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1.
J. Blackburn G. Thorp A. Dobrovin‐Pennington S. Pietravalle G. Kerins T. R. Allnutt C. M. Henry 《Plant pathology》2011,60(6):1077-1085
Temperature and exposure time effects on Phytophthora kernoviae and Phytophthora ramorum viability were examined in flasks of compost and in a large‐scale composting system containing plant waste. Cellophane, rhododendron leaf and peat‐based inoculum of P. kernoviae and P. ramorum isolates were used in flasks; naturally infected leaves were inserted into a large‐scale system. Exposures of 5 and 10 days respectively at a mean temperature of 35°C in flask and large‐scale composts reduced P. kernoviae and P. ramorum inocula to below detection limits using semi‐selective culturing. Although P. ramorum was undetectable after a 1‐day exposure of inoculum to compost at 40°C in flasks, it survived on leaves exposed to a mean temperature of 40·9°C for 5 days in a large‐scale composting system. No survival of P. ramorum was detected after exposure of infected leaves for 5 days to a mean temperature of ≥41·9°C (32·8°C for P. kernoviae) or for 10 days at ≥31·8°C (25·9°C for Phytophthora pseudosyringae on infected bilberry stems) in large‐scale systems. Fitted survival probabilities of P. ramorum on infected leaves exposed in a large‐scale system for 5 days at 45°C or for 10 days at 35°C were <3%, for an average initial infection level of leaves of 59·2%. RNA quantification to measure viability was shown to be unreliable in environments that favour RNA preservation: high levels of ITS1 RNA were recovered from P. kernoviae‐ and P. ramorum‐infected leaves exposed to composting plant wastes at >53°C, when all culture results were negative. 相似文献
2.
The development ofBracon vulgaris Ashmead (Hymenoptera: Braconidae), parasitoid of the cotton boll weevilAnthonomus grandis Boheman (Coleoptera: Curculionidae), was studied at constant temperatures of 18, 20, 23, 25, 28, 30, 33, 35 and 38°C, 70±10%
r.h. and 14:10 L:D period. The period from egg to adult ofB. vulgaris varied from 8.6 (35°C) to 32.9 days (18°C). The eggs of this parasitoid became desiccated and did not hatch at 38°C. The
lower development threshold (LDT) and thermal constants for development varied withB. vulgaris instar, but they were similar for males and females. The duration of the 1st, 2nd, 3rd and 4thB. vulgaris instars required, respectively, 9.36 degree-days above one LDT=12.27°C, 13.48 degree-days above one LDT=6.83°C, 11.65 degree-days
above one LDT=9.41°C, and 12.82 degree-days above one LDT=10.78°C.B. vulgaris has physiological adaptations to different threshold temperatures and it shows high potential to be used againstA. grandis in cotton crops. 相似文献
3.
F. S. Ramalho P. A. Wanderley J. B. Malaquias K. C. V. Rodrigues J. V. S. Souza J. C. Zanuncio 《Phytoparasitica》2009,37(1):17-25
The duration of development of Bracon vulgaris Ashmead, parasitoid of the boll weevil Anthonomus grandis Boheman, was determined at nine constant temperatures between 18°C and 38°C. Nonlinear regression analysis was used to test
the fit of temperature-dependent development rates to the Sharpe and DeMichele and Lactin et al. models. At the highest tested
temperature (38°C) all the parasitoid eggs died before hatching and no evidence of development was observed. The high values
of R
2 for the models of Sharpe and DeMichele (0.8432 to 0.9834), and Lactin et al. (0.9071 to 0.9795) indicated that these models
are suitable to estimate the development rate of B. vulgaris as a function of temperature. B. vulgaris showed tolerance to high temperature which is represented by the high value of H
H (change in enthalpy associated with high-temperature inactivation of the enzyme) for the prepupa stage of this insect obtained
with the Sharpe and DeMichele model. According to that model, B. vulgaris exhibits thermal stress at 35.7°C, which indicates that maximum thermal stress estimated by this model was close to the real
one. 相似文献
4.
Effects of temperature on germination of sporangia,infection and protein secretion by Phytophthora kernoviae 
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下载免费PDF全文 B. A. Shelley D. G. Luster W. M. Garrett M. B. McMahon T. L. Widmer 《Plant pathology》2018,67(3):719-728
Phytophthora kernoviae is a pathogen on a wide range of plants, but little is known of optimal infection conditions. Rhododendron ponticum leaves were inoculated with six different isolates of P. kernoviae sporangia and incubated at different temperatures from 10 to 28 °C. After 1 week, lesion development and pathogen recovery were only observed from all isolates at 15 and 20 °C and a few isolates at 10 °C. In an experiment with temperatures ranging from 20 to 25 °C, lesion development and pathogen recovery on R. ponticum, Magnolia stellata and Viburnum tinus occurred consistently at 20 and 21 °C, was limited at 22 °C, and did not occur at 23 °C and above. There was no difference in sporangia and zoospore germination at 20–25 °C. In a temperature fluctuation experiment, the necrotic area of inoculated R. ponticum leaves increased with longer incubation at 20 °C and decreased with longer incubation at 24 °C. Crude extracts of secreted proteins from P. kernoviae cultures grown at 20 and 24 °C were compared to determine any effects of temperature on pathogenicity. When spot tested on R. ponticum leaves, crude protein suspensions from cultures grown at 20 °C induced necrosis, while proteins from cultures grown at 24 °C did not. Proteomic analysis confirmed that a 10 kDa protein secreted at both 20 and 24 °C shared sequence homology to the conserved domains of known elicitins of other Phytophthora spp. The protein secreted at 20 °C that was responsible for necrosis has not been identified. 相似文献
5.
Elzbieta G Magnucka Yoshikatsu Suzuki Stanislaw J Pietr Arkadiusz Kozubek Robert Zarnowski 《Pest management science》2009,65(10):1065-1070
BACKGROUND: Cycloate inhibits the biosynthesis of very‐long‐chain fatty acids, the essential constituents of plant waxes and suberin. Fatty acids also serve as precursors of aliphatic carbon chains in resorcinolic lipids, which play a fundamental role in the plant defence system against fungal pathogens. In this study, the effect of cycloate on the biosynthesis of 5‐n‐alkylresorcinols in rye seedlings (Secale cereale L.) grown under various light and thermal conditions was examined. RESULTS: The content of alkylresorcinols biosynthesised in rye was generally increased by the herbicide in both green and etiolated plants. The presence of cycloate also affected patterns of alkylresorcinol homologues in plants grown at 15 and 22 °C; very‐long‐side‐chain compounds were less abundant, whereas both short‐chain saturated and unsaturated homologues were generally accumulated. No cycloate‐related effects caused by homologue pattern modifications were observed at elevated temperature. CONCLUSION: This study extends present understanding of the mode of action of thiocarbamate herbicides. Cycloate markedly affected the biosynthesis of very‐long‐side‐chain resorcinolic lipids in rye seedlings, confirming the existence of parallels in both fatty acid and alkylresorcinol biosynthetic pathways. The observed cycloate‐driven accumulation of 5‐n‐alkylresorcinols may improve the resistance of cereals to infections caused by microbial pathogens. Copyright © 2009 Society of Chemical Industry 相似文献
6.
The effect ofBacillus subtilis on the contents of total lipids, neutral lipids, phospholipids and fatty acids in cotyledonary leaves of peanut (Arachis hypogaea L. cv. ‘Giza 6’) was studied in the presence and absence of the mycotoxin fusaric acid. In experiments conducted in a water
culture in test tubes, the amount of total lipids was decreased by fusaric acid and increased byB. subtilis; combined treatment reduced the amount. With respect to the effect of fusaric acid on neutral lipids, a non-significant increase
in diacylglycerol, significant decreases in triacylglycerol and sterol, and significant increases in sterol ester and non-esterified
fatty acids, were obtained, whereasB. subtilis had the opposite effect. Generally, the amounts of the detected phospholipid fractions and the percentages of unsaturation
index as well as fatty acids (palmitic, stearic and oleic) were reduced by fusaric acid. Linoleic acid, on the other hand,
showed a reverse response: it was increased by fusaric acid alone or in combination withB. subtilis, the increase in the first case being greater than in the second, whereas linoleic acid disappeared in theB. subtilis treatment.
http://www.phytoparasitica.org posting Dec. 16, 2003. 相似文献
7.
Hans H. Hoppe 《Pesticide biochemistry and physiology》1985,23(3):297-308
The herbicide diclofop-methyl caused an early and pronounced inhibition of the incorporation of [14C]acetate into leaf lipids of the sensitive plant species maize (Zea may L.), wild oat (Avena fatua L.), and barnyardgrass (Echinochloa crus-galli L.). With an EC50 value of approximately 10?7M inhibition was already apparent 0.5–4 hr after herbicide application. The fatty acid biosynthesis of tolerant bean (Phaseolus vulgaris L.), sugar beet (Beta vulgaris L.), and soybean (Glycine max L.) was not affected, with one exception [wheat (Triticum aestivum L.) belongs to the more tolerant species]; the inhibition of fatty acid biosynthesis, however, was in the same order of magnitude as in sensitive plants. More detailed studies showed that in wheat a recovery from inhibition of fatty acid biosynthesis occurred. Four days after herbicide application (0.18 kg diclofop-methyl/ha) in wheat normal fatty acid biosynthesis was restored, whereas in sensitive maize a 60% inhibition was maintained over the whole experimental period (8 days). The results support the view that tolerance of wheat to diclofop-methyl is based on its inactivation in leaves, whereas the tolerance of dicotyledonous species may probably lie at the level of the site of action of diclofop-methyl. In experiments with intact leaves, the inhibition of fatty acid biosynthesis resulted in an enhanced flow of [14C]acetate into organic acids and amino acids. This effect, however, was not always reproducible in experiments with leaf pieces or isolated root tips. 相似文献
8.
Calonectria pseudonaviculata causes lesions on boxwood leaves and twigs. Controlled-environment experiments were conducted to determine the effects of temperature and leaf wetness period on C. pseudonaviculata sporulation on diseased (cv. Suffruticosa) leaves and of dryness periods and high temperature on conidial survival. Infected leaves were incubated in moist chambers and subjected to six temperatures (9, 13, 17, 21, 25, and 29°C) and six leaf wetness periods (0, 12, 24, 40, 48, and 72 h). Spore production was influenced significantly by wetness period, temperature, and their interaction. Increasing duration of leaf wetness and increasing temperature generally increased sporulation, with no sporulation occurring at 29°C or 9 and 13°C, except at 72 h of wetness exposure, while it was optimal at 21°C. Detached leaves with profuse conidia were subjected to a range of drying (relative humidity at 65%) times (0, 2, 4, 6, and 8 h) at two temperatures of 21 and 29°C. Conidia were then harvested and plated on water agar. Germinating conidia were counted to measure the spore viability. Spore mortality increased with increasing dryness duration at both temperatures but occurred more quickly and severely at 29 than 21°C. Overall, this study extended biological knowledge of conditions required for crucial stages of the C. pseudonaviculata disease cycle and the obtained results will be vital for developing boxwood blight forecasting and management tools. 相似文献
9.
Yoshihiro OHTSU Maitree PROMMINTARA Seiichi OKUDA Tomoaki GOTO Takeshi KANO Kazuo NAKASHIMA Meisaku KOIZUMI Jun IMADA Koji KAWASHIMA 《Journal of General Plant Pathology》2002,68(4):372-377
We aimed to improve the purification of citrus Huanglongbing (greening) bacterium (HB), Candidatus Liberobacter asiaticum and to produce an antiserum against HB. Periwinkle plants Catharantus roseum L. graft-inoculated with HB were used to produce an antiserum. All young leaves of new shoots incubated at 20–25°C and 25–30°C,
a few mature leaves incubated at 20–25°C, and all mature leaves incubated first at 25–30°C and later transferred to 20–25°C
developed yellowing symptoms and were then used to prepare immunogen. The HB was partially purified from these leaves by an
improved method that included a macerating enzyme treatment of the midribs of infected leaves and homogenization of infected
phloem sieve tissues. An antiserum raised against partially purified HB reacted clearly at a dilution of 1/16 with HB-infected
citrus extract prepared at a concentration of 40 times, but did not react with healthy or tristeza virus-infected citrus extract
in microprecipitin tests.
Received 23 August 2002/ Accepted in revised form 4 December 2002 相似文献
10.
Viral movement in the leaf tissues of a resistant host, Cucumis figarei, inoculated with the pepo strain of Cucumber mosaic virus (CMV) and incubated at 24°C or 36°C was investigated by fluorescence in situ hybridization (FISH), leaf-press blotting, tissue printing and immunogold-silver staining techniques. Observation by FISH
revealed that at 24°C most infection sites with CMV at 0.01 mg/ml or 0.1 mg/ml were limited to a single cell during the incubation
period, that the number of infection sites increased from 24hpi (hours post inoculation) to 80 hpi in the leaves inoculated
with CMV at 0.5 mg/ml, and that the size as well as the number of infection sites rapidly increased with time in the leaves
inoculated with CMV at 2.0 mg/ml. These results suggested that one factor for the resistance of C. figarei at 24°C might be an inhibition of viral movement in and out of the infection sites. Leaf-press blotting and tissue blotting
indicated that CMV remained in the infection sites at 24°C, whereas it spread from the inoculated leaves to other parts of
the plants through vascular systems at 36°C. Immunogold-silver staining demonstrated that at 24°C CMV infected bundle sheath
(BS) cells in minor veins, whereas at 36°C it invaded not only BS cells, but also phloem parenchyma (PP)/ companion cell (CC)
or PP/intermediary cell (IC) complexes in minor veins in the regions with chlorotic symptoms. These results indicated that
at 24°C CMV had difficulty in passing through the interface between BS and PP/CC or PP/ IC complexes and that viral entry
from mesophyll to the phloem pathway was inhibited in the inoculated leaves.
Received 26 August 1999/ Accepted in revised form 14 December 1999 相似文献
11.
Abstract The cold-hardiness of Liriomyza chinensis pupae was measured in the laboratory by observing pupal mortality at low temperatures. Pupal mortality increased with decreasing temperature and with extended cold exposure time. No recently pupated pupae (6 h) were able to survive after 16 days of chilling at 0, 2.5 and 5°C, but 42.9% survival was observed at 10°C. Pupae at different developmental stages showed significant difference in mortality, with very low levels of mortality observed for older pupae (4 and 7 days) after exposure to 0°C for 16 days. The lethal time for 50% survival (LT50) increased with increasing age of pupae. LT50 for 4-day-old pupae exposed to 0°C was 52.1 days. Analysis of mean temperatures at several localities indicated that L. chinensis is able to overwinter outdoors in southern regions, but is unable to overwinter in open fields in northern regions of Japan, suggesting that overwintering in these regions would only occur in greenhouses. 相似文献
12.
When the petioles of detached tobacco leaves (10–17 cm2) were incubated in aqueous solutions containing [14C]metalaxyl, uptake of the fungicide was dependent on the temperature and photoperiod. Detached leaves took up 78% more [14C]metalaxyl at 26°C than at 16°C. The rate of uptake in the light at 21°C was linear, but after an additional 20h in the dark, there was only twice as much fungicide in the leaves. Different sized leaves contained the same amount of fungicide per cm2 area. Uptake by detached leaves of the 14C-labelled anilide lactones ofurace and RE-26940 [2-methoxy-N-(tetrahydro-2-oxo-3-thienyl)acet-2′,6′-xylidide] was similar to that of metalaxyl. At the concentration of metalaxyl (66 ng ml?1) that controlled blue mould (Peronospora tabacina) on detached tobacco leaves, the amount of fungicide in the leaves was found to be 7.25 ng. Autoradiography showed that the distribution of [14C]metalaxyl in detached leaves after incubation for 23h was uniform, although higher concentrations of the label were present in the smaller veins of the leaves. 相似文献
13.
The effect of microclimate variables on development ofClonostachys rosea and biocontrol ofBotrytis cinerea was investigated on rose leaves and crop residues. C.rosea established and sporulated abundantly on inoculated leaflets incubated for 7–35 days at 10°, 20° and 30°C and then placed
on paraquat—chloramphenical agar (PCA) for 15 days at 20°C. On leaflets kept at 10°C, the sporulation after incubation on
PCA increased from 60% to 93% on samples taken 7 to 21 days after inoculation, but decreased to 45% on material sampled after
35 days. A similar pattern was observed on leaves incubated at either 20° or 30°C. The sporulation ofC. rosea on leaf disks on PCA was not affected when the onset of high humidity occurred 0, 4, 8, 12 or 16 h after inoculation. However,
sporulation was reduced to 54–58% on leaflets kept for 20–24 h under dry conditions after inoculation and before being placed
on PCA. The fungus sporulated on 68–74% of the surface of leaf disks kept for up to 24 h at high humidity after inoculation,
but decreased to 40–51% if the high humidity period before transferral to PCA was prolonged to 36–48 h. The growth ofC. rosea on leaflets was reduced at low inoculum concentrations (103 and 104 conidia/ml) because of competition with indigenous microorganisms, but at higher concentrations (105 and 106 conidia/ml) the indigenous fungi were inhibited. Regardless of the time of application ofC. rosea in relation toB. cinerea, the pathogen’s sporulation was reduced by more than 99%. The antagonist was able to parasitize hyphae and conidiophores
ofB. cinerea in the leaf residues. AsC. rosea exhibited flexibility in association with rose leaves under a wide range of microclimatic conditions, and in reducingB. cinerea sporulation on rose leaves and residues, it can be expected to suppress the pathogen effectively in rose production systems. 相似文献
14.
Miyuki Fukuda Yasuko Tsujino Takane Fujimori Ko Wakabayashi Peter Bger 《Pesticide biochemistry and physiology》2004,80(3):143-150
Phytotoxic activity of several middle-chain fatty acids, especially pelargonic acid (C9 acid) was investigated. C9–C11 acids caused strong non-selective damage to plants such as crabgrass, cucumber, velvetleaf, and tobacco, while C6 and C14 fatty acids had almost no activity. Middle-chain fatty acids caused a strong and rapid electrolyte leakage. They reached highest conductivity in 3 h in the case of cucumber cotyledons. Middle-chain fatty acids caused a decrease of the amount of polar lipids, particularly MGDG and PG, and chlorophylls. They also caused an increase of free fatty acids in 24 h after treatment. These results suggested that middle-chain fatty acids caused severe damage to cell membranes and thylakoid membranes of treated leaves. C6 volatile compounds such as cis-3-hexenal, trans-2-hexenal, and cis-3-hexenol were generated in less than 1 h after spraying pelargonic acid to tobacco leaves. The application of pelargonic acid was thought to be the trigger for linolenic acid degradation in the thylakoid membranes. 相似文献
15.
Thomas Thomidis Themis J. Michailides Efstathia Exadaktylou 《European journal of plant pathology / European Foundation for Plant Pathology》2011,131(2):171-178
Shoot blights are common diseases of peach trees in Greece. This study is the first report of a shoot blight and canker disease
of peach in Greece caused by the fungus Phoma glomerata (Corda) Wollenw. & Hochapfel. The pathogen caused distinct cankers with abundant gumming on shoots of peach trees. The rate
of development of P. glomerata in vitro was reduced as temperatures increased from 25°C to 30°C, decreased from 25°C to 15°C, and was totally inhibited
at 35 and 10°C. The rate of conidial germination and the germ tube elongation in vitro was reduced as temperatures increased
from 25°C to 35°C, decreased from 25°C to 10°C, and was totally inhibited at 2–4°C. Pathogenicity tests showed that 24 peach
and nectarine cultivars grown in Imathia Perfecture, Greece, were equally susceptible to P. glomerata. The fungicides thiophanate methyl, carbendazim, and tebuconazole were evaluated against the development of P. glomerata and disease symptoms. All fungicides inhibited the growth and conidial germination of P. glomereta and disease symptoms, and all 30 isolates tested were sensitive to the above fungicides. The disease caused by P. glomerata could be a threat to peach cultivation in Greece and its management should be investigated in the field. 相似文献
16.
Kazutaka Kido Tomofumi Mochizuki Kazutoshi Matsuo Chika Tanaka Kenji Kubota Takehiro Ohki Shinya Tsuda 《European journal of plant pathology / European Foundation for Plant Pathology》2008,121(2):189-194
The single recessive gene, nsv, which confers resistance against Melon necrotic spot virus (MNSV), has recently been used to develop virus-resistant melon cultivars in Japan. However, the Chiba isolate of MNSV, a
common isolate in Japan, infected resistant cultivars when inoculated melon plants were grown at 15°C. Viral RNAs accumulated
in protoplasts from resistant cultivars at both 15 and 20°C. Mechanical inoculation of the cotyledons caused MNSV to spread
throughout the leaves at 15°C, but not at 20°C. These results support our novel hypothesis that a temperature-sensitive inactivation
of disease resistance genes occurs at the nsv locus in melon cultivars with the resistance gene grown at temperatures below 20°C.
The first and second authors contributed equally to this research. 相似文献
17.
Oranges and lemons infected with Phytophthora citrophthora and P. syringae were placed among healthy fruits in boxes kept at 5, 10 and 14°C. The spread of the rot by contact infection was assessed after 3,6,12 and 18 days and again after 7 days' shelf-life at 17°C. P. citrophthora infected adjacent fruits after 12 days at 10°C and 3 days at 14°C. No infection occurred at 5°C. P. syringue infected the fruits at all the temperatures tested. On fruits kept for 6 days at 5°C, the rot developed after shelf-life. The presence of Phytophthora-infected fruits in orange and lemon packing boxes enhanced the development of penicillium rots. Post-harvest dips in metalaxyl at 0.05 and 0.1% concentrations and fosetyl-Al at 0.1,0.2 and 0.3% concentrations prevented the spread of P. citrophthora in packing boxes kept for 30,40 and 60 days at 11°C, but had no effect on penicillium rots. The mixture of the above fungicides with thiabendazole at 0.1%] or imazalil at 0.05%, concentrations gave best control against phytophthora and penicillium rots. 相似文献
18.
When the influence of host species, inoculum density, temperature, leaf wetness duration, and leaf position on the incidence
of gentian brown leaf spot caused by Mycochaetophora gentianae, was examined, the fungus severely infected all seven Gentiana triflora cultivars, but failed to infect two cultivars of G. scabra and an interspecific hybrid cultivar. Inoculum density correlated closely with disease incidence, and a minimum of 102 conidia/mL was enough to cause infection. In an analysis of variance, temperature and leaf wetness duration had a significant
effect upon disease incidence, which increased with higher temperature (15–25°C) and longer duration of leaf wetness (36–72 h).
No disease developed at temperatures lower than 10°C or when leaf wetness lasted <24 h. At 48-h leaf wetness, disease incidence
was 0, 28, 77, and 85% at 10, 15, 20, and 25°C, respectively. Middle and lower leaves on the plant were more susceptible than
upper leaves. In microscopic observations of inoculated leaves, >50% of conidia germinated at temperatures >15°C after 24-h
leaf wetness. More appressoria formed at higher temperatures (15–25°C) with extended duration of leaf wetness (24–72 h). At
48-h leaf wetness, appressorium formation was 0, 8, 26, and 73% at 10, 15, 20, and 25°C, respectively. These results suggest
that temperature and leaf wetness duration were important factors for infection of gentian leaves. 相似文献
19.
Fifty‐four Dickeya solani thermoregulated genes were identified using Tn5 transposon mutagenesis with an inducible gusA reporter system; 45 genes were up‐regulated at 37 °C, whereas nine were up‐regulated at 18 °C. The relative level of gene up‐regulation ranged from 2–1200 and 5–650 U/mg total proteins at 18 and 37 °C, respectively. Among the temperature‐regulated loci, genes coding for proteins involved in fundamental bacterial metabolism, membrane‐related proteins and pathogenicity‐corresponding factors and several hypothetical unknown proteins were found. The mutants were tested for their pathogenicity in planta and for features known to be important for D. solani virulence viz. production of pectinolytic enzymes, cellulases, proteases, siderophores and auxins as well as for motility and the ability to form a biofilm. Eight Tn5 mutants, four up‐regulated at high and four up‐regulated at low temperature, expressed visible phenotypes including the decreased ability to cause symptoms on potato tubers and chicory leaves, impairment in phospholipase production and/or deficiency in biofilm formation. The implications of environmental temperature on the ability of D. solani to cause disease symptoms in potato are discussed. 相似文献
20.
Grapevine leaves infected with powdery mildew are a source of inoculum for fruit infection. Leaves emerging on a single primary shoot of Vitis vinifera cv. Cabernet Sauvignon were exposed to average glasshouse temperatures of 18°C (0·23 leaves emerging/day) or 25°C (0·54 leaves emerging/day). All leaves on 8–10 shoots with approximately 20 leaves each were inoculated with Erysiphe necator conidia to assess disease severity after 14 days in the 25°C glasshouse. Two photosynthetic ‘source’ leaves per shoot on the remaining 8–10 shoots were treated with 14CO2 to identify, by autoradiography, the leaf position completing the carbohydrate sink‐to‐source transition. There was a clear association between the mean modal leaf position for maximum severity of powdery mildew (position 3·7 for 18°C; position 4·4 for 25°C) and the mean position of the leaf completing the sink‐to‐source transition (position 3·8 for 18°C; position 4·7 for 25°C). The mean modal leaf position for the maximum percentage of conidia germinating to form secondary hyphae was 4·2 for additional plants grown in the 25°C glasshouse. A higher rate of leaf emergence resulted in a greater proportion of diseased leaves per shoot. A Bayesian model, consisting of component models for disease severity and leaf ontogenic resistance, had parameters representing the rate and magnitude of pathogen colonization that differed for shoots developing in different preinoculation environments. The results support the hypothesis that the population of leaves in a vineyard capable of supporting substantial pathogen colonization will vary according to conditions for shoot development. 相似文献