RT Dissertation/Thesis
T1 Genetic analysis of resistance to ear rot and mycotoxin contamination caused by Fusarium graminearum in European maize
A1 Martin,Matthias
WP 2012/04/18
AB Maize is affected by a number of diseases. Among the various ear rots of maize, Gibberella ear rot (GER) caused by Fusarium graminearum is prevalent in Central Europe. This fungal pathogen produces secondary metabolites (mycotoxins), which adversely affect the health of humans and animals. Two important mycotoxins are the immunosuppressant deoxynivalenol (DON) and the mycoestrogen zearalenone (ZEA). The most efficient method to reduce mycotoxin contamination in maize is cultivation of resistant varieties. However, resistance breeding using classical phenotypic selection is laborious and time-consuming. Therefore, marker-assisted selection (MAS) may be a promising alternative to classical selection. Furthermore, for setting up a breeding program, knowledge about the relevance of the different modes of gene action and genotypic correlations among resistance and agronomic traits is required.
The objectives of this study were to (1) estimate quantitative genetic parameters for GER severity and mycotoxin concentration in connected populations of doubled haploid (DH) lines, (2) map quantitative trait loci (QTL) for GER resistance and reduced mycotoxin contamination in these populations, (3) examine the congruency of QTL in these populations, (4) evaluate the prospects of using MAS to breed for GER resistance and reduced mycotoxin contamination, (5) estimate the genotypic correlation between the resistance of DH lines per se and the resistance of their testcrosses, (6) evaluate the influence of selection for increased resistance on agronomic performance of hybrids and (7) examine the relevance of different modes of gene action involved in the expression of the resistance in flint maize.
Three field experiments were conducted, each of which comprised a different set of plant material. Experiment I comprised five DH line populations derived from the following F1 crosses among elite flint inbred lines: D152×UH006, D152×UH007, UH007×UH006, UH009×UH006 and UH009×UH007. Experiment II comprised testcross progenies of 94 DH lines and a dent single cross tester. Experiment III comprised the five F1 crosses, from which the DH populations had been derived, the F2 and the first backcross generations to the parents (BC1-P1, BC1-P2) as well as the two parent lines of each cross. Plants were artificially infected with spores of F. graminearum shortly after mid-silking using the silk channel inoculation technique. The DH lines were genotyped with simple sequence repeat (SSR) DNA markers, genetic linkage maps were constructed and QTL analyses were performed for resistance to GER, DON and ZEA contamination. 
Estimates of genotypic and genotype-by-environment interaction variances in Experiment I for GER severity and mycotoxin concentration were significant and heritabilities were moderately high to high in all populations. Thus, differences among DH lines for the resistance traits were mainly caused genetically and the resistance response varied depending on the environment. Owing to the effectiveness of artificial inoculation, the prospects are good to improve line resistance using a small number of test environments. 
QTL were detected in the four largest populations. Depending on the population, the mapped QTL together explained 21-51% of the genotypic variance for GER severity and 19-45% for DON concentration and 52% for ZEA concentration. Additive gene action was more important than digenic interactions of QTL, as indicated by the number of QTL having significant additive effects, their relative contributions to the total genotypic variance explained and the magnitude of their effects.
Colocalized QTL for resistance to GER and mycotoxin contamination were identified in each mapping population. This was in agreement with strong genotypic correlations among these traits. QTL located at similar positions were detected across three populations in two chromosomal regions and across two populations in additional two regions. The results of this study indicated that a combination of classical phenotypic selection and MAS is a promising strategy for resistance breeding.
In Experiment II, significant genotypic variation for resistance in lines and testcrosses showed that selection will be successful in both groups. Owing to low genotypic correlations between lines and testcrosses, however, resources should be mainly allocated to the evaluation of GER in testcrosses. Correlations of resistance with agronomic traits were weak or not significant. Therefore, selection for resistance and better agronomic performance can be carried out simultaneously. 
In Experiment III, generation means analysis indicated a prevalence of additive gene action for resistance. Significant dominance effects were found in only one cross for resistance to GER, but in four crosses for resistance to DON contamination. Owing to prevalence of additive gene action, the prospects are good to improve the resistance of the flint germplasm and to accumulate more favorable gene combinations in future breeding lines. Comparing the hybrid performance of flint×flint crosses of Experiment II and flint×dent crosses of Experiment III with their corresponding mid-parent performances indicated mid-parent heterosis for resistance. Therefore, prediction of hybrid performance based on performance of their parents will be possible only to a very limited extent. 
Future research should focus on fine mapping and validating of the detected QTL. For an efficient use of the QTL in a marker-assisted breeding program, knowledge about their effects in different genetic backgrounds is needed. Of particular importance are thereby the QTL effects in flint×dent crosses, which represent the preferred type of hybrid in Central European maize breeding programs.

K1 Mais
K1 Fusarium graminearum
K1 Deoxynivalenol
K1 QTL
K1 Resistenzzüchtung
PP Hohenheim
PB Kommunikations-, Informations- und Medienzentrum der Universität Hohenheim
UL http://opus.uni-hohenheim.de/volltexte/2012/694