Identification and validation of QTLs associated with pre-harvest sprouting tolerance in bread wheat
Pre-harvest sprouting (PHS) is the in-spike germination of physiologically mature grain in response to relatively high humidity due to untimely rains prior to harvest. PHS in bread wheat (Triticum aestivum L.) results in substantial economic loss, as it decreases the functional quality of wheat grain. The Canadian Grain Commission sets the limit of percentage severely sprouted and total sprouted grain depending on the grade and wheat classes. Pre-harvest sprouted wheat is reduced in grade and value, depending on the quantity of sprouted kernels present in a sample. Breeding for PHS tolerance in wheat is challenging on phenotypic basis because PHS is inherited quantitatively and highly influenced by environmental conditions. Seed dormancy is the main factor responsible for conferring the PHS resistance to the grains of bread wheat. The objectives of this study were to identify and validate the major quantitative loci (QTL) for pre-harvest sprouting (PHS) resistance in bread wheat. A F1-derived doubled haploid (DH) population of 151 lines from a cross between two spring wheat cultivars ND690 (nondormant) and W98616 (dormant) was used to identify the genomic regions associated with PHS tolerance. A total of 950 polymorphic markers (369 SSR, 306 AFLP, 267 DArT and 8 EST) have been used to develop a genetic map and to identify QTLs for PHS tolerance. Interval mapping revealed a major QTL on chromosome 4A explaining 25% phenotypic variation in this mapping population. Forty two Canadian wheat cultivars and germplasm lines were screened with the DNA marker in the QTL region on chromosome 4A for validation. 113 BC1F1 plants from four different backcrosses were screened with the marker associated with PHS resistance. Marker assisted back crossing reduced the population size in BC1F1 generation by 40.7%. This information will help the plant breeders to pyramid this QTL with other QTLs from different PHS resistance sources.
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