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1.
Outbreaks of late blight occurred in commercial potato fields in northwestern Washington in 1989 and reached epidemic proportions in 1990. Since most blighted fields reportedly had received 2–4 late-season applications of metalaxyl, the possibility existed that pathogenic strains ofPhytophthora infestans had developed resistance to this systemic fungicide. In testing this hypothesis,P. infestans was isolated consistently from diseased leaves, stems, and tubers of potato when small tissue pieces were surface-disinfected in 0.5% NaOCl for 3 min. Virulence of isolates was assessed on detached leaflets of eight differential (R-gene) potato genotypes. Although simple races (single and double) were recovered, there was also a high frequency of complex race combinations. When tested in metalaxyl-amended media, 81% of the 73 isolates recovered from diseased tissues were highly resistant to 10 μg metalaxyl/ml and 19% yielded intermediate resistance. Sensitive isolates were not recovered. Fifty-five percent of 40 isolates sporulated on potato tuber disks in the presence of ≥10 ug metalaxyl/ml. On leaf tissues, 85% of 20 isolates sporulated in the presence of 10 μg metalaxyl/ml, and 50% sporulated in the presence of 100 μg/ml. This is the first report ofP. infestans resistance to metalaxyl in the U.S.  相似文献   

2.
A total of 930 isolates ofPhytophthora infestans collected during 1997 and 1998 from commercial potato and tomato fields, home gardens, and potato storages in Canada was analyzed for glucose phosphate-isomerase (Gpi) genotype, mating type, and resistance to metalaxyl. Both mating types and diversity in resistance to metalaxyl were detected within and amongGpi-genotypes. Pathogen populations were dominated by the 100:111:122Gpi-genotype (characteristic of US-8) in all the provinces where late blight was detected, except in 1997 in British Columbia (BC) where the 100:100:111Gpi-genotype (characteristic of US-11) predominated.Gpi-genotypes 100:111, 111:122, and 100:122 (characteristic of US-7, US-10 and US-14/US-17, respectively) were less common. Nearly all of the isolates with the 100:100:111Gpi-genotype were the A1 mating type, except for a few collected in BC in 1997. A majority of isolates with the 100:111:122Gpi-genotype were A2 except for a few found in Québec in 1998. Based on colony growth on media amended with 1,10, or 100 μg/ml metalaxyl, the 100:100:111Gpi-genotype isolates had higher levels of resistance to the fungicide in 1998 compared to 1997. In 1998, level of metalaxyl resistance was higher within the 100:100:111Gpi-genotype whereas it was lower within the 100:111: 122Gpi-genotype, when compared to 1997. BC was the only Canadian province where an increase in metalaxyl resistance within the 100:111:122Gpi-genotype was recorded between 1997 and 1998. Isolates from leaves had higher metalaxyl resistance levels than stem or tuber isolates, regardless of genotype.  相似文献   

3.
Disease development was monitored weekly in field plots inoculated withPhytophthora infestans and treated with metalaxyl, mancozeb or metalaxyl/ mancozeb combinations. Late blight pressure was moderate to severe in 1981 and 1983 and was slight to moderate in 1982 and 1984. In 1982–84 all treated plots had significantly less foliar damage and late blight tuber rot than untreated plots. Use of metalaxyl alone resulted in the greatest increase in disease (up to 80% defoliation) in the latter part of the growing season. Under slight to moderate disease pressure, metalaxyl/mancozeb and mancozeb treatments provided significantly better disease control than metalaxyl. Under moderate to severe disease pressure, high levels of disease (65% defoliation) occurred by the end of the season with mancozeb and metalzxyl/mancozeb on 7- and 14-day spray schedules, respectively. However, significantly better control (about 20% defoliation) was obtained during early season, rapidly developing epidemic conditions when only three applications of metalaxyl/mancozeb were included in a 7-day mancozeb spray program.  相似文献   

4.
The A2 mating type ofPhytophthora infestans was first reported in the United States in 1990. Concurrently,P. infestans strains resistant to metalaxyl ere found in the Pacific Northwest. Collaborative surveys were undertaken during 1991–1993 to investigate the frequency of occurrence of A2 mating types and metalaxyl resistant strains in populations ofP. infestans isolated from outbreaks of late blight in potato and tomato crops in North America.In vitro testing indicated that isolates from the northeastern U.S. and Atlantic Canada were primarily (52/55) metalaxyl sensitive and all were A1 mating types. Among 85 isolates from late blight epidemics in Florida and Texas, greater than 61% were both metalaxyl resistant and A2 mating type. Metalaxyl resistance and A2 mating types were identified also in a few tomato isolates from North Carolina. Although the majority of 134 isolates from the Pacific Northwest (British Columbia and Washington) were metalaxyl resistant, only 2 isolates from Washington were A2 mating types. Among 111 isolates from 2 sites in central Mexico, 63% and 77% were both metalaxyl resistant and A2 mating types. The data indicate also a higher frequency of metalaxyl resistance in A2 isolates, than in A1 isolates, among isolates from Florida and Texas. Highest metalaxyl resistance levels were found, however, in A1 isolates from California, where no A2 isolates were recovered.  相似文献   

5.
A total of 134 Czech Pseudoperonospora cubensis isolates originating from Cucumis sativus were used for fungicide resistance screening. Efficacy of six commonly used and registered fungicides was screened in Czech P. cubensis populations. The investigations covered the frequency and occurrence of sensitive, moderately resistant and resistant isolates to the individual fungicides during the period 2005–2010. Fosetyl-Al (Aliette 80 W) and propamocarb (Previcur 607 SL) were the most effective fungicides. All tested isolates were sensitive on all tested fosetyl-Al concentrations. However, some isolates expressed resistance (profuse sporulation) or moderate resistance (limited sporulation) to lower and/or even to recommended concentrations of propamocarb in the years 2006 and 2008–2010. Metalaxyl (Ridomil PLUS 48 WP) and metalaxyl-M (Ridomil Gold MZ 68 WP) were ineffective. Isolates collected in 2008 and 2009 showed large variation in moderate resistance or resistance even at high fungicide dosages. However, this result was not confirmed in 2010, when efficacy of these fungicides increased slightly, and 69% and 43% of isolates were controlled at the recommended concentration of metalaxyl-M and metalaxyl, respectively. Limited or profuse sporulation was observed only sporadically at high concentrations. Sensitivity of isolates to cymoxanil (Curzate K) differed among the studied years. While cymoxanil was ineffective in the years 2005–2008 and in 2010, 68% of isolates were controlled at the recommended concentration in 2009. During the years 2005 through 2010, a shift towards higher sensitivity to dimethomorph was observed at all screened concentrations.  相似文献   

6.
The activity of the phenylamide fungicides metalaxyl, cyprofuram, benalaxyl and oxadixyl against phenylamide-sensitive and phenylamide-resistant strains of Phytophthora megasperma f. sp. medicaginis and Phytophthora infestans has been compared in several tests. Metalaxyl showed the highest activity amongst the four fungicides against mycelial growth of sensitive strains on agar media. Benalaxyl and cyprofuram showed the highest activity against resistant strains. RNA synthesis of sensitive strains, measured as [3H]uridine incorporation, was inhibited by about 80% (P. megasperma) and by about 40% (P. infestans) by all phenylamides at concentrations of 1 μg/ml. At higher concentrations inhibition remained at this level, indicating that only part of the RNA synthesis was inhibited. RNA synthesis of resistant strains was completely insensitive to metalaxyl and oxadixyl at concentrations as high as 200 μg/ml. Cyprofuram, however, at concentrations above 1 μg/ml (P. megasperma) and 10 μg/ml (P. infestans) was inhibitory and at 200 μg/ml this compound almost completely inhibited the phenylamide-sensitive part of the RNA synthesis of both strains. In contrast to the other phenylamides, benalaxyl affected [3H]uridine uptake into mycelium at concentrations higher than 10 μg/ml, and at 100 μg/ml inhibition of uptake was almost total with both sensitive and resistant strains of both Phytophthora species. Inhibition of [3H]uridine uptake obviously is a feature of a second mechanism of action of benalaxyl. Endogenous RNA polymerase activity of isolated nuclei from sensitive strains of P. megasperma was inhibited at phenylamide concentrations as low as 0·1 μg/ml whereas that from resistant strains was not affected at concentrations as high as 100 μg/ml. Similarly, endogenous nuclear RNA polymerase activity of sensitive P. infestans strains appeared to be more sensitive to the phenylamides than that of resistant P. infestans strains. This suggests that resistance that developed in field strains of P. infestans has a basis similar to that of mutagen-induced resistance in laboratory strains of P. megasperma. Tests of the fungicidal activity of the phenylamides determined in a lucerne seedling assay (P. megasperma) and a detached potato leaf assay (P. infestans) clearly differentiated between sensitive and resistant strains. Resistance levels to cyprofuram and benalaxyl were as high as those to metalaxyl and oxadixyl, indicating that the additional effect of a second mechanism of action of benalaxyl and the property of cyprofuram to inhibit RNA synthesis of resistant strains at higher concentrations are of limited practical importance for counteracting phenylamide resistance.  相似文献   

7.
In northwest Washington State, fungicidal control of late blight caused byPhytophthora infestons was evaluated for three years. During 1977, a high rainfall year with supplemental sprinkler irrigations, all metalaxyl and chlorothalonil treatments reduced tuber rot at harvest, but only metalaxyl extended control of tuber rot after 4 months’ storage. During 1978, a high rainfall year, one application of metalaxyl sprayed over or dusted on potato seed pieces at planting or applied five times to foliage at 2 or 4 wk intervals gave excellent blight control equal to that with chlorothalonil applied to foliage every 2 wk. In 1979, a low rainfall year,P. infestons did not kill plants in untreated plots until October. Five applications of metalaxyl sprayed every 2 wk on foliage did not control foliage blight. However, metalaxyl reduced foliage blight when dusted on cut potato seed pieces. Mancozeb sprayed every 2 wk also gave excellent control. The possibility that metalaxyl applied to foliage is effective in late blight control only when washed into the soil by rainfall or irrigation for uptake by roots is discussed. Yields and percent U.S. No. 1 grade tubers were not significantly affected by any treatment in these 3-year trials.  相似文献   

8.
Samples of Phytophthora infestans were isolated from 12 city and county fields in the main potato production areas of Heilongjiang province of China between 2004 and 2008. A total of 72 isolates were tested for virulence on a potato R gene differential set and 39 of these isolates were also analysed for their resistance to the fungicide metalaxyl. All 11 differential plants were infected by one or more of the isolates collected; the most commonly overcome differentials were R1, R3, R4, R7, R10, and R11. Most (89.7%) of the tested isolates were resistant to metalaxyl and the rest (10.3%) were sensitive. The proportion of metalaxyl-resistant isolates differed between sites (χ 2?=?25.42, df?=?10, p?<?0.005), but not between years (χ 2?=?4.63, df?=?4, p?>?0.05). Taken together and in comparison with earlier pathogen population studies, our findings suggest that the population of P. infestans in Heilongjiang is different from that existing in the province two decades ago and that at various locations within the province, the new population has a high frequency of resistance to metalaxyl.  相似文献   

9.
The distribution of A1 and A2 mating types, and of metalaxyl-sensitive (MS), metalaxyl-intermediate (MI), and metalaxyl-resistant (MR) strains ofPhytophthora infestans, the causal pathogen of late blight, were determined in Canada in 1997. Potato plants or tubers and tomato plants or fruits, suspected to have late blight infection, were received from seven Canadian provinces in 1997, and were assessed for the presence ofP. infestans. Among 220 samples suspected to have late blight,P. infestans was recovered from 132 samples (60%) received from British Columbia (BC), Manitoba, New Brunswick, Prince Edward Island, and Quebec. From the 132 samples, 364 isolates were obtained and tested for their mating type and response to metalaxyl. Populations ofP. infestans within Canadian provinces were homogeneous for mating types, except within BC, where populations comprised both A1 and A2 mating types both within fields and sometimes within samples. The A2 mating type was found in all provinces where late blight was present. The A1 mating type was found only in Manitoba (1 isolate) and in BC (38 isolates). Unlike the old A1 isolates, those found in BC in 1997 were highly resistant to metalaxyl. These A1 isolates are even more resistant than A2 isolates. Based on assays with 10 ug.ml?1 of metalaxyl, 14% of all tested isolates were MS, 69.8% were MI and 16.2% were MR. In addition, all provinces contained MS, MI, and MR isolates. No specific mating type or metalaxyl sensitivity level were specific to tomato or potato.  相似文献   

10.
The persistence of fungicides on two commercial cultivars of potato was determined under field conditions at Punjab Agricultural University, Ludhiana, Punjab. Initial deposits of mancozeb on potato leaves were found to be 26.9 and 38.7 mg kg(-1), following application of ready mixture of fungicide metalaxyl 8% + mancozeb 64% (Ridomil MZ) at the rate of 1260 and 2520 g a.i. ha(-1), whereas metalaxyl residues were found to be 35.1 and 49.5 mg kg(-1), respectively. The residue level of mancozeb in potato leaves 15 days after application at single and double doze were 19.0 and 27.0 mg kg(-1) showing a loss of 29.6 and 30.3%, whereas the values for metalaxyl at single and double doze were 0.40 and 0.80 mg kg(-1) showing a loss of 98.9 and 98.4%, respectively. Residues of mancozeb and metalaxyl were not detected at 0.04 and 0.02 mg kg(-1) level in potato tubers at harvest (PHI = 53 days) at both the dosages, respectively. The persistence and dissipation of mancozeb with the application of Ridomil MZ followed similar trend as in Indofil M-45. The rate of fungicide dissipation increased with time after application in both the potato cultivars 'Kufri Chandramukhi' and 'Chipsona'. No significant difference was observed on initial deposit, persistence and dissipation of the two molecules between the two potato cultivars.  相似文献   

11.
Relationships between pathotypes and other markers such as mating types, metalaxyl resistance, Gpi-allozyme and random amplified polymorphic DNA (RAPD) patterns, were investigated among 33 isolates ofPhytophthora infestans obtained from both potato and tomato across Canada in 1997. Pathogenicity testings, based on virulence against potato differentials carrying single-resistance genes and the size of lesions on leaves, revealed higher pathogenic diversity in 1997 than in the few past years, with more pathotypes and more race-complex isolates. A higher pathogenic diversity was observed within A2 (US-8) than within A1 (US-11) isolates. There was no correlation between the level of resistance to metalaxyl of an isolate and its pathogenicity. Nevertheless, when grouped into metalaxyl-sensitive (MS), -intermediate (MI), and -resistant (MR) classes, both average pathotype complexity and average lesion size were lowest for MS group. RAPD data revealed a good distinction between A1 (US-11) and A2 (US-8) mating type groups, and between isolates from British Columbia and those from other provinces. The detection in the last few years of both A1 and A2 mating types in Canada and the occurrence in 1997 of some isolates sharing different characteristics of both of these two groups suggest that sexual reproduction may have occurred locally.  相似文献   

12.
Strains of Phytophthora megasperma insensitive to the fungicide metalaxyl showed limited cross-resistance to the structurally related fungicide cyprofuram and to metolachlor, a herbicide with antifungal properties. The three compounds each inhibited nucleic acid synthesis, but the wide variation in resistance factors and in the degree of nucleic acid inhibition at the concentrations inhibiting mycelial growth by 50% indicated that cyprofuram and metolachlor possess alternative mechanisms of toxicity. Studies with protoplasts suggested that cyprofuram has a direct effect on the plasma membrane which may be important against those resistant strains where nucleic acid synthesis is least affected. Metolachlor also was extremely effective in causing protoplast lysis. Sporangia production by P. palmivora was stimulated by low concentrations of cyprofuram, and germination was delayed. As with other ‘acylalanine-type’ fungicides, inhibition of nucleic acid synthesis is considered to be the main mode of action. Some degree of cross-resistance between cyprofuram and other acylalanines is likely to occur in the field but the dual mode of action of cyprofuram might delay its onset. The effect of increased sporogenesis on the development of resistance is more difficult to assess.  相似文献   

13.
The effect of combinations of night ventilation regimes and fungicide treatments on levels of downy mildew (Bremia lactucae) was investigated in a November-sown glasshouse lettuce crop. Environmental regimes were allocated in a randomized-block design to glasshouse compartments in which fungicide treatments were applied to sub-plots from which sub-sub-plots were harvested on each of four dates. The benefit of night ventilation was strikingly shown. It was almost as effective as the systemic fungicide metalaxyl which gave complete control of B. lactucae for 20 weeks after its incorporation in the peat blocks. A ‘heat-purging’ treatment increased the incidence of downy mildew, while other fungicidal regimes failed to control late infection. In the period close to cutting, when fungicide usage is not permitted, night ventilation may be the only effective means of controlling the disease.  相似文献   

14.
Tobacco black shank caused by Phytophthora parasitica is a devastating soil-borne disease of tobacco in China. Control of tobacco black shank relies on numerous fungicide applications. A new carboxylic acid amide (CAA) fungicide, mandipropamid, was examined for its effects on various asexual developmental stages of P. parasitica in vitro and in tobacco seedlings. Although mandipropamid did not affect discharge of zoospores from sporangia, it strongly inhibited mycelial growth (mean EC50 value of 0.0112 μg ml−1), sporangia production (mean EC50 value of 0.009 μg ml−1), germination of encysted zoospores (mean EC50 value of 0.014 μg ml−1), and germination of sporangia (mean EC50 value of 0.017 μg ml−1). For protective activity in tobacco seedlings, various applications of mandipropamid were superior in reducing black shank compared to that of metalaxyl and of azoxystrobin; while for curative activity assay, 100 μg ml−1 of mandipropamid exhibited the same efficacy as that of metalaxyl, and presented superior activity than that of azoxystrobin. In 2010 and 2011, 119 isolates of P. parasitica from Guizhou Province of China were characterized for the baseline sensitivity to mandipropamid by measuring mycelial growth. Values of effective concentrations for 50% mycelia growth inhibition varied from 0.0068 to 0.0285 μg ml−1 and averaged 0.013 (±0.0045) μg ml−1, with a unimodal distribution. This information will serve as a baseline for tracking future changes in sensitivities of P. parasitica populations to mandipropamid in China.  相似文献   

15.
Summary Potato late blight has appeared in epidemic proportions in Nepal since the mid 1990s and fungicides have been reported to be decreasingly effective in managing the disease.Phytophthora infestans isolates were collected from potato crops during 1999–2000 and analysis of 371 isolates for mating types and 270 isolates for metalaxyl sensitivity revealed the presence of both new and old populations. This is the first report on the presence of metalaxyl-resistant isolates in Nepal. The frequencies of A1 and A2 were 83 and 17%, respectively. Metalaxyl-resistant, intermediate and sensitive isolates were recorded as 10%, 12% and 78% respectively. Metalaxyl resistance was distributed in both mating types. Sites with a history of metalaxyl use had a significantly higher number of resistant and intermediate isolates ({ie337-1}, P<0.01) than sites where metalaxyl had not been used. This study confirms the changes in population structure ofP. infestans in Nepal.  相似文献   

16.
Abstract

In Japan, soybean is usually cultivated in fields that have been converted from rice paddies, and poor seedling establishment due to pre-emergence seedling damping-off is often observed during the rainy season. In this study, the factors that cause the damping-off in flooded soil were investigated under high soil moisture conditions in a greenhouse and in agricultural fields. In sterilized soil sampled from a soybean field, seedlings emerged well under 48-hr flooded conditions. In unsterilized soil, soybean seeds treated with the fungicide, mancozeb+metalaxyl exhibited much higher emergence rates even under 48-hr flooded conditions than the seeds treated with oxytetracycline +streptomycin, benomyl, or flutolanil. Pythium, Phytophthora, Mucorales, Trichoderma, Geotrichum-like microorganisms, and some fungi producing conidia in a false head, were isolated from decayed seedlings. Of the isolated microorganisms, oomycete microorganisms, Pythium helicoides, other Pythium sp., and Phytophthora sp. were pathogenic to soybeans under flooded conditions. As the length of the flooding period increased, pre-emergence seedling rot also increased. However, the pathogenic oomycetes rarely caused pre-emergence seedling rot under conditions without flooding. Furthermore, under flooded conditions, the damage caused by these pathogens was reduced by treating the seeds with mancozeb+metalaxyl. These results indicate that oomycete microorganisms are involved in pre-emergence seedling damping-off under flooded soil conditions.  相似文献   

17.
《Crop Protection》1988,7(5):314-318
Aqueous solutions of 1·0 or 10·0 g a.i/l of phosphorous acid (H3PO3) neutralized with KOH and applied as a foliar spray or soil drench inhibited the development of stem lesions on potted almond and cherry plants inoculated with Phytophthora cambivora and in most cases were effective as either 0·25 g a.i./l metalaxyl or 3·2 g a.i./l fosetyl-A1 drenches. Sprays or drenches of 10 g a.i. H3PO3/l were phytotoxic to potted almonds causing marginal leaf scorch, leaf drop and brown necrotic lesions on young shoots. Foliar sprays of 1 g a.i. H3PO3/l or drenches of 20 g a.i. H3PO3/l were not phytotoxic to 4-year-old Mahaleb cherry trees and restricted lesions caused by P. cambivora for up to 17 weeks after application. A 10% neutralized solution of H3PO3 injected directly into the trunk of cherry trees inhibited P. cambivora lesions for a similar period but the treatment was initially phytotoxic.  相似文献   

18.
Summary A total of 37 single-lesion isolates ofPhytophthora infestans were collected during 2000 from different potato growing regions in the central part of Serbia. They were paired in Al and A2 matings to determine their mating types. Of these 37 isolates, 28 were found to belong to the A2 mating type, eight to the Al type and one was found to be self-fertile (A1/A2). Using the in vitro mycelial radial growth method no metalaxyl resistantP. infestans isolate could be found. The rate of occurrence of intermediate isolates was not high, on the average 2.70%. All other isolates were sensitive to metalaxyl. There was no correlation between mating type and the intermediate metalaxyl resistance found.  相似文献   

19.
Summary Samples of potato foliage infected withPhytophthora infestans were collected from the main potato growing areas in Ireland over a three-year period starting in 1981 when metalaxyl-based fungicides were no longer commercially available. Using the floating disc method, 75% of the isolates tested were found to be resistant to metalaxyl in 1981, 21% in 1982 and only 6% in 1983. The reliability of the test method and the sampling procedure to detect low levels of resistance is discussed.  相似文献   

20.
A total of 93 single-lesion isolates of Phytophthora infestans were collected from late blight diseased potatoes grown in several locations in Poland, in the years 2002–2004. They were tested for mating type, virulence, aggressiveness and metalaxyl resistance. Sixty one percent of the isolates was of the A1 and 39% of the A2 mating type. Regarding virulence, complex races predominated. Most of the isolates were highly and moderately aggressive. Among isolates, tested together with 38 previously collected (1995–2001) ones, 14.5% was metalaxyl resistant, 3.5% intermediately resistant and 82.0% of the isolates was sensitive to metalaxyl. In addition, 14 isolates tested with three simple sequence repeat markers showed high genetic diversity. These data indicate that Polish population of P. infestans is diverse and aggressive, with potential for sexual recombination and spreading of fungicide insensitivity.  相似文献   

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