scholarly journals Measuring Immigration and Sexual Reproduction in Field Populations of Mycosphaerella graminicola

1998 ◽  
Vol 88 (12) ◽  
pp. 1330-1337 ◽  
Author(s):  
J. Zhan ◽  
C. C. Mundt ◽  
B. A. McDonald
Keyword(s):  
Genetic Structure ◽  
Sexual Reproduction ◽  
Random Mating ◽  
Growing Season ◽  
Mycosphaerella Graminicola ◽  
Dna Fingerprints ◽  
Gametic Disequilibrium ◽  
Late Season ◽  
Length Polymorphisms ◽  
Restriction Fragment Length

A field experiment was conducted to determine the relative contributions of immigration and sexual reproduction to the genetic structure of Mycosphaerella graminicola populations during the course of an epidemic. The genetic structure of M. graminicola populations sampled from wheat plots inoculated artificially with 10 isolates was compared with control plots infected naturally by airborne ascospores. Restriction fragment length polymorphisms (RFLPs) were used to test the randomness of associations among loci, and DNA fingerprints were used to identify clones. All isolates in the control plots had unique genotypes and RFLP loci were at gametic equilibrium, findings consistent with random mating. The proportion of isolates in the inoculated plots with DNA fingerprints that differed from the 10 inoculated isolates increased from 3% in the early to 39 and 34% in the mid- and late season, respectively. The degree of gametic disequilibrium was higher in the mid-season than in the late-season population. By the end of the growing season, we estimate that 66% of the isolates in the inoculated plots were asexual progeny of the 10 inoculated isolates, 10% were immigrants, and 24% were sexual recombinants. The proportion of infections caused by ascospores increased over the growing season.

scholarly journals Sexual Reproduction Plays a Major Role in the Genetic Structure of Populations of the Fungus Mycosphaerella graminicola

Genetics ◽  
1996 ◽  
Vol 142 (4) ◽  
pp. 1119-1127 ◽  
Author(s):  
Ruey-Shyang Chen ◽  
Bruce A McDonald
Keyword(s):  
Genetic Structure ◽  
Asexual Reproduction ◽  
Pathogenic Fungus ◽  
Random Mating ◽  
Genotypic Diversity ◽  
Mycosphaerella Graminicola ◽  
Dna Fingerprints ◽  
Genetic Structure Of Populations ◽  
Sexual And Asexual Reproduction ◽  
Single Field

Abstract The relative contributions of sexual and asexual reproduction to the genetic structure of populations can be difficult to determine for fungi that use a mixture of both types of propagation. Nuclear RFLPs and DNA fingerprints were used to make indirect and direct measures of departures from random mating in a population of the plant pathogenic fungus Mycosphaerella graminicola during the course of an epidemic cycle. DNA fingerprints resolved 617 different genotypes among 673 isolates sampled from a single field over a 3-month period. Only 7% of the isolates represented asexual clones that were found more than once in the sample. The most common clone was found four times. Genotypic diversity averaged 85% of its maximum possible value during the course of the epidemic. Analyses of multilocus structure showed that allelic distributions among RFLP loci were independent. Pairwise comparisons between individual RFLP loci showed that the majority of alleles at these loci were in gametic equilibrium. Though this fungus has the capacity for a significant level of asexual reproduction, each analysis suggested that M. graminicola populations maintain a genetic structure more consistent with random-mating over the course of an epidemic cycle.

scholarly journals Using Restriction Fragment Length Polymorphisms to Assess Temporal Variation and Estimate the Number of Ascospores that Initiate Epidemics in Field Populations of Mycosphaerella graminicola

2001 ◽  
Vol 91 (10) ◽  
pp. 1011-1017 ◽  
Author(s):  
J. Zhan ◽  
C. C. Mundt ◽  
B. A. McDonald
Keyword(s):  
Temporal Variation ◽  
Population Size ◽  
Effective Population Size ◽  
Restriction Fragment ◽  
Fragment Length ◽  
Mycosphaerella Graminicola ◽  
Source Population ◽  
Effective Population ◽  
Length Polymorphisms ◽  
Restriction Fragment Length

Restriction fragment length polymorphisms (RFLPs) and DNA fingerprints were used to assess temporal variation and estimate the effective population size of the wheat pathogen Mycosphaerella graminicola over a 6-year period. In each year, the fungal population was founded by ascospores originating from outside the sampled fields. A total of 605 fungal isolates were included in this study. Our results indicate that the genetic structure of these M. graminicola populations were stable over the 6-year period. The common alleles at each RFLP locus were present at similar frequencies each year. More than 99% of gene diversity was distributed within populations sampled from the same year and less than 1% was attributed to differences among years. The lack of population differentiation among collections taken in different years indicated that the effective size of the source population was sufficiently large that genetic drift was insignificant in this location. It also suggests that the initial colonists from ascospore founder populations were a fair reflection of the source population. We estimate that the effective sizes of these field populations ranged from 3,400 to 700,000 individuals, depending on the size of the field sampled and assumptions about mutation rates. Estimates of the number of ascospores initiating epidemics of leaf blotch disease in each field plot and factors that contribute to the large effective population size of M. graminicola are discussed.

Genetic relationship of wood and plains bison based on restriction fragment length polymorphisms

1991 ◽  
Vol 69 (1) ◽  
pp. 43-48 ◽  
Author(s):  
A. M. Bork ◽  
C. M. Strobeck ◽  
F. C. Yeh ◽  
R. J. Hudson ◽  
R. K. Salmon
Keyword(s):  
Growth Hormone ◽  
Restriction Fragment ◽  
Genetic Relationship ◽  
Fragment Length ◽  
Random Mating ◽  
Restriction Fragment Length Polymorphisms ◽  
Evolutionary Divergence ◽  
Growth Hormone Releasing Factor ◽  
Length Polymorphisms ◽  
Restriction Fragment Length

To evaluate the genetic relationship within and between wood and plains bison of Elk Island National Park, genomic DNA samples were screened for restriction fragment length polymorphisms (RFLP) with cDNA probes for growth hormone, growth hormone releasing factor, somatostatin, and insulin-like growth factor-1. Of the 28 fragments identified, two revealed RFLPs, both of which were associated with the growth hormone releasing factor locus. The observed frequencies of the polymorphic sites did not differ from a Hardy–Weinberg distribution in either population, which is indicative of random mating populations. The contingency χ2 tests for homogeneity indicate that the fragment frequencies of the polymorphic restriction sites differ significantly (P = 0.00) between the wood and plains bison. The number of net nucleotide substitutions between the two populations was 0.0007, indicative of a recent divergence. Conversion of the bison nucleotide divergence results in a relative protein divergence of 0.007 to 0.018. This converted divergence corresponds closely to the divergence reported for other geographically isolated populations; thus, this preliminary analysis suggests the bison have at least reached the stage of geographic isolation in their evolutionary divergence.

The population genetics of Septoria tritici (teleomorph Mycosphaerella graminicola)

1995 ◽  
Vol 73 (S1) ◽  
pp. 292-301 ◽  
Author(s):  
B. A. McDonald ◽  
R. E. Pettway ◽  
R. S. Chen ◽  
J. M. Boeger ◽  
J. P. Martinez
Keyword(s):  
Population Genetics ◽  
Genetic Markers ◽  
Population Biology ◽  
Mycosphaerella Graminicola ◽  
Septoria Tritici ◽  
Gametic Disequilibrium ◽  
Length Polymorphisms ◽  
Wheat Gene ◽  
High Degree ◽  
Analytical Tools

The DNA-based markers of molecular genetics were combined with the analytical tools of population genetics to learn about the population biology of the wheat pathogen Mycosphaerella graminicola. DNA-based genetic markers, including restriction fragment length polymorphisms in nuclear and mitochondrial DNA, DNA fingerprints, and electrophoretic karyotypes were used in combination to show that the amount and distribution of genetic variation within and among field populations of M. graminicola is similar around the world. Measures of gametic disequilibrium suggested that the sexual stage of reproduction has a more significant impact on the genetic structure of M. graminicola populations than asexual reproduction. A field experiment conducted over a 3-year period showed that populations had a high degree of genetic stability over time. The potential effects of selection were quantified in a cultivar mixture experiment with four wheat cultivars that varied in resistance to M. graminicola. In combination, these experiments demonstrated the utility of selectively neutral genetic markers to elucidate the population genetics of fungi. Key words: genetic diversity, wheat, gene flow, RFLPs, DNA fingerprinting.

scholarly journals Genetic Structure and Temporal Dynamics of a Colletotrichum graminicola Population in a Sorghum Disease Nursery

1998 ◽  
Vol 88 (10) ◽  
pp. 1087-1093 ◽  
Author(s):  
U. L. Rosewich ◽  
R. E. Pettway ◽  
B. A. McDonald ◽  
R. R. Duncan ◽  
R. A. Frederiksen
Keyword(s):  
Genetic Structure ◽  
Genomic Library ◽  
Temporal Dynamics ◽  
Gene Diversity ◽  
Genotypic Diversity ◽  
Colletotrichum Graminicola ◽  
Length Polymorphisms ◽  
Sorghum Anthracnose ◽  
Haplotype Frequencies ◽  
Restriction Fragment Length

Restriction fragment length polymorphisms (RFLPs) were used to study the population genetics of Colletotrichum graminicola (= C. sublineolum), the causal agent of sorghum anthracnose. Screening of 80 anonymous probes from a genomic library detected polymorphisms in 81% of 299 probe-enzyme combinations among nine international isolates. Seven single- or low-copy probes were used to study a collection of 411 isolates sampled during 1991 to 1993 from a sorghum disease nursery in Georgia. Nei's gene diversity was moderately high, with = 0.215 on average, while genotypic diversity was extremely low with an average genotypic diversity value of Ĝ = 1.513. Only nine multilocus haplotypes were identified, with one haplotype being present at a frequency of approximately 80% each year. Two other haplotypes were found at significant frequencies (4 to 10%). Allele and haplotype frequencies did not differ over the 3 years, indicating that this population was stable. Our findings suggest that genetic drift and gene flow were not major contributors to genetic structure, while asexual reproduction had a significant effect.

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