RESUMO
During 2004, Geraldton wax plants (Chamaelaucium uncinatum cv. BM Violet) from commercial greenhouses in La Plata, Argentina showed gall-like structures on collars and roots similar to those reported by Carsten et al. (2). No pathogenic fungi were associated with lesions. Bacteria isolated from galls grown on medium 1A and D1M agar yielded colonies typical of Agrobacterium sp. (4). Four isolates were selected for further study. All isolates were aerobic, gram-negative rods and produced 3-ketolactose, but did not produce alkali from l-tartrate or accumulate poly-ß-hydroxybutyrate inclusions. The isolates were able to grow with 2% NaCl, at 35°C, and also on potato dextrose agar medium containing CaCO3 (4) but without acid clarification. Polymerase chain reaction analysis with primers VCF/VCR that amplified the expected 730-bp product of virC operon confirmed that all strains harboured a Ti plasmid (3,4). In addition, strains were screened for extrachromosomal DNA by the in-well lysis and electrophoresis procedure of Eckhardt with minor modifications as reported by Albiach and Lopez (1) and compared with strain Agrobacterium tumefaciens LBA 958, all Argentinean strains tested harbored a plasmid similar in size. Pathogenicity was verified on Geraldton wax and tobacco plants. Bacterial suspensions of each isolate (108 CFU/ml) were pricked into the stems. Control plants were pricked with sterile distilled water. Plants were maintained at 23 ± 3°C and symptoms were recorded after 45 days. Development of almost spherical, white-to-flesh-colored, rough, spongy and wart-like galls at the inoculation sites of the inoculated collars, stems, and trunks were registered. In Geraldton wax, as galls aged, they become dark brown to black, rough, and woody. Bacteria were reisolated from these galls fulfilling Koch's postulates. No lesions were observed on the controls. To our knowledge, this is the first report of A. tumefaciens on C. uncinatum in Argentina. References: (1) M. R. Albiach and M. M. López. Appl. Environ. Microbiol. 58:2683, 1992. (2) E. Carstens et al. Plant Dis. 83:783, 1999. (3) H. Sawada et al. Appl. Environ. Microbiol. 61:828, 1995. (4) N. W. Schaad et al. Laboratory Guide for Identification of Plant Pathogenic Bacteria. 3rd ed. The American Phytopathological Society. St. Paul, MN, 2001.
RESUMO
Fusarium solani Mart. (Sacc.) is the causal agent of stem rot and damping-off of lisianthus (Eustoma grandiflorum (Raf.) Shinn.) (1). Since the end of the 1980s, when this flower crop was introduced in Argentina, it has been affected by a basal stem rot (2). A previously undescribed disease was observed in 100% of the greenhouses in the Buenos Aires Province that grow lisianthus. Symptoms that developed after seedlings were transplanted included stunting, shortened internodes with reduced stem diameter, and small narrow leaves that were a dull green color. Some affected plants turned yellow-brownish and died 2 to 3 months after transplanting. Other plants recovered but produced low quality flowers later than normal. A third group of plants remained stunted (5 to 10 cm high) until the last flower harvest (about 8 to 10 months). F. solani was consistently isolated from basal stems and roots of diseased plants. For pathogenicity tests, inoculum was produced by culturing the fungus for 10 days in petri dishes containing sterile moistened rice. Inoculum was air dried, crushed, and mixed with soil that had been autoclaved at 112°C for 40 min on each of two consecutive days. The propagules in the soil were estimated by soil plate dilutions on the Nash & Snyder-PCNB medium at a ratio of about 104 CFU/g soil. Twenty plants of each cultivar Echo White and Echo Blue, whose roots had been pruned, were planted in both infested and noninfested soil. After about 40 days, stunting was observed in 85% of the inoculated plants, while controls remained asymptomatic. F. solani was reisolated from symptomatic plants, thus fulfilling Koch's postulates. A test also was conducted in a commercial greenhouse that produced lisianthus for several years, in which healthy plants were planted in three plots fumigated with methyl bromide and in three nonfumigated plots. The mean cfu/g soil of F. solani in the methyl-bromide treated plots was 5 × 102 and 1.6 × 104 CFU/g in the nontreated plot. After 120 days, the incidence of stunting in the treated plots was 0.6 and about 88% in the control plots. F. solani was recovered from symptomatic plants. Because disinfestation of soil is generally practiced in flower production, stunted plants are limited and can be confused with root problems. This is the first report of F. solani causing stunt on lisianthus. References: (1) J. J. Taubenhaus and W. N. Ezekiel. Phytopathology 24:19, 1934. (2) S. M. Wolcan and G. A. Lori. Invest. Agr. Prot. Veg. 11:465, 1996.
RESUMO
Geraldton waxplant (Chamaelauciun uncinatum Schauer.) is a shrub that produces flowered branches used in bouquets. Waxplant was introduced into Argentina (Buenos Aires province) in the 1990s and currently is cultivated in greenhouses. In the summer of 1995, a previously undescribed disease was observed on plants at different stages of growth. Plants showed a progressive yellowing of the branches from the base to the top of the stems. Leaves of diseased plants became grayish green, then yellow, and finally straw colored. Leaves remained attached to the branches after the plants died. Roots and stem discoloration was observed and the root cortex sloughed off. A Phytophthora sp. was isolated from the roots and lower stems of symptomatic plants. Koch's postulates were completed in a greenhouse at 28 to 34°C using the cvs. Snowflake, Violet, and Orchid. Inoculum was obtained by growing the fungus for 7 days in Petri dishes containing an autoclaved wet mixture of polished rice + wheat bran + V8 juice + perlite (1:1:1:1, by volume). The inoculum was mixed with soil (4:100, wt/wt) in pots, and 15 4-month-old plants per cultivar were transplanted into infested and noninfested soil. Plants of the cv. Snowflake were the most susceptible with symptoms starting 25 days after inoculation. At the end of the trial (five months) 86% of these plants died. Disease development was delayed on plants of cvs. Orchid and Violet and mortality was only 20% on Orchid and 26% on Violet. Control plants remained healthy. The Phytophthora sp. was reisolated from plants showing typical symptoms. The fungus was cultivated on potato-dextrose agar at 25°C and morphological characteristics were recorded. The colony diameter was 3.7 cm after 5 days. Ovoid, obturbinate and obpyriform to limoniform, papillate and caducous sporangia were observed. They averaged 42.1 ± 10.7 × 31.7 ± 9.2 µm (range 25.0 to 65.0 × 18.7 to 55.0 µm) with a length-breadth ratio = 1:1 to 1.81, av. 1.25:1. Many sporangia were distorted in their shapes and averaged 61.7 ± 30.5 × 24.8 ± 4.5 µm (range 27.5 to 125.0 × 20.0 to 32.5 µm) with a length-breadth ratio = 1.31:1 to 4.6:1, av. 2.1:1. After the zoospores were discharged, a narrow exit pore was observed (3.7 to 8.7 µm, av. 6.9 µm). Pedicels were not conspicuous or were short when present. Oogonia and amphigynous antheridia were readily observed in single culture. Spherical oospores nearly filling the oogonium and containing many subcellular inclusions averaged 29.7 ± 8.9 µm (range 17.5 to 47.5 µm). Terminal or intercalary, rounded to ovoid chlamydospores developed in smooth or swollen hyphae. Based on cultural and morphological characteristics, the species infecting waxplant was identified as P. boehmeriae Sawada (1). This is the first record of P. boehmeriae on geraldton waxplant. References: (1) D. C. Erwin and O. K. Ribeiro. 1996. Phytophthora Diseases Worldwide. The American Phytopathological Society, St. Paul, MN.
RESUMO
In 1995, powdery mildew was observed on commercial greenhousegrown Aster ericoides L. from La Plata, Buenos Aires Province. The disease affected about 95% of the growers. Mildew first appeared as white circular patches on the adaxial surface of leaves. As disease progressed, the abaxial surface of leaves, petioles, stems, and calyces were covered by cottony masses of mycelium and conidia, and basal leaves later wilted and died. Young plants (4 to 5 leaves) through flowering plants were affected. Conidia were ovoid-cylindrical, often slightly constricted at the ends, and were produced in chains on unbranched conidiophores. Conidia lacked fibrosin bodies and ranged from 30 to 41 µm × 10 to 19 µm. Long unbranched germ tubes were formed from the ends of conidia. The morphological characteristics of the fungus fit those described for Erysiphe cichoracearum DC (1). In addition, the perfect stage was found on older tissues. Subglobose, dark brown cleistothecia (105 to 210 µm in diameter) with a basal ring of myceloid appendages were observed. Cleistothecia contained multiple ellipsoid asci (48 to 69 µm × 30 to 37 µm) with two hyaline, one-celled, ellipsoid ascospores (22 to 26 µm × 11 to 15 µm). Pathogenicity was tested by pressing diseased leaves onto healthy leaves of aster cv. Sunset and incubating plants in humidity chambers for 48 h. The powdery mildew that developed was morphologically identical to the original isolate. This is the first report of E. cichoracearum on heath aster in Argentina. Reference: (1) H. J. Boesewinkel. Bot. Rev. 46:167, 1980.
RESUMO
Passion fruit (Passiflora edulis Sims.) is a subtropical fruit recently cultivated in Misiones Province, Argentina. In spring 1997, a severe epidemic of anthracnose was observed. Disease incidence was â95%, causing high yield losses. Sunken, gray lesions on the whole surface of young fruits were observed. Under humid conditions, acervuli containing masses of spores and dark setae were found within lesions. On leaves, tendrils, and twigs, circular and irregular brown spots with darker edges were observed. Abortion of flowers also was recorded. Cultures on potato dextrose agar yielded abundant, gray aerial mycelium and one-celled, hyaline, oblong conidia with obtuse or rounded ends (11.2 to 15.0 × 3.8 to 4.6 µm). Perithecia were scarce (90.2 to 220.0 µm). Asci were not conspicuous, and ascospores measured 10.8 to 23.4 × 3.5 to 7.0 µm. Based on morphological characteristics, the fungus was identified as Glomerella cingulata (anamorph Colletotrichum gloeosporioides) (2). Fruits and leaves of P. edulis with and without wounds were sprayed with a conidial suspension (106/ml) and incubated in plastic bags for 48 h. Lesions similar to original symptoms were observed after 2 weeks only on wounded leaves and fruits. G. cingulata was reisolated, confirming Koch's postulates. This disease has been recorded in Brazil and Japan (1). This is the first report of G. cingulata on passion fruit in Argentina. Reference: (1) E. Francisco Neto et al. Summa Phytopathol. 21:25, 1995. (2) J. A. von Arx. Phytopathol. Z. 29:413, 1957.
RESUMO
In June 1998, during a cool, humid period, typical bacterial spot symptoms were observed on basil plantlets (Ocimun basilicum L. 'Royal Louis' and 'Zaes') in a commercial greenhouse in La Plata, Argentina. Affected plants had dark brown to black lesions on cotyledons. Spots on leaves were first water soaked, then became necrotic and progressed inward from the margins. Disease incidence approached 30%. Symptoms were similar to those reported by Little et al. (2) on basil affected by Pseudomonas viridiflava. No pathogenic fungi or viruses were associated with symptomatic plants. Bacterial streaming was observed from lesion margins. Bacteria consistently isolated from leaf lesions formed cream-colored, glistening, convex colonies on sucrose peptone agar and a green fluorescent pigment on King's medium B. Bacterial growth produced a distinctive olive green pigment on glycerol agar medium and a pink pigment on T-5 medium (1). Four isolates selected for further study were aerobic, Gram-negative, non-spore-forming rods. In LOPAT (levan-oxidase-potato rot-arginine dihydrolase-tobacco hypersensitivity) tests, all induced a hypersensitive response in tobacco plants, caused soft rot of potato tubers, and were negative for levan, oxidase, and arginine dihydrolase. In addition, strains rotted onion slices and produced a reddish sunken lesion on bean pods. Acid was produced aerobically from D-glucose, mannitol, mesoinositol and sorbitol, but not from D-arabinose, L-rhamnose, melibiose, amygdalin, or sucrose. Bacteria used D-tartrate, pyruvate, and citrate, but not benzoate. The strains did not hydrolyze starch, exhibited an oxidative metabolism of glucose, and did not reduce nitrates to nitrites or accumulate poly-ß-hydroxybutyrate inclusions. Negative reactions were obtained with indole, ornithine, and D-tryptophan. Isolates hydrolyzed gelatine, used Tween 80, were positive for catalase, and were unable to grow in the presence of 5% NaCl. Colonies developed at 4°C but not 37°C. Reactions were identical to those of reference strains ICMP 5776 and 12363, which were included in all tests for comparison. Pathogenicity was verified on 35-day-old basil plants by both spraying and infiltration inoculations with bacterial suspensions (108 and 105 cells per ml, respectively). Carborundum was included in the inoculum used for a set of plants inoculated by spraying. Controls were injected or sprayed (with and without Carborundum) with sterile, distilled water. In addition, bean (Phaseolus vulgaris cv. Nag12 INTA) and lettuce (Lactuca sativa cv. criolla), both reported as host plants, were inoculated by spraying with bacterial suspensions of 107 cells per ml plus Carborundum. After 48 h in a humid chamber, inoculated plants and controls were maintained at 23 ± 3°C. Symptoms on basil plants inoculated by injection or spraying with Carborundum were identical to those observed on basil in the field. Symptoms on bean and lettuce were similar to those described for P. viridiflava. The bacterium was reisolated from lesions of all species tested, fulfilling Koch's postulates. No lesions were observed on controls or on plants sprayed without Carborundum, suggesting that bacteria gain entry through wounds. The microorganism was identified by physiological tests and polymerase chain reaction as P. viridiflava. This is the first report of bacterial leaf spot of basil in Argentina. References: (1) R. Gitaitis et al. Plant Dis. 81:897, 1997. (2) E. L. Little et al. Plant Dis. 78:831, 1994.
RESUMO
During the summer of 1995-1996, an 80-ha field of 6-year-old asparagus plants (cv. UC 72) in Saladillo (Province of Buenos Aires) was affected by a decline syndrome (1). The plants showed a decline in vigor and approximately 60 to 70% of the plants died. The symptomatic plants were chlorotic, stunted, with stem lesions and crown and root rot. Fusarium moniliforme and F. proliferatum were isolated from vascular and epidermal tissues of roots, crowns, and stems. Identification of Fusarium to species was made by examining conidiogenous cells from colonies cultured on KCl medium (2). Microconidia were born in long and short chains and false heads. The isolates were identified based on the the presence of polyphialides in F. proliferatum and their absence in F. moniliforme, which produces monophialides only (2). In two separate trials, asparagus seeds (cv. UC 72) were surface sterilized and placed in steamed soil infested with a conidial suspension of each species. The viable propagules in the soil (CFU per g) were estimated by soil plate dilutions on Nash & Snyder-PCNB (pentachloronitrobenzene) medium. The F. moniliforme and F. proliferatum soil densities were 19.2 × 103 and 23 × 103 CFU per g of soil, respectively. The pots were placed in the greenhouse on different benches to avoid cross-contamination. After 4 months, inoculated plants showed root and crown discoloration. F. moniliforme and F. proliferatum were reisolated (64 and 75%, respectively) from discolored portions of internal and external root and crown tissues. Although the stems did not show symptoms, F. moniliforme and F. proliferatum were also recovered (27 and 38%, respectively) from asymptomatic tissues. Six months after inoculation the plants developed chlorotic symptoms with crown and root rot, and then wilted. F. moniliforme and F. proliferatum were reisolated from root systems, crowns, and stems of all inoculated plants. F. moniliforme and F. proliferatum are involved in corn stalk and ear rot in Argentina. Corn and asparagus are frequently grown in close proximity and often follow one another at a particular site. Airborne and soil debris carrying F. moniliforme and F proliferatum from corn may be an additional source of inoculum for asparagus in Argentina. The results indicate that the presence of F. moniliforme and F. proliferatum is a factor that contributes to asparagus decline in Argentina. References: (1) W. H. Elmer et al. Plant Dis. 80:117, 1996. (2) P. E. Nelson et al. Fusarium Species: An Illustrated Manual for Identification. Pennsylvania State University, University Park, 1983.