Anne L. McKendry

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

Fusarium head blight (FHB), mainly caused by Fusarium graminearum Schwabe [telomorph: Gibberella zeae Schw. (Petch)], is an increasingly important disease of wheat (Triticum aestivum L.). Host-plant resistance provides the best hope for reducing economic losses associated with FHB, but new sources of resistance are limited. The moderately resistant winter wheat cultivar, Ernie, may provide a source of resistance that differs from Sumai 3 but these genes have not been mapped. Also hindering resistance breeding may be associations of resistance with agronomic traits such as late maturity that may be undesirable in some production environments. This research was conducted to identify QTL associated with type II FHB resistance (FHB severity, FHBS), and to determine if they are associated with days to anthesis (DTA), number of spikelets (NOS), and the presence/absence of awns. Two hundred and forty-three F8 recombinant inbred lines from a cross between the resistant cultivar, Ernie and susceptible parent, MO 94-317 were phenotyped for type II FHB resistance using point inoculation in the greenhouse during 2002 and 2003. Genetic linkage maps were constructed using 94 simple sequence repeat (SSR) and 146 amplified fragment length polymorphic (AFLP) markers. Over years four QTL regions on chromosomes 2B, 3B, 4BL and 5A were consistently associated with FHB resistance. These QTL explained 43.3% of the phenotypic variation in FHBS. Major QTL conditioning DTA and NOS were identified on chromosome 2D. Neither the QTL associated with DTA and NOS nor the presence/absence of awns were associated with FHB resistance in Ernie. Our results suggest that the FHB resistance in Ernie appears to differ from that in Sumai 3, thus pyramiding the QTL in Ernie with those from Sumai 3 could result in enhanced levels of FHB resistance in wheat.

Inheritance of Fusarium head blight resistance in the soft red winter wheat Ernie

Fusarium head blight (FHB), caused by Fusarium graminearum Schwabe [telomorph:Gibberella zeae Schw. (Petch)], is an increasingly important disease of wheat (Triticum aestivum L.). Host-plant resistance is considered to be the most economical means of control, but a lack of unique sources of resistance has hindered efforts to breed resistant varieties. The soft red winter wheat, Ernie, has moderately high FHB resistance and is widely used in U.S. breeding programs; however, the genetics of resistance have not been studied. The objectives of this study were to estimate the genetic effects, gene numbers, and heritability for traits related to FHB resistance in Ernie through generation means analyses and variance analyses of 243 F3-derived F8 and F9 recombinant inbred lines (RILs). Replicated experiments were grown in the greenhouse, inoculated with F. graminearum, and evaluated for disease spread and the FHB index (FHBI). The latter was calculated as the percentage of diseased spikelets in inoculated spikes and is often referred to as type-II resistance. Gene action for both disease spread and FHBI was primarily additive with partial dominance for low disease. Broad-sense heritabilities for spread and FHBI were 78.2% and 78.3%, respectively, while the narrow-sense heritabilities were 51.3% and 55.4%, respectively. Line-mean heritabilities from analyses of variance of RILs were 0.70 and 0.87 for spread and FHBI, respectively. A minimum of four genes conditioned both disease spread and FHBI. These results suggest that breeders should be able to enhance FHB resistance by combining the resistance in Ernie with other complementary additive sources of resistance.

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.

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.

Genetic analysis of heading date in winter and spring wheat

Climate change will have severe effects on wheat production, but crop phenology can be an important component of wheat adaptation. In this study, elite soft winter wheat and hard spring wheat (HSW) populations were phenotyped for heading date (HD) in North America and Tanzania (HSW only). All lines were genotyped with common single nucleotide polymorphism markers to compare the genetics and prediction accuracy of genomic selection (GS) for HD in winter and spring wheat. Lines were tested under diverse environments and the HSW germplasm was assessed for their early maturity performance in Africa. Two clusters of environments were formed for each population. One cluster consisted of southern environments and the other consisted of northern environments. The latter produced a more narrow range of HD than the southern cluster. Thirteen highly significant (p < 0.0005) quantitative trait loci (QTLs) for HD were detected in two populations. Within each population, the QTL effects were consistent between clusters of environments. Within each population, GS model developed using data from one cluster of environments could predict HD in the other cluster. The prediction accuracy of GS between two populations was minimal. Similarly, only a few minor effects QTL were in common between the two populations. Additionally, we identified 15 spring wheat genotypes with HD earlier than commercial Tanzanian wheat varieties. These genotypes could be used as a resource for creating early HD wheat varieties for Tanzania.