David A. Van Sanford

Differential effects of partial spikelet removal and defoliation on kernel growth and assimilate partitioning among wheat cultivars

Abstract Among soft red winter wheat ( Triticum aestivum L.) cultivars, compensatory kernel set does not occur with 50% spikelet removal (SR) at anthesis, but there are differential responses in final kernel mass. It seems that these cultivar differences resulted from sink limitations for nonresponsive cultivars and from source limitations for responsive cultivars. Individual kernel masses and kernel growth rates of sink-limited cultivars are not expected to respond to an increased ratio of source to sink and should be less affected than source-limited cultivars when this ratio is reduced. To compare kernel growth traits of six cultivars that differed in response to 50% SR in a previous experiment, a range of SR treatments and defoliation were used to manipulate ratios of source to sink. Two field experiments were conducted for four years. In the first experiment, all spikes on a plant had 0, 25, 50, 75 and 100% SR treatments at anthesis. In the second experiment, sink size was reduced at anthesis by restricting 50% SR to a single culm, and source size was reduced at anthesis by removing all leaf blades from a single culm. Partial SR increased final kernel mass of only responsive cultivars (15–25%), but differences in final kernel mass between the 50 and 75% SR-treated plants were not significant. At maturity, water-soluble carbohydrate levels in stems of all cultivars with 75% SR were less than or equal to those with 100% SR, but greater than those with ≤ 50% SR. Partial SR increased the kernel growth rate of responsive cultivars, which increased the final mass of individual kernels. Kernel N concentrations also were increased. Defoliation decreased kernel growth rate and individual kernel mass of all cultivars; relative decreases were greater for responsive cultivars than for nonresponsive cultivars. The mass and kernel growth rate of individual kernels of responsive cultivars were normally source-limited, while source and sink strengths of nonresponsive cultivars were more closely balanced than those of responsive cultivars.

Kernel mass and assimilate accumulation of wheat: cultivar responses to 50% spikelet removal at anthesis

Abstract Removal of spikelets at anthesis from primary culms of soft red winter wheat ( Triticum aestivum L.) decreased kernel number and induced a range of compensatory growth responses for kernels on the primary culm. Cultivars with kernels on the primary culm that failed to increase in mass were classified as nonresponsive to 50% spikelet removal (SR), while those that increased were classified as responsive. With SR from only the primary culm, differences in assimilate synthesis and export from the primary culm to tillers with intact spikes might explain differential compensatory growth responses for kernels on the primary culm. Consequently, effects were compared for SR from only the primary culm and/or all culms on assimilate levels and kernel mass of two nonresponsive and four responsive cultivars. For nonresponsive cultivars, growth of kernels on the primary culm and tillers was unaffected by either SR treatments. For responsive cultivars, growth of kernels on the primary culm was significantly increased (9 to 23%) to a similar extent for both SR treatments, but growth of tiller kernels increased (10 to 26%) only when all spikes received SR treatment. Apparently, growth of primary-culm kernels after SR was unaffected by the reproductive-sink size of tillers. At maturity, the total water soluble carbohydrate content of stem tissues from both nonresponsive and responsive cultivars was increased by SR, but the higher levels of assimilate were associated with greater kernel growth of only responsive cultivars. Enhanced availability of assimilates and differential kernel responses caused by SR indicate kernel growth of nonresponsive cultivars was sink-limited, while kernel growth of responsive cultivars was initially source-limited and later sink-limited once maximum kernel growth was reached.

Novel QTL associated with the Fusarium head blight resistance in Truman soft red winter wheat

Fusarium head blight (FHB) mainly caused by Fusarium graminearum Schwabe causes devastating losses in wheat globally. ‘Truman’ winter wheat, developed and released by the University of Missouri has excellent broad-based FHB resistance in a superior soft red winter wheat background. This research identified QTL associated with greenhouse type II resistance and field resistance for incidence, severity, Fusarium damaged kernels (FDK), and deoxynivalenol (DON) based on phenotypic data collected in Missouri, Kentucky and Indiana. Two years of replicated phenotypic data were collected on a set of 167 recombinant inbred lines. Genetic linkage maps were constructed using 160 SSR and 530 DArT polymorphic markers. Across years, QTL for type II resistance were identified on chromosomes 1BSc, 2BL, 2DS and 3BSc, for incidence on 2ASc, 2DS, and 3DS and for severity on 2DS and 3BSc. QTL were also detected for incidence on 1DLc and 2DS and for severity on 1BL, 3AL and 3BLC from data collected in Indiana and Kentucky, respectively. Common QTL for FDK on chromosomes 2ASc and 3BLc and for DON on chromosomes 2ASc and 2DS were identified from data from both Missouri and Kentucky, respectively with additional individual QTL for FDK and DON identified from tests at each independent location. All alleles were from Truman and associated with significant reductions in the respective traits. QTL on 2ASC, 2DS and 3DS may be novel and once further validated, should diversify the FHB gene pool globally and be useful for enhancing FHB resistance through marker assisted selection.

Identifying Rare FHB-Resistant Segregants in Intransigent Backcross and F2 Winter Wheat Populations

Fusarium head blight (FHB), caused mainly by Fusarium graminearum Schwabe [telomorph: Gibberella zeae Schwein.(Petch)] in the US, is one of the most destructive diseases of wheat (Triticum aestivum L. and T. durum L.). Infected grain is usually contaminated with deoxynivalenol (DON), a serious mycotoxin. The challenge in FHB resistance breeding is combining resistance with superior agronomic and quality characteristics. Exotic QTL are widely used to improve FHB resistance. Success depends on the genetic background into which the QTL are introgressed, whether through backcrossing or forward crossing; QTL expression is impossible to predict. In this study four high-yielding soft red winter wheat breeding lines with little or no scab resistance were each crossed to a donor parent (VA01W-476) with resistance alleles at two QTL: Fhb1 (chromosome 3BS) and QFhs.nau-2DL (chromosome 2DL) to generate backcross and F2 progeny. F2 individuals were genotyped and assigned to 4 groups according to presence/ absence of resistance alleles at one or both QTL. The effectiveness of these QTL in reducing FHB rating, incidence, index, severity, Fusarium-damaged kernels (FDK) and DON, in F2-derived lines was assessed over 2 years. Fhb1 showed an average reduction in DON of 17.5%, and conferred significant resistance in 3 of 4 populations. QFhs.nau-2DL reduced DON 6.7% on average and conferred significant resistance in 2 of 4 populations. The combination of Fhb1 and QFhs.nau-2DL resistance reduced DON 25.5% across all populations. Double resistant lines had significantly reduced DON compared to double susceptible lines in 3 populations. Backcross derived progeny were planted in replicated yield trials (2011 and 2012) and in a scab nursery in 2012. Several top yielding lines performed well in the scab nursery, with acceptable DON concentrations, even though the average effect of either QTL in this population was not significant. Population selection is often viewed as an “all or nothing” process: if the average resistance level is insufficient, the population is discarded. These results indicate that it may be possible to find rare segregants which combine scab resistance, superior agronomic performance and acceptable quality even in populations in which the average effect of the QTL is muted or negligible.

Kernel growth of in vitro cultured wheat spikes of cultivars with divergent source-sink limitations

Abstract A 50% reduction at anthesis in the main stem reproductive sink size of soft red winter wheat (Triticum aestivum L. em. Thell) elicits differential kernel size (KS) responses among cultivars. In this study, source levels were manipulated to evaluate cultivar source and sink limitations to kernel growth. Detached spikes of ‘Arthur’ (non-responsive, KS unaffected by 50% spikelet removal), ‘Caldwell’, ‘FL 302’ and ‘Adena’ (responsive, KS increases with 50% spikelet removal) cultivars were cultured in vitro from 14 days after anthesis (during endosperm cell expansion stage) to maturity with sucrose levels of 25, 50, 100 and 200 mM. Relative differences in KS among cultivars for each sucrose level were similar to those of field-grown plants at maturity. The KS of all in vitro cultured cultivars reached maximum at sucrose levels of 50 mM or greater; however, these kernels were 11–21% smaller than those of field-grown plants. On average, kernels on spikes cultured in 100 mM sucrose grew at the same rate as kernels on field-grown plants, but for a significantly shorter duration (22.8 vs. 31.7 days). Sucrose concentrations of peduncle and chaff tissues increased as sucrose levels increased. Compared to field-grown plants, peduncle and chaff tissues of cultured spikes averaged over all sucrose levels and cultivars had 4.6-fold greater water soluble carbohydrate concentration and 59% more tissue dry weight at maturity. Smaller kernels but abundant accumulation of water soluble carbohydrates in peduncle and chaff indicate that factors other than carbohydrate supply limited kernel growth of spikes cultured in vitro. When cultured in vitro, the non-responsive cultivar Arthur did not reach maximum KS at a lower sucrose concentration than the responsive cultivars. Thus, the apparent kernel growth limitation due to sink activity observed after partial spikelet removal of field-grown Arthur was not observed when spikes of this cultivar were cultured in vitro.

Impact of Climate Change on Wheat Production in Kentucky

 From 2002 to 2012, Kentucky winter wheat ranged in value from

Genetic analysis of heading date in winter and spring wheat

52 million to

Discovery and Deployment of Molecular Markers Linked to Fusarium Head Blight Resistance: An Integrated System for Wheat and Barley

209 million.  Climate change and variability have the potential to significantly impact this important economic enterprise within our state.  This report summarizes the current state of knowledge of the potential of climate change to impact wheat production in Kentucky and surrounding states. 2 Soft red winter wheat is one of the major row crops in Kentucky, along with corn and soybean. Together these crops are valued at about

Fusarium graminearum infection during wheat seed development and its effect on seed quality

1.4 billion, or 35% of all agricultural receipts in the Commonwealth. In Kentucky, from 2002 to 2012, winter wheat ranged in value from

Molecular characterization of field resistance to Fusarium head blight in two US soft red winter wheat cultivars

52 million to