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QTL Studies in Tetraploid Wheat

QTL mapping studies carried out to date in durum wheat have been based on resistance deriving from tetraploid sources including wild emmer Triticum dicoccoides, cultivated emmer Triticum dicoccum, Persian wheat Triticum carthlicum and durum wheat landraces. A list including information on the resistance source used in the mapping analysis, the inoculation methods performed and the type of resistance assessed for each study is given in Table 37.1.

We gather here QTL reported in tetraploid wheat which were repeatedly found in different years or in independent studies. A total of 13 small to moderately effective QTL were mapped to 11 chromosomes. Their positions are indicated with vertical bars in Fig. 37.1, and the names of the genotypes contributing to resistance allele and the applied inoculation methods are also specified.

Durum wheat itself contributed resistance-improving alleles for the QTL on 2B (Gladysz et al. 2007; Somers et al. 2006), 3B (Buerstmayr et al. 2012; Ghavami et al. 2011) and 5B (Ghavami et al. 2011). This backs up the idea that in current durum wheat a certain level of FHB resistance is already available. A potential susceptibility factor which increases durum wheat susceptibility was detected on 2A

Table 37.1 QTL studies carried out in durum wheat mentioning resistance source, inoculation method and type of resistance evaluated

Resistance source

Inoc.

Resistance

T. dicoccoides

Israel A (2A; 3A)

SFI

FHB spread

Otto et al. (2002); Chen et al. (2007); Garvin et al. (2009)

T. dicoccoides

PI478742 (7A)

SFI

FHB spread

Kumar et al. (2007)

T. dicoccoides

Mt.Hermon#22

SFI

FHB spread

Gladysz et al. (2007)

T. dicoccoides

Mt.Gerizim#36

SFI

FHB spread

Buerstmayr et al. (2013)

T. carthlicum

Blackbird

SFI

FHB spread

Somers et al. (2006)

T. dicoccum

T. dic-161

spray

FHB severity

Buerstmayr et al. (2012)

T. dicoccum

BGRC3487

SFI

FHB spread

Ruan et al. (2012)

spray

FHB severity

T. durum

4 Tunisian lines

SFI

FHB spread

Ghavami et al. (2011)

SFI single floret inoculation, spray spray inoculation, FHB spread resistance to spread of the disease within the spike (type 2 resistance), FHB severity disease severity per plot after spray inoculation

Fig. 37.1 Locations of QTL for FHB resistance on durum wheat chromosomes. QTL are identified with the names of the line contributing to the resistant alleles. The inoculation methods performed are also indicated: SFI single floret inoculation, spray spray inoculation

derived from T. dicoccoides Israel A (Garvin et al. 2009; Stack et al. 2002). Ghavami et al. (2011) also suspected the existence of a QTL influencing FHB resistance in the same chromosomal region in durum wheat.

Positions of many of the resistance QTL identified in tetraploid wheat coincided with QTL discovered in hexaploid wheat, suggesting common genes for resistance:

e.g. QTL on 2B, 3A, 3B, 6B and 7B were found in the same regions where several QTL have been reported in hexaploid wheat (Buerstmayr et al. 2009). Positions of the QTL on 3B and 6B overlapped with those of the well documented genes Fhb1 and Fhb2, respectively, which were first described in the hexaploid cultivar Sumai-3 (Buerstmayr et al. 2009). Allele survey at these loci by Buerstmayr et al. (2012) revealed different SSR marker haplotypes between tetraploid lines and Sumai-3. The existence of resistance improving alleles at these loci in tetraploid wheat may circumvent the need to transfer resistance from hexaploid Asian sources into durum wheat.

Developmental and morphological traits often correlate with FHB response both in hexaploid wheat (Buerstmayr et al. 2009) and in tetraploid wheat. For example, under field conditions with spray inoculation a large effect QTL for FHB resistance was mapped at the position of the major plant height gene Rht-B1 on chromosome 4B and a FHB resistance QTL on 7B coincided with a QTL for heading date (Buerstmayr et al. 2012). It is not clear yet whether or not these genes have pleiotropic effects or rather an indirect influence on FHB resistance due to plant height and flowering date per se.

Conclusions and Perspectives

Only few accessions have been used as sources for FHB resistance in durum wheat to date, yet results are promising, yielding multiple QTL with small to medium effects. Common genetic basis for FHB resistance in tetraploid and hexaploid wheat is likely as the positions of their QTL overlap to a large extent. Introgression of positive alleles into durum wheat is feasible and markers located near the mapped QTL are amenable for marker-assisting backcrossing. Pyramiding multiple resistance improving QTL combined with selection against suspected susceptibility factors is a promising breeding strategy to improve FHB resistance in novel cultivars. Improvements in durum wheat breeding are underway. Recently, the evaluation of novel experimental lines descending from multiple crosses of T. durum with T. aestivum, T. dicoccum and T. dicoccoides in our field trials in Tulln (Austria) showed enhanced variation for FHB resistance including lines with improved and stable FHB resistance performance.

Acknowledgments We gratefully acknowledge financial support from the Austrian Science Fund (FWF), projects P17310-B05 and F3711, and from the French Ministry of Higher Education and Research, CIFRE funding 2012/1405.

 
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