Library

Notes: Hybrid rye breeding and seed production relies on the cytoplasmic male sterility-inducing Pampa (P)-Cytoplasm. High levels of restoration were recently found in non-adapted rye accessions from Argentina (Pico Gentario, Pastoreo Massaux) and Iran (IRAN IX). To analyse their relative superiority, five seed-parent lines in P cytoplasm were crossed with five inbred lines of these sources and four adapted restorer lines. The 45 F1 hybrids were tested for male-fertility restoration in three locations. Significant (P = 0.01) general and specific combining ability (GCA and SCA respectively) for male-fertility restoration were found. The non-adapted restorer lines were able to restore all seed-parent lines similarly, resulting in hybrids with 55-90% pollen shedding (mean 78%) compared with 2-74% pollen shedding (mean 44%) when adapted restorer lines were used. Significant (P = 0.05) SCA effects were detected in 11 of 45 combinations, nine of them were crosses with adapted pollinator lines. Non-adapted restorer lines showed a high phenotypic stability of male-fertility restoration across locations. Introgression of these exotic sources into the adapted restorer gene pool by repeated backcrossing should result in environmentally stable male fertility in Pampa-based rye hybrids.

Notes: Leaf rust is the most frequent leaf disease of winter rye in Germany. All widely grown population and hybrid varieties are susceptible. This study was undertaken to estimate quantitative-genetic parameters of leaf-rust resistance in self-fertile breeding materials with introgressed foreign leaf-rust resistances and to analyze the relative importance of seedling and adult-plant resistance. Forty-four inbred lines and their corresponding testcrosses with a highly susceptible tester line were grown in a field in four different environments (location-year combinations) with artificial inoculation. Plots were separated by a nonhost to promote autoinfections and minimize interplot interference. Leaf-rust severity was rated on three leaf insertions at three dates. The testcrosses showed a considerably higher disease severity than the lines. High correlations (r ≅ 0.9, P = 0.01) existed among the leaf insertions and the rating dates. Large genotypic variation for resistance was found in both the inbred and testcross populations. Genotype-environment interaction and error variances were of minor importance, thus high entry-mean heritabilities were achieved. A tight correlation between the inbreds and their corresponding testcrosses was found (r = 0.88, P = 0.01). Heterosis for resistance was significant (P = 0.05), but not very important. In a seedling test with 20—30 single-pustule isolates, 34 out of 44 inbreds reacted race-specifically. From the remaining inbred lines, three were medium and seven highly susceptible. In a further greenhouse test with 16 inbreds, seven were susceptible and five were resistant in both seedling and adult-plant stages. The remaining four lines had adult-plant resistance. In conclusion, race-specific leaf-rust resistance can be selected among inbred lines per se. Lines should also be tested in the adult-plant stage.

Notes: The amount of genetic variation among inbred lines and testcrosses, and covariation between both genetic materials, are of crucial importance for selection efficiency in hybrid breeding. To estimate these quantitative genetic parameters for resistance of winter rye (Secale cereale) to head blight caused by Fusarium culmorum, 88 three-way cross hybrids, produced by crossing each of 44 S2 Carsten inbred lines with two unrelated Petkus single-cross testers, were evaluated along with the parental lines over 2 years. Resistance traits were head-blight rating and grain weight per spike relative to the non-inoculated control. Significant genotypic variation occurred among lines and in both testcross series. S2 lines displayed considerably more variation than testcross series. Genotype × environment interaction was more marked among the inbred lines, while estimates of heritability were similar for both genetic materials. Testcrosses showed heterosis for head-blight resistance. No relationship existed between S2 lines and the two testcross series for any resistance trait. This might be caused by an association between inbreeding and Fusarium-head-blight susceptibility and different inbreeding depression among the S2 population. The phenotypic correlations between the testcross series were moderate for both traits (r = 0.58, P 〈 0.01). In conclusion, Fusarium-head-blight resistance has to be selected at the respective heterozygosity levels.

Notes: The first results of three test systems for evaluating the susceptibility of rye inbred lines to foot rot caused by Fusarium culmorum and F. graminearum are presented. The test systems were specifically designed for greenhouse, foliar tent and field experiments. The inbred lines, some of which are being used in commercial hybrids, showed significant variation for resistance. Significant interactions occurred between genotypes and test systems, and within the test systems between genotypes and years or growth stages. A significant correlation existed between susceptibility in the greenhouse and in the field (r = 0.84, P = 0.05), when inoculation in the greenhouse took place at the jointing stage (EC 31). In earlier growth stages, however, this correlation was not significant. In both greenhouse and foliar tent experiments, susceptibility to F. culmorum and F. graminearum was strongly correlated (r = 0.71, 0.87, resp., P = 0.01). In the field, F. culmorum alone was used for artificial inoculation. Genotypic variance and repeatability in the field were highest after inoculation in spring with conidia suspensions. It is concluded that, in inbreeding generations with limited seed quantities, the greenhouse and the foliar-tent test systems offer good possibilities of indirectly improving foot-rot resistance in rye.

Notes: The most effective strategy to control Fusarium head blight (FHB), a devastating disease of small-grain cereals, is breeding resistant cultivars. This resistance study of F1 crosses, F2 and backcross generations of triticale estimates heterosis, general and specific combining ability (GCA, SCA), additive and dominance effects and compares parents with segregating generations. The genetic material consisted of 10 parents with their 45 F1 crosses and of six parents with their 15 F2 progeny and backcrosses to each parent. Genotypes were grown in various environments and artificially inoculated with an aggressive isolate of F. culmorum. FHB was assessed, by visual rating, as the mean of four to five individual ratings of disease development. Heterosis for FHB was of little importance. The correlation between the FHB rating of F1 crosses and their mid-parent performance was close. GCA was the predominant source of variation, although the significance of the SCA variance also implied non-additive allelic interaction. The preponderance of additive gene effects is encouraging for increasing resistance by a recurrent selection programme. The relationship between the GCA effect of a parent and its per se performance was close, which gives the possibility of predicting FHB resistance in F1 crosses. Additive effects were predominant in the F2 progeny and also in the backcrosses. Transgressive segregants could not be detected. Searching for them should be postponed to the F3 or later generations.

Notes: Fusarium culmorum is one of the most important Fusarium species causing head blight infections in wheat, rye, and triticale. It is known as a potent mycotoxin producer with deoxynivalenol (DON), 3-acetyl deoxynivalenol (3-ADON), and nivalenol (NIV) being the most prevalent toxins. In this study, the effect of winter cereal species, host genotype, and environment on DON accumulation and Fusarium head blight (FHB) was analysed by inoculating 12 rye, eight wheat, and six triticale genotypes of different resistance levels with a DON-producing isolate at three locations in 2 years (six environments). Seven resistance traits were assessed, including head blight rating and relative plot yield. In addition, ergosterol, DON and 3-ADON contents in the grain were determined. A growth-chamber experiment with an artificially synchronized flowering date was also conducted with a subset of two rye, wheat and triticale genotypes. Although rye genotypes were, on average, affected by Fusarium infections much the same as wheat genotypes, wheat accumulated twice as much DON as rye. Triticale was least affected and the grain contained slightly more DON than rye. In the growth-chamber experiment, wheat and rye again showed similar head blight ratings, but rye had a somewhat lower relative head weight and a DON content nine times lower than wheat (3.9 vs. 35.3 mg/kg). Triticale was least susceptible with a five times lower DON content than wheat. Significant (P = 0.01) genotypic variation for DON accumulation existed in wheat and rye. The differences between and within cereal species in the field experiments were highly influenced by environment for resistance traits and mycotoxin contents. Nevertheless, mean mycotoxin content of the grain could not be associated with general weather conditions in the individual environments. Strong genotype-environment interactions were found for all cereal species. This was mainly due to three wheat varieties and one rye genotype being environmentally extremely unstable. The more resistant entries, however, showed a higher environmental stability of FHB resistance and tolerance to DON accumulation. Correlations between resistance traits and DON content were high in wheat (P = 0.01), with the most resistant varieties also accumulating less DON, but with variability in rye. In conclusion, the medium to large genotypic variation in wheat and rye offers good possibilities for reducing DON content in the grains by resistance selection. Large confounding effects caused by the environment will require multiple locations and/or years to evaluate FHB resistance and mycotoxin accumulation.

Notes: Fusarium culmorum and F. graminearum Groups 1 and 2 cause seedling blight, crown rot, foot rot and head blight in wheat and rye that may affect grain yield and quality for baking and feeding. This review starts with an analysis of Fusarium populations with regard to their genetic variation for aggressiveness, mycotoxin production, and isolate-by-host genotype interaction. To assess resistance in the different host growth stages, quantitative inoculation and disease assessment techniques are necessary. Based on estimated population parameters, breeding strategies are reviewed to improve Fusarium resistance in wheat and rye. Epidemiological and toxicological aspects of Fusarium resistance that are important for resistance breeding are discussed. F. culmorum and F. graminearum display large genetic variation for aggressiveness in isolate collections and in naturally occurring populations. The production of mycotoxins, especially deoxynivalenol and its derivatives, is a common trait in these populations. Significant isolate-by-host genotype interactions were not found across environments in wheat and rye.Artificial infections in the field are indispensable for improving Fusarium crown rot, foot rot and head blight resistance in wheat and rye. For a reliable disease assessment of large populations, disease severity ratings were found to be the most convenient. The differentiation of host resistance is greatly influenced by an array of nongenetic factors (macro-environment, microclimate, host growth stage, host organ) that show significant interactions with host genotype. Selection for environmentally stable resistance has to be performed in several environments under a maximum array of different infection levels. Selection in early growth stages or on one plant organ does not in most cases allow prediction of resistance in adult-plant stages or another plant organ.Significant genetic variation for resistance exists for all Fusarium-incited diseases in breeding populations of wheat and rye. The patho-systems studied displayed a prevalence of additive gene action with no consistent specific combining ability effects and thus rapid progress can be expected from recurrent selection. In wheat, intensive testing of parental genotypes allows good prediction of the mean head blight resistance after crossing. Subsequent selection during selfing generations enables the use of transgression towards resistance. In hybrid breeding of winter rye, the close correlation between foot rot resistance of inbred lines and their GCA effects implies that selection based on the lines per se should be highly effective. This is not valid for F. culmorum head blight of winter rye caused by a greater susceptibility of the inbred lines compared to their crosses.For both foot rot and head blight resistance, a high correlation between the resistance to F. graminearum and F. culmorum was found in wheat and rye. Mycotoxin accumulation occurs to a great extent in naturally and artificially infected plant stands. The correlation between resistance traits and mycotoxin contents are medium and highly dependent on the environment. Further experiments are needed to clarify whether greater resistance will lead to a correlated reduction of the mycotoxin content of the grains under natural infection.

Notes: Gibberella zeae (anamorph Fusarium graminearum) causes head blight of cereals and contaminates grains with mycotoxins such as deoxynivalenol (DON). To determine the correlations among aggressiveness traits, fungal colonization and DON production, 50 progeny from a segregating population of G. zeae were inoculated onto a susceptible winter wheat cultivar in three field environments (year–location combinations). Aggressiveness traits were measured as head-blight rating and plot yield relative to noninoculated plots. Fungal colonization, measured as Fusarium exoantigen (ExAg) content, and DON production were analysed with two ELISA formats. Disease severity was moderate to high based on head-blight rating and relative plot yield. Fusarium ExAg content and DON production ranged from 0·26–1·41 units and from 4·18–43·70 mg kg−1, respectively. Significant (P = 0·01) genotypic variation was found for all traits. Heritability for Fusarium ExAg content was rather low because of high progeny–environment interaction and error. DON/Fusarium ExAg ratio did not vary significantly (P 〉 0·1) among progeny. Correlation between DON production and Fusarium ExAg content across environments was high (r = 0·8, P = 0·01), but no covariation existed between aggressiveness traits and DON/Fusarium ExAg content ratio.

Notes: Abstract The amount of genetic variation for resistance to foot rot caused by Pseudocercosporella herpotrichoides, Fusarium spp., and Microdochium nivale and for resistance to head blight caused by Fusarium culmorum are important parameters when estimating selection gain from recurrent selection in winter rye. One-hundred and eighty-six full-sib families of the selfincompatible population variety Halo, representing the Petkus gene pool, were tested for foot-rot resistance at five German location-year combinations (environments) and for head-blight resistance in three environments with artificial inoculation in all but one environment. Foot-rot rating was based on 25 stems per plot scored individually on a 1–9 scale. Head-blight resistance was plotwise scored on a 1–9 scale and, additionally, grain-weight per spike was measured relative to the non-inoculated control plots. Significant estimates of genotypic variance and medium-sized heritabilities (h 2=0.51–0.69) were observed in the combined analyses for all resistance traits. In four out of five environments, the amount of genetic variance was substantially smaller for foot-rot than for head-blight rating. Considerable environmental effects and significant genotype-environment interactions were found for both foot-rot and head-blight resistance. Coefficients of error-corrected correlation among environments were considerably closer than phenotypic correlations. No significant association was found between the resistances to both diseases (r=-0.20 to 0.17). In conclusion, intra-population improvement by recurrent selection should lead to substantial higher foot-rot and head-blight resistances due to significant quantitative genetic variation within Halo. Selection should be carried out in several environments. Lack of correlation between foot-rot and head-blight resistance requires separate infection tests for improving both resistances.

Notes: Abstract  Hybrid rye breeding and seed production is based on the cytoplasmic male sterility (CMS)-inducing Pampa (P)-cytoplasm. For restoring male fertility in the hybrids, dominant, nuclear restorer genes are necessary. However, current pollinator lines are only partial restorers. Effective restorers were recently detected in the German inbred line L18 and in materials originating from the Argentinian rye cultivar Pico Gentario and an Iranian primitive rye accession called IRAN IX. F2 populations were developed for each of these three restorer sources to map the responsible genes by means of RFLP (restriction fragment length polymorphism) markers. For this purpose, homo- and heterologous DNA probes were used leading to 101 polymorphic marker loci in total. For phenotypic evaluation, 100 to 134 randomly chosen plants from each of the populations were cloned and grown at two or three locations with two plants each. Segregation ratios of pollen fertility in the F2 populations with L18 and IRAN IX were in accordance with a monogenic dominant inheritance. The segregation pattern for Pico Gentario indicated complementary gene action. Major dominant restorer genes were detected on chromosomes 1RS (L18) and 4RL (Pico Gentario, IRAN IX). The gene on 1RS explained 54% of the phenotypic variation and that on 4 RL 59% and 68% in the Pico Gentario and IRAN IX populations, respectively. Additionally, three minor genes from L18 were identified on chromosomes 3RL, 4RL and 5R. In the Pico Gentario population, a dominant modifier gene contributed by the female parent was found on chromosome 6R. This gene significantly enhanced the expression of the major restorer gene but on its own was not able to restore any degree of fertility. The map-distances between the major restorer loci and at least one flanking marker were small in all three F2 populations (5–6 cM). In Pico Gentario an unfavorable linkage exists between the major restorer gene and a QTL for plant height. Since highly effective restorers are scarce in actual breeding populations, the major restorer genes detected on chromosomes 1 RS and 4RL should be introgressed into actual restorer lines. This is facilitated by using the closely linked molecular markers described.