Changes in allele frequencies of avirulence genes in the blackleg fungus, Leptosphaeria maculans, over two decades in Australia

2018 ◽  
Vol 69 (1) ◽  
pp. 20 ◽  
Author(s):  
Angela P. Van de Wouw ◽  
Barbara J. Howlett ◽  
Alexander Idnurm
Keyword(s):  
Resistance Genes ◽  
Specific Resistance ◽  
Leptosphaeria Maculans ◽  
Allele Frequencies ◽  
Avirulence Genes ◽  
Time Analysis ◽  
Pathogen Population ◽  
Growing Seasons ◽  
The World ◽  
Blackleg Fungus

Cultivation of canola (oilseed rape, rapeseed; Brassica napus) in many parts of the world relies on the use of cultivars carrying resistance genes that recognise avirulence products of the major canola pathogen, Leptosphaeria maculans. However, widespread cultivation of plants with such resistance provides the potential for evolution of the pathogen population to overcome resistance by altering the proportion of avirulence v. virulence alleles. In this study, the frequencies of avirulence genes were measured for 2091 Australian isolates dating from the late 1980s to present. Frequencies of avirulence genes changed over time. Analysis of isolates from the Eyre Peninsula, where canola is intensively cultivated, indicated that changes in allele frequencies at the AvrLm1, AvrLm4 and AvrLm6 loci could be correlated with the widespread planting of cultivars carrying specific resistance genes. These data show that determining avirulence allele frequencies in L. maculans populations provides power to anticipate which cultivars will be most successful in future growing seasons.

scholarly journals A Cluster of Major Specific Resistance Genes to Leptosphaeria maculans in Brassica napus

2004 ◽  
Vol 94 (6) ◽  
pp. 578-583 ◽  
Author(s):  
R. Delourme ◽  
M. L. Pilet-Nayel ◽  
M. Archipiano ◽  
R. Horvais ◽  
X. Tanguy ◽  
...  
Keyword(s):  
Brassica Napus ◽  
Resistance Genes ◽  
Specific Resistance ◽  
Quantitative Resistance ◽  
Specific Interaction ◽  
Leptosphaeria Maculans ◽  
Field Resistance ◽  
Genetic Identification ◽  
Adult Plant ◽  
Avirulence Genes

Two types of genetic resistance to Leptosphaeria maculans usually are distinguished in Brassica napus: qualitative, total resistance expressed at the seedling stage and quantitative, partial resistance expressed at the adult plant stage. The latter is under the control of many genetic factors that have been mapped through quantitative trait loci (QTL) studies using ‘Darmor’ resistance. The former usually is ascribed to race-specific resistance controlled by single resistance to L. maculans (Rlm) genes. Three B. napus-originating specific Rlm genes (Rlm1, Rlm2, and Rlm4) previously were characterized. Here, we report on the genetic identification of two novel resistance genes, Rlm3 and Rlm7, corresponding to the avirulence genes AvrLm3 and AvrLm7. The identification of a novel L. maculans- B. napus specific interaction allowed the detection of another putative new specific resistance gene, Rlm9. The resistance genes were mapped in two genomic regions on LG10 and LG16 linkage groups. A cluster of five resistance genes (Rlm1, Rlm3, Rlm4, Rlm7, and Rlm9) was strongly suggested on LG10. The relation between all these specific resistance genes and their potential role in adult-plant field resistance is discussed. These two Rlm-carrying regions do not correspond to major QTL for Darmor quantitative resistance.

scholarly journals Induced Rice Resistance to Blast Varies as a Function of Magnaporthe grisea Avirulence Genes

Plant Disease ◽  
2008 ◽  
Vol 92 (8) ◽  
pp. 1144-1149 ◽  
Author(s):  
N. Yasuda ◽  
M. T. Noguchi ◽  
Y. Fujita
Keyword(s):  
Genetic Analysis ◽  
Resistance Genes ◽  
Magnaporthe Grisea ◽  
Specific Resistance ◽  
Blast Disease ◽  
Avirulence Gene ◽  
Avirulence Genes ◽  
Leaf Blast ◽  
Incompatibility Reactions ◽  
Avirulent Isolate

Incompatibility reactions between rice and the blast fungus Magnaporthe grisea produce various degrees of lesions, from large brown flecks to small, nearly invisible lesions. We previously identified four avirulence genes (AvrPia, AvrPii, AvrPit, and Avr-Hattan3) in M. grisea isolates by genetic analysis of progeny from crosses between isolates with differing pathogenicity. Using progeny known to contain a specific avirulence gene, we demonstrated that the type of resistance lesion produced in rice by an avirulent isolate and the degree of leaf blast suppression by preinoculation with that isolate were determined by the combination of avirulence and resistance genes in the isolate and the cultivar. The degree of leaf blast suppression by preinoculation with an avirulent isolate increased with larger resistance lesions. When two genes were involved in an isolate's avirulence, lesions appeared that resembled those expected for the gene that produced the smaller lesion. The degree of leaf blast suppression by the isolate with two avirulence genes was comparable with that induced by the isolate with the avirulence gene that produced the smaller effect. The ability of specific resistance gene combinations that effectively suppress blast disease is discussed for each avirulence gene.

scholarly journals Virulence spectra determination in selected Blumeria graminis f. sp. hordei isolates

2010 ◽  
Vol 58 (5) ◽  
pp. 83-90
Author(s):  
Antonín Dreiseitl ◽  
Petra Adamcová
Keyword(s):  
Czech Republic ◽  
Powdery Mildew ◽  
Resistance Genes ◽  
Specific Resistance ◽  
Pathogen Population ◽  
The Czech Republic ◽  
Barley Powdery Mildew ◽  
Significant Step ◽  
Complete Set ◽  
Powdery Mildew Pathogen

Virulence spectra for 14 isolates of the barley powdery mildew pathogen considered to be added to the pathogen genebank were determined. The isolates were obtained from a sample of aerial pathogen population collected across the Czech Republic in 2009. The spectra were determined on 28 barley varieties, possessing mostly specific resistance genes and inoculated with the isolates exa­mi­ned. Based on differentiation among each other, all 14 isolates showed their originality. None of the isolates exhibited increased pathogenicity to a variety with the non-specific resistance gene mlo9. All isolates were virulent on varieties carrying specific resistance genes Mla8 and Mlra, and in contrast, none of the isolates was virulent on a variety with the gene Mla23 and with a combination of genes Mla3, MlaTu2. Required characters, such as virulence on the resistance Lv or avirulence on the gene Mlh, were confirmed in some isolates. The results represent a significant step toward obtaining a complete set of information about every isolate before its including in the working genebank of the pathogen.

scholarly journals Identification of Race-Specific Resistance in North American Vitis spp. Limiting Erysiphe necator Hyphal Growth

2012 ◽  
Vol 102 (1) ◽  
pp. 83-93 ◽  
Author(s):  
David W. Ramming ◽  
Franka Gabler ◽  
Joseph L. Smilanick ◽  
Dennis A. Margosan ◽  
Molly Cadle-Davidson ◽  
...  
Keyword(s):  
Powdery Mildew ◽  
Resistance Genes ◽  
Specific Resistance ◽  
Hyphal Growth ◽  
Resistance Mechanisms ◽  
Hybrid Breeding ◽  
Erysiphe Necator ◽  
Vitis Rotundifolia ◽  
Resistance Sources

Race-specific resistance against powdery mildews is well documented in small grains but, in other crops such as grapevine, controlled analysis of host–pathogen interactions on resistant plants is uncommon. In the current study, we attempted to confirm powdery mildew resistance phenotypes through vineyard, greenhouse, and in vitro inoculations for test cross-mapping populations for two resistance sources: (i) a complex hybrid breeding line, ‘Bloodworth 81-107-11', of at least Vitis rotundifolia, V. vinifera, V. berlandieri, V. rupestris, V. labrusca, and V. aestivalis background; and (ii) Vitis hybrid ‘Tamiami’ of V. aestivalis and V. vinifera origin. Statistical analysis of vineyard resistance data suggested the segregation of two and three race-specific resistance genes from the two sources, respectively. However, in each population, some resistant progeny were susceptible in greenhouse or in vitro screens, which suggested the presence of Erysiphe necator isolates virulent on progeny segregating for one or more resistance genes. Controlled inoculation of resistant and susceptible progeny with a diverse set of E. necator isolates clearly demonstrated the presence of fungal races differentially interacting with race-specific resistance genes, providing proof of race specificity in the grape powdery mildew pathosystem. Consistent with known race-specific resistance mechanisms, both resistance sources were characterized by programmed cell death of host epidermal cells under appressoria, which arrested or slowed hyphal growth; this response was also accompanied by collapse of conidia, germ tubes, appressoria, and secondary hyphae. The observation of prevalent isolates virulent on progeny with multiple race-specific resistance genes before resistance gene deployment has implications for grape breeding strategies. We suggest that grape breeders should characterize the mechanisms of resistance and pyramid multiple resistance genes with different mechanisms for improved durability.

scholarly journals Fungicide sensitivity and resistance in the blackleg fungus, Leptosphaeria maculans, across canola growing regions in Australia

2021 ◽  
Author(s):  
A. P. Van de Wouw ◽  
J. L. Scanlan ◽  
S. J. Marcroft ◽  
A. J. Smith ◽  
E. M. Sheedy ◽  
...  
Keyword(s):  
Leptosphaeria Maculans ◽  
Fungicide Sensitivity ◽  
Blackleg Fungus

scholarly journals Multiple Evolutionary Trajectories Have Led to the Emergence of Races in Fusarium oxysporum f. sp. lycopersici

2016 ◽  
Vol 83 (4) ◽  
Author(s):  
V. Chellappan Biju ◽  
Like Fokkens ◽  
Petra M. Houterman ◽  
Martijn Rep ◽  
Ben J. C. Cornelissen
Keyword(s):  
Transposable Elements ◽  
Fusarium Oxysporum ◽  
Resistance Genes ◽  
Pcr Analysis ◽  
Genomic Fragment ◽  
Avirulence Genes ◽  
Content Type ◽  
Race 1 ◽  
Tomato Cultivars ◽  
Race 2

ABSTRACT Race 1 isolates of Fusarium oxysporum f. sp. lycopersici (FOL) are characterized by the presence of AVR1 in their genomes. The product of this gene, Avr1, triggers resistance in tomato cultivars carrying resistance gene I. In FOL race 2 and race 3 isolates, AVR1 is absent, and hence they are virulent on tomato cultivars carrying I. In this study, we analyzed an approximately 100-kb genomic fragment containing the AVR1 locus of FOL race 1 isolate 004 (FOL004) and compared it to the sequenced genome of FOL race 2 isolate 4287 (FOL4287). A genomic fragment of 31 kb containing AVR1 was found to be missing in FOL4287. Further analysis suggests that race 2 evolved from race 1 by deletion of this 31-kb fragment due to a recombination event between two transposable elements bordering the fragment. A worldwide collection of 71 FOL isolates representing races 1, 2, and 3, all known vegetative compatibility groups (VCGs), and five continents was subjected to PCR analysis of the AVR1 locus, including the two bordering transposable elements. Based on phylogenetic analysis using the EF1-α gene, five evolutionary lineages for FOL that correlate well with VCGs were identified. More importantly, we show that FOL races evolved in a stepwise manner within each VCG by the loss of function of avirulence genes in a number of alternative ways. IMPORTANCE Plant-pathogenic microorganisms frequently mutate to overcome disease resistance genes that have been introduced in crops. For the fungus Fusarium oxysporum f. sp. lycopersici, the causal agent of Fusarium wilt in tomato, we have identified the nature of the mutations that have led to the overcoming of the I and I-2 resistance genes in all five known clonal lineages, which include a newly discovered lineage. Five different deletion events, at least several of which are caused by recombination between transposable elements, have led to loss of AVR1 and overcoming of I. Two new events affecting AVR2 that led to overcoming of I-2 have been identified. We propose a reconstruction of the evolution of races in FOL, in which the same mutations in AVR2 and AVR3 have occurred in different lineages and the FOL pathogenicity chromosome has been transferred to new lineages several times.

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