Quantitative trait loci for Fusarium head blight resistance in a recombinant inbred population of Wangshuibai/Wheaton.

Use of diverse sources of Fusarium head blight (FHB)-resistant germplasm in breeding may significantly improve wheat resistance to FHB. Wangshuibai is an FHB-resistant Chinese landrace unrelated to cv. Sumai 3, the most commonly used FHB-resistant source. In all, 139 F(6) recombinant inbred lines were developed from a cross between Wangshuibai and an FHB-susceptible cultivar, Wheaton, to map quantitative trait loci (QTL) for wheat resistance to initial infection (type I resistance), spread of FHB symptoms within a spike (type II resistance), and deoxynivalenol (DON) accumulation (type III resistance) in infected grain. The experiments were conducted in a greenhouse at Manhattan, KS from 2003 to 2005. More than 1,300 simple-sequence repeat and amplified fragment length polymorphism markers were analyzed in this population. Five QTL for type I resistance were detected on chromosomes 3AS, 3BS, 4B, 5AS, and 5DL after spray inoculation; seven QTL for type II resistance were identified on chromosomes 1A, 3BS, 3DL, 5AS, 5DL, and 7AL after point inoculation; and seven QTL for type III resistance were detected on chromosomes 1A, 1BL, 3BS, 5AS, 5DL, and 7AL with the data from both inoculation methods. These QTL jointly explained up to 31.7, 64, and 52.8% of the phenotypic variation for the three types of FHB resistance, respectively. The narrow-sense heritabilities were low for type I resistance (0.37 to 0.41) but moderately high for type II resistance (0.45 to 0.61) and type III resistance (0.44 to 0.67). The QTL on the distal end of 3BS, 5AS, and 5DL contributed to all three types of resistance. Two QTL, on 7AL and 1A, as well as one QTL near the centromere of 3BS (3BSc), showed effects on both type II and type III resistance. Selection for type II resistance may simultaneously improve type I and type III resistance as well. The QTL for FHB resistance identified in Wangshuibai have potential to be used to pyramid FHB-resistance QTL from different sources.

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.

Molecular mapping of genomic regions underlying barley yellow dwarf tolerance in cultivated oat (Avena sativa L.).

Barley yellow dwarf (BYD) is one of the most important viral diseases in small grains, including oat (Avena sativa L.). Breeding for BYD tolerance is an effective and efficient means to control the disease. Characterization of major sources of tolerance, and identification of marker and the trait associations, will directly benefit breeding for BYD tolerance. Genomic regions underlying BYD tolerance were mapped and characterized in an oat population consisting of 152 recombinant inbred lines from the cross of 'Ogle' (tolerant)/MAM17-5 (sensitive). Tolerance was evaluated in replicated field trials across 2 years under artificial inoculation with viruliferous aphids harboring BYD virus isolate PAV-IL. Composite interval mapping was used for quantitative trait loci (QTLs) analysis with a framework map consisting of 272 molecular markers. Four QTLs, BYDq1, BYDq2, BYDq3 and BYDq4, for BYD tolerance were identified on linkage groups OM1, 5, 7 and 24, respectively. All but BYDq2 were consistently detected across both years. Significant epistasis was found between some QTLs. The final model including the epistatic effect explained 50.3 to 58.2% of the total phenotypic variation for BYD tolerance. Some QTLs for BYD tolerance were closely linked to QTLs for plant height and days to heading. Potential problems with QTL mapping for BYD tolerance have been discussed. The identified association of markers and tolerance should be useful to pyramid favorable alleles for BYD tolerance into individual oat lines.

Effect of individual Sumai 3 chromosomes on resistance to scab spread within spikes and deoxynivalenol accumulation within kernels in wheat.

Two sets of substitution lines were developed by crossing individual monosomic lines of Chinese Spring (recipient) with scab (Fusarium graminearum) resistant cultivar Sumai 3 (donor) and then using the monosomics as the recurrent male parent for four backcrosses (without selfing after each backcross). The disomic substitution lines were separated from selfed BC4F2 plants. Chromosome specific SSR markers were analyzed for polymorphism between Sumai 3 and Chinese Spring. Polymorphic markers were used to identify substitution lines for specific chromosomes. Based on the specific SSR markers, chromosome substitutions occurred in thirty-six lines, and six lines segregated alleles from the two parents or were homozygous for the allele from Chinese Spring. These substitution lines were used to evaluate Type II (spread within the head) and Type V (deoxynivalenol accumulation within kernels) scab resistance. The objective was to use the substitution lines to evaluate the effect of individual chromosomes of Sumai 3 on Type 11 and Type V scab resistance in the greenhouse. Significant differences in Type II scab resistance and deoxynivalenol (DON) levels among different Chinese Spring (Sumai 3) substitution lines were detected. Positive chromosome substitution effects on Type II scab resistance were found on chromosomes 2B, 3B. 6B, and 7A from Sumai 3. Chromosomes 3B and 7A also reduced DON accumulation within the kernels, while chromosomes IB, 2D, and 4D from Sumai 3 increased DON concentration. Chromosome 7A from Sumai 3 had the largest effect on resistance to scab spread and DON accumulation. Additional research is in progress on the scab resistance conferred by chromosome 7A.

Combined AFLP and RFLP mapping in two hexaploid oat recombinant inbred populations.

A combined RFLP and AFLP map was constructed for hexaploid oat (Avena spp.). The segregation of AFLP markers was scored in two hexaploid oat recombinant inbred line (RIL) populations, the 'Kanota' x 'Ogle' RFLP population, and a population derived from 'Clintland64' and 'IL86-5698', barley yellow dwarf virus (BYDV)-sensitive and BYDV-tolerant lines, respectively. More than 300 AFLP markers were scored in each population, of which 97 could be scored in both populations. AFLP markers were linked to RFLP markers in 32 of 36 'Kanota' x 'Ogle' RFLP linkage groups. The addition of the AFLP markers to the 'Kanota' x 'Ogle' RFLP data set combined markers from four pairs of linkage groups and increased the size of the map from 1402 cM to 2351 cM. Thirty linkage groups were observed in the 'Clintland64' x 'IL86-5698' population, two of which could be consolidated by comparing the maps from both populations. The AFLP and RFLP markers showed very similar distributions in the 'Kanota' x 'Ogle' population with a tendency of each type of marker to cluster with markers of the same type. The placement of a set of AFLP markers on the 'Kanota' x 'Ogle' linkage map will enrich the RFLP map and allow others to relate AFLP markers for agronomically important genes to the reference 'Kanota' x 'Ogle' linkage map.

Yield Effects of Barley yellow dwarf virus in Soft Red Winter Wheat.

ABSTRACT Three cultivars of soft red winter wheat were evaluated to determine the relationship between the incidence and time of infection by Barley yellow dwarf virus (BYDV) and yield. Wheat was planted in 1995, 1996, and 1997 in a split-plot design with six replicates at sites in Indiana and Illinois. Yield plots were infested with different amounts of viruliferous aphids, and the incidence of BYDV in each plot was measured. In a 2-year study in Illinois with cv. Clark and the PAV-IL isolate of BYDV, yields were assessed following aphid infestation in fall, early spring, and late spring. Early spring infections resulted in larger yield reductions than late spring infections in both years and larger than fall infections in one year. Regression analyses to relate incidence of infection and yield with data from fall and early spring infections provided R(2) values of 0.89 and 0.51 for the 1996 to 1997 and 1997 to 1998 seasons, respectively. An additional study at the same site in the 1996 to 1997 season compared the yield responses of cvs. Clark, Y88-3e, and PT8935b. Increases in the incidence of BYDV correlated with decreases in yield, with R(2) values of 0.80, 0.78, and 0.90 for the three cultivars, respectively. Estimated yield losses in both studies and all cultivars ranged from 27 to 45 kg/ha or 0.34 to 0.55% for each percent increase in virus infection. In a third study over a 2-year period in Indiana with the same three wheat genot ypes and a second BYDV isolate (PAV-P), BYDV treatments resulted in significant reductions in yield, but yield loss and the incidence of BYDV were not linearly correlated. Given the differences in yield reductions caused by the two BYDV isolates, PAV-P may be an attenuated strain of BYDV and may cross-protect plants from naturally occurring strains of the virus.

Amplified fragment length polymorphism markers linked to a major quantitative trait locus controlling scab resistance in wheat.

ABSTRACT Scab is a destructive disease of wheat. To accelerate development of scab-resistant wheat cultivars, molecular markers linked to scab resistance genes have been identified by using recombinant inbred lines (RILs) derived by single-seed descent from a cross between the resistant wheat cultivar Ning 7840 (resistant to spread of scab within the spike) and the susceptible cultivar Clark. In the greenhouse, F(5), F(6), F(7), and F(10) families were evaluated for resistance to spread of scab within a spike by injecting about 1,000 conidiospores of Fusarium graminearum into a central spikelet. Inoculated plants were kept in moist chambers for 3 days to promote initial infection and then transferred to greenhouse benches. Scab symptoms were evaluated four times (3, 9, 15, and 21 days after inoculation). The frequency distribution of scab severity indicated that resistance to spread of scab within a spike was controlled by a few major genes. DNA was isolated from both parents and F(9) plants of the 133 RILs. A total of 300 combinations of amplified fragment length polymorphism (AFLP) primers were screened for polymorphisms using bulked segregant analysis. Twenty pairs of primers revealed at least one polymorphic band between the two contrasting bulks. The segregation of each of these bands was evaluated in the 133 RILs. Eleven AFLP markers showed significant association with scab resistance, and an individual marker explained up to 53% of the total variation (R(2)). The markers with high R(2) values mapped to a single linkage group. By interval analysis, one major quantitative trait locus for scab resistance explaining up to 60% of the genetic variation for scab resistance was identified. Some of the AFLP markers may be useful in marker-assisted breeding to improve resistance to scab in wheat.

Effects of Barley Yellow Dwarf Virus on Yield and Yield Components of Drilled Winter Wheat.

Yield reduction in eight soft red winter wheat cultivars (Triticum aestivum) in response to barley yellow dwarf (BYDV) infection was evaluated in drilled plots. The experiment was conducted in 1993 and 1994 at the Crop Sciences Research and Education Center of the University of Illinois at Urbana-Champaign. Cultivars Caldwell, Cardinal, Clark, Howell, IL 87-2834, Tyler, and Pioneer brands 2548 and 2555 were selected for the study based on root system size, yield potential, and adaptation to local growing conditions. Plots were planted with a six-row drill to approximate conditions in growers' fields. A split-plot treatment design was used, with treatments as whole plots, and cultivars as subplots. The three treatments were BYDV-inoculated, natural BYDV infection, and a control (sprayed with Cygon to control naturally occurring aphids). Significant yield reductions in inoculated plots indicated the potential for severe yield loss due to BYDV infection under drilled conditions. The component of yield most severely affected by virus infection was number of kernels per spike. Kernel weight was affected but to a lesser extent than kernels per spike. Tiller number was generally not altered by infection but was positively correlated with yield in infected plots. Since kernels per spike and kernel weight were reduced by BYDV infection, it may be possible to select for tolerant genotypes by identifying lines in which these parameters are least affected by BYD disease pressure.

Identification of quantitative Loci for tolerance to barley yellow dwarf virus in oat.

ABSTRACT Molecular markers linked to quantitative trait loci conditioning tolerance to barley yellow dwarf virus (BYDV) were identified in oat (Avena sativa) using amplified fragment length polymorphism (AFLP) analysis. Near-isogenic and recombinant inbred lines (NILs and RILs, respectively) derived from a cross of Clintland64 (BYDV-sensitive) and IL86-5698 (BYDV-tolerant) were evaluated for their responses to an Illinois isolate of the PAV strain of BYDV. Individual markers identified in the analysis of the NILs explained up to 35% of the variability seen in the tolerance response. Single-point analysis of the marker data from the RIL population identified 24 markers in three linkage groups that were associated with tolerance to BYDV infection at P /= 3.0. These loci explained about 50% total of the variation in BYDV tolerance in multimarker regression analysis in both years. The BYDV tolerance loci A, C, E, and R were mapped to hexaploid oat restriction fragment length polymorphism linkage groups 2, 8, 36, and 5, respectively, by analyzing the segregation of the AFLP markers in the Kanota x Ogle RIL population.

Effects of Barley Yellow Dwarf Virus on Root and Shoot Growth of Winter Wheat Seedlings Grown in Aeroponic Culture.

Seedlings of eight soft red winter wheat (Triticum aestivum) cultivars were grown in an aeroponic mist box to study the effects of barley yellow dwarf virus (BYDV) on root and shoot growth and to look for differences in root and shoot growth among cultivars. The cultivars selected for the study were Caldwell, Cardinal, Clark, Howell, IL 87-2834, Tyler, and Pioneer brands 2548 and 2555. A split-plot treatment design was used, with uninfected and inoculated treatments as whole plots and cultivars as subplots. Differences among cultivars were found for most growth characteristics under both control and BYDV-infected conditions. There was a strong positive correlation between shoot and root dry weights in both the control and BYDV treatments, indicating that cultivars with vigorous shoot growth tended to have more vigorous root growth. BYDV severely reduced root length, distance from seminal root tip to the nearest lateral root, and the root to shoot ratio for all cultivars tested. The number of adventitious roots and shoot percent dry matter were increased by BYDV infection for some cultivars. Chlorosis and stunting were not observed in shoots during the 18 days of the experiment, whereas roots were visibly stunted approximately 4 days after inoculation. Results indicate that, initially, the root system is affected more severely than the shoot in BYDV-infected wheat seedlings.

Prediction of F3 row performance from F2 individual plant data in oats.

Parameters estimated from a Gardner-Eberhart analysis of the F2 generation of a six-parent diallel in oats (Avena sativa L.) were used to compare methods for predicting the performance of F3 row plots. The prediction methods were: (1) individual F2 plant performance (F2I), (2) parent average plus F2 plot deviations (PF2), (3) parent average plus weighted F2 plot deviations (PF2P), (4) best linear unbiased prediction (BLUP) of parent average plus F2 plot deviations (BPF2), and (5) BLUP plus weighted F2 deviations (BF2). The F2 single-plant traits used for prediction were biological yield to predict F3 biological yield, whole plant and primary tiller grain yield for prediction of F3 grain yield, and whole plant and primary tiller harvest index (HI) to predict F3 HI. Prediction methods were evaluated by correlations between predicted and observed F3 performance. Prediction methods and traits for which correlations were greater than for F2I included: BF2 for biological yield, PF2, PF2P and BF2 for whole plant grain yield, PF2, BPF2, and BF2 for primary tiller grain yield. None had a correlation significantly greater than F2I for either measure of HI, where heritability was large. PF2 is the recommended method for traits with low heritability because of its simplicity and because it had the largest or nearly the largest correlation for each of the yield traits. F2I is the recommended method for traits with larger heritability.