Detached Leaf Segments Research Articles

Identification of quantitative trait loci associated with leaf rust resistance in rye by precision mapping

BackgroundLeaf rust (LR) is among the most destructive fungal diseases of rye (Secale cereale L.). Despite intensive research using various analytical and methodological approaches, such as quantitative trait locus (QTL) mapping, candidate gene expression analysis, and transcriptome sequencing, the genetic basis of the rye immune response to LR remains unclear.ResultsA genome-wide association study was employed to detect QTLs controlling the immune response to LR of rye. A mapping population, G38A, was constructed by crossing two inbred lines: 723 (susceptible to LR) and JKI-NIL-Pr3 (a donor of the LR resistance gene Pr3). For genotyping, SNP-DArT and silico-DArT markers were used. Resistance phenotyping was conducted by visual assessment of the infection severity in detached leaf segments inoculated with two isolates of Puccinia recondita f. sp. secalis, namely, 60/17/2.1 (isolate S) in the main experiment and 86/n/2.1_5x (isolate N) in the validation experiment, at 10 and 17 days post-infection (dpi), respectively.In total, 42,773 SNP-DArT and 105,866 silico-DArT markers were included in the main analysis including isolate S, of which 129 and 140 SNP-DArTs and 767 and 776 silico-DArTs were significantly associated (p ≤ 0.001; − log10(p) ≥ 3.0) with the immune response to LR at 10 and 17 dpi, respectively. Most significant markers were mapped to chromosome 1R. The number of common markers from both systems and at both time points occupying common chromosomal positions was 37, of which 21 were positioned in genes, comprising 18 markers located in exons and three in introns. This gene pool included genes encoding proteins with a known function in response to LR (e.g., a NBS-LRR disease resistance protein-like protein and carboxyl-terminal peptidase).ConclusionThis study has expanded and supplemented existing knowledge of the genetic basis of rye resistance to LR by (1) detecting two QTLs associated with the LR immune response of rye, of which one located on the long arm of chromosome 1R is newly detected, (2) assigning hundreds of markers significantly associated with the immune response to LR to genes in the ‘Lo7’ genome, and (3) predicting the potential translational effects of polymorphisms of SNP-DArT markers located within protein-coding genes.

An in vitro bioassay for evaluating the virulence of Pseudomonas savastanoi pv savastanoi isolates on olive

Pseudomonas savastanoi pv. savastanoi causes olive knot disease that afflicts olive trees globally. A sensitive and reproducible in vitro pathogenicity bioassay using detached leaf segments was developed after isolation of Psav on KB medium amended with vancomycin, cephalexin and cycloheximide. Symptoms were clear under 20X magnification after 10 days. This bioassay will facilitate rapid screening of olive germplasm collection for resistance to Psav.

Sugar Starvation Enhances Leaf Senescence and Genes Involved in Sugar Signaling Pathways Regulate Early Leaf Senescence in Mutant Rice

To clarify the complex regulatory relationship between changes in sugar content and leaf senescence during the grain-filling stage of rice, genotype-dependent differences in sugar content and the temporal transcriptional patterns of genes involved in sugar signaling pathways were determined in mutant rice exhibiting early leaf senescence and its wild type Zhefu 142. The effects of exogenous glucose or sucrose on the senescence of detached leaves under dark conditions were also investigated. Chlorophyll, soluble sugar, sucrose and fructose contents decreased, whereas electrolytic leakage and malondialdehyde levels increased in mutant leaves at the grain-filling stage. These results suggested that sugar starvation is positively correlated with the early leaf senescence of mutant plants. Detached leaf segments incubated in exogenous sugar solutions under dark conditions exhibited delayed senescence. The high expression of Hxk1 in leaves of mutant plants at the initial grain-filling stage suggested that Hxk1 is involved in the hexose-sensing process at the early stage of leaf senescence. The low expression levels of Hxk2 and Frk1 in the senescing leaves of mutant rice during the grain-filling stage are indicative of weakened hexose phosphorylation. In addition, the high expression levels of SuSy1, SuSy2 and SuSy4 in leaves of mutant plants at the initial grain-filling stage are accompanied by the high transcript levels of SUT1, which favor sucrose translocation and remobilization from the early senescing leaves of mutant rice. The relatively reduced transcript levels of chFBP, cyFBP, SPS1, SPS2 and SPS6 indicated that during the grain-filling stage, sucrose biosynthesis is weakened in the senescing leaves of mutant rice.

Expression of Pinellia pedatisecta Lectin Gene in Transgenic Wheat Enhances Resistance to Wheat Aphids.

Wheat aphids are major pests during the seed filling stage of wheat. Plant lectins are toxic to sap-sucking pests such as wheat aphids. In this study, Pinellia pedatisecta agglutinin (ppa), a gene encoding mannose binding lectin, was cloned, and it shared 92.69% nucleotide similarity and 94% amino acid similarity with Pinellia ternata agglutinin (pta). The ppa gene, driven by the constitutive and phloem-specific ribulose bisphosphate carboxylase small subunit gene (rbcs) promoter in pBAC-rbcs-ppa expression vector, was transferred into the wheat cultivar Baofeng104 (BF104) by particle bombardment transformation. Fifty-four T0 transgenic plants were generated. The inheritance and expression of the ppa gene were confirmed by PCR and RT-PCR analysis respectively, and seven homozygous transgenic lines were obtained. An aphid bioassay on detached leaf segments revealed that seven ppa transgenic wheat lines had lower aphid growth rates and higher inhibition rates than BF104. Furthermore, two-year aphid bioassays in isolated fields showed that aphid numbers per tiller of transgenic lines were significantly decreased, compared with wild type BF104. Therefore, ppa could be a strong biotechnological candidate to produce aphid-resistant wheat.

Involvement of NADPH oxidase isoforms in the production of O2- manipulated by ABA in the senescing leaves of early-senescence-leaf (esl) mutant rice (Oryza sativa).

In this study, the differences in reactive oxygen species (ROS) generation and abscisic acid (ABA) accumulation in senescing leaves were investigated by early-senescence-leaf (esl) mutant and its wild type, to clarify the relationship among ABA levels, ROS generation, and NADPH oxidase (Nox) in senescing leaves of rice (Oryza sativa). The temporal expression levels of OsNox isoforms in senescing leaves and their expression patterns in response to ABA treatment were determined through quantitative real-time reverse transcription PCR (qRT-PCR). Results showed that the flag leaf of the esl mutant generated more O2- concentrations and accumulated higher ABA levels than the wild-type cultivar did in the grain-filling stage. Exogenous ABA treatment induced O2- generation; however, it was depressed by diphenyleneiodonium chloride (DPI) pretreatment in the detached leaf segments. This finding suggested the involvement of NADPH oxidase in ABA-induced O2- generation. The esl mutant exhibited significantly higher expression of OsNox2, OsNox5, OsNox6, and OsNox7 in the initial of grain-filling stage, followed by sharply decrease. The transcriptional levels of OsNox1, OsNox3, and OsFR07 in the flag leaf of the esl mutant were significantly lower than those in the wild-type cultivar. The expression levels of OsNox2, OsNox5, OsNox6, and OsNox7 were significantly enhanced by exogenous ABA treatments. The enhanced expression levels of OsNox2 and OsNox6 were dependent on the duration of ABA treatment. The inducible expression levels of OsNox5 and OsNox7 were dependent on ABA concentrations. By contrast, exogenous ABA treatment severely repressed the transcripts of OsNox1, OsNox3, and OsFR07 in the detached leaf segments. Therefore, OsNox2, OsNox5, OsNox6, and OsNox7 were probably involved in the ABA-induced O2- generation in the initial stage of leaf senescence. Subsequently, other oxidases activated in deteriorating cells were associated with ROS generation and accumulation in the senescing leaves of the esl mutant. Conversely, OsNox1, OsNox3, and OsFR07 were not associated with ABA-induced O2- generation during leaf senescence.

Biocontrol potential of endophytic fungi in medicinal plants from Wuhan Botanical Garden in China

Many medicinal plants possess antimicrobial activities, and have antagonistic endophytic fungi that help them protect from pathogen attack. The aim of this study was to examine endophytic fungi in traditional Chinese medicinal plants, and understand if these organisms have antimicrobial activities and they can be potentially used for biological control of plant diseases. A total of 208 endophytic fungal isolates were collected from stems (83), leaves (121) and flowers (4) of 26 medicinal plant species. The majority of the isolates belonged to Alternaria, Phomopsis, Colletotrichum, Phoma and Acremonium as well as several species allocated to Mycelia sterilia. A detached leaf assay was conducted by testing these isolates on wheat powdery mildew (Blumeria graminis f. sp. tritici, or Bgt). Fifteen isolates of endophytic fungi inhibited Bgt, exhibiting control efficacies ranging from 65.4% to 100%. Of these isolates, LPS-1, SCS-6 and 16-6, exhibited significant inhibition of Bgt proliferation (>90%). Isolate LPS-1 isolated from the stem of Ilex cornuta Lindl. ex Paxt. had the highest efficacy, resulting in 100% inhibition of Bgt growth on detached leaf segments. Based on morphological characteristics and phylogenetic analyses of the ITS rDNA sequences and translation elongation factor 1-alpha (TEF-1α) gene regions, LPS-1 was identified as Lasiodiplodia pseudotheobromae. A range of culture conditions for LPS-1 were examined and the results indicated that optimal antifungal activity resulted from static cultures in PDB (pH 7.0) inoculated with three mycelial plugs and incubated at 30°C for 6days. With further study, LPS-1 can be a candidate for biological control.

Genotypic-dependent alteration in transcriptional expression of various CAT isoenzyme genes in esl mutant rice and its relation to H2O2-induced leaf senescence

To clarify the intricate relationship of H2O2-induced leaf senescence with distinct CAT gene expression, the genotypic-dependent alteration in the temporal patterns of H2O2 content, malondialdehyde (MDA) accumulation, relative conductivity, and the transcript expression of three CAT isoform genes during leaf senescence was investigated using two rice genotypes, namely, the early senescence leaf (esl) mutant and its wild type. Detached leaf segments were used to examine the effects of different exogenous H2O2 and ABA treatments on the expression of three CAT genes and other senescence-related physiological parameters. The results showed that the esl mutant had higher H2O2 level than its wild type at the initial phase of leaf senescence, which was followed by a sharp increase in MDA accumulation. Then, membrane integrity was severely destroyed and chlorophyll content decreased rapidly, which accelerated the senescence symptoms and significantly decreased the seed-setting rate in the esl mutant. The association of expression of the three CAT genes with rice leaf senescence lesions induced by H2O2 was isoform dependent, and the CATA and CATB expression exhibited remarkable genotype-dependent variation in the amount of transcript and their temporal pattern during leaf senescence. CATA and CATB also showed more sensitive response to exogenous H2O2 treatment compared with CATC, which suggests that CATA and CATB genes have a more important role than CATC in H2O2 inactivation of rice leaf senescence. The contribution of CATA expression to H2O2 scavenging in senescing rice leaves was most prominent at the initial stage of leaf senescence, with higher levels observed at the onset of leaf senescence, whereas CATB expression in esl flag leaf peaked later compared with CATA and was also responsible for the execution and acceleration of H2O2 inactivation particularly after the initiation of leaf senescence. CATB expression partially overlapped with CATA expression during H2O2 scavenging. For the CATC expression in rice leaves, its temporal pattern was poorly associated with H2O2-induced leaf senescence, but CATC was expressed preferentially in rice leaves and sheath and was involved in organ/tissue specificity. Exogenous ABA treatment can cause senescence-related increase in MDA accumulation and relative conductivity in the detached leaf segments, concomitant with a remarkable increase in H2O2 level. However, the expression of the three CAT isoforms under exogenous ABA treatment differed from those induced directly by H2O2 treatment, indicating the different ways for scavenging H2O2 accumulation during leaf senescence despite the increase in H2O2 level in senescing leaves induced by ABA.

Characterization of photosynthetic performance during senescence in stay-green and quick-leaf-senescence Zea mays L. inbred lines.

The net photosynthetic rate, chlorophyll content, chlorophyll fluorescence and 820 nm transmission were investigated to explore the behavior of the photosynthetic apparatus, including light absorption, energy transformation and the photoactivities of photosystem II (PSII) and photosystem I (PSI) during senescence in the stay-green inbred line of maize (Zea mays) Q319 and the quick-leaf-senescence inbred line of maize HZ4. The relationship between the photosynthetic performance and the decrease in chlorophyll content in the two inbred lines was also studied. Both the field and laboratory data indicated that the chlorophyll content, net photosynthetic rate, and the photoactivities of PSII and PSI decreased later and slower in Q319 than in HZ4, indicating that Q319 is a functional stay-green inbred line. In order to avoid the influence of different development stages and environmental factors on senescence, age-matched detached leaf segments from the two inbred lines were treated with ethephon under controlled conditions to induce senescence. The net photosynthetic rate, light absorption, energy transformation, the activities of PSII acceptor side and donor side and the PSI activities decreased much slower in Q319 than in HZ4 during the ethephon-induced senescence. These results suggest that the retention of light absorption, energy transformation and activity of electron transfer contribute to the extended duration of active photosynthesis in Q319. Although the chlorophyll content decreased faster in HZ4, with decrease of chlorophyll content induced by ethephon, photosynthetic performance of Q319 deteriorated much more severely than that of HZ4, indicating that, compared with Q319, HZ4 has an advantage at maintaining higher photosynthetic activity with decrease of chlorophyll although HZ4 is a quick-leaf-senescence inbred line. We conclude that attention should be paid to two favorable characteristics in breeding long duration of active photosynthesis hybrids: 1) maintaining more chlorophyll content during senescence and 2) maintaining higher photosynthetic activity during the loss of chlorophyll.

Identification and mapping of two powdery mildew resistance genes in Triticum boeoticum L.

Powdery mildew (PM) caused by Blumeria graminis f. sp. tritici (Bgt), is one of the important foliar diseases of wheat that can cause serious yield losses. Breeding for cultivars with diverse resources of resistance is the most promising approach for combating this disease. The diploid A genome progenitor species of wheat are an important resource for new variability for disease resistance genes. An accession of Triticum boeoticum (A(b)A(b)) showed resistance against a number of Bgt isolates, when tested using detached leaf segments. Inheritance studies in a recombinant inbred line population (RIL), developed from crosses of PM resistant T. boeoticum acc. pau5088 with a PM susceptible T. monococcum acc. pau14087, indicated the presence of two powdery mildew resistance genes in T. boeoticum acc. pau5088. Analysis of powdery mildew infection and molecular marker data of the RIL population revealed that both powdery mildew resistance genes are located on the long arm of chromosome 7A. Mapping was conducted using an integrated linkage map of 7A consisting of SSR, RFLP, STS, and DArT markers. These powdery mildew resistance genes are tentatively designated as PmTb7A.1 and PmTb7A.2. The PmTb7A.2 is closely linked to STS markers MAG2185 and MAG1759 derived from RFLP probes which are linked to powdery mildew resistance gene Pm1. This indicated that PmTb7A.2 might be allelic to Pm1. The PmTb7A.1, flanked by a DArT marker wPt4553 and an SSR marker Xcfa2019 in a 4.3cM interval, maps proximal to PmT7A.2. PmTb7A.1 is putatively a new powdery mildew resistance gene. The powdery mildew resistance genes from T. boeoticum are currently being transferred to cultivated wheat background through marker-assisted backcrossing, using T. durum as bridging species.

Virulence Frequences of Puccinia triticina in Germany and the European Regions of the Russian Federation

AbstractFrom 2001 to 2003, leaf rust was collected in different regions of Germany and the Russian Federation to generate single spore isolates and to study the structure of the pathogen populations by analyses of virulence. The virulence of isolates was tested with 38 near‐isogenic lines each carrying a different resistance gene. The analyses of variance revealed significant effects for the frequency of virulent isolates, the regions and most interactions with years and regions, but no significance was found for the effects of years. In Germany, an increase of virulence frequencies was detected for Lr1 and Lr2a while a decrease was found for Lr3a, Lr3bg and Lr3ka. Such clear trends did not occur in Russia which may be due to the great agroclimatic differences between regions. The variance of the frequency of virulent isolates was used to estimate adequate sample sizes for the analysis of regional populations of leaf rust. This procedure resulted in more reliable information about the dynamic processes within the pathogen populations. In 2002 and 2003, all pathotypes in Germany had a combined virulence to Lr1, Lr2a, Lr2b, Lr15, Lr17 and Lr20 supplemented by a few other genes. The complexity of virulence was lower in the most frequent pathotypes. In Russia virulence to the alleles at locus Lr3 was very common. Using detached leaf segments in Germany and Russia it turned out that the most virulent pathotypes carry 34 and 32 virulence genes, respectively. Virulence to Lr9, Lr19, Lr24 and Lr38 was rare or even absent. The use of major genes, not overcome by corresponding virulent pathotypes, may contribute to more durable types of resistance in case they are combined with genes having different effects, e.g. adult plant resistance.

DEVELOPMENTAL STAGE RESP ONSE OF PE ARL MILLET DOWNY MILDEW (SCLEROSPO RA GRAMINICOLA) TO FUNGICIDES

Inhibitory effect of 21 commercial and 6 experimental fungicides was assessed in model experiments against pearl millet downy mildew disease. Chemicals differed strongly by their anti-mildew activity, however neither the pathogen nor the host plant showed complete tolerance to any of compounds tested. Nevertheless, the plants outgrew depressant effect of compounds observed in germling stage and this activity did not significantly influence the yield. There was a significant correlation between yield performance and disease inhibitory effects assessed either in vitro or in vivo tests. The response of pathogen to investigated compounds varied during ontogeny, where zoosporangium formation was found to be the most sensitive ontogenetic event. When comparing responses of pathogen and host with fungicides by means of principal component analysis, the presence of two independent components has been demonstrated accounting for 86% of the total variation to which responses of host and pathogen contributed differently. The antisporulant activity of compounds evaluated on detached leaf segments and their positive effect on yield significantly correlated allowing to predict the expectable grain yield significantly (p>0.05). Beside acylanilides andoprim, drazoxolon and efosit offered efficacy on the level requested. Metalaxyl and tridemorph as well as andoprim and cymoxanil acted synergistically against S. graminicola.

Components of Pink Snow Mould Resistance in Winter Wheat are Expressed Prior to Cold Hardening and in Detached Leaves

AbstractResistance to pink snow mould, caused by Microdochium nivale, was investigated in four resistant winter wheat lines from the USDA World Cereal Collection (CI9342, CI14106, PI173440 and PI181268) and three Nordic wheat lines (Bjørke, Rida and V1004). Pink snow mould resistance was tested in non‐hardened and cold‐hardened plants incubated under artificial snow cover and in detached leaf segments mounted on water agar and incubated at either 3°C in darkness or at room temperature with light during the day. The wheat lines CI9342, CI14106 and PI181268 were more resistant than the Nordic lines, both before and after cold hardening. Thus, although cold hardening strongly increases the level of snow mould resistance in all the wheat lines, some resistance mechanisms are also present prior to cold hardening in some of the resistant lines. CI9342, CI14106 and PI181268 also had a higher level of resistance than the other lines in the detached leaf assay, indicating that these lines have some resistance mechanisms acting in the leaves. The resistance of PI173440 was expressed only in intact hardened plants and not in non‐hardened plants or in detached leaves. This indicates that this line relies on cold hardening‐related changes in the crown for its resistance. In the detached leaf assay the rate of lesion development varied greatly between leaves of different order. The highest correlation with the whole plant test was obtained when using secondary leaves and incubation at 3°C in the dark.

Manifestation of black spot disease (Alternaria brassicicola) in intact leaves and detached leaf segments of cabbage plants grown in nutrient solutions without N, P, K and Ca

In two experiments young cabbage plants in the 4/6-leaf stage were supplied for eight weeks with nutrient solutions without nitrogen (oN), phosphorus (oP), calcium (oCa) or potassium (oK) in order to investigate the impact of withholding essential major elements on the development of black spot disease (Alternaria brassicicola) in intact leaves (variant Int) and detached leaf segments (variant Seg). A complete solution (Co) that contained all mineral elements essential for the growth of the host plant served as control. Lesion size in millimetres was measured as parameter of the pathogen activity. In the first trial, solutions oN, oP, oCa, and Co were tested simultaneously in four replications. Lesion size was estimated 5 days after inoculation (dai). In the second trial, only the solutions oK and Co were supplied in one replication and lesions were determined at 5 and 22 dai.

The mechanism of the ozone-induced changes in thermoluminescence glow curves of barley leaves

The changes in thermoluminescence (TL) signals induced by short-term ozone exposure of leaves are characterized by a down-shift of the peak-temperature of the TLB-band and an increase of a TL band at 55°C. We investigated the relationship of these changes to photosystem 2 (PS2) photochemistry. The changes were not only detectable in the presence of ozone, but also after irradiation of dark-adapted leaves and after aging of irradiated detached leaf segments. The opposite effect on TL, an up-shift of the peak-temperature of the B-band and the decrease of the intensity of the band at 55°C were found after infiltration of leaves with nigericin, antimycin A, and diphenyleneiodonium chloride (DPI). Propyl gallate down-shifted the peak-temperature of the B-band. 2,5-dimethyl-1,4-benzoquinone up-shifted the peak-temperature of the B-band and decreased the intensity of the 55°C band. The intensity of the 55°C band did not change significantly in the presence of oxygen in comparison to that in nitrogen atmosphere. It decreased with time of dark adaptation (50% intensity was observed after 3 h of dark adaptation at room temperature), however, it was reactivated to its initial value (at 5 min of dark adaptation) after 1 single-turnover flash. The 55°C band was not significantly changed in the presence of DCMU. Thus the ozone-induced band at 55°C is assigned to charge recombination in PS2. Changes in the electron transport chain at the acceptor side of PS2, probably related to the cyclic electron transport around photosystem 1 and/or chlororespiration, could play an important role in the increase of the 55°C band and the down-shift of the B-band. The changes at the acceptor side indicated by TL can be an ex pression of a physiological regulatory mechanism functional under stress conditions.

Response of pearl millet downy mildew ( Sclerospora graminicola ) to diverse fungicides

The inhibitory effect of 15 commercial and five experimental fungicides was assessed both in greenhouse and field experiments against Sclerospora graminicola, the causative agent of pearl millet downy mildew disease. Chemicals differed in anti-mildew activity. However, neither the pathogen nor the host plant was completely tolerant to any compounds tested. The plants depressed by fungicides in the germling stage recovered until formation of inflorescence, so this activity did not significantly influence grain yield. There was a significant correlation between antisporulant activity of compounds evaluated on detached leaf segments and their positive effect on yield performance. All compounds increased the grain yield of downy mildewed pearl millet when applied in the maximum doses tolerated by pearl millet. However, analysis of the cost-return budget showed that disease control < 30% is uneconomic. Fungicides of the acylanilide series exhibited the highest protective effect (over 95%) and andoprim, drazoxolon and efosit were also effective.

Chloroplasts affect the leaf response to cytokinin

The effect of cytokinin on green and white leaves of the mutant line albostrians of barley was studied. Chloroplast development is completely blocked in white leaves of albostrians barley due to a nuclear mutation causing a lack of plastid ribosomes. We found white leaves to contain distinctly less abscisic acid than green leaves. In contrast, cytokinin (zeatin, zeatinriboside) content was higher in white vs. green leaves. Both white and green leaves contain a cytokinin-binding protein (CBP) of 67 kDa. CBP from white and green leaves, together with trans-zeatin (10−7 mol/L), activated RNA synthesis in an in vitro transcription elongation system containing chromatin associated with RNA polymerase I isolated from wild-type barley leaves. In spite of the high cytokinin content and the presence of a protein showing properties of a cytokinin receptor, white leaves differed markedly from green ones in their response to added cytokinin. Cytokinin promoted stomatal opening in both types of leaves, though white leaves proved to be less sensitive. During senescence of detached leaf segments, protein degradation in white leaves occurred much more rapidly and was less retarded by cytokinin than in green leaves. Cytokinin enhanced the incorporation of methionine into protein in green leaves, but did so to a much lower degree in white leaves. Therefore, we conclude that unimpaired chloroplast development and/or chloroplast gene expression is required for normal leaf responses to cytokinin.

Towards the Development of a Novel In Vitro Strategy for Early Screening of Fusarium Ear Blight Resistance in Adult Winter Wheat Plants

A novel in vitro bioassay is described for screening Fusarium ear blight (FEB) resistance in adult winter wheat plants. Seven winter wheat cultivars were assessed for components of partial disease resistance as 28 day-old detached leaf segments in the laboratory using isolates of Microdochium nivale var. nivale and M. nivale var. majus. Results were compared with disease data obtained at anthesis using the same cultivars as whole plants and the same isolates under glasshouse conditions. Significant cultivar differences were observed using detached leaves, with cv. Avalon (a Fusarium culmorum ear susceptible cultivar) having the shortest leaf incubation period, greatest leaf lesion development and shortest leaf latent period compared to cv. Spark (a Fusarium culmorum ear resistant cultivar), which had the longest leaf incubation period, least leaf lesion development and longest leaf latent period. Using whole plants, cv. Avalon had the shortest ear incubation period and greatest ear disease severity, whilst cv. Spark had the longest incubation period and least ear disease severity. Overall, cultivars of intermediate F. culmorum ear resistance expressed intermediate responses to M. nivale isolates, using both detached leaves and whole plants. Significant correlations were found with ear disease severity and ear incubation period in whole plants and components of partial disease resistance in detached leaves, with significant correlations obtained between leaf incubation period and ear disease parameters using the M. nivale var. nivale isolate. In addition, leaf latent period and leaf lesion size showed significant correlations with whole plant reactions using M. nivale var. nivale and var. majus isolates. The in vitro screening of cultivars as detached leaves using M. nivale isolates may offer a real possibility of a rapid bioassay for the early screening of FEB resistance in wheat and other cereals.

The Use of Detached Seedling Leaves of Triticum aestivum to Study Pathogenicity in Puccinia recondita f. sp. tritici

AbstractA method is described for establishing isolates of Puccinia recondita f. sp. tritici (causal agent of brown rust of wheat) on detached seedling leaf segments. The method was used to compare the responses of leaf segments and intact seedling leaves for 28 differential genotypes inoculated with eight rust isolates. Leaf segments were incubated at two post‐inoculation temperatures (17 and 23C) and intact seedlings at 20–25 C. Reliable determinations of isolate pathogenicity was obtained using detached leaf segments of wheats with genes Lr l. Lr2a, Lr3a, Lr3bg., Lr3ka, Lr9, Lr15, Lrl9. Lr20, Lr24, Lr25. Lr26, Lr28, and Lr30 at both post‐inoculation temperatures, and for wheats with genes Lr2b. Lr2c, Lrl7, Lr23, Lr27 + Lr31 and LrH, at 23°C. Differences between leaf segments and intact leaves for the remaining eight differentials were attributed to inconsistent or poor expression of genes in detached leaf segments. By repeating tests with detached leaf segments, it was possible to establish the pathogenicities of the isolates on all of these differentials except those carrying Lr13, Lr14a, Lr16 and Lr18. Potential uses and limitations of the technique in studies of Puccinia recondita f. sp. tritici are discussed.

Identification of specific powdery‐mildew‐resistance genes in individual wheat plants using the first two seedling leaves

AbstractIdentification of resistance genes in individual plants requires the use of leaves that have homogeneous reactions to the pathogen. The reactions of the first two leaves of seedlings of 12 wheat differential varieties to 20 Erysiphe graminis f.sp. tritici isolates were compared using in vitro tests on detached leaf segments. The expression of resistance and susceptibility did not differ significantly between the first two leaves with the 12 resistance genes tested. Consequently, the identification of specific powdery‐mildew‐resistance genes in individual plants is possible if approximately 10 segments of the primary and secondary leaves are used, each of them inoculated by one out of a set of 10 differential isolates. The reaction pattern of a plant to the tester isolates is interpreted according to a procedure in two steps, that are easily computerized. Identification of resistance genes in individual plants is particularly useful for resistance studies in heterogeneous plant populations.

Variation in adult plant resistance to powdery mildew in spring oats under field and laboratory conditions

Ten oat genotypes were assessed for adult plant resistance (APR) to powdery mildew (Erysiphe graminis f.sp. avenae) in small field plots and on detached leaf segments in the laboratory using glasshouse‐grown plants. Significant genotype differences were observed in the field and on leaf segments for latent period, infection frequency and spore production, components used to assess APR. The genotype OM1711, which was selected because it expressed a higher level of mildew resistance than its most resistant parent, cv. Maldwyn, showed this transgressive resistance in both field and laboratory tests. By contrast, the genotype OM1387, also selected for high mildew resistance, only showed this enhancement in the field. It is concluded that quantitative assessment of mildew in detached leaves is not sufficiently precise to be used alone in selecting segregants for high levels of APR, and that field data are also needed.