observed on field-grown plants, and P. corrugata was recovered from the margins of areas with necrotic pith. Control plants, which were injected with water, remained healthy throughout the experiments. P. corrugata has been reported to cause pith necrosis in tomato plants in California (3), Florida (2), and the northern part of the Baja California peninsula (1). This report confirms the presence of P. corrugata in the Baja California peninsula, and to our knowledge, this is the first report of P. corrugata causing pith necrosis in tomato plants in the southern state of Baja California Sur, Mexico. References: (1) N. B. Carroll et al. N.C. Agric. Res. Serv. Tech. Bull. No. 300, 1992. (2) J. B. Jones et al. Plant Dis. 67:425, 1983. (3) M. Lai et al. Plant Dis. 67:110, 1983.