D. A. Van Sanford

Variation in nitrogen use efficiency among soft red winter wheat genotypes

SummaryNitrogen use efficiency (NUE), defined as grain dry weight or grain nitrogen as a function of N supply, was evaluated in 25 soft red winter wheat genotypes for two years at one location. Significant genotypic variation was observed for NUE, nitrogen harvest index, and grain yield. Genotype x environment interaction for these traits was not significant. Several variables including N uptake efficiency (total plant N as a function of N supply), grain harvest index, and N concentration at maturity were evaluated for their role in determining differences in NUE. Nitrogen uptake efficiency accounted for 54% of the genotypic variation in NUE for yield and 72% of the genotypic variation in NUE for protein. A path coefficient analysis revealed that the direct effect of uptake efficiency on NUE was high relative to indirect effects.

Evaluation of Components of Fusarium Head Blight Resistance in Soft Red Winter Wheat Germ Plasm Using a Detached Leaf Assay

A large environmental influence on phenotypic estimates of disease resistance and the complex polygenic nature of Fusarium head blight (FHB) resistance in wheat (Triticum aestivum) are impediments to developing resistant cultivars. The objective of this research was to investigate the utility of a detached leaf assay, inoculated using inoculum from isolates of Microdochium nivale var. majus, to identify components of FHB resistance among 30 entries of U.S. soft red winter wheat in the 2002 Uniform Southern FHB Nursery (USFHBN). Whole plant FHB resistance of the USFHBN entries was evaluated in replicated, mist-irrigated field trials at 10 locations in eight states during the 2001-2002 season. Incubation period (days from inoculation to the first appearance of a dull gray-green water-soaked lesion) was the only detached leaf variable significantly correlated across all FHB resistance parameters accounting for 45% of the variation in FHB incidence, 27% of FHB severity, 30% of Fusarium damaged kernels, and 26% of the variation in grain deoxynivalenol (DON) concentration. The results for incubation period contrasted with previous studies of moderately resistant European cultivars, in that longer incubation period was correlated with greater FHB susceptibility, but agreed with previous findings for the Chinese cultivar Sumai 3 and CIMMYT germ plasm containing diverse sources of FHB resistance. The results support the view that the detached leaf assay method has potential for use to distinguish between specific sources of FHB resistance when combined with data on FHB reaction and pedigree information. For example, entry 28, a di-haploid line from the cross between the moderately resistant U.S. cultivar Roane and the resistant Chinese line W14, exhibited detached leaf parameters that suggested a combination of both sources of FHB resistance. The USFHBN represents the combination of adapted and exotic germ plasm, but four moderately resistant U.S. commercial cultivars (Roane, McCormick, NC-Neuse, and Pat) had long incubation and latent periods and short lesion lengths in the detached leaf assay as observed in moderately FHB resistant European cultivars. The dichotomy in the relationship between incubation period and FHB resistance indicates that this may need to be considered to effectively combine exotic and existing/adapted sources of FHB resistance.

Partial resistance to powdery mildew in soft red winter wheat.

Powdery mildew (caused by Erysiphe graminis f. sp. tritici) is a disease that can cause significant yield loss in soft red winter wheat (Triticum aestivum). In selecting for resistance, one strategy is to incorporate partial resistance into breeding populations. The objectives of this study were to (i) estimate heritability of partial resistance to powdery mildew, (ii) determine which growth stage is optimal for measuring powdery mildew in terms of predicting yield loss, and (iii) measure yield loss associated with powdery mildew. In 1991, we evaluated 94 F 3 lines from a single-cross population believed to be segregating for partial resistance in a replicated experiment near Lexington, KY. The bulked F 5 progeny were evaluated in a replicated experiment in 1993. Plants were rated according to leaf infected (LI), an index of powdery mildew on the flag leaf and the subtending two leaves at Feekes growth stages (GS) 9 and 10.5. Severity of infection was assessed only on the uppermost leaf on which powdery mildew was present. Broad sense heritability estimates ranged from 0.31 (LI, 1991) to 0.65 (severity, 1991). Heritability of severity of infection was considerably higher at GS 9 than at GS 10.5 (0.57 versus 0.34). Severity of infection at GS 9 also had the strongest correlation with yield (r = -0.55; P < 0.01) of any powdery mildew rating. We observed an average yield loss of 20% associated with powdery mildew over the 2 years of the study. Our data indicate that GS 9 is better than GS 10.5 for evaluating powdery mildew in terms of likely yield loss and heritability.

Effect of Inoculation with Selected Isolates of Stagonospora nodorum on Field Evaluations of Host Resistance in Winter Wheat

Although Stagonospora nodorum blotch occurs annually in North Carolina, selection for resistance in wheat (Triticum aestivum) breeding nurseries is hampered by the infrequent occurrence of heavy and timely disease pressure. The objective of this study was to compare estimates of host resistance in a population of 147 random winter wheat lines evaluated in epidemics produced by natural infection versus epidemics supplemented by inoculation with selected isolates. Two isolates were chosen from a set of 43 collected in North Carolina based on their aggressiveness on four wheat cultivars in a controlled environment test. Field experiments utilized a split-plot design with three replications. The main plots were inoculation treatments and the subplots were the 147 wheat genotypes. The inoculation treatments were (i) selected isolate A (more aggressive) alone, (ii) selected isolate B (less aggressive) alone, (iii) a combination of isolates A plus B, and (iv) natural infection. Selected isolate treatments were applied at Feekes growth stage 9 to 10.1, and disease intensity was measured two or three times at 14-day intervals postinoculation. The study was conducted at one location in the 1996-97 season and two locations in the 1997-98 season. High levels of natural infection occurred, and no differences were observed among the four inoculation treatments for mean disease intensity in any of the three environments. Within environments, genotype-by-inoculation treatment variance was significant in the two environments inoculated with selected isolates at growth stage 9 but not in the environment inoculated at growth stage 10.1. Magnitudes of genetic variation and heritability for Stagonospora nodorum blotch resistance were not consistently associated with main plot treatments, and inoculation with selected isolates masked genetic variation for resistance in two treatments in one environment. Genotype rank correlations for Stagonospora nodorum blotch resistance between inoculation treatments varied from zero to 0.69 within environments, but only a single correlation between inoculation treatments in different environments was observed. Estimates of host resistance in epidemics supplemented with selected isolates did not consistently agree with estimates in epidemics produced by natural infection. Our results did not support the routine use of supplemental inoculation of wheat breeding nurseries with selected isolates of S. nodorum as a means of increasing genetic gain for host resistance.

Characterization of Fusarium Strains Recovered From Wheat With Symptoms of Head Blight in Kentucky

Fusarium graminearum species complex (FGSC) members cause Fusarium head blight (FHB) of wheat (Triticum aestivum L.) and small grains in the United States. The U.S. population is diverse and includes several genetically distinct local emergent subpopulations, some more aggressive and toxigenic than the majority population. Kentucky is a transition zone between the Mid-Atlantic and Midwestern wheat production areas. Sixty-eight Fusarium strains were isolated from symptomatic wheat heads from central and western Kentucky and southern Indiana in 2007. A multilocus genotyping assay and a variety of additional molecular markers, including some novel markers developed using the F. graminearum genome sequence, were used to characterize the pathogen population. Five of the isolates were identified as members of two non-FGSC species, F. acuminatum and F. cf. reticulatum, but they did not cause symptoms in greenhouse tests. All the FGSC isolates belonged to the 15-ADON chemotype of F. graminearum. Comparative genetic analysis using variable nuclear tandem repeat (VNTR) markers indicated that the population in Kentucky and Indiana belonged to the dominant North American population, with some diversification likely due to local evolution. Telomere and RFLP fingerprinting markers based on repetitive sequences revealed a high degree of genetic diversity within the population, with unique genotypes found at each location, and multiple genotypes isolated from the same head.

Winter and Specialty Wheat

Wheat is the most widely grown crop in the world. Winter wheat is primarily common wheat (2n = 6x = 42) which has extensive germplasm resources that are used in breeding, often for disease and insect resistance. Though wheat can be used as a forage crop and its grain for animal feed, the primary uses of common wheat are to make products used for human consumption; hence end-use quality is also a major breeding objective. The quality characteristics of these products are often associated with kernel hardness which affects milling, kernel color, and specific climatic zones or regions. The soft red and white wheat cultivars of the Eastern and Southeastern U.S. are generally used to make breakfast cereals, cookies, cakes, and crackers. The hard red and white wheat cultivars of the Great Plains are used predominantly for leavened products such as bread. The soft white wheat cultivars of the Pacific Northwest are often exported and used to make noodles or steam breads. These end-uses and production (adaptation) regions determine the germplasm pools used by wheat breeders. All of the common self pollinated breeding methods are used to breed new wheat cultivars. The choice of breeding method is usually based upon breeding objective and program resources. Breeding methods and objectives are evolving with new technology and market changes.

Nitrate assimilation and partitioning in detached culms of wheat

Abstract Detached wheat culms ( Triticum aestivum L. cv. Doublecrop) collected from field-grown plants 16 days after anthesis were cultured for 5 days with nutrient solution containing glutamine (7.5 mM), K 15 NO 3 (15 mM), or glutamine (7.5 mM) plus K 15 NO 3 (15 mM). Kernel growth rate of cultured culms equaled or exceeded that of intact field-grown plants (1.46 mg kernel −1 day −1 ). Net mobilization of reduced N from the peduncle occured, but this accounted for less than 23% of the net increase in grain N after 5th day of culture, regardless of N source. Glutamine had no effect on the assimilation of [ 15 N]nitrate or the partitioning of reduced [ 15 N]-labelled products. Peduncles contained less than 4–8% of total reduced[ 15 N] excess recovered in all plant parts. Grain accumulation of reduced [ 15 N] was linear,as was solution depletion, and accounted for an increasing proportion of the total reduced[ 15 N] excess in all culm parts. These results provide direct evidence for nitrate assimilation by spike components.