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Martin Porchas - One of the best experts on this subject based on the ideXlab platform.
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comparative ability of six fungicides to inhibit development of Phytophthora gummosis on citrus
Plant Disease, 2002Co-Authors: Michael E. Matheron, Martin PorchasAbstract:ABSTRACT The activity of the registered fungicides fosetyl-Al and metalaxyl (subsequently replaced with mefenoxam by the manufacturer) was compared with other potentially useful compounds, azoxystrobin, dimethomorph, fluazinam, and zoxamide, for suppression of canker development on citrus bark after inoculation with Phytophthora citrophthora or P. nicotianae. The number of sweet orange trees on which cankers developed after inoculation with P. citrophthora and the average size of cankers when present were lower on plants treated with dimethomorph, fosetyl-Al, or metalaxyl compared with nontreated trees and those treated with azoxystrobin or fluazinam. When bark removed from treated trees was inoculated with P. citrophthora on the cambium surface at 5, 30, or 60 days after treatment (DAT), inhibition of lesion development on bark strips treated with dimethomorph, fosetyl-Al, or metalaxyl was significantly greater than that detected on bark treated with azoxystrobin, fluazinam, or zoxamide. When inoculated ...
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resistance to Phytophthora citrophthora and p parasitica and nursery characteristics of several citrus rootstocks
Plant Disease, 1998Co-Authors: Michael E. Matheron, G C Wright, Martin PorchasAbstract:ABSTRACT Studies were conducted to compare existing and potential citrus rootstocks with respect to resistance to root rot and gummosis caused by Phytophthora citrophthora and P. parasitica in greenhouse and growth chamber experiments and horticultural performance under simulated nursery conditions. Depending upon rootstock and experiment, mean root weights resulting from inoculation with P. citrophthora were 27 to 96% lower than the comparable controls. In similar experiments with the same rootstocks, inoculation with P. parasitica resulted in root weights that were 38 to 95% less than weights of the noninoculated controls. During 1994 or 1995, mean root weight reduction compared with noninoculated plants among Citrus macrophylla, rough lemon, C. volkameriana, and Sunki mandarin × Flying Dragon trifoliate (62-109-19) attributable to P. citrophthora and mean root weight reduction among C. macrophylla, C. volkameriana, rough lemon, Sacaton citrumelo, Sunki mandarin × Flying Dragon trifoliate (62-109-19), A...
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distribution and seasonal population dynamics of Phytophthora citrophthora and p parasitica in arizona citrus orchards and effect of fungicides on tree health
Plant Disease, 1997Co-Authors: Michael E. Matheron, Martin Porchas, J. C. MatejkaAbstract:ABSTRACT The distribution and seasonal population dynamics of Phytophthora citrophthora and P. parasitica within citrus orchards in southwestern and central Arizona were determined over a multiple-year period. In central Arizona, P. citrophthora alone, P. parasitica alone, or both pathogens together were recovered from 7, 37, and 41% of sampled orchards, respectively, whereas in the southwestern production area, the same pathogens alone or in combination were recovered from 17, 50, and 17% of sampled orchards, respectively. For a 6-year period, the average population density of P. parasitica in southwestern Arizona was 16.7 propagules/g of dry soil. For 2 of 3 years, the population density of P. citrophthora at the 10-cm soil depth was significantly higher in the spring than in the preceding winter or the following autumn season. There were no significant seasonal multiple-year differences in population levels of P. parasitica. Propagule densities of both pathogens, as well as root densities, generally de...
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Colonization of citrus roots by Phytophthora citrophthora and P. parasitica in daily soil temperature fluctuations between favorable and inhibitory levels
Plant Disease, 1996Co-Authors: Michael E. Matheron, Martin PorchasAbstract:Studies compared colonization of citrus rootlets by Phytophthora citrophthora or P. parasitica under constant favorable or inhibitory temperatures to root colonization under various daily combinations of favorable and inhibitory temperatures. Colonization of rough lemon rootlets after incubation for 96 h in the presence of soil naturally infested with P. citrophthora was detected at 9 through 27°C; however, the extent of colonization detected at 27°C was significantly lower than that observed at the other temperatures. In comparison, colonization of rootlets in the presence of soil naturally infested with P parasitica was detected at constant incubation temperatures ranging from 12 to 33°C; however, the extent of colonization at 33°C was significantly lower than that observed at the other temperatures. Critical threshold temperatures, defined as thermal values at or above which colonization of rootlets was significantly restricted or prevented, were 27°C for P. citrophthora and 33°C for P. parasitica. After four consecutive 24-h periods, the magnitude of rootlet colonization by both pathogens was significantly less under incubation that included a daily time of at least 2.5 h at or above the threshold temperature when compared to rootlet colonization for 96 h at a constant favorable temperature. Significantly fewer sporangia were produced by P. citrophthora or P. parasitica at 24 h than after 48 and 72 h. The extent of root infection caused by P. citrophthora and P. parasitica at 24 or 30°C, respectively, was significantly lower at incubation periods of 4, 8, and 16 h than at periods of 24, 48, and 72 h. A fivefold increase in duration of zoospore motility was observed for P. citrophthora at 24°C than at 30°C, temperatures that respectively favor and prevent rootlet colonization; while an 11-fold increase was detected for zoospores of P. parasitica at favorable compared to inhibitory temperatures of 30 and 36°C, respectively. Temperature periods partially as well as entirely at or above the critical threshold values may reduce the degree of citrus rootlet colonization by P. citrophthora and P. parasitica by retarding the rate of sporangium formation and zoospore production and the duration of zoospore motility, compared to periods of equal duration that are entirely favorable for rootlet colonization. More efficient use of fungicides for control of Phytophthora root rot of citrus could be possible by application only when soil temperatures favor disease development.
Michael E. Matheron - One of the best experts on this subject based on the ideXlab platform.
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comparative ability of six fungicides to inhibit development of Phytophthora gummosis on citrus
Plant Disease, 2002Co-Authors: Michael E. Matheron, Martin PorchasAbstract:ABSTRACT The activity of the registered fungicides fosetyl-Al and metalaxyl (subsequently replaced with mefenoxam by the manufacturer) was compared with other potentially useful compounds, azoxystrobin, dimethomorph, fluazinam, and zoxamide, for suppression of canker development on citrus bark after inoculation with Phytophthora citrophthora or P. nicotianae. The number of sweet orange trees on which cankers developed after inoculation with P. citrophthora and the average size of cankers when present were lower on plants treated with dimethomorph, fosetyl-Al, or metalaxyl compared with nontreated trees and those treated with azoxystrobin or fluazinam. When bark removed from treated trees was inoculated with P. citrophthora on the cambium surface at 5, 30, or 60 days after treatment (DAT), inhibition of lesion development on bark strips treated with dimethomorph, fosetyl-Al, or metalaxyl was significantly greater than that detected on bark treated with azoxystrobin, fluazinam, or zoxamide. When inoculated ...
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resistance to Phytophthora citrophthora and p parasitica and nursery characteristics of several citrus rootstocks
Plant Disease, 1998Co-Authors: Michael E. Matheron, G C Wright, Martin PorchasAbstract:ABSTRACT Studies were conducted to compare existing and potential citrus rootstocks with respect to resistance to root rot and gummosis caused by Phytophthora citrophthora and P. parasitica in greenhouse and growth chamber experiments and horticultural performance under simulated nursery conditions. Depending upon rootstock and experiment, mean root weights resulting from inoculation with P. citrophthora were 27 to 96% lower than the comparable controls. In similar experiments with the same rootstocks, inoculation with P. parasitica resulted in root weights that were 38 to 95% less than weights of the noninoculated controls. During 1994 or 1995, mean root weight reduction compared with noninoculated plants among Citrus macrophylla, rough lemon, C. volkameriana, and Sunki mandarin × Flying Dragon trifoliate (62-109-19) attributable to P. citrophthora and mean root weight reduction among C. macrophylla, C. volkameriana, rough lemon, Sacaton citrumelo, Sunki mandarin × Flying Dragon trifoliate (62-109-19), A...
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distribution and seasonal population dynamics of Phytophthora citrophthora and p parasitica in arizona citrus orchards and effect of fungicides on tree health
Plant Disease, 1997Co-Authors: Michael E. Matheron, Martin Porchas, J. C. MatejkaAbstract:ABSTRACT The distribution and seasonal population dynamics of Phytophthora citrophthora and P. parasitica within citrus orchards in southwestern and central Arizona were determined over a multiple-year period. In central Arizona, P. citrophthora alone, P. parasitica alone, or both pathogens together were recovered from 7, 37, and 41% of sampled orchards, respectively, whereas in the southwestern production area, the same pathogens alone or in combination were recovered from 17, 50, and 17% of sampled orchards, respectively. For a 6-year period, the average population density of P. parasitica in southwestern Arizona was 16.7 propagules/g of dry soil. For 2 of 3 years, the population density of P. citrophthora at the 10-cm soil depth was significantly higher in the spring than in the preceding winter or the following autumn season. There were no significant seasonal multiple-year differences in population levels of P. parasitica. Propagule densities of both pathogens, as well as root densities, generally de...
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Colonization of citrus roots by Phytophthora citrophthora and P. parasitica in daily soil temperature fluctuations between favorable and inhibitory levels
Plant Disease, 1996Co-Authors: Michael E. Matheron, Martin PorchasAbstract:Studies compared colonization of citrus rootlets by Phytophthora citrophthora or P. parasitica under constant favorable or inhibitory temperatures to root colonization under various daily combinations of favorable and inhibitory temperatures. Colonization of rough lemon rootlets after incubation for 96 h in the presence of soil naturally infested with P. citrophthora was detected at 9 through 27°C; however, the extent of colonization detected at 27°C was significantly lower than that observed at the other temperatures. In comparison, colonization of rootlets in the presence of soil naturally infested with P parasitica was detected at constant incubation temperatures ranging from 12 to 33°C; however, the extent of colonization at 33°C was significantly lower than that observed at the other temperatures. Critical threshold temperatures, defined as thermal values at or above which colonization of rootlets was significantly restricted or prevented, were 27°C for P. citrophthora and 33°C for P. parasitica. After four consecutive 24-h periods, the magnitude of rootlet colonization by both pathogens was significantly less under incubation that included a daily time of at least 2.5 h at or above the threshold temperature when compared to rootlet colonization for 96 h at a constant favorable temperature. Significantly fewer sporangia were produced by P. citrophthora or P. parasitica at 24 h than after 48 and 72 h. The extent of root infection caused by P. citrophthora and P. parasitica at 24 or 30°C, respectively, was significantly lower at incubation periods of 4, 8, and 16 h than at periods of 24, 48, and 72 h. A fivefold increase in duration of zoospore motility was observed for P. citrophthora at 24°C than at 30°C, temperatures that respectively favor and prevent rootlet colonization; while an 11-fold increase was detected for zoospores of P. parasitica at favorable compared to inhibitory temperatures of 30 and 36°C, respectively. Temperature periods partially as well as entirely at or above the critical threshold values may reduce the degree of citrus rootlet colonization by P. citrophthora and P. parasitica by retarding the rate of sporangium formation and zoospore production and the duration of zoospore motility, compared to periods of equal duration that are entirely favorable for rootlet colonization. More efficient use of fungicides for control of Phytophthora root rot of citrus could be possible by application only when soil temperatures favor disease development.
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Seasonal differences in susceptibility of three citrus rootstocks to root lesions caused by Phytophthora citrophthora and P. parasitica
Plant Disease, 1993Co-Authors: Michael E. Matheron, J. C. MatejkaAbstract:Root and shoot segments from Lisbon lemon trees established on sour orange, rough lemon, and volkamer lemon rootstocks were evaluated for seasonal changes in susceptibility to Phytophthora citrophthora and P. parasitica. Plant material was wounded, inoculated with P. citrophthora or P. parasitica, then incubated in moist chambers. Root segments of sour orange, rough lemon, and volkamer lemon inoculated with P. citrophthora developed shorter lesions during January-February than during July-October. Similarly, lesions on excised root tissue of sour orange inoculated with P. parasitica were shorter during January-February than during July-December
J A Menge - One of the best experts on this subject based on the ideXlab platform.
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comparison of seasonal infection of citrus roots by Phytophthora citrophthora and p nicotianae var parasitica
Plant Disease, 2003Co-Authors: Monica F Dirac, J A Menge, Monica A MadoreAbstract:Excised feeder roots from mature citrus trees located in climatically different regions were infected with zoospores of Phytophthora citrophthora and P. nicotianae var. parasitica at different times of the year under identical laboratory conditions. Zoospores encysted on and caused infection in roots from all locations year round. Both pathogens had the most encysted zoospores on roots from November to January and the least from March to May. Infection by P. nicotianae var. parasitica was consistently higher than P. citrophthora in the excised summer roots (May to September) and lower in January 1998 and November 1997. Infection by both species of Phytophthora dropped to a minimum in March when carbohydrate levels in roots were lowest. Temperature was not solely responsible for determining seasonal fluctuations of P. nicotianae var. parasitica and P. citrophthora. Root carbohydrate content also could not be correlated with seasonal infection. Other physiological or microbial factors associated with citrus roots may cause seasonal Phytophthora infection fluctuations. Infection of citrus seedling roots by P. citrophthora at 16°C reduced root starch content but not glucose compared to P. nicotianae var. parasitica, whereas infection at 30°C by P. nicotianae var. parasitica lowered root glucose but not starch content compared to P. citrophthora.
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influence of fusarium solani on chemotaxis of zoospores of Phytophthora parasitica and Phytophthora citrophthora and on distribution of 14c in citrus tissues and root exudate
Soil Biology & Biochemistry, 1994Co-Authors: L. M. Dandurand, J A MengeAbstract:Abstract Chemotaxis of zoospores of Phytophthora parasitica and P. citrophthora was reduced when sweet orange or Troyer citrange roots were colonized by Fusarium solani as compared to non-colonized roots. The proportions of 14 C in the leaves and stems of plants inoculated with P. citrophthora were greater than either the controls or plants inoculated with F. solani . Whereas, the proportions of 14 C in roots and root exudates of plants infected with P. citrophthora were less than those of the controls or plants inoculated with F. solani alone. When plants were inoculated with P. parasitica either alone or with F. solani , the proportion of 14 C in the root exudate fraction was less than the controls. There was no difference in partitioning of 14 C among leaf, stem or roots of infected plants as compared to the controls
Adéle Mcleod - One of the best experts on this subject based on the ideXlab platform.
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Christoffel F.J. Spies1
2016Co-Authors: J. C. Meitz-hopkins, Shaun D. Langenhoven, Mathys C. Pretorius, Adéle McleodAbstract:Two clonal lineages of Phytophthora citrophthora from citrus in South Africa represent a singl
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Two clonal lineages of Phytophthora citrophthora from citrus in South Africa represent a single phylogenetic species
Mycologia, 2014Co-Authors: Christoffel F.j. Spies, J. C. Meitz-hopkins, Shaun D. Langenhoven, Mathys C. Pretorius, Adéle McleodAbstract:Phytophthora citrophthora from citrus in eastern Corsica and Spain consists of distinct clonal lineages. In South Africa the extent of genetic variation among citrus-associated P. citrophthora isol...
Santa Olga Cacciola - One of the best experts on this subject based on the ideXlab platform.
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Root and Basal Stem Rot of Rose Caused by Phytophthora citrophthora in Italy.
Plant disease, 2011Co-Authors: A. Salamone, Antonella Pane, Giuseppa Scarito, Santa Olga CacciolaAbstract:Approximately 800 ha of cut flower roses are cultivated for commercial production in Italy. During autumn of 2004 in an experimental greenhouse in western Sicily (southern Italy), 60% of 2-year-old plants of rose cv. Red France on Rosa indica cv. Major rootstock grown in soil showed leaf chlorosis and wilt. A dark brown lesion lined by a water-soaked area was noticeable at the stem base near the soil surface. Root rot was found consistently associated with aboveground symptoms and plants collapsed within 4 months after the appearance of the first symptoms. The same symptoms were observed sporadically on rose plants of the same cultivar during the last 6 years in commercial nurseries in western Sicily. In all cases, a Phytophthora species has been consistently isolated from rotted roots and stems on Phytophthora-selective media. Pure cultures were obtained by single-hypha transfers. The species was identified as Phytophthora citrophthora on the basis of morphological characters and electrophoretic analysis of mycelial proteins on polyacrylamide gel (1). On potato dextrose agar, isolates produced petaloid colonies with optimum growth temperature at 25°C. On V8 agar, mono- and occasionally bipapillate, ovoid to limoniform sporangia, measuring 44 to 55 × 27 to 28 μm, with a mean length/breadth ratio of 1.4:1 were produced. All isolates were heterothallic but did not produce gametangia in dual cultures with P. nicotianae isolates of A1 and A2 mating type. Electrophoretic patterns of total mycelial proteins and four isozyme (acid and alkaline phosphatases, esterase, and malato dehydrogenase) of the isolates from rose were identical to those of reference isolates of P. citrophthora, but clearly distinct from isolates of other heterothallic species with papillate sporangia, including P. capsici, P. nicotianae, P. palmivora, and P. tropicalis. All isolates from rose showed the same electrophoretic profiles. Blast search of rDNA-ITS sequence from PCR-amplified ITS4/ITS6 primers (2) of a representative isolate from rose (IMI 392044) showed 98% homology with a reference isolate of P. citrophthora (GenBank No. EU0000631), thus confirming the identification. Pathogenicity of isolate IMI 392044 was tested on 10 12-month-old plants of rose cv. Red France grafted on R. indica cv. Major transplanted in pots containing a mixture of sphagnum peat moss and sandy loam soil (1:1 vol/vol) infested with 80 g of inoculum per liter of mixture. Inoculum was produced by growing the isolate on wheat kernels. Plants transplanted in pots containing noninfested soil served as controls. Plants were kept in a greenhouse at 22 ± 3°C and watered to soil saturation once a week. Inoculated plants developed symptoms of leaf chlorosis and root and crown rot within 15 to 30 days and wilted within 40 to 80 days after inoculation. Control plants remained healthy. P. citrophthora was consistently reisolated from inoculated plants. Root and basal stem rot of rose may be caused by several Phytophthora spp. and has been reported in various countries of Asia, Europe, and North America (3,4). However, to our knowledge, this is the first report in Italy. The occurrence of this disease may be attributed to excessive irrigation practices. References: (1) S. O. Cacciola et al. EPPO Bull. 20:47, 1990. (2) D. E. L. Cooke et al. Fungal Genet. Biol. 30:17, 2000. (3) Y. Nagai et al. Phytopathology 68:684, 1978. (4) B. W. Schwingle et al. Plant Dis. 91:97, 2007.
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First Report of Phytophthora citrophthora Causing Fruit Brown Rot of Feijoa in Italy
Plant disease, 2001Co-Authors: Antonella Pane, M. G. Li Destri Nicosia, Santa Olga CacciolaAbstract:Feijoa (Feijoa sellowiana) is native to South America. In the early 20th Century it was introduced into Sicily (southern Italy), where it is grown as an ornamental plant and for its fruits. In 1985 a Phytophthora brown rot of feijoa fruits was reported in the province of Syracuse (eastern Sicily) (2). Several species of Phytophthora, including P. citricola, P. citrophthora, and P. nicotianae, were recovered from soil samples taken from trees with infected fruits. These species were experimentally inoculated on detached feijoa fruits and all incited symptoms of brown rot. However, only P. citricola was isolated from naturally infected fruits. In early autumn 1999, an outbreak of Phytophthora brown rot of feijoa fruits was observed in the Syracuse province, in the same site where the disease had been first recorded. P. citricola (95% of the isolates) and P. citrophthora (5% of the isolates) were recovered from symptomatic fruits. The species were identified on the basis of morphological and cultural charact...