Gibberella Ear Rot Severity Research Articles

Kernel Bioassay Evaluation of Maize Ear Rot and Genome-Wide Association Analysis for Identifying Genetic Loci Associated with Resistance to Fusarium graminearum Infection.

Gibberella ear rot (GER) caused by Fusarium graminearum (teleomorph Gibberella zeae) is one of the most destructive diseases in maize, which severely reduces yield and contaminates several potential mycotoxins in the grain. However, few efforts had been devoted to dissecting the genetic basis of maize GER resistance. In the present study, a genome-wide association study (GWAS) was conducted in a maize association panel consisting of 303 diverse inbred lines. The phenotypes of GER severity were evaluated using kernel bioassay across multiple time points in the laboratory. Then, three models, including the fixed and random model circulating probability unification model (FarmCPU), general linear model (GLM), and mixed linear model (MLM), were conducted simultaneously in GWAS to identify single-nucleotide polymorphisms (SNPs) significantly associated with GER resistance. A total of four individual significant association SNPs with the phenotypic variation explained (PVE) ranging from 3.51 to 6.42% were obtained. Interestingly, the peak SNP (PUT-163a-71443302-3341) with the greatest PVE value, was co-localized in all models. Subsequently, 12 putative genes were captured from the peak SNP, and several of these genes were directly or indirectly involved in disease resistance. Overall, these findings contribute to understanding the complex plant-pathogen interactions in maize GER resistance. The regions and genes identified herein provide a list of candidate targets for further investigation, in addition to the kernel bioassay that can be used for evaluating and selecting elite germplasm resources with GER resistance in maize.

Genome-wide association study discovers novel germplasm resources and genetic loci with resistance to Gibberella ear rot caused by Fusarium graminearum.

Gibberella ear rot (GER) in maize caused by Fusarium graminearum is one of the most devastating maize diseases reducing grain yield and quality worldwide. The genetic bases of maize GER resistance remain largely unknown. Using artificial inoculation across multiple environments, GER severity of an association panel consisting of 316 diverse inbred lines was observed with wide phenotypic variation. In the association panel, a genome-wide association study (GWAS) using a general linear model (GLM) identified 69 single-nucleotide polymorphisms (SNPs) significantly associated with GER resistance at the threshold of 2.04 x 10-5, and the average phenotypic variation explained (PVE) of these SNPs was 5.09%. We also conducted a GWAS analysis using a mixed linear model (MLM) at a threshold of 1.0 x 10-4, and 16 significant association SNPs with an average PVE of 4.73% were detected. A combined GLM and MLM method obtained 10 co-localized significant association SNPs linked to GER resistance including the most significant SNP (PZE-105079915) with the greatest PVE value, 9.07%, at bin 5.05 following ten candidate genes. These findings are significant for the exploration of the complicated genetic variations in maize GER resistance. The regions and genes identified herein provide a list of candidate targets for further investigation, in addition to the elite germplasm resources that can be used for breeding GER resistance in maize.

A Combination of QTL Mapping and GradedPool-Seq to Dissect Genetic Complexity for Gibberella Ear Rot Resistance in Maize Using an IBM Syn10 DH Population.

Gibberella ear rot (GER) caused by Fusarium graminearum (teleomorph Gibberella zeae) is one of the most devastating maize diseases that reduces grain yield and quality worldwide. Utilization of host genetic resistance has become one of the most suitable strategies to control GER. In this study, a set of 246 diverse inbred lines derived from the intermated B 73 × Mo 17 doubled haploid population (IBM Syn10 DH) were used to detect quantitative trait loci (QTL) associated with resistance to GER. Meanwhile, a GradedPool-Seq (GPS) approach was performed to identify genomic variations involved in GER resistance. Using artificial inoculation across multiple environments, GER severity of the population was observed with wide phenotypic variation. Based on the linkage mapping, a total of 14 resistant QTLs were detected, accounting for 5.11 to 14.87% of the phenotypic variation, respectively. In GPS analysis, five significant single nucleotide polymorphisms (SNPs) associated with GER resistance were identified. Combining QTL mapping and GPS analysis, a peak-value SNP on chromosome 4 from GPS was overlapped with the QTL qGER4.2, suggesting that the colocalized region could be the most possible target location conferring resistance to GER. Subsequently, seven candidate genes were identified within the peak SNP, linking them to GER resistance. These findings are useful for exploring the complicated genetic variations in maize GER resistance. The genomic regions and genes identified herein provide a list of candidate targets for further investigation, in addition to the combined strategy that can be used for quantitative traits in plant species.

Effectiveness of introgression of resistance loci for Gibberella ear rot from two European flint landraces into adapted elite maize (Zea mays L.).

European flint landraces are a major class of maize possessing favorable alleles for improving host resistance to Gibberella ear rot (GER) disease which reduces yield and contaminates the grains with mycotoxins. However, the incorporation of these landraces into breeding programs requires a clear understanding of the effectiveness of their introgression into elite materials. We evaluated 15 pre-selected doubled haploid (DH) lines from two European flint landraces, "Kemater Landmais Gelb" (KE) and "Petkuser Ferdinand Rot" (PE), together with two adapted elite flint lines and seven standard lines for GER severity as the main trait, and several adaptation traits (plant height, days to silking, seed-set, plant vigor) across four environments. From this evaluation, three KE DH lines and one PE DH line, with the lowest GER severity, were selected and used as donor parents that were crossed with the two adapted and GER susceptible flint lines (Flint1 and Flint2) to develop six bi-parental DH populations with 34-145 DH lines each. Each DH population was evaluated across two locations. Correlations between GER severity, which was the target trait, and adaptation traits were weak (-0.02 to 0.19). GER severity of lines from PE landrace was on average 2-fold higher than lines from KE landrace, indicating a clear superiority of the KE landrace lines. Mean GER severity of the DH populations was 39.4-61.0% lower than the adapted elite flint lines. All KE-derived DH populations were on average more resistant (27.0-36.7%) than the PE-derived population (51.0%). Highly resistant lines (1.3-5.2%) were found in all of the populations, suggesting that the DH populations can be successfully integrated into elite breeding programs. The findings demonstrate that selected KE landrace lines used as donors were effective in improving GER resistance of the adapted elite inbreds.

Impact of agronomic practices onFusarium mycotoxin accumulation in maize grain

In the Great Lakes region of North America,Gibberella ear rot (GER), caused byFusarium graminearum, affects grain quality due to the accumulation of mycotoxins. GER severity is strongly influenced by environmental conditions; however, agronomic practices can also influence disease severity and mycotoxin accumulation. In this study, three separate small-plot experiments were conducted at Ridgetown, ON, Canada during 2019 and 2020 under an inoculated-misted system to determineFusarium mycotoxin accumulation as affected by: (1) plant population density; (2) in-row-plant developmental variability; and (3) the effect of integrated Bt refuge genetics. In this study, DON concentrations were at least 49% higher in maize at 113,600 plants/ha compared to 79,000 plants/ha. Moreover, mycotoxin accumulation was higher in plants that were delayed developmentally in the crop row; total DON concentrations were at least 310% higher in late silked plants adjacent to early silked plants. Results of the plant population density and in-row-plant developmental variability suggest that the main driver for mycotoxin accumulation was stress induced by plant competition rather than environmental conditions; this highlights the importance of avoiding plant competitive stress as a strategy to reduce the risks of mycotoxin accumulation. In this study, there was no statistical difference in DON accumulation between the Bt component and the non-Bt component in each of the four hybrids tested; however, there was evidence that hybrids varied in susceptibility, including the Bt and non-Bt components that were paired commercially in a bag of seed maize. Reducing mycotoxins in maize requires integrated management, which includes agronomic considerations. These results indicate that mycotoxins are favoured with high plant populations and plant-to-plant variability in the row, especially in susceptible hybrids.

Aggressiveness and Mycotoxin Production by Fusarium meridionale Compared with F. graminearum on Maize Ears and Stalks in the Field.

Fusarium meridionale and F. graminearum both cause Gibberella ear rot (GER) and Gibberella stalk rot (GSR) of maize in Brazil, but the former is much more common. Recent work with two isolates of each from maize suggested this dominance could be caused by greater aggressiveness and competitiveness of F. meridionale on maize. We evaluated pathogenicity and toxigenicity of 16 isolates of F. graminearum and 24 isolates of F. meridionale recovered from both wheat and maize. Strains were individually inoculated into ears of four maize hybrids in field trials. GER severity varied significantly between isolates within each species. Although ranges overlapped, the average GER severity induced by F. meridionale (25.2%) was two times as high overall as that induced by F. graminearum (12.8%) for isolates obtained from maize but was similar for those isolated from wheat (19.9 and 21.4%, respectively). In contrast, severity of GSR was slightly higher for F. graminearum (22.2%) than for F. meridionale (19.8%), with no effect of the host of origin. Deoxynivalenol and its acetylated form 15ADON were the main mycotoxins produced by F. graminearum (7/16 strains), and nivalenol toxin was produced by F. meridionale (17/24 strains). Six isolates of F. graminearum and three of F. meridionale also produced zearalenone. Results confirmed that F. meridionale from maize is, on average, more aggressive on maize but also suggested greater complexity related to diversity among the isolates within each species and their interactions with different hybrids. Further studies involving other components of the disease cycle are needed to more fully explain observed patterns of host dominance.

Variance Components and Correlations between Doubled Haploid Lines from Two European Flint Landraces and Their Corresponding Testcrosses for Gibberella Ear Rot Resistance, Silking Time, and Plant Height in Maize

Predicting the resistance of hybrids from lines is a relevant approach for accelerating the improvement of disease resistance in hybrid breeding. In this study, genetic variation and covariation among 76 DH lines from two flint landraces, Kemater (KE) and Petkuser (PE), and their corresponding testcrosses (TC) were estimated for the first time for this material for Gibberella ear rot (GER), days to silking (DS), and plant height (PHT). Lines and TC were evaluated in four and two environments, respectively, under artificial infection with GER. TC were, on average, 42% less GER infected than their lines. TC matured 3–4 days earlier and were about 110 cm taller than the lines. GER resistance was 10% higher in KE lines and TC than PE lines and TC. Significant (p < 0.001) genotypic and genotype-by-environment interaction variances were found for all traits. Genotypic variances were generally smaller among TC than lines. Broad-sense heritability estimates were moderate to high for GER severity (0.56–0.82) and high for DS (0.78–0.88) and PHT (0.86–0.94) with higher values always observed in lines. Significant, moderate correlations between TC and line per se performance were found for GER resistance in both KE and PE (r = 0.37 and 0.55, respectively). For the two agronomic traits, correlations were higher (r = 0.59–0.76) than for GER resistance. Genomic prediction accuracies were moderate to high for GER resistance (r = 0.49–0.63) and generally higher for DS and PHT. In conclusion, a pre-selection of DH lines for GER resistance should be feasible; however, TC should be additionally tested on a later selection stage to aim for GER-resistant hybrid cultivars.

Exploiting genetic diversity in two European maize landraces for improving Gibberella ear rot resistance using genomic tools

Key messageHigh genetic variation in two European maize landraces can be harnessed to improve Gibberella ear rot resistance by integrated genomic tools.Fusarium graminearum (Fg) causes Gibberella ear rot (GER) in maize leading to yield reduction and contamination of grains with several mycotoxins. This study aimed to elucidate the molecular basis of GER resistance among 500 doubled haploid lines derived from two European maize landraces, “Kemater Landmais Gelb” (KE) and “Petkuser Ferdinand Rot” (PE). The two landraces were analyzed individually using genome-wide association studies and genomic selection (GS). The lines were genotyped with a 600-k maize array and phenotyped for GER severity, days to silking, plant height, and seed-set in four environments using artificial infection with a highly aggressive Fg isolate. High genotypic variances and broad-sense heritabilities were found for all traits. Genotype-environment interaction was important throughout. The phenotypic (r) and genotypic ({r}_{g}) correlations between GER severity and three agronomic traits were low (r = − 0.27 to 0.20; {r}_{g}hspace{0.17em}= − 0.32 to 0.22). For GER severity, eight QTLs were detected in KE jointly explaining 34% of the genetic variance. In PE, no significant QTLs for GER severity were detected. No common QTLs were found between GER severity and the three agronomic traits. The mean prediction accuracies (rho ) of weighted GS (wRR-BLUP) were higher than rho of marker-assisted selection (MAS) and unweighted GS (RR-BLUP) for GER severity. Using KE as the training set and PE as the validation set resulted in very low rho that could be improved by using fixed marker effects in the GS model.

Fungicide performance on Fusarium meridionale control, grain yield and grain damage in maize

ABSTRACT Gibberella ear rot (GER) in maize, caused by Fusarium graminearum species complex, is a destructive disease in southern Brazil and worldwide. Five field-experiments were conducted to determine fungicide efficacy, grain yield and grain quality (study I), as well as response of increasing rates (study II) on GER control, grain yield (GY) and grain damage (GD) in maize during the 2014/15 and 2015/16 growing seasons. Fungicides were sprayed 48 h before (preventive action) or 48 h after (curative action) inoculation of two Fusarium meridionale isolates (PR and MG). Study I consisted in applying nine active ingredients (metconazole, pyraclostrobin, tebuconazole, trifloxystrobin, prothioconazole, thiophanate-methyl, azoxystrobin, cyproconazole and carbendazim) present in eight commercial formulations at two sowing dates. Study II consisted in applying increasing rates of three fungicides evaluated at three sowing dates using only PR isolate. In study I, no differences were observed among fungicides when the variables GER, GY and GD were analyzed together. There were interactions between time of fungicide application and F. meridionale isolates when GER severity and GY were considered. Preventive fungicide application at different sowing dates and the use of MG isolate reduced GER by 11.6% and increased GY by 5.3%, compared to curative application. In study II, there was a significant interaction between fungicides and application time for GER, GY and GD. Preventive application of trifloxystrobin + prothioconazole (0.15 + 0.17 and 0.22 + 0.26 L ha-1), pyraclostrobin + metconazole (0.19 + 0.12 and 0.29 + 0.18 L ha-1) and carbendazim (2 L ha-1) reduced GER by 41 and 50%, 47 and 54%, and 54% at the three sowing dates, respectively. There was an increment of 45.7% and 46.8% in GY when trifloxystrobin + prothioconazole (0.15 + 0.17 and 0.22 + 0.26 L ha-1), respectively, were preventively sprayed at the three sowing dates, compared to the control treatment. Trifloxystrobin + prothiocanazole, pyraclostrobin + metconazole and carbendazim (1.0 and 2.0 L ha-1) preventively sprayed at two rates reduced GD incidence by 53.5 and 48.7%, 47.7 and 57.5%, 48.1 and 50.5%, respectively, for each fungicide and rate, and could be incorporated into a disease management program.

Genomic prediction and GWAS of Gibberella ear rot resistance traits in dent and flint lines of a public maize breeding program

Gibberella ear rot (GER) is a serious threat to maize cultivation, causing grain yield losses and contamination with mycotoxins. Genomic prediction (GP) has great potential to accelerate resistance breeding against GER. However, small training sets (TS) consisting of both phenotyped and genotyped individuals are a challenge for obtaining high prediction accuracy (ρ) in GP. A potential solution would be combining small-size populations across heterotic pools. However, genetic heterogeneity between populations in terms of segregating QTL, linkage disequilibrium (LD) pattern and genomic relationships can impair ρ of GP. In this study, we investigated the genetic architecture of GER severity, deoxynivalenol concentration (DON) and days to silking with genome-wide association studies within two elite panels of 130 dent and 114 flint lines from the maize breeding program of the University of Hohenheim tested in four environments. We also assessed the consistency of LD pattern and genomic relationships between the two heterotic pools. Furthermore, we compared four GP approaches differing in the composition of the TS with lines from a single or combined pool(s) and statistical models with marker effects identical or different but correlated between pools. We detected two and six QTL for DON within the dent and flint pool, respectively, but no common QTL. The LD pattern was consistent between pools for marker pairs ≤ 10 kb apart. GP across pools yielded low or even negative ρ. Combined-pool GP had no higher ρ than within-pool GP, regardless of the statistical model. Our findings underline the importance of investigating the genetic heterogeneity between populations prior to implementing GP using combined TS.

Impact of Foliar Fungicides on Gibberella Ear Rot and Deoxynivalenol Levels in Indiana Corn

Gibberella ear rot, caused by the fungus Fusarium graminearum (Schawbe), can cause significant yield reductions in corn (Zea mays L.) as well as reduce grain quality. Field experiments were conducted at two locations in Indiana to assess the impact of commercially available fungicides on Gibberella ear rot severity and deoxynivalenol (DON) accumulation in hybrid corn grain. The experiments were arranged in a random complete block design with both inoculated and noninoculated treatments. Three fungicides—azoxystrobin + propiconazole, prothioconazole, and pyraclostrobin—were applied during silking (R1), and Gibberella ear rot severity, DON accumulation in grain, and corn yield were measured. Inoculated treatments had higher disease severity and DON and lower yield (P < 0.001) compared with noninoculated treatments. Fungicides reduced Gibberella ear rot severity in two location-years, but did not reduce DON in those experiments. All other fungicide treatments in all locations and years did not reduce disease severity or DON when compared with treatments not sprayed with fungicide. No fungicide increased DON levels in grain in any location or year. These results indicate that fungicide applications during the silking stage of corn may not consistently reduce DON levels in hybrid corn.

Low validation rate of quantitative trait loci for Gibberella ear rot resistance in European maize.

Six quantitative trait loci (QTL) for Gibberella ear rot resistance in maize were tested in two different genetic backgrounds; three QTL displayed an effect in few near isogenic line pairs. Few quantitative trait loci (QTL) mapping studies for Gibberella ear rot (GER) have been conducted, but no QTL have been verified so far. QTL validation is prudent before their implementation into marker-assisted selection (MAS) programs. Our objectives were to (1) validate six QTL for GER resistance, (2) evaluate the QTL across two genetic backgrounds, (3) investigate the genetic background outside the targeted introgressions. Pairs of near isogenic lines (NILs) segregating for a single QTL (Qger1, Qger2, Qger10, Qger13, Qger16, or Qger21) were developed by recurrent backcross until generation BC3S2. Donor parents (DP) carrying QTL were backcrossed to a susceptible (UH009) and a moderately resistant (UH007) recurrent parent. MAS was performed using five SNP markers covering a region of 40cM around each QTL. All NILs were genotyped with the MaizeSNP50 assay and phenotyped for GER severity and deoxynivalenol and zearalenone content. Traits were significantly (P<0.001) intercorrelated. Out of 34 NIL pairs with the UH009 genetic background, three pairs showed significant differences in at least one trait for three QTL (Qger1, Qger2, Qger13). Out of 25 NIL pairs with the UH007 genetic background, five pairs showed significant differences in at least one trait for two QTL (Qger2, Qger21). However, Qger16, Qger10 and Qger13 were most likely false positives. The genetic background possibly affected NIL pairs comparisons due to linkage drag and/or epistasis with residual loci from the DP in non-target regions. In conclusion, validation rates were disappointingly low, which further indicates that GER resistance is controlled by many low-effect QTL.

Timing of fungicide application for the control of Gibberella ear rot of maize

Gibberella ear rot (GER) of maize is of common occurrence in southern Brazil. The increased risk of the disease in this region is associated with wide adoption of no-till and seasonal weather conducive for epidemics, thus requiring fungicide applications to protect against the disease. However, limited information is available about the best timing for fungicide applications aiming at disease suppression. A two-year split-plot randomized complete block design experiment was conducted to determine whether early or late application of a fungicide at various intervals up to week relative to inoculation 5–6 days after silk emergence affects disease control. Treatments consisted of an application of a mix of three active ingredients present in two commercial formulations (azoxystrobin + cyproconazole and carbendazim) at different times relative to inoculation: 2, 4 or 6 days either prior (preventatively) or after (curatively) inoculation. The non-treated check consisted of non-sprayed plots. All plots were inoculated using the silk-channel-method by injecting 2 ml of macroconidia suspension (2 × 105 macroconidia/ml) of an aggressive F. meridionale isolate at 5–6 days after silk-emergence. The mean GER severity of the non-treated plots was 24.4 and 27.1 % for Maximus and P32R48H hybrids, respectively. Mean GER severity differed among application times for both hybrids (P < 0.0001). The application timing of 2, 4, and 6 days showed an average control efficacy of 52, 34, and 20 %, for Maximus hybrid and 40, 15, and 9 % for P32R48H hybrid. Although maize yield was not significantly improved, a fungicide application at two days around inoculation (preventative or curative) was the best fungicide application timing to reduce GER severity in matured grain, and could be incorporated into a disease management program.

Larval western bean cutworm feeding damage encourages the development of Gibberella ear rot on field corn.

A 2 year study was conducted to determine whether western bean cutworm (Striacosta albicosta Smith) (WBC) larval feeding damage increases severity of the fungal disease Gibberella ear rot [Fusarium graminearum (Schwein.) Petch] in field corn (Zea mays L.). The effect of a quinone-outside inhibiting fungicide, pyraclostrobin, on Gibberella ear rot severity and mycotoxin production, both with and without WBC pressure, was also evaluated. The impact of each variable was assessed individually and in combination to determine the effect of each upon ear disease severity. There was a positive correlation between the presence of WBC larvae in field corn and Gibberella ear rot severity under inoculated conditions in the 2 years of the experiment. An application of pyraclostrobin did not impact Gibberella ear rot development when applied at corn growth stage R1 (silks first emerging). Feeding damage from WBC larvae significantly increases the development of F. graminearum in field corn. We conclude that an effective integrated management strategy for Gibberella ear rot should target the insect pest first, in an effort to limit disease severity and subsequent mycotoxin production by F. graminearum in kernels. © 2016 Society of Chemical Industry.

Field evaluation of maize for Gibberella ear rot resistance using silk channel and kernel inoculation with Fusarium meridionale

Gibberella ear rot (GER) is a fungal disease of increasing concern to maize production in southern Brazil. A 2-year field experiment was conducted to evaluate GER resistance in 14 hybrids inoculated with a Fusarium meridionale isolate using the silk-channel and the pin inoculation method. Two disease-related variables, GER severity and Fusarium-infected kernel (FIK), and plot yield were assessed. Significant hybrid x inoculation method interaction was found for GER severity (P < 0.0001), FIK (P < 0.0001), and yield (P = 0.0328). No significant correlation was observed between all pair of variables for both methods. GER resistance varied among hybrids; most were classified as moderately susceptible based on the pin inoculation method (11/14) and the silk-channel method (8/14). No maize hybrid was completely resistant, which confirms the challenges of using host plant resistance for GER control.

Fusarium graminearum Isolates from Wheat and Maize in New York Show Similar Range of Aggressiveness and Toxigenicity in Cross-Species Pathogenicity Tests.

This study aimed to assess whether pathogenic Fusarium graminearum isolates from wheat and maize were more aggressive on their host of origin and whether aggressiveness was influenced further by B-trichothecene chemotype. Fifteen isolates were selected from a contemporary collection of isolates surveyed in New York in 2011 to 2012 to represent diversity of host of origin and chemotype. Three pathogenicity assays were used to evaluate and compare these isolates. Fusarium head blight (FHB) severity and trichothecene production in wheat, and maize seedling blight were evaluated in greenhouse inoculation experiments, and Gibberella ear rot (GER) severity and trichothecene production were evaluated in maize ears inoculated in the field. Our results showed among F. graminearum isolates a wide variation in aggressiveness and mycotoxin production toward wheat and maize and these isolates could not be structured by their host of origin or by chemotype. Moreover, aggressiveness rank order changed according to the host/organ evaluated. This indicates that relative susceptibility at the seedling stage may not predict susceptibility of ears. Significant correlations were observed of total trichothecenes (deoxynivalenol [DON] and its acetylated derivatives) produced with FHB and GER severity on wheat and maize, respectively. One isolate did not produce DON or ADON in wheat or maize kernels, yet was aggressive on both hosts. Nine of the fifteen isolates produced small amounts of zearalenone (ZON) in maize kernels, but not in wheat kernels, and ZON level was not correlated with GER severity. F. graminearum isolates from New York showed wide variation in aggressiveness and mycotoxin production toward susceptible wheat and maize. Neither host of origin nor trichothecene chemotype appeared to structure the populations we sampled.

Genomic Predictability of Interconnected Biparental Maize Populations

Intense structuring of plant breeding populations challenges the design of the training set (TS) in genomic selection (GS). An important open question is how the TS should be constructed from multiple related or unrelated small biparental families to predict progeny from individual crosses. Here, we used a set of five interconnected maize (Zea mays L.) populations of doubled-haploid (DH) lines derived from four parents to systematically investigate how the composition of the TS affects the prediction accuracy for lines from individual crosses. A total of 635 DH lines genotyped with 16,741 polymorphic SNPs were evaluated for five traits including Gibberella ear rot severity and three kernel yield component traits. The populations showed a genomic similarity pattern, which reflects the crossing scheme with a clear separation of full sibs, half sibs, and unrelated groups. Prediction accuracies within full-sib families of DH lines followed closely theoretical expectations, accounting for the influence of sample size and heritability of the trait. Prediction accuracies declined by 42% if full-sib DH lines were replaced by half-sib DH lines, but statistically significantly better results could be achieved if half-sib DH lines were available from both instead of only one parent of the validation population. Once both parents of the validation population were represented in the TS, including more crosses with a constant TS size did not increase accuracies. Unrelated crosses showing opposite linkage phases with the validation population resulted in negative or reduced prediction accuracies, if used alone or in combination with related families, respectively. We suggest identifying and excluding such crosses from the TS. Moreover, the observed variability among populations and traits suggests that these uncertainties must be taken into account in models optimizing the allocation of resources in GS.

Variation and covariation for Gibberella ear rot resistance and agronomic traits in testcrosses of doubled haploid maize lines

Gibberella ear rot (GER) of maize caused by Fusarium graminearum reduces grain yield and leads to contamination of the grains with deoxynivalenol (DON), a mycotoxin that adversely affects the health of humans and animals. The objectives of this study were to (1) analyze means and genotypic variances for line per se performance (LP) and testcross performance (TP) of doubled haploid (DH) lines for GER severity and DON concentration as well as for some agronomic traits, (2) examine correlations among these traits, (3) validate QTL for resistance detected in previous studies for LP and their effect on TP and (4) investigate the relative efficiency of indirect selection (RE) for LP to improve TP. Testcross progenies of 94 DH lines originating from four flint populations were developed using a susceptible dent tester as pollinator. Artificial inoculations with F. graminearum led to appreciable disease development. Average TP for GER severity and DON concentration were lower than the mean mid-parent values of the tester and DH lines, indicating mid-parent heterosis for resistance. Genotypic variation for resistance was significant for LP and TP. Genotypic correlations between LP and TP were low and resistance QTL for LP had no significant effects on TP. Accordingly, RE for resistance was low, suggesting to allocate resources mostly to the evaluation of testcrosses. Correlations of resistance to GER and DON contamination with grain yield (measured under non-inoculated conditions) were not significant, indicating that selection for resistance and higher grain yield can be carried out simultaneously.

Colocalization of QTL for Gibberella Ear Rot Resistance and Low Mycotoxin Contamination in Early European Maize

Gibberella ear rot (GER) of maize (Zea mays L.) caused by Fusarium graminearum Schwabe is a major disease in Europe that reduces grain yield and leads to contamination with deoxynivalenol (DON) and zearalenone (ZEA), two important mycotoxins. The objectives of our study were to (i) estimate quantitative‐genetic parameters for GER severity and DON and ZEA contaminations, (ii) map quantitative trait loci (QTL) for GER resistance and low DON and ZEA contaminations, and (iii) examine the prospects of marker‐assisted selection (MAS) for these traits. The materials comprised 150 doubled haploid lines from a cross of two maize inbreds that were evaluated in four environments under artificial inoculation with F. graminearum. On the basis of entry means across environments, heritabilities were moderately high (0.65–0.77), and QTL analyses identified four to six QTL for these traits. Colocalization of QTL in bins 1.11 and 2.04, which had large effects and together explained 29 to 35% of the total genotypic variance, suggested the presence of pleiotropic QTL. This was supported by strong genotypic correlations among these traits (0.89–0.95). In view of the lower costs of genotyping compared with field trials and mycotoxin determinations, our study showed that in breeding for GER resistance and low DON and ZEA contaminations, MAS should be conducted in off‐season nurseries and MAS in combination with phenotypic selection in the crop season.