The genetical control of incomplete forms of resistance to Erysiphe graminis in spring barley

Eight spring barley lines exhibiting incomplete resistance to powdery mildew in field trials were crossed and back-crossed to a common susceptible parent to produce the basic generations (P₁ P₂, F₁ F₂, B₂ B₂) required for a genetical investigation. By means of joint scaling tests, disease assessments on adult plants in a field trial were used to estimate the genetic parameters contributing to resistance. Lines with major genes, which appeared partially resistant due to the presence of corresponding virulence, were characterised by the presence of a significant dominance component in the analysis. Partially resistant lines which either lacked identifiable major genes or with major genes that were ineffective in the trial, but with good background resistance, could also be distinguished. Significant additive and epistatic effects were detected in all crosses. The prospect of enhancing partial resistance through hybridisation and selection is discussed.     

Observations on the effects of mildew, Erysiphe graminis, on growth of spring and winter barley

In field plots, early and severe attacks of powdery mildew on spring barley plants greatly reduced the vigour, decreased the amount of root, the number of ear-bearing tillers and the grain size. In less severe, or later attacks, mildew mainly affected the grain size. On winter barley, where mildew attacked both in autumn and in spring, yield was decreased more than when only a spring attack occurred. The early attack retarded development of the root system, increased winter kill and decreased the number of ears reaching maturity. Because early mildew attack affects yield, it is not always possible to correlate yield loss with intensity of mildew at any one growth stage of the crop.     

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.     

Progress of infection by Erysiphe graminis on fungicide-treated and untreated barley

Tridemorph-treated and untreated barley plants wre grown either in separate growth rooms or together. They were inoculated either with a sensitive or a tolerant isolate, and the progress of mildew was recorded. Comparisons were made between the rates of progress of sensitive and tolerant isolates on separated and unseparated fungicide treatments. Results suggested that interactions took place between pathogen populations on adjacent treated and untreated plants. Barley cv. Golden Promise was sown in plots made up of two adjacent fungicide treatments. Triadimefon, triforine, tridemorph and ethirimol were paired with each other and with untreated crops in all combinations. The progress of mildew on each plot was recorded, and differences were found between similar fungicide treatments from different plot pairs. The likelihood of interactions between mildew populations exposed in the field to different fungicide treatments is discussed.     

Seasonal changes in infection of barley seedlings by Erysiphe graminis f.sp. hordei

Infection of artificially inoculated barley seedlings, exposed out of doors, was variable but there was a seasonal trend. As temperature affects both incubation time and the proportion of successful infections, these two factors will have additive effects on disease development. Infections developed only slowly in winter but, in both 1972 and 1973, conditions became much more favourable to infection in late April or early May.     

Dispersal of Erysiphe graminis and Lycopodium clavatum spores near to the source in a barley crop

In experiments to study dispersal of spores in a crop of barley, a 4-m wide strip of the cultivar Zephyr (a mildew-susceptible variety) was a source of mildew (Eyrsiphe graminis) conidia. Small suction traps, previously calibrated in a wind tunnel, were used to measure spore concentration within and above the crop. Large concentrations of conidia were measured in the crop at the downwind edge of the Zephyr strip but these decreased rapidly with distance downwind. At 1 m concentrations were halved and by 4 m they were no greater than the background concentration measured in the crop upwind of the source. Next to the source, concentrations were much greater within than above the crop and net spore movement (flux) was upwards out of the crop; by 4 m downwind concentrations were greater above the crop and spore flux was reversed. Lycopodium clavatum spores were released in the same crop from a line of point sources. Concentrations also decreased rapidly downwind but, with no background of spores, numbers remained greater within than above the crop further from the source than for E. graminis. Even so by 7 m downwind concentrations in the crop had declined to less than those above. Deposition of L. clavatum spores onto horizontal glass slides in the crop agreed with that expected by settling. However, impaction onto vertical cylinders among plants was much greater than predicted. The reason is not known although turbulent air-flow around plants may, in some way, enhance impaction. Many E. graminis conidia near the source were deposited in clumps. This prevented any accurate prediction of deposition rates as fall speeds of clumps (necessary for prediction) were not known. Not surprisingly, deposition on horizontal slides often exceeded that expected from settling of single spores although it was not always greatest where clumps predominated. The proportion of spores deposited on vertical cylinders and horizontal slides located among plants ranged from 0–02 to 0–27 and from 0–019 to 0–127 of the area dose, respectively. Although these may seem to be small trapping efficiencies, the same deposition rates in a crop with many leaves and stems would rapidly filter most spores from air in the crop and can explain why concentrations were observed to decline so rapidly.     

Polyamines in discrete regions of barley leaves infected with the powdery mildew fungus, Erysiphe graminis

The concentrations of putrescine, spermidine and spermine and the activities of arginine decarboxylase (ADC; EC 4.1.1.19) and ornithine decarboxylase (ODC: EC 4.1.1.17) were determined in discrete regions of barley leaves ( Hordeum vulgare L. cv. Golden Promise) infected with the powdery mildew fungus ( Erysiphe graminis f.sp. hordei Marchal). Polyamine concentrations and the activities of both enzymes were always greatest within the region surrounding the fungal pustule, with the lowest values always being found in the region furthest away from the pustule. Although the concentrations of the three amines and ADC and ODC activities within the fungal pustule were always less than values from the zone surrounding the pustule, these differences were never significant. Polyamine concentrations and ODC activity were not significantly reduced, and ADC activity remained unchanged in mildewed leaves with all surface fungal growth removed. It would appear therefore that not only does most of the increase in amines and ODC activity reside in the leaf itself, but that very little of this increase is due to fungal growth and sporulation. Furthermore, it seems possible that the increase in polyamines in mildewed barley could be involved in 'green-island' formation, where regions around mildew pustules remain green and physiologically active while the rest of the leaf senesces.     

Effects of dual infections of Puccinia hordei and Erysiphe graminis on barley, cv. Zephyr

Seed tubers of the varieties King Edward, Majestic and Pentland Crown selected as ‘clean’ (lesion-free), moderately, or severely affected by gangrene lesions were planted in field experiments. Infection delayed plant emergence, increased the number of stems/plant, sometimes caused gaps in crops and was associated with increased blackleg. On average severely affected seed yielded 20% less than ‘clean’ seed. Seed infection also increased the proportion of tubers in smaller size grades so that crops from severely infected King Edward seed averaged 1·4 ton/acre (3·5 t/ha) less small ware and 2·5 ton/acre (6·3 t/ha) less large ware than ‘clean’ seed. With Majestic, small ware was increased (0·7 ton/acre (1·8 t/ha)) and large ware decreased (4·4 ton/acre(11·0 t/ha)); Pentland Crown was similarly affected (small ware increased 0·8 ton/acre (2·0 t/ha); large ware decreased 3·9 ton/acre (9·8 t/ha)). In eight of twelve experiments unselected diseased stocks yielded significantly less than ‘clean’ tubers. Other experiments compared seed stocks with different proportions of gangrene-infected seed tubers. Yields decreased as the proportion of diseased seed tubers increased, but differences were significant only when more than 60% were affected. Surprisingly, yields from ‘clean’ tubers also decreased as the proportion of diseased tubers increased in the stocks from which they were selected. Gangrene on progeny tubers after storage was not always related to the amount of gangrene visible on the seed. It was increased by riddling or wounding and decreased by dipping tubers in organo-mercury fungicide before or soon after wounding.     

cDNA cloning of mRNAs induced in resistant barley during infection by Erysiphe graminis f.sp. Hordei

Summary Near-isogenic cultivars of Hordeum vulgare which differ for the Mlp gene for resistance to Erysiphe graminis f.sp. hordei were inoculated with race 3 of this pathogen and in vitro translation products of mRNA populations compared by 2-dimensional gel electrophoresis and fluorography. This revealed the presence of new mRNA species in infected leaves compared to non-inoculated controls. These new mRNA species were more abundant in resistant leaves than susceptible leaves. A cDNA library was prepared from poly(A)⁺RNA isolated from infected leaves carrying the Mlp gene for resistance (cvMlp). The library was screened by differential hybridization using [³²P]-labelled cDNA prepared from poly(A)⁺RNA of both control and infected leaves. Six cDNA clones showing greater hybridization to cDNA prepared from infected leaves were selected. These six cDNA clones hybridized to DNA isolated from barley leaves but not to DNA from conidia of the fungus. In Northern blot analysis of RNA from infected leaves the six cDNA clones each hybridized to mRNA species of different size. Translation products for three of the cDNA clones corresponded to infection-related translation products identified on 2-dimensional fluorograms. The cDNA clones were used to study the kinetics of host mRNA induction during infection of the near-isogenic cultivars of barley. The host mRNA species corresponding to the cDNA clones were induced prior to 24 h after inoculation during the primary penetration processes. In addition the mRNAs corresponding to four of the cDNA clones increased to greater amounts in cvMlp than in the near-isogenic susceptible cultivar (cvmlp) over a 2-d period following inoculation. These results suggest that the Mlp gene has a regulatory role in host gene expression resulting in enhanced expression of several host mRNA species following infection by the powdery mildew fungus.     

The influence of powdery mildew (Erysiphe graminis) infection on the development of four spring wheats

Infection with Erysiphe graminis reduced the weight of the roots and aerial parts of four wheat cultivars of contrasting susceptibility at the three-leaf stage. It had little effect on the more resistant varieties at the five-leaf and flag-leaf stages. When ¹⁴C was supplied to the youngest fully expanded leaves at successive stages of growth, the proportion recovered from the roots, and that translocated to other tillers when present, was reduced, especially in the more susceptible cultivars.     

An analysis of rain-mediated dispersal of Drechslera teres conidia in field plots of spring barley

In two separate trials rain-mediated dispersal of Drechslera teres conidia was observed in field plots of cv. Beatrice spring barley. Within the crop spore number was greater towards the base reflecting both the downward movement of conidia and the greater availability of spores on older leaves. From the edge of the crop half as many conidia were trapped at 100 cm as at 25 cm. In both trials the cumulative spore catch total lagged behind the increase in net blotch infection levels on the top two leaves. The number of spores sampled appeared closely related to rainfall intensity.     

Histochemical observation of the halo on the epidermal cell wall of barley leaves attacked by Erysiphe graminis hordei

Summary Histochemical characters of the halo on the epidermal cell wall of barley leaves attacked byErysiphe graminis hordei were investigated with light microscope. The area corresponding to the halo showed reduced intensity of stain reactions for cuticle, pectin and cellulose, especially at the penetration point. From the several histochemical reactions, it was concluded that reducing substances with aldehyde groups (such as hexose), pentoses and possibly uronic acids occur in the halo. According to these results, it can be concluded that the halo is caused by the degeneration of the epidermal cell wall by the fungal enzymes.Contributions from Laboratory of Plant Pathology, Kyoto Univ., No. 230.     

Untersuchungen zur physiologischen Spezialisierung von Erysiphe graminis DC

Zusammenfassung In den vorliegenden Untersuchungen wurde der Wirtspflanzenbereich einer Mehltaupopulation von Dactylis glomerata L., Sorte Motterwitzer, überprüft. Von 460 infizierten Grasarten blieben 420 befallsfrei, 40 erwiesen sich als anfällig. Am stärksten befallen wurden die drei Arten Dactylis aschersoniana Graebner, Dactylis glomerata L. und Dactylis polygama Horvat sowie die Subspecies D. glomerata L. spp. aschersoniana (Graebn.) Thell., die aber insgesamt in ihrem Verhalten sehr unausgeglichen waren. Eine unerwartet geringe Anfälligkeit von Dactylis woronowii Ovcz. müßte nochmals überprüft werden. Als sehr anfällig erwiesen sich die drei Grasarten Bouteloua hirsuta Lag., Danthonia provinzialis DC. und Sesleria latifolia (Adam) Degen. Geringer Befall konnte auch an einigen Wildgräsern der Gattungen Agropyron, Bromus, Festuca, Mibora, Poa und Sesleria nachgewiesen werden. Vom Getreide wird nur die Gerste vom Knaulgras-Mehltau befallen. Da sowohl bei der Wildform als auch bei der Zuchtsorte Motterwitzer von Dactylis glomerata L. über 10% befallsfreie Pflanzen gefunden wurden, erscheint die Züchtung mehltauresistenter Sorten von Dactylis glomerata L. nicht ohne Aussicht auf Erfolg.

---

Studies on the physiological specialization of Erysiphe graminis DCIV. The host plants of cocksfoot mildew

Summary In the described experiments the interaction of 460 grass species with a mildew population obtained from Dactylis glomerata L. Motterwitzer was examined. 420 species remained free of symptoms, while 40 species were susceptible. The most susceptible ones were Dactylis aschersoniana Graebner, Dactylis glomerata L., Dactylis glomerata spp. aschersoniana (Graebn.) Thell., and Dactylis polygama Horvat, but all showed differences in their behaviour. The unexpectedly low susceptibility of Dactylis woronowii Ovcz. should be examined again. Three grass species Bouteloua hirsuta Lag., Danthonia provinzialis DC., and Sesleria latifolia (Adam) Degen were also highly susceptible to cocksfoot mildew, while on wild grasses of the species Agropyron, Bromus, Festuca, Mibora, Poa, and Sesleria only few symptoms could be seen. Among cereals only barley could be infected by cocksfoot mildew. Not only in the wild form of Dactylis glomerata L. but also in the cultivated variety Motterwitzer, above 10% were found to be free from infection. Therefore the breeding of resistant varieties of Dactylis glomerata L. seems to be feasible.

---

---

Für die freundliche Unterstützung der Arbeiten möchten wir den Botanischen Gärten der Deutschen Demokratischen Republik sowie der Deutschen Bundesrepublik unseren herzlichen Dank aussprechen.

---

Angenommen durch H. Stubbe