Impact of the D genome and quantitative trait loci on quantitative traits in a spring durum by spring bread wheat cross

The impact of the D genome and QTL in the A and B genomes on agronomic performance of hexaploid wheat and tetraploid durum was determined using novel recombinant inbred line populations derived from interploid crosses. Genetic differences between common hexaploid (6X) bread wheat (Triticum aestivum, 2n = 6x = 42, genome, AABBDD) and tetraploid (4X) durum wheat (T. turgidum subsp. durum, 2n = 4x = 28, genome, AABB) may exist due to effects of the D genome and allelic differences at loci in the A and B genomes. Previous work allowed identification of a 6X by 4X cross combination that resulted in a large number of fertile recombinant progeny at both ploidy levels. In this study, interspecific recombinant inbred line populations at both 4X and 6X ploidy with 88 and 117 individuals, respectively, were developed from a cross between Choteau spring wheat (6X) and Mountrail durum wheat (4X). The presence of the D genome in the 6X population resulted in increased yield, tiller number, kernel weight, and kernel size, as well as a decrease in stem solidness, test weight and seed per spike. Similar results were found with a second RIL population containing 152 lines from 18 additional 6X by 4X crosses. Several QTL for agronomic and quality traits were identified in both the 4X and 6X populations. Although negatively impacted by the lack of the D genome, kernel weight in Mountrail (4X) was higher than Choteau (6X) due to positive alleles from Mountrail on chromosomes 3B and 7A. These and other favorable alleles may be useful for introgression between ploidy levels.

Identification of quantitative trait loci for productive tiller number and its relationship to agronomic traits in spring wheat

Productive tiller number (PTN), defined as the number of tillers that produce spikes and seeds, is a key component of grain yield in wheat. Spring wheat cultivars in the northern Great Plains of North America differ in PTN. The objectives of this study were (1) to determine the relationship of PTN to agronomic traits using recombinant inbred line (RIL) populations derived from crosses Reeder/Conan, McNeal/Thatcher and Reeder/McNeal grown under a range of environments, and (2) to identify and validate quantitative trait loci (QTL) associated with high PTN. Correlation between PTN and plot weight ranged from r = 0.4-0.6 among the populations based on combined means over years, and was positive in every environment for all crosses (P < 0.05). A genetic map generated for the Reeder/Conan RIL allowed identification of a QTL for PTN consistent over environments, located on chromosome 6B. The QTL on chromosome 6B (QTn.mst-6B) explained 9-17% of the variation of PTN and co-segregated with a QTL for yield in the Reeder/Conan RIL. QTn.mst-6B was validated by single marker analysis in the McNeal/Thatcher RIL, McNeal/Reeder RIL, and a set of near isogenic line (NIL) developed for QTn.mst-6B. The allele for high PTN significantly increased PTN by 8.7, 4, and 13% in the McNeal/Reeder RIL, McNeal/Thatcher RIL and Choteau/Reeder NIL, respectively. The allele for high PTN also had a significant positive effect on plot weight in the McNeal/Reeder RIL. Our results suggest that high PTN, controlled to a significant extent by QTn.mst-6B, contributed to increased yield potential over a range of environmental conditions. QTn.mst-6B may be useful for improving spring wheat in the northern Great Plains of North America and similar environments.

Field Evaluation of Transgenic and Classical Sources of Wheat streak mosaic virus Resistance

The development of wheat (Triticum aestivum L.) cultivars that are resistant to Wheat streak mosaic virus (WSMV), yet competitive in yield under nondiseased conditions, is an objective for breeding programs in the Great Plains. This field study was conducted to compare classical and transgenic sources of resistance to WSMV. Three sets of germplasm were evaluated. These included adapted cultivars with various levels of tolerance, transgenic wheat lines containing viral coat protein or replicase sequences from WSMV that showed resistance in greenhouse trials, and germplasm with resistance to WSMV due to a translocated segment of chromosome 4Ai-2 from Thinopyrum intermedium (Host) Barkworth and Dewey containing Wsm1. A replicated field trial was conducted at Bozeman, MT, over a two-year period to evaluate the effectiveness of these different sources of resistance to mechanical inoculation of WSMV. Adapted cultivars differed in their ability to tolerate WSMV with mean reductions in yield over the two years ranging from 41 to 74%. Incorporation of the replicase or coat protein gene from WSMV did not provide field resistance to viral infection and in general, transgenic lines yielded less than their parent cultivar, 'Hi-Line'. Wheat-Thinopyrum lines positive for a DNA marker linked to the Wsm1 gene had significantly reduced yield losses ranging from 5 to 39% compared with yield losses of 57 to 88% in near isogenic lines not having the Wsm1 gene. Yield of lines with Wsm1 in the absence of disease ranged from 11 to 28% less than yield of lines without Wsm1. Our results suggest Wsm1 provides the best source of WSMV resistance but a yield penalty may exist because of the presence of the translocation.