Zum Auftreten von Kakaomotte (Ephestia elutella Hübner) und Dörrobstmotte (Plodia interpunctella Hübner) in Rohkakaolagern und Fabrikräumen der Süßwarenindustrie

In mehrjährigen Freiland‐ und Laborversuchen wurde der Einfluß auf den Populationsaufbau von Sitobion (Macrosiphum) avenae (Fabr.) und Rhopalosiphum padi L. an mit der Spelzenbräune des Weizens, Septoria nodorum Berk., besiedelten Weizenpflanzen untersucht. Neben einer höheren Sterberate der Aphiden vor dem Erreichen der Geschlechtsreife konnte eine Verkürzung der reproduktiven Phase, eine Verringerung der Anzahl der Nachkommen sowie eine Abnahme der Gesamtlebenszeit der auf infizierten Geweben siedelnden Aphiden ermittelt werden.     

Sporulation of Septoria nodorurn (and S. tritici) on spring wheat cvs Kolibri and Maris Butler in relation to growth stage, plant part and time of season

Sporulation of Septoria nodorum was assessed on inoculated spring wheat cvs Kolibri and Maris Butler. The time from inoculation to first production of spores (latent period) was similar over a range of constant temperatures (12–18°C) but was shorter for Kolibri at 6°C and at 24°C. Spore production was greatest during the period of stem extension and, for equal amounts of disease, was twice as great on Kolibri as on Maris Butler. Spore production on leaves was much more intense with Septoria tritici than S. nodorum for equal amounts of disease, and was less intense on heads than on leaves for both pathogens. Inoculation of plants resulted in significant losses in yield. Mans Butler consistently out-performed Kolibri on each component of yield. Kolibri was particular affected: 1000-grain weights were reduced at each growth stage tested especially by S. nodorum, grain numbers and yield/head were reduced particularly following inoculation at heading. Spore production of S. nodorum during the period of stem extension increased to a peak in early July and then declined but no reliable relationship with monitored weather accounted for this seasonal trend.     

Components of partial resistance as criteria for identifying resistance

The components of partial resistance, incubation period, lesion area, latent period and sporulation were recorded on plants of six winter and two spring wheat cultivars which had been artificially inoculated with Septoria nodorum spores. Incubation period gave a guide as to how the cultivars would respond in the field to Septoria nodorum but statistical analysis showed that it could not be used alone to predict accurately the resistance of each cultivar to the pathogen. Average sporulation, however, could be used with more confidence for predicting the field resistance of the cultivars. From a regression analysis of NIAB rating versus incubation period, lesion area, latent period and sporulation, an equation was devised to obtain resistance indices for each cultivar. These resistance indices clearly reflected the NIAB ratings for the cultivars. It would therefore appear that resistance indices could be used as a pre-field evaluation method for identifying resistance to Septoria nodorum and thus be a valuable technique in breeding programmes.     

Genetic analysis of disease susceptibility contributed by the compatible Tsn1–SnToxA and Snn1–SnTox1 interactions in the wheat-Stagonospora nodorum pathosystem

Stagonospora nodorum is a foliar pathogen of wheat that produces several host-selective toxins (HSTs) and causes the disease Stagonospora nodorum blotch (SNB). The wheat genes Snn1 and Tsn1 confer sensitivity to the HSTs SnTox1 and SnToxA, respectively. The objectives of this study were to dissect, quantify, and compare the effects of compatible Snn1–SnTox1 and Tsn1–SnToxA interactions on susceptibility in the wheat-S. nodorum pathosystem. Inoculation of a wheat doubled haploid population that segregates for both Snn1 and Tsn1 with an S. nodorum isolate that produces both SnTox1 and SnToxA indicated that both interactions were strongly associated with SNB susceptibility. The Snn1–SnTox1 and Tsn1–SnToxA interactions explained 22 and 28% of the variation in disease, respectively, and together they explained 48% indicating that their effects are largely additive. The Snn1–SnTox1 interaction accounted for 50% of the variation when the population was inoculated with an S. nodorum strain where the SnToxA gene had been mutated, eliminating the Tsn1–SnToxA interaction. These results support the theory that the wheat-S. nodorum pathosystem is largely based on multiple host–toxin interactions that follow an inverse gene-for-gene scenario at the host–toxin interface, but disease exhibits quantitative variation due to the mainly additive nature of compatible interactions. The elimination of either Snn1 or Tsn1 toxin sensitivity alleles resulted in decreased susceptibility, but the elimination of both interactions was required to obtain high levels of resistance. We propose the use of molecular markers to select against Snn1, Tsn1, and other toxin sensitivity alleles to develop wheat varieties with high levels of SNB resistance.     

Salicylic and Jasmonic acids in regulation of the proantioxidant state in wheat leaves infected by <Emphasis Type="Italic">Septoria nodorum</Emphasis> Berk

Influence of mediators of the signal systems of salicylic (SA) and jasmonic (JA) acids and their mixture on reactive oxygen species’ (ROS) (superoxide radical and O₂^·− H₂O₂) generation and activity of oxidoreductases (oxalate oxidase, peroxidase and catalase) in leaves of wheat Triticum aestivum L. infected by Septoria leaf blotch pathogen Septoria nodorum Berk has been studied. Presowing treatment of seeds by SA and JA decreased the development rate of fungus on wheat leaves. SA provided earlier inductive effect on production of O₂^·− and H₂O₂ compared with JA. The protective effect of the salicylic and jasmonic acids against Septoria leaf blotch pathogen was caused by activation of oxalate oxidase, induction of anion and cation peroxidases, and decrease of catalase activity. Ability of compounds to stimulate ROS in the plant tissues can be used as criteria for evaluation of immune-modulating activity of new substances for protection of the plants.     

Inheritance of Resistance to Septoria Blotch in Common Wheat Sample MN81330

Wheat samples described in literature as resistant to septoria glume blotch were assessed for their response to inoculation with Septoria nodorum Berk. Three days after inoculation with the causal agent, samples Klein Titan (k-41772), Mian Jang (k-61568), Walter (k-54585), Reisler (k-59505), Rempart (k-59493), PIN/BOW (k-62838), MN81330 (k-60785), Frondoso (k-46736), Sokrates (k-58179) were classified as resistant to infection. Seven days after inoculation, only samples Reisler and Mian Jang were regarded as resistant. The genetic control of glume blotch resistance was studied by hybridological analysis in sample MN81330. Resistance of this sample manifested in a longer latent period of the disease is controlled by two dominant complementary genes not linked to the gene Lr24 responsible for resistance to leaf rust, to the genes responsible for coleoptile coloration, and to minor genes that increase expression of the major ones.     

Endophytic Fungi in Four Winter Wheat Cultivars (Triticum aestivum L.) Differing in Resistance Against Stagonospora nodorum (Berk.) Cast. & Germ. =Septoria nodorum (Berk.) Berk.

Four winter wheat cultivars with different levels of resistance to Septoria nodorum were investigated at four locations during two vegetation periods. Forty plants per cultivar and site were collected at random at seven defined growth stages from crop emergence to harvest. Samples from roots, culms, leaves, glumes and kernels were examined for the occurrence of endophytic fungi after surface sterilization. 83% of the 26944 isolates sporulated and were assigned to 213 species. The most frequent were: Septoria nodorum (20.1%), Alternaria tenuissima (9.8%), Epicoccum purpurascens (9.1%), Idriella bolleyi (6.9%), Fusarium graminearum (5.3%), Fusarium culmorum (4.0%), Cladosporium oxysporum (3.7%), Didymella exitialis (3.1%), Fusarium nivale (2.8%) and Rhizoctonia solani (2.1%). Each species occurred preferentially in one or more plant organs. A factorial analysis of variance showed that plant organ, sampling site, vegetation, period and cultivar in decreasing order of importance influenced the quantitative and qualitative composition of the fungal populations. No relationship between endophytic fungi was found to be constantly antagonistic or mutualistic. Septoria nodorum was isolated mainly from culms. The number of S. nodorum isolates differed significantly between cultivars in culms and glumes but not in flag leaves. The results are discussed in relation to resistance breeding and the effect endophytic fungi, might have on yield.     

The relationship between the resistance of Aegilops umbellulata Zhuk. seedlings to Septoria nodorum Berk. and peroxidase isozyme pattern

The resistance of Aegilops umbellulata Zhuk. to blotch pathogen Septoria nodorum Berk. has been studied. Cytoplasmic peroxidase activity in normal seedlings could not be used for biochemical prediction of Ae. umbellulata resistance to Septoria blotch. At the same time, isoperoxidases with pI ～7.5 and infection-induced activity of anionic isoforms with pI ～3.5 were markers of the resistant Aegilops plants. Aegilops resistance to the fungus depended on the activity of cell wall peroxidases.     

Identification of molecular markers for resistance to Septoria nodorum blotch in durum wheat

The development of Septoria nodorum blotch-resistant cultivars has become a high priority objective for durum wheat breeding programs. Marker-assisted selection enables breeders to improve selection efficiency. In order to develop markers for resistance to Septoria nodorum blotch, a set of F₅ recombinant inbred lines, derived from the crosses Sceptre/3–6, Sceptre/S9–10 and Sceptre/S12–1, was developed based on the F₂-derived family method. Two RAPD markers, designated UBC521₆₅₀ and RC37₅₁₀, were detected by bulked segregant analysis and located approximately 15 and 13.1 centiMorgans (cM) from the resistance gene snbTM, respectively. A SCAR marker was also successfully developed for marker-assisted selection in breeding programs based on the sequence of the RAPD marker UBC521₆₅₀. This is the first report of DNA-based markers linked to resistance for Septoria nodorum blotch in durum wheat. Received: 8 March 2000 / Accepted: 25 June 2000     

Strains of <Emphasis Type="Italic">Bacillus</Emphasis> ssp. regulate wheat resistance to <Emphasis Type="Italic">Septoria nodorum</Emphasis> Berk.

The ability of Bacillus subtilis Cohn and Bacillus thuringiensis Berliner to induce systemic resistance in wheat plants to the casual agent of Septoria nodorum Berk., blotch has been studied. It has been shown that strains of Bacillus ssp. that possess the capacity for endophytic survival have antagonistic activity against this pathogen in vitro. A reduction of the degree of Septoria nodorum blotch development on wheat leaves under the influence of Bacillus spp. was accompanied by the suppression of catalase activity, an increase in peroxidase activity and H₂O₂ content, and expression of defence related genes such us PR-1, PR-6, and PR-9. It has been shown that B. subtilis 26 D induces expression levels of wheat pathogenesis-related (PR) genes which marks a SA-dependent pathway of sustainable development and that B. thuringiensis V-5689 and V-6066 induces a JA/ET-dependent pathway. These results suggest that these strain Bacillus spp. promotes the formation of wheat plant resistance to S. nodorum through systemic activation of the plant defense system. The designed bacterial consortium formed a complex biological response in wheat plants infected phytopathogen.     

The activity of peroxidase in various cell fractions of wheat plants infected with Septoria nodorum berk.

The activities of peroxidase isoforms and hydrogen peroxide content in leaf cuttings of wheat (Triticum aestivum L., cv. Diamant) resistant to Septoria blotch were studied during aging and following the infection with Septoria nodorum Berk. The differential activation of peroxidase isoforms was regulated by hydrogen peroxide level in the tissue. At early stages of fungus development in plant tissues, the decrease in the activities of soluble, membrane and ion-bound fractions of peroxidase elevated the level of hydrogen peroxide in infected tissues and rapidly activated peroxidase isoforms in infected tissues as compared to the aging ones even before disease symptoms appeared. The anionic peroxidases, which were first to respond to the pathogen, seem to stand for wheat resistance to fungal infections and the protection of leaf tissues from oxidative stress.     

Hydrogen peroxide production in wheat leaves infected with the fungus Septoria nodorum Berk. Strains with different virulence

The effect of two strains of the phytopathogenic fungus Septoria nodorum Berk. of different virulence on the intensity of local generation of hydrogen peroxide in common wheat leaves and the role of oxidoreductases in this process was studied. Differences in the pattern of hydrogen peroxide production in wheat plants infected with high- and low-virulence pathogen strains have been found. The low-virulent S. nodorum strain caused a long-term hydrogen peroxide (H₂O₂) generation in the infection zone, whereas the inoculation of leaves with the highly virulent strain resulted in a transient short-term increase in the H₂O₂ concentration at the initial moment of contact between the plant and the fungus. It was shown that the low level of H₂O₂ production by plant cells at the initial stages of pathogenesis facilitates S. nodorum growth and development. The decrease in the H₂O₂ concentration induced by the highly virulent S. nodorum strain is determined by inhibition of the oxalate oxidase activity in plant tissues and by the ability of the fungus to actively synthesize an extracellular catalase. The pattern of hydrogen peroxide generation at the initial stages of septoriosis may serve as an index of virulence of S. nodorum population.     

Effects of inoculation with Septoria nodorum on yield components of spring wheat

Spring wheat, cv. Kolibri, was artificially inoculated with spore suspensions of Septoria nodorum, from the time of full expansion of the third leaf to the end of flowering and the effect on yield components recorded. Most components were reduced by increasing severity of infection and grain weight losses of 56 and 35% were produced on single-stemmed and tillering plants respectively, by the most severe infection. The effects on components of yield differed considerably between the main stems and the tillers and an increase in grain number on moderately infected tillers partly compensated for reductions in yield on the main stem.     

Assessment of Sitotroga cerealella losses in different sorghum varieties under controlled conditions

Crop seeds are generally stored for next crop season and bear losses from vertebrate and invertebrate pests. In invertebrates, stored grain insect pests are mainly responsible for loss in weight and viability issues. Five sorghum varieties, viz. RS-29, Rari-S-4, Rari-SV-10, SPV-462 and Johar-1 were compared for infestation of Sitotroga cerealella under laboratory and semi-field conditions. RS-29 was found to be the most resistant variety and Johar-1 to be the most susceptible when losses were observed after 30, 60 and 90?days of infestation. Maximum infestation and weight loss was observed in Johar-1 (28%). Germination percentage was found to be decreased to 65% in RS-29 and 47% in Johar-1 in laboratory, and 60% in RS-1 and 43% in Johar-1 under semi-field conditions. Possibilities to decrease these losses have been discussed for effective management of stored grain pest losses.     

Hull split date and shell seal in relation to navel orangeworm (Lepidoptera: Pyralidae) infestation of almonds

Hull split date, shell seal, and navel orangeworm, Amyelois transitella (Walker) (Lepidoptera: Pyralidae), infestation data for 19 varieties of almonds, Prunus dulcis (Mill.) D.A. Webb, were analyzed to determine the relationship of shell seal and hull split date on A. transitella infestation. Data for all varieties were collected from three University of California regional almond variety trials from 2003 to 2005, with a total of 8,550 nuts evaluated. A significant negative relationship was found between percentage of shell seal and percentage of navel orangeworm infestation, with lower percentage of shell seal correlating to higher percentage of infestation. Similarly, hull split date was negatively correlated with percentage of infestation, with later splitting varieties trending toward lower percentage of infestation. Although there are outlying varieties, hull split and shell seal are indeed significant components in varietal differences in almond navel orangeworm infestation. Understanding such factors gives insight into both the predictive value of almond characteristics related to navel orangeworm damage as well as other potential indicators.     

Preferential grazing of five varieties of spring barley by wild rabbits (Oryctolagus cuniculus)

Assessment of grazing damage to five varieties of spring barley (Hordeum vulgare L.) by wild rabbits in an enclosed site revealed varietal differences. The variety Atem was consistently least grazed and Triumph most grazed by rabbits. When variety effects were removed from the analysis significant negative correlations were observed between plant height and stem damage. Differences in sugar content of varieties did not fully explain varietal selection by grazing rabbits.     

In vitro screening for resistance against Septoria nodorum blotch in wheat

This study was carried out to develop an in vitro test for the identification of genotypes resistant to Septoria nodorum blotch. The basis for this project was a previous study in which a crude extract of S. nodorum was used as a selective agent (Keller et al. 1994). It was possible to distinguish resistant and susceptible cultivars in an in vitro test with zygotic embryos. In our project we wanted to test whether this in vitro test can also be used to detect resistant and susceptible genotypes in early segregating populations. Specific crosses between eight winter wheat lines showing contrasting resistance reaction for S. nodorum blotch on leaves and ears were made. The resistance level of both leaf and ear was evaluated after artificial inoculation in the field for the parental lines, the F₁ progenies, as well as for segregating F₃ and F₄ populations. In addition, this plant material was tested in vitro using methods similar to those described by Keller et al. (1994), i.e. culturing immature zygotic embryos and mature seeds on selective media. A good agreement between in vitro screening and field resistance on the ear was found for the parental lines, the F₁ and F₄ generation but not for the F₃ generations. This leads to the conclusion that the in vitro screening might be integrated into wheat breeding programs. Populations showing a high susceptibility to the pathogen metabolites in vitro could be discarded. Another promising implementation for wheat breeding would be the screening of advanced breeding material or candidate partners in a crossing program for resistance on the ear. However, the in vitro screening is not precise enough to select single plants in early segregating populations. Received: 18 January 1999 / Accepted: 30 April 1999     

Disease progress of non-specialised fungal pathogens in intraspecific mixed stands of cereal cultivars. II. Field experiments

Epidemic development of Septoria nodorum was examined in pure stands and mixtures of two spring wheat cultivars, Kolibri and Maris Butler. In mixtures, disease development was reduced almost to that of the more resistant pure stand (Maris Butler). Disease levels, however, were low and no significant differences in grain yield per head were demonstrated. Disease development was further investigated for the host-pathogen combinations winter wheat/S. nodorum and winter barley/Rhynchosporium secalis. With both combinations the mixed stands again reduced disease levels to almost that of the more resistant pure stands. In general, mixed stands were more effective against R. secalis, although, with S. nodorum, disease levels were low. The yield response in mixed stands differed for the host cultivars and was not significantly changed by the presence of disease. The complexity of analysing such situations and the implications of these findings for mixtures of cultivars differing in resistance to non-specialised pathogens are discussed.