Effect of barley yellow dwarf virus on susceptibility of barley cultivars to net blotch (Pyrenophora teres) and leaf blotch (Rhynchosporium secalis)

The effect of barley yellow dwarf virus (BYDV) on the development of net blotch (Pyrenophora eves) and leaf blotch (Rhynchosporium secalis) was examined on seven barley cuitivars. Seedlings were infected with BYDV at the two-leaf stage (G.S. 12). Their susceptibility to three isolates of p teres and isolates of two races (U.K. 1, U.K. 2) of R. secalis was examined at the four-leaf stsge (G.S. 14) and when plants were more mature (G.S. 33/38). At G.S. 14 numbers of lesions produced by P. teres and R. secalis were reduced, on average, by 37 and 72% respectively, and at G.S. 33/38 by 61 and 74%.     

COMPARISION OF RATES OF PARAQUAT PRIOR TO DIRECT-DRILLING CEREALS

Summary. Trials were conducted in East Anglia to compare direct-drilling following paraquat at 1 and 2 lb/ac with normal cultivations for both winter wheat and spring barley. The three treatments were compared at two levels of nitrogen.
With direct-drilled winter wheat, yields were higher after using paraquat at 2 lb/ac and at this rate there was little difference between direct-drilling and normal cultivations when 100 units of nitrogen were applied in spring. When only 50 units were given the results were more variable, with direct-drilling significantly outyielding normal cultivations in one trial, being outyielded in another and showing no difference in the third.
Yields of spring barley were slightly higher after paraquat at 2 lb/ac as compared with 1 lb/ac, but not significantly so. The time of application of paraquat influenced yield; when applied in December yields from direct-drilling and normal cultivations were similar, but when applied in February higher yields were recorded with normal cultivations.
Comparaison des doses de paraquat a utiliser avant un semis direct de dreales     

Proteinaceous Metabolites from Pyrenophora teres Contribute to Symptom Development of Barley Net Blotch

ABSTRACT Pyrenophora teres, the causal agent of net blotch of barley (Hordeum vulgare L.), induces a combination of necrosis and extensive chlorosis in susceptible barley cultivars. Cell-free filtrates from both net and spot forms of P. teres; P. teres f. sp. teres, and P. teres f. sp. maculata were found to contain phytotoxic low molecular weight compounds (LMWCs) and proteinaceous metabolites which appear to be responsible for different components of the symptoms induced by the two forms of the pathogen in a susceptible cultivar of barley (cv. Sloop). Proteins induced only brown necrotic spots or lesions similar to those induced by the pathogens 72 h after inoculation. In contrast, LMWCs induced general chlorosis seen 240 h after inoculation but not the localized necrosis. Neither hydrolyzed or heat- or protease-treated proteinaceous metabolites induced the symptoms. This is the first report of the involvement of proteins produced by P. teres in symptom development during net blotch disease of barley.     

Effects of wheat crop debris on the sporulation and survival of Pseudocercosporella herpotrichoides

Three separate experiments showed that wheat tissue infected with the cereal eyespot fungus, Pseudocercosporella herpotrichoides , produced fewer spores in the presence of chopped wheat straw than when it was absent. This provides a possible explanation for earlier observations that there was often less eyespot in plots where straw had been incorporated than where it had been burnt. Sporulation on eyespot infected wheat tissue was not closely correlated with the viability of P. herpotrichoides , which could usually be isolated from infected tissue for some time after it had apparently lost the ability to produce spores. Many of the colonies that were isolated from such tissue also failed to sporulate under the conditions used but non sporulating colonies were less common amongst those isolated from tissue that had been mixed with chopped straw than from tissue that had not.     

Identification of Molecular Genetic Markers in Pyrenophora teres f. teres Associated with Low Virulence on 'Harbin' Barley

ABSTRACT Two isolates of the barley net blotch pathogen (Pyrenophora teres f. teres), one possessing high virulence (0-1) and the other possessing low virulence (15A) on the barley cultivar Harbin, were crossed and the progeny of the mating were isolated. Conidia from cultures of the parent and progeny isolates were used as inoculum to determine the inheritance of virulence in the pathogen. Of the 82 progeny tested, 42 exhibited high virulence and 40 exhibited low virulence on 'Harbin' barley. The data support a model in which a single, major gene controls virulence in P. teres f. teres on this barley cultivar (1:1 ratio; chi(2) = 0.05, P = 0.83). Preparations of DNA were made from parental and progeny isolates, and the DNA was subjected to the random amplified polymorphic DNA (RAPD) technique in a search for molecular genetic markers associated with the virulence phenotype. Five RAPD markers were obtained that were associated in coupling with low virulence. The data indicate that the RAPD technique can be used to tag genetic determinants for virulence in P. teres f. teres.     

Influence of aldicarb on root lesion nematodes, leaf disease and root rot in wheat and barley

The effects of aldicarb on populations of root lesion nematodes (primarily Pratylenchus penetrans ) and on grain yields of spring barley and wheat were examined in the field over 3 years, 1981*83. The incidence of barley net blotch ( Pyrenophora teres ), wheat leaf blotch ( Leptosphaeria nodorum ), and common root rot ( Cochliobolus sativus ) was also recorded in 1982 and 1983. Aldicarb treatments reduced the size of root lesion nematode populations in soil and roots in all years, except in the mid-season soil sample in 1983. The severity of leaf disease was decreased only in 1982, but the incidence of root rot was not significantly affected by the nematticide. Although aldicarb increased cereal grain yields by approximately 15% there was no significant relationship between numbers of root lesion nematodes in roots and soil and fungal disease symptoms on barley and wheat.     

THE USE OF HERBICIDES IN ALTERNATE HUSBANDRY AS A SUBSTITUTE FOR PLOUGHING

Summary. It is practicable to use herbicides as an alternative to ploughing grass swards for the preparation of a seedbed for the sowing of cereals and kale. The yields of spring barley and kale following a glaass/clover sward killed with 10 lb/ac amitrole-T were similar to those obtained following ploughing. Yields of tip to 40 cwt/ac of winter wheat were obtained following grass swards killed with amitrole-T compared with up to 45 cwt/ac after ploughing.
The ideal herbicide must kill all plants in a sward and have no residual toxicity to the subsequent crop. At 10 lb/ac, amitrole-T killed most plants in the sword, but it was considered necessary to delay sowing for at least 3 weeks after spraying to minimize the danger of residual toxicity. Ploughing gave the lowest incidence of grasses persisting from the sward. Paraquat did not control clover and Agropyron repens , while broad-leaved weeds were more common on the ploughed than on the sprayed land.
There were differences in the amount of nitrogen mineralized in ploughed and In undisturbed soil, but these were insufficient to affect crop yields materially. When a lower yield followed herbicidal destruction of the sward, this was not accompanied by a reduced percentage nitrogen content.
L'emploi des déherbants pour la rénovation des prairies     

AFLP-based PCR markers that differentiate spot and net forms of Pyrenophora teres

Specific polymerase chain reaction (PCR) primers were developed from amplified fragment length polymorphism (AFLP) fragments of Pyrenophora teres , the causal agent of net blotch on barley leaves. The primers were designed specifically to amplify DNA from P. teres f. teres (net form) and allow its differentiation from P. teres f. maculata (spot form), which is morphologically very similar to P. teres f. teres in culture. The PCR amplification was carried out successfully from DNA extracted from fungal mycelium. The PCR assay was validated with 60 samples of Pyrenophora species. The amplification with four designed PCR primer pairs provided P. teres form-specific products. No cross-reaction was observed with DNA of several other species, such as P. tritici-repentis , P. graminea and Helminthosporium sativum .     

DIRECT-DRILLING OF CEREALS AFTER USE OF PARAQUAT

Summary. Cereal crops were grown at Jealott's Hill in 1962 and 1963 without cultivations, following the use, before drilling, of paraquat to kill unwanted vegetation. This investigation was extended with a series of trials at outside centres. Three trials with winter wheat were drilled in the autumn of 1963, two into pasture and one into stubble. Three barley trials were drilled into stubble in spring 1964.
All the autumn trials and one spring trial compared direct-drilling with normal cultivations at two levels of nitrogen. The other two spring trials compared rates and times of application of paraquat without any plough comparison.
Individual trials showed significant yield differences between direct-drilling and ploughing, but there was no consistent advantage in favour of either technique.
Spraying in advance of drilling generally resulted in similar yields to spraying and drilling on the same day. Winter wheat drilled into pastures showed some retardation of spring growth when spraying and drilling had been carried out on the same day.
When averaged over times of application, yields after spraying paraquat at 2 lb/ac were significantly higher than after 1 lb/ac.
In the trials where two levels of nitrogen were included crops responded to an increase from 60 to 120 units nitrogen/ac as top dressing for winter wheat and from 60 to 90 units nitrogen/ac combine-drilled for spring barley; the response was not always significant.
Semis direct de céréales après application de paraquat     

Variation in the resistance of barley cultivars and in the pathogenicity of Drechslera teres f. sp. maculata and D. teres f. sp. teres isolates from France

Isolates of Drechslera teres that cause net or spot-type symptoms on barley ( Hordeum vulgare ) were collected in 1986 and 1987 from fields in different regions of France. Variations in pathogenicity were evaluated using 12 barley cultivars. The Middle-Eastern cultivars Arrivate and 79-S10-10 were resistant to all isolates except R5 and S5. The Ethiopian cultivar C1 5791, previously reported to be resistant, was susceptible to the R5 and S5 biotypes. There was a high correlation coefficient between the classification of cultivars for resistance to D. teres f. sp. teres and D. teres f. sp. maculata. A method for conserving the virulence of the isolates on straw is evaluated. The virulence level of the isolates was the same after 4 years of storage using this method.     

Effects of Pyrenophora teres on dry matter production and yield components of winter barley

Inoculation of winter barley plants in a glasshouse with Pyrenophora teres at three different growth stages (GS 11, 13 or 30) greatly decreased root and shoot dry matter production and the size of healthy leaves produced subsequently, but there was no significant yield loss with a single inoculation at GS 11 or 30. Inoculation at GS 13, GS 31 or GS 39 decreased grain yield by 12,17 and 20% respectively, and also straw yield. Larger yield losses resulted from repeated inoculations on five successive occasions (GS 11, 13, 30, 31 and 39) which caused much disease on all leaves throughout the life of the plant. All components of yield measured were decreased by the cumulative effect of successive inoculations; ear number by 15%), grain sites per ear by 20%, grain yield by 48% and straw yield by 32%.     

大麦种质对叶斑病的抗性鉴定与评价

 由麦根腐平脐蠕胞菌引起的叶斑病在世界各大麦种植区均有发生,严重影响大麦的产量和品质。选育和应用抗性品种是防控该病害最有效的策略,然而可利用的抗源非常有限。在本研究中对中国233份具有代表性的大麦种质资源进行成株期抗叶斑病田间人工接种鉴定,发现只有垦啤麦5号等10份材料对3个供试菌株都表现抗病,仅占供试材料的4.3%。另外对37份国内外重要的叶斑病抗源材料进行苗期及成株期抗叶斑病鉴定,结果显示成株期抗叶斑病材料所占比例为41%~46%,苗期抗性材料所占比例为50%~64%,其中ND17293等11份材料在苗期和成株期对3个菌株均表现为抗病,可作为抗源继续加以利用;基于上述鉴定结果,进一步分析发现供试大麦苗期对三个菌株的抗病比例均高于成株期抗病比例,说明大麦在不同生育期对叶斑病的抗性存在较大差异。另外发现大麦对B. sorokiniana不同致病类型的抗性也存在明显的专化性。     

Sources, survival and transmission of Cladosporium allii and C. allii-cepae, leaf blotch pathogens of leek and onion

Neither Cladosporium allii nor C . allii-cepae was detected in seed samples of 46 commercial cultivars of leek and nine of onion.
In glasshouse tests where flower inflorescences of onions and leeks were dusted with conidia of C. alliicepae and C. allii , respectively, few onion seeds and no leek seeds became contaminated. In field crops of leeks some spathes and inflorescences became diseased and gave 0 002% C. allii contaminated seeds. No infected onion seeds were obtained from naturally-infected plants in the field.
Conidia of both fungi survived for less than 6 weeks in sterile and non-sterile soil (during which time the temperature varied from -8 to +11 C); pseudothecial bodies survived longer.
Both pathogens survived for 3 months in debris of onion or leek on the surface of soil in pots under similar conditions. In debris buried at a depth of 7 cm in sterile or unsterile soil they survived for 2 months. Although C. allii survived only 1 month in debris on the soil surfaces following a leek crop, conidia of the fungus were trapped from the air above the area for at least 6 months and healthy leeks transplanted into this area developed the disease. No leaf blotch developed in leeks grown on land which had not previously borne that crop.     

Conidial dispersal by Alternaria brassicicola on Chinese cabbage (Brassica pekinensis) in the field and under simulated conditions

This study investigated conidial dispersal in the field, and effects of simulated wind and rain on the dispersal of A. brassicicola on Chinese cabbage ( Brassica pekinensis ). Spores were sampled using a Burkard volumetric spore sampler and rotorod samplers in a Chinese cabbage crop. Disease incidence in the field was well fitted by a Gompertz curve with an adjusted r ² of >0·99. Conidia of A. brassicicola were trapped in the field throughout the growing season. Peaks of high spore concentrations were usually associated with dry days, shortly after rain, high temperature or high wind speed. Diurnal periodicity of spore dispersal showed a peak of conidia trapped around 10·00 h. The number of conidia trapped at a height of 25 cm above ground level was greater than that at 50, 75 and 100 cm. Conidial dispersal was also studied under simulated conditions in a wind tunnel and a rain simulator. Generalized linear models were used to model these data. The number of conidia caught increased significantly at higher wind speeds and at higher rain intensities. Under simulated wind conditions, the number of conidia dispersed from source plants with wet leaves was only 22% of that for plants with dry leaves. Linear relationships were found between the number of conidia caught and the degree of infection of trap plants.     

Identification of Molecular Markers Linked to a Pyrenophora teres Avirulence Gene

ABSTRACT Genetic control of avirulence in the net blotch pathogen, Pyrenophora teres, was investigated. To establish an appropriate study system, a collection of 10 net form (P. teres f. teres) and spot form (P. teres f. maculata) isolates were evaluated on a set of eight barley lines to identify two isolates with differential virulence on an individual host line. Two net form isolates, WRS 1906, exhibiting avirulence on the cv. Heartland, and WRS 1607, exhibiting high virulence, were mated and 67 progeny were isolated and phenotyped for reaction on Heartland. The population segregated in a 1:1 ratio, 34 avirulent to 33 virulent (chi(2) = 0.0, P = 1.0), indicating single gene control of WRS 1906 avirulence on Heartland. Bulked segregant analysis was used to identify six amplified fragment length polymorphism markers closely linked to the avirulence gene (Avr(Heartland)). This work provides evidence that the P. teres-barley pathosystem conforms to the gene-for-gene model and represents an initial step toward map-based cloning of this gene.     

Response of spring cereal crops to soil residues of ethofumesate*

For evaluation of soil residues of ethofumseate [(±)2-ethoxy-2,3-dihydro-3,3-dimethylbenzofuran-5-yl-methylsulphonate], spring barley (Hordeum vulgare L.) and spring wheat (Triticum aestivum L.) were sown in soil planted 11 months previously with sugar-beet (Beta vulgaris L.) and previously treated with band or broad-cast applications of the herbicide at rates of 1.68-4.48 kg/ha. The height of barley and wheat was suppressed only where ethofumesate was applied broadcast and the soil was not ploughed after sugar-beet harvest. Three months after sowing, the 4.48 kg/ha rate suppressed the height of barley 18% and wheat 34%. In another experiment, barley grew normally on soil treated the previous year with pre-planting and post-emergence applications of ethofumesate where ploughing followed sugar-beet harvest. For all treatments, yields of straw and grain were not significantly lower than those of the untreated check plots. The dissipation of ethofumesate 24 weeks after application to sugar-beet was 89–100% when applied on a band compared to 85-95% when applied broadcast.     

Pyrenophora teres growth and severity of net blotch on barley under salt stress

European Journal of Plant Pathology - Pyrenophora teres causes one of the most destructive barley diseases in semi-arid production areas worldwide. With the burgeoning issue of soil salinization,...     

Mating types ofExserohilum turcicum in Israel

Fifty-one single conidial isolates ofExserohilum turcicum were collected from seven locations in Israel and three in the USA and tested for mating type and aggressiveness. Sixteen isolates mated were mating type a; 29 were mating type A; and six failed to mate with either the A or the a mating type. Isolates differed significantly in their ability to cause lesions of different sizes, and in their ability to produce conidia on the susceptible corn hybrid Jubilee. They also differed in their rate of growth on lactose casein agar. No significant difference in lesion size or conidial production was noted between mating types. Conidial production and radial growth were significantly lower for isolates with no mating capacity as compared with conidial production of defined mating types. Pseudothecia were produced after 14–16 and 21 days when mating occurred onSorghum halepense straw or barley straw, respectively. The average number of pseudothecia produced on 10 cm² of straw was 17 and 8 forS. halepense and barley, respectively. Pseudothecia were not produced on corn straw.     

The influence of crop rotation and soil tillage on seed population dynamics of A vena sterilis ssp. ludoviciana

The dynamics of seed populations of Avena sterilis ssp. ludoviciana (Durieu) Nyman in plots maintained under different crop rotations and tillage systems was studied over a 5-year period. The seed reserves buried in the soil were practically depleted during this period by using any of the three cropping systems evaluated. No significant differences were found between using a continuous barley rotation with annual application of herbicides and using a barley:fallow rotation with herbicides applied only as needed. The decline in seed populations was not affected by the tiliage system used during the fallow period (ploughing or no tillage). The tillage practices used in the various treatments, combined with the variable seed output from each treatment, resulted in different vertical distribution of the seeds in the soil profile. Shallow cultivation resulted in an accumulation of seeds in the upper soil layers; in contrast, a large proportion of the seeds were buried and maintained below 15 cm in the ploughed treatments. Although the seed distribution patterns produced by the various tillage systems had an effect on seedling recruitment, the largest changes in this parameter were associated with the different cropping sequences. Four times more seedlings were recruited in years under barley cropping than in those under fallow.     

Assessment of the reaction of some spring barley cultivars to Pyrenophora teres using whole plants, detached leaves and toxin bioassay

Twenty-one spring barley cultivars were tested for their reaction to Pyrenophora teres using three methods of assessment: inoculation of plants grown outdoors, a detached-leaf inoculation assay, and bioassay with P. teres toxins produced in vitro. Dram was the most resistant of the cultivars tested; a number of other cultivars including Goldmarker, Egmont and Georgie were also moderately resistant. Akka and Havila were highly susceptible. Good correlation was obtained between results from the three test methods.