Combinations of Fungicides with Phylloplane Yeasts for Improved Control of Botrytis cinerea on Geranium Seedlings

ABSTRACT Control of Botrytis cinerea on geranium seedlings was evaluated in treatments with phylloplane yeasts in combination with 10 fungicides used to manage Botrytis blight of ornamental plants. Rhodotorula glutinis PM4 significantly reduced the development of lesions caused by B. cinerea on geranium cotyledons; however, yeast biocontrol efficacy was highly variable between trials. Treatment with the yeast in combination with azoxystrobin or trifloxystrobin at one tenth the labeled rate (7.5 mug a.i. ml(-1)) or the full labeled rate (7.5 mug a.i. ml(-1)) reduced lesion development, compared to treatment with the yeast or the fungicide alone. Vinclozolin at half the labeled rate or the full labeled rate (250 or 500 mug a.i. ml(-1)), in combination with R. glutinis PM4, significantly reduced the development of lesions caused by an isolate of B. cinerea resistant to vinclozolin. Copper hydroxide and iprodione at one-tenth the labeled rates, with or without yeast, were highly effective in limiting lesion development. Mancozeb did not increase the biocontrol efficacy of the yeast, and thiophanate-methyl negatively affected the yeast efficacy. Improved disease control was observed in treatments with vinclozolin at the labeled rate and R. glutinis PM4 at cell densities of 5 x 10(5) and 1 x 10(6) cells ml(-1), but not 1 x 10(5) cells ml(-1), on seedlings co-inoculated with B. cinerea in a suspension containing 1 x 10(5) conidia ml(-1). Disease control improved in treatments with combinations of vinclozolin and eight other isolates of R. glutinis, two isolates of R. graminis, and two isolates of R. mucilaginosa. Biocontrol was not observed in treatments with two isolates of R. minuta. The combination of yeast and vinclozolin significantly reduced the germination of conidia of B. cinerea and the growth of R. glutinis PM4 in vitro. All combinations of R. glutinis PM4 with azoxystrobin, trifloxystrobin, or vinclozolin provided highly effective and consistent disease control not observed in treatments with the fungicides alone or the yeast alone.     

The use of Trichoderma species to control strawberry fruit rots

The effect of temperature on the growth and antagonistic properties of Trichoderma species against Botrytis cinerea and Mucor mucedo (strawberry fruit pathogens) was studied. Five strongly antagonistic isolates were further used in field experiments. The incidence of pre-harvest rots caused by B. cinerea and the rate of post-harvest spoilage were similarly reduced when strawberry flowers were sprayed either with the fungicide dichlofluanid or with spores of selected Trichoderma isolates.     

Evaluation of Microbial Antagonists for Biological Control of Botrytis cinerea Stem Infection in Cucumber and Tomato

Of fifteen isolates of yeasts, filamentous fungi and bacteria and a commercial product, tested in a bioassay with stem segments, eleven isolates consistently reduced incidence of disease and sporulation of Botrytis cinerea Pers; Fr in tomato and seven isolates in cucumber. Several isolates reduced disease by more than 75% in all experiments. Six antagonists that performed well in the bioassays and that were fairly easy to produce in vitro, were selected for further testing in two glasshouse experiments with cucumbers. After application of spores of B. cinerea and the antagonists or the fungicide tolylfluanid to pruning wounds, disease incidence was reduced by 50–100% by all antagonists in both experiments and only in one experiment by tolylfluanid.For Trichoderma harzianum T39, Aureobasidium pullulans and Cryptococcus albidus, biological control efficacy in bioassays with cucumber stem segments was not strongly influenced by temperatures in the range between 18 and 30°C, but at 24°C the efficacy of the three antagonists strongly decreased at relative humidities of 90% and 80% (vapour pressure deficits 0.299 and 0.598kPa, respectively) compared to 100.     

The Influence of Fungicide Sprays on Infection Of Apple cv. Bramley's Seedling By Nectria galligena

In 1990, a long-term trial was initiated by planting young apple trees, cv. Bramley's Seedling, inoculated, at single sites in the leader shoots, with Nectria galligena. The effect of spring–summer and autumn fungicide spray programmes, applied during 1991–1993, on the development of new cankers was assessed up to May 1994. Spring–summer fungicide programmes, applied as for the control of apple scab, reduced numbers of new cankers by between 65% and 76% compared with the untreated control. Sterol demethylation inhibiting fungicides (hexaconazole, myclobutanil, penconazole) had a similar effect on canker to dithianon. Autumn application of copper oxychloride at 5% and 50% leaf-fall further reduced numbers of new cankers. The combination of a spring–summer benzimidazole (carbendazim or thiophanate-methyl) with a scab fungicide (dithianon) and autumn copper oxychloride did not improve canker control compared with applying copper oxychloride after spring–summer myclobutanil+mancozeb. The percentage of fruit which developed rots in long-term storage was decreased by spring–summer benzimidazole application, but not by other fungicide programmes even those which achieved similar levels of canker control.     

Characterization of Glomerella cingulata isolates from almond fruit using VCG,molecular, fungicide sensitivity and pathogenicity tests 1

Almond anthracnose caused by Glomerella cingulata is a major disease of this crop in Israel. The pathogen infects young fruit resulting in fruit rot. Leaf wilting and shoot dieback accompany fruit rot, even though the pathogen cannot be isolated from leaves or twigs. Isolates of G. cingulata from diseased almond fruit were compared using vegetative compatibility grouping (VCG), molecular methods, fungicide sensitivity and pathogenicity assays in order to determine the genetic diversity and host specificity among different populations. Polymerase chain reaction amplification of genomic DNA, using four primers produced uniform banding patterns for all the almond isolates from different geographic locations in Israel. HaeIII digestion patterns of A + T-rich DNA, and Southern hybridization of the repetitive nuclear DNA element (GcpR1) to PstI-digested genomic DNA of almond isolates also revealed no polymorphism. Chlorate-resistant nitrate-nonutilizing (nit) mutants were generated and used in heterokaryon tests. Complementary heterokaryons formed between the mutants of different isolates indicated a single VCG. Isolates of G. cingulata from almond had optimal growth temperatures of 20–22°C as opposed to 26–28°C for avocado isolates. In addition, almond isolates of G. cingulata are insensitive to benzimidazole fungicides in contrast to sensitivity of isolates from avocado. In artificial inoculations, almond isolates infected almond, avocado, apple, mango and nectarine fruit at a slower rate than G. cingulata isolates from avocado, apple and mango. Only the anamorph Colletotrichum gloeosporioides has been detected on almond in Israel, whereas isolates of G. cingulata from other hosts produce ascocarps.     

Resistance of postharvest biocontrol yeasts to oxidative stress: a possible new mechanism of action

ABSTRACT We detected the generation of the reactive oxygen species (ROS) superoxide anion ( O.(-) (2)) and hydrogen peroxide (H(2)O(2)) in apple wounds 2 immediately after wounding, and assessed the relationships between (i) timely colonization of apple wounds by biocontrol yeasts, (ii) resistance of these microorganisms to oxidative stress caused by ROS, and (iii) their antagonism against postharvest wound pathogens. We analyzed a model system consisting of two yeasts with higher (Cryptococcus laurentii LS-28) or lower (Rhodotorula glutinis LS-11) antagonistic activity against the postharvest pathogens Botrytis cinerea and Penicillium expansum. LS-28 exhibited faster and greater colonization of wounds than LS-11. In contrast to LS-28, the number of LS-11 cells dropped 1 and 2 h after application, and then increased only later. In vitro, LS-28 was more resistant to ROS-generated oxidative stress. The combined application of biocontrol yeasts and ROS-deactivating enzymes in apple wounds prevented the decrease in number of LS-11 cells mentioned above, and enhanced colonization and antagonistic activity of both biocontrol yeasts against B. cinerea and P. expansum. Polar lipids of LS-11 contained the more unsaturated and oxidizable alpha-linolenic acid, which was absent in LS-28. Resistance to oxidative stress could be a key mechanism of biocontrol yeasts antagonism against postharvest wound pathogens.     

Characterization of Colletotrichum acutatum Isolates Causing Anthracnose of Almond and Peach in California

ABSTRACT The causal organism responsible for the recent outbreak of almond and peach anthracnose in California was identified and characterized as Colletotrichum acutatum. Isolates of C. acutatum from almond were found to be similar to California strawberry isolates and South Carolina peach and apple isolates of C. acutatum based on conidial morphology, temperature relationships, fungicide sensitivity, and polymerase chain reaction (PCR) methods using DNA species-specific primers. On almond, blossoms and immature or mature fruit were affected by the disease, causing direct losses of crop. On peach, the disease was observed only on mature fruit. Pathogenicity of almond and peach isolates of C. acutatum was demonstrated on wound- and nonwound-inoculated almond or peach fruit by fulfilling Koch's postulates. Conidial morphology of isolates was variable, depending on the medium or substrate used to culture the isolates. Isolates of C. acutatum from strawberry, almond, and peach were grouped together based on a similar response to temperature, with an optimal growth rate at 25 degrees C (generally less than 10 mm/day), whereas isolates of C. gloeosporioides from citrus and papaya had an optimal growth rate at 30 degrees C (generally greater than 10 mm/day). In fungicide disk assays, isolates of C. acutatum from strawberry, peach, and apple, as well as almond and peach isolates from California, were less sensitive to benomyl at 300, 600, or 1,200 mug/ml. In contrast, C. gloeosporioides isolates from citrus and papaya were very sensitive to benomyl at all concentrations evaluated. All isolates of both species were sensitive to captan (300, 600, or 1,200 mug/ml). Oligonucleotide primers were synthesized for C. acutatum, C. fragariae, or C. gloeosporioides using published DNA sequences from the internal transcribed spacer 1 region of ribosomal DNA. Thirty-two Colletotrichum isolates from almond fruit produced DNA products with a C. acutatum primer (CaInt-2) that matched products and approximate molecular weight of known C. acutatum isolates. No PCR products were produced with primers for C. gloeosporioides or C. fragariae. Isolates from citrus and papaya produced DNA products only with primers from C. gloeosporioides or C. fragariae. Thus, worldwide, anthracnose of almonds may be caused by either C. gloeosporioides, as previously reported, or by C. acutatum, as indicated in this study.     

Yeasts as antagonists against fireblight

Yeasts are potential antagonists of microorganisms in the phyllosphere. Due to their osmotolerance, they should also be able to colonize apple flowers. In field experiments, we applied yeast agents against fireblight at two different sites in the southern part of Germany. They showed efficiencies 0–20% below Plantomycin (streptomycin). Co-culture experiments in liquid basal media with synthetic nectar resulted in suppression of Erwinia amylovora by yeast. This effect could not be confirmed with population studies of yeasts and E. amylovora in flower clusters. Field and laboratory experiments indicated that yeasts have antagonistic properties against fireblight but further research is needed to investigate this potential.     

Alternative disease control agents induce resistance to blue mold in harvested 'red delicious' apple fruit

ABSTRACT Alternative control agents, including UV-type C (254 nm) irradiation, yeasts antagonistic to fungal growth, chitosan and harpin, were evaluated for their ability to induce resistance in cv. Red Delicious apple fruit against postharvest blue mold caused by Penicillium expansum. Freshly harvested and controlled atmosphere (CA)-stored fruit were treated with these agents at different doses and concentrations or with paired combinations of the agents. Treated fruit were inoculated with P. expansum 24, 48, or 96 h following treatment, and stored at 24 degrees C in the dark. The fruit were evaluated for development of disease every 2 days for 14 days by measuring the diameter of lesions that formed. The area under the disease progress curve (AUDPC) was calculated and analyzed statistically. All treatments were effective in reducing the AUDPC; UV-C was most effective, followed by harpin, chitosan, and the yeasts, respectively. Regardless of treatment, fresh fruit were more responsive to treatments than CA-stored fruit. There was a clear time-dependent response of the fruit to the treatments, in which treatments applied 96 h before inoculation provided the best results. In a few situations, the combinations of agents did provide an additive effect, but no synergistic effects were detected. Moreover, disease severity in fruit treated by any combination was markedly better than that in the controls. Although the combinations of treatments was overall less effective than the single treatments, they did provide significant reductions of the progress of disease in comparison with the controls. Because the fungus did not come into contact with any of the control agents, this study showed conclusively that the agents studied were able to induce resistance in the fruit rather than merely inhibit the pathogen directly. It also showed, for the first time, that harpin is able to induce resistance in harvested apple fruit. The use of these control agents may minimize the costs of control strategies and reduce the risks associated with the excessive use of fungicides in harvested apple fruit.     

Interaction of Four Antagonistic Fungi with Botrytis aclada in Dead Onion Leaves: A Comparative Microscopic and Ultrastructural Study

ABSTRACT The colonization of dead onion leaves by Botrytis aclada and the fungal antagonists Aureobasidium pullulans, Chaetomium globosum, Glio-cladium catenulatum, and Ulocladium atrum and the interactions between B. aclada and each of the four antagonists were studied at the microscopic and ultrastructural level. This approach was used in an attempt to understand the colonization pattern of these fungi and the nature of the biocontrol activity of the antagonists that have shown a potential to suppress spore production of Botrytis spp. on necrotic plant tissues. When applied alone, B. aclada and U. atrum were found throughout the leaf tissues in high densities after an incubation period of 6 days at 18 degrees C in a moist chamber. C. globosum and G. catenulatum colonized only the outer portions of the leaf, whereas A. pullulans appeared to be concentrated in the leaf stomata. When pathogen and antagonists were applied together, ultrastructural observations revealed that cells of B. aclada were plasmolyzed in the presence of G. catenulatum, suggesting a reaction to antifungal molecules. Antibiosis also seemed to be involved, albeit to a lesser extent, in the antagonistic interactions between B. aclada and A. pullulans or C. globosum. No evidence of direct parasitism was recorded. On the other hand, U. atrum appeared to completely exclude B. aclada from dead onion tissues when both fungi competed for the substrate. Ultrastructural observations of the in vitro interaction between the two fungi did not reveal parasitism or antibiosis by either fungus. Based on previous records of its biocontrol potential and observations of its colonizing properties, it appears that U. atrum can compete for and utilize necrotic tissues rapidly and extensively, thus, excluding competitors without any other antagonistic action.     

防治苹果轮纹烂果病药剂筛选及用药技术

经过两年室内药效测定 ,初步建立起部分杀菌剂对苹果轮纹烂果病菌丝抑制作用的毒力档案 ,选出防效较高的几种单剂 ,并通过两年田间用药技术研究 ,明确果实生长前期 ,喷洒多菌灵、苯菌灵 ,中后期波尔多液与多菌灵、苯菌灵、福星等加三乙膦酸铝交替使用 ,对防治苹果轮纹烂果病有良好防治效果。同时探讨了只在果实潜伏侵染病菌开始活化扩展期喷药 ,对防治苹果轮纹烂果病的可能性     

Cross-infection of subtropical and temperate fruits byColletotrichumspecies from various hosts

Forty-two isolates ofColletotrichum gloeosporioidesfrom almond, apple, avocado, mango, pecan, and eight isolates ofC. acutatumfrom apple, peach and pecan were compared by molecular analyses and a pathogenicity assay in order to determine genetic variability and host specificity. Polymerase chain reaction (PCR) amplification of genomic DNA using four different primers andHaeIII digestion patterns of genomic DNA (A+T-rich DNA) grouped theC. acutatumisolates separately from theC. gloeosporioidesisolates. Based on arbitrarily primed PCR (ap-PCR), intraspecies similarity among the isolates ofC. acutatumandC. gloeosporioidesranged from 78 to 93% and from 0 to 38%, respectively. Similarity between the isolates ofC. acutatumandC. gloeosporioidesranged from 0 to 26.5%. A+T-rich DNA grouped theC. acutatumisolates separately from those ofC. gloeosporioides, corresponding to ap-PCR analyses. Artificial inoculations with nine representative isolates on almond, apple, avocado, mango and nectarine fruit showed a variation in levels of infection. TheC. gloeosporioidesisolates from almond grew more slowly, causing significantly smaller lesions on all inoculated fruit than the other isolates. TheC. acutatumisolates from apple and peach caused similar levels of infection on all fruit, but differed significantly from theC. gloeosporioidesisolate from apple. Variation in lesion size was also observed with isolates ofC. gloeosporioidesfrom apple, avocado and mango for most fruit inoculations.     

Factors affecting build-up of fungicide resistance in powdery mildew in spring barley

In replicate-plot field experiments done in the UK, at one site in Avon for 3 years and another in Warwickshire for 2 years, application of ethirimol or triadimenol sprays or seed treatments was followed by decreases in sensitivity of mildew samples to the particular fungicide applied. Application of ethirimol-triadimenol or tridemorph-triadimenol mixtures caused smaller or no decreases in sensitivity. Differences between isolates in responses to ethirimol and to triadimenol treatment were usually negatively correlated. Early-season inoculum differed in fungicide sensitivity between sites. At one site sensitivity shifted markedly from one season to another. No clear interactions between cultivar, mildew pathotype and shifts in fungicide response could be discerned. There were no major differences in resistance build-up between seed or spray treatments.     

Effect of the Biocontrol Yeast Rhodotorula glutinis Strain LS11 on Patulin Accumulation in Stored Apples

ABSTRACT Contamination of apples (Malus domestica) and derived juices with fungicide residues and patulin produced by Penicillium expansum are major issues of food safety. Biocontrol agents represent an alternative or supplement to chemicals for disease control. Our data show that these microbes could also contribute to actively decreasing patulin accumulation in apples. Three biocontrol agents, Rhodotorula glutinis LS11, Cryptococcus laurentii LS28, and Aureobasidium pullulans LS30, were examined for their in vitro growth in the presence of patulin and for their capability to decrease mycotoxin recovery from the medium. Strain LS11 yielded the highest growth rates and the greatest decrease of toxin recoveries. Further, it caused the appearance of two major spots on thin-layer chromatography (TLC) plates, suggesting possible metabolization of the mycotoxin. In vivo, i.e., in the low percentage of LS11-pretreated apples infected by P. expansum, patulin accumulation was significantly lower than in nontreated infected fruits. Yeast cells survived and increased in infected apples and, in a model system emulating decaying apple, resulted in accelerated breakdown of patulin and the production of the same TLC spots as those detected in vitro. These data suggest that biocontrol yeast cells surviving in decaying apples could metabolize patulin and/or negatively affect its accumulation or synthesis. To our knowledge, this is the first report describing the effect of a biocontrol agent on patulin accumulation in vivo.     

有机硅助剂在苹果炭疽叶枯病化学防控中的减药增效作用评价

有机硅助剂具有低毒、易降解的特性,可提高农药的药液展布性和渗透性。本研究分别采用室内离体叶片法和田间试验评价了2种有机硅助剂对吡唑醚菌酯和代森锰锌防治苹果炭疽叶枯病的减药增效作用。室内离体试验结果表明,杀菌剂浓度减半的处理以及模拟雨水冲刷处理均导致吡唑醚菌酯和代森锰锌的防效显著下降;而添加了有机硅助剂后,2种处理的防效显著提高,并且恢复到与正常施药量相同的水平。田间试验结果表明,正常情况下杀菌剂浓度减半后防效显著下降;而施用有机硅助剂后,浓度减半的吡唑醚菌酯和代森锰锌的防效显著高于不施用有机硅的处理。本研究结果表明,施用有机硅助剂可以在减少化学农药实际用量的情况下,保持较高的防效,这对于化学农药的减施增效具有重要意义。     

Influence of spray programmes on development of fungicide resistance in the eyespot pathogen of wheat, Pseudocercospovella herpotrichoides

A site with no known history of cereal growing or carbendazim fungicide use was inoculated in 1983 with an equal mixture of spores of R-type and W-type isolates of Pseudocercosporella herpotrichoides. all sensitive to carbendazim. Following three consecutive years of carbendazim sprays, more than 90% of isolates recovered were carbendazim-resistant. A majority of R-type isolates was recovered after 3 years and resistance was found to be more frequent in R-type than in W-type isolates. A mixture of carbendazim with prochloraz initially delayed the development of carbendazim resistance, but after 3 years the incidence of resistance was similar to that where carbendazim alone was applied. The best control of eyespot was given by the mixture and by a split application of prochloraz in the first year, by the mixture in the second year, and by the split prochloraz application in the final year. A greater proportion of R-type isolates was recovered from prochloraz-treated plots than from unsprayed plots; the proportion of these that were resistant to carbendazim was lower than that from carbendazim treatments. Throughout this study isolates resistant to prochloraz were not detected.     

Field evaluation of a predictive model to control anthracnose disease of mango in the Philippines

Infection estimates determined by a predictive model developed by Dodd et al . (1991b) were used to time fungicide sprays to control anthracnose disease of mango in the Philippines. For an amount of disease on fruits after harvest which was acceptable to growers, this approach resulted in the application of five fewer sprays compared with a standard spray programme used by the growers in a field trial conducted in 1991–1992. The model predicted only two high anthracnose-risk periods (>40% of conidia forming appressoria) throughout the duration of the growing period. Rainfall intensity and its time of occurrence during fruit development was found to greatly influence the amount of anthracnose and stem-end rot disease on fruits after harvest. Three relatively strong precipitations (>20 mm) within a month before harvest resulted in relatively high anthracnose infection of fruits after harvest. At a second field trial, rainfall periods during fruit development did not exceed 4 mm and resulted in virtually disease-free fruits after harvest, including those not treated with fungicide. Again the use of the predictive model resulted in the elimination of five fungicide treatments compared with the standard programme. The amount of rainfall and the time of its occurrence should be considered when planning a disease management scheme for the control of anthracnose on mango fruit.     

Early brown rot infections in sweet cherry fruit are detected by monilinia-specific DNA primers

ABSTRACT Visible and nonvisible quiescent infections of immature and mature fruit are an integral component of the disease cycle of brown rot of sweet cherry in California. Detection of these infections is critical for developing efficient and efficacious fungicide management programs. The previously published DNA amplification primers mfs3 and NS5 for the identification of Monilinia fructicola were very specific in amplifying DNA of M. fructicola only and not M. laxa. This primer set, however, only detected DNA from some of the California isolates of M. fructicola. This genetic diversity was supported by random amplified polymorphic DNA (RAPD) analysis. Using eight 10-mer primers, seven M. fructicola isolates from California were all identified as genetically distinct. Using the same primers, only one polymorphism was detected among seven isolates of M. laxa. The multiple genotypes identified within the small population sample of M. fructicola, but not of M. laxa, using RAPD analysis could be indicative of genetic recombination within M. fructicola but not within M. laxa. To detect early brown rot infections in fruit, two primer sets that were developed from DNA sequences of either ribosomal DNA (MF5/ITS4/ITS3) or a RAPD fragment (X-09intF3/X-09R) specifically amplified DNA from isolates of M. fructicola and Monilinia species, respectively. No amplification products were present when using DNA from Botrytis cinerea or from other fungi commonly found on sweet cherry fruit. Primers X-09intF3 and X-09R were more sensitive and reliable for detecting small amounts of target DNA either extracted from conidia or from laboratory-inoculated cherry fruit with early brown rot infections that showed no visual symptoms or with visible quiescent infections. Furthermore, these primers also were effective for detecting visible quiescent infections in cherry fruit that were collected in the field.     

Biological control of fusarium crown and root rot of tomato with antagonistic bacteria and integrated control when combined with the fungicide carbendazim

Two bacterial isolates, Bacillus megaterium (c96) and Burkholderia cepacia (c91), demonstrated to be antagonistic against Fusarium oxysporum f.sp. radicis-lycopersici , the causal organism of fusarium crown and root rot of tomato, were evaluated as biocontrol agents alone and when integrated with the fungicide carbendazim. In an initial screening, these isolates reduced disease incidence by 75 and 88%, respectively. In vitro , both biocontrol agents were highly tolerant to the fungicide carbendazim, commonly used to control fusarium diseases. Carbendazim reduced disease symptoms by over 50% when used at > 50  µ g mL⁻¹, but had little effect at lower concentrations. Combination of the bacterial isolates and carbendazim gave significant ( P  ≤ 0·05) control of the disease when plants were artificially inoculated with the pathogen. Application of carbendazim at a low concentration (1  µ g mL⁻¹) in combination with B. cepacia c91 reduced disease symptoms by 46%, compared with a reduction of 20% obtained with the bacterium alone and no control with the chemical treatment alone. A combination of B. megaterium c96 with an increased application rate of 10  µ g mL⁻¹ carbendazim significantly reduced disease symptoms by 84% compared with inoculated controls and by 77% compared with carbendazim treatment alone. In this experiment, the integrated treatment also slightly outperformed application of 100  µ g mL⁻¹ carbendazim, and bacteria applied without fungicide also provided good disease control.     

河北省苹果果实黑点病的症状与病原研究初报

为明确河北省苹果果实黑点病的症状类型及其对应的病原菌,本研究对河北省6个市的果园进行了病害调查和样品采集,并对引起不同症状类型的病果进行了病原菌的分离和鉴定.结果表明,河北省的套袋苹果黑点病可以分为四大类型,分别是萼洼黑点型、果面黑点型、果面晕斑型和梗洼褐斑型.除了果面晕斑型为单一病原侵染之外,其他类型的病斑均分离获得...