scholarly journals Formation of Phytophthora infestans Oospores in Nature on Tubers in Central Mexico

Plant Disease ◽  
2002 ◽  
Vol 86 (1) ◽  
pp. 73-73 ◽  
Author(s):  
S. P. Fernández-Pavía ◽  
N. J. Grünwald ◽  
W. E. Fry
Keyword(s):  
Late Blight ◽  
Phytophthora Infestans ◽  
Field Conditions ◽  
Central Mexico ◽  
Potato Tubers ◽  
Dry Rot ◽  
Pink Rot ◽  
Phytophthora Erythroseptica ◽  
Oospore Formation ◽  
Toluca Valley

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.

scholarly journals Efficiency of phylloplane bacteria in controlling aerial tomato diseases under field conditions

2008 ◽  
Vol 34 (1) ◽  
pp. 86-87 ◽  
Author(s):  
Bernardo A. Halfeld-Vieira ◽  
Reginaldo S. Romeiro ◽  
Ann Mounteer ◽  
Eduardo S.G. Mizubuti
Keyword(s):  
Late Blight ◽  
Bacillus Cereus ◽  
Phytophthora Infestans ◽  
Field Conditions ◽  
Water Control ◽  
Tomato Plants ◽  
Tomato Diseases

The capacity of two bacteria isolated from the tomato phylloplane to control late blight (Phytophthora infestans) was investigated in the field, and compared against the effectiveness of spraying with the fungicide chlorothalonil (1.5 g a.i. L-1) or water (control). A 55% reduction in late blight intensity was observed in the leaves of the middle of the plant and 62% in those of the upper leaves when using the antagonist UFV-STB 6 (Novosphingobium capsulatum) as compared to the control. Isolate UFV-IEA 6 (Bacillus cereus) was able to reduce disease intensity by 55%, but only in the upper leaves of the tomato plants. Treatment with isolate UFV-STB 6 also led to a significant reduction in the percentage of fruits with late blight symptoms. The results demonstrate the potential of these two bacteria in controlling this disease.

scholarly journals Sprinkling Irrigation Enhances Production of Oospores of Phytophthora Infestans in Field-Grown Crops of Potato

2000 ◽  
Vol 90 (10) ◽  
pp. 1105-1111 ◽  
Author(s):  
Yigal Cohen ◽  
Sonja Farkash ◽  
Alexander Baider ◽  
David S. Shaw
Keyword(s):  
Late Blight ◽  
Phytophthora Infestans ◽  
Mating Type ◽  
Field Experiments ◽  
Soil Surface ◽  
Field Trials ◽  
Detached Leaves ◽  
Oospore Formation ◽  
Potato Crops ◽  
Host Tissues

Two field experiments were conducted to study the effect of overhead sprinkling irrigation on oospore formation by the late blight fungus Phytophthora infestans in potato. Total rain (natural + sprinkling) accumulated in treatments of experiment 1 (winter 1997 to 1998) were 765, 287, and 219 mm and treatments of experiment 2 (winter 1999 to 2000) were 641, 193, and 129 mm. Sporangia from 11 isolates of P. infestans were combined in eight pairs, seven of A1 and A2 and one of A2 and A2 mating type, and were sprayed on field-grown potato crops (42 plants per plot at 7 m2 each) and examined for their ability to form oospores in the host tissues. In experiment 1, oospores were recorded in a total of 132 of 1,680 leaflets (7.9%), 24 of 105 stems, and 2 of 90 tubers. In experiment 2, oospores were recorded in 40 of 519 leaflets (7.7%), but not in any of the 90 stems or the 45 tubers examined. Both the proportion of leaflets containing oospores and the number of oospores per leaflet increased with time after inoculation and were dependent on the rain regime, the position of leaves on the plant, and the isolate pair combination. In both field trials, increasing the rainfall significantly enhanced oospore production in leaves. Leaf samples collected from the soil surface had significantly more oospores than those collected from the midcanopy. Two pairs in experiment 1 were more fertile than the others, whereas the pair used in experiment 2 was the least fertile. The total number of oospores per leaflet usually ranged from 10 to 100 in experiment 1, but only from 2 to 10 in experiment 2. Maximal oospore counts in the field were 200 and 50 in experiments 1 and 2, respectively, but ranged from ≈2,000 to 12,000 oospores per leaflet in detached leaves in the laboratory. We concluded that P. infestans can produce oospores in the foliage of field-grown potato crops, especially when kept wet by regular overhead sprinkling irrigation, but production was far below that in the laboratory.

scholarly journals Sensitivity of North American Isolates of Phytophthora erythroseptica and Pythium ultimum to Mefenoxam (Metalaxyl)

Plant Disease ◽  
2002 ◽  
Vol 86 (7) ◽  
pp. 797-802 ◽  
Author(s):  
R. J. Taylor ◽  
B. Salas ◽  
G. A. Secor ◽  
V. Rivera ◽  
N. C. Gudmestad
Keyword(s):  
Pythium Ultimum ◽  
Effective Management ◽  
Potato Tubers ◽  
Pink Rot ◽  
Phytophthora Erythroseptica ◽  
Disease Management Strategy ◽  
Potato Tuber Rot ◽  
Canadian Provinces ◽  
Production Areas ◽  
First Time

A 4-year study (1997 to 2000) was conducted to determine the sensitivities of the potato tuber rot pathogens, Phytophthora erythroseptica and Pythium ultimum, to mefenoxam (metalaxyl). A total of 2,277 tubers showing symptoms of “water rot” were collected from 16 states and 2 Canadian provinces. From these, 849 isolates of P. erythroseptica and 213 isolates of P. ultimum were obtained, and 805 and 190 isolates, respectively, were tested for their ability to grow on V8 medium amended at 0.01 to 100 μg/ml with fungicide. Isolates ranged widely in their responses to mefenoxam. The presence of resistant isolates (EC50 > 100 μg ml-1) of P. erythroseptica in the potato producing areas of Maine was confirmed. The presence of P. erythroseptica isolates in Idaho and Minnesota resistant to mefenoxam is reported for the first time. The proportion of P. erythroseptica isolates resistant to mefenoxam varied from 2.9 to 36.2% between 1997 and 2000. The proportion of resistant P. ultimum isolates represented only a small proportion of the isolates tested (3.7%). A single resistant P. ultimum isolate was recovered from Washington, whereas most of the resistant isolates obtained (5 of 7) were collected in Minnesota during the final year of the study. This is the first report of resistance in P. ultimum pathogenic to potato tubers. These observations suggest that pink rot and leak could become significant problems in the future, particularly in those areas where resistance has been detected. Our results have implications for the effective management of water rot. Monitoring the sensitivity of the pathogen population to mefenoxam in all production areas should be considered and integrated as a part of the overall disease management strategy.

scholarly journals Differences in Etiology Affect Mefenoxam Efficacy and the Control of Pink Rot and Leak Tuber Diseases of Potato

Plant Disease ◽  
2004 ◽  
Vol 88 (3) ◽  
pp. 301-307 ◽  
Author(s):  
Raymond J. Taylor ◽  
Bacilio Salas ◽  
Neil C. Gudmestad
Keyword(s):  
Foliar Application ◽  
Potato Production ◽  
Pythium Ultimum ◽  
Potato Tubers ◽  
Disease Etiology ◽  
Factors Affecting ◽  
Pink Rot ◽  
Application Rates ◽  
Phytophthora Erythroseptica ◽  
Production Areas

Data supplementing a previously published survey of North American isolates of Phytophthora erythroseptica and Pythium ultimum demonstrated that the proportion of the populations sensitive to mefenoxam remains high, 79.6 and 96.9% with EC50 sensitivities ranging from <0.01 to 0.9 µg ml-1 and <0.01 to 0.8 µg ml-1, respectively. Mefenoxam should provide control of these pathogens in most potato production areas. Factors affecting the development of pink rot and leak in potato tubers and the efficacy of mefenoxam to control these diseases with different etiologies were examined. Results confirmed that P. erythroseptica is capable of directly infecting potato tubers causing pink rot, whereas Pythium ultimum requires a wound to infect and cause leak. Mefenoxam was applied to replicated field plots as a single in-furrow application at planting, as an in-furrow application at planting followed by an additional sidedress application 3 weeks after planting, as a single foliar application when tubers were 7 to 8 mm in diameter, and as two foliar applications when the tubers were 7 to 8 mm in diameter and 14 days later. The recommended label rate plus two additional lower application rates were used with each method. For tubers challenge-inoculated after harvest, mefenoxam was found to be more effective in controlling pink rot relative to leak over all application methods. The greatest level of pink rot control (89%) was attained with the in-furrow at planting and sidedress application. All rates tested provided similar levels of control with this application method, but this method provided only a modest level of leak control (35%), and leak was not controlled by foliar applications of mefenoxam at any rate tested. In contrast, the foliar applications of mefenoxam resulted in 10 to 50% control of pink rot. Since the isolates of both pathogens were highly sensitive to me-fenoxam, disease-specific control was attributed to differences in disease etiology. Therefore, the use of mefenoxam to control pink rot in the field and storage appears to be well founded.

scholarly journals First Report of Solanum physalifolium as a Host Plant for Phytophthora infestans in Sweden

Plant Disease ◽  
2003 ◽  
Vol 87 (12) ◽  
pp. 1538-1538 ◽  
Author(s):  
B. Andersson ◽  
M. Johansson ◽  
B. Jönsson
Keyword(s):  
Late Blight ◽  
Phytophthora Infestans ◽  
Host Plant ◽  
Mating Type ◽  
Early Summer ◽  
Growing Seasons ◽  
Oospore Formation ◽  
Petri Dishes ◽  
Global Threat ◽  
Shape And Size

In the early summer of 2003, lesions resembling those caused by Phytophthora infestans (Mont.) de Bary on potato were observed on Solanum physalifolium Rusby var. nitidibaccatum (Bitter) Edmonds (2) that was growing as a weed in a parsnip (Pastinaca sativa) field in southern Sweden. When infected leaves of S. physalifolium were observed under the microscope (×200 magnification), sporangia with the same shape and size as those of P. infestans were observed. Pieces of infected leaves of S. physalifolium were put under tuber slices of S. tuberosum (cv. Bintje) in petri dishes and kept at 20°C. After 4 days, mycelium grew through the slices and sporulated profusely. The sporangia on the slices were of the same shape and size as those observed on the infected S. physalifolium leaves. In Sweden, the ratio of A1 and A2 mating types of P. infestans is 50:50, and oospores are commonly found in infected potato crops (1), so isolates from S. physalifolium were tested for mating type by growing them together with reference isolates of a known mating type on agar plates. Nine of the tested isolates were A1 mating type and six were A2 mating type. One self-fertile isolate was found. Naturally infected leaves of S. physalifolium were incubated at 20°C at 100% relative humidity so the lesions could coalesce and to facilitate oospore formation. After 5 days, oospores identical to those of P. infestans were observed under the microscope (×200 magnification). Sporangia produced by isolates originating from S. physalifolium and S. tuberosum were harvested, and a suspension containing 104 sporangia per ml from each isolate was prepared. Five leaves each of S. nigrum, S. physalifolium, and S. tuberosum (cv. Bintje), were inoculated with 10 μl of each sporangial suspension. Inoculated leaves were incubated in sealed petri dishes at 15°C. After 4 days, all S. tuberosum leaves were infected. After 7 days, two of five leaves of S. physalifolium inoculated with the S. tuberosum isolate and two of five S. physalifolium leaves inoculated with the isolate from S. physalifolium were infected. All lesions produced sporangia similar to those formed by P. infestans. S. nigrum was not infected by any of the isolates. The ability of S. physalifolium to act as a host plant for P. infestans producing sporangia during the growing season and oospores for survival between growing seasons may increase the problems of controlling late blight in potato in Sweden. References: (1) J. Dahlberg et al. Field survey of oospore formation by Phytophthora infestans. (Poster Abstr.) Pages 134–135 In: Late Blight: Managing the Global Threat. Proc Global Late Blight Conf. Charlotte Lizarraga, ed. Centro Internacional De La Papa, On-line publication, ISBN 929060-215-5, 2002. (2) J. M. Edmonds. Bot. J. Linn. Soc. 92:1, 1986.

scholarly journals In vitro and in vivo effect of poplar bud (Populi gemma) Extracts on late blight (Phytophthora infestans)

2014 ◽  
Vol 6 (1) ◽  
pp. 5-12
Author(s):  
János Bálint ◽  
Botond Turóczi ◽  
István Máthé ◽  
Klára Benedek ◽  
Károly-Attila Szabó ◽  
...  
Keyword(s):  
Growth Rate ◽  
Late Blight ◽  
Phytophthora Infestans ◽  
Environmentally Friendly ◽  
Populus Nigra ◽  
Field Conditions ◽  
Black Poplar

Abstract The effect of populin extract from black poplar (Populus nigra) on late blight was assessed under laboratory and field conditions. The growth rate of hyphae was found to be significantly lower after 1v/v% populin application, and no hyphae growth was detected under 3 and 6v/v% populin application. Populin also reduced the light blight severity on potato leaves under field conditions. From our results, we have concluded that populin extract can be considered as a new and environmentally-friendly alternative for the control of late blight under field conditions.

scholarly journals Oospore Formation by Phytophthora infestans in Potato Tubers

2001 ◽  
Vol 91 (6) ◽  
pp. 579-585 ◽  
Author(s):  
Aaron Levin ◽  
Alexander Baider ◽  
Evgenia Rubin ◽  
Ulrich Gisi ◽  
Yigal Cohen
Keyword(s):  
Potato Tuber ◽  
Phytophthora Infestans ◽  
Field Experiments ◽  
Casein Hydrolysate ◽  
Leaf Tissue ◽  
Potato Tubers ◽  
Tuber Tissue ◽  
Potato Tuber Tissue ◽  
Oospore Formation ◽  
Petri Dishes

The ability of Phytophthora infestans, the causal agent of potato and tomato late blight, to produce oospores in potato tuber tissue was studied in the field and under laboratory conditions. In 1998 and 2000 field experiments, the canopy of potato cvs. Alpha and Mondial, respectively, were coinoculated with A1 + A2 sporangia of the fungus, and the infected tubers collected at harvest were examined for the presence of oospores. In 1998, only 2 of 90 infected tubers had oospores, whereas none of the 90 tubers examined in 2000 had any oospores. In the latter experiment, infected tubers kept in storage up to 12 weeks after harvest had no oospores. Artificial co-inoculations of whole tubers with A1 + A2 sporangia resulted only rarely in the formation of oospores inside the tubers. Co-inoculations of potato tuber discs taken from dormant tubers 0 to 16 weeks after harvest failed to support any oospore production, whereas discs taken from sprouting tubers of ≥18 weeks after harvest allowed oospores to form. Tuber discs showed enhanced oospore formation when treated before inoculation with either sugars, amino acids, casein hydrolysate, β-sitosterol, or chloroethylphosphonic acid. In contrast, reducing airflow into the petri dishes where potato tuber discs were incubated reduced the number of oospores produced. The number of oospores produced in tuber tissue was lower compared with that in leaf tissue regardless of the origin of isolates used. The data show that the ability of Phytophthora infestans to produce oospores in potato tuber tissue is very limited and increases with tuber aging.

scholarly journals Commercial Fungicide Formulations Induce In Vitro Oospore Formation and Phenotypic Change in Mating Type in Phytophthora infestans

2000 ◽  
Vol 90 (11) ◽  
pp. 1201-1208 ◽  
Author(s):  
Carol Trout Groves ◽  
Jean Beagle Ristaino
Keyword(s):  
Late Blight ◽  
Phytophthora Infestans ◽  
Mating Type ◽  
Petri Dish ◽  
Phenotypic Change ◽  
Tomato Production ◽  
Wide Range ◽  
Oospore Formation ◽  
Commercial Fungicide

A wide range of commercially formulated fungicides cause in vitro effects on mating behavior in specific isolates of Phytophthora infestans, the causal agent of late blight of potato and tomato. Four isolates of P. infestans representing each of the four common US genotypes, US-1, US-6, US-7, and US-8 and varying in their sensitivity to metalaxyl, were exposed to a variety of fungicides used to control late blight in petri dish assays at concentrations ranging from 1 to 100 μg a.i./ml. Exposure of each of these normally heterothallic single mating type isolates of P. infestans to 9 of the 11 commercial fungicide formulations tested resulted in the formation of oospores after 2 to 4 weeks. The highest numbers of oospores were formed on media amended with Ridomil 2E (metalaxyl) and Ridomil Gold EC (mefenoxam) at 0.1 to 10 μg a.i./ml, averaging as many as 471 and 450 oospores per petri dish, respectively. Several other fungicides including Maneb, Manzate (Mancozeb), Curzate (cymoxanil + mancozeb), and Acrobat MZ (dimethomorph + mancozeb) also induced oospore formation, producing from 0 to 200 oospores per plate at fungicide concentrations from 0.1 to 10 μg a.i./ml. The metalaxyl resistant isolates formed oospores in response to the fungicides more often than the metalaxyl sensitive isolates. No oospores were formed on media amended with Bravo (chlorothalonil) or Tattoo C (chlorothalonil + propamocarb HCl) and these compounds completely suppressed growth of the isolates at 0.1 and 1 μg a.i./ml. Three metalaxyl resistant A2 isolates mated with both A1 and A2 isolates after exposure to the fungicides Ridomil 2E and Ridomil Gold EC. Alterations in mating type expression were also observed in a metalaxyl sensitive A1 isolate after exposure to Benlate (benomyl). Copious amounts of chemicals are applied annually to potato and tomato production areas to control late blight. Our results indicate that a wide range of chemically diverse fungicides can induce normally heterothallic metalaxyl resistant isolates of P. infestans to form oospores in vitro after short exposures to the fungicides.

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