US-8 and US-11 genotypes ofPhytophthora infestans from potato and tomato respond differently to commercial fungicides

Isolates ofPhytophthora infestans collected in Canada in 1997 from both potatoes and tomatoes, were tested on potato leaf discs for their response to an equal active ingredient concentration (10 μg a.i./mL) of the following commercial fungicides: Acrobat MZ (Dimethomorph and Mancozeb), Ridomil Gold (metalaxyl-m), Dithane (Mancozeb), Curzate (Cymoxanil), Bravo (Chlorothalonil), and Tattoo C (Propamocarb and Chlorothalonil). Relative percent leaf infection values, estimated on fungicide-treated vs fungicide-free leaf discs, were compared among isolates from the US-8 and US-11 genotypes isolated from the two host plants. Based on an equal concentration of each fungicide’s active ingredients, variations in relative percent leaf infection were recorded between US-8 and US-11 genotypes, and between potato and tomato isolates within each genotype. Bravo and Tattoo C used with similar active ingredients concentrations were the most inhibitory to all groups of isolates. Dithane and Ridomil Gold provided uniform low inhibition againstP. infestans when tested on potato leaf discs. The different behavior ofP. infestans isolates from potato vs tomato suggests that management of late blight in these two important crops must take such differences into consideration. In particular, the nature and concentration of the fungicides to be applied must take into account any information available about genotypes present on each crop.     

Fungicidal control ofPhytophthora erythroseptica: The cause of pink rot on potato

Two shade house and six field experiments were undertaken to evaluate fungicides and timing of application for the control of pink rot of potatoes caused byPhytophthora erythroseptica. Pink rot developed in up to 60% of tubers grown in artificially inoculated soil and 21% of the tubers in naturally infected soil. Ridomil (metalaxyl) and Ridomil Gold (mefenoxan) granules applied to the soil at planting completely or nearly completely controlled pink rot throughout the season in both pot and field experiments. Foliar applications of Ridomil Gold MZ (mefenoxan plus mancozeb) applied when tubers were around 20 mm diameter and another one or two sprays 12 to 28 days later also provided more than 80% control of pink rot in most experiments. Foliar applications of Shirlan (fluazanim) or Acrobat MZ (dimethomorph plus mancozeb) showed some activity against pink rot, but were significantly less effective than Ridomil Gold MZ. Foli-R-Fos 200 (phosphonic acid) or Dithane M45 (mancozeb) applied to the canopy showed little activity against pink rot in most experiments. Yield increases of between 6 and 17 tons ha^?1 resulted from the application of either Ridomil granules at planting or two to three Ridomil Gold MZ foliar sprays around “tuber set.”     

Efficacy of fosetyl-Al,propamocarb, dimethomorph,cymoxanil, metalaxyl and metalaxyl-M in Czech Pseudoperonospora cubensis populations during the years 2005 through 2010

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.     

Temporal sensitivity ofAlternaria solani to foliar fungicides

Alternaria solani Sorauer (Ellis) is a causal agent of early blight of potato (Solanum tuberosum L.). Sensitivity to chlorothalonil, triphenyl tin hydroxide (TPTH), and mancozeb was determined for field isolatesof A. solani in 1998 and 1999. Specifically, the relative sensitivity ofA. solani to foliar fungicides in field populations collected from several commercial fields was evaluated over the course of two growing seasons. Sensitivity to these foliar fungicides was determined with anin vitro spore-germination assay method. The fungicide concentration that inhibited conidial germination by 50% (EC₅₀) was estimated for each isolate. Sensitivity ofA. solani isolates to TPTH and mancozeb varied little during the growing season, possibly because there were few TPTH and mancozeb applications made to the fields studied. At several locations, however, repeated exposure ofA. solani populations to chlorothalonil resulted in considerable variability in sensitivity, frequently causing isolates to have decreased sensitivity to this fungicide at the end of the growing season. In five of seven fields, isolates of A.solani collected at the end of the season were significantly less sensitive to chlorothalonil than isolates collected at the beginning of the season.     

Deposition and redistribution of fungicides applied by air and chemigation for control of late blight in commercial potato fields

The fungicides metiram, mancozeb, metiram + triphenyltin hydroxide, propamocarb hydrochloride + chlorothalonil, dimethomorph + mancozeb, cymoxanil + mancozeb, and chlorothalonil were applied by aircraft and through center-pivot irrigation systems (chemigation) to replicated plots in commercial fields of ‘Russet Burbank’ potato. Fungicide deposition and redistribution were indirectly determined by inoculation of excised leaves withPhytophthora infestans and directly by chlorothalonil residue analysis from upper, middle, and lower crop canopies. The effectiveness of two surfactants added with fungicide and applied by aircraft, an increased water volume rate used by aircraft, and a reduced water volume used with chemigation was also determined. The addition of synthetic latex and siliconepolyether surfactants did not increase efficacy of metiram or mancozeb in controlling late blight when applied by aircraft. The protectant fungicides metiram, mancozeb, and chlorothalonil were not significantly different from dimethomorph + mancozeb, cymoxanil + mancozeb, and propamocarb hydrochloride + chlorothalonil in late blight control when applied by aircraft. However, cymoxanil + mancozeb had limited efficacy when applied by chemigation. Fungicide deposition through the canopy differed when air applications were made before or after canopy closure (row closure). Fungicides applied by aircraft prior to row closure protected the entire canopy; whereas, fungicide application after row closure initially protected the top and middle canopies, and subsequent applications and redistribution of the fungicides were needed for adequate protection throughout the canopy. The fungicides and fungicide mixtures tested were evenly deposited throughout the potato canopy with each chemigation application. Severity of late blight did not differ on leaves treated with mancozeb or chlorothalonil applied by aircraft at water volumes of 47 L/ha and 94 I/ha and then inoculated withP. infestans, nor did severity of late blight differ on inoculated leaves previously treated with chlorothalonil by chemigation at water volumes of 15,145 and 50, 571 L/ha.     

Potato fungicides interfere with entomopathogenic fungi impacting population dynamics of green peach aphid

Fungicides applied to potato can enhance green peach aphid,Myzus persicae (Sulzer), outbreaks by interference with entomopathogenic fungi. (Order Entomophthorales). Late season aphid numbers were highest in potatoes sprayed with metalaxyl + mancozeb, captafol, or mancozeb, and lowest in potatoes sprayed with benomyl, triphenyltin hydroxide, chlorothalonil, or copper hydroxide. In field-collected aphids,Pandora (= Ernyia) neoaphidis (Remaudière et Hennebert) andEntomophthora planchoniana Cornu (F. Entomophthtoraceae) were the predominant cause of mycoses, 66.7% and 22.3%, respectively.Conidiobolus obscurus (Hall and Dunn) Remaudièe and Keller (F. Ancylistaceae) accounted for 8.5% of mycoses. In the laboratory, fungicides were shown to have direct effects on these entomopathogens. Metalaxyl + mancozeb, mancozeb and captafol were strongly inhibitory of germination of conidia, copper hydroxide was intermediate, and chlorothalonil had little effect. Triphenyltin hydroxide, benomyl, metalaxyl + mancozeb, and mancozeb were strongly inhibitory of growth of mycelia, copper hydroxide was intermediate, and chlorothalonil and copper hydroxide had least effect. Benomyl was highly toxic to green peach aphid, copper hydroxide and chlorothalonil intermediate, and captafol, mancozeb, and metalaxyl + mancozeb least toxic. Possible interference of potato fungicides with aphid pathogens is now an important consideration because of the intensity of spraying required to protect the crop from infection by metalaxyl-resistant strains of the late blight pathogen,Phytophthora infestans (Mont.) de Bary. Minnesota potato growers reported high green peach pressure in both 1995 and 1996, years of intensive fungicide spraying. Concomitantly, there was a marked increased in the incidence of PLRV in seed lots entered for winter testing.     

Response of tubers of five potato cultivars to co-inoculation with US-1 and US-8 genotypes ofPhytophthora infestans

Summary The severity of late blight tuber rot in five potato cultivars (Green Mountain, Sebago, Dorita, AC Brador and Island Sunshine) resulting from inoculation with US-1/US-8 combinations of Canadian isolates ofPhytophthora infestans was evaluated. In addition, the potential for mixed (A1∶A2) inoculations to result in oospore formation was examined. In studies conducted in 1996 and 1997, cv. Dorita (and Island Sunshine in 1997) developed the least amount of surface or internal necrosis relative to the other cultivars following co-inoculation with US-1 and US-8 isolates ofP. infestans. Differences also were revealed among isolate combinations used for inoculation. The combination of a US-1 isolate from Prince Edward Island with a US-8 isolate from New Brunswick consistently produced the least amount of necrosis in tubers of the various cultivars. There was no evidence of oospore production in any of the tubers examined. AAFC Contribution No. 919     

Efficacy over time of cymoxanil mixtures in controlling late blight in potatoes incited by a phenylamide-resistant isolate of Phytophthora infestans

Field-grown potatoes (cv. Alpha) were sprayed with fungicides at the commercially recommended rates 0–15 days before being inoculated with a phenylamide-resistant isolate of Phytophthora infestans (Mont.) DeBary. Numbers of lesions, or disease severity, in fungicide-treated versus fungicide-free plants were used to calculate the percentage control efficacy of fungicides over time. Efficacy over time fitted a declining logistic model in 26 out of 31 cases. Non-transformed data showed a significantly longer duration of > 90% efficacy of the cymoxanil mixtures Mancur (mancozeb + cymoxanil, 4 + 1), Pulsan (mancozeb + oxadixyl + cymoxanil, 7 + 1 + 0 · 4) and Sandocur-M (mancozeb + oxadixyl + cymoxanil, 7+1+2) (9–11 days) compared with SAN-518 (mancozeb + oxadixyl, 7+1), Ridomil-MZ (mancozeb + metalaxyl, 1 + 7 · 5), mancozeb or Curzate (4–6 days). Predicted T₅₀ values (number of days with >50% efficacy) were significantly larger for Pulsan and Sandocur-M (16 days) than for Ridomil-MZ (11 days), SAN-518 (10 days), mancozeb (9 · 5 days) and Curzate (7 · 5 days). Numeric integration of the area under the predicted control efficacy curves gave significantly larger values for Pulsan and Sandocur-M compared with the other fungicides except Mancur. Linear regression of logit disease control values over time resulted in the smallest slope for Sandocur-M. Analysis of variance showed no significant interaction between fungicide and cumulative rain. We predict that Pulsan and Sandocur-M may effectively control phenylamide-resistant Phytophthora infestans in the field at 14-day spray intervals, and Mancur at 10-day intervals.     

不同杀菌剂防治马铃薯晚疫病田间药效试验

试验研究了7种杀菌剂对马铃薯晚疫病的防治作用。结果表明:68.75%银法利悬浮剂1125 g/hm2、53%金雷多米尔水分散颗粒剂1500g/hm2、60%氟吗啉.代森锰锌可湿性粉剂1225g/hm2、72%克露可湿性粉剂2000g/hm2对马铃薯晚疫病防效分别为88.38%、86.15%、84.55%、81.68%,是防治马铃薯晚疫病较理想的药剂,且增产效果明显,建议在生产上交替使用。     

Persistence of metalaxyl and mancozeb on potato leaves and their residues in tubers

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.     

Comparison of deposition patterns in two programs for applying protectant fungicides to potato stems and leaves for the control of late blight (Phytophthora infestans)

Fungicides are applied by air, chemigation, and ground in the Columbia Basin of Oregon and Washington. These methods of fungicide application differ in deposition of fungicide to the canopy and cost. This study compared the alternate use of air and chemigation application of fungicides (AIRCHEM) with chemigation alone (CHEM), by either measuring chlorothalonil or manganese (mancozeb) amounts in three canopy levels (upper, middle, lower), both on leaflets and stems, after multiple fungicide applications on a 7-day schedule. Greater amounts of chlorothalonil or mancozeb were usually found on the leaflets in the upper and middle canopy locations from AIRCHEM compared to CHEM, the day of fungicide application and 7 days later. Deposition of fungicides on stems generally follow the same pattern as leaflets, but the amount deposited and maintained on stems was significantly less than leaflets. Mancozeb deposition in the three canopy levels followed the same pattern as was found for chlorothalonil. The greater the amounts of chlorothalonil on leaflets and stems resulted in better disease reduction during inoculation assays. Reduced fungicide amounts on stems compared to leaflets may be the reason for increased stems infections in recent years by more aggressive strains of late blight. This is the first report quantifying chlorothalonil or mancozeb amounts on potato stems and the first to report amounts of mancozeb on potato foliage after fungicide application.     

Impact of seed potatoes infected withPhytophthora infestans (US-1 or US-8 genotypes) on crop growth and disease risk

As the surface area with late blight symptoms of seed tubers increased, the incidence of plant emergence decreased. This relationship was more dramatic with the US-8 genotype than the US-1 genotype ofhytophthora infestans, causal agent of late blight. However, when seed tubers were inoculated with both US-1 and US-8 isolates, the plant growth responses were generally intermediate to those obtained with the two genotypes alone. More resistant cultivars (eg. Dorita, Island Sunshine, and Sebago) had greater plant emergence and less seed rot than more susceptible cultivars (eg. Green Mountain and Shepody) but the response differences between resistant and susceptible cultivars was less clear with US-8 as most cultivars had 100% seed rot. Seed handling treatments affected crop growth and disease risk; as the inoculum levels and in some cases, the pre-planting storage period increased, plant emergence decreased generally due to greater seed rot incidences. Of the one registered seed treatment fungicide and several non-registered and/or experimental fungicides tested, only two significantly improved plant emergence. During three years of study, “diseased” seed treatments generally led to seed rot except in 1996 when one plant in one experimental plot of infected seed had subsequent spread of the disease to the foliage. Furthermore, within one week, a field epidemic developed outwardly from the single infected plant due to the occurrence of favourable weather conditions. Further research opportunities are discussed relative to the impact of infected seed on crop growth and disease risk     

Relationships between pathotypes and RAPDs, Gpi-allozyme patterns, mating types, and resistance to metalaxyl ofPhytophthora infestans in Canada in 1997

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.     

Novel genotypes ofPhytophthora infestans in Canada during 1994 and 1995

Populations ofPhytophthora infestans, causing late blight of potato, changed significantly in Canada in the mid-1990s. The US-1 genotype (A1, metalaxylsensitive [MS]) was displaced by novel genotypes (mainly US-8) in much of the country in 1994 and 1995. Many of the new genotypes were insensitive to metalaxyl and were of the A2 mating type, although metalaxyl-insensitive (MI) Al isolates of the gll (or US-11) genotype were found in British Columbia. A total of 14 unique multilocus genotypes were described over the two years of the study based on mating type (Al or A2), metalaxyl sensitivity (MS or MI), allozyme banding patterns (Gpi andPep), and random amplified polymorphic DNA (RAPD) markers. Six of these genotypes could be distinguished by allozyme banding patterns at theGpi locus alone; RAPD analysis revealed additional variation within allozyme groupings and defined additional genotypes. Among 82 isolates collected from various Canadian provinces in 1994, US-1 and US-8 constituted 30% and 49% of isolates, respectively; other genotypes occurred in minor frequency. Among 50 isolates collected in 1995, US-1 and US-8 constituted 10% and 74%, respectively. Isolates of gll (US-11) were found in British Columbia in 1995. Diversity of genotypes was greater in 1994 (11 genotypes) than in 1995 (six genotypes). We hypothesize that sexual reproduction may have been responsible for generating some of the genetic variability inP. infestans populations, during a time period in which A2 isolates first migrated into many provinces in Canada.     

Using chemical and biological treatments to reduce the potential of potato leak caused byPythium aphanidermatum in Tunisia

Summary The effect of fungicides and the antagonistic fungusTrichoderma harzianum (Th) on the potato leak pathogenPythium aphanidermatum (Pa) was investigated in vitro. Rot was reduced by 73% to 89% when tubers inoculated withPa were treated by immersion in solutions (0.5% w/v) of the fungicides Ridomil MZ58. Dithane M45. Manebe 80 and Tachigaren 360. Complete protection was achieved by dusting inoculated tubers with Ridomil MZ58 diluted in kaolin at a final concentration of 0.1% (w/w). The biological treatments of dipping inoculated tubers in a conidial water suspension ofTh at 10⁸ conidia/ml or of dusting with a mixture of a barley culture ofTh and kaolin to a final concentration of 2×10⁹ conidia/g were as effective as the chemical treatments. Control was still effective when inoculated tubers were treated with Ridomil MZ58. Tachigaren 360 or the conidial suspension ofTh after 24h incubation at 25°C.     

Application of fungicides to reduce yield loss in anthracnose-infected lupins

A range of fungicides were evaluated for control of anthracnose (Colletotrichum lupini) in lupin. Glasshouse investigation identified fungicides that reduced disease severity with varying degrees of efficacy. When applied 1 d prior to infection, azoxystrobin, chlorothalonil, mancozeb and copper oxychloride fungicides were highly effective. Systemic fungicides such as tebuconazole, benomyl and carbendazim were less effective. Application timing was important; fungicides such as chlorothalonil and mancozeb were less effective when applied 5 d prior to infection compared with 1 d prior. Application after infection was ineffective for all fungicides. In field experiments application of azoxystrobin, mancozeb or chlorothalonil during flowering and podding reduced incidence of anthracnose infection on pods. Yield responses occurred in moderately susceptible, moderately resistant or resistant cultivars. Seed infection was reduced but not eradicated. Application of foliar fungicides for anthracnose control is potentially a viable management option for lupin production in high anthracnose risk areas of Western Australia.     

Differences in tuber rot development for North American clones ofPhytophthora infestans

The relative aggressiveness ofPhytophthora infestons clones in potato tubers was compared in three trials using 7 to 24 isolates of 2 to 4 clones. Visible rot developed slowly at 13C with isolates of the US-1 genotype, the only significant clone found in North America prior to 1979, but substantially faster with most isolates of the newer clonal genotypes US-6, US-7 and US-8. Certain US-7 isolates were similar to US-1, and US-6 isolates also had a broad range of aggressiveness. Secondary infection byFusarium sp. increased rot development in many instances, but this effect was not clone-related. Differences in rot development may affect potato storage or late blight disease transmission.     

Evaluation of fungicides to control circular leaf spot of persimmon caused by Mycosphaerella nawae

The efficacy of ten fungicides against Mycosphaerella nawae, the causal agent of circular leaf spot (CLS) of persimmon, was evaluated in vitro and in field experiments. Field trials were conducted in 2009 and 2010 to investigate the comparative efficacy of the fungicides alone or combined using alternating sequences in spray programmes based on two, three or four applications. Disease incidence was assessed by estimating the percentage of affected leaves, which included leaves showing at least one necrotic spot and defoliation. Fenpropimorph, pyraclostrobin, tebuconazole and thiophanate-methyl were the most effective fungicides in inhibiting mycelial growth of M. nawae isolates (EC₅₀ < 2 ppm). In field experiments, the most effective fungicides using two spray applications were captan, chlorothalonil, mancozeb and pyraclostrobin which significantly reduced disease incidence compared with untreated plots. Regarding the number of spray applications, two applications of captan and mancozeb were less efficient than three to control the disease. However, the percentage of affected leaves provided by three applications of captan and mancozeb alone or combined with pyraclostrobin using alternating sequences in spray programmes, was not significantly different from that provided by four applications. Experimental results demonstrated that spray programmes based on three applications of these fungicides could effectively control CLS of persimmon. The advantages of spray programmes based on alternated use of strobilurins and protective fungicides are discussed.     

6种杀菌剂对马铃薯晚疫病菌的室内毒力测定

采用菌落直径法测定了金雷多米尔、杀毒矾、克露、克霜氰、大生M-45和进富6种杀菌剂对马铃薯晚疫病菌的毒力。结果表明供试的6种杀菌剂对马铃薯晚疫病菌丝生长都有较好的抑制作用,克露对晚疫病菌毒力最强,其EC50值为0.16μg·mL-1,毒力最差的是大生,其EC50值为2.89μg·mL-1,其余4种药剂按毒力大小依次为克霜氰、金雷多米尔、进富和杀毒矾,其EC50值分别为0.24μg.mL-1、0.28μg·mL-1、0.43μg·mL-1和1.17μg·mL-1。根据室内毒力测定结果及药剂特性,供试的6种杀菌剂在生产上可视病害的发生情况交替使用,以避免或延缓抗药性的产生。     

Characterization ofPhytophthora infestans from Maine during 1999 and 2000

A total of 77 isolates ofPhytophthora infestans was collected in 1999 and 93 isolates were collected in 2000 from growers’ fields, home gardens, and research plots in Maine. Genotype diversity based onglucose-6-phosphate isomerase (Gpi) allozyme analysis was greater in the collections from 2000, with six genotypes identified vs two genotypes identified in 1999. The US-8 (Gpi 100/111/122) genotype constituted 88% of the isolates collected in 1999 and 75% of those collected in 2000. The US-14 (Gpi 100/122) genotype constituted 12% and 7% of the isolates collected in 1999 and 2000, respectively. Three newGpi genotypes constituted 7% of the isolates collected from potato in northern Maine in 2000. A new genotype (A1 mating type,Gpi 100/100) that was aggressive on both tomato and potato was identified from home gardens in western Maine and constituted 11% of the isolates collected in 2000. A1, A2, and A1A2 mating types as well as self-fertile isolates were collected in both years. Self-fertility in artificial culture appeared to be relatively common in field isolatesof P. infestans. Potential origins of the new genotypes are discussed.