The aim of this review was to survey all fungal pathologists with an association with the journal Molecular Plant Pathology and ask them to nominate which fungal pathogens they would place in a 'Top 10' based on scientific/economic importance. The survey generated 495 votes from the international community, and resulted in the generation of a Top 10 fungal plant pathogen list for Molecular Plant Pathology. The Top 10 list includes, in rank order, (1) Magnaporthe oryzae; (2) Botrytis cinerea; (3) Puccinia spp.; (4) Fusarium graminearum; (5) Fusarium oxysporum; (6) Blumeria graminis; (7) Mycosphaerella graminicola; (8) Colletotrichum spp.; (9) Ustilago maydis; (10) Melampsora lini, with honourable mentions for fungi just missing out on the Top 10, including Phakopsora pachyrhizi and Rhizoctonia solani. This article presents a short resume of each fungus in the Top 10 list and its importance, with the intent of initiating discussion and debate amongst the plant mycology community, as well as laying down a bench-mark. It will be interesting to see in future years how perceptions change and what fungi will comprise any future Top 10.

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The Top 10 fungal pathogens in molecular plant pathology

1: Wheat Rusts and the Genetic Bases on Disease Resistance. Introduction. Biology of Pathogen and Host. Host:Pathogen Genetics. Methodologies in Wheat Rust Disease. A Coordinated Strategy for Rust Control. Conclusion. Guide to Gene Descriptions and Illustrations. 2: The Genes for Resistance to Leaf Rust in Wheat and Triticale. Catalogued Leaf Rust Resistance Genes. Temporarily Designated and Miscellaneous Leaf Rust Resistance Genes. 3: The Genes for Resistance to Stem Rust in Wheat and Triticale. Catalogued Leaf Rust Resistance Genes. Temporarily Designated and Miscellaneous Stem Rust Resistance Genes. 4: The Genes for Resistance to Stripe Rust in Wheat and Triticale. Catalogued Stripe Rust Resistance Genes. Temporarily Designated and Miscellaneous Stripe Rust Resistance Genes. References. Appendix I: Species Names Used in the Text, Genomic Formulae and Synonyms. Appendix II: Pathotypes and Accessions (Cultures) Used in Photography.

Wheat Rusts: An Atlas of Resistance Genes

Wild relatives of common wheat, Triticum aestivum, and related species are an important source of disease and pest resistance and several useful traits have been transferred from these species to wheat. C-banding and in situ hybridization analyses are powerful cytological techniques allowing the detection of alien chromatin in wheat. C-banding permits identification of the wheat and alien chromosomes involved in wheat-alien translocations, whereas genomic in situ hybridization analysis allows determination of their size and breakpoint positions. The present review summarizes the available data on wheat-alien transfers conferring resistance to diseases and pests. Ten of the 57 spontaneous and induced wheat-alien translocations were identified as whole arm translocations with the breakpoints within the centromeric regions. The majority of transfers (45) were identified as terminal translocations with distal alien segments translocated to wheat chromosome arms. Only two intercalary wheat-alien transloctions were identified, one induced by radiation treatment with a small segment of rye chromosome 6RL (H25) inserted into the long arm of wheat chromosome 4A, and the other probably induced by homoeologous recombination with a segment derived from the long arm of a group 7 Agropyron elongatum chromosome with Lr19 inserted into the long arm of 7D. The presented information should be useful for further directed chromosome engineering aimed at producing superior germplasm.

Characterization of wheat-alien translocations conferring resistance to diseases and pests: current status

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The Top 10 fungal pathogens in molecular plant pathology: Top 10 fungal pathogens

The development and use of molecular markers for the detection and exploitation of DNA polymorphism is one of the most significant developments in the field of molecular genetics. The presence of various types of molecular markers, and differences in their principles, methodologies, and applications require careful consideration in choosing one or more of such methods. No molecular markers are available yet that fulfill all requirements needed by researchers. According to the kind of study to be undertaken, one can choose among the variety of molecular techniques, each of which combines at least some desirable properties. This article provides detail review for 11 different molecular marker methods: restriction fragment length polymorphism (RFLP), random amplified polymorphic DNA (RAPD), amplified fragment length polymorphism (AFLP), inter-simple sequence repeats (ISSRs), sequence characterized regions (SCARs), sequence tag sites (STSs), cleaved amplified polymorphic sequences (CAPS), microsatellites or simple sequence repeats (SSRs), expressed sequence tags (ESTs), single nucleotide polymorphisms (SNPs), and diversity arrays technology (DArT).

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An overview of molecular marker methods for plants

The Sr27 translocation in WRT238 was found to consist of chromosome arms 3RS of rye and 3AS of common wheat. An attempt was made to purposely produce compensating translocations having 3RS and a wheat homoeologous group 3L arm. To achieve this, plants, double monosomic for 3R and a wheat homoeologous group 3 chromosome, were irradiated (7.5 Gy gamma rays) or left untreated before being used to pollinate stem rust susceptible testers. Segregation for stem rust resistance was studied to identify F2 families with Sr27-carrying translocated chromosomes, these were confirmed by means of C-banding. Compensating translocations 3RS3AL and 3RS3BL) were obtained readily and at similar frequencies from untreated and irradiated plants (respectively, 7.2% and 9.3%). Both translocation types have impaired transmission and segregate approximately 3: 2 (present: absent) in the F2.

The derivation of compensating translocations involving homoeologous group 3 chromosomes of wheat and rye

Amplified fragment length polymorphism (AFLP) markers linked to the Aegilops ventricosa-derived chromosome segment in ‘VPM1’ on which the eyespot resistance gene, Pch1, and the endopeptidase gene, Ep-D1b, occur were identified. One marker was isolated from the gel, cloned and sequenced. Sequence analysis revealed a microsatellite repeat motif. Sequence-specific primers were designed to amplify a product containing the repeat motif, and the microsatellite marker was tested for cosegregation with the Ep-D1b allele. Distinct alleles were produced by the Pch1 sources, normal wheat and wheat containing the Lr19 translocation. A recombination frequency of 0.02 was calculated between the microsatellite marker and Ep-D1.

Amplified fragment length polymorphism-derived microsatellite sequence linked to the Pch1 and Ep-D1 loci in common wheat.

The Lr19 translocation was introgressed from Thinopyrum ponticum in 1966. It has not been used in wheat breeding in many countries despite it being an excellent source of leaf rust resistance as it carries an undesirable gene(s) coding for yellow endosperm pigmentation. A shortened form, Lr19-149, was since produced and lacks the yellow pigment genes. A yield trial with near isogenic lines of both the original and shortened translocations suggested that Lr19 may cause a small reduction in kernel size and anincrease in loaf volume, effects which are not associated with Lr19-149. In Lr19-149 heterozygotes the translocation generally showed reduced pollen transmission whereas its transmission through egg cells was mostly normal. An attempt to shorten Lr19-149 through allosyndetic recombination in the absence of Ph1b produced four recombinants which were characterized by means of RFLP and AFLP polymorphisms and physically mapped with a set of 27 deletion lines. In three recombinants (252, 299 and 462) Thinopyrum chromatin proximally to Lr19 was exchanged for wheat chromatin. In one recombinant (478) chromatin distally from Lr19 was replaced. Based on physical map distance estimates it appears that the Lr19 translocation in the shortest recombinant (299) may have been reduced to about one third or less of its original size. It may now be possible to obtain a further, albeit relatively small, decrease in the size of the translocation through homologous crossover between recombinants 299 and 478. Similar to Lr19-149, the new recombinants show self elimination in heterozygotes and they have apparently retained the Sd2 locus.

Evaluation and reduction of Lr19-149, a recombined form of the Lr19 translocation of wheat

Endopeptidase zymograms of the translocation line ‘Indis’ revealed the presence of several major and minor bands that had differential expression in coleoptile and seed tissues. While ‘Indis’ lacks Ep-D1a, which is present in the parental cultivar ‘Inia 66’, it also may not express any of the Th. distichum bands. The ‘Indis’ zymogram was found to be identical to that of an isogenic line of ‘Inia 66’ possessing Lr19. Since the absence of an Ep-D1a product appears to be linked to the 7DL translocation, it is possible to use the null condition as a marker for both the Lr19 or ‘Indis’ translocations. The ‘Indis’ translocation also did not show recombination with the cn-D1 chlorophyl mutant on 7DL, confirming that a part of 7D was involved. The results of a telocentric mapping experiment involving the 7D telosomes indicated that in ‘Indis’ a chromosome segment from Th. distichum replaced a large section of 7DL of ‘Inia 66’.

The assignment of a Thinopyrum distichum (Thunb.) Löve-derived translocation to the long arm of wheat chromosome 7D using endopeptidase polymorphisms.

A Thinopyrum distichum chromosome segment translocated on chromosome arm 7DL. of the line ‘Indis’, was shown to be preferentially transmitted in crosses with other bread wheats. The translocated segment carries a gene for leaf rust resistance and produces a null condition for the endopeptidase product, EP-Dla. These characters were used to follow the transmission of the translocated chromosome in segregating and testcross progenies derived by crossing ‘Indis’ to four bread wheat cultivars. The severity of the gametocidal response in the heterozygotes ranged from a virtually exclusive transfer of the translocation to an almost normal transmission of the homologues. In some genetic backgrounds an intermediate level of transmission occurred. In the F1 with a gametocidal response, the transmission of the normal chromosome 7D was reduced in both sexes, but the reduction may be more severe in the male germline.

G. F. Marais

Papers

The derivation of compensating translocations involving homoeologous group 3 chromosomes of wheat and rye

Amplified fragment length polymorphism-derived microsatellite sequence linked to the Pch1 and Ep-D1 loci in common wheat.

Evaluation and reduction of Lr19-149, a recombined form of the Lr19 translocation of wheat

The assignment of a Thinopyrum distichum (Thunb.) Löve-derived translocation to the long arm of wheat chromosome 7D using endopeptidase polymorphisms.

Preferential Transmission in Bread Wheat of a Chromosome Segment Derived from Thinopyrum distichum (Thunb.) Löve