The susceptibility of stems of different potato cultivars to blackleg caused by Erwinia carotovora subsp. atroseptica

The susceptibility of stems of six potato cultivars to Erwinia carotovora subsp. atroseptica was assessed in two years (1981 and 1982) either by direct inoculation in the field or by inoculation of detached stems in the laboratory. These six and a further 22 cultivars were also assessed in three years (1982-84) by inoculating stems of glasshouse-grown plants. Different methods of inoculation and types of inocula were tested. In the field, wooden toothpicks rubbed in bacterial slime were more successful in establishing infection than when dipped in a bacterial suspension, but injection of bacterial suspension with a hypodermic needle was reliable in establishing infection over a range of concentrations. Detached stems were more readily infected and gave more consistent results compared with inoculation in the field. The range of reaction of the six cultivars was similar in both detached stem and glasshouse tests. The early cultivars Pentland Javelin and Ulster Sceptre were most susceptible and of the maincrop cultivars, Maris Piper was intermediate and Desiree and King Edward least susceptible whereas Pentland Crown showed greater resistance in the glasshouse than in the field. Glasshouse tests using hypodermic inoculation indicated a range of susceptibilities; the early cultivars Manna, Maris Bard and Estima were most susceptible and the maincrop Pentland cultivars Crown, Dell, Hawk, Ivory and Squire least susceptible.     

The use of cultivar trials records in assessing the incidence of cereal disease in England and Wales. I. Septoria nodorum in wheat and Rhynchosporium secalis in barley

The incidence of Septoria nodorum and Rhynchosporium secalis in N.I.A.B. cultivar trials of wheat and barley respectively showed marked regional and seasonal variation. Peak annual incidence of the two diseases often coincided. Levels of S. nodorum infection in winter wheat generally exceeded those in spring wheat, while levels of R. secalis in winter and spring barley were usually similar. Annual peaks in mean disease levels were associated with above average rainfall and raindays and below average temperatures, especially during the period of epidemic development. Regional variation in disease incidence reflected the association with high rainfall. S. nodorum infection in wheat was more widespread, and incidence of leaf infection was higher, than R. secalis in barley. Annual and regional incidence of S. nodorum and R. secalis in trials was similar to that recorded in the Plant Pathology Laboratory surveys of commercial crops. Disease records from cultivar trials can provide useful additional information on the behaviour of S. nodorum and R. secalis nationally.     

The susceptibility of barley cultivars to barley yellow mosaic virus (BaYMV) and its fungal vector, Polymyxa graminis

In glasshouse experiments, barley seedlings were inoculated with barley yellow mosaic virus (BaYMV) either mechanically or by using zoospores or cystosori of a viruliferous isolate of the vector, Polymyxa graminis, maintained on barley in sand culture. Experiments using mechanical inoculation showed that seedlings became more resistant with age. Consistent cultivar differences were obtained: cvs Maris Otter and Halcyon were very susceptible and cv. Athene seemed immune. Symptoms developed more rapidly at 23 than at 17 or 11 ^oC. After vector inoculation, symptoms developed more slowly than after mechanical inoculation but cultivar ranking was similar. Cultivars did not differ in susceptibility to the vector, as measured by zoospore production on their roots. Spring barley cultivars supported the growth of the vector which remained viruliferous and some showed symptoms although, in the field, symptoms do not appear on spring-sown crops.     

Effects of fungicide timing on control of Rhynchosporium secalis in barley plants

Sprays of captafol, carbendazim, carbendazim + tridemorph + maneb, diclobutrazol, triadimefon or triadimefon + carbendazim all completely protected barley plants in a glasshouse against R. secalis for at least 30 days. However, their effectiveness in preventing disease development when applied after inoculation differed: triadimefon, traidimefon + carbendazim, or diclobutrazol were the most effective, completely preventing symptom development when applied up to 5 days after inoculation to plants grown above 16 °C, and up to 8 days below 8 °C. All the fungicides decreased the number of viable conidia produced by leaf blotch lesions, and when applied to infected plants at G. S. 30, greatly decreased the upward spread of the disease under simulated rain conditions; the most effective fungicides in these respects were triadimefon and triadimefon + carbendazim. The above fungicides and fungicide mixtures, together with the recently introduced materials fenpropimorph and propiconazole were applied to diseased winter barley crops in winter or in spring. All treatments decreased leaf blotch development and increased yields. In most cases, a winter application was more effective than spring applications, particularly if applied in mid-November. The most effective fungicides were triadimefon and propiconazole. The field trials data fitted well with the predictions of performance indicated by the glasshouse investigations.     

辣椒种质资源抗青枯病的鉴定与评价

采用青枯菌FJC100301菌株对田间辣椒（Capsicum annuum）抗病品种76a和感病品种TW-1分别作了不同温度、不同接种量和不同接种方法的接种试验。结果表明,辣椒青枯病抗性的室内鉴定以接种温度28℃、浸根20 min和3×10^8cfu/mL接种浓度为宜;辣椒种质田间抗青枯病接种鉴定宜选择5月上旬进行,浸根20 min,接种浓度为3×10^8cfu/mL。采用田间抗性接种鉴定的方法,用青枯菌FJC100301菌株对106份辣椒材料进行了抗性鉴定。田间接种后每隔10 d统计病情指数,划分辣椒抗青枯病鉴定分级标准,获得了高抗材料14份、抗病材料8份、中抗材料23份、中感材料23份、感病材料20份、高感材料18份;采用离体叶片接种法对田间筛选得到的高抗和高感纯度较高品种进行抗性分析,结果与田间鉴定一致。     

Components of partial resistance of barley to Rhynchosporium secalis: use of seedling tests to predict field resistance

Components of partial resistance [disease incidence (DI), infection frequency (IF), latent period (LP), spores per lesion (SPL)] were assessed on glasshouse-grown barley seedlings following inoculation with spore suspensions of Rhynchosporium secalis at growth stage 12 (Zadoks, Chang & Konzak, 1974). Four experiments were carried out at different times during 1988. Three spring barley cultivars [two from Cyprus (cvs Kantara and Athenais) and one from the UK (cv. Triumph)] were used in the first three experiments. In the fourth experiment eight additional UK cultivars with NIAB resistance ratings ranging from 3 to 9 were used. Two races of R. secalis were used in the first three experiments and three in the fourth. The three cultivars, Kantara, Athenais and Triumph, were examined in all four experiments and significant differences detected for virtually all components of partial resistance in each. Differences, however, were often small and ranking of cultivars varied in different experiments. The greater susceptibility of cv. Kantara compared to cv. Athenais, observed under field conditions in Cyprus, would not be anticipated from the small differences in components of partial resistance observed in these experiments, but, for these cultivars, the possibility of a marked genotype x environment interaction cannot be discounted. Mean values for the components of partial resistance differed in the four experiments. LP was correlated with mean glasshouse temperature from inoculation to the onset of sporulation but differences in IF and SPL were not correlated with temperature. For these components, light quality and/or duration appeared to be more important. Overall, there were no differences between races but significant race X cultivar interactions were observed in two experiments. In the fourth experiment, examining 11 cultivars, there were significant differences between cultivars for all components of partial resistance. IF and LP were correlated but neither of these components was correlated with SPL indicating independent control of this latter component. Both IF and LP were correlated with field performance (NIAB ratings) but there was no correlation with SPL. However, combining IF with mean values of SPL restricted to the 5 days following the end of the LP, produced the best correlation (r= 0.92) with NIAB ratings. Problems of assessing components of partial resistance and possible means of improving assessments are discussed.     

Assimilatverteilung in Sommergerstensorten mit unterschiedlicher Resistenz gegenüber dem Echten Mehltau (Erysiphe graminis f. sp. hordei)

Distribution of assimilates in cultivars of spring barley with different resistance against powdery mildew (Erysiphe graminis f. sp. hordei) Transport and distribution of radioactive labelled assimilates in spring barley cultivars with different degrees of resistance to powdery mildew were studied after ¹⁴CO₂-treatment of single leaves. Plants of the cultivars ‘Amsel’ (susceptible), ‘Asse’ (adult plant resistant), and ‘Rupee’ (resistant) were analyzed at the vegetative growth stage (5. leaf unfolded) and the generative growth stage (anthesis). At the vegetative growth stage the assimilate export from the mildew inoculated 5. leaf of ‘Amsel’ and ‘Rupee’ is decreased; in ‘Asse’, there is no considerable change of assimilate distribution due to infection. At the generative growth stage the assimilate export from the infected flag leaf of ‘Amsel’ is reduced when the fungus, is sporulating. In the cultivar ‘Asse’ the assimilates are bound at the infection site until the seventh day after inoculation, then the transport of assimilates to the ear is increased. In ‘Rupee’ mildew inoculation causes an enhanced assimilate transport to the ear. The changes in assimilate distribution due to mildew inoculation are discussed with respect to the different types of host-parasite-interactions and the source-sink-activities in the different cultivars.     

Performance of transgenic spring wheat plants and effects on non-target organisms under glasshouse and semi-field conditions

Abstract:  A convertible glasshouse was established to study annual transgenic plants under near-field environmental conditions while simultaneously ensuring a high level of biological containment. This system can provide a useful step in the assessment of transgenic plants prior to open-field experiments. Two transgenic wheat lines (cv. Bobwhite) were investigated and compared with their corresponding non-transformed wildtypes with respect to plant performance, expression of the transgenic trait and interactions with antagonists. The first line expressed snowdrop lectin [ Galanthus nivalis agglutinin (GNA)] for enhanced resistance to aphids, and the second one overexpressed the endogenous Lr10 gene to enhance resistance to leaf rust. Interestingly, 1000-kernel weight of Lr10 -transgenic plants was significantly reduced, indicating that the overexpression of the Lr10 gene caused a significant fitness cost for the plant. GNA-transgenic plants expressed the lectin at levels too low to affect the target aphids. A detached leaf bioassay with Lr10 -transgenic plants revealed an increased resistance to leaf rust. No differences in the performance of aphids or cereal leaf beetles on transgenic and non-transformed plants were recorded in the convertible glasshouse and in complementary glasshouse studies. Similarly, infection levels with powdery mildew did not differ between transgenic and non-transformed plants but Bobwhite plants were significantly more infected when compared with conventional Swiss spring wheat cultivars. Overall, the assessment revealed that for the plants investigated here, their genetic background had a stronger impact on the performance of a plant and its interactions with insect herbivores and pathogens than the expression of the transgene.     

The effect of sowing date on adult plant resistance to Erysiphe graminis f.sp. avenae in oats

A technique developed for detecting small differences in mildew infection under glasshouse/laboratory conditions is described. A satisfactory correlation was found between results obtained by this method and infections in the field. Detailed examination of the levels of infection in cultivars Maldwyn and Milford showed that the upper and more recently developed leaves of Maldwyn had a significantly smaller area infected than those of Milford, although seedling leaves of both genotypes were very susceptible. This was most marked when plants were in the 6- to 7-leaf stage. Comparison of host plants sown on successive dates during the spring and early summer showed that with the acceleration of the rate of growth occurring in later-sown plants, resistance was expressed progressively earlier in the life of the plant. Newly expanded leaves which show very low level of infection at the 6- to 7-leaf stage become susceptible as they age, resistance being then expressed in the younger leaves.     

An assessment of genetic variability in somacloned lettuce plants (Lactuca sativa) and their offspring

Plants were regenerated from callus derived from cotyledons and first true-leaves of the lettuce cultivars Salad Bowl, Lobjoits Cos and Pennlake. Sexual progeny of these regenerants were assessed under glasshouse and field conditions for variation including reaction to lettuce mosaic virus (LMV) and downy mildew (Bremia lactucae). All three cultivars exhibited somaclonal variation. Mutations detected at the seedling stage included reduced vigour, albinism and changes in chlorophyll content, with most being recessive. Variation for leaf shape and vigour was detected in mature plants. One line exhibited increased yield and chlorophyll content together with early flowering. Enhanced and reduced susceptibility to both LMV and B. lactucae were observed. Reduced susceptibility to B. lactucae was indicated by an extended latent period following inoculation in two lines. Reduced susceptibility to LMV in glasshouse trials could not be confirmed in the field although one such line exhibited an improved yield and a second line segregated 1:1 in glasshouse tests for plants which were obviously infected and those without symptoms. All variable lines were diploid.     

Response to Fusarium culmorum inoculation in barley

In field tests replicated in 2004 and 2005, 32 cultivars of spring barley were assessed for resistance to Fusarium head blight (FHB) by single floret inoculation and spray inoculation with Fusarium culmorum (W. G. Smith) Sacc. It was found that the weather conditions in individual years affect to a large extent the progression of FHB and production of mycotoxin deoxynivalenol (DON). At the same time, in both years the cultivars reacted to F. culmorum infection similarly with respect to areas under disease progress curve (AUDPC) values and content of mycotoxin DON. Spraying inoculation led to stronger infection. The biggest differences in AUDPC values were observed between the cultivars Brise and Celinka, and weak reaction was found in the cultivars Kompakt and Madonna. The cultivars Kompakt and Tolar were most resistant towards FHB. In both monitored years the variety Ludan contained the lowest amounts of mycotoxin DON. Cultivars with high infection and low DON content (r = 0.78) showed weak positive relationship between resistance to FBH and accumulation of DON (concentration 70–200 mg/kg). This is the first information on FHB and in vivo concentrations of DON in certificated barley cultivars in Slovakia.     

Field screening for resistance to barley net blotch

Inoculation with barley net blotch from infested straw debris was compared with that from diseased plants after sowing infected grains. The straw debris had a high, uniform inoculation potential which gave an early, continuing infection and easily reproducible results that were effective for screening barley cultivars in the field for resistance against a natural population of the pathogen. Further, it minimises an eventual influence from other leaf pathogens coming from the surroundings. Irrigation was decisive for the success of the method - especially in the initial phase. Ten m separation with an immune crop was insufficient to completely prevent infection in the uninoculated plots. The tested 25 cvs were differentiated in six categories of resistant and susceptible on the basis of disease development and final level of attack. None of them was free of symptoms. The most resistant cvs kept a constant, low level of attack during the whole growing season, whereas the most susceptible cvs showed an early and rapidly increasing attack. Intermediate cvs were characterised with more or less slow increase of the attack. The size and proportion of the brown necrotic spots and the surrounding yellow halo varied greatly from one cultivar to the other. The grain yield reduction was due solely to an effect on the thousand grain weight which decreased linearly with the squared point score for net blotch. Further, the disease affected the quality of the grains as less nitrogen was transported from straw to grain in the severely diseased plants.     

Seed transmission of broad bean stain virus and Echtes Ackerbohnenmosaik-Virus in field beans (Viciafaba)

When grown in a glasshouse during spring or autumn field bean (Vicia faba minor) seedlings infected with seed-borne broad bean stain virus (BBSV) or Echtes Ackerbohnenmosaik-Virus (EAMV) usually showed symptoms on some leaves within 4 wk of emergence. Symptoms caused by each virus were indistinguishable. The viruses were transmitted as often through unblemished seeds as through seeds with necrotic patches or stains on the seed coat, and sometimes as often through large as through small seeds. Soaking seeds for 24 h in solutions of 8-azaguanine or polyacrylic acid did not decrease transmission. Both viruses were detected in nearly mature seeds by inoculation to Phaseolus vulgaris but neither virus was detected in fully ripened seeds by inoculation or serological tests. The percentage of seeds from field plots that produced infected seedlings when sown in a glasshouse was closely related to the percentage of parent plants that showed symptoms of BBSV and/or EAMV at the end of flowering. The relationship seemed similar in different cultivars. On average EAMV was transmitted through more seeds than BBSV, probably because more parent plants were infected with EAMV. Inspection of seed crops for symptoms of BBSV and EAMV at the seedling stage and again at the end of flowering is probably the most practicable way of identifying progeny seed lots with little or no infection.     

Factors affecting bacterial black spot of mangoes caused by Xanthomonas campestris pv. mangiferaeindicae

Bacterial black spot of mango caused by Xanthomonas campestris by. mangiferaeindicae was found to be essentially a wound pathogen of leaves under glasshouse conditions, with maximum infection occurring at a temperature regime of 22/26 ^oC (night/day). There were significant differences in leaf susceptibility among cultivars, cv. Sensation being less, and cv. Haden more susceptible than cvs Zill and Kent, which agrees with field observations of fruit infection. The organism is a phylloplane resident year round in the field and inoculum levels in the tree canopy affect ultimate fruit infection. The major weather factor affecting fruit infection was rainfall which showed a significant correlation (r = 0–77) with levels of infection after allowing for an approximate 2 wk latent period. Other significant correlations were with a wind/rain index (r = 0–73) and a storm index (r = 0–66). The correlation of disease with the duration of free water was non-significant (r = 0–22).     

Some effects of barley yellow dwarf virus on spring and winter cereals in glasshouse trials

The tolerance of spring and winter varieties of wheat, oats and barley to infection by barley yellow dwarf virus (BYDV) was examined in glasshouse tests. Severely affected plants were stunted and grain yields were considerably decreased because of decreases in both ear number and numbers and sizes of grains. Winter barley varieties were very susceptible and many were killed by BYDV infection. The winter wheat varieties were more widely tolerant than those of oats and barley. Individual seedling symptoms, although correlated with reductions in yield, could not be relied upon for accurate classification of all varieties in order of their susceptibility to infection. Symptoms of seedling infection incorporated into an index of infection permit estimates to be made o eventual decreases in yield by applying the formula DY = 1.4 × (SH+LA+LL)+18. Thus decrease in grain yield (DY) can be related to decreases in height (SH) and leaf length (LL) and increases in leaf area discoloured (LA) in seedling plants infected with BYDV.     

The influence of photoperiod on growth patterns of Erysiphe graminis f. sp. hordei

Detached seedling leaf segments of five spring barley genotypes were inoculated with an isolate of barley mildew to which they possessed different levels of resistance. Segments of each host genotype were then incubated under either continuous light or treatments with 2, 4, 8 or 16 h darkness per 24 h cycle. Macroscopic observation showed that the latent period of infection was reduced slightly in treatments with at least 4 h darkness/24 h. Yellowing of detached segments occurred fastest under continuous light and slowest under a 16 h dark/8 h light cycle. Microscope observation of segments fixed 4·5 days after inoculation showed that as the length of the dark period increased, so the number of haustoria formed per colony also increased. This increase in haustorial production appeared to be associated with an accentuation in the synchrony of production of the secondary and tertiary haustorial generations. Varietal differences in susceptibility were also more marked in segments incubated under short days. It is concluded that under the conditions of temperature and light intensity used, a 16 h dark/8 h light system is most desirable for quantifying mildew resistance because it allows confident identification of distinct haustorial generations, accentuates differences in varietal susceptibility and delays chlorophyll degradation in detached barley leaves infected with mildew.     

Phosphorus allocation in P-efficient and inefficient barley cultivars as affected by mycorrhizal infection

A glasshouse experiment was undertaken to investigate the effect of mycorrhizal infection on the allocation of phosphorus (P) in agronomically P-efficient (i.e. high yields at low P supply) and inefficient barley (Hordeum vulgare L.) cultivars. Four barley cultivars differing in agronomic P-efficiency were inoculated or not inoculated with Glomus etunicatum. Cultivars did not differ in percentage of root length infected. The concentration of P in roots of the inefficient cultivars was higher than that of the efficient cultivars. However, because of changes in root to shoot dry weight ratio and below-ground productivity, mycorrhizal infection significantly reduced the percentage of total plant P in roots of the inefficient cultivars. The distribution of P between root and shoot of P-efficient cultivars was not affected by mycorrhizal infection. Root to shoot dry weight ratio of the P-efficient cultivars was lower than that of the inefficient cultivars, and the decrease in the ratio following infection was significant in inefficient but not in P-efficient cultivars. This study indicates that mycorrhizal infection alters the allocation of P in inefficient cultivars and effectively improves the efficiency of P utilization with respect to shoot growth.     

Some effects of barley yellow dwarf virus on spring and winter cereals in field trials

The tolerance of spring and winter cultivars of wheat, barley and oats to infection by barley yellow dwarf virus (BYDV) was examined in field tests. Sererely affected plants were stunted and grain yields were considerably reduced. These changes in infected spring barley cultivars were associated with decreases in both ear length and number and sizes of grain. Most barley and oat cultivars were more susceptible than wheat cultivars. Yield losses decreased with successively later dates of inocultaiton, the yield response being characteristic of the tolerance of individual cultivars. Differences between tolerant and susceptible cultivars were insignificant in most cases where infection occurred after growth stage 7. Individual seedling symptoms assessed in April and May were more closely related to each other and to yield losses than those recorded in March and June. The incorporation of seedling symptoms into indices of infection permits estimates of decrease in yield to be made by applying the formulae, DY = (LC+LA+SH)/3 to barley cultivars and DY = 1.7 × (LC+LA+SH)/3 - 7 to oat cultivars. Thus decreases in grain yield (DY) can be related to decreases in seedling height (SH) and increases in percentage of leaf area discoloured (LA) and intensity of discoloration (LC). Plot symptoms of infection, scored on a 0–7 scale, offered a more convenient method of assessment than individual seedling symptoms. Plot scores (PA) were closely correlated with other seedling symptoms and with decreases in grain yield (DY), and can thus be used to estimate yield losses by substituting into the formula, DY = 14PA (April)-8. This formula was found to be applicable to all cereal cultivars examined in N.I.A.B. trials, there being no distinction between wheat, barley and oats.     

Interaction Between Root and Leaf Disease Development in Barley Cultivars after Inoculation with Different Isolates of Bipolaris sorokiniana

The relationship between root and leaf infection in 11 cultivars of barley ( Hordeum vulgare ) by different isolates of Bipolaris sorokiniana was investigated in young plants. Roots of 10-day-old seedlings, grown in filterpaper rolls, and the third leaf of 17-day-old seedlings were inoculated with the different isolates and a Disease Development Index (DDI) was calculated.
The rate of lesion development in leaves was higher than in roots, indicated by generally higher DDI after leaf inoculation than after root inoculation. Significant differences in resistance were found among the barley cultivars. Inoculation with different isolates of B. sorokiniana caused significant differences in DDI for both roots and leaves. In the leaves, but not in the roots, a significant cultivar–isolate interaction was found. No significant correlations, neither in isolate aggressiveness nor in cultivar reaction between root and leaf, were observed.