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Clint W. Magill - One of the best experts on this subject based on the ideXlab platform.
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Genome wide association analysis of sorghum mini core lines regarding anthracnose, downy mildew, and head smut
PloS one, 2019Co-Authors: Ezekiel Ahn, Ramasamy Perumal, Louis K Prom, Gary N Odvody, Hari D. Upadhyaya, Clint W. MagillAbstract:In previous studies, a sorghum mini core collection was scored over several years for response to Colletotrichum sublineola, Peronosclerospora sorghi, and Sporisorium reilianum, the causal agents of the disease anthracnose, downy mildew, and head smut, respectively. The screening results were combined with over 290,000 Single nucleotide polymorphic (SNP) loci from an updated version of a publicly available genotype by sequencing (GBS) dataset available for the mini core collection. GAPIT (Genome Association and Prediction Integrated Tool) R package was used to identify chromosomal locations that differ in disease response. When the top scoring SNPs were mapped to the most recent version of the published sorghum genome, in each case, a nearby and most often the closest annotated gene has precedence for a role in host defense.
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Screening Exotic Sorghum Germplasm, Hybrids, and Elite Lines for Resistance to a New Virulent Pathotype (P6) of Peronosclerospora sorghi Causing Downy Mildew
Plant Health Progress, 2011Co-Authors: Ghada Radwan, Clint W. Magill, Ramasamy Perumal, Louis K Prom, T. Isakeit, Christopher R. LittleAbstract:A recent outbreak of sorghum downy mildew (SDM) in Texas has led to the discovery of both metalaxyl fungicide resistance and a new pathotype, P6, in the causal organism Peronosclerospora sorghi. New and alternate sources of host plant resistance are needed for successful management of SDM. To identify sources of resistance, a total of 333 (242 minicore lines representing diverse germplasm from India, 67 commercial hybrids from Kansas, and 24 elite breeding lines from Texas) were inoculated in the greenhouse. Using an established sandwich inoculation technique, artificial inoculation of test lines with P. sorghi conidia, resulting in < 10% infection, were scored as “resistant.” Fifty-two minicore and 20 accessions from Kansas exhibited ≤ 10% infection and were selected as resistant. Out of 52 resistant minicore accessions, 28 were photoinsensitive. Eleven of 20 commercial hybrids from Kansas showed zero percent infection. Thirteen of 24 elite breeding lines from Texas were also resistant. In this study, resistance sources for the new P6 SDM pathotype were identified. The diversity among these materials is expected to provide different single-gene sources as well as quantitative sources of SDM resistance for use in breeding programs.
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Simple sequence repeat markers useful for sorghum downy mildew (Peronosclerospora sorghi) and related species
BMC Genetics, 2008Co-Authors: Ramasamy Perumal, Padmavathi Nimmakayala, Saradha R Erattaimuthu, Umesh K Reddy, Louis K Prom, Gary N Odvody, Douglas G Luster, Clint W. MagillAbstract:Background A recent outbreak of sorghum downy mildew in Texas has led to the discovery of both metalaxyl resistance and a new pathotype in the causal organism, Peronosclerospora sorghi . These observations and the difficulty in resolving among phylogenetically related downy mildew pathogens dramatically point out the need for simply scored markers in order to differentiate among isolates and species, and to study the population structure within these obligate oomycetes. Here we present the initial results from the use of a biotin capture method to discover, clone and develop PCR primers that permit the use of simple sequence repeats (microsatellites) to detect differences at the DNA level. Results Among the 55 primers pairs designed from clones from pathotype 3 of P. sorghi , 36 flanked microsatellite loci containing simple repeats, including 28 (55%) with dinucleotide repeats and 6 (11%) with trinucleotide repeats. A total of 22 microsatellites with CA/AC or GT/TG repeats were the most abundant (40%) and GA/AG or CT/TC types contribute 15% in our collection. When used to amplify DNA from 19 isolates from P. sorghi , as well as from 5 related species that cause downy mildew on other hosts, the number of different bands detected for each SSR primer pair using a LI-COR- DNA Analyzer ranged from two to eight. Successful cross-amplification for 12 primer pairs studied in detail using DNA from downy mildews that attack maize ( P. maydis & P. philippinensis ), sugar cane ( P. sacchari ), pearl millet ( Sclerospora graminicola ) and rose ( Peronospora sparsa ) indicate that the flanking regions are conserved in all these species. A total of 15 SSR amplicons unique to P. philippinensis (one of the potential threats to US maize production) were detected, and these have potential for development of diagnostic tests. A total of 260 alleles were obtained using 54 microsatellites primer combinations, with an average of 4.8 polymorphic markers per SSR across 34 Peronosclerospora, Peronospora and Sclerospora spp isolates studied. Cluster analysis by UPGMA as well as principal coordinate analysis (PCA) grouped the 34 isolates into three distinct groups (all 19 isolates of Peronosclerospora sorghi in cluster I, five isolates of P. maydis and three isolates of P. sacchari in cluster II and five isolates of Sclerospora graminicola in cluster III). Conclusion To our knowledge, this is the first attempt to extensively develop SSR markers from Peronosclerospora genomic DNA. The newly developed SSR markers can be readily used to distinguish isolates within several species of the oomycetes that cause downy mildew diseases. Also, microsatellite fragments likely include retrotransposon regions of DNA and these sequences can serve as useful genetic markers for strain identification, due to their degree of variability and their widespread occurrence among sorghum, maize, sugarcane, pearl millet and rose downy mildew isolates.
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Simple sequence repeat markers useful for sorghum downy mildew (Peronosclerospora sorghi) and related species
BMC genetics, 2008Co-Authors: Ramasamy Perumal, Padmavathi Nimmakayala, Saradha R Erattaimuthu, Umesh K Reddy, Louis K Prom, Gary N Odvody, Douglas G Luster, Clint W. MagillAbstract:A recent outbreak of sorghum downy mildew in Texas has led to the discovery of both metalaxyl resistance and a new pathotype in the causal organism, Peronosclerospora sorghi. These observations and the difficulty in resolving among phylogenetically related downy mildew pathogens dramatically point out the need for simply scored markers in order to differentiate among isolates and species, and to study the population structure within these obligate oomycetes. Here we present the initial results from the use of a biotin capture method to discover, clone and develop PCR primers that permit the use of simple sequence repeats (microsatellites) to detect differences at the DNA level. Among the 55 primers pairs designed from clones from pathotype 3 of P. sorghi, 36 flanked microsatellite loci containing simple repeats, including 28 (55%) with dinucleotide repeats and 6 (11%) with trinucleotide repeats. A total of 22 microsatellites with CA/AC or GT/TG repeats were the most abundant (40%) and GA/AG or CT/TC types contribute 15% in our collection. When used to amplify DNA from 19 isolates from P. sorghi, as well as from 5 related species that cause downy mildew on other hosts, the number of different bands detected for each SSR primer pair using a LI-COR- DNA Analyzer ranged from two to eight. Successful cross-amplification for 12 primer pairs studied in detail using DNA from downy mildews that attack maize (P. maydis & P. philippinensis), sugar cane (P. sacchari), pearl millet (Sclerospora graminicola) and rose (Peronospora sparsa) indicate that the flanking regions are conserved in all these species. A total of 15 SSR amplicons unique to P. philippinensis (one of the potential threats to US maize production) were detected, and these have potential for development of diagnostic tests. A total of 260 alleles were obtained using 54 microsatellites primer combinations, with an average of 4.8 polymorphic markers per SSR across 34 Peronosclerospora, Peronospora and Sclerospora spp isolates studied. Cluster analysis by UPGMA as well as principal coordinate analysis (PCA) grouped the 34 isolates into three distinct groups (all 19 isolates of Peronosclerospora sorghi in cluster I, five isolates of P. maydis and three isolates of P. sacchari in cluster II and five isolates of Sclerospora graminicola in cluster III). To our knowledge, this is the first attempt to extensively develop SSR markers from Peronosclerospora genomic DNA. The newly developed SSR markers can be readily used to distinguish isolates within several species of the oomycetes that cause downy mildew diseases. Also, microsatellite fragments likely include retrotransposon regions of DNA and these sequences can serve as useful genetic markers for strain identification, due to their degree of variability and their widespread occurrence among sorghum, maize, sugarcane, pearl millet and rose downy mildew isolates.
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BioMed Central
2008Co-Authors: Bmc Genetics, Ramasamy Perumal, Padmavathi Nimmakayala, Saradha R Erattaimuthu, Umesh K Reddy, Louis K Prom, Gary N Odvody, Douglas G Luster, Clint W. MagillAbstract:Research article Simple sequence repeat markers useful for sorghum downy mildew (Peronosclerospora sorghi) and related specie
Ramasamy Perumal - One of the best experts on this subject based on the ideXlab platform.
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Genome wide association analysis of sorghum mini core lines regarding anthracnose, downy mildew, and head smut
PloS one, 2019Co-Authors: Ezekiel Ahn, Ramasamy Perumal, Louis K Prom, Gary N Odvody, Hari D. Upadhyaya, Clint W. MagillAbstract:In previous studies, a sorghum mini core collection was scored over several years for response to Colletotrichum sublineola, Peronosclerospora sorghi, and Sporisorium reilianum, the causal agents of the disease anthracnose, downy mildew, and head smut, respectively. The screening results were combined with over 290,000 Single nucleotide polymorphic (SNP) loci from an updated version of a publicly available genotype by sequencing (GBS) dataset available for the mini core collection. GAPIT (Genome Association and Prediction Integrated Tool) R package was used to identify chromosomal locations that differ in disease response. When the top scoring SNPs were mapped to the most recent version of the published sorghum genome, in each case, a nearby and most often the closest annotated gene has precedence for a role in host defense.
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Evaluation of Gambian and Malian sorghum germplasm against downy mildew pathogen, Peronosclerospora sorghi, in Mexico and the USA
Journal of General Plant Pathology, 2015Co-Authors: Louis K Prom, Thomas Isakeit, Ramasamy Perumal, Gary N Odvody, Noe Montes-garcia, William L. Rooney, Christopher R. Little, Clint MagillAbstract:The recent outbreak of sorghum downy mildew (SDM) in Texas, USA caused by pathotype P3 of Peronosclerospora sorghi , which is resistant to standard fungicide seed treatment, and the subsequent development of a new pathotype, P6, that overcame resistance in some hybrids, has emphasized the importance of continuing to develop new sources with genetic resistance. Eighty-two exotic Gambian and Malian germplasms and 10 sorghum lines commonly used as SDM pathotype differentials were field-evaluated in a randomized complete block design replicated three times at one Mexican location (Ocotlán, Jalisco) in 2004 and 2005, and two USA locations (Louise and New Taiton, TX, USA) in 2005 to identify new sources of SDM resistance. Accessions PI609151 and PI609442 from Mali had high levels of SDM resistance at all locations. Malian accession PI612815 also had a moderate to resistant reaction to SDM in two of the three locations. Accession PI522108 from Gambia was resistant in Mexico but susceptible in Louise, TX, USA. The reaction of the 10 lines used as differentials suggested the presence of a pathotype in Mexico that differed from those in the USA.
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Screening Exotic Sorghum Germplasm, Hybrids, and Elite Lines for Resistance to a New Virulent Pathotype (P6) of Peronosclerospora sorghi Causing Downy Mildew
Plant Health Progress, 2011Co-Authors: Ghada Radwan, Clint W. Magill, Ramasamy Perumal, Louis K Prom, T. Isakeit, Christopher R. LittleAbstract:A recent outbreak of sorghum downy mildew (SDM) in Texas has led to the discovery of both metalaxyl fungicide resistance and a new pathotype, P6, in the causal organism Peronosclerospora sorghi. New and alternate sources of host plant resistance are needed for successful management of SDM. To identify sources of resistance, a total of 333 (242 minicore lines representing diverse germplasm from India, 67 commercial hybrids from Kansas, and 24 elite breeding lines from Texas) were inoculated in the greenhouse. Using an established sandwich inoculation technique, artificial inoculation of test lines with P. sorghi conidia, resulting in < 10% infection, were scored as “resistant.” Fifty-two minicore and 20 accessions from Kansas exhibited ≤ 10% infection and were selected as resistant. Out of 52 resistant minicore accessions, 28 were photoinsensitive. Eleven of 20 commercial hybrids from Kansas showed zero percent infection. Thirteen of 24 elite breeding lines from Texas were also resistant. In this study, resistance sources for the new P6 SDM pathotype were identified. The diversity among these materials is expected to provide different single-gene sources as well as quantitative sources of SDM resistance for use in breeding programs.
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Simple sequence repeat markers useful for sorghum downy mildew (Peronosclerospora sorghi) and related species
BMC Genetics, 2008Co-Authors: Ramasamy Perumal, Padmavathi Nimmakayala, Saradha R Erattaimuthu, Umesh K Reddy, Louis K Prom, Gary N Odvody, Douglas G Luster, Clint W. MagillAbstract:Background A recent outbreak of sorghum downy mildew in Texas has led to the discovery of both metalaxyl resistance and a new pathotype in the causal organism, Peronosclerospora sorghi . These observations and the difficulty in resolving among phylogenetically related downy mildew pathogens dramatically point out the need for simply scored markers in order to differentiate among isolates and species, and to study the population structure within these obligate oomycetes. Here we present the initial results from the use of a biotin capture method to discover, clone and develop PCR primers that permit the use of simple sequence repeats (microsatellites) to detect differences at the DNA level. Results Among the 55 primers pairs designed from clones from pathotype 3 of P. sorghi , 36 flanked microsatellite loci containing simple repeats, including 28 (55%) with dinucleotide repeats and 6 (11%) with trinucleotide repeats. A total of 22 microsatellites with CA/AC or GT/TG repeats were the most abundant (40%) and GA/AG or CT/TC types contribute 15% in our collection. When used to amplify DNA from 19 isolates from P. sorghi , as well as from 5 related species that cause downy mildew on other hosts, the number of different bands detected for each SSR primer pair using a LI-COR- DNA Analyzer ranged from two to eight. Successful cross-amplification for 12 primer pairs studied in detail using DNA from downy mildews that attack maize ( P. maydis & P. philippinensis ), sugar cane ( P. sacchari ), pearl millet ( Sclerospora graminicola ) and rose ( Peronospora sparsa ) indicate that the flanking regions are conserved in all these species. A total of 15 SSR amplicons unique to P. philippinensis (one of the potential threats to US maize production) were detected, and these have potential for development of diagnostic tests. A total of 260 alleles were obtained using 54 microsatellites primer combinations, with an average of 4.8 polymorphic markers per SSR across 34 Peronosclerospora, Peronospora and Sclerospora spp isolates studied. Cluster analysis by UPGMA as well as principal coordinate analysis (PCA) grouped the 34 isolates into three distinct groups (all 19 isolates of Peronosclerospora sorghi in cluster I, five isolates of P. maydis and three isolates of P. sacchari in cluster II and five isolates of Sclerospora graminicola in cluster III). Conclusion To our knowledge, this is the first attempt to extensively develop SSR markers from Peronosclerospora genomic DNA. The newly developed SSR markers can be readily used to distinguish isolates within several species of the oomycetes that cause downy mildew diseases. Also, microsatellite fragments likely include retrotransposon regions of DNA and these sequences can serve as useful genetic markers for strain identification, due to their degree of variability and their widespread occurrence among sorghum, maize, sugarcane, pearl millet and rose downy mildew isolates.
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Simple sequence repeat markers useful for sorghum downy mildew (Peronosclerospora sorghi) and related species
BMC genetics, 2008Co-Authors: Ramasamy Perumal, Padmavathi Nimmakayala, Saradha R Erattaimuthu, Umesh K Reddy, Louis K Prom, Gary N Odvody, Douglas G Luster, Clint W. MagillAbstract:A recent outbreak of sorghum downy mildew in Texas has led to the discovery of both metalaxyl resistance and a new pathotype in the causal organism, Peronosclerospora sorghi. These observations and the difficulty in resolving among phylogenetically related downy mildew pathogens dramatically point out the need for simply scored markers in order to differentiate among isolates and species, and to study the population structure within these obligate oomycetes. Here we present the initial results from the use of a biotin capture method to discover, clone and develop PCR primers that permit the use of simple sequence repeats (microsatellites) to detect differences at the DNA level. Among the 55 primers pairs designed from clones from pathotype 3 of P. sorghi, 36 flanked microsatellite loci containing simple repeats, including 28 (55%) with dinucleotide repeats and 6 (11%) with trinucleotide repeats. A total of 22 microsatellites with CA/AC or GT/TG repeats were the most abundant (40%) and GA/AG or CT/TC types contribute 15% in our collection. When used to amplify DNA from 19 isolates from P. sorghi, as well as from 5 related species that cause downy mildew on other hosts, the number of different bands detected for each SSR primer pair using a LI-COR- DNA Analyzer ranged from two to eight. Successful cross-amplification for 12 primer pairs studied in detail using DNA from downy mildews that attack maize (P. maydis & P. philippinensis), sugar cane (P. sacchari), pearl millet (Sclerospora graminicola) and rose (Peronospora sparsa) indicate that the flanking regions are conserved in all these species. A total of 15 SSR amplicons unique to P. philippinensis (one of the potential threats to US maize production) were detected, and these have potential for development of diagnostic tests. A total of 260 alleles were obtained using 54 microsatellites primer combinations, with an average of 4.8 polymorphic markers per SSR across 34 Peronosclerospora, Peronospora and Sclerospora spp isolates studied. Cluster analysis by UPGMA as well as principal coordinate analysis (PCA) grouped the 34 isolates into three distinct groups (all 19 isolates of Peronosclerospora sorghi in cluster I, five isolates of P. maydis and three isolates of P. sacchari in cluster II and five isolates of Sclerospora graminicola in cluster III). To our knowledge, this is the first attempt to extensively develop SSR markers from Peronosclerospora genomic DNA. The newly developed SSR markers can be readily used to distinguish isolates within several species of the oomycetes that cause downy mildew diseases. Also, microsatellite fragments likely include retrotransposon regions of DNA and these sequences can serve as useful genetic markers for strain identification, due to their degree of variability and their widespread occurrence among sorghum, maize, sugarcane, pearl millet and rose downy mildew isolates.
Louis K Prom - One of the best experts on this subject based on the ideXlab platform.
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Genome wide association analysis of sorghum mini core lines regarding anthracnose, downy mildew, and head smut
PloS one, 2019Co-Authors: Ezekiel Ahn, Ramasamy Perumal, Louis K Prom, Gary N Odvody, Hari D. Upadhyaya, Clint W. MagillAbstract:In previous studies, a sorghum mini core collection was scored over several years for response to Colletotrichum sublineola, Peronosclerospora sorghi, and Sporisorium reilianum, the causal agents of the disease anthracnose, downy mildew, and head smut, respectively. The screening results were combined with over 290,000 Single nucleotide polymorphic (SNP) loci from an updated version of a publicly available genotype by sequencing (GBS) dataset available for the mini core collection. GAPIT (Genome Association and Prediction Integrated Tool) R package was used to identify chromosomal locations that differ in disease response. When the top scoring SNPs were mapped to the most recent version of the published sorghum genome, in each case, a nearby and most often the closest annotated gene has precedence for a role in host defense.
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Evaluation of Gambian and Malian sorghum germplasm against downy mildew pathogen, Peronosclerospora sorghi, in Mexico and the USA
Journal of General Plant Pathology, 2015Co-Authors: Louis K Prom, Thomas Isakeit, Ramasamy Perumal, Gary N Odvody, Noe Montes-garcia, William L. Rooney, Christopher R. Little, Clint MagillAbstract:The recent outbreak of sorghum downy mildew (SDM) in Texas, USA caused by pathotype P3 of Peronosclerospora sorghi , which is resistant to standard fungicide seed treatment, and the subsequent development of a new pathotype, P6, that overcame resistance in some hybrids, has emphasized the importance of continuing to develop new sources with genetic resistance. Eighty-two exotic Gambian and Malian germplasms and 10 sorghum lines commonly used as SDM pathotype differentials were field-evaluated in a randomized complete block design replicated three times at one Mexican location (Ocotlán, Jalisco) in 2004 and 2005, and two USA locations (Louise and New Taiton, TX, USA) in 2005 to identify new sources of SDM resistance. Accessions PI609151 and PI609442 from Mali had high levels of SDM resistance at all locations. Malian accession PI612815 also had a moderate to resistant reaction to SDM in two of the three locations. Accession PI522108 from Gambia was resistant in Mexico but susceptible in Louise, TX, USA. The reaction of the 10 lines used as differentials suggested the presence of a pathotype in Mexico that differed from those in the USA.
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Screening Exotic Sorghum Germplasm, Hybrids, and Elite Lines for Resistance to a New Virulent Pathotype (P6) of Peronosclerospora sorghi Causing Downy Mildew
Plant Health Progress, 2011Co-Authors: Ghada Radwan, Clint W. Magill, Ramasamy Perumal, Louis K Prom, T. Isakeit, Christopher R. LittleAbstract:A recent outbreak of sorghum downy mildew (SDM) in Texas has led to the discovery of both metalaxyl fungicide resistance and a new pathotype, P6, in the causal organism Peronosclerospora sorghi. New and alternate sources of host plant resistance are needed for successful management of SDM. To identify sources of resistance, a total of 333 (242 minicore lines representing diverse germplasm from India, 67 commercial hybrids from Kansas, and 24 elite breeding lines from Texas) were inoculated in the greenhouse. Using an established sandwich inoculation technique, artificial inoculation of test lines with P. sorghi conidia, resulting in < 10% infection, were scored as “resistant.” Fifty-two minicore and 20 accessions from Kansas exhibited ≤ 10% infection and were selected as resistant. Out of 52 resistant minicore accessions, 28 were photoinsensitive. Eleven of 20 commercial hybrids from Kansas showed zero percent infection. Thirteen of 24 elite breeding lines from Texas were also resistant. In this study, resistance sources for the new P6 SDM pathotype were identified. The diversity among these materials is expected to provide different single-gene sources as well as quantitative sources of SDM resistance for use in breeding programs.
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Simple sequence repeat markers useful for sorghum downy mildew (Peronosclerospora sorghi) and related species
BMC Genetics, 2008Co-Authors: Ramasamy Perumal, Padmavathi Nimmakayala, Saradha R Erattaimuthu, Umesh K Reddy, Louis K Prom, Gary N Odvody, Douglas G Luster, Clint W. MagillAbstract:Background A recent outbreak of sorghum downy mildew in Texas has led to the discovery of both metalaxyl resistance and a new pathotype in the causal organism, Peronosclerospora sorghi . These observations and the difficulty in resolving among phylogenetically related downy mildew pathogens dramatically point out the need for simply scored markers in order to differentiate among isolates and species, and to study the population structure within these obligate oomycetes. Here we present the initial results from the use of a biotin capture method to discover, clone and develop PCR primers that permit the use of simple sequence repeats (microsatellites) to detect differences at the DNA level. Results Among the 55 primers pairs designed from clones from pathotype 3 of P. sorghi , 36 flanked microsatellite loci containing simple repeats, including 28 (55%) with dinucleotide repeats and 6 (11%) with trinucleotide repeats. A total of 22 microsatellites with CA/AC or GT/TG repeats were the most abundant (40%) and GA/AG or CT/TC types contribute 15% in our collection. When used to amplify DNA from 19 isolates from P. sorghi , as well as from 5 related species that cause downy mildew on other hosts, the number of different bands detected for each SSR primer pair using a LI-COR- DNA Analyzer ranged from two to eight. Successful cross-amplification for 12 primer pairs studied in detail using DNA from downy mildews that attack maize ( P. maydis & P. philippinensis ), sugar cane ( P. sacchari ), pearl millet ( Sclerospora graminicola ) and rose ( Peronospora sparsa ) indicate that the flanking regions are conserved in all these species. A total of 15 SSR amplicons unique to P. philippinensis (one of the potential threats to US maize production) were detected, and these have potential for development of diagnostic tests. A total of 260 alleles were obtained using 54 microsatellites primer combinations, with an average of 4.8 polymorphic markers per SSR across 34 Peronosclerospora, Peronospora and Sclerospora spp isolates studied. Cluster analysis by UPGMA as well as principal coordinate analysis (PCA) grouped the 34 isolates into three distinct groups (all 19 isolates of Peronosclerospora sorghi in cluster I, five isolates of P. maydis and three isolates of P. sacchari in cluster II and five isolates of Sclerospora graminicola in cluster III). Conclusion To our knowledge, this is the first attempt to extensively develop SSR markers from Peronosclerospora genomic DNA. The newly developed SSR markers can be readily used to distinguish isolates within several species of the oomycetes that cause downy mildew diseases. Also, microsatellite fragments likely include retrotransposon regions of DNA and these sequences can serve as useful genetic markers for strain identification, due to their degree of variability and their widespread occurrence among sorghum, maize, sugarcane, pearl millet and rose downy mildew isolates.
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Simple sequence repeat markers useful for sorghum downy mildew (Peronosclerospora sorghi) and related species
BMC genetics, 2008Co-Authors: Ramasamy Perumal, Padmavathi Nimmakayala, Saradha R Erattaimuthu, Umesh K Reddy, Louis K Prom, Gary N Odvody, Douglas G Luster, Clint W. MagillAbstract:A recent outbreak of sorghum downy mildew in Texas has led to the discovery of both metalaxyl resistance and a new pathotype in the causal organism, Peronosclerospora sorghi. These observations and the difficulty in resolving among phylogenetically related downy mildew pathogens dramatically point out the need for simply scored markers in order to differentiate among isolates and species, and to study the population structure within these obligate oomycetes. Here we present the initial results from the use of a biotin capture method to discover, clone and develop PCR primers that permit the use of simple sequence repeats (microsatellites) to detect differences at the DNA level. Among the 55 primers pairs designed from clones from pathotype 3 of P. sorghi, 36 flanked microsatellite loci containing simple repeats, including 28 (55%) with dinucleotide repeats and 6 (11%) with trinucleotide repeats. A total of 22 microsatellites with CA/AC or GT/TG repeats were the most abundant (40%) and GA/AG or CT/TC types contribute 15% in our collection. When used to amplify DNA from 19 isolates from P. sorghi, as well as from 5 related species that cause downy mildew on other hosts, the number of different bands detected for each SSR primer pair using a LI-COR- DNA Analyzer ranged from two to eight. Successful cross-amplification for 12 primer pairs studied in detail using DNA from downy mildews that attack maize (P. maydis & P. philippinensis), sugar cane (P. sacchari), pearl millet (Sclerospora graminicola) and rose (Peronospora sparsa) indicate that the flanking regions are conserved in all these species. A total of 15 SSR amplicons unique to P. philippinensis (one of the potential threats to US maize production) were detected, and these have potential for development of diagnostic tests. A total of 260 alleles were obtained using 54 microsatellites primer combinations, with an average of 4.8 polymorphic markers per SSR across 34 Peronosclerospora, Peronospora and Sclerospora spp isolates studied. Cluster analysis by UPGMA as well as principal coordinate analysis (PCA) grouped the 34 isolates into three distinct groups (all 19 isolates of Peronosclerospora sorghi in cluster I, five isolates of P. maydis and three isolates of P. sacchari in cluster II and five isolates of Sclerospora graminicola in cluster III). To our knowledge, this is the first attempt to extensively develop SSR markers from Peronosclerospora genomic DNA. The newly developed SSR markers can be readily used to distinguish isolates within several species of the oomycetes that cause downy mildew diseases. Also, microsatellite fragments likely include retrotransposon regions of DNA and these sequences can serve as useful genetic markers for strain identification, due to their degree of variability and their widespread occurrence among sorghum, maize, sugarcane, pearl millet and rose downy mildew isolates.
K. F. Cardwell - One of the best experts on this subject based on the ideXlab platform.
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Reaction of maize, sorghum and Johnson grass to Peronosclerospora sorghi
International Journal of Pest Management, 2000Co-Authors: G. Bigirwa, E. Adipala, J. P. Esele, K. F. CardwellAbstract:Development of sorghum downy mildew, incited by Peronoscleospora sorghi (Weston and Uppal) C.G. Shaw, on maize, sorghum and Johnson grass was investigated at two locations in Uganda during three seasons (1994 and 1995). More sorghum downy mildew developed on the Johnson grass and sorghum than on the maize at all locations and in all seasons. No significant differences were observed in sporulation of P. soghi on the three hosts. Leaf shredding occurred on the three hosts but was the least on maize. Cross-inoculation with both conidia and oospores was achieved on the three hosts. Since the fungal population formed oospores and sporulated readily on the three hosts, which is typical of the sorghum strain, the disease in Uganda is attributed to the sorghum strain.
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Seed transmission of maize downy mildew (Peronosclerospora sorghi) in Nigeria
Plant Pathology, 2000Co-Authors: V. O. Adenle, K. F. CardwellAbstract:In an area of Nigeria where downy mildew of maize is present, histological assessment of maize seed revealed the presence of mycelium and oospores of Peronosclerospora sorghi in the kernels. Seed transmission of downy mildew of maize was demonstrated when grain purchased at local markets gave mean seedling infection rates of 12·3% (untreated seeds) and 10·0% (in metalaxyl-treated seeds) within 7 days of emergence, after storage in a desiccator for 30 days. When untreated seeds taken from nubbin ears of systemically infected plants from four states in southern Nigeria were planted at 9 days (17–22% moisture content) and 27 days (9–22% moisture content) after harvest, 20·0% infected seedlings resulted in both trials. Seeds from Borno state in northern Nigeria had 26·6% systemic seedling infection after 9 months of storage at 11% moisture content. When seeds harvested from maize plants inoculated with P. sorghi through silks were examined histologically, hyphae of P. sorghi were observed mostly in the scutellum of the embryo. Transmission of disease to seedlings was observed when the silk-inoculated seeds (9% moisture content) were planted in pots in a greenhouse; however, no disease transmission was observed when such seeds were planted in the field. The epidemiological significance of seed transmission is discussed with particular reference to survival of inoculum and development of epidemics. Also noteworthy is the overall significance of seed transmission in Nigeria, where the major source of seed is that saved by farmers from their grain crop, occasionally supplemented by seed bought from the local market.
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Variability of Peronosclerospora sorghi isolates from different geographic locations and hosts in Africa.
Mycological Research, 2000Co-Authors: Clive H. Bock, K. F. Cardwell, L. K. Mughogho, E. Mtisi, M.j. Jeger, G. Kaula, D. MukansabimanaAbstract:Nine isolates of Peronosclerospora sorghi from maize, sorghum and wild sorghum were sampled from Zimbabwe, Zambia, Rwanda, Mozambique and Kenya. They were compared for variation in conidium and conidiophore morphology, temperature requirements for sporulation, germination and germ-tube growth and for pathogenicity on different sorghum and maize cultivars. Although there were significant differences in isolate morphology, all conformed to the known range for P. sorghi. Mean conidial length × width ranged from 21–23 μm × 16·9–19·2 μm, and mean conidiophore length (basal cell-branching) ranged from 116·3–135·6 μm. All isolates sporulated in the range 14–26°C (optimal at 16–23°), although one isolate from maize from Umbeluzi in Mozambique had a broader optimal range for sporulation (12–25°). Conidia of all isolates germinated between 10° and 34°. Germ-tube response to temperature was similar for all isolates (10–34°). The isolates varied in their pathogenicity towards sorghum cultivars, with an isolate from Rwanda being pathogenic to more sorghum differentials than any other. Cluster analysis of isolates based on host reaction indicated five groups at the 85% similarity level. The existence of pathogenic variability has ramifications for the breeding of sorghum for resistance to downy mildew in Africa.
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Effect of dew point temperature and conidium age on germination, germ tube growth and infection of maize and sorghum by Peronosclerospora sorghi
Mycological Research, 1999Co-Authors: Clive H. Bock, K. F. Cardwell, L. K. Mughogho, M.j. Jeger, E. MtisiAbstract:The effect of the environment on the germination, survival and infection of sorghum by conidia of Peronosclerospora sorghi is unknown in Africa. Dew point temperature, and the effect of conidium age was characterized for an isolate of P. sorghi from Zimbabwe. Germination and germ tube growth took place in the range 10–34°C (optimal at 10–34 and 20–33°, respectively). Infection was optimal at 14–30°. Incidence of infection at different temperatures was correlated with germ tube growth ( r = 0.8, P P. sorghi from the U.S.A. and India.
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occurrence and distribution of Peronosclerospora sorghi weston and uppal shaw in selected countries of west and southern africa
Crop Protection, 1998Co-Authors: Clive H. Bock, K. F. Cardwell, E. Mtisi, M.j. Jeger, L.k. Mughoho, V. Adenle, A.d. Akpa, G. Kaula, D. Mukasambina, C BlairmyersAbstract:Surveys of sorghum and maize crops were undertaken in Nigeria, Zimbabwe, Zambia, Mozambique and Rwanda during 1991 and 1992. The occurrence and prevalence of sorghum downy mildew (SDM) caused by Peronosclerospora sorghi [(Weston and Uppal) Shaw] was assessed in regions of each country. In Nigeria only maize was systemically infected in the southern humid zone, where rainfall was 1200–1800 mm and the altitude 300–1000 m. This epidemic zone appeared to be geographically isolated from other areas of Nigeria where SDM was observed. Within the southern epidemic zone, yield loss was estimated to be 11.7%. Individual fields had up to 95% incidence of systemically infected plants. In the arid north of Nigeria (rainfall < 1300 mm, altitude 600–1200 m) both maize and sorghum were infected, and disease incidence was invariably low (<5%). Systemic SDM incidence on maize was negatively correlated with growth stage (r = −0.7746, P = 0.01). In Zimbabwe, Zambia, Mozambique and Rwanda sorghum and maize were infected with SDM in areas with an annual rainfall of 600–1200 mm and an altitude range of <300–1800 m. Incidence of infection within crops was generally low, and sites with infected crops were scattered in these countries. SDM local lesion infection was observed only on sorghum. Yield loss due to SDM in Zambia, Zimbabwe and Rwanda at the time of the survey was negligible. However, SDM is widespread in Africa and occurs in many different agricultural areas, and thus remains a threat to sorghum and maize production. Management of the disease using resistant varieties, cultural and chemical control should reduce the risk of future epidemics.
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texas has a new pathotype of Peronosclerospora sorghi the cause of sorghum downy mildew
Plant Disease, 2005Co-Authors: Thomas Isakeit, J. JasterAbstract:Three pathotypes of Peronosclerospora sorghi were known to occur in Texas as of 1980, with pathotype 3 (P3) predominant on sorghum (Sorghum bicolor) grown in the Upper Coast area. Following the use of hybrids resistant to P3, combined with metalaxyl or mefenoxam seed treatment, sorghum downy mildew (SDM) became a minor disease in Texas until the occurrence of a widespread outbreak caused by a P3 strain resistant to metalaxyl and mefenoxam in Wharton County in 2001 (2). During July 2004, <1% of plants in a commercial field in Wharton County planted to two Pioneer Brand P3-resistant hybrids had white stripes on the leaves and leaf shredding typical of systemic SDM. To obtain inoculum for pathogenicity studies, several infected plants were removed from the field and transplanted to pots for growth in a greenhouse. Systemically infected leaves suitable for inoculum production subsequently developed from tillers. Conidia were collected from leaves using a tiered temperature system (1). One-week-old seedlings o...
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Texas Has a New Pathotype of Peronosclerospora sorghi, the Cause of Sorghum Downy Mildew.
Plant disease, 2005Co-Authors: Thomas Isakeit, J. JasterAbstract:Three pathotypes of Peronosclerospora sorghi were known to occur in Texas as of 1980, with pathotype 3 (P3) predominant on sorghum (Sorghum bicolor) grown in the Upper Coast area. Following the use of hybrids resistant to P3, combined with metalaxyl or mefenoxam seed treatment, sorghum downy mildew (SDM) became a minor disease in Texas until the occurrence of a widespread outbreak caused by a P3 strain resistant to metalaxyl and mefenoxam in Wharton County in 2001 (2). During July 2004,