Phylogeny of cercosporoid fungi (Mycosphaerellaceae, Mycosphaerellales) from Hawaii and New York reveals novel species within the Cercospora beticola complex

Cercospora leaf spot (CLS), caused by Cercospora beticola, is one of the major diseases affecting productivity and profitability of beet production worldwide. Fungicides are critical for the control of this disease and one of the most commonly used products is the quinone outside inhibitor (QOI) azoxystrobin. In total, 150 C. beticola isolates were collected from two commercial processing table beet fields in Batavia, NY in 2014. The mating types of the entire population were determined, and genetic diversity of a subset of samples (n = 48) was assessed using five microsatellite loci. Sensitivity to azoxystrobin was tested using a spore germination assay. The cytochrome b gene was sequenced to check for the presence of point mutations known to confer QOI resistance in fungi. High allelic diversity (He = 0.50) and genotypic diversity (D* = 0.96), gametic equilibrium of the microsatellite loci, and equal ratios of mating types were suggestive of a mixed mode of reproduction for C. beticola. Resistance to azoxystrobin was prevalent because 41% of the isolates had values for effective concentrations reducing spore germination by 50% (EC50) > 0.2 μg/ml. The G143A mutation, known to cause QOI resistance in C. beticola, was found in isolates with EC50 values between 0.207 and 19.397 μg/ml. A single isolate with an EC50 of 0.272 μg/ml carried the F129L mutation, known to be associated with low levels of QOI resistance in fungi. This is the first report of the F129L mutation in C. beticola. The implications of these findings for the epidemiology and control of CLS in table beet fields in New York are discussed.

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Temporal Genetic Differentiation of Cercospora beticola Populations in New York Table Beet Fields

Plant Disease ◽

10.1094/pdis-01-18-0175-re ◽

2018 ◽

Vol 102 (11) ◽

pp. 2074-2082 ◽

Cited By ~ 10

Author(s):

Noel L. Knight ◽

Niloofar Vaghefi ◽

Zachariah R. Hansen ◽

Julie R. Kikkert ◽

Sarah J. Pethybridge

Keyword(s):

New York ◽

Genetic Differentiation ◽

Temporal Stability ◽

Cropping System ◽

Genotypic Diversity ◽

Cercospora Beticola ◽

Multilocus Genotype ◽

Cercospora Leaf Spot ◽

Corrected Data

Annual epidemics of Cercospora leaf spot (CLS), caused by the fungus Cercospora beticola, can result in substantial defoliation in table beet fields in New York. High allelic and genotypic diversity have been described within C. beticola populations; however, information on the temporal stability of populations is lacking. C. beticola isolates were obtained from symptomatic leaves in three table beet fields in successive years. Two of the fields were organic mixed-cropping farms and the third was managed conventionally in a broad-acre cropping system. C. beticola isolates (n = 304) were genotyped using 12 microsatellite markers. Genotypic diversity (Simpson’s complement index = 0.178 to 0.990), allele frequencies, and indices of differentiation between years varied. Pairwise index of differentiation values ranged from 0.02 to 0.25 for clone-corrected data, and indicated significant genetic differentiation at Farm 2. No multilocus genotype was shared between years. The shift in multilocus genotypes between years questions the role of clonally reproducing primary inoculum. Collectively, these results suggest that a dominant inoculum source for initiating annual CLS epidemics is external to the field of interest. These findings have implications for CLS disease management in conventional and organic table beet production.

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Genetic structure of Cercospora beticola populations on Beta vulgaris in New York and Hawaii

Scientific Reports ◽

10.1038/s41598-017-01929-4 ◽

2017 ◽

Vol 7 (1) ◽

Cited By ~ 15

Author(s):

Niloofar Vaghefi ◽

Scot C. Nelson ◽

Julie R. Kikkert ◽

Sarah J. Pethybridge

Keyword(s):

New York ◽

Genetic Structure ◽

Beta Vulgaris ◽

Cercospora Beticola

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Alternative Hosts of Cercospora beticola in Field Surveys and Inoculation Trials

Plant Disease ◽

10.1094/pdis-01-19-0229-re ◽

2019 ◽

Vol 103 (8) ◽

pp. 1983-1990 ◽

Cited By ~ 3

Author(s):

Noel L. Knight ◽

Niloofar Vaghefi ◽

Julie R. Kikkert ◽

Sarah J. Pethybridge

Keyword(s):

New York ◽

Spinacia Oleracea ◽

Chenopodium Album ◽

Carthamus Tinctorius ◽

Cercospora Beticola ◽

Cercospora Leaf Spot ◽

Field Surveys ◽

Alternative Hosts ◽

Brassica Kaber

Cercospora beticola, the cause of Cercospora leaf spot (CLS) of sugar beet and table beet, has a broad range of potential alternative hosts. The role of these hosts as inoculum sources in the field is unclear and has had limited investigation since the advent of DNA-based pathogen identification. The presence of C. beticola on alternative hosts associated with table beet fields of New York was assessed in field surveys during 2016. Lesions were collected, and 71 cercosporoid conidia were isolated for phylogenetic comparison. C. beticola was identified from Solanum ptycanthum (n = 4), Chenopodium album (n = 2), and Spinacia oleracea (n = 1), whereas C. chenopodii was identified on Chenopodium album (n = 51). Artificial inoculation of 21 plants species demonstrated that C. beticola was pathogenic to Brassica kaber, Chenopodium album, Carthamus tinctorius, Rumex obtusifolius, and Spinacia oleracea. These results indicate that although C. beticola may be pathogenic to a range of plant species, the role of symptomatic tissue for inoculum production on alternative hosts in the field appears limited. Observations of C. beticola on necrotic and naturally senescent tissue suggest saprophytic survival on plant debris of a range of species, which has implications for CLS epidemics and disease management.

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