The Experts below are selected from a list of 108 Experts worldwide ranked by ideXlab platform
J. A. G. Irwin - One of the best experts on this subject based on the ideXlab platform.
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Comparative studies on Phytophthora megasperma isolates from chickpea collected in Australia and Spain
Mycological Research, 1994Co-Authors: E.c.y. Liew, J. A. G. IrwinAbstract:The relationships between isolates of the complex species Phytophthora megasperma from chickpea in Spain and from chickpea and lucerne in Australia were investigated. In the isolates from Spain > 90% of the sporangia had flattened apices, whereas in the Australian isolates only 5·6% of sporangia had conspicuously flattened apices, the remainder being convex. No differences were found between the sex organs of the two groups, except that oospore walls were thinner in the Spanish isolates (&- x = 2·2 ± 0·6 μm) than in the Australian collection (&- x = 3·4 ± 1·0 μm). The isolates from Spain had an optimum temperature for growth of ca 24°C and a maximum temperature range of 30–33°, whereas the Australian isolates had a higher optimum growth temperature (26°) and a higher maximum temperature range (33–35°). RAPD analysis of total DNA revealed a genetic dissimilarity of ca 80% between the two groups of isolates. The study therefore differentiated two genetically distinct groups among isolates causing chickpea root and stem rot in Spain and Australia. However, it is suggested that designation of a new taxon for the Spanish isolates should be deferred until all extant representatives of the P. megasperma complex have been fully molecularly and phylogenetically analysed.
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Genetic-Relationships Among Australian and North-American Isolates of Phytophthora-megasperma F-Sp Glycinea Assessed by Multicopy Dna Probes
Phytopathology, 1992Co-Authors: Stephen C. Whisson, Donald J. Maclean, John M. Manners, J. A. G. IrwinAbstract:Genetic relationships among five Australian and five North American isolates of Phytophthora megasperma f. sp. glycinea were explored using 10 random multicopy clones from a genomic DNA library of P. m. glycinea. Total DNA was cut with eight restriction endonucleases, giving 80 probe X enzyme combinations for each P. m. glycinea isolate. Analysis of restriction fragment length polymorphisms (RFLPs) generated by each probe revealed two size classes of RFLP difference between isolates (...)
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Stomata as an infection court for Phytophthora megasperma f.sp. medicaginis in chickpea and a histological study of infection.
Phytopathology, 1991Co-Authors: M. L. Dale, J. A. G. IrwinAbstract:Stomata located beneath the cotyledons of 7-day-old chickpea seedlings were the preferential infection court for zoos pores of Phytophthora megasperma f. sp. medicaginis. Zoospores also accumulated preferentially in the root-hair zone. Penetration usually was intercellular between anticlinal epidermal cell walls, but intracellular penetration did occur via infection pegs produced from swollen germ-tube tips. Although no differences in prepenetration or penetration events were found between a field resistant (CPl56564} and a susceptible cuhivar (ICC6334} of chickpea, hyphal growth rate of the fungus was greater through wounded roots of the susceptible cultivar than in the resistant cultivar. There was no significant difference between hyphal growth rates through wounded epicotyl tissue of the resistant and susceptible cultivars. Stomata located at or below the soil line could act as an infection court for zoospores present in surface water, and cultivars that express resistance in the root tissue would appear susceptible if the resistance was not also expressed in the hypocotyl and the lower epicotyl. A soil-line infection court also could be involved in spreading the disease via zoospores present in surface water in the field.
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Glasshouse and field screening of chickpea cultivars for resistance to Phytophthora megasperma f. Sp. medicaginis
Australian Journal of Experimental Agriculture, 1991Co-Authors: M. L. Dale, J. A. G. IrwinAbstract:The resistance expressed by a range of chickpea cultivars to Phytophthora root rot in glasshouse and field trials was examined. Van der Plank’s compound interest equation was the most suitable transformation for providing parameters to describe epidemic development for most of the cultivars when compared to the simple interest equation by plotting residuals and coefficients of determination. The area under the disease progress curve (AUDPC) was significantly correlated with the final disease incidence (FDI), which was also significantly correlated with the apparent infection rate (r), but r and AUDPC were not significantly correlated. The AUDPC proved to be relatively indiscriminate in this study for selecting resistant cultivars, since the value for the susceptible control cultivar was high, and many cultivars therefore had statistically lower AUDPC values. Several cultivars (i.e. CQ1591, ICC7568 and 232-4) were resistant on the basis of both the FDI and r parameters in the field trial and considered worthy of further investigation. When the parameters FDI or r were used to categorise the disease reactions of cultivars in the field, only half of the 30 cultivars assessed showed similar responses in both the glasshouse and field trials. The glasshouse assay used here does not allow the detection of all potentially useful forms of field resistance, and further work is needed in the development of a glasshouse assay which gives an accurate representation of field response to Phytophthora megasperma Drechs. f. sp. medicaginis Kuan and Erwin.
J. D. Paxton - One of the best experts on this subject based on the ideXlab platform.
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Metataxyl sensitivity selection within Phytophthora megasperma f. sp. glycinea
Plant Disease, 1992Co-Authors: J. S. Lamboy, J. D. PaxtonAbstract:After six successive transfers on cornmeal agar amended with 0.1 μg/ml metalaxyl, an isolate of Phytophthora megasperma f. sp. glycinea displayed reduced sensitivity to metalaxyl and increased virulence on metalaxyl-treated seedlings of Harosoy 63 soybean (Glycine max). Analysis of 10 single-zoospore progeny from the isolate, derived before the isolate was grown on metalaxyl-amended medium, demonstrated innate variation in virulence and metalaxyl sensitivity. Virulence of several isolates was compared on Harosoy and Harosoy 63 seedlings pretreated with 0, 0.5, 1.0, 2.5, and 5.0 μg/ml metalaxyl in water (.)
N. R. Obst - One of the best experts on this subject based on the ideXlab platform.
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Race-specific resistance in soybean cv. Davis to Phytophthora megasperma f.sp. glycinea
Plant Disease, 1992Co-Authors: M. J. Ryley, N. R. ObstAbstract:In Queensland, Australia, the soybean (Glycine max) cultivar Davis has been used extensively in the public breeding program as a source of resistance to Phytophthora megasperma f. sp. glycinea. This type of resistance, associated with roots and conditioned by the Rps2 gene, provided a high level of protection against many races until recently. Davis and other cultivars derived from it are grown throughout the state and have rarely been affected by Phytophthora root and stem rot. Since 1988, P. m. glycinea has been isolated from affected plants of these cultivars at several localities (.)
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A new race of Phytophthora megasperma f.sp. glycinea on soybean in Australia.
Australasian Plant Pathology, 1991Co-Authors: M. J. Ryley, N. R. Obst, G. E. StovoldAbstract:An isolate of Phytophthora megasperma f.sp. glycinea from soybean cv. Ridley growing near Forbes in the Lachlan Valley, New South Wales, was classified as race 4 after hypocotyl inoculation on a United States differential set consisting of Harosoy, Harosoy 63, Sanga, Wells II, PI 103091, PI 86972-1 and Altona. This is the first record of race 4 in Australia. The cultivars Nessen, Ridley and Lachlan, all immune to the other races of P. megasperma f.sp. glycinea in Australia (viz. races 1 and 15), were susceptible to the new race. The appearance of race 4 is undoubtedly due to the growing of cultivars with race-specific resistance.
J. S. Lamboy - One of the best experts on this subject based on the ideXlab platform.
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Metataxyl sensitivity selection within Phytophthora megasperma f. sp. glycinea
Plant Disease, 1992Co-Authors: J. S. Lamboy, J. D. PaxtonAbstract:After six successive transfers on cornmeal agar amended with 0.1 μg/ml metalaxyl, an isolate of Phytophthora megasperma f. sp. glycinea displayed reduced sensitivity to metalaxyl and increased virulence on metalaxyl-treated seedlings of Harosoy 63 soybean (Glycine max). Analysis of 10 single-zoospore progeny from the isolate, derived before the isolate was grown on metalaxyl-amended medium, demonstrated innate variation in virulence and metalaxyl sensitivity. Virulence of several isolates was compared on Harosoy and Harosoy 63 seedlings pretreated with 0, 0.5, 1.0, 2.5, and 5.0 μg/ml metalaxyl in water (.)
M. L. Dale - One of the best experts on this subject based on the ideXlab platform.
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Stomata as an infection court for Phytophthora megasperma f.sp. medicaginis in chickpea and a histological study of infection.
Phytopathology, 1991Co-Authors: M. L. Dale, J. A. G. IrwinAbstract:Stomata located beneath the cotyledons of 7-day-old chickpea seedlings were the preferential infection court for zoos pores of Phytophthora megasperma f. sp. medicaginis. Zoospores also accumulated preferentially in the root-hair zone. Penetration usually was intercellular between anticlinal epidermal cell walls, but intracellular penetration did occur via infection pegs produced from swollen germ-tube tips. Although no differences in prepenetration or penetration events were found between a field resistant (CPl56564} and a susceptible cuhivar (ICC6334} of chickpea, hyphal growth rate of the fungus was greater through wounded roots of the susceptible cultivar than in the resistant cultivar. There was no significant difference between hyphal growth rates through wounded epicotyl tissue of the resistant and susceptible cultivars. Stomata located at or below the soil line could act as an infection court for zoospores present in surface water, and cultivars that express resistance in the root tissue would appear susceptible if the resistance was not also expressed in the hypocotyl and the lower epicotyl. A soil-line infection court also could be involved in spreading the disease via zoospores present in surface water in the field.
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Glasshouse and field screening of chickpea cultivars for resistance to Phytophthora megasperma f. Sp. medicaginis
Australian Journal of Experimental Agriculture, 1991Co-Authors: M. L. Dale, J. A. G. IrwinAbstract:The resistance expressed by a range of chickpea cultivars to Phytophthora root rot in glasshouse and field trials was examined. Van der Plank’s compound interest equation was the most suitable transformation for providing parameters to describe epidemic development for most of the cultivars when compared to the simple interest equation by plotting residuals and coefficients of determination. The area under the disease progress curve (AUDPC) was significantly correlated with the final disease incidence (FDI), which was also significantly correlated with the apparent infection rate (r), but r and AUDPC were not significantly correlated. The AUDPC proved to be relatively indiscriminate in this study for selecting resistant cultivars, since the value for the susceptible control cultivar was high, and many cultivars therefore had statistically lower AUDPC values. Several cultivars (i.e. CQ1591, ICC7568 and 232-4) were resistant on the basis of both the FDI and r parameters in the field trial and considered worthy of further investigation. When the parameters FDI or r were used to categorise the disease reactions of cultivars in the field, only half of the 30 cultivars assessed showed similar responses in both the glasshouse and field trials. The glasshouse assay used here does not allow the detection of all potentially useful forms of field resistance, and further work is needed in the development of a glasshouse assay which gives an accurate representation of field response to Phytophthora megasperma Drechs. f. sp. medicaginis Kuan and Erwin.