2013 Annual Report
1a.Objectives (from AD-416):
To characterize experimental Nebraska-adapted hard white wheats in terms of tolerance to preharvest sprouting, and to determine whether DNA markers may be used as an alternative means of selection for the trait.
1b.Approach (from AD-416):
Five genetic populations, each composed of approximately 100 recombinant in-bred lines (RICLs), have been developed. Each involves matings of the keystone sprouting tolerant cultivar RioBlanco, and hard white wheat experimental breeding lines or cultivars adapted to Nebraska. These populations are grown in an augmented design, along with several hard red and hard white check cultivars. In the augmented design, individual RICLs are un-replicated, but randomly assigned to blocks; check cultivars are planted within each block, and used to provide an experiment-wise error estimate. The experiment has been grown in 2008 harvest years, and will be seeded for observation and data acquisition again in September, 2008. In addition, all hard white wheats from the University of Nebraska wheat breeding program, advanced from the 2008 NIN, TRP and DUP nurseries, will be included. Sprouting tolerance is assessed by snapping heads after before harvest maturity, drying in a greenhouse, and storing at –20 C until assayed in a misting chamber. DNA markers, derived from literature and database searches, will be used to test their utility as an alternate means of selection. After the 2009 data collection, sprout-tolerant hard white winter wheats will be selected and entered in USDA-ARS regional nurseries for testing of disease responses and agronomic performance.
The goal of the project was to identify hard white winter wheat lines tolerant to pre-harvest sprouting, and develop efficient means of selecting them in breeding programs. Pre-harvest sprouting of wheat results in significant financial loss at all steps in the production and marketing chain. Due to its intermittent nature in many wheat growing regions, direct selection for tolerance to pre-harvest sprouting is difficult. DNA markers linked to genes conditioning tolerance offer a more consistent and reliable approach to genetic improvement in tolerance. This investigation assessed the value of previously identified markers linked to genetic loci contributing to tolerance, across multiple genetic backgrounds. A significant contribution to tolerance was demonstrated for a gene known as QPhs.pseru-3AS, previously identified from the hard white winter wheat Rio Blanco. Marker alleles for this locus were associated with enhanced tolerance in three of four investigated populations. In addition, positive contributions of additional genes QPhs.pseru-2B1 and QPhs.pseru-2B2 also were documented. Simultaneous selection for putative marker alleles at two independent loci resulted in significantly higher mean tolerance scores, usually mediated by additive gene action. DNA markers linked to loci contributing to variation in pre-harvest sprouting tolerance offer an efficient and effective alternative to direct phenotypic selection. Several germplasm lines containing these key genes for tolerance were used in greenhouse matings in the spring of 2013 to develop new breeding populations enriched for the trait.
The project also employed direct phenotypic selection to identify wheat breeding lines tolerant to sprouting. Samples from twenty-two breeding populations were placed in a misting chamber; early germinating heads (sprout-susceptible) were discarded, and the ten last to germinate in each population were directly planted in greenhouse pots. The materials were grown to maturity, and will be sown in the field in the fall of 2014 for further observations including disease resistance responses and agronomic performance. All plants selected were hard white wheats derived from matings of white wheat cultivars and germplasm lines crossed to key Nebraska red wheat cultivars, including Wesley, Arapahoe and Niobrara. During the process of their development, automated seed sorting technology, developed by the USDA-ARS Center for Grain and Animal Health Research in Manhattan, KS, was used to develop populations composed only of hard white wheats. This procedure allowed the rapid transfer of genes conditioning tolerance to sprouting from hard red to hard white genetic backgrounds. Hard white wheats now are in demand by both domestic and export markets. Pre-harvest sprouting tolerance is an essential attribute of any new hard white wheat cultivar, and this research has developed a broad range of germplasm fundamental to this market class.