scholarly journals First Report of Phytophthora megasperma and Pythium irregulare As Olive Tree Root Pathogens

Plant Disease ◽  
1997 ◽  
Vol 81 (10) ◽  
pp. 1216-1216 ◽  
Author(s):  
M. E. Sánchez-Hernández ◽  
A. Ruiz-Dávila ◽  
A. Trapero-Casas

Several species of the genus Phytophthora are associated with root rot and trunk cankers in olive trees (Olea europaea L.). Among them, Phytophthora megasperma has been cited as being associated with olive root rots in Greece (1). Unidentified species of Pythium and Phytophthora have also been associated with olive tree root rots in the United States. However, the status of P. megasperma and Pythium spp. as olive tree root pathogens has remained unclear. Following a 5-year period of severe drought in southern Spain, autumn-winter rainfall rates in 1996 to 1997 steadily increased in both quantity and frequency. Under these unusually wet conditions, olive trees remained waterlogged for several months. During this period, we observed foliar wilting, dieback, and death of young trees, and later found extensive root necrosis. In 46 of 49 affected plantations surveyed, P. megasperma was consistently isolated from the rotted rootlets, particularly in young (<1- to 10-year-old trees) plantations. This fungus was not detected on plant material affected by damping-off from several Spanish olive tree nurseries. The opposite situation occurred with P. irregulare. This species was not associated with rotted rootlets in the field. In contrast, it was consistently isolated from necrotic rootlets from young olive plants affected by damping-off. These plants were grown in a sand-lime-peat soil mixture under greenhouse conditions and showed foliar wilting and extensive necrosis of the root systems. Pathogenicity tests were conducted with several isolates of P. megasperma and P. irregulare on 6-month-old rooted cuttings of olive, under both weekly watering and waterlogged conditions. Under waterlogged conditions, both fungal species produced extensive root necrosis 2 weeks after inoculation that resulted in wilting of the aerial parts and rapid plant death. Waterlogged control plants remained without foliar symptoms but a low degree of root necrosis was recorded. In addition, under weekly watering conditions, plants inoculated with either species showed some degree of root rot but foliar symptoms were not evident. No differences in pathogenicity were observed within the Phytophthora or Pythium isolates. Reference: (1) H. Kouyeas and A. Chitzanidis. Ann. Inst. Phytopathol. Benaki 8:175, 1968.

Plant Disease ◽  
2016 ◽  
Vol 100 (12) ◽  
pp. 2427-2433 ◽  
Author(s):  
Sahar Arabiat ◽  
Mohamed F. R. Khan

Rhizoctonia damping-off and crown and root rot caused by Rhizoctonia solani are major diseases of sugar beet (Beta vulgaris L.) worldwide, and growers in the United States rely on fungicides for disease management. Sensitivity of R. solani to fungicides was evaluated in vitro using a mycelial radial growth assay and by evaluating disease severity on R. solani AG 2-2 inoculated plants treated with fungicides in the greenhouse. The mean concentration that caused 50% mycelial growth inhibition (EC50) values for baseline isolates (collected before the fungicides were registered for sugar beet) were 49.7, 97.1, 0.3, 0.2, and 0.9 μg ml−1 and for nonbaseline isolates (collected after registration and use of fungicides) were 296.1, 341.7, 0.9, 0.2, and 0.6 μg ml−1 for azoxystrobin, trifloxystrobin, pyraclostrobin, penthiopyrad, and prothioconazole, respectively. The mean EC50 values of azoxystrobin, trifloxystrobin, and pyraclostrobin significantly increased in the nonbaseline isolates compared with baseline isolates, with a resistant factor of 6.0, 3.5, and 3.0, respectively. Frequency of isolates with EC50 values >10 μg ml−1 for azoxystrobin and trifloxystrobin increased from 25% in baseline isolates to 80% in nonbaseline isolates. Although sensitivity of nonbaseline isolates of R. solani to quinone outside inhibitors decreased, these fungicides at labeled rates were still effective at controlling the pathogen under greenhouse conditions.


Author(s):  
Lipi Parikh ◽  
Swarnalatha Moparthi ◽  
Frankie Crutcher ◽  
Mary Burrows

Pythium root rot and damping-off caused by Pythium spp. are important diseases of pulse crops. In a 2016 pathogen survey from dry pea growing fields in Montana, along with commonly known causal agents P. ultimum and P. irregulare, an isolate identified as P. sylvaticum (LPPY17) was isolated from the rhizosphere of a diseased pea plant collected from Valley County, MT. Root rots and damping-off caused by P. sylvaticum have not previously been reported for chickpea, pea, and lentil crops. The isolate LPPY17 was tested for fungicide resistance in vitro, and results indicated a reduced sensitivity to metalaxyl and ethaboxam containing fungicides. LPPY17 was also tested for pathogenicity on chickpea, pea, and lentil seedlings in the greenhouse, and the results from the study revealed LPPY17 is capable of causing both root rots and damping off. Due to the potential pathogenicity and reduced fungicide sensitivity of this species, in the future it will be important to monitor for P. sylvaticum in pulse root rot surveys and diagnostics, as management options may be different from other common Pythium spp.


2005 ◽  
Vol 77 (3) ◽  
pp. 99-111 ◽  
Author(s):  
P.R. Verma

Rhizoctonia solani AG2-1 is the principal pathogen causing damping-off and seedling and mature plant root rot (brown girdling root rot) in oilseed rape and canola (Brassica napus and B. rapa) in western Canada and the United States; AG4 isolates mainly attack adult plants and cause basai stem rot. Seedling infection by AG2-1 is favoured by cool weather atthe time of planting, whereas warm weather late in the growing season is more conducive for infection of mature plants by AG4 isolates. Survey data show that disease development is favoured by high soil moisture, low levels of nitrogen, phosphorus and potassium and high levels of copper in fine-textured soils. Moderate resistance in condiment mustard (Sinapis alba) and some other species appears to be genetically controlled and should be utilised in breeding programmes. Carboxin and iprodione in mixtures with insecticide gamma-HCH are recommended in Canada as seed treatments to control damping-off and seedling root rot, but do not control brown girdling root rot.


Plant Disease ◽  
2001 ◽  
Vol 85 (1) ◽  
pp. 96-96 ◽  
Author(s):  
S. O. Cacciola ◽  
G. E. Agosteo ◽  
G. Magnano di San Lio

Olive (Olea europea L.) is grown on about 154,000 ha in Sicily (southern Italy). In the summer of 1999, a few 3-year-old olive trees with decline symptoms were observed in a recently planted commercial orchard in the Enna province (Sicily). The trees were propagated on wild olive (O. europea L. var. sylvestris Brot.) rootstock. Aerial symptoms, consisting of leaf chlorosis, wilting, defoliation, and twig dieback followed in most cases by plant death, were associated with root rot and basal stem cankers. A Phytophthora sp. was consistently isolated from rotted rootlets and trunk cankers using the BNPRAH (benomyl, nystatin, pentachloronitrobenzene, rifampicin, ampicillin, and hymexazol) selective medium. Pure cultures were obtained by single-hypha transfers. The species isolated from symptomatic olive trees was identified as P. megasperma Drechsler on the basis of morphological and cultural characteristics. All isolates were homothallic, with paragynous antheridia. The diameter of oospores varied from 28 to 42 μm (mean ± SE = 36.3 ± 0.4) when they were produced on potato-dextrose agar (PDA) and from 30 to 43 μm (mean ± SE = 37.8 ± 0.4) when they were produced in saline solution. Sporangia were non-papillate. Optimum and maximum temperatures for radial growth of the colonies on PDA were 25 and 30°C, respectively. At 25°C, radial growth rate was about 6 mm per day. The identification was confirmed by the electrophoresis of mycelial proteins on a polyacrylamide slab gel. The electrophoretic banding patterns of total soluble proteins and three isozymes (esterase, fumarase, and malate dehydrogenase) of the isolate from olive were identical to those of two isolates of P. megasperma obtained from cherry and from carrot in Italy and characterized previously (1). Conversely, they were clearly distinct from the electrophoretic patterns of four isolates of P. megasperma var. sojae Hildebr. from soybean (= P. sojae Kauf. & Ger.), from those of three isolates from asparagus tentatively identified as P. megasperma sensu lato (1) and from those of reference isolates of various species producing non-papillate sporangia, including P. cambivora (Petri) Buisman, P. cinnamomi Rands, P. cryptogea Pethybr. & Laff., P. drechsleri Tucker, and P. erythroseptica Pethybr. Pathogenicity of the isolate from olive was tested in the greenhouse at 18 to 25°C using 18-month-old rooted cuttings of olive cv. Biancolilla. Cuttings were inoculated on the lower stem by inserting a 3-mm plug taken from actively growing colonies on PDA into an incision made with a sterile scalpel. The wound was sealed with waterproof tape. Agar plugs with no mycelium were placed into the stem of cuttings used as a control. The bark was stripped and lesion areas were traced and measured 60 days after inoculation. The isolate from olive produced a brown necrotic lesion (mean size = 500 mm2) around the inoculation wound and was reisolated from the lesion. Conversely, the wound healed up on control plants. P. megasperma has previously been recognized as a pathogen of olive in Greece and Spain (3). However, this is the first report of P. megasperma causing root and collar rot of olive in Italy. References: (1) S. O. Cacciola et al. Inf. Fitopatol. 46:33, 1996. (2) D. C. Erwin and O. K. Ribeiro, 1996. Phytophthora Diseases Worldwide. The American Phytopathological Society, St. Paul, MN. (3) M. E. Sánchez-Hernádez et al. Plant Dis. 81:1216, 1997.


Plant Disease ◽  
2012 ◽  
Vol 96 (9) ◽  
pp. 1378-1378 ◽  
Author(s):  
J. R. Úrbez-Torres ◽  
F. Peduto ◽  
W. D. Gubler

The California olive industry produces 99% of the U.S. olive crop, which represented a value of over $113 million in 2010. During the 2008 and 2009 growing seasons, decline of young super-high-density olive cvs. Arbequina, Arbosana, and Koroneiki trees (<4 years old) was observed in orchards throughout Glenn, Yolo, and San Joaquin Counties. Symptomatic trees showed stunted growth and chlorotic leaves with roots having black, sunken, necrotic lesions, which frequently prolonged into the base and crown of the tree. Twenty-five trees were collected from different orchards and necrotic roots as well as infected trunk tissue were plated onto potato dextrose agar amended with 0.01% tetracycline hydrochloride. Cultures were incubated at room temperature (23 ± 2°C) until fungal colonies were observed. In 17 out of 25 trees collected (68%), light yellow fungal colonies were observed from the symptomatic tissue after 7 to 10 days. Colonies turned dark yellow to orange with age and showed an orange-dark brown reverse. Both microconidia (hyaline, ellipsoidal to ovoidal and aseptate (n = 60) (6.5) 11.5 to 13.5 (17.1) × (3) 3.4 to 4.5 (5.6) μm) and macroconidia (hyaline, cylindrical, straight and/or slightly curved with one, two or three septa (n = 60) (12.5) 26.5 to 38.5 (44.1) × (4) 5.5 to 7.5 (8.5) μm) were observed. Culture and conidial morphology were in concordance with previous published description of Ilyonectria macrodidyma (Halleen, Schroers & Crous) P. Chaverri & C. Salgado (1,3,4). Identification to species level was confirmed by sequence comparison of four Californian isolates (UCCE958, UCCE959, UCCE960, and UCCE961) with sequences available in GenBank using the internal transcribed spacer region (ITS1-5.8S-ITS2) of the rDNA (primers ITS1/ITS4), a portion of the β-tubulin gene (BT1a/BT1b), and a partial sequence of the mitochondrial small subunit rDNA (NMS1/NMS2) (4). Fungal sequences of isolates from olive from California (GenBank JQ868543 to JQ868554) showed 99 to 100% homology with previously identified and deposited I. macrodidyma isolates in Genbank for all three genes. Pathogenicity of I. macrodidyma in olive cvs. Arbequina, Arbosan, and Koroneiki was investigated using two fungal isolates (UCCE958 and UCCE960) as reported by Petit and Gubler (4). The roots of 10 1-year-old trees per fungal isolate for each olive cultivar were individually inoculated with 25 ml of a 106 conidia/ml spore suspension and placed in a lath house at the UC Davis field station. Additionally, 10 trees per cultivar were inoculated with sterile water as controls. Six months after inoculation, most of the inoculated olive plants showed chlorotic leaves similar to those observed in commercial orchards. Root necrosis for each cv. was expressed as the percentage of root length having lesions (2). No significant difference was observed between isolates and average root necrosis was 29.4, 35.6, and 38.3% in Koroniki, Arbosana, and Arbequina, respectiveley. I. macrodidyma was recovered from symptomatic roots in each of the cvs. and identified based on morphology. No root rot symptoms were observed in the controls. To our knowledge, this is the first report of I. macrodidyma causing root rot of olive trees not only in California but anywhere in the world. References: (1) P. Chaverri et al. Stud. Mycol. 68:57, 2011. (2) M. Giovanetti and B. Mosse. New Phytol. 84:489, 1980. (3) F. Halleen et al. Stud. Mycol. 50:421, 2004. (4) E. Petit and W. D. Gubler. Plant Dis. 89:1051, 2005.


1991 ◽  
Vol 67 (5) ◽  
pp. 481-485 ◽  
Author(s):  
Jack R. Sutherland

The biology, damage and impact, and recent innovations in management of the major diseases affecting seed orchard trees and cones and forest nursery seedlings across Canada are discussed. Specific diseases covered are Armillaria root rot (A. ostoyae) and inland spruce cone rust (Chrysomyxa pirolata) in seed orchards, and damping-off and root rots, especially Cylindrocladium floridanum, and gray (Botrytis cinerea) and storage moulds of forest nursery seedlings. Areas needing research are also mentioned. Key words: Root rots, cone rust, damping-off, gray mould, storage moulds


1959 ◽  
Vol 37 (5) ◽  
pp. 927-957 ◽  
Author(s):  
A. A. Hildebrand

Since 1954, a destructive root and stalk rot of soybeans, identical with one reported from several of the soybean-growing areas in the United States, has been prevalent in southwestern Ontario. It is proposed that Phytophthora megasperma Drechsler var. sojae nov. var. replace P. cactorum (Lib. and Cohn) Schroet., and P. sojae Kaufmann and Gerdemann, as the more correct taxonomic designation of the causal fungus. P. megasperma var. sojae comprises strains which though indistinguishable morphologically, differ physiologically and pathologically. Artificial inoculation of varieties and of breeding lines and selections of soybeans with the causal fungus, chiefly by the highly reliable toothpick method, indicated two well-defined types of disease reaction, resistance and susceptibility. Harosoy, the variety which currently is grown most extensively in Ontario, is highly susceptible to the disease. Pathogenicity trials involving many possible wild and cultivated hosts emphasized the marked specificity of P. megasperma var. sojae to Glycine max L. Merrill. The soybean Phytophthora, having been called P. cactorum and thereby associated nomenclaturally with a representative of that species causing a root rot of sweet clover in Ontario, was found to be quite different from the sweet clover pathogen.


Author(s):  
D. J. Stamps

Abstract A description is provided for Phytophthora palmivora. Information is included on the disease caused by the organism, its transmission, geographical distribution, and hosts. HOSTS: A wide range; 138 species of economic, ornamental, shade and hedge plants were listed (48, 337-344). DISEASE: Black pod and canker of cacao; patch canker, black stripe and leaf fall of Hevea rubber; bud rot of coconut and other palms; fruit and stem rot of pawpaw; root rots and damping-off of seedlings. GEOGRAPHICAL DISTRIBUTION: World-wide in tropical and warm temperature regions with high rainfall. TRANSMISSION: In cacao by direct contact between diseased and healthy pods, by rain splash from diseased pods, leaves and infested soil, and by insect vectors and ant tents. In rubber by rain. Soil as a source of inoculum for pawpaw root rot.


2017 ◽  
Vol 2 (2) ◽  
pp. 130-135
Author(s):  
Mohamed Chliyeh ◽  
Amina Ouazzani Touhami ◽  
Abdelkarim Filali-Maltouf ◽  
Cherkaoui El Modafar ◽  
Abdelmajid Moukhli ◽  
...  

In spring of 2012, olive-trees with crown dieback, root rot and defoliation were observed in two years old olive tree in commercial plantations of tree nurseries in Sidi Taibi and in twenty to fifty years old field trees in Souk El Arbaa olive crops in Northwest of Morocco (Gharb area). The objective of this study was to isolate the responsible pathogen of the observed symptoms to the olive trees, to demonstrate its pathogenicity and fulfill the Koch´s postulate. Phytophthora palmivora was consistently isolated from roots (56%) and stems (73.6%) of the young olive trees and 85% from stems of field trees. Koch’s postulate was completed using two isolates of Phytophthora palmivora on 2-year old plants of Dahbia and Haouzia varieties grafted onto wild olive-trees. The affected branches percentages (Pab%) of the inoculated olive plants with the isolate 1 were higher (81.8% for Dahbia and 68% for Haouzia) than those what were inoculated with the isolate 2 (43% for Dahbia and 32% for Haouzia). The reisolation percentages (Pr%) of isolate 1 (84%) and isolate 2 (76%) in the roots of Dahbia variety were higher than isolate 1 (48%) and isolate 2 (55%) in roots of Haouzia variety. The reisolation percentage of isolate 1 in the stem of Dahbia (64%) was higher than that in the stem of Haouzia (41.33%). No significant difference was observed between the Reisolation percentages of isolate 2 in stem of Dahbia olive plants (38%) and in stem of Haouzia olive plants (33%). The pathogenicity of P. palmivora was demonstrated in the olive plants and this was the first report of this pathogen in Moroccan olive trees.


Plant Disease ◽  
2010 ◽  
Vol 94 (8) ◽  
pp. 1069-1069 ◽  
Author(s):  
J. C. Bienapfl ◽  
D. K. Malvick ◽  
J. A. Percich

Multiple Fusarium species have been found in association with soybean (Glycine max) plants exhibiting root rot in the United States (3). Soybean plants that lacked apparent foliar symptoms, but exhibited 2- to 5-mm brown, necrotic taproot lesions and lateral root necrosis were observed in Minnesota in one field each in Marshall and Otter Tail counties in July of 2007, as well as in one field in Marshall County in July of 2008. Sampling was conducted as part of a study investigating root rot in major soybean-production areas of Minnesota. Plants were arbitrarily dug up at the R3 growth stage. Root systems were washed, surface disinfested in 0.5% NaOCl for 3 min, rinsed in deionized water, and dried. Fusarium isolates were recovered from root sections with necrotic lesions embedded in modified Nash-Snyder medium (1). One resulting Fusarium colony from one plant per county was transferred to half-strength acidified potato dextrose agar (PDA) and carnation leaf agar (CLA) to examine morphological characteristics (4). Culture morphology on PDA consisted of flat mycelium with sparse white aerial mycelium. On CLA, thick-walled macroconidia with a hooked apical cell and a foot-shaped basal cell were produced in cream-colored sporodochia. Macroconidia ranged from 32.5 to 45.0 μm long. Microconidia were oval to cylindrical with 0 to 1 septa, ranged from 7.5 to 11.25 μm long, and were produced on monophialides. Chlamydospores were produced abundantly in chains that were terminal and intercalary in the hyphae of 4-week-old cultures. Morphological characteristics of the three isolates were consistent with descriptions of F. redolens (2,4). The identity of each isolate was confirmed by sequencing the translation elongation factor 1-α (TEF) locus (4). BLAST analysis of the TEF sequences from each isolate against the FUSARIUM-ID database resulted in a 100% match for 17 accessions of F. redolens (e.g., FD 01103, FD 01369). Each F. redolens isolate was tested for pathogenicity on soybean. Sterile sorghum grain was infested with each isolate and incubated for 2 weeks. Sterile sorghum was used for control plants. Soybean seeds of cv. AG2107 were planted in 11.4-cm pots ~1 cm above a 25-cm3 layer of infested sorghum or sterile sorghum. Two replicate pots containing four plants each were used per treatment and the experiment was repeated once. Root rot was assessed 28 days after planting. Each F. redolens isolate consistently caused taproot necrosis on inoculated plants, whereas control plants did not exhibit root necrosis. Isolations were made from roots of inoculated and control plants and the isolates recovered from inoculated plants were identified as F. redolens based on morphological characteristics and TEF sequences. Fusarium species were not isolated from control plants. To our knowledge, this is the first report of F. redolens causing root rot of soybean; however, it is possible F. redolens has been found previously and misidentified as F. oxysporum (2,4). Results from inoculations suggest that F. redolens may be an important root rot pathogen in Minnesota soybean fields. References: (1) J. C. Bienapfl et al. Acta Hortic. 668:123, 2004. (2) C. Booth and J. M. Waterston. No. 27 in: CMI Descriptions of Pathogenic Fungi and Bacteria. CMI, Kew, England, 1964. (3) G. L. Hartman et al. Compendium of Soybean Diseases. 4th ed. The American Phytopathological Society, St. Paul, MN, 1999. (4) J. F. Leslie and B. A. Summerell. The Fusarium Laboratory Manual. Blackwell Publishing, Ames, IA, 2006.


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