Infected Tillers Research Articles

Incidence and control of barley leaf stripe (Pyrenophora graminea) in Scottish barley during the period 1987–1992

The incidence of Pyrenophora graminea was determined in winter and spring barley seed harvested in each of the 6 years 1987 to 1992. The occurrence of P. graminea was highest in spring barley seed harvested in 1989 and 1990, with 69% of samples in 1989 and 82% in 1990 infected. The mean infection levels were 6·1% in 1989 and 7·5% in 1990. The introduction of a voluntary Code of Practice in January 1991 significantly reduced infection: in 1992 only 10% of spring barley samples were infected, and the mean infection level was less than 0·2%. In spring barley, there was a significant relationship between the level of seed infection and the percentage of diseased tillers in commercial crops (r= 0·890, P < 0·001). However, tiller infection was consistently lower than seed infection. During the period of the study the mean annual leaf stripe infection on winter barley seed did not exceed 1%.

Studies of the severity and incidence of Paspalum leaf blight

Levels of paspalum leaf blight (Ascochyta paspali) severity (%LAD), diseased dry matter (%DDM) and incidence on tillers and leaves on dairy pastures in northern Victoria assessed during the summer months (November-March) of 1983-84, 1984-85, 1985-86 and 1986-87 fluctuated between samplings and farms. Infected tissues accounted for 19-22% of the total dry matter in 1983-84 and 1984-85. Disease severity (%LAD) was significantly (P<0.001) linearly related to incidence of infected tillers (IT) or leaves (IL) and highest correlations were obtained following natural logarithmic transformations of severity and incidence data. Incidence of infected tillers on a 1 ha site in Northern Victoria ranged over 7- 19% in 1985-86 when samples were taken along a M-transect and 1.75-30% in 1986-87 when stratified random samples were taken using a microcomputer-based program 'Field Runner'. The latter reduced sampling bias, indicated that the distribution of disease was aggregated and a minimum sample size of 450 tillers was required. The fluctuating incidence levels with time were correlated with sampling intervals following grazing. Incidence of infected tillers on 11 farms in northern Victoria and Finley, N.S.W., in January 1987, ranged from 11.8 to 56.4%. The significance of the severity-incidence relationships, the aggregated distribution of paspalum leaf blight, variation in levels between farms, the effects of grazing on epidemics of paspalum leaf blight and crop loss and the use of 'Field Runner' in disease surveys is discussed.

Status of False Smut (Fs) of Rice in Eastern Uttar Pradesh, India

FS (false smut) caused by Claviceps oryzae-sativa Hashioka [Ustilaginoidea virens (CKe) Tak.] has become a very important disease of wet season rice in eastern Uttar Pradesh. Meteorological factors relationships to FS incidence indicate that relatively lower temperatures (around 20 C) and high humidity (above 90%), coupled with well-distributed moderate rainfall during flowering, favored the disease. Late sowing usually resulted in higher FS infection. The disease was more severe at higher fertility levels (100-50-50 kg NPK/ha) than at lower fertility levels (50-25-25 kg NPK/ha). The percentage of smutted grains/panicle varied considerably in different varieties, but there was little variation in the size of smut balls. There appears to be a direct correlation between percentage of infected tillers and percentage of smutted grains/panicle. FS infection reduces grains/panicle and 1,000-grain weight, compounding yield reductions. It increases the number of partially filled and unfil1060led grains leading to high chaffiness. The seeds near smutted grains have lower germination than seeds from healthy panicle. Eastern Uttar Pradesh had a FS epidemic 1984-1985 to 1985-86. FS incidents ranged from 10 to 30% in affected rice plots. Newer cropping technology, including planting high N-responsive varieties, enhancing the moisture supply, and including late sown wheat in the crop rotation, aggravated the disease in farmer's fields. In years of severe incidence, FS losses equaled losses to bacterial blight and sheath

Pyrenophora graminea on Winter Barley Seed: Effect on Disease Incidence and Yield Losses

AbstractField experiments were carried out in 1982–83 and 1983–84 in Northern and Central Italy (3 locations) in order to investigate the effect of different levels of seed infection of Pyrenophora graminea on disease incidence and yield losses in ‘Perga’ winter barley.Six levels of natural seed infection, assessed by the deep‐freezing blotter method have been compared in 8 row‐plots, 7.5 m long, arranged in randomized blocks with 4 replications.The percentage of infected plants and tillers has been recorded in all locations and the yield in two of them.A highly significant correlation was found between seed infection, plant infection, tiller infection and yield reduction. Major ratios found were: infected seeds/infected seedlings 1: 0.4, infected tillers/yield loss 1: 0.9, infected seeds/yield loss 1: 0.3.The threshold of seed infection at which production was not significantly different from the healthy control was 14%. Therefore seed treatment is advisable, under the conditions of Northern and Central Italy, when the percentage of seed infection in commercial seed lots is above this level. A tolerance near zero is recommended in prebasic and basic seeds.

Visual assessment of seasonal changes in amount of mycelium ofAcremonium loliaein leaf sheaths of perennial ryegrass

Abstract Counts were made of hyphae of the endophyte Acremonium loliae Latch, Christensen & Samuels in leaf sheaths of perennial ryegrass (Lolium perenne L.) cv. Ellett. Material was collected from grazed plots at 4 North Island sites during a 2-year period. Numbers of hyphae/mm breadth of leaf sheath varied by over tenfold in infected tillers collected from the same site at the same time, but mean counts from 40 tillers/collection showed regular and repeatable trends. At 3 sites with yearly rainfalls of 1100–1200 mm, mean counts were similar at the same time, being highest in summer and lowest in winter. At these sites the rise and fall between the 2 extremes was regular. However, at the fourth site, with a yearly rainfall of about 800 mm, counts were high in November and December, were depressed from January to March, reached a peak in April or May, and then declined. A second endophyte was seen in some plants. However, the incidence of each endophyte was generally independent of the other.

LOLIUM ENDOPHYTE AND SHEEP PERFORMANCE ON PERENNIAL RYEGRASS CULTIVARS

Some effects of lolium endophyte (Acremonium lolioe) on sheep production were evaluated using pure swards of high (SO%>) and low (< 5%) endophyte Nui and Ariki ryegrass. The proportion of infected tillers in high endophyte treatments increased by 19% in 15 months. Ryegrass staggers occurred on both high endophyte ryegrasses - being slightly worse on Nui. The peak ryegrass staggers outbreak did not coincide with peak endophyte mycelium concentration in ryegrass plants. Hoggets grazing the low endophyte ryegrasses had a 1.6 kg advantage in liveweight gain in spring, when allowances were equal, but fewer sheep grazing days. In summer and autumn sward damage by Argentine stem weevil, drought and over-grazing eliminated low endophyte Ariki treatments and reduced herbage production from low Nui to 70% of high endophyte Nui. Tiller densities in low endophyte treatments were 28% of those in high endophyte treatments. High endophyte Ariki had the highest overall production: 7.8 t/ha of herbage and 15 kg/head liveweight gain compared with 6.9 t/ha and 12.5 kg/head for high endophyte Nui and 4.7 t/ha and 9 kg/head for low endophyte Nui. Differences in production due to endophyte highlight the need for caution in interpreting results from trials when endophyte status of ryegrass is unknown. Keywords: Lolium endophyte, Acremonium loliae, ryegrass staggers, Lol~m perenne, live weight gain, pasture production, Ariki, Nui

Resistances of grasses to two sobemoviruses, cocksfoot mottle and cynosurus mottle

AbstractInfection of Dactyls glomerata with cocksfoot mottle virus (Cf MV) and of Cynosurus cristatus with cynosurus mottle virus (CyMV) is frequently lethal. However, varieties of each species differ in the proportion of genotypes which survive, and in the damage suffered by these surviving plains. Infected plants of the CfMV‐resistant cocksfoot, cv. Cambria, were generally much more aggressive in the competitive environment of the sward than were infected plants of the susceptible cv. S37. Thus, Cambria populations outyielded comparable populations of S37 by only 7% when healthy, but by 40% when infected with CfMV. A few genotypes in the infected Cambria population apparently recovered from the disease, became virus‐free and were immune to further infection Resistance to CyMV in C. cristatus takes the form of resistance to systemic spread. A few symptomless and apparently virus‐free tillers grow up from the bases of infected tillers. However, these tillers are susceptible to further infection. It is suggested that, in resistant genotypes, CfMV and CyMV trigger the production of antiviral agent(s) which block or restrict virus replication. There is some evidence that CfMV resistance is virus isolate specific, and this could present problems when breeding for durable resistance.

Influence of Nutrition on Stripe Smut Severity in Kentucky Bluegrass Turf1

AbstractStripe smut, caused by the fungus Ustilago striiformis (West.) Niessl., is highly destructive to several fine turf cultivars of Kentucky bluegrass (Poa pratensis L.). while there is evidence that turf management practices can modify disease injury, the role of nutrient status in disease development is uncertain. Stripe smut severity and fertility management was studied using ‘Merion’ Kentucky bluegrass plots fertilized with four nutrient combinations (N:O:O, N:P:O, N:O:K, and N:P:K) applied at three rates (12:2:4, 24:4:8, and 48:8:16 g N, P, and K per m2 per year). A natural infection of stripe smut occurred throughout the plot area in 1972 and persisted through 1975. After infection, a close correlation between turf quality and disease incidence was noted. Heavily infected plots, as indicated by disease scores and counts of infected tillers, were those fertilized at high rates with incomplete fertilizers. Grass receiving high rates of N‐P‐K fertilizer was less diseased than that receiving high N alone or N plus P or K. Tiller counts revealed stand thinning in all plots as the disease continued but low fertility plots contained more plants than heavily fertilized plots. Stripe smut severity in susceptible Kentucky bluegrass cultivars is influenced by fertility level and balance.

Effects of inoculation with Septoria nodorum on yield components of spring wheat

SUMMARYSpring wheat, cv. Kolibri, was artificially inoculated with spore suspensions of Septoria nodorum, from the time of full expansion of the third leaf to the end of flowering and the effect on yield components recorded. Most components were reduced by increasing severity of infection and grain weight losses of 56 and 35% were produced on single‐stemmed and tillering plants respectively, by the most severe infection. The effects on components of yield differed considerably between the main stems and the tillers and an increase in grain number on moderately infected tillers partly compensated for reductions in yield on the main stem.

Incidence of barley yellow dwarf virus in ryegrass pastures in New Zealand

Abstract The percentage of plants infected with barley yellow dwarf virus (BYDV) was determined in each of 45 New Zealand ryegrass pastures during the summer of 1975–1976. Incidence of BYDV infection was extremely variable in pastures of similar age, but 1- to 2-year-old pastures generally had fewer infected tillers than did older swards. Many 6- to 30-year-old pastures had over 50% of plants infected with BYDV. Highest virus infection was 84% in two perennial ryegrass pastures aged 8 and 15 years. Pastures at Palmerston North had a slightly higher incidence of BYDV than those at Kaikohe and Lincoln. Pastures in the far south of the South Island appeared to have a low incidence.

The measurement of disease severity in cereal smut.

For smut diseases of cereal crops in which the presence of disease is signaled by the occurrence of diseased culms, the tradition has been developed whereby disease severity is measured in percentages, either of plants or of culms, which show the disease. However, the data that have accrued have contributed relatively little to an understanding of either the disease or host resistance to it. In this study the percentages of infected tillers on diseased plants (within-plant disease severity) were both recorded and were found, on analysis, to be strongly correlated. Although the strong correlation suggested a general identity of genes responsible for among-and within-plant disease severity, other aspects of the analysis suggest that the fungus must pass through two distinct barriers, or thresholds, in order to produce teliospores. If the first threshold is surmounted, the fungus will be able to cause smutting in at least one tiller of the plant (as measured by among-plant disease severity); if the second threshold is also crossed, additional culms will also be smutted (as measured by within-plant disease severity). One can regard the individual culm as having two separate (but not independent) opportunities of remaining healthy following inoculation of the seed. Both are measured and defined in terms of probability.

A Histological Study of the Grass Heteropogon contortus Infected by the Smut Sorosporium caledonicum

A study of the spatial and temporal relationships of Heteropogon contortus and the smut Sorosporium caledonicum has been made. It has been shown that hyphae move into the axillary buds on the bases of infected tillers at various stages of bud development. Hyphal distribution in the base of the parent tiller determines whether or not a bud receives mycelium, and the extent to which hyphae grow through the tissues of the buds and young tillers determines whether a tiller bears a sorus or an inflorescence. A sorus forms only if hyphae are close to the apical meristem at the time of floral initiation. Floral initiation occurs abnormally early in smutted tillers which elongate at the beginning of a season. A clear relationship exists between the presence of hyphae in close proximity to the apical meristem, and early floral initiation.

Crown rot of lucerne in Queensland caused by Colletotrichum trifolii

A detailed description of a crown rot of lucerne caused by Colletotrichum trifolii is given for the first time in Australia. The characteristic symptom of the disease, which causes serious losses in Queensland, is an internal black discolouration extending from the base of infected tillers, through the crown and often into the tap root. The fungus spreads internally into the crown tissue from anthracnose lesions produced on the stem bases. Field trials at Gatton and Biloela have shown that the cultivars Denmat, African, Siro Peruvian, and Gabes are particularly susceptible. High levels of field resistance are available in the cultivars Rhizoma, Lahontan, and the experimental lines ESI, BDSI, and ECRSI. The common commercial cultivar, Hunter River, was less susceptible than many of the cultivars tested.

Ecopathological Investigations (1) Influence of Plant Pathogenic Fungus on Productivity of Dichanthium annulatum (Forsk) Stapf

Dichanthium annulatum is an important fodder grass, severely infected by Sphacelotheca annulata causing smut disease. The plant pathogenic fungus acts as a consumer. Habit of infected tillers was changed. Reduction in height, diameter, number of leaves per tiller, area per leaf and moisture content was observed in infected plant. There is an increase in respiratory rate of leaf but reduction in NPP and GP of leaf in infected plant. Pigment study reveals that reduction in a particular pigment may result in apparent increase in rest of the pigments. Thus such drastic change in the biology of the host is due to overall activity of pathogen

Studies on cereal mildew in Britain

Overwintering cleistocarps of Erysiphe graminis do not contribute to spring outbreaks of cereal mildew in this country. Ascospores, shed from July to late September, are the source of infection for successive crops of winter wheat and barley, but conidia from infected late tillers are the chief source for winter oats. Ascospore differentiation only takes place under high moisture, following the completion of a ‘ripe-to-spore’ stage. Optimum conditions for this are located at the base of the straws and the stubbles are the main source of the ascospore shower. The intensity of the shower in any season is related to the environmental conditions during the growth of the crop and the degree of humidity at and following harvest. Direct infection of autumn-sown cereals may occur but more generally it derives from stubble volunteer seedlings infected by the ascospores. The timing of the ascospore shower and the extent to which volunteer seedlings develop on the stubbles determine the incidence of mildew in early-sown winter cereals, but susceptibility to disease decreases as the date of sowing is delayed. Although existing lesions continue growth and sporulation, during the winter there is little further spread of infection through the crops. The incidence of infection foci for the build-up of mildew in spring is thus dependent upon the climatic conditions prevailing during the previous year and the extent and timing of the autumn cultivations.