G. F. Marais

Bio: G. F. Marais is an academic researcher from Stellenbosch University. The author has contributed to research in topics: Common wheat & Chromosomal translocation. The author has an hindex of 21, co-authored 42 publications receiving 1292 citations. Previous affiliations of G. F. Marais include University of the Free State.

AFLP and STS tagging of Lr19, a gene conferring resistance to leaf rust in wheat

Abstract: Amplified fragment length polymorphism (AFLP) markers were used to enrich the map of the wheat chromosomal region containing the Thinopyrum-derived Lr19 leaf rust resistance gene. The region closest to Lr19 was targeted through the use of deletion and recombinant lines of the translocated segment. One of the AFLP bands thus identified was converted into a sequence-tagged-site (STS) marker. This assay generated a 130-bp PCR fragment in all Lr19-carrying lines tested, except for one deletion mutant, while non-carrier template failed to amplify any product. This sequence represents the first marker to map on the distal side of Lr19 on chromosome 7el1. The conversion process of AFLP fragments to STS markers was technically difficult, mainly because of the presence of contaminating fragments. Various approaches were taken to reduce the frequency of false positives and to identify the correct clone. We were able to formulate a general verification strategy prior to clone sequencing. Various other factors causing problems with converting AFLP bands to an STS assays are also discussed.

Leaf rust and stripe rust resistance genes transferred to common wheat from Triticum dicoccoides

Abstract: Linked leaf rust and stripe rust resistance genes introduced from Triticum dicoccoides protected common wheat seedlings against a range of pathotypes of the respective pathogens. The genes were chromosomally mapped using monosomic and telosomic analyses, C-banding and RFLPs. The data indicated that an introgressed region is located on wheat chromosome arm 6BS. The introgressed region did not pair with the ‘Chinese Spring’ 6BS arm during meiosis possibly as a result of reduced homology, but appeared to pair with 6BS of W84-17 (57% of pollen mother cells) and ‘Avocet S’. The introgressed region had a very strong preferential pollen transmission (0.96–0.98) whereas its transmission through egg cells (0.41–0.66) varied with the genetic background of the heterozygote. Homozygous resistant plants had a normal phenotype, were fertile and produced plump seeds. Symbols Lr53 and Yr35 are proposed to designate the respective genes.

Intergeneric transfer (rye to wheat) of a gene(s) for Russian wheat aphid resistance

Abstract: An octoploid triticale was derived from the F 1 of a Russian wheat aphid-resistant rye, «Turkey 77», and «Chinese Spring» wheat. The alloploid was crossed to common wheat, and to «Imperial» rye/«Chinese Spring» disomic addition lines. F 2 progeny from these crosses were tested for Russian wheat aphid resistance and C-banded. A resistance gene(s) was found to be associated with chromosome arm 1RS of the «Turkey 77» rye genome. A monotelosomic 1RS («Turkey 77») addition plant was then crossed with the wheat cultivar «Gamtoos», which has the 1BL.1RS «Veery» translocation. Unlike the 1RS segment in «Gamtoos», the «Turkey 77»-derived 1RS telosome did not express the rust resistance genes Sr31 and Lr26, which could then be used as markers. From the F 1 a monotelosomic 1RS addition plant that was also heterozygous for the 1BL.1RS translocation was selected and testcrossed with an aphid-susceptible common wheat, «Inia 66». Meiotic pairing between the rye arms resulted in the recovery of five euploid Russian-wheat-aphid-resistant plants. One recombinant also retained Sr31 and Lr26 and was selfed to produce translocation homozygotes

Leaf rust and stripe rust resistance genes Lr54 and Yr37 transferred to wheat from Aegilops kotschyi

Abstract: The tendency of unpaired meiotic chromosomes to undergo centric misdivision was exploited to translocate leaf rust and stripe rust resistance genes from an Aegilops kotschyi addition chromosome to a group 2 chromosome of wheat. Monosomic and telosoanic analyses showed that the translocation occurred to wheat chromosome arm 2DL. The introgressed region did not pair with the corresponding wheat 2DL telosome during meiosis suggesting that a whole arm may have been transferred. Female transmission of the resistance was about 55% whereas male transmission was strongly preferential (96%). The symbols Lr54 and Yr37 are proposed to designate the new resistance genes.

Leaf Rust and Stripe Rust Resistance Genes Derived from Aegilops Sharonensis

Abstract: Linked leaf and stripe rust resistance genes introgressed into hexaploid wheat from Aegilops sharonensis provided protection in the seedling stage to a wide range of pathotypes of the two diseases. Monosomic and telosomic analyses showed that the resistance genes occur on wheat chromosome 6A. This result could be confirmed making use of mapped chromosome 6A microsatellite markers. The introgressed chromatin appeared to involve the proximal part of 6AL and the complete 6AS arm and it was thus not possible to deduce the chromosome arm harbouring the resistance genes. The resistance showed non-Mendelian transmission. The genetic background of a heterozygote interacted with the introgressed region to result in either preferential or impaired female transmission. Male transmission appeared to be affected in a different way from female transmission and was exclusive in the genetic background studied. Symbols Lr56 and Yr38 are proposed to designate the respective genes of which line 0352-4 is the appropriate source material.

The Top 10 fungal pathogens in molecular plant pathology

Abstract: 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.

Wheat Rusts: An Atlas of Resistance Genes

Abstract: 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.

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

Abstract: 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.

An overview of molecular marker methods for plants

Abstract: 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).