Effect of wind on the dispersal of oospores of Peronosclerospora sorghi from sorghum

The effect of wind on the dispersal of oospores of Peronosclerospora sorghi , cause of sorghum downy mildew (SDM) is described. The oospores are produced within the leaves of aging, systemically infected sorghum plants. These leaves typically undergo shredding, releasing oospores into the air. Oospores are produced in large numbers (6.1 × 10³ cm⁻² of systemically infected leaf) and an estimate of the settling velocity of single oospores (0.0437 m s⁻¹) of P. sorghi indicated their suitability for wind dispersal. In wind tunnel studies wind speeds as low as 2 m s⁻¹ dispersed up to 665 oospores per m³ air from a group of leaves previously exposed to wind and displaying symptoms of leaf shredding. The number of oospores dispersed increased exponentially with increasing wind speed. At 6 m s⁻¹, up to 12 890 oospores per m³ air were dispersed. Gusts increased oospore dispersal. A constant wind speed of 3 m s⁻¹ dispersed a mean of 416 oospores per m³. When gusts were applied the mean was 15 592 oospores per m³. In field experiments in Zimbabwe, oospores were sampled downwind from infected plants in the field and at a height of 3.8 m above ground level immediately downwind of an infected crop. These data indicate that wind could play a major role in the dispersal of oospores from infected plants in areas where SDM infects sorghum, perhaps dispersing oospores over long distances.     

Competitive effects of redroot pigweed (Amaranthus retroflexus) on the growth indices and yield of corn

The mutual effects of redroot pigweed ( Amaranthus retroflexus ) on corn ( Zea mays ) were evaluated in an experiment conducted in 2005 at the Iranian Plant Protection Research Institute at Qazvin, considering the different densities of redroot pigweed against four different corn densities. Redroot pigweed, at 0, 35, 50, 65, and 80 plants m⁻¹ row⁻¹, was arranged factorially with corn at four, five, six, and seven plants m⁻¹ row⁻¹ in a randomized complete block design. Crop–weed competition resulted in a reduction in the total dry matter, Leaf Area Index, and crop growth rate of corn. Furthermore, an increasing weed density ≤65 plants m⁻¹ row⁻¹ reduced the corn grain yield and biological yield. Overall, six corn plants m⁻¹ row⁻¹ was suggested as the optimum density of this crop in competition with redroot pigweed.     

Use of density to predict crop yield loss between variable seasons

Summary Density:yield loss models rely on fixed coefficients, parameterized from a particular site and season to predict the impact of weeds on crop yields. However, the empiricism of this approach and failure to incorporate environmental effects, has major biological and economic implications. In this study, seasonal variability in wheat yield loss and associated economic costs from Avena spp. were quantitated. A competition experiment at Wagga Wagga, NSW, showed large seasonal differences in wheat yield loss from densities of Avena spp. across 2 years. Gross margins, simulated over a 51-year period, decreased as Avena spp. density increased and were more variable at low crop densities and higher weed densities. For example, at a density of 200 Avena spp. plants m⁻², coefficient of variation in crop gross margin ( CV ) was $AUS 47 ha⁻¹ for a crop density of 200 wheat plants m⁻² compared with a CV of $AUS 75 ha⁻¹ for a crop density of 50 wheat plants m⁻². The value of yield loss predictions will be vastly improved by making parameter values in yield loss models a function of seasonal factors such as rainfall.     

Substantial reductions in winter wheat diseases caused by addition of straw but not manure to soil

Over a period of 3 years, five agronomically distinct crops of winter wheat were grown in plots in which straw (1 kg m⁻²), manure (4 kg m⁻²) or nothing were incorporated into the soil. Plant establishment and height, but not leaf area per tiller, were lower in straw-treated plots. Fertilizer regimes differed between years. Soil and leaf nitrogen were recorded; there was no obvious link between N and any disease or soil amendment. The numbers of leaf layers scorable for disease were similar in all treatments. At the end of the season, plants from straw-treated plots had consistently reduced septoria tritici blotch (caused by Mycosphaerella graminicola ), powdery mildew [caused by Erysiphe ( Blumeria ) graminis ], brown rust (caused by Puccinia recondita ) and foot rot (caused by Fusarium spp.). Early on, M. graminicola was worse in straw-treated plots. In manure-treated plots, P. recondita was reduced but effects on other diseases were inconsistent and slight. A fungicide, chlorothalonil, was applied in one crop; its effects did not interact with those of other treatments. Mycosphaerella graminicola was not suppressed by straw in outdoor pot experiments. Late in the season, straw-treated plants had significantly higher leaf silica ( P  < 0·01). In a glasshouse experiment, plants supplied with silicon had less E. graminis infection ( P  < 0·001) and higher leaf silica, but effects on M. graminicola were inconsistent. A prior inoculation of M. graminicola primed plant defences against a subsequent attack of E. graminis , but only in the presence of adequate Si. It is postulated that straw acts in the field by increasing Si availability.     

Establishment of, and preliminary impact studies on, the rust, Maravalia cryptostegiae, of the invasive alien weed, Cryptostegia grandiflora in Queensland, Australia

The rust fungus Maravalia cryptostegiae , from south-west Madagascar, was introduced into Australia in 1995 as a classical biological control agent against the highly invasive rubber-vine weed Cryptostegia grandiflora , a woody climber endemic to Madagascar. The rust was released at 69 sites between 1995 and 1997 and is now established throughout the plant's exotic range in Queensland, estimated at over 40 000 km². Dispersal was low in the first 3–4 months but was virtually linear thereafter, and the rust spread over 100 km within the first year; after 3 years it was recorded 550 km away from the nearest release site. Spraying both dry and aqueous inoculum of uredinioid teliospores from the ground using mist-blowers, as well as from the air by atomizing spore suspensions, resulted in rust-induced defoliation, producing an overall reduction in fecundity and biomass of the weed. In sites with low water tables, weed growth decreased markedly, with a reduction in plant volume from 9 m⁻³ to 1 m⁻³ over a 4-year period. Both rust- and drought-induced stress combined to cause up to 75% plant mortality at some sites, and at all monitored sites, seedling recruitment was virtually nil. Improved growth of indigenous grasses amongst rubber-vine thickets has increased fuel loads and created opportunities to use fire as a component of an integrated approach to the management of this economically and ecologically damaging weed.     

Control of the invasive liana, Hiptage benghalensis

The liana, hiptage ( Hiptage benghalensis ), is currently invading the wet tropics of northern Queensland and remnant bushland in south-eastern Queensland, Australia. Trials using seven herbicides and three application methods (foliar, basal bark, and cut stump) were undertaken at a site in north Queensland (158 700 hiptage plants ha⁻¹). The foliar-applied herbicides were only effective in controlling the hiptage seedlings. Of the foliar herbicides trialed, dicamba, fluroxypyr, and triclopyr/picloram controlled >75% of the treated seedlings. On the larger plants, the cut stump applications were more effective than the basal bark treatments. Kills of >95% were obtained when the plants were cut close to ground level (5 cm) and treated with herbicides that were mixed with diesel (fluroxypyr and triclopyr/picloram), with water (glyphosate), or were applied neat (picloram). The costings for the cut stump treatment of a hiptage infestation (85 000 plants ha⁻¹), excluding labor, would be $A14 324 ha⁻¹ using picloram and $A5294 ha⁻¹ and $A2676 ha⁻¹, respectively, using glyphosate and fluroxypyr. Foliar application using dicamba for seedling control would cost $A1830 ha⁻¹. The costs range from 2–17 cents per plant depending on the treatment. A lack of hiptage seeds below the soil surface, a high germinability (>98%) of the viable seeds, a low viability (0%) of 2 year old, laboratory-stored fruit, and a seedling density of 0.1 seedlings m⁻² 12 months after a control program indicate that hiptage might have a short-term seed bank. Protracted recolonization from the seed bank would therefore be unlikely after established seed-producing plants have been controlled.     

Effect of salinity on pythium damping-off of cucumber and on the tolerance of Pythium aphanidermatum

A study was conducted to investigate the effect of salinity on pythium damping-off and tolerance to salinity among Pythium aphanidermatum isolates from different geographical origins, genetic backgrounds and saline/non-saline soils. Increasing irrigation-water salinity from 0·01 to 5 dS m⁻¹ significantly increased mortality in cucumber seedlings inoculated with P. aphanidermatum and reduced dry weight of non-inoculated seedlings. In vitro tests in culture media amended with different concentrations of NaCl showed that growth of P. aphanidermatum, P. spinosum and P. splendens isolates was stimulated or unaffected at salinity levels stressful for cucumber (electrical conductivity = 5 dS m⁻¹). Significant differences were found in tolerance to salinity among 47 P. aphanidermatum isolates obtained from different greenhouses. The concentration of NaCl required to reduce growth of P. aphanidermatum isolates by 50% varied from 23 to 62 dS m⁻¹, with an average of 46 dS m⁻¹, however, oospore production was more sensitive to salinity and no oospores were produced above 20 dS m⁻¹. Analysis of tolerance of P. aphanidermatum isolates to salinity showed no relationship between tolerance to salinity and geographical origins or genetic data. Isolates of P. aphanidermatum from greenhouses with no salinity problems were as tolerant to salinity as isolates obtained from salinity-affected greenhouses, suggesting lack of evidence for ecological adaptation within P. aphanidermatum in Oman. Increased mortality in cucumber seedlings at higher salinity levels may imply a synergistic interaction between salinity stress and salinity-tolerant Pythium species on cucumber seedlings, resulting in greater seedling losses.     

Improved management of Avena ludoviciana and Phalaris paradoxa with more densely sown wheat and less herbicide

Summary The effectiveness of crop competition for better weed control and reducing herbicide rates was determined for Avena ludoviciana and Phalaris paradoxa . Four experiments, previously broadcast with seeds of the two weeds in separate plots, were sown with three wheat densities, and emerged weeds were treated with four herbicide doses (0–100% of recommended rate). The measured crop and weed traits were first analysed across experiments for treatment effects. Grain yield and weed seed production data were then analysed using cubic smoothing splines to model the response surfaces. Although herbicide rate for both weeds and crop density for P. paradoxa had significant linear effects on yield, there was a significant non-linearity of the response surface. Similarly, herbicide rate and crop density had significant linear effects on weed seed production, and there was significant non-linearity of the response surface that differed for the weed species. Maximum crop yield and reduction in seed production of P. paradoxa was achieved with approximately 80 wheat plants m⁻² and weeds treated with 100% herbicide rate. For A. ludoviciana , this was 130 wheat plants m⁻² applied with 75% herbicide rate. Alternatively, these benefits were achieved by increasing crop density to 150 plants m⁻² applied with 50% herbicide rate. At high crop density, application of the 100% herbicide rate tended to reduce yield, particularly with the A. ludoviciana herbicide, and this impacted adversely on the suppression of weed seed production. Thus, more competitive wheat crops have the potential for improving weed control and reducing herbicide rates.     

Visual and PCR assessment of light leaf spot (Pyrenopeziza brassicae) on winter oilseed rape (Brassica napus) cultivars

Methods to assess light leaf spot ( Pyrenopeziza brassicae ) on winter oilseed rape cultivars were compared in laboratory, controlled-environment and field experiments. In controlled-environment experiments with seedling leaves inoculated at GS 1,4, the greatest differences in percentage area affected by P. brassicae sporulation were observed with inoculum concentrations of 4 × 10³ or 4 × 10⁴ spores mL⁻¹, rather than 4 × 10² or 4 × 10⁵ spores mL⁻¹, but older leaves had begun to senesce before assessment, particularly where they were severely affected by P. brassicae . In winter oilseed rape field experiments, a severe light leaf spot epidemic developed in 2002/03 (inoculated, September/October rainfall 127·2 mm) but not in 2003/04 (uninoculated, September/October rainfall 40·7 mm). In-plot assessments discriminated between cultivars best in February/March in 2003 and June in 2004, but sometimes failed to detect plots with many infected plants (e.g. March/April 2004). Ranking of cultivar resistance differed between seedling experiments done under controlled-environment conditions and field experiments. The sensitivity of detection of P. brassicae DNA extracted from culture was greater using the PCR primer pair PbITSF/PbITSR than using primers Pb1/Pb2. P. brassicae was detected by PCR (PbITS primers) in leaves from controlled-environment experiments immediately and up to 14 days after inoculation, and in leaves sampled from field experiments 2 months before detection by visual assessment.     

Host–parasite relationships of Meloidogyne incognita on spinach

Host–parasite relationships in root-knot disease of spinach caused by Meloidogyne incognita race 1 were studied under glasshouse conditions. Nematode-induced mature galls were large and usually contained one or more females and egg masses with eggs. Feeding sites were characterized by the development of giant cells containing granular cytoplasm and many hypertrophied nuclei. The cytoplasm in these giant cells was aggregated alongside the thickened cell walls. Stelar tissues within galls appeared disorganized. The relationship between initial nematode population density ( P _i) in a series from 0–128 eggs and second-stage juveniles per cm³ soil and growth of spinach cv. Symphony F₁ seedlings was tested under glasshouse conditions. A Seinhorst model [ y = m  + (1 −  m ) z ^P–T ] was fitted to fresh top- and total plant-weight data for inoculated and control plants. Tolerance limits ( T ) of spinach cv. Symphony F₁ to M. incognita race 1 for fresh top and total plant weights were 0·25 and 0·5 eggs and second-stage juveniles per cm³ soil, respectively. The minimum relative values for fresh top and total plant weights were zero in both cases at P _i ≥ 32 eggs and second-stage juveniles per cm³ soil. Root galling was least at low initial population densities and greatest at 16 eggs and second-stage juveniles per cm³ soil. Maximum nematode reproduction rate was 33·1-fold at the lowest P _i.     

Pathogenicity of the root-knot nematode Meloidogyne javanica on potato

Host–parasite relationships and pathogenicity of Meloidogyne javanica on potatoes (newly recorded from Malta) were studied under glasshouse and natural conditions. Potato cvs Cara and Spunta showed a typical susceptible reaction to M. javanica under natural and artificial infections, respectively. In potato tubers, M. javanica induced feeding sites that consisted of three to four hypertrophied giant cells per adult female. Infection of feeder roots by the nematode resulted in mature large galls which usually contained at least one mature female and egg mass. In both tubers and roots, feeding sites were characterized by giant cells containing granular cytoplasm and many hypertrophied nuclei. Cytoplasm in giant cells was aggregated alongside the thickened cell walls. Stelar tissues within galls appeared disorganized. The relationship between initial nematode population density ( P ) [0–64 eggs + second-stage juveniles (J2s) per cm³ soil] and growth of cv. Spunta potato seedlings was tested under glasshouse conditions. A Seinhorst model [ y = m  + (1 −  m ) z ^{( P − T )}] was fitted to fresh shoot weight and shoot height data of nematode-inoculated and control plants. Tolerance limits ( T ) for fresh shoot weight and shoot height of cv. Spunta plants infected with M. javanica were 0·50 and 0·64 eggs + J2s per cm³ soil, respectively. The m parameter in that model (i.e. the minimum possible y -values) for fresh shoot weight and shoot height were 0·60 and 0·20, respectively, at P  = 64 eggs + J2s per cm³ soil. Root galling was proportional to the initial nematode population density. Maximum nematode reproduction rate was 51·2 at a moderate initial population density ( P  = 4 eggs + J2s per cm³ soil).     

Effect of inoculum type and timing of application of Coniothyrium minitans on Sclerotinia sclerotiorum: control of sclerotinia disease in glasshouse lettuce

The effects of Coniothyrium minitans inoculum quality and an 8-week interval between inoculum application and crop planting on sclerotinia ( Sclerotinia sclerotiorum ) disease in three successive lettuce crops were investigated in a glasshouse trial. Spore suspensions of three isolates of C. minitans (Conio, IVT1 and Contans) applied at 10⁸ CFU m⁻² and a standard Conio maizemeal–perlite application (06 L m⁻², 10¹¹ CFU m⁻²) were assessed for their ability to control S. sclerotiorum . Only the maizemeal–perlite inoculum (isolate Conio) consistently reduced sclerotinia disease. In the third lettuce crop only, isolates IVT1 and Contans formulated by Prophyta and isolate IVT as an oil–water formulation, all applied as spore suspensions, reduced disease at harvest compared with the untreated control. Recovery, viability and C. minitans infection of sclerotia buried during the 8-week period prior to each of the three lettuce crops, and of sclerotia formed on the crop, were tested. Only the maizemeal–perlite inoculum (isolate Conio) reduced the recovery of sclerotia buried in soil for weeks between inoculum application and crop planting, reducing their viability and increasing infection by C. minitans . Eight weeks was sufficient to enable C. minitans to infect sclerotia of S. sclerotiorum , and may account for disease control. After harvest of the second and third crops, maizemeal–perlite treatment (isolate Conio) reduced the number and viability of sclerotia recovered on the soil surface and increased infection by C. minitans compared with spore-suspension treatments. The effect of inoculum concentration and the influence of soil temperature (varying with time of year) on infection of sclerotia by C. minitans are discussed.     

Sensitivity to cymoxanil in populations of Plasmopara viticola in northern Italy

In 1993, control failures were reported on grapevine in northern Italy under severe downy mildew pressure after postinfection application of cymoxanil in mixtures with copper or mancozeb. A monitoring survey was started immediately in Piedmont (north-western Italy) in order to determine the sensitivity of populations of Plasmopara viticola to cymoxanil from those vineyards where the fungicide was not controlling the disease satisfactorily. In 1994 and 1995, monitoring surveys were extended to north-eastern Italy, where cymoxanil mixtures were not performing as well as in the past. Sampled populations were tested on detached leaf discs and on whole potted plants under controlled conditions. In 1993, 12 populations, sampled in Piedmont, showed MIC values (minimum inhibitory concentration) varying from 10 to more than 100 mg L⁻¹ cymoxanil. With a baseline reference population having a MIC value of 3 mg L⁻¹, resistance factors ranged from 3 to more than 30. In 1994, 17 populations out of 27 sampled in Trentino (north-eastern Italy) showed MIC values of 100 mg L⁻¹ or higher and in 1995, 32 populations out of 38 showed the same behaviour. In similar experiments, the MIC values of populations from nontreated plots were between 3 and 10 mg L⁻¹. In whole potted plant tests, populations with MIC values higher than 200 mg L⁻¹ in a leaf disc test were not controlled by 500 mg L⁻¹ of cymoxanil. The results of our study suggest that resistance to cymoxanil in P. viticola may contribute to a lack of disease control in Italian vineyards.     

Quantitative evaluation of wheat against volunteer rye in Iran

Rye infestations have increased in frequency and severity in the wheat fields of Iran and have caused yield reductions in wheat production. In order to study the competition effects of wheat against rye, an experiment was conducted at the research centers of Karaj and Varamin, Iran, during 2001 and 2002. The experimental design was a randomized complete block with 24 treatments and four replications. The treatments included pure stands of wheat at densities of 350, 450, 550, and 650 plants m⁻² and volunteer rye densities of 10, 30, 50, and 70 plants m⁻², and mixed stands of wheat and rye at complete factorial densities. The results indicated that rye was a superior competitor compared to wheat. The biological and economic yields of wheat were mainly affected by interspecific competition in the Karaj region. This was also true during the first year in the Varamin region but, in the second year, the biological and economic yields of wheat were equally affected by interspecific and intraspecific competition because of increasing precipitation. The evaluation of competitive ability, using regression coefficients, showed that in Karaj, the effect of one rye plant on wheat was approximately equivalent to three and two plants of wheat in reducing the grain yield of wheat in the first and second years, respectively, while in Varamin, it was equivalent to three and 1.2 plants of wheat, respectively. In other words, each 0.36 and 0.51 rye plant in Karaj and each 0.36 and 0.84 rye plant in Varamin had the same impact on the reciprocal wheat grain yield as did one wheat plant in the first and second years, respectively.     

Influence of developmental stage and time of assessment on hot water weed control

Summary The influence of plant developmental stage in hot water weed control was studied on the test weed Sinapis alba in field experiments. The dose was measured as thermal energy in the hot water (kJ m⁻²) and the response as reduction in plant weight. The energy dose for a 90% reduction in plant weight was 340 kJ m⁻² at the two-leaf stage, which is one-third of the energy required for the same reduction at the six-leaf stage. Treatment at an early stage saves energy, increases the driving speed and lowers the costs. Hard surface areas with naturally developed weeds were used to study the required treatment interval and the influence of time of assessment on the reduction in weed cover. The required treatment interval was 25 d on average, which is similar to that of flame weeding. A longer lasting effect requires a higher energy dose. A 50% higher energy dose was needed to obtain a 90% reduction in weed cover that lasted for 15 d instead of 7 d. After 3–4 weeks, hardly any reduction could be recorded because of regrowth of perennial weeds. However, hot water weed control has a potential on urban hard surfaces and railroad embankments, especially where the use of herbicides is restricted.     

The influence of interspecific interference on the seed production of Stellaria media and Hordeum vulgare (volunteer barley)

The effects of the density and proportion of both volunteer barley ( Hordeum vulgare L.) and Stellaria media (L.) Vill. (common chickweed) on the seed yield of both species was investigated in linseed ( Linum usitatissimum L.) and autumn-sown field bean ( Vicia faba L.). A model was created to estimate these effects. It was a combination of two models. The first was a simple linear model relating weed seed number m² to weed dry weight m². The second was an inverse linear model relating weed dry weight per plant to weed density. A very good relationship existed between barley dry weight and number of seeds m² and between S. media dry weight and number of seed capsules m². This relationship was relatively consistent between experiments. The inverse linear model provided a good estimation of the relationship between weed density and weed dry weight per plant for both barley and S. media . Model variables, however, differed between experiments. Using the combined model it was estimated that, in the absence of other weed species and at a density of 800 plants m², S. media would produce between 4000 and 48 000 seeds m², whereas volunteer barley, at a density of 400 plants m², would produce between 2000 and 8000 seeds m². The presence of barley always reduced S. media seed yield and a barley population of 100 plants m² could reduce S. media seed yield by up to 79%. The presence of S. media reduced barley seed yield in only one of three experiments, in which a S. media density of 800 plants m² reduced barley seed yield by up to 68%. It was concluded that interspecific weed competition should not be ignored as a factor in models of weed population dynamics     

A green fluorescent protein-based screening method for identification of resistance in anthurium to systemic infection by Xanthomonas axonopodis pv. dieffenbachiae

Resistance of cultivars of Anthurium andraeanum to systemic infection by Xanthomonas axonopodis pv. dieffenbachiae , the causal organism of bacterial blight disease of anthurium, was investigated using a bioengineered bacterial strain containing p519ngfp plasmid. Successful infection establishment in anthurium was found to be cultivar and inoculum density dependent, but independent of plant age. Injection of cut petioles (stage-2 leaf) with 100  µ L inoculum (10⁹ CFU mL⁻¹) resulted in 100% infection establishment in susceptible cultivars on a repeatable basis, and differentiated between various levels of observed field resistance. Time to death (weeks) and proportion of dead plants best differentiated between levels of resistance and cultivars were placed in four groups based on these criteria. The susceptible group (32 cultivars) rapidly declined within 6–12 weeks of inoculation (WAI) and resulted in 100% plant death; the moderately resistant group (10 cultivars) declined within 12 WAI, but resulted in less than 100% plant death; the resistant category had less than 100% plant death with a slow decline taking over 20 weeks; and the highly resistant category (15 cultivars) showed 0% infection. The correlation coefficient between green fluorescent protein (GFP)-fluorescence and eventual death of plants was 0·90, indicating that the final death of individual plants can be reasonably well predicted based on GFP-fluorescence data at 5 WAI. Hence GFP data at 5 WAI can be used for early detection of latently infected plants and may assist screening for resistance in segregating populations of anthurium.     

Production of conidia by Peronosclerospora sorghi on sorghum crops in Zimbabwe

Factors affecting the production of conidia of Peronosclerospora sorghi , causing sorghum downy mildew (SDM), were investigated during 1993 and 1994 in Zimbabwe. In the field conidia were detected on nights when the minimum temperature was in the range 10–19°C. On 73% of nights when conidia were detected rain had fallen within the previous 72 h and on 64% of nights wind speed was < 2.0 m s⁻¹. The time period over which conidia were detected was 2–9 h. Using incubated leaf material, conidia were produced in the temperature range 10–26°C. Local lesions and systemically infected leaf material produced 2.4–5.7 × 10³ conidia per cm². Under controlled conditions conidia were released from conidiophores for 2.5 h after maturation and were shown to be well adapted to wind dispersal, having a settling velocity of 1.5 × 10⁻⁴ m s⁻¹. Conditions that are suitable for conidia production occur in Zimbabwe and other semi-arid regions of southern Africa during the cropping season.     

Interference between Avena sterilis, Phalaris minor and five barley cultivars

Field experiments were carried out in Northern Greece from 1994 to 1997 to study interference between Avena sterilis L. or Phalaris minor Retz. and five autumn-sown barley cultivars. Weed:crop interference began in early April. Avena sterilis at 120 plants m⁻² showed greater interference against barley than P. minor at 400 plants m⁻². The greatest grain yield and ear number reduction due to interference by either weed was recorded for cvs Klipper and Plaisant, and the least for cv. Athinaida; with cvs Carina and Thermi intermediate. Yield reduction due to A. sterilis for cvs Athinaida, Carina, Thermi, Klipper and Plaisant was 8, 16, 27, 61 and 67%, respectively, while corresponding losses to P. minor were 1, 8, 14, 45 and 55%. These results clearly indicate that growth and consequently yield components of cv. Athinaida were unaffected by the presence of either weed species, while those of cv. Carina were affected by A. sterilis , but not by P. minor . However, dry weight and panicle number of both weed species were severely reduced by interference with cvs Carina, Athinaida and Thermi compared with cvs Klipper and Plaisant. The order of interference of the five barley cultivars tested against A. sterilis and P. minor was Athinaida > Carina > Thermi > Klipper ≥ Plaisant.     

PCR-based specific and sensitive detection of Pectobacterium carotovorum ssp. carotovorum by primers generated from a URP-PCR fingerprinting-derived polymorphic band

A 24-mer primer pair was generated by sequencing a URP-PCR fingerprinting-derived polymorphic band that is uniquely shared in Pectobacterium carotovorum ssp . carotovorum strains (Pcc). The primer set (EXPCCF/EXPCCR) amplified a single band of expected size (0·55 kb) from genomic DNA obtained from 29 Pcc strains and three Pectobacterium carotovorum ssp. wasabiae (Pcw) strains, but not from other P. carotovorum subspecies atrosepticum , betavasculorum or odoriferum , or from other Erwinia spp. or bacterial genera. The Rsa I digestion profile of the amplified bands divided Pcc strains into five groups with a unique profile from Pcw strains. First-round PCR detected between 5 × 10² and 1 × 10³ colony forming units (CFU) mL⁻¹ and detection sensitivity was increased to as few as 2–4 CFU mL⁻¹ after second-round (nested) PCR. This PCR protocol was used directly to detect Pcc strains in infected plant tissues.