Development of wheat lines with complex resistance to rusts and Fusarium head blight
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Date
2017-06
Authors
Maré, Ansori
Journal Title
Journal ISSN
Volume Title
Publisher
University of the Free State
Abstract
Wheat is the second most important food crop worldwide. The world human population is
increasing daily. Sustainable food production is necessary to ensure sufficient future
food supply. Wheat production is negatively affected by various pathogens that
challenge breeders to develop more disease resistant wheat cultivars. Leaf-, stem- and
stripe rust as well as Fusarium head blight (FHB) are considered some of the most
destructive fungal pathogens of wheat. Resistance breeding is considered the most
economic and eco-friendly solution to control wheat diseases in the long-term.
Combining of several effective resistance genes/quantitative trait loci (QTL) into a single
wheat line is necessary to increase the probability of obtaining durable resistance.
Molecular markers linked to resistance genes/QTL can assist breeders in selecting the
best offspring throughout their breeding scheme.
The main aim of this study was to develop a wheat line with combined resistance to the
rusts and FHB. Both wheat rust and FHB resistant lines used in this study were
developed in previous studies. The best resistant lines developed in these studies were
identified using marker-assisted selection (MAS) and were then used in a breeding
scheme to combine wheat rust and FHB resistance genes/QTL. Offspring from crosses
was evaluated for the presence of six rust resistance genes/QTL: Lr19, Lr34/Yr18/Sr57,
Sr2/Yr30, Sr26, Sr39 and QYr.sgi.2B-1, as well as for three FHB resistance genes/QTL:
Fhb1, Qfhs.ifa-5A-1 and Qfhs.ifa-5A-2. The best identified lines obtained from a series of
crosses were selected to develop two double-cross populations as well as self-pollinated
populations. Selected pre-breeding lines were also used to optimise and apply the
doubled haploid (DH) technique to develop lines with fixed genotypes. Molecular
markers linked to the high-molecular-weight glutenin subunits (HMW-GS) and the
1BL.1RS translocation were used for screening the final populations developed because
the primary focus for selection was rust and FHB resistance genes/QTL and not HMWGS
and the 1BL.1RS translocation.
Validation of the phenotypic expression of the rust and FHB resistance genes/QTL was
done through greenhouse inoculation of the parental, control and experimental
lines/cultivars containing different resistance gene/QTL combinations. Seedling and adult
plants were inoculated with the three rusts respectively, firstly for the timeline study to
determine the optimal day’s post inoculation (dpi) to collect sample material for
quantitative-polymerase chain reaction (qPCR) analysis and secondly to determine
fungal gene expression in the experimental lines. Both point and spray inoculations for
FHB were used and disease development was evaluated at 4, 7, 10, 14, 18 and 21 dpi.
Sample collection for qPCR analysis was done at 21 dpi. Good correlations between the
data obtained from the phenotypic evaluations, qPCR and MAS were obtained for both
rust and FHB resistance evaluations. Therefore, markers linked to rust and FHB
resistance genes were phenotypically expressed.
Lines with combined wheat rust and FHB resistance were obtained from the selfpollinated
populations but are still segregating for some of the genes/QTL. Lines with
combined rust and/or FHB resistance genes/QTL were also developed through the DH
technique. No markers linked to stripe rust resistance were used in this study except for
genes with multiple disease resistance such as Lr34/Yr18/Sr57 and Sr2/Yr30. Additional
stripe rust resistance genes are however present in the genetic background of the
experimental lines as they were present in the parental cultivars/lines originally used to
develop these lines like Kariega, AvocetYrSP, 2S#/163 and CM-82036. Valuable prebreeding
wheat lines with combined rust and FHB resistance have been developed
which can be used in future disease resistance breeding programmes.
Description
Keywords
Disease resistance breeding, Doubled haploids, Fusarium head blight, Marker-assisted selection, Phenotypic evaluation, Quantitative-polymerase chain reaction, Triticum aestivum/hexaploid wheat, Leaf-, stem- and stripe rust, Fusarium diseases of plants, Wheat -- Diseases and pests, Thesis (Ph.D. (Plant Sciences: Plant Breeding))--University of the Free State, 2017