1、PATHOGEN RISK LIST(December 2005)PurposeInformation is provided about the risk of pathogens to develop resistance to fungicides under specific agronomic conditions.IntroductionBecause no scientific criteria are available to accurately determine the risk of a pathogen to develop resistance, our class
2、ification is based on experience and reported resistance claims over the last 40 years. Generally, the risk increases when a pathogen undergoes many and short disease cycles per season, the dispersal through spores over time and space is high, sexual recombination is mandatory in the disease cycle a
3、nd the competitive ability of resistant individual is at least as high as that of the wild type (in the absence of selection pressure). Furthermore, the risk is considered as high when resistance evolved already after few years of product use.Examples to illustrate pathogen riskIt is quite easy to d
4、etect single isolates of a pathogen with reduced sensitivity to a given fungicide but only their frequency over time and space will decide whether product performance will be affected significantly. Therefore, we consider the pathogen risk as medium to high only if resistance was reported in commerc
5、ial situations for more than one fungicide class.Wheat powdery mildew is considered as high risk pathogen because resistance evolved to six different chemical classes within 2 to 5 years, whereas wheat brown rust is a low risk pathogen because no resistance evolved to the major fungicide classes (DM
6、Is, QoIs, morpholines) used against this pathogen, even not after 25 year (DMIs). Eyespot in wheat bears a medium risk, resistance evolved to MBCs and prochloraz (DMIs) only after 10 to 15 years.An interesting case is Phytophthora infestans that developed resistance quite rapidly to the phenylamide
7、fungicides but not at all to dimethomorph, iprovalicarb, fluazinam, cymoxanil, azoxystrobin and fenamidone (QoI fungicides), cyazofamid (QiI fungicide), propamocarb, and organotins. Therefore, we re-classified P. infestans as high risk pathogen for the RNA1polymerase target only and as a medium risk
8、 pathogen for all other modes of action (see Table 1 and 2).Pathogen risk classesThe following plant pathogens (Table 1) from major world markets have evolved resistance to fungicides in a time span sufficiently short to be a serious threat to the commercial success of more than one fungicide class.
9、Table 1: Plant pathogens accepted as showing a high risk of development of resistance to fungicides (adapted from EPPO 2002, FRAC Monograph No. 3, Russell, 2003)Pathogen Crop DiseaseBotryotinia fuckeliana (Botrytiscinerea)various, especiallygrapevinegrey mouldErysiphe (=Blumeria) graminis wheat/barl
10、ey powdery mildewMycosphaerella fijiensis banana black sigatokaPenicillium spp. citrus, various post harvest rotPhytophthora infestans (RNApolymerase)potato/tomato late blightPlasmopara viticola grapevine downy mildewPseudoperonospora cubensisand related spp.cucurbits, various downy mildewsPyricular
11、ia spp. rice, turf rice blast, leaf spotSphaerotheca fuliginea andrelated spp.cucurbits, various powdery mildewsVenturia spp. apple, pear scabThe following pathogens (Table 2) are regarded as posing a much lower risk because resistance is not a major problem or has been slow to develop. In some case
12、s this due to the pattern of product use. Cases of specific isolates being classed as resistant may be known in some instances, but in commercial practice resistance has not created major disease control problems. The EPPO Guideline does not list these and decisions on baseline production must be ma
13、de on individual case reviews.2Table 2: Plant pathogens accepted as showing a medium risk of development of resistance to fungicidesPathogen Crop DiseaseBremia lactucae lettuce downy mildewCercospora spp. sugar beet, peanuts, various leaf spotsGibberella fujikuori* rice bakanaeMonilinia spp. various
14、 Monilia rotMycosphaerella graminicola(Septoria tritici)wheat leaf spotMycosphaerella musicola banana yellow sigatokaPeronospora spp. various downy mildewsPhytophthora infestans (targetoutside RNA polymerase)potato/tomato late blightPyrenophora teres barley net blotchRhynchosporium secalis barley le
15、af blotch/scaldSclerotinia spp. (especiallyhomoeocarpa, sclerotiorum)various (turf, oil seed rape) Sclerotinia diseases,dollar spotTapesia spp. wheat/barley eyespotUncinula (= Erysiphe) necator* grapevine powdery mildew* The EPPO Guideline lists these pathogens as high risk pathogens of which baseli
16、nesensitivity is normally requestedIn some cases the financial outlay in establishing baselines will not be justified by the small markets involved irrespective of their risk of resistance development. Typical pathogens and diseases are given in Table 3. Pathogens in this group are of local importan
17、ce, but in commercial market terms are considered as minor pathogens. Decisions on baseline production must be made on a case by case basis. For certain pathogens (e.g. Phytophthora infestans), resistance occurred only to one chemical class (phenylamides) but not to others and therefore, the pathoge
18、n is considered as low risk pathogen.Table 3: Plant pathogens with low risk of development of resistance to fungicides or of minor commercial importancePathogen Crop DiseaseAlternaria spp. various leaf spotsColletotrichum spp. various anthracnoseFusarium and related spp. various FusariosesHemileia v
19、astatrix coffee rustLeptosphaera(=Stagonospora) nodorumwheat leaf spotPhytophthora spp. (soil borne) various damping offPodosphaera leucotricha apple powdery mildewPuccinia and related rust spp. wheat/barley, various rustsPythium spp. various damping offRhizoctonia spp. various foot and root rotScle
20、rotium spp. various blightTilletia spp. cereals buntsUstilago spp. cereals smuts3When the pathogen risk is plotted against the inherent resistance risk of the fungicide class, the combined resistance risk for each pathogen/fungicide combination can be estimated (Figure 1).Figure 1: Combined resistan
21、ce risk diagram based on inherent fungicide risk and inherent pathogen risk (* only most important classes and groups mentioned) (according to FRAC Monograph No. 2, by K.J. Brent and D.W. Hollomon, 1998, * QoI fungicides have been moved from medium to high risk)FungicideClasses *FungicideRisk Combin
22、ed RiskbenzimidazolesdicarboximidesphenylamidesQoI fungicides *high = 3 3 6 9carboxamidesSBI fungicidesanilinopyrimidinesphenylpyrrolesphosphorothiolatesmedium = 2 2 4 6multi site fungicides(e.g.dithiocarbamatesCopper, Sulphur)MBI-R inhibitorsSAR inducerslow = 1 1 2 3Pathogen risk low = 1 medium = 2
23、 high = 3Pathogen groups *seed bornepathogens (e.g.Pyrenophora spp.Ustilago spp.)soil-bornepathogens (e.g.Phytophthoraspp .)rust fungiRhizoctonia spp.Tapesia spp.RhynchosporiumsecalisSeptoria triticiErysiphe graminisBotrytis cinereaPenicillium spp.MagnaporthegriseaVenturiainaequalisMycosphaerellafij
24、iensisPhytophthorainfestansThe pathogen risk should be estimated also in regard to the local intensity of disease development that is based on weather conditions, fertilization, irrigation, cultural practices and degree of resistance of cultivars. Therefore, we propose to modify the risk diagram in
25、the following manner (Figure 2). Detail can be found in the article written by KH Kuck, “Fungicide Resistance Management in a New Regulatory Environment”, in the Proceedings of the Reinhardsbrunn Symposium 2004 (Modern fungicides and antifungal agents, Dehne, Gisi, Kuck, Russell, eds., BCPC 2005).4F
26、igure 2: Combined resistance risk diagram based on inherent fungicide risk, inherent pathogen risk, and agronomic risk (* only most important classes and groups mentioned) (according to Kuck, 2005)FungicideClasses *FungicideRisk Combined RiskAgronomicRiskbenzimidazoles 6 12 18 high = 1dicarboximides
27、 high = 6 3 6 9 medium = 0.5phenylamides 1,5 3 4,5 low = 0.25QoI fungicidescarboxamides 4 8 12 high = 1SBI fungicides medium = 4 2 4 6 medium = 0.5anilinopyrimidines 1 2 3 low = 0.25phenylpyrrolesmulti site fungicides 1 2 3 high = 1(e.g.dithiocarbamates) low = 1 0,5 1 1,5 medium = 0.5MBI-R inhibitor
28、s 0,25 0,5 0,75 low = 0.25SAR inducersPathogen risk low = 1 medium = 2 high = 3seed borneUncinulanecatorGibberella Erysiphe graminisBotrytis cinereapathogens (e.g. fujikuori PlasmoparaPyrenophora sp. Tapesia sp. viticolaUstilago sp.) Rhynchosporium MagnaporthePatho g en grou p s * secalissoil-borne griseapathogens (e.g. Pyrenophora VenturiaPhytophthora sp.) teres inaequalisrust fungi Septoria tritici MycosphaerellaRhizoctonia sp. Sclerotinia sp. fijiensisFusarium sp. Monilinia sp. PhytophthoraCercospora sp.Phytophthorainfestans/othermodes of actioninfestans/RNApolymerase5
