Components of partial resistance of barley to Rhynchosporium secalis: use of seedling tests to predict field resistance

Components of partial resistance [disease incidence (DI), infection frequency (IF), latent period (LP), spores per lesion (SPL)] were assessed on glasshouse-grown barley seedlings following inoculation with spore suspensions of Rhynchosporium secalis at growth stage 12 (Zadoks, Chang & Konzak, 1974). Four experiments were carried out at different times during 1988. Three spring barley cultivars [two from Cyprus (cvs Kantara and Athenais) and one from the UK (cv. Triumph)] were used in the first three experiments. In the fourth experiment eight additional UK cultivars with NIAB resistance ratings ranging from 3 to 9 were used. Two races of R. secalis were used in the first three experiments and three in the fourth. The three cultivars, Kantara, Athenais and Triumph, were examined in all four experiments and significant differences detected for virtually all components of partial resistance in each. Differences, however, were often small and ranking of cultivars varied in different experiments. The greater susceptibility of cv. Kantara compared to cv. Athenais, observed under field conditions in Cyprus, would not be anticipated from the small differences in components of partial resistance observed in these experiments, but, for these cultivars, the possibility of a marked genotype x environment interaction cannot be discounted. Mean values for the components of partial resistance differed in the four experiments. LP was correlated with mean glasshouse temperature from inoculation to the onset of sporulation but differences in IF and SPL were not correlated with temperature. For these components, light quality and/or duration appeared to be more important. Overall, there were no differences between races but significant race X cultivar interactions were observed in two experiments. In the fourth experiment, examining 11 cultivars, there were significant differences between cultivars for all components of partial resistance. IF and LP were correlated but neither of these components was correlated with SPL indicating independent control of this latter component. Both IF and LP were correlated with field performance (NIAB ratings) but there was no correlation with SPL. However, combining IF with mean values of SPL restricted to the 5 days following the end of the LP, produced the best correlation (r= 0.92) with NIAB ratings. Problems of assessing components of partial resistance and possible means of improving assessments are discussed.     

Resistance of cocoa to vascular-streak dieback disease

Water-soluble exudates from young cocoa leaves markedly inhibited germination of spores of Oncobasidium theobromae in vitro, but there was no correlation between the inhibitory activity of a clone and its field resistance to vascular-streak dieback. Germinating spores penetrated young leaves and the path of penetration was marked by the browning of adjacent epidermal and mesophyll cells. At the appearance of the earliest leaf symptoms the infections in the stem were confined to the vascular traces of that leaf, but spread subsequently into the secondary xylem. Clones varied in their ability to produce tyloses in response to wounding or infection and a ranking of 10 clones on tylose frequency correlated significantly with the ranking based on field resistance, but the variability was too great for this to be useful in resistance prediction. There was no significant difference in vessel size between resistant and susceptible clones. A highly significant correlation existed between vessel and branch cross-sectional areas in six clones.     

Choice of methodology for quantifying cancer structures in tissue sections. A comparison of 2- and 3-dimensional estimators of mitotic activity, cellularity and nuclear size in breast cancer

OBJECTIVE: To analyze the relationships between a range of 2-(2D) and 3-dimensional (3D) estimators of important tumor features (mitotic activity, cellularity and nuclear size). STUDY DESIGN: Measurements were performed in systematically sampled fields of vision of 3-microns-thick sections and in optical disectors of 40-microns-thick sections of 93 breast cancers. RESULTS: 2D mitotic profile density and frequency correlate highly with 3D mitotic density and frequency (r > or = .75); the choice of estimator was of minor importance. 2D nuclear profile density correlated quite closely with 3D nuclear volume fraction and nuclear density (r > or = .66). Cellularity estimators were, however, influenced differently by nuclear size. 2D mean nuclear profile area and 3D volume- and number-weighted mean nuclear size correlated less closely (r > or = .51). Tumors with high mitotic counts generally had large nuclei, reflecting the fact that both variables are associated with aggressiveness. CONCLUSION: 2D and 3D quantitative estimates of corresponding tumor features often correlate closely. Easily applicable and unbiased 3D techniques are recommended for obtaining the mean size of nuclei (or other particles) and of volume fractions of structures. For ranking of cellularity and mitotic activity, 2D measurements are usually sufficiently accurate and close to corresponding 3D estimates. However, if exact quantities of tissue structures are required, unbiased (3D) techniques must be used.     

Search for partial resistance to leaf rust in a collection of ancient Spanish wheats

A collection of 917 accessions of Spanish durum and bread wheat was screened for resistance to leaf rust (Puccinia triticina) under field conditions at three locations. Resistance levels ranged from very low to very high, high susceptibility being most frequent. Relative disease severity (referred to the most susceptible accession = 100%) was lower than 20% in about 6% of the accessions in each location. In the collection most of the lines (84%) displayed a susceptible infection type. A final selection of seven accessions (one of them durum) displaying low severity level in the field and high infection type in a growth chamber was chosen for further studies. High levels of partial resistant with longer latency period and high percentage of early aborted colonies without necrosis were found. They might be used in breeding programmes.     

Molecular and phenotypic characterization of seedling and adult plant leaf rust resistance in a world wheat collection

Genetic resistance is the most effective approach to managing wheat leaf rust. The aim of this study was to characterize seedling and adult plant leaf rust resistance of a world wheat collection. Using controlled inoculation with ten races of Puccinia triticina, 14 seedling resistance genes were determined or postulated to be present in the collection. Lr1, Lr3, Lr10 and Lr20 were the most prevalent genes around the world while Lr9, Lr14b, Lr3ka and/or Lr30 and Lr26 were rare. To confirm some gene postulations, the collection was screened with gene-specific molecular markers for Lr1, Lr10, Lr21 and Lr34. Although possessing the Lr1 and/or Lr10 gene-specific marker, 51 accessions showed unexpected high infection types to P. triticina race BBBD. The collection was tested in the field, where rust resistance ranged from nearly immune or highly resistant with severity of 1 % and resistant host response to highly susceptible with severity of 84 % and susceptible host response. The majority of the accessions possessing the adult plant resistance (APR) gene Lr34 had a maximum rust severity of 0–35 %, similar to or better than accession RL6058, a Thatcher-Lr34 near-isogenic line. Many accessions displayed an immune response or a high level of resistance under field conditions, likely as a result of synergy between APR genes or between APR and seedling resistance genes. However, accessions with three or more seedling resistance genes had an overall lower field severity than those with two or fewer. Immune or highly resistant accessions are potential sources for improvement of leaf rust resistance. In addition, some lines were postulated to have known but unidentified genes/alleles or novel genes, also constituting potentially important sources of novel resistance.     

Expression of Resistance of Wheat to Fusarium graminearum and F. culmorum Under Various Experimental Conditions

The resistance ranking was very similar under different periods of incubation except the 17 and 24 h variants under plastic bags and with the presence or absence of Bayleton treatment. Very similar ranking was recorded also in the tests where four plot replicates were used, e.g. the reaction severity was so close in different plot replicates that one plot per genotype seemed to be enough for serial resistance tests. The significant plot × genotype interaction shows that relative resistance ranking may vary to some extent, but basic changes do not occur. Also similar cultivar reactions were observed at different levels of disease severity resulting from inoculation with isolates differing in pathogenicity. An average reaction to these levels is closer to the genetically determined resistance. Analysis of the behaviour of a cultivar at different disease severity levels helps to predict the field behaviour of a given genotype. The Bayleton treatment was ineffective against scab, although there was some interaction with cultivars.     

Partial resistance to leaf rust in a collection of ancient Spanish barleys

A collection of 569 Spanish barley accessions was screened for resistance to leaf rust (Puccinia hordei Otth) in the field at Córdoba during the 2000-2001 season. The level of resistance ranged from very low to very high. In 14% of the accessions the relative AUDPC (L94 = 100%) was lower than 10%. Selected accessions that were most resistant in the field, were tested in the seedling stage under controlled conditions. Macroscopic components of resistance indicated that six lines had a high level of partial resistance close to check cv. Vada and one line a similar level of partial resistance. Histological studies indicated that the resistance was based on a high percentage of early aborted colonies and reduction in colony size without plant cell necrosis. Three of the selected lines showed high percentage of plant cell necrosis associated with established colonies, which indicates a combination of prehaustorial resistance with late acting incomplete posthaustorial resistance. Although the new barley varieties already incorporate some partial resistance, new sources of partial resistance like these are needed to improve durability of the resistance.     

Regulation of reproduction in wild and cultivatedLycopersicon esculentum Mill. by vesicular-arbuscular mycorrhizal infection

Summary We examined how mycorrhizal infection byGlomus etunicatum Becker and Gerd. affected flowering phenology and components of reproduction in eight wild accessions and two cultivars ofLycopersicon esculentum Mill. We did this by performing a detailed demographic study of flower, fruit and seed production. Mycorrhizal infection had variable effects on the ten accessions. Infection significantly decreased the time taken to initiate flowering in some accessions. In addition, infection increased flowering duration in some accessions. In many accessions, infection significantly increased seed production, primarily by increasing the number of inflorescences and infructescences. In some accessions, mycorrhizal infection also increased the proportion of flowers that produced mature fruits or the number of seeds per fruit. Among accessions, shoot phosphorus content was correlated with seed productivity for both mycorrhizal and non-mycorrhizal plants. However, non-mycorrhizal plants produced more seed biomass per mg of shoot phosphorus than mycorrhizal plants.     

Evaluation of Water Yam (Dioscorea alata L.) Germplasm for Reaction to Yam Anthracnose and Virus Diseases and their Effect on Yield

Use of genetic resistance is the most practical and economic way to manage major diseases of yams. In a search for sources of resistance, 40 water yam (Dioscorea alata L.) accessions from Benin, Ghana, Nigeria and Puerto Rico were screened under natural disease infection conditions in Ibadan, Nigeria. The accessions were evaluated at 1, 3 and 6 months after planting (MAP) for severity of yam anthracnose and viral diseases. The effect of the pathogens on yield was also evaluated at harvest 9 MAP. There were significant differences (P < 0.001) between accessions for severities of anthracnose and viral diseases. Eight (20%) of them had lower anthracnose area under disease progress curves (AUDPC) values than the resistant check while 10 (25%) had AUDPC values below the trial mean. There were significant variations (P < 0.001) in yield components among the accessions. There was significant negative correlation of anthracnose severity with fresh tuber yield (r = −0.51) and with number of tubers per plot (r = −0.40). Similarly, significant negative correlations were observed of virus disease severity with fresh tuber yield (r = −0.78) and number of tubers per plot (r = −0.65). Linear regression models also showed that the fresh yield had significant negative relationships with anthracnose (R² = 0.26) and viral (R² = 0.62) diseases. The accessions identified as resistant constitute a valuable resource for breeding of resistant germplasm.     

Medicago truncatula in Interaction with Fusarium and Rhizoctonia Phytopathogenic Fungi: Fungal Aggressiveness,Plant Response Biodiversity and Character Heritability Indices

Fusarium and Rhizoctonia genera are important pathogens of many field crops worldwide. They are constantly evolving and expanding their host range. Selecting resistant cultivars is an effective strategy to break their infection cycles. To this end, we screened a collection of Medicago truncatula accessions against Fusarium oxysporum, Fusarium solani, and Rhizoctonia solani strains isolated from different plant species. Despite the small collection, a biodiversity in the disease response of M. truncatula accessions ranging from resistant phenotypes to highly susceptible ones was observed. A17 showed relative resistance to all fungal strains with the lowest disease incidence and ratings while TN1.11 was among the susceptible accessions. As an initiation of the characterization of resistance mechanisms, the antioxidant enzymes’ activities, at the early stages of infections, were compared between these contrasting accessions. Our results showed an increment of the antioxidant activities within A17 plants in leaves and roots. We also analyzed the responses of a population of recombinant inbred lines derived from the crossing of A17 and TN1.11 to the infection with the same fungal strains. The broad-sense heritability of measured traits ranged from 0.87 to 0.95, from 0.72 to 0.96, and from 0.14 to 0.85 under control, F. oxysporum, and R. solani conditions, respectively. This high estimated heritability underlines the importance of further molecular analysis of the observed resistance to identify selection markers that could be incorporated into a breeding program and thus improving soil-borne pathogens resistance in crops.     

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.     

Different Assessment Techniques of Leaf Blotch (Rhynchosporium secalis (Oud.) J. Davis) in Winter Barley after Artificial Inoculation

Seven winter barley cultivars expressing different field resistance against leaf blotch (Rhynchosporium secalis) and 60 doubled haploid (DH) lines descending from and F₁ hybrid resistant x susceptible were used to develop a test for the quantitative determination of disease severity. Differences in the level of resistance could be measured very precisely after artificial infection of seedlings at the 4-leaf-stage and subseqent incubation at 7 C. The protein of six isolates was usedf, or antiserum production which was subsequently supplied for serological testing (Enzyme-Linked-Immunosorbent-Assay) of infected leaves. The results of visible scoring of the seedlings was significantly correlated with measuring with the ELISA reader. The, results of the seedling test also corresponded to field scores after natural infection.     

Features of Resistance to Take-all Disease in Cereal Species Evaluated by Laboratory Assays

Development of take-all disease, caused by Gaeumannomyces graminis var. tritici, on wheat, barley and rye, respectively, susceptible, moderately susceptible and resistant under field conditions, was evaluated by laboratory assays. The root system, which grew either in vermiculite in plastic tubes or polyethylene sleeves, or in a sand mix in plastic pots, was inculated, and lesion frequency and extension, both considered as resistance factors, were monitored. In assays in tubes and pots, both enabling multiple infection points, the infection scores of wheat, barley and rye on a scale of 0–5 were in decreasing order. In assays in sleeves, with a single point inoculation, lesion length on barley and rye was similar and less than thaton, wheat, but percentage of infected roots was markedly lower on rye than on barley. For large-scale screening programs we suggest to employ both the Tube Assay, which is reliable and easy to perform and the Slanted Sleeve Assay, which is more sensitive allowing detection of even a small degree of resistance. Selected accessions could be subsequently evaluated by the Pot Assay, under more natural conditions, and the resistance to take-all must eventually be verified under field conditions.     

Biology of the mysid Mesopodopsis slabberi (van Beneden, 1861) (Crustacea, Mysidacea) in a coastal lagoon of the Ebro delta (NW Mediterranean)

Aspects of the population and reproductive biologyof the mysid Mesopodopsis slabberi were studiedin the western Mediterranean (Encanyissada coastallagoon, Ebre delta, Spain). Misids were sampling atmonthly intervals from August 1993 to June 1995. InDecember 1994 and February 1995 any individuals werefound. The relationship between carapace length (Lc)and total length (Lt) was isometric:logLt = 1.0612logLc + 0.9411 (n = 178,r = 0.9411). Thesize of mature males and females was at a maximum inthe winter, and a minimum in the summer. The longevityof individuals changed throughout the year; those withthe longest life expectancy were members of theoverwintering generation. Brooding females wererecorded throughout the year, except in December 1993and April 1994; they were most numerous in spring andautumn. The number of embryos or larvae (N) carried byfemales was related to the size of the females (range:1–22, mean value: 4.8): logN = 1.8705logLc–0.0985(n = 361, r = 0.4097, P < 0.01). Thesize of the eggs(maximum diameter, Le) was related to the size of thefemales (range: 0.35–0.6 mm in total length):logLe = 0.3404logLc–0.4820 (n = 277, r = 0.5420, P < 0.01).     

Genome size variation in Corchorus olitorius (Malvaceae s.l.) and its correlation with elevation and phenotypic traits

In this study, we report genome size variations in Corchorus olitorius L. (Malvaceae s.l.), a crop species known for its morphological plasticity and broad geographical distribution, and Corchorus capsularis L., the second widely cultivated species in the genus. Flow cytometric analyses were conducted with several tissues and nuclei isolation buffers using 69 accessions of C. olitorius and 4 accessions of C. capsularis, representing different habitats and geographical origins. The mean 2C nuclear DNA content (± SD) of C. olitorius was estimated to be 0.918 ± 0.011 pg, with a minimum of 0.882 ± 0.004 pg, and a maximum of 0.942 ± 0.004 pg. All studied plant materials were found to be diploid with 2n = 14. The genome size is negatively correlated with days to flowering (r = -0.29, p < 0.05) and positively with seed surface area (r = 0.38, p < 0.05). Moreover, a statistically significant positive correlation was detected between genome size and growing elevation (r = 0.59, p < 0.001) in wild populations. The mean 2C nuclear DNA content of C. capsularis was estimated to be 0.802 ± 0.008 pg. In comparison to other economically important crop species, the genome sizes of C. olitorius and C. capsularis are much smaller, and therewith closer to that of rice. The relatively small genome sizes will be of general advantage for any efforts into genomics or sequencing approaches of these species.     

An investigation into the involvement of defense signaling pathways in components of the nonhost resistance of Arabidopsis thaliana to rust fungi also reveals a model system for studying rust fungal compatibility

Seventeen accessions of Arabidopsis thaliana inoculated with the cowpea rust fungus Uromyces vignae exhibited a variety of expressions of nonhost resistance, although infection hypha growth typically ceased before the formation of the first haustorium, except in Ws-0. Compared with wild-type plants, there was no increased fungal growth in ndr1 or eds1 mutants defective in two of the signal cascades regulated by the major class of Arabidopsis host resistance genes. However, in the Col-0 background, infection hyphae of U. vignae and two other rust fungi were longer in sid2 mutants defective in an enzyme that synthesizes salicylic acid (SA), in npr1 mutants deficient in a regulator of the expression of SA-dependent pathogenesis related (PR) genes, and in NahG plants containing a bacterial salicylate hydroxylase. Infection hyphae of U. vignae and U. appendiculatus but not of Puccinia helianthi were also longer in jar1 mutants, which are defective in the jasmonic acid defense signaling pathway. Nevertheless, haustorium formation increased only for the Uromyces spp. and only in sid2 mutants or NahG plants. Rather than the hypersensitive cell death that usually accompanies haustorium formation in nonhost plants, Arabidopsis typically encased haustoria in calloselike material. Growing fungal colonies of both Uromyces spp., indicative of a successful biotrophic relationship between plant and fungus, formed in NahG plants, but only U. vignae formed growing colonies in the sid2 mutants and cycloheximide-treated wild-type plants. Growing colonies did not develop in NahG tobacco or tomato plants. These data suggest that nonhost resistance of Arabidopsis to rust fungi primarily involves the restriction of infection hypha growth as a result of defense gene expression. However, there is a subsequent involvement of SA but not SA-dependent PR genes in preventing the Uromyces spp. from forming the first haustorium and establishing a sufficient biotrophic relationship to support further fungal growth. The U. vignae-Arabidopsis combination could allow the application of the powerful genetic capabilities of this model plant to the study of compatibility as well as nonhost resistance to rust fungi.     

Evaluation of Rice Cultivars under Greenhouse Conditions for Adult-Plant Resistance to Pyricularia oryzae

Six rice cultivars showing various types of resistance or susceptibility to Pyricularia oryzae in the field were compared under controlled environmental conditions. The resistance of the cultivars with adult-plant resistance was race-specificat early growth stage. On all cultivars tested, blast infection became increasingly reduced on either leaves of adult plants or older leaves, as observed in rice plants of different leaf stages infected with different individual races. Their increase inhost resistance was marked by an apparent transition in infection type and reduced blast severity depending on leaf age and developmental stage of plants. The ranking of disease severity of the adult-plantresistant cultivars to different races was constant during plant development, whereas that of the susceptible cultivars was differential. It is suggested that different degrees of resistance in rice cultivars may exist in seedlings and be consistently maintained during plant development, probably becoming more distinct as rice plants mature.     

Porcine sperm zona binding ability as an indicator of fertility

The escalated use of artificial insemination in swine has increased the importance of determining fertility of a semen sample before it is used. Multiple laboratory assays have been developed to assess fertilizing potential but they have yielded inconsistent results. This experiment sought to determine the relationship between in vitro competitive zona binding ability and in vivo fertility based on heterospermic inseminations and paternity testing. The zona pellucida binding ability and fertility of sperm from 15 boars was assessed by comparing sperm from one boar with sperm from other individual boars in a pairwise fashion using four ejaculates. The relationship of zona binding ability to the mean number of piglets sired per litter for each boar as well as historic fertility data (litter size and farrowing rate) was assessed. The in vitro competition assay consisted of labeling sperm from each boar of the pair with a different fluorophore and incubating an equal number of sperm from each boar in the same droplet with porcine oocytes. The competitive assay was highly effective in ranking boars by zona binding ability (R2=0.94). Paternity testing using microsatellite markers was used to determine the mean number of piglets sired per litter for each boar during heterospermic inseminations. The pairwise heterospermic insemination assay was effective in ranking boar fertility (R2=0.59). Using historical data from these boars, average litter size and farrowing rate were correlated (r=0.81, p<0.001). However, zona binding ability was not significantly correlated with historic farrowing rate data or historic average litter size. Boar sperm zona binding ability was also not correlated significantly with the mean number of piglets sired per litter following heterospermic insemination. But the number of piglets sired by each boar was related to a combination of zona binding ability, sperm motility, normal morphology, acrosomal integrity, and the presence of distal droplets (R2=0.70). These results suggest that zona binding ability is not an accurate predictor of fertilizing ability when used alone; however, when coupled with other sperm assessments, fertility may be predicted successfully.     

Effect of Growth Stage on Resistance to Drechslera teres f. teres in Barley

Three experiments were conducted to evaluate seedling and adult plant resistance to Drechslera teres f. teres in barley lines with a potential use as resistance sources in barley breeding. Disease resistance of barley seedlings, inoculated in the glasshouse and growth chamber at the one- and two-leaf stages, was significantly (P 0.05) correlated with disease reactions on the fourth and flag leaves of barley plants grown in growth chambers ( r = 0.84- 0.94) as well as with disease levels recorded on the three uppermost leaves in a field experiment ( r = 0.64). Several of the barley lines showed no correlation, demonstrating either improved or decreased disease resistance at later growth stages. Six barley lines (Alexis, Heartland, Kinnan, CI4922, CI9776 and SWl114-93) had the same ranking in disease resistance to D. teres when damaged (punctured) leaves were inoculated with a drop of spore suspension as when undamaged leaves were spray-inoculated with a spore suspension.     

Evaluation of Certain Cowpea Genotypes for Partial Resistance to Powdery Mildew (Erysiphe polygoni)

Partial resistance to powdery mildew (Erysiphe polygoni) in twenty one cowpea cultivars was assessed over two to three seasons under field conditions. Mildew incidence was recorded as number of leaflets affected/plant and severity as AUDPC or infection rate using Gompertz transformation. Irrespective of the parameter used to measure mildew resistance or the season, mean response of cvs V-105, V-269, V-276, V-282 and V-385 showed clear slow-mildewing, while RC-48, S-488, TVX-944-02E, V-27, V-36 and V-118 were rated as susceptible. Mildew resistance in some cultivars was negatively correlated with that for the leaf rust (Uromyces vignae). AUDPC was a more robust disease parameter than infection rate and showed a good correlation (r²= 0.79) with incidence.