Diagnostic DNA markers for cereal cyst nematode resistance in bread wheat

Abstract

The development of cultivars resistant to cereal cyst nematode (CCN) is a primary objective in wheat breeding in the southern wheatbelt of Australia. Nine CCN resistance genes have been identified in wheat and its relatives, some of which confer resistance to the Australian pathotype of CCN (Ha13). Cultivars released in Australia with CCN resistance carry either the Cre1 or CreF gene, with the Cre3 gene present in advanced breeding lines. The biological assay for CCN resistance screening in wheat is time-consuming, not reliable on a single-plant basis, and prone to inconsistencies, thus reducing the efficiency of selection amongst breeding lines. Using gene sequences initially isolated from the Cre3 locus, a DNA-based marker selection system was developed and applied to unambiguously identify wheat lines carrying resistance alleles at theCre1 and/or Cre3 loci in breeding populations derived from diverse genetic backgrounds. Homologues of sequences from the Cre3 locus, located elsewhere in the wheat genome, can also be used to select wheat lines with a newly identified CCN resistance gene (Cre6) introgressed from Aegilops ventricosa. Application of these markers has become an integral part of the southern Australian breeding programs.

An introduction to markers, quantitative trait loci (QTL) mapping and marker-assisted selection for crop improvement: The basic concepts

“…The identification of genes controlling important traits will enable plant scientists to predict gene function, isolate homologues and conduct transgenic experiments. To enhance the efficiency of MAS, knowledge of the DNA sequence of the gene enables the design of 'perfect' or 'diagnostic' markers, which are located within the actual gene sequence, thus eliminating the possibility of recombination between marker and gene (Ellis et al, 2002;Ogbonnaya et al, 2001). However, DNA sequences for the majority of genes controlling agronomically important traits remain unknown, and most probably, will remain unknown for sometime.…”

Physiological traits and cereal germplasm for sustainable agricultural systems

“…Searches for suitable genetic variation for many root diseases in cereals are still in their infancy but there have been some significant successes arising from longterm research. For the control of cereal cyst nematode (CCN), several resistance genes have been identified and these have been incorporated into some temperate cereals (Ogbonnaya et al, 2001). There is also good genetic resistance/ tolerance to root lesion nematode (Schmidt et al, 2005) and crown rot (Collard et al, 2005).…”

Molecular markers: actual and potential contributions to wheat genome characterization and breeding

“…Recombination between the marker allele and the gene of interest, however, limits the use of MAS. This was the case in an attempt to combine two independent genes for boron tolerance (Bo1 and Bo2), when a signiWcant proportion of the breeding material carrying the marker alleles did not possess the tolerance genes (Eagles et al 2001). The co-selection of markers Xanking a gene enables the use of higher individual linkage values, but the added reliability of gene transfer may be at the cost of greater linkage drag.…”

“…Conventional screening for CCN resistance is laborious, expensive and prone to inconsistencies. A RFLP marker and an allele-speciWc PCR marker showing complete linkage to the CCN resistance genes Cre1 and Cre3, respectively, were developed and applied in more than 3,800 molecular markerassays in a one-year period to select for resistance to CCN (Eagles et al 2001;Ogbonnaya et al 2001). A widely used CCN resistance donor in breeding programs is cultivar 'Molineux' (Cre8; 6B) (Williams et al 2003).…”

“…This approach was applied for successful integration of three Pm gene combinations (Pm2 + Pm4a; Pm2 + Pm21 and Pm4a + Pm21) into an elite locally adapted Chinese cultivar (Liu et al 2000). Markers linked with genes Sr38/Lr37/Yr17 and Sr39 have been implemented by the National Cereal Rust Control Program at the University of Sydney, Australia, to accumulate several resistance genes (Eagles et al 2001).…”