Slow Rusting of Wheat to Puccinia recondita

Seven cultivars of winter wheat were studied in field trials to determine their level of slow rusting ability towards brown rust. Cv. Bouquet was the most resistant, with greatly reduced infection levels, areas under die disease progress curve and infection rate compared with those measured on the control cv. Armadda. Cultivars Atou and Maris Freeman also showed evidence of slow rusting, but the responses of cultivars Waggoner and Flinor were not consistent in successive trials. Cv. Flanders appeared to be almost as susceptible as cv. Armada. The use of the Gompertz transformation of desease progress data for the calculation of apparent infection rates allowed better comparison of rates between cultivars than when the logistic transformation was used.     

The Expression of Partial Resistance of Wheat to Puccinia recondita

A range of winter wheat cultivars, which appeared to show no race-specific resistance to Puccinia recondita f. sp. tritici, was studied at seedling and adult growth stages to determine the components of partial resistance which might contribute to slow-rusting in the field. Under controlled environmental conditions, adult plants of cvs Atou, Bouquet, Cappelle-Desprez and Maris Freeman produced less uredospores per unit area than the control cv. Armada, and uredosori were smaller on these cultivars. Fewer uredosori erupted on cv. Cappelle-Desprez than on the control, and both cv. Bouquet and cv. Cappelle-Desprez showed longer latent periods than other cultivars. Cultivar Holdfast had a shorter latent period, with larger and more numerous uredosori than even the highly susceptible cv. Armada. Cultivar Waggoner displayed a similar response to infection to that of the control. The components of partial resistance detected in adult plants were not displayed by seedling leaves.     

The Expression of Race-Specific Resistance of Wheat Seedlings to Puccinia recondita

A range of wheat cultivars with resistance factors effective against Puccinia recondita f. sp. tritici was studied to investigate the mode of action and expression of resistance at first and third seedling leaf stages. In most cultivars, resistance to isolate 74/2 resulted in extremely low levels of infection, apparently linked with a predominantly hypersensitive response by the host. In seedlings of cultivars Mans Fundin and Sterna, however, race-specific resistance was expressed as increased pathogen latent period and intermediate infection levels.     

Histology of the Infection and Development of Puccinia recondita f. sp. tritici in a Wheat Line with Lr37

The degree of adult-plant resistance conferred by the gene Lr37 in RL6081 (Thatcher*8/Lr37) to four avirulent leaf rust pathotypes was quantified by assessing histological components as well as latent period, uredinium density and uredinium size. Histological observations on the adaxial flag leaf surfaces revealed significant arrest of fungal structures in RL6081 at early infection stages. Furthermore, host cell necrosis typical of a posthaustorial host-resistance mechanism was conspicuous in sizeably reduced colonies on this genotype. Lr37 significantly decreased the rate of uredinial appearance of all four pathotypes. Compared with Thatcher, fewer uredinia of smaller dimensions developed on flag leaves of RL6081. Characterization of resistance indicated that disease development in genotypes with the gene Lr37 should be extremely limited.     

Effects of Bacterial Inoculation to Immobilize Nickel in Wheat Grown on Ni-Contaminated Soil

Abstract

Plant growth stimulating bacteria are very effective in immobilization of metals and reducing their translocation in plants through precipitation, and adsorption. A pot experiment was conducted to investigate the effectiveness of chitosan- and hematite-modified biochar and bacterial inoculations on the immobilization of nickel (Ni) in polluted soil under wheat cultivation. Application of modified biochars and inoculation with Pseudomonas putida significantly increased both wheat root and shoot dry matter yields but decreased Ni phytoextraction efficiency. The Ni concentration, translocation factor and uptake in wheat shoot and root significantly decreased the application of either modified or unmodified biochars. Bacterial inoculation significantly decreased mean translocation factor and also root and shoot concentration and the uptake Ni in the shoot. Chitosan-modified biochar was the most influential treatment in decreasing Ni uptake by wheat followed by P. putida inoculation treatment. The results demonstrated positive effects of chitosan modified biochar and inoculation with P. putida in increasing dry matter yield and decreasing Ni uptake in wheat grown on Ni-contaminated soil. According to the results of present study, modified biochars application and bacterial inoculation are influential treatments which prevent Ni toxicity probably.     

Induction of Susceptibility and Resistance of Wheat Leaves by Preinoculation with High and Low Virulence Races of Puccinia recondita f. sp. Tritici

Isolates R1 and R2 of Puccinia recondita f. sp. tritici of low or high virulence on leaves of a series of cultivars of wheat behaved very similarly up to the formation of appressoria above stomata and sub-stomatal vesicles. Differences in growth of hyphae and in responses of host cells became clearly apparent only 24 h after infection; they then increased so that 10 days after inoculation high virulence isolates had produced freely sporulating sori (infection type 4) whereas low virulence isolates produced small colonies which did not erupt and sporulate and were associated with large numbers of dead host cells. The cultivar Timmo was selected for experiments on induced susceptibility and induced resistance. It was highly susceptible (infection type 4) to isolate Rl and to a mutant RlM, similar in pathogenicity on many cultivars but with uredospores different in colour from those of R1 and those of isolate R2 to which Timmo was highly resistant (infection type 0). This difference facilitated interpretation of results of experiments in which leaves were inoculated with more than one isolate. Inoculation with R1 (or with RUM which always behaved similarly) made leaves susceptible to R2 inoculated 4 days later. R2 sori were about 70 % the area of and about 70 % as frequent as Rl sori when inoculated on the same area on the same surface or on an area on the lower surface below a similar area on the upper surface inoculated with Rl. There also developed in the same area small, non-erumpent colonies associated with large numbers of dead host cells; these necrotic lesions were very similar to those produced in leaves inoculated only with R2. There were significantly fewer sori and more necrotic lesions when Rl was inoculated 1 or 2 days before R2. Totals of sori and necrotic lesions were about the same when the interval between inoculations was 1, 2 or 4 days; they were also similar with an interval of 3 days when numbers of sori were substantially less than after 4 days. Inoculation with Rl had some but much less effect in making tissues susceptible to R2 when again it was inoculated later but about 2 mm away. Although inoculation with R1 sufficiently in advance had the striking effect of making tissue almost as susceptible to normally low virulence R2 as it was to R1, colonies and sori of R1 which developed in association with those of R2 were substantially smaller than those which developed when R1 was inoculated alone. But there were similar differences in sizes of colonies and sori when R1 and RIM were inoculated together or separately. They probably depended on competition for nutrients. Possible mechanisms of induced susceptibility and induced resistance and implications for disease in the field are discussed briefly.     

铁线莲上隐匿柄锈菌性孢子器和锈孢子器发育的组织学和细胞学观察

通过光学显微镜技术和电镜技术对铁线莲上隐匿柄锈菌Puccinia recondita性孢子器和锈孢子器发育进行了组织学和超微结构的观察。观察表明,铁线莲上隐匿柄锈菌性孢子器呈瓶状,内生有大量单核的性孢子梗和侧丝。性孢子梗顶端产生大量的性孢子,每形成一个性孢子后,都在性孢子梗上留下一环痕。性孢子长椭圆形,表面无特殊纹饰。铁线莲上隐匿柄锈菌锈孢子器呈杯状,其内生长大量平行排列的长形双核锈孢子梗,每个锈孢子梗由上向下连续产生多个锈孢子。锈孢子梗通过产生隔膜先形成锈孢子原体,再分隔形成锈孢子和间生细胞。随着锈孢子的进一步发育,间生细胞解体,锈孢子彼此分开。成熟的锈孢子表面产生有密集的瘤状结构。     

Catabolic activity of two phosphoric diester hydrolases in wheat leaves inoculated with brown rust,Puccinia recondita

Changes in total phospholipids and activities of two phosphoric diester hydrolases,i.e. phospholipase C and phospholipase D have been studied in inoculated wheat leaves of 25-day old plants, interacting differentially with three races of brown rust,Puccinia recondita, during early stages of pathogenesis. With progressive rust iafection the lipids and phospholipids were found to decrease in all the three interactions except at later stages (48 h and 72 h) in race 104-interaction. However, total phospholipids at various stages were found to be higher in resistant interaction (race 63) as compared to the other two interactions. An initial increase in activities of phospholipase C and D in all the three interactions was followed by a decline at the intermediate stages which continued in case of phospholipase C activity while a reverse trend was observed in phospholipase D activity towards later stages of infection. Further the enzymatic activities at various stages were found to be higher in the susceptible and intermediate interactions (with races 77 and 104 respectively) as compared to the resistant interaction.     

A Comparison of the Reaction Sites Associated with the Resistance of Coleoptiles of Barley, Oats and Wheat to Infection by Septoria nodorum

A novel technique has been developed to inoculate the outer epidermal cells of coleoptiles of barley, oats and wheat with S. nodorum. Using this technique, which results in a large number of attempted penetrations, the composition of the material deposited at unsuccessful penetration sites in these cereals have been compared. Although the deposits reacted in a similar manner with some histochemical reagents (ammoniacal silver solution, Coppick-Fowler reaction, p-nitrobenzene tetrafluoroborate and Coomassie brilliant blue R250) marked differences occurred between the reactions sites formed by barley and wheat and by oats with other stains (bromophenol blue, nile blue sulphate and Toluidine blue). Chemical treatments used to delignify tissue also revealed differences in these reaction sites. It is concluded that although the reaction sites share some similar components there are significant differences in their chemical structure.     

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

A 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.     

Alternative Gramineous Hosts of Leptosphaeria nodorum Including Two New Records for the U. S. A.

Repeated trunk injections of tetracycline hydrochloride and oxytetra-cycline over a 27 month period, retarded the rate at which clove trees in Zanzibar, died from sudden death (SD) disease. This result provides additional support for an MLO aetiology for SD, but indicates that the tetracycline formulations and method of application, as described here, is not a feasible method of SD control in the field. Bioassay of leaf discs and root sections using agar plates seeded with Bacillus subtilis, at various times after injection, indicated that antibiotic distribution to the canopy was extensive, but that down to the roots was minimal. The proportion of leaf discs showing tetracycline activity declined over a 54 day period post-injection, from 75,% to 17%. Mean tetracycline levels in leaves per tree peaked at 2.4 μg/ml, 21 days after injection. The highest individual leaf disc level was 7 μg/ml. Most trees maintained concentrations of tetracycline inhibitory to B. subtilis growth for 2,1–41 days.     

Possible Effects of Microbial Ecto-Nucleoside Triphosphate Diphosphohydrolases on Host-Pathogen Interactions

Summary: In humans, purinergic signaling plays an important role in the modulation of immune responses through specific receptors that recognize nucleoside tri- and diphosphates as signaling molecules. Ecto-nucleoside triphosphate diphosphohydrolases (ecto-NTPDases) have important roles in the regulation of purinergic signaling by controlling levels of extracellular nucleotides. This process is key to pathophysiological protective responses such as hemostasis and inflammation. Ecto-NTPDases are found in all higher eukaryotes, and recently it has become apparent that a number of important parasitic pathogens of humans express surface-located NTPDases that have been linked to virulence. For those parasites that are purine auxotrophs, these enzymes may play an important role in purine scavenging, although they may also influence the host response to infection. Although ecto-NTPDases are rare in bacteria, expression of a secreted NTPDase in Legionella pneumophila was recently described. This ecto-enzyme enhances intracellular growth of the bacterium and potentially affects virulence. This discovery represents an important advance in the understanding of the contribution of other microbial NTPDases to host-pathogen interactions. Here we review other progress made to date in the characterization of ecto-NTPDases from microbial pathogens, how they differ from mammalian enzymes, and their association with organism viability and virulence. In addition, we postulate how ecto-NTPDases may contribute to the host-pathogen interaction by reviewing the effect of selected microbial pathogens on purinergic signaling. Finally, we raise the possibility of targeting ecto-NTPDases in the development of novel anti-infective agents based on potential structural and clear enzymatic differences from the mammalian ecto-NTPDases.     

The Expression of Partial Resistance to Puccinia striiformis in Wheat. Effects on Colony Growth and Spore Production

Abstract The resistance of wheat to Puccinia striiformis f. sp. tritici was investigated. The durable resistance of Hybride de Bersée and that resistance controlled by the factor YR14 , in cvs Solitaire and Wembley were studied at the second and sixth leaf stages, using a point inoculation technique. Both resistance types had significant effects at both leaf stages but the most marked effects were evident on adult plants. At both leaf stages there was a high correlation between colony, length and urediniospore prodction.     

Interactions of Puccinia hordei and Erysiphe graminis on seedling barley

The development of Puccinia hordei on the first leaf of barley seedlings previously inoculated with Erysiphe graminis was compared with that on uninoculated leaves of comparable age. On cv. Zephyr, more rust pustules developed when leaves were inoculated with both fungi within 24 h but fewer pustules if the period between the two inoculations was longer than 2 days. The reduction in numbers of rust pustules was especially marked where leaves were previously inoculated with many conidia of E. graminis. The size of rust pustules was reduced whatever the period between the two inoculations. Arresting mildew development by applying ethirimol as a soil drench to pots of seedlings inoculated with E. graminis 6 days previously, or floating segments of leaves inoculated with both fungi on 2% sucrose, in part counteracted these effects on rust pustule size. Similar effects were observed with cv. Mazurka where inoculations with E. graminis produced only small necrotic flecks but did induce premature loss of chlorophyll. On this cultivar (in contrast to Zephyr) the inoculation of one leaf surface affected the development of P. hordei on the other. In comparable experiments using Zephyr, E. graminis produced smaller colonies with fewer conidiophores on leaves previously inoculated with P. hordei. These effects could be alleviated by arresting rust development with a spray containing benodanil or by floating segments of leaves inoculated with both fungi on 2% sucrose. Germination of the conidia of E. graminis, formation of appressoria and initiation of colonies were not affected by the presence of P. hordei.     

A Light and Electron Microscope Study of the Interaction of Yellow Rust (Puccinia striiformis) with a Susceptible Wheat Cultivar

The microscopy and ultrastructure of the interaction of Pucciniastriiformis with a susceptible wheat cultivar was examined atintervals from the time of first haustorium formation to theonset of sporulation. At any particular point in the radiallyexpanding area of infection a sequence of morphological changesoccurred in the infected host cells and the fungus which werecorrelated with successive phases of active fungal growth, accumulationof reserves and finally export of reserves to the developingreproductive structures. The observations are compared withprevious work on other host-rust interactions. yellow rust, Puccinia striiformis, wheat, host-pathogen interaction     

Effects of Leaf Infections by Septoria nodorum Berk. on the Translocation of 14C-labelled Assimilates in Spring Wheat

The influence of infection with Septoria nodorum of leaves belowthe flag leaf on the translocation of ¹⁴C-labelled assimilatesin wheat was followed. In the vegetative phase export of assimilatesfrom a single infected leaf was reduced, but export from a healthyleaf on a heavily infected plant was increased. During the reproductivephase export from leaves was not affected by disease. Heavyleaf infection had little effect on the patterns of distributionof export especially during reproductive growth when only changesin the proportion of assimilates in leaf sheaths and tillerstumps were found. Distribution of export from a healthy flagleaf on an otherwise heavily infected plant was unaltered. Duringvegetative growth changes in the distribution of assimilateswere more marked, the greatest changes occurring when a singleinfected leaf on a healthy plant was exposed to ¹⁴CO₂.