Insensitivity to Metalaxyl Among Isolates of Phytophthora capsici Causing Root and Crown Rot of Pepper in Southern Italy

Pepper (Capsicum annuum L.) has become an economically important crop in the coastal provinces of Catanzaro and Vibo Valentia, in Calabria (southern Italy). An old local selection Riggitano, very susceptible to root and crown rot caused by Phytophthora capsici Leonian, is the prevalent cultivar in this area. Although repeated applications of metalaxyl are used as a soil drench, severe outbreaks occur each year on greenhouse crops. To examine metalaxyl resistance in P. capsici, 60 single-hypha isolates of P. capsici were tested in vitro for their level of sensitivity to metalaxyl. The isolates were collected from 1992 to 1997, during epidemic outbreaks of root and crown rot, from two commercial greenhouse pepper crops, near Vibo Valentia and Lametia Terme (Catanzaro). Fungicide sensitivity was determined by plating mycelial plugs onto potato dextrose agar (PDA) amended with metalaxyl. The fungicide was added to PDA after autoclaving, at final concentrations of 0.1, 1, 5, 10, 50, 100, and 200 μg/ml a.i. The percentage of inhibition of radial growth on metalaxyl-amended medium compared with the growth on unamended medium was determined after 6 days of incubation in the dark at 25°C. Three replicate petri dishes were used per treatment and each test was performed twice. The isolates were paired in culture on V8 agar with isolates of P. capsici of known mating type and all proved to be A2 mating type. Significant variation was observed among the isolates tested in responce to metalaxyl. The ED50 values for in vitro inhibition of mycelial growth by metalaxyl ranged from 1 to 11 μg/ml, whereas an ED 50 value of 0.1 μg/ml had been reported for a wild-type isolate of P. capsici obtained from pepper in northern Italy (3). The variation observed among the isolates from Calabria appeared unrelated to both the geographical origin and the year of isolation. The isolates from Calabria were inhibited by between 1 and 12% at 0.1 μg/ml and by between 7 and 27% at 1 μg/ml, proving to be less sensitive to metalaxyl than isolates from Capsicum spp. originating from Central America, tested by other authors (1). According to the criterion used in a recent screening for sensitivity to metalaxyl (2), 19% of the isolates from Calabria should be considered sensitive, as they were inhibited by more than 60% at 5 μg/ml, while all the others were intermediate, as they were inhibited less than 60% at 5 μg/ml but more than 60% at 100 μg/ml. On the basis of this preliminary screening, we report the presence of insensitivity to metalaxyl in field isolates of P. capsici in southern Italy. Although no isolate tested appeared highly resistant to metalaxyl, the presence of a high proportion of isolates with an intermediate level of resistance should be a reason for the growers to use metalaxyl more cautiously to control root and collar rot. References: (1) M. D. Coffey and L. A. Bower. Phytopathology 74:502, 1984. (2) G. Parra and J. Ristaino. Plant Dis. 82:711, 1998. (3) M. L. Romano and A. Garibaldi. La difesa delle piante 3:153, 1984.

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First Report of Crown and Root Rot Caused by Phytophthora capsici on Hydroponically Grown Cucumbers in Norway

Plant Disease ◽

10.1094/pdis-92-7-1138c ◽

2008 ◽

Vol 92 (7) ◽

pp. 1138-1138 ◽

Cited By ~ 3

Author(s):

M. L. Herrero ◽

M. B. Brurberg ◽

A. Hermansen

Keyword(s):

Mating Type ◽

Phytophthora Capsici ◽

Crown Rot ◽

Yield Reduction ◽

Cox1 Gene ◽

Pathogenicity Test ◽

Internal Transcribed Spacer Region ◽

First Report ◽

Leaf Stage ◽

Root And Crown Rot

In December 2004, symptoms of root and crown rot were observed on cucumbers (Cucumis sativus L.) in a greenhouse in Norway. Cucumbers were the only crop of the greenhouse that used rockwool as a growing substrate in a hydroponical system. The first symptoms were detected in propagation material. One week after planting, symptoms of root and crown rot were observed and approximately 10% of the plants died. Later, losses of 50% in some greenhouses were observed. A yield reduction as much as 65% was estimated in the winter period (January and February). The two main cucumber cultivars planted were Armada and Lopez. In February 2005, Phytophthora capsici (Leonian) (1) was isolated on potato dextrose agar from a sample of cv. Lopez. The isolate produced deciduous, papillate sporangia (occasionally with two or three papilla) and pedicels that were sometimes longer than the sporangia. Sequencing of amplicons of the internal transcribed spacer region (ITS) rDNA and of the mitochondrial cytochrome c oxidase subunit 1 (Cox1) gene (2) confirmed the identification. Three isolates collected through 2005 from the same greenhouse were crossed with tester strains of P. cryptogea. Formation of oogonia and amphigynous antheridia was always observed in crosses with mating type A2; thus, all isolates were the A1 mating type. All three isolates grew well at 35°C and did not produce chlamydospores. A pathogenicity test was performed with one isolate of P. capsici. Four plants of cucumber cvs. Indira and Jessica were grown in a growth chamber at 24°C. Plants at the two-leaf stage were drenched with 20 ml of a zoospore suspension of 106 zoospores per ml per plant. After 18 days, all plants of both cultivars developed symptoms of crown rot or wilted and died. P. capsici was reisolated from inoculated plants of both cultivars. The pathogenicity test was repeated in the same way, but in a greenhouse with temperatures that ranged between 18 and 29°C. In addition, four plants of both cultivars at the four-leaf stage were inoculated with a suspension of 105 zoospores per ml. After 1 week, all plants developed crown rot or were irreversibly wilted, independently of the plant age or the zoospore concentration. To our knowledge, this is the first report of P. capsici in Norway. References: (1) D. C. Erwin and O. K. Ribeiro. Phytophthora Diseases Worldwide. The American Phytopathological Society St. Paul MN, 1996. (2) L. P. N. M. Kroon et al. Phytopathology 94:613, 2004.

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First Report of Phytophthora capsici on Cucumber and Melon in Southeastern Spain

Plant Disease ◽

10.1094/pdis.2002.86.5.558a ◽

2002 ◽

Vol 86 (5) ◽

pp. 558-558 ◽

Cited By ~ 5

Author(s):

M. L. Herrero ◽

R. Blanco ◽

M. Santos ◽

J. C. Tello

Keyword(s):

Mating Type ◽

Phytophthora Capsici ◽

Crown Rot ◽

Cucumis Sativus L ◽

Leaf Stage ◽

Southeastern Spain ◽

Root And Crown Rot ◽

Crown And Root Rot ◽

Cucumis Melo L ◽

First Time

In autumn 1999, crown and root rot along with wilting of cucumber (Cucumis sativus L.) were observed in greenhouses in southeastern Spain (Granada). Symptoms appeared again during the 2000 to 2001 growing season. In spring 2001, root and crown symptoms were observed also on melon (Cucumis melo L.) in greenhouses in another area of southeastern Spain (Almeria). Isolates from diseased plants from both locations were identified as Phytophthora capsici (Leonian). Isolates produced papillate sporangia of variable shape, some of them with two or three papilla. Sporangia were caducous with pedicels of variable lengths that could be longer than the sporangia. Three isolates were crossed with P. capsici strains of known mating type. All isolates produced amphigynous antheridia and were mating type A1. Isolates grew well at 35°C and did not produce chlamydospores. Pathogenicity was examined for one isolate from cucumber and one from melon. Cucumber and melon plants at the four-leaf stage and pumpkin (Cucurbita maxima × C. moschata) plants at the five-leaf stage were inoculated with a mycelium suspension. Both isolates caused wilting and death of plants on the three host species tested. The pathogen was reisolated from roots and stems of diseased plants. To our knowledge, this is the first time P. capsici has been found on cucumber in Spain. It is also the first time P. capsici has been found on melon in the greenhouses of southeastern Spain, and the first time it has been reported to cause root and crown rot of melon. Previously, P. capsici has been reported to cause disease of field-grown melon (2) and greenhouse-grown pepper (Capsicum annum) (1) in eastern and southeastern Spain, respectively. References: (1) J. C Tello. Comun. INIA 22, 1984. (2) J. J. Tuset Barrachina. An. INIA 7:11, 1977.

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Diversity of Phytophthora capsici in Northwest Spain: Analysis of Virulence, Metalaxyl Response, and Molecular Characterization

Plant Disease ◽

10.1094/pd-90-1135 ◽

2006 ◽

Vol 90 (9) ◽

pp. 1135-1142 ◽

Cited By ~ 54

Author(s):

C. Silvar ◽

F. Merino ◽

J. Díaz

Keyword(s):

Mating Type ◽

Rapd Analysis ◽

Random Amplified Polymorphic Dna ◽

Phytophthora Capsici ◽

Crown Rot ◽

Group Method ◽

Pair Group ◽

Highly Sensitive ◽

Virulence Assay ◽

Pepper Cultivar

Phytophthora crown rot, caused by Phytophthora capsici, is potentially the most destructive disease of pepper in Spain. Phenotypic and genetic diversity of 16 P. capsici isolates collected from 11 farms in northwest Spain was characterized based on virulence, mating type, sensitivity to metalaxyl, and genetic analysis using random amplified polymorphic DNA (RAPD) methods. Low variability was observed among the isolates in their metalaxyl response, with 87.5% being highly sensitive. No isolates of the A2 mating type were detected. More variability was found in the virulence assay, and isolates were classified into two groups according to their pathogenicity on a set of four pepper cultivar differentials. Genetic variation examined with eight RAPD primers generated 92 polymorphic bands and revealed the existence of different patterns among isolates. Cluster analysis using the unweighted pair-group method with arithmetic averages (UPGMA) separated the Spanish isolates into three RAPD groups and established a relationship between the Spanish population and a representative worldwide group of isolates. No correlation was found between groups obtained by RAPD analysis and groups defined by virulence or metalaxyl response.

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Epipremnum, a new host for Phytophthora capsici

Plant Disease ◽

10.1094/pdis.2002.86.9.1050b ◽

2002 ◽

Vol 86 (9) ◽

pp. 1050-1050 ◽

Cited By ~ 3

Author(s):

R. L. Wick ◽

M. B. Dicklow

Keyword(s):

Mating Type ◽

Phytophthora Capsici ◽

Crown Rot ◽

Fluorescent Light ◽

Pathogenicity Test ◽

Agar Culture ◽

New Host ◽

Solid Media ◽

Breadth Ratio ◽

Response To Temperature

From 1999 to 2001, a Massachusetts nursery received a number of shipments of Pothos, Epipremnum aureum (Lindl. & André) Bunting, with significant crown, petiole, and leaf rot. The plants were imported from Costa Rica. Sporangia were observed on diseased tissues, and five presumptive isolates of Phytophthora were recovered from infected petioles and stems for species identification. The five isolates were morphologically indistinguishable from each other. Sporangia were produced in water and on V8 juice agar under fluorescent light at 22°C. Mating type was determined by pairing isolates with A1 and A2 mating types of Phytophthora capsici Leonian. Sporangial measurements were taken from water cultures. Determination of caducity, and measurements of pedicels and oospores were taken from V8 agar cultures. Measurements represent an average of 50 observations a single isolate. In water culture, sporangia were borne in umbellate clusters. Sporangium length/breadth was 48.29 and 22.33 μm respectively; length/breadth ratio 2.16. On solid media, sporangia were upright and caducous. The bases of the sporangia were mostly tapered. Pedicel lengths were 22 to 49 μm (average 35 μm). Oogonia had amphigynous antheridia and developed only in the presence of an opposite mating type, and oospores measured 25.74 μm diameter. All five isolates were the A1 mating type. Chlamydospores were absent in V8 and corn meal agar (CMA) cultures. Metalaxyl sensitivity was determined at 0, 0.1, 0.5, and 5 ppm in CMA with five replications. The isolate was completely sensitive to 5 ppm metalaxyl, but grew as well as the controls at 0.1 ppm metalaxyl. Growth response to temperature was determined on V8 agar at 15, 20, 25, 30, and 35°C in five replications. After 4 days, colony diameters at 20, 25, and 30°C were not significantly different (P = 0.01) and colonies filled the 100-mm petri dishes. At 15 and 35°C, average colony diameter was 65.7 and 71.4 mm, respectively. Based on the above characteristics, the isolates were identified as P. capsici. Koch's postulates were carried out on pepper, Capsicum annuum ‘Italia’, squash, Cucurbita pepo ‘Patty Pan’ seedlings, and rooted cuttings of pothos. Pepper and squash seedlings and rooted pothos were transplanted in 4-in. (10 cm) pots containing a soilless growing medium (Metro Mix 360, W.R. Grace, Columbia, MD). Phytophthora cultures were grown on V8 juice agar for 4 days. An agar culture was added to 200 ml of sterile distilled water and briefly blended. Ten milliliters of the resulting mycelial slurry were pipetted in the soil one cm from the crown on two sides of the plant. Controls received no mycelial slurry. Petiole, leaf, and crown rot of pothos developed within 2 weeks following inoculation. Squash and pepper plants did not become diseased. In a second pathogenicity test, a 1-cm-diameter plug of mycelial growth from a V8 agar culture was placed between the stem and petiole of the lowest leaf of pothos cuttings directly after transplanting. Inoculated plants died within 3 days. The development of umbellate clusters of sporangia, sporangial shape, length/breadth ratio, and lack of pathogenicity to pepper suggest that the P. capsici isolated from pothos belong to the CAPB (tropical) subgroup of Mchau and Coffey (2). References: (1) S. S. A. Al-Hedaithy and P. H. Tsao. Mycologia 71:392, 1979. (2) G. R. Mchau. and M. D. Coffey. Mycol. Res. 99:89, 1995.

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Effect of Phosphite on Tomato and Pepper Plants and on Susceptibility of Pepper to Phytophthora Root and Crown Rot in Hydroponic Culture

Plant Disease ◽

10.1094/pdis.1998.82.10.1165 ◽

1998 ◽

Vol 82 (10) ◽

pp. 1165-1170 ◽

Cited By ~ 67

Author(s):

H. Förster ◽

J. E. Adaskaveg ◽

D. H. Kim ◽

M. E. Stanghellini

Keyword(s):

Leaf Area ◽

Plant Development ◽

Phosphorus Deficiency ◽

Phytophthora Capsici ◽

Hydroponic Culture ◽

Phosphorus Nutrition ◽

Crown Rot ◽

Deficiency Symptoms ◽

Root And Crown Rot ◽

Pepper Plants

Tomato and pepper plants were grown hydroponically in a greenhouse using phosphate or technical and commercial formulations of phosphite as sources of phosphorus nutrition to determine the effects on plant development and susceptibility to Phytophthora root and crown rot. Phosphite-treated tomato and pepper plants were deficient of phosphate and developed phosphorus-deficiency symptoms. Growth of plants (leaf area and leaf, stem, and root dry weights) that were fertilized with phosphite was significantly (P < 0.05) reduced compared with phosphate-fertilized plants. In Phytophthora capsici–inoculated pepper plants, incidence of Phytophthora crown rot was significantly reduced in phosphite-treated plants compared with no phosphorus or phosphate-treated plants. Incidence of crown rot in pepper plants treated with 1 mM phosphate plus 0.3 mM phosphite was intermediate between plants treated with only phosphite (1 mM or 0.1 mM) and plants treated with phosphate (1 mM).

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Genetically Diverse Long-Lived Clonal Lineages of Phytophthora capsici from Pepper in Gansu, China

Phytopathology ◽

10.1094/phyto-01-13-0016-r ◽

2013 ◽

Vol 103 (9) ◽

pp. 920-926 ◽

Cited By ~ 24

Author(s):

Jian Hu ◽

Zhili Pang ◽

Yang Bi ◽

Jingpeng Shao ◽

Yongzhao Diao ◽

...

Keyword(s):

Mating Type ◽

Recombinant Inbred Lines ◽

Phytophthora Capsici ◽

Significant Loss ◽

Gansu Province ◽

Mating Types ◽

Metalaxyl Resistance ◽

Important Variation ◽

Physiological Race ◽

Simple Sequence

Phytophthora capsici causes significant loss to pepper production in China, and our objective was to investigate the population structure in Gansu province. Between 2007 and 2011, 279 isolates were collected from pepper at 24 locations. Isolates (or subsets) were assessed for simple sequence repeat (SSR) genotype, metalaxyl resistance, mating type, and physiological race using cultivars from the World Vegetable Center (AVRDC) and New Mexico recombinant inbred lines (NMRILs). The A1 and A2 mating types were recovered from nine locations and metalaxyl-resistant isolates from three locations. A total of 104 isolates tested on the AVRDC panel resolved five physiological races. None of 42 isolates tested on the NMRIL panel caused visible infection. SSR genotyping of 127 isolates revealed 59 unique genotypes, with 42 present as singletons and 17 having 2 to 13 isolates. Isolates with identical genotypes were recovered from multiple sites across multiple years and, in many cases, had different race types or metalaxyl sensitivities. Isolates clustered into three groups with each group having almost exclusively the A1 or A2 mating type. Overall it appears long-lived genetically diverse clonal lineages are dispersed across Gansu, outcrossing is rare, and functionally important variation exists within a clonal framework.

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Comparative variation of Phoma medicaginis Malbr. Roum. var. medicaginis Boerema for cultural characteristics and virulence to roots and crowns of alfalfa

The Journal of Agriculture of the University of Puerto Rico ◽

10.46429/jaupr.v89i3-4.1044 ◽

1969 ◽

Vol 89 (3-4) ◽

pp. 229-242

Author(s):

Rocío del P. Rodríguez

Keyword(s):

Environmental Conditions ◽

Geographic Location ◽

Crown Rot ◽

Cultural Characteristics ◽

Greenhouse Experiments ◽

Phoma Medicaginis ◽

Sources Of Variation ◽

Root And Crown Rot

The in vitro and in vivo variation of selected isolates of Phoma medicaginis var. medicaginis was studied in controlled environmental conditions. Isolates were relatively stable in morphology and pigmentation of the colony but varied more in final diameter of the colony, rate of growth and sporulation. The isolate, the organ and geographic location from which it was obtained were significant sources of variation. All isolates caused root and crown rot symptoms in growth chamber and greenhouse experiments. Differences in virulence among isolates were expressed in the length of root lesions. Plant dry weights were reduced by 82% in greenhouse trials.

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First Report of Phytophthora capsici Causing Wilting and Root and Crown Rot on Capsicum annuum (Bell Pepper) in Ecuador

Plant Disease ◽

10.1094/pdis-11-19-2432-pdn ◽

2020 ◽

Vol 104 (7) ◽

pp. 2032-2032 ◽

Cited By ~ 1

Author(s):

Jefferson Bertin Vélez-Olmedo ◽

Luis Saltos ◽

Liliana Corozo ◽

Bianca Samay Bonfim ◽

Sergio Vélez-Zambrano ◽

...

Keyword(s):

Capsicum Annuum ◽

Phytophthora Capsici ◽

Bell Pepper ◽

Crown Rot ◽

First Report ◽

Root And Crown Rot

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A combined BSA-Seq and linkage mapping approach identifies genomic regions associated with Phytophthora root and crown rot resistance in squash

10.1101/2020.09.13.295527 ◽

2020 ◽

Author(s):

Gregory Vogel ◽

Kyle E. LaPlant ◽

Michael Mazourek ◽

Michael A. Gore ◽

Christine D. Smart

Keyword(s):

Disease Severity ◽

Linkage Mapping ◽

Prediction Models ◽

Bulked Segregant Analysis ◽

Phytophthora Capsici ◽

Multiple Linear Regression Model ◽

Crown Rot ◽

Phenotypic Variance ◽

Root And Crown Rot ◽

Genomic Regions

AbstractPhytophthora root and crown rot, caused by the soilborne oomycete pathogen Phytophthora capsici, leads to severe yield losses in squash (Cucurbita pepo). To identify quantitative trait loci (QTL) involved in resistance to this disease, we crossed a partially resistant squash breeding line with a susceptible zucchini cultivar and evaluated over 13,000 F2 seedlings in a greenhouse screen. Bulked segregant analysis with whole genome resequencing (BSA-Seq) resulted in the identification of five genomic regions – on chromosomes 4, 5, 8, 12, and 16 – featuring significant allele frequency differentiation between susceptible and resistant bulks in each of two independent replicates. In addition, we conducted linkage mapping using a population of 176 F3 families derived from individually genotyped F2 individuals. Variation in disease severity among these families was best explained by a four-QTL model, comprising the same loci identified via BSA-Seq on chromosomes 4, 5, and 8 as well as an additional locus on chromosome 19, for a combined total of six QTL identified between both methods. Loci, whether those identified by BSA-Seq or linkage mapping, were of small to moderate effect, collectively accounting for 28-35% and individually for 2-10% of the phenotypic variance explained. However, a multiple linear regression model using one marker in each BSA-Seq QTL could predict F2:3 disease severity with only a slight drop in cross-validation accuracy compared to genomic prediction models using genome-wide markers. These results suggest that marker-assisted selection could be a suitable approach for improving Phytophthora crown and root rot resistance in squash.

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First Report of Sclerotinia sclerotiorum on Buckwheat (Fagopyrum esculentum) in Italy

Plant Disease ◽

10.1094/pdis-91-11-1519c ◽

2007 ◽

Vol 91 (11) ◽

pp. 1519-1519

Author(s):

E. Lahoz ◽

R. Caiazzo ◽

A. Carella ◽

E. Cozzolino

Keyword(s):

Sclerotinia Sclerotiorum ◽

Southern Italy ◽

Pathogenic Fungi ◽

Fagopyrum Esculentum ◽

Crown Rot ◽

Limiting Factors ◽

First Report ◽

Root And Crown Rot ◽

Internal Transcribed Spacer Sequences ◽

Severity Of The Disease

In each of two fields of buckwheat (Fagopyrum esculentum L.) grown in Benevento Province (southern Italy), 60 to 70% of the plants developed severe root and crown rot. Symptoms included irregular, water-soaked spots on stems that were eventually covered with cottony mycelia as the lesions enlarged. Black sclerotia usually developed within the mycelium. The fungus was isolated on potato dextrose agar and 2% water agar. On the basis of colony morphology, including the production of black sclerotia (1), the fungus was identified as Sclerotinia sclerotiorum (Lib.) De Bary. The identity of the fungus was confirmed by near exact identity of internal transcribed spacer sequences (99%) with two isolates of S. sclerotiorum in GenBank (Accession Nos. Z73800 and Z73799). Pathogenicity of the fungus on buckwheat was evaluated by transplanting 20 20-day-old healthy plants in a mixture of soil and fungal inoculum (0.5% of wet millet seeds colonized by four isolates of S. sclerotiorum). Lesions on crowns and roots developed after 12 days and sclerotia appeared approximately 20 days later. No symptoms developed on noninoculated plants. Reisolation from inoculated plants yielded colonies of S. sclerotiorum. To our knowledge, this is the first report of S. sclerotiorum on buckwheat in Italy. The high incidence and severity of the disease may be limiting factors in the development of buckwheat as an alternative crop of tobacco in southern Italy. Reference: (1) J. E. M. Mordue and P. Holliday. Sclerotinia sclerotiorum. No. 513 in: Descriptions of Pathogenic Fungi and Bacteria. CMI, Kew, Surrey, UK, 1976.

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