Heat stress during the seedling stage of early-planted winter wheat (Triticum aestivum L.) is one of the most abiotic stresses of the crop restricting forage and grain production in the Southern Plains of the United States. To map quantitative trait loci (QTLs) and identify single-nucleotide polymorphism (SNP) markers associated with seedling heat tolerance, a genome-wide association mapping study (GWAS) was conducted using 200 diverse representative lines of the hard red winter wheat association mapping panel, which was established by the Triticeae Coordinated Agricultural Project (TCAP) and genotyped with the wheat iSelect 90K SNP array. The plants were initially planted under optimal temperature conditions in two growth chambers. At the three-leaf stage, one chamber was set to 40/35°C day/night as heat stress treatment, while the other chamber was kept at optimal temperature (25/20°C day/night) as control for 14 days. Data were collected on leaf chlorophyll content, shoot length, number of leaves per seedling, and seedling recovery after removal of heat stress treatment. Phenotypic variability for seedling heat tolerance among wheat lines was observed in this study. Using the mixed linear model (MLM), we detected multiple significant QTLs for seedling heat tolerance on different chromosomes. Some of the QTLs were detected on chromosomes that were previously reported to harbor QTLs for heat tolerance during the flowering stage of wheat. These results suggest that some heat tolerance QTLs are effective from the seedling to reproductive stages in wheat. However, new QTLs that have never been reported at the reproductive stage were found responding to seedling heat stress in the present study. Candidate gene analysis revealed high sequence similarities of some significant loci with candidate genes involved in plant stress responses including heat, drought, and salt stress. This study provides valuable information about the genetic basis of seedling heat tolerance in wheat. To the best of our knowledge, this is the first GWAS to map QTLs associated with seedling heat tolerance targeting early planting of dual-purpose winter wheat. The SNP markers identified in this study will be used for marker-assisted selection (MAS) of seedling heat tolerance during dual-purpose wheat breeding.

Wheat (Triticum aestivum L.) has been widely grown as a winter forage crop in the southern Great Plains. However, development of wheat cultivars for winter forage production has not been a major goal of wheat breeding programs in the USA. Also, little information on forage yield and nutritive value of currently grown wheat varieties is available. The objective of this study was to test 15 wheat varieties to compare their forage yield and nutritive value and to identity superior varieties for winter forage production. The field trials were conducted during three growing seasons in southern Oklahoma. There were significant effects of variety, clipping-date, and environment for mean forage yield. The mean forage yield of the varieties ranged from 2,200 kg ha -1 for NF95134A to 1,655 kg ha -1 for Forage Max. The crude protein content varied from 24.2 to 20.8 %. When mean forage yield and crude protein yield were considered, NF95134A was the best variety for the tested regions. However, when low detergent fiber content and high energy value were considered, Forage Max was the best variety in the tested environments. When forage production, especially during the coldest months December through February was considered, NF96107A and NF96131 produced the best forage yield. This study showed that significant differences in forage yield and nutritive value existed among the winter wheat varieties and the results of the study could provide useful guidelines for livestock producers and for forage wheat breeding programs.

Wheat (Triticum aestivum L.) has been widely grown for winter forage production across the world. However, improvement of forage yield and nutritive characteristics has not been a major goal of wheat breeding programs, and little is known about genetic diversity in the traits of winter wheat germplasm. A set of 299 hard winter wheat germplasm from the Great Plains was evaluated during two growing seasons in Oklahoma and 15 forage‐related traits were evaluated. There were significant (P < 0.0001) genetic variations in all the traits but effects of environment and germplasm × environment interaction were significant for seven and eight traits, respectively. A significant portion of the variation for forage traits was due to genetics, indicating an ability to breed for improved forage traits. Dry matter yield (DMY, kg ha−1) of the germplasm ranged from 1260 for Cheyenne to 4158 for Sturdy2K. Crude protein (CP, g kg−1) ranged from 161 for OK05108 to 268 for Nuplains. When crude protein yield (kg ha−1) was considered, Sturdy2K was the best germplasm, followed by 2180 and OK1068009. State of origin of the germplasm was also a significant source of variation for most of the traits. Heading date was positively and negatively associated with CP and DMY, respectively. This study identified significant genetic variations of the hard winter wheat germplasm for forage traits and the results of this study could provide useful guidelines for winter forage wheat breeding programs.

In the southern Great Plains of the United States, winter wheat grown for dual-purpose is often planted early, which puts it at risk for drought stress at the seedling stage in the autumn. To map quantitative trait loci (QTL) associated with seedling drought tolerance, a genome-wide association study (GWAS) was performed on a hard winter wheat association mapping panel. Two sets of plants were planted in the greenhouse initially under well-watered conditions. At the five-leaf stage, one set continued to receive the optimum amount of water, whereas watering was withdrawn from the other set (drought stress treatment) for 14 days to mimic drought stress. Large phenotypic variation was observed in leaf chlorophyll content, leaf chlorophyll fluorescence, shoot length, number of leaves per seedling, and seedling recovery. A mixed linear model analysis detected multiple significant QTL associated with seedling drought tolerance-related traits on chromosomes 1B,

W inter wheat (Triticum aestivum L.) is commonly grown as a dual-purpose crop for forage and grain production in the southern Great Plains of the United States, including Kansas, Oklahoma, and Texas. The crop is grown for forage production during the winter season, when warm-season forage crops are dormant or not able to grow due to cold weather, and is later harvested for grain (Kim et al., 2016;MacKown et al., 2011;MacKown and Northup, 2010). The feed quality of any forage crop is one of the most desirable traits considered for forage

Small-grain cereals are widely adapted and used as annual cool-season pastures in the Southern Great Plains (SGP) of the United States, where livestock and forage production are the largest contributors to agricultural income. The advantage of growing small grains in the region is evident due to the widespread adoption and flexibility of production for grain only, forage only, or both grain and forage (i.e., dual purpose). Farmers in the SGP often prefer the use of small grains for dual purpose mainly because of alternative income options from livestock and/or grain, ensuring stable income especially when product prices fluctuate with market demands. Small-grain forage is exceptionally important during autumn, winter, and early spring when forage availability from other sources is low. By providing nutritionally high-quality forage, small grains minimize the need for protein and energy supplements. Besides being used for winter pasture, small grains also serve as cool-season cover crops. While small grains offer different advantages in the integrated crop-livestock system in the region, farming management practices can play an important role to maximize the benefit. The objectives of this chapter are to summarize the significance of small grains as winter pasture and highlight the production status of each small-grain species in the SGP of the United States.

There has been an increasing use of rye (Secale cereale L.) for winter forage production in the United States because of its good forage yield, nutritive value, and winter hardiness. However, limited information on forage rye is available. To identify variations and germplasm with superior forage yield and/or nutritive value, winter rye germplasm, including elite cultivars and advanced breeding lines, were evaluated during two growing seasons. Effects of germplasm, clipping date, and germplasm by clipping date interactions were significant for dry matter yield (DMY). Clipping date and germplasm by clipping date interactions were significant for crude protein (CP), minerals, and nutritive value, but germplasm effect was not significant. Across the environments, seasonal DMY ranged from 789 kg ha−1 for ThunderGreen at the first clipping to 3733 kg ha−1 for NF97352 at the first clipping. Crude protein concentration varied from 17.7 to 27.9% for ThunderGreen at the third and first clipping, respectively. Cumulative DMY ranged from 5301 kg ha−1 for ThunderGreen to 8114 kg ha−1 for NF95319B. The results of this study identified significant variations in DMY and nutritive value among the rye germplasm, which may provide useful information for rye breeding programs for winter forage production and livestock producers.

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