THE EFFECT OF TIME OF APPLICATION OF NITROGENOUS FERTILIZER ON POWDERY MILDEW OF WINTER WHEAT

Applying nitrogenous fertilizer (N) to wheat plants of different ages affected the incidence of powdery mildew, Erysiphe graminis DC, differently. When N was applied before the flag leaf had emerged, the infection-index (number of pustules per 100 sq.cm. of leaf blade) increased to a maximum and then declined. If N was applied after the flag leaf had emerged, the infection-index increased steadily without reaching a peak, and the increased susceptibility was not associated with an increased relative leaf growth rate as when N was applied earlier.
The integral of the number of pustules per unit area with time, and the number of perithecia on the leaves of the main stem, both increased with increasing delay in the application of N. Plants given N in either April or May had at least three times as many pustules as those given N in January. The time when N was applied did not affect the date when perithecia appeared.
After adding N to nitrogen-deficient plants, the already mature leaves which had resisted mildew infection, became susceptible. This change is not associated with changes in the epidermal wall.     

SOME EFFECTS OF HIGH TEMPERATURE ON THE SUSCEPTIBILITY OF PLANTS TO INFECTION WITH VIRUSES

When plants were kept at 36°C. for some time before inoculation, their susceptibility to infection by five mechanically transmissible viruses was greatly increased. When kept at 36° after inoculation, fewer local lesions were produced than at lower temperatures, but the effects of the post-inoculation treatment differed with different viruses. Tomato spotted wilt and tobacco mosaic viruses multiply in plants at 36°, and the post-inoculation treatment reduced the local lesions they caused to numbers that varied between 10 and 90% of the control; these two viruses also have large thermal coefficients of heat inactivation. By contrast, tobacco necrosis, tomato bushy stunt and cucumber mosaic viruses, were much affected by post-inoculation treatment, lesion formation being completely prevented by exposure to 36° for a day or more. These three viruses appear not to multiply in plants at 36°, and although they have high thermal inactivation points, they have small temperature coefficients of thermal inactivation.
The extent to which lesion formation was affected by pre- or post-inoculation exposure of plants to 36° depended not only on the length of the treatment, but also on the physiological condition of the plants.
The symptoms of infected plants changed considerably if kept at 36°. At 36° Nicotiana glutinosa , inoculated with tobacco mosaic virus, gave chlorotic local lesions instead of necrotic ones, and became systemically infected. When systemically infected plants were brought to ordinary glasshouse temperature, the infected tissues all collapsed and died in a day.     

新疆地区小麦白粉病菌寄主范围的研究

用小麦白粉病菌11个生理小种的混合菌种,对新疆地区的小麦近缘植物的7个属22个种的47份材料进行接种,除6份免疫外,其余均接种成功.用其中6个属19个种的29份小麦近缘植物产生的白粉病菌,对小麦回接,参试的29份材料全部回接成功.小麦白粉病菌对小麦近缘植物的寄生像在小麦上一样,有明显的寄生专化性.感病的小麦近缘植物的78.0%对小麦白粉病菌的感病性,随生育期增长而急剧下降.文中并对小麦白粉病中间寄主的作用进行了讨论.     

Effect of parental genotypes, cross direction and temperature on the crossability of bread wheat with triticale and on the viability of f1 embryos

The relevant importance of parental crossability genes, cross direction and ambient temperature in bread wheat/triticale hybridisation were evaluated. Crossability genes were found to be useful but not essential. The use of triticale as the female gave significantly fewer embryos, but these embryos were symmetrically shaped and normal. The use of bread wheat as the female gave a seed set generally above 30% and sometimes as high as 86%, but embryo necrosis resulted in rapid death in vivo or non-regeneration in vitro . By keeping the plants at 14 °C during pollination and in vivo embryo growth, necrosis was partly eliminated, so that in one case the rate of plant production in crossing bread wheat/triticale became about as good as for the triticale/bread wheat cross direction. Crossing at 14°C could be useful when a bread wheat cytoplasm is desired by the breeder.     

Nitrogen availability and susceptibility of tomato leaves to Botrytis cinerea

The aim of this study was to investigate the effect of nitrogen availability on susceptibility of tomato leaves to the fungal pathogen Botrytis cinerea. Plants with varying nitrogen availability were grown by adding N daily in exponentially increasing amounts to a nutrient solution at different rates. Leaves of plants grown at low nitrogen availability had a high leaf C/N ratio (21 g g^-1) and were about 2.5 times more susceptible to primary lesion formation by B. cinerea compared to plant grown at high nitrogen availability, which had a low leaf C/N ratio (11 g g^-1). Leaf C/N ratio accounted for 95% of variation in susceptibility. This relationship between C/N ratio and susceptibility persisted when plants were grown with exponential P addition and optimal N supply, and was thus independent of plant growth rate or related factors. We could not explain the effect of nitrogen availability by variation in the most obvious N-based resistance compound α-tomatine because more susceptible leaves with a high C/N ratio contained more α-tomatine. These leaves also contained more soluble carbohydrates. The level of soluble carbohydrates correlated positively with susceptibility, independent of the growth method. We therefore suggest that the effect of N availability on susceptibility must be explained by variation in levels of soluble carbohydrates and speculate about the role of these carbohydrates in the infection process. This revised version was published online in June 2006 with corrections to the Cover Date.     

A role for young leaves in vernalization of cauliflower: I. Analysis of leaf development during curd induction

Growth analysis techniques are used to test the hypothesis that chilling induces curd (flower) initiation in the cauliflower ( Brassica oleracea Botrytis L. cv. Perfection) through inhibiting leaf growth, thereby increasing the availability of growth factors to the stem apex and enabling differentiation of the curd. Effects of chilling on leaf growth and curd induction are compared in juvenile and mature, vegetative plants. Chilling at 5°C reduced dry matter accumulation in the total leaf complement by ca 60% in juvenile plants and 40% in mature plants, compared to control plants growth at 20°C. Juvenile plants showed slower rates of leaf initiation than mature plants. Leaf initiation was retarded by chilling in both plant types with the most marked effect seen in the juvenile plants. This was consistent with dry matter availability to the stem apex limiting differentiation more severely in juvenile plants than in mature plants. The rate of dry matter accumulation in existing leaves, however, was faster in juvenile plants than in mature plants at 20°C. Plants that were juvenile during chilling produced an average of 43 leaves below the curd whereas those that were mature produced 25.
Dry matter accumulation in younger leaves was more markedly inhibited by chilling than in older leaves. Chilling also reduced the rate at which enlarging leaves became positionally more remote from the stem apex. Possible roles for such leaves in regulating apical development are considered.     

Die Reaktion anfälliger und resistenter Gerstensorten auf pilzliche Krankheitserreger

Response to fungus pathogen in susceptible and resistant barley cultivars IV. Water- and dry matter content
The changes in dry matter- and water content dynamics in the root and shoots of barley infected with the fungus Erysiphe graminis f. sp. hordei Marchal were studied in variously receptive cultivars. Cultivation of plants in solid (perlite) or liquid medium was compared.
The response of susceptible barley to mildew infection is characterized at First by an increase in water content and slightly in dry matter of shoots accompanied with an unsignificant decrease in root growth. However, as the fructification progressed, barley growth is reduced in all investigated parameters. The infected resistant barley indicates unsignificantly increased values in water content of shoots, only.
In the susceptible host the growth of roots in relation to shoots is markedly reduced after infection.
The percentage of water content of shoots is slightly increased in both cultivars during the first phases of infection. Then, in susceptible barley it declines, compared with the control, from the stage of full developed fructification. In the resistant barley it doesn't change more expressively. In roots of infected plants the increased hydratation is found during the whole observation period (in the resistant barley only with plants growing in liquid medium).     

The effect of temperature and growth rate on the susceptibility of Listeria monocytogenes to environmental stress conditions

R.A. PATCHETT, N. WATSON, P.S. FERNANDEZ AND R.G. KROLL. 1996. The effect of growth temperature and growth rate on the susceptibility to heat and pH stress were investigated in Listeria monocytogenes grown in continuous culture where these two growth variables could be varied independently of each other, and in batch culture. After growth at 30°C or 10°C at constant growth rate, or at 30°C at different growth rates, cells did not differ in their resistance to heat at 55°C. Cells grown at 30°C were more resistant to acid stress at pH 2.5 than cells grown at the same growth rates at 10°C. Cells grown at low growth rate at 30°C gave greater resistance to acid stress than those grown at high growth rate. Growth temperature and growth rate had independent effects on the susceptibility of L. monocytogenes to acid stress conditions. This may have implications for the survival of L. monocytogenes in acidic foods.     

THE EFFECTS OF VARYING THE WATER SUPPLY OF PLANTS ON THEIR SUSCEPTIBILITY TO INFECTION WITH VIRUSES

Increasing the amount of water supplied to plants before they were inoculated with viruses greatly increased their susceptibility to infection; plants that received unlimited water produced 10 or more times as many local lesions as plants that received only enough to prevent wilting. Susceptibility was increased throughout the year, but the full response occurred in 2 weeks in winter and 4 weeks in summer. Plants that received unlimited water for the 2 weeks immediately preceding inoculation were no more susceptible than those that received it during the previous 2 weeks, although the external appearance of the plants differed at the time of inoculation. Varying water supply after inoculation did not affect the numbers of lesions.
The differences in susceptibility to infection produced by differential watering were decreased, but not abolished, by growing plants under shade or by incorporating a diatomaceous earth in the inoculum.
Increasing water produced plants with larger and more succulent leaves; the cuticular layer was thinner, and the palisade tissue was less regularly arranged than in the plants kept dry. The increased susceptibility caused by an abundant water supply may be at least partly due to these structural differences, which allow the leaf to be damaged more easily when rubbed with inocula and so present more entry points for virus particles.     

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.     

Growth and food choice by two species of limnephilid caddis larvae given natural and artiflcial foods

SUMMARY 1. Larvae of the caddisfly Limnephilus externus grew faster than those of Nemotaulius hostilis in a permanent pond in southern Alberta.
2. We investigated whether this was due to more efficient food processing by L. externus , whether their growth coincided with high environmental temperatures, or whether they had the ability to choose and exploit higher quality food.
3. Of five foods used, protein content was highest in wheat flakes, similar in alder, bur-reed and willow leaves, and lowest in the moss Leptodictyum .
4. Both species grew faster and survived better on the wheat flakes, but there was no statistically significant difference between species on the same food when reared at 4 or 8°C in the laboratory.
5. At 16°C L. externus grew better than N. hostilis when fed wheat, but N. hostilis survived better on alder. Both species had higher survival and growth rates per day-degree at 8 and 4 than at 16°C.
6. Thus, faster growth rates of L. externtus in the field appear to be due simply to higher temperatures during the larval growth period. Indeed, N. hostilis had a significantly higher growth rate per day-degree in a field experiment.
7. In food preference experiments, L. externus chose wheat first, moss second, alder third, and willow last; N. hostilis chose alder first, bur-reed second, moss third, and wheat last.
8. Protein content, leaf texture, microbial conditioning, and an interaction between larval behaviours selecting for food quality and case materials, are potential factors that influence'food preference'results.     

Resident population of Xanthomonas campestris pv. malvacearum on cotton leaves: a source of inoculum for bacterial blight

Xanthomonas campestris pv. malvacearum was transmitted from infested seed to the cotyledons of cotton cv. Deltapine 61 seedlings at 28°C and relative humidities (RH) of 90% or 73%. A resident population was present on the first and second true leaves but not on the third true leaf of plants at either RH. There were smaller numbers of resident bacteria on fewer leaves of plants at the lower RH than on plants at the higher RH. Cotton plants grown from infested seed at 25°C and 30°C and incubated at 100% RH at different stages of growth developed bacterial blight on leaves that were in bud or partly expanded when incubated. Resident cells of this pathogen can thus invade susceptible leaves when conditions are favourable for infection. Bacterial blight developed on more plants at 30°C than at 25°C. In a field trial, X. campestris pv. malvacearum transmitted from seed was present as resident bacteria on the third leaf from the growing point during the vegetative development of the plant. Resident bacteria, which infected young leaves during rainy periods, were isolated from the bacterial blight lesions which subsequently developed.     

Sensibilité du Melon àSphaerotheca fuliginea en Fonction de L'Etage Foliaire

Effect of leaf position on the susceptibility of melon plants to artificial infection with powdery mildew, Sphaerotheca fuliginea The leaf position of melon plants seems to play a role on their susceptibility when they are artificially infected with powdery mildew Sphaerotheca fuliginea. The cotyledons are generally very susceptible, while the first leaf relatively resistant; the susceptibility again continues up to the 4th–5th leaf (but less susceptible than the cotyledons) and then after it decreases; these results can be obtained on plants in greenhouse or on detached leaves in Petri dishes. From this observation, we think that the screening of melon genotypes for resistance to powdery mildew can be evaluated neither on the cotyledons which are very susceptible nor on the first leaf which is resistant, but on the third leaf which is moderately susceptible. In fact, there is a good correlation between the reaction of the third leaf and the resistance or susceptibility of genotypes.     

TaRPP13-3, a CC-NBS-LRR-like gene located on chr 7D,promotes disease resistance to wheat powdery mildew in Brock

Disease resistance (R) gene, RPP13, plays an important role in the resistance of plants to pathogen infections; its function in resistance of wheat to powdery mildew remains unknown. In this study, a RNA-Seq technique was used to monitor expression of genes in susceptible wheat ‘Jing411’ and resistant near-isogenic line ‘BJ-1’ in response to powdery mildew infection. Overall, 413 differential expression genes were observed and identified as involved in disease resistance. RPP13 homologous gene on wheat chromosome 7D was preliminarily identified using the wheat 660K SNP chip. RPP13 was highly expressed in ‘BJ-1’ and encodes 1,027 amino acids, including CC, NB and LRR domain, termed TaRPP13-3. After inoculation with powdery mildew, expression of TaRPP13-3 in resistant wheat changed with time, but average expression was higher when compared to susceptible variety, thus indicating that TaRPP13-3 is involved in resistance to powdery mildew. Virus-induced gene silencing (VIGS) was used to inhibit expression of TaRPP13-3 in resistant parent ‘Brock’. Results indicated that silencing of TaRPP13-3 led to decreased disease resistance in ‘Brock’. Overall results of this study indicate that TaRPP13-3 gene is involved in the defence response of wheat to powdery mildew and plays a positive role in wheat powdery mildew interactions.     

Powdery mildew of tobacco (Erysiphe cichoracearum DC.)

In water culture experiments, tobacco plants of Hicks variety were supplied with factorial combinations of high and low concentrations of nitrogen, phosphorus and potassium. Incidence of powdery mildew and growth and chemical composition of infected and healthy plants were compared.
There was more disease when all elements were supplied at the higher of two concentrations, but the increase in infection was less than the increase in growth. Plants grown in media containing a low ratio of potassium to nitrogen produced the least susceptible leaves; their disease indices were up to 30 times less than those of plants that received the full nutrient treatment. Potassium-deficient leaves had thinner cell walls, larger water content, smaller sugar and potassium contents, and greater amino nitrogen and magnesium contents, compared with those of plants grown in any of the other media. The possible relation between these characteristics and susceptibility to Erysiphe cichoracearum DC. are discussed.     

THE EFFECT OF TEMPERATURE AND HUMIDITY ON THE RATE OF DEVELOPMENT AND MORTALITY OF TRIBOLIUM CASTANEUM (HERBST) (COLEOPTERA, TENEBRIONIDAE)

The speed of development and the developmental mortality of Tribolium castaneum were studied over a series of temperatures between 15 and 40°C. at 10, 30, 70 and 90% R.H. using wheatfeed as food.
Eggs did not hatch at any humidity at 17·5°C. or less, nor at 10% R.H. at 40°C. At all other conditions about 80% of eggs hatched. Humidity does not affect the duration of the egg period. The effect of temperature on the egg period is shown graphically, the shortest period occurring at 37·5°C.
Larvae fail to develop into normal adults at 20°C. and also fail at 90 and 30% R.H. at 40°C. At 20°C. and 70% R.H. pupae may be formed but they do not become normal adults. The rate of larval development is affected by both temperature and humidity. Development is quickest at the highest humidity used at any temperature and at 35°C. for each humidity. Larval mortality is less than 20% except at 40°C. and at combinations of low humidity and low temperature. The results correspond with published results using similar foodstuffs.
Groundnuts were used as a food in a series of experiments at 30°C. and another series at 70% R.H. Larvae on this food were much more susceptible to the effects of humidity and were unable to develop at 20 or 40°C. at 70% R.H. In all conditions development was slower and mortality higher than on wheatfeed.
The pupal period is not affected by humidity and is shortest at 37·5°C.
The conditions in which Park found that cultures of T. castaneum became extinct, 24°C. and 30% R.H., lie inside the zone in which development is possible. The possible causes for this discrepancy are discussed.     

Temperature and daylength control of flower initiation in winter oilseed rape (Brassica napus L.)

The influence of low temperature and daylength on pre-floral growth and flower initiation in winter oilseed rape cv. Mikado was examined under controlled environment conditions at the University of Newcastle upon Tyne during 1985 and 1986.
The vernalisation requirement of Mikado was most effectively fulfilled by temperatures of 6 °C and 9 °C. Plants maintained at both higher and lower temperatures had an extended pre-floral growth phase. The transition from vegetative to reproductive growth in plants maintained at 12 °C was delayed by slow accumulation of the cold requirement, whereas flower initiation appeared to be delayed by limited leaf production, dry matter accumulation and/or assimilate availability in plants grown at 3 °C. The mechanism of floral induction remained unresolved but it was clear that flower initiation was not controlled by low temperature per se . Short days partially substituted for the cold requirement at 12 °C but photoperiodic induction of flower initiation was less important than the influence of low temperature.     

Indirect Effect of a Transgenic Wheat on Aphids through Enhanced Powdery Mildew Resistance

In agricultural ecosystems, arthropod herbivores and fungal pathogens are likely to colonise the same plant and may therefore affect each other directly or indirectly. The fungus that causes powdery mildew (Blumeria graminis tritici) and cereal aphids are important pests of wheat but interactions between them have seldom been investigated. We studied the effects of powdery mildew of wheat on two cereal aphid species, Metopolophium dirhodum and Rhopalosiphum padi. We hypothesized that aphid number and size will be smaller on powdery mildew-infected plants than on non-infected plants. In a first experiment we used six commercially available wheat varieties whereas in the second experiment we used a genetically modified (GM) mildew-resistant wheat line and its non-transgenic sister line. Because the two lines differed only in the presence of the transgene and in powdery mildew resistance, experiment 2 avoided the confounding effect of variety. In both experiments, the number of M. dirhodum but not of R. padi was reduced by powdery mildew infection. Transgenic mildew-resistant lines therefore harboured bigger aphid populations than the non-transgenic lines. For both aphid species individual size was mostly influenced by aphid number. Our results indicate that plants that are protected from a particular pest (powdery mildew) became more favourable for another pest (aphids).     

Cost of prey capture, growth rate and ration size in pike, Esox lucius L., as functions of prey wheight

Prey intake, amount of time feeding, pursuit and manipulation times and growth rate were studied in the pike, Esox lucius , in relation to prey weight. Predator and prey were observed in tanks at 15°C and with a 14:10 h LD photoperiod. A total of 444 captures were recorded from five 1 g prey weight groups varying from 0 to 4.9 g. Ten pike were used weighing between 50 and 149 g.
As prey weight increased, the number and weight of prey consumed decreased as did the time spent feeding, which became concentrated into the first trial of the day. Pursuit time did not vary with prey weight, but manipulation time and the weight of prey gained per unit pursuit plus manipulation time increased with prey weight.
The growth rate of pike was a positive function of ration size and a negative function of the amount of time spent capturing each gramme of prey (capture cost). Growth rate was also correlated with the mean length and weight of prey eaten.
The most profitable prey, as estimated from optimal foraging theory, need only be available once every 84 min for pike to maximize their net energy gain. The data show that feeding behaviour can have a direct influence on the reproductive success of pike through its effect on growth rate.     

Nematospiroides dubius: genetic control of immunity to infections of mice

Inbred strains of mice differ in their susceptibility and resistance to challenge infections with Nematospiroides dubius. In our studies, F1 hybrid mice from resistant SJL and susceptible CBA parents were resistant to N. dubius challenge infections. Only 22% of backcrosses to SJL were susceptible while backcrosses to CBA had a wide range of susceptibility. Male mice were more susceptible than female mice. In another experiment, inbred strains of mice were compared in their ability to resist N. dubius challenge infection: SJL and A.SW (H-2s) mice became resistant after one immunizing infection, A, A/He (both H-2a), as well as BALB/c and DBA/2 (both H-2d) mice became resistant after two immunizing infections, while C57BL/6 (H-2b), C3H/He, CBA, and AKR (H-2k) mice remained susceptible. The resistance to reinfections was characterized by reduction of worm burdens between Days 6 and 14 postinfection. It was concluded that (1) resistance to N. dubius challenge infections is inherited in a dominant fashion and that multiple genes may influence such response, which in turn might be modulated by the Y chromosome; (2) both MHC and non-MHC genes may influence, in conjunction with the number of exposures to parasite antigens, the resistance to challenge infections.