Identification of a constitutive 45 kDa soluble protein associated with resistance to downy mildew in muskmelon (Cucumis melo L.), line PI 124111 F

Analysis by sodium dodecylsulphate-polyacrylamide gel electrophoresis of the soluble proteins extracted from muskmelon (Cucumis melo L.), inbred line PI 124111F (PI) with resistance to Pseudoperonospora cubensis (Berk, et Curt.) Rost, and two susceptible cvs, Hemed and AnanasYokneam revealed the presence of a unique 45 kDa protein (P45) in the resistant but not in the susceptible plants. Subcellular fractionation indicated that P45 is a cytoplasmic soluble protein. It was detected in leaves and cotyledons but not in stems or roots. F₁ hybrid plants (Hemed × PI) that displayed only a partial resistance against P. cubensis expressed P45 at an intermediate level, whereas plants of the inbred generations F₅, F₇ and F₁₀ that displayed a high degree of resistance, expressed P45 at a level similar to the parental PI. Back-cross progeny plants [(Hemed × PI) × Hemed] segregate 1:2:1 partially resistant: susceptible: highly susceptible to the disease. The partially resistant plants showed an intermediate level of P45 (similar to F₁) whereas the highly susceptible plants had no P45, thus indicating cosegregation of P45 with resistance. The resistance of PI to P. cubensis was found to decrease at a colonization temperature of 12 °C. ³⁵S-methionine in vivo protein labelling revealed a reduction in the intensity of the P45 band in plants incubated for 11 h at 12 °C. The application of P45 in breeding programs of muskmelon for downy mildew resistance and its possible involvement in resistance to P. cubensis are discussed.     

Resistance mechanism to carboxylic acid amide fungicides in the cucurbit downy mildew pathogen Pseudoperonospora cubensis

BACKGROUND: Pseudoperonospora cubensis, the causal oomycete agent of cucurbit downy mildew, is responsible for enormous crop losses in many species of Cucurbitaceae, particularly in cucumber and melon. Disease control is mainly achieved by combinations of host resistance and fungicide applications. However, since 2004, resistance to downy mildew in cucumber has been overcome by the pathogen, thus driving farmers to rely only on fungicide spray applications, including carboxylic acid amide (CAA) fungicides. Recently, CAA‐resistant isolates of P. cubensis were recovered, but the underlying mechanism of resistance was not revealed. The purpose of the present study was to identify the molecular mechanism controlling resistance to CAAs in P. cubensis. RESULTS: The four CesA (cellulose synthase) genes responsible for cellulose biosynthesis in P. cubensis were characterised. Resistant strains showed a mutation in the CesA3 gene, at position 1105, leading to an amino acid exchange from glycine to valine or tryptophan. Cross‐resistance tests with different CAAs indicated that these mutations lead to resistance against all tested CAAs. CONCLUSION: Point mutations in the CesA3 gene of P. cubensis lead to CAA resistance. Accurate monitoring of these mutations among P. cubensis populations may improve/facilitate adequate recommendation/deployment of fungicides in the field. Copyright © 2011 Society of Chemical Industry     

Resistance to acylalanines in Pseudoperonospora cubensis1

Resistance to acylalanine fungicides in Pseudoperonospora cubensis, the downy mildew of cucurbits, is reviewed. Insensitive strains of the fungus predominated during the second year of metalaxyl application in cucumber glasshouses in Greece and Israel. Resistance was detected either on detached cucumber leaves floated on metalaxyl solutions or on potted plants treated (sprayed or drenched) with this fungicide. Metalaxyl-resistant strains of P. cubensis showed good pathogenicity and fitness, and competed favorably with the sensitive strains in the absence of the fungicide. A synergism between these two biotypes resulted in an increased virulence of the resistant forms on metalaxyl-treated plants. Metalaxyl-resistant strains of the pathogen exhibited cross resistance to other acylalanine fungicides. Strains resistant to acylalanines and to the chemically unrelated oomycete-fungicides fosetyl-Al and propamocarb were isolated in Israel, as well. In Greece, however, protective sprays with fosetyl-Al, cymoxanil and mancozeb gave good control of cucumber downy mildew when the pathogen was resistant to metalaxyl. P. cubensis is the first case of fungus which developed resistance to acylalanines in the field.     

Occurrence and molecular characterization of azoxystrobin resistance in cucumber downy mildew in Shandong province of China

Cucumber downy mildew caused byPseudoperonospora cubensis (Berk. and Curt.) Rostov. limits crop production in Shandong Province of China. Since management of downy mildew is strongly dependent on fungicides, a rational design of control programs requires a good understanding of the fungicide resistance phenomenon in field populations of the pathogen. A total of 106 and 97 isolates ofP. cubensis were obtained in 2006 and 2007, respectively. The EC₅₀ values for the growth of all the 106 isolates collected in 2006 were 0.0063–0.0688μg ml⁻¹ (average: 0.0196±0.0048μg ml⁻¹) azoxystrobin and these were therefore considered sensitive isolates. However, 57 field isolates ofP. cubensis of the 97 collected in 2007 with EC₅₀ values that ranged from 0.609 to >51.2μg ml⁻¹ were considered resistant to azoxystrobin. Fragments of the fungicide-targeted mitochondrial cytochromeb gene from total pathogen DNA were amplified using polymerase chain reaction and their sequences analyzed to elucidate the molecular mechanism of resistance. A single point mutation (GGT to GCT) in the cytochromeb gene, resulting in substitution of glycine by alanine at position 143, was found in the three selected azoxystrobin-resistant isolates of downy mildew. This substitution in cytochromeb exhibited different resistance levels, with the resistance factor from 21.15 to greater than 2618.9. In addition, the different resistance levels seemed to appear within 1 year (between 2006 and 2007). Therefore, growers of Shandong Province in China now are faced with a challenge in managing the azoxystrobin resistance in cucumber downy mildew. http://www.phytoparasitica.org posting March 10, 2008.     

Field evaluation of mungbeans for resistance to Cercospora leaf spot and powdery mildew

Abstract

Cercospora leaf spot, caused by Cercospora canescens and powdery mildew, caused by Erysiphe polygoni are two of the most important fungal diseases of mungbeans. Nearly 4000 accessions of the global mungbean collection at the Asian Vegetable Research and Development Center were screened for resistance to these two pathogens. Less than 4% and 12% of the accessions showed resistance to Cercospora leaf spot and powdery mildew, respectively. The level of resistance to Cercospora leaf spot varied and highly resistant lines were not found. A few lines were rated highly resistant to powdery mildew over several years but others were rated moderately resistant or susceptible in other years.     

Differential expression of resistance to powdery mildew incited by race 1 or 2 ofsphaerotheca fuliginea inCucumis melo genotypes at various stages of plant development

Thirty-nine genotypes ofCucumis melo (plant introduction entries, open-pollinated cultivars and F₁ hybrids) were evaluated for resistance to powdery mildew under either natural field conditions or artificial inoculation in growth chambers at the cotyledonary stage and the 2-true-leaf stage. Results confirmed that susceptibility in cotyledons was not necessarily associated with susceptibility in either true leaves in growth chambers or adult plants in the field. However, resistance at the 2-true-leaf stage in growth chambers was highly correlated with resistance of field-grown plants. Results also showed that 20 muskmelon genotypes resistant to race 1 at the cotyledonary stage were also resistant at the 2-leaf-stage and as adult plants in the field. The same was true for ten genotypes with race 2 inoculations. Because muskmelon genotypes expressing resistance in cotyledons were also resistant in true leaves in growth chambers or the field, the use of plants at the cotyledonary stage is recommended for screening for powdery mildew resistance caused by race 1 or race 2 ofS. fuliginea. When cotyledons are susceptible, screening should be done at the 2-true-leaf stage.     

Cucurbit downy mildew (<Emphasis Type="Italic">Pseudoperonospora cubensis</Emphasis>)—biology,ecology, epidemiology,host-pathogen interaction and control

Cucurbit downy mildew, caused by the oomycete Pseudoperonospora cubensis, is a devastating, worldwide-distributed disease of cucurbit crops in the open field and under cover. This review provides recent data on the taxonomy, biology, ecology, host range, geographic distribution and epidemiology of P. cubensis. Special attention is given to host-pathogen interactions between P. cubensis and its economically-important cucurbit hosts (Cucumis sativus, C. melo, Cucurbita pepo, C. maxima, and Citrullus lanatus); pathogenic variability in P. cubensis at the species, genus, and population levels; and, differentiation of pathotypes and races. Genetics and variability of host resistance and cellular and molecular aspects of such resistance are considered. A focus is given to methods of crop protection, including prevention and agrotechnical aspects, breeding for resistance—classical and transgenic approaches, chemical control and fungicide resistance. Novel technologies in biological and integrated control are also discussed. This review also summarizes the most important topics for future research and international collaboration.     

The <Emphasis Type="Italic">cyv-2</Emphasis> resistance to <Emphasis Type="Italic">Clover yellow vein virus</Emphasis> in pea is controlled by the eukaryotic initiation factor 4E

The same mutant allele of eukaryotic initiation factor 4E (eIF4E) that confers resistance to Pea seed-borne mosaic virus (sbm-1) and the white lupine strain of Bean yellow mosaic virus (wlv) also confers resistance to Clover yellow vein virus (ClYVV) in pea. The eIF4E genes from several pea lines were isolated and sequenced. Analysis of the eIF4E amino acid sequences from several resistant lines revealed that some lines, including PI 378159, have the same sequence as reported for sbm-1 and wlv. When eIF4E from a susceptible pea line was expressed from a ClYVV vector after mechanical inoculation of resistant PI 378159, the virus caused systemic infection, similar to its effects in susceptible line PI 250438. The resistance to ClYVV in line PI 378159 was characterized through a cross with PI 193835, which reportedly carries cyv-2. Mechanical inoculation of the F1 progeny with ClYVV resulted in no infection, indicating that the resistance gene in PI 378159 is identical to cyv-2 in PI 193835. Furthermore, particle bombardment of pea line PI 193835 with infectious cDNA of ClYVV (pClYVV/C3-S65T) resulted in the same resistance mode as that described for PI 378159. These results demonstrate that the resistance to ClYVV conferred by cyv-2 is mediated by eIF4E and that cyv-2 is identical to sbm-1 and wlv.     

46份野生葡萄株系对霜霉病的抗性鉴定及其相关基因的表达

为明确不同野生葡萄株系对霜霉病的抗性差异,以18个种的46份野生葡萄株系为试材,采用叶盘法鉴定其对霜霉病的抗性,并利用实时荧光定量PCR(real-time quantitative polymerase chain reaction,RT-qPCR)技术对部分关键基因进行定量分析,探讨其在不同抗病株系中的表达模式差异。结果表明,46份野生葡萄株系的病情指数为0～34.72,其中17份为感病株系,病情指数在25.93～34.72;21份为抗病株系,病情指数在5.32～24.35;5份圆叶葡萄株系均表现为免疫,病情指数为0.00;云南-元谋2、云南-2和木扎岭-3为高抗株系,病情指数分别为1.81、4.40和1.62。当被霜霉病菌侵染后,抗病株系和感病株系中的PAL、PR1、TLP和NPR1基因的诱导表达模式不同;与感病株系相比,抗病株系中的TLP、PR1和NPR1基因有强烈的诱导表达,PAL基因在感病株系比在抗病株系中表达量高。在免疫株系普莱德和高抗株系云南-元谋2中,NPR1与其它3个基因的表达模式差异最大;TLP在抗病株系蘡薁-林县中与其它3个基因的表达模式差异最大;在感病株系秋-嵩县中,NPR1与TLP表达模式相近,PAL和PR1表达模式相近。研究表明,在中国野生葡萄种质中,云南-元谋2、云南-2和木扎岭-3对霜霉病有良好的抗性,可作为抗病育种的原始材料;抗性基因可能在抗病株系中发挥着重要作用。     

甘肃小麦白粉病抗源材料的筛选及抗病基因库的组建

2002-2005年,对收集到的30份已知抗白粉病基因载体品种在甘肃省的不同生态区进行了抗病性监测,结果表明:Pm1、Pm3 a、Pm3 b、Pm3 c、Pm3 f、Pm4 a、Pm5、Pm6、Pm7、Pm8、Pm17在田间抗病性丧失,失去利用价值;Pm2、Pm19、Pm4+8、Pm4、Pm5+6、Pm13在田间抗病性较低,不宜单独作为亲本利用;Pm1+2+9、Pm2+6、Pm2+mld、Pm2+talent、Pm4+2 x、Pm4 b、Pm4 b+5、Pm20、Pm21、Pmxbd在田间抗性表现良好,在今后的育种工作中应充分加以利用。同时经过4年抗病性监测,从省内外2 638份小麦品种(系)材料中筛选出了抗病性强、综合农艺性状优良的92R137、贵农21等优异材料10余份,初步组建了抗白粉病基因库。文中还对抗病基因现状和利用及今后如何避免由于抗源单一化带来的白粉病流行进行了初步探讨。     

Mating type and sexual reproduction of <Emphasis Type="Italic">Pseudoperonospora cubensis</Emphasis>, the downy mildew agent of cucurbits

The oomycete Pseudoperonospora cubensis is a leaf pathogen causing severe damage to members of the Cucurbitaceae, especially cucumber and melon. It propagates clonally by sporangia. Oospores of P. cubensis were previously observed in nature but their formation in the laboratory was never reported nor their germination or infection. Here we report on the sexual reproduction of P. cubensis under controlled conditions in the laboratory. When field isolates were inoculated singly onto detached leaves of cucurbits in growth chambers no oospores were produced. However, when pairs of selected isolates were mixed and inoculated onto detached leaves, oospores were formed in the mesophyll within 6–11 days, suggesting that P. cubensis is heterothallic, having two opposite mating types, A1 and A2. Isolates belonging to pathotype 3 were all A1 whereas isolates belonging to the new pathotype 6 were either A1 or A2. Oospores were spherical, ~40 μm in diameter, hyaline to red-brown in color. Oospores were produced regularly, in large numbers, in Cucumis sativum and Cucumis melo, very seldom and in very small numbers in Cucurbita pepo, Cucurbita maxima and Citrullus lanatus, and not in Cucurbita moschata. Oospores were formed at 12.5–21°C but not at 25°C. Under moisture-saturated atmosphere oospores were also produced in leaves of intact plants. Oospores inoculated onto detached leaves in growth chambers produced F1 downy mildew lesions at 6–21 days after inoculation, many in Cucumis sativum, Cucumis melo and Cucurbita moschata, very few in Cucurbita pepo or Citrullus lanatus, and none in Cucurbita maxima. This report shows that P. cubensis is heterothallic, having A1 and A2 mating types which can cross and enable sexual reproduction in cucurbits. A preliminary report on part of the results has been published earlier.     

A standardised method for the quantitative analysis of resistance to grapevine powdery mildew

Powdery mildew caused by Erysiphe necator is one of the most important diseases affecting grapevine (Vitis vinifera, L.). Control of this pathogen is based on the use of fungicides, which cause environmental damage and increase production costs. A cost-effective and environmentally friendly alternative to control the disease relies on using resistant varieties. While most V. vinifera cultivars are susceptible to powdery mildew, several species belonging to the Vitaceae have been described as resistant. Several loci for resistance to grapevine powdery mildew have been identified through genetic analysis of segregating populations derived from different resistance sources. Identifying quantitative trait loci (QTL) with minor effects on the resistance may prove valuable in a strategy of pyramiding, which aims at increasing the durability of the resistance. However, current methods for evaluation of resistance either do not take into account quantitative variations, or, if they do, are not adapted to large sample sets. Here we develop a method for the analysis of quantitative resistance to grapevine powdery mildew in large populations. We devised a semi-quantitative resistance scale and confirmed the usefulness of a cell counter to quantify sporulation. We compared three inoculation methods and identified dry inoculation using a settling tower as the one giving the best infection. Finally, we confirmed the value of the method by applying it to a set of plants segregating for resistance to E. necator. Using the method described here for the quantitative analysis of the resistance to powdery mildew will prove valuable for breeding for durable resistance.     

Genetics of resistance to downy mildew in Brassica oleracea and breeding towards durable disease control for UK vegetable production

Downy mildew resistance was previously identified from screening a Brassica oleracea collection against two standard UK isolates of Hyaloperonospora parasitica. Sources of resistance were chosen from this material and developed further in this study by generating doubled haploid (DH) and inbred lines. Seedlings from the new lines were tested for resistance to a larger collection of H. parasitica isolates collected in 2001–2002 and 2007–2008 from the main broccoli and cauliflower production regions of the UK. Three lines (derived from borecole or summer cabbage) were broadly resistant to the pathogen isolates. Three of the remaining lines exhibited strong isolate‐specific resistance; several examples of weak or basal level of resistance to some isolates were observed. A new H. parasitica variant collected in 2008 was virulent in the broadly resistant lines, but was avirulent in a line with narrow specificity of resistance. The F₂ and BC₁ seedlings derived from outcrossing each of the three broadly resistant lines to susceptible broccoli and cauliflower lines segregated in a manner indicating that the resistance was controlled by a single dominant gene. No susceptibility was observed amongst F₂ seedlings derived from intercrossing the three resistant lines, indicating that they all share the same or closely linked broad‐spectrum resistance gene(s). DH lines were produced from F₁ plants, and resistant plants were further backcrossed to produce broccoli and cauliflower‐like lines that could be useful pre‐breeding material. A combination of resistance from lines with broad and narrow specificity is recommended for controlling downy mildew in UK brassica production.     

河北省和山东省黄瓜霜霉病菌对氟吡菌胺的抗性及常规药剂对黄瓜霜霉病的田间防效

为明确黄瓜霜霉病菌Pseudoperonospora cubensis对氟吡菌胺的抗性时空动态,2011—2016年从河北省和山东省黄瓜主产区采集1 821株霜霉病菌,采用叶盘漂浮法检测供试菌株对氟吡菌胺的敏感性,并以茎叶喷雾法评估5种常规药剂对黄瓜霜霉病的田间防效。结果表明,河北省和山东省黄瓜主产区的黄瓜霜霉病菌对氟吡菌胺已普遍产生了低度抗性,平均抗性倍数为5.86;所有供试菌株的抗性频率为51.89%,其中低抗菌株及中抗菌株分别占36.18%和15.71%;平均抗性指数为0.34,每年检测的抗性频率、抗性倍数及抗性指数呈增长趋势,且随着监测区域的变化而变化。在河北省定兴县和山东省寿光市进行的田间防效试验结果显示,按推荐剂量喷施,687.5 g/L氟吡菌胺·霜霉威盐酸盐SC对黄瓜霜霉病防效显著高于常规对照药剂68%精甲霜灵·代森锰锌WG、58%甲霜灵·代森锰锌WP、80%代森锰锌WP及250 g/L嘧菌酯SC的防效,但防效明显下降,由2011年的92.58%～93.31%降至2016年的80.07%～80.82%。表明需要制定和实施抗药性治理对策,如限制山东和河北2省黄瓜的每个生长季节中687.5 g/L氟菌·霜霉威SC的使用不超过2次,而且要与不同作用机理的卵菌杀菌剂交替使用防治黄瓜霜霉病。     

A potential perennial host for <Emphasis Type="Italic">Pseudoperonospora cubensis</Emphasis> in temperate regions

Pseudoperonospora cubensis causes great losses in cucurbitaceous crops worldwide. In cool temperate climates of northern Europe or North America overwintering as active mycelium is not possible, because all hosts so far reported there are summer annuals. Oospores have not yet been found in these regions under field conditions. The only perennial member of the Cucurbitaceae found naturally in central and northern Europe is Bryonia dioica. To date this plant has not been recorded as a host for downy mildews, but our infection trials demonstrate that P. cubensis is able to infest this plant. Amplification and sequencing of the ITS rDNA confirmed the observed downy mildew disease on B. dioica as P. cubensis. From these findings, the possibility that P. cubensis may be able to overwinter on this perennial host cannot be excluded. Whether or not B. dioica plays a part in the epidemology of P. cubensis in Europe requires evaluation by further studies.     

The reliability of leaf bioassays for predicting disease resistance on fruit: a case study on grapevine resistance to downy and powdery mildew

This study was designed to assess the reliability of grapevine leaf bioassays for predicting disease resistance on fruit in the field. The efficacy of various grapevine quantitative trait loci (QTLs) for conferring resistance to downy and powdery mildew was evaluated in bioassays and in a 2‐year field experiment for downy mildew. The resistance genes studied were inherited from Muscadinia rotundifolia (Rpv1 and Run1) and from American Vitis species through cv. Regent (QTLRgP and QTLRgD). In bioassays, genotypes carrying Run1 blocked powdery mildew development at early stages. Genotypes combining Run1 with QTLRgP displayed no greater level of resistance. For downy mildew, genotypes carrying Rpv1 and/or QTLRgD were more resistant than the susceptible cv. Merlot, and showed a high level of leaf resistance in the field (<10% severity). Disease levels on bunches were much higher than those on leaves, with a high variability between Rpv1 genotypes (1–48%). A Bayesian decision theory framework predicted that an OIV‐452 threshold of 5 in leaf bioassays allowed accurate selection of grapevine genotypes (P = 0·83) with satisfactory disease severity on bunches. Therefore, this study validates that the use of early bioassays on leaves, as currently performed by grapevine breeders, ensures a satisfactory level of resistance to downy mildew of bunches in the field.     

河北省黄瓜霜霉病菌对甲霜灵和嘧菌酯的抗性动态及七种药剂的田间防效

为明确黄瓜霜霉病菌对甲霜灵和嘧菌酯的抗性动态及相应药剂对黄瓜霜霉病的田间防效,采用叶盘漂浮法监测了2011—2015年河北省黄瓜霜霉病菌对甲霜灵和嘧菌酯的抗性,采用茎叶喷雾法测定了含甲霜灵或精甲霜灵的混剂及嘧菌酯单剂等7种药剂的田间防效。结果表明:采自河北省不同地区的838株黄瓜霜霉病菌对甲霜灵和嘧菌酯普遍产生抗性,抗性频率为100.00%,抗性倍数为482.99和354.97,黄瓜霜霉病菌对甲霜灵和嘧菌酯的抗性随着监测地区和监测年限而波动,唐山、沧州、石家庄、衡水、廊坊和保定市的菌株对甲霜灵和嘧菌酯的抗性指数高于其它地区,黄瓜霜霉病菌对甲霜灵和嘧菌酯的抗性指数在不同年度间高位波动。按照田间推荐剂量喷施,250 g/L嘧菌酯悬浮剂对黄瓜霜霉病的防效为72.15%~74.13%;68%精甲霜灵·代森锰锌水分散粒剂和58%甲霜灵·代森锰锌可湿性粉剂的防效分别为65.30%~70.19%和63.26%~68.35%,与80%代森锰锌可湿性粉剂防效相当;50%烯酰吗啉可湿性粉剂、250 g/L双炔酰菌胺悬浮剂和687.5 g/L氟吡菌胺·霜霉威盐酸盐悬浮剂的防效达82.00%以上,对黄瓜霜霉病具有较好的防效,在黄瓜霜霉病菌对嘧菌酯、甲霜灵和精甲霜灵产生抗性的地区,可作为替代或混配药剂使用。     

Evaluation and QTL mapping of resistance to powdery mildew in lettuce

Lettuce (Lactuca sativa) is the major leafy vegetable that is susceptible to powdery mildew disease under greenhouse and field conditions. Quantitative trait loci (QTLs) for resistance to powdery mildew under greenhouse conditions were mapped in an interspecific population derived from a cross between susceptible L. sativa cultivar Salinas and the highly susceptible L. serriola accession UC96US23. Four significant QTLs were detected on linkage groups LG 1 (pm‐1.1), LG 2 (pm‐2.1 and pm‐2.2) and LG 7 (pm‐7.1), each explaining between 35 to 42% of the phenotypic variation. The four QTLs are not located in the documented hotspots of lettuce resistance genes. Alleles for the disease resistance at the four QTLs originated from both parents (two from each), demonstrating that even highly susceptible accessions may provide alleles for resistance to powdery mildew. These QTLs appeared to operate during limited periods of time. Results of the field trials with F_2:3 and F_3:4 families derived from a Soraya (moderately resistant) × Salinas cross demonstrated effective transfer of resistance to powdery mildew in this material. An integrated rating approach was used to estimate relative levels of resistance in 80 cultivars and accessions tested in a total of 23 field and greenhouse experiments. Generally, very low resistance was observed in crisphead‐type lettuces, while the highest relative resistance was recorded in leaf and butterhead types. Comparison of two disease assessment methods (percentage rating and the area under the disease progress steps, AUDPS) for detection of QTLs shows that the two approaches complement each other.     

Synergistic interaction between BABA and mancozeb in controlling<Emphasis Type="Italic">Phytophthora infestans</Emphasis> in potato and tomato and<Emphasis Type="Italic">Pseudoperonospora cubensis</Emphasis> in cucumber

Spray mixtures consisting of the plant activator BABA (DL-3-aminobutyric acid) and the protectant fungicide mancozeb were significantly more effective than BABA or mancozeb alone in controlling late blight (Phytophthora infestans) in potato and tomato and downy mildew (Pseudoperonospora cubensis) in cucumber. A mixture composed of 5 parts BABA and 1 part mancozeb (w/w, a.i.) exhibited a higher synergy factor than the 1+1 or the 1+5 (BABA + mancozeb) mixtures. No synergistic interaction was detected between BABA plus mancozeb in controlling sporangial or cystospore germination, nor mycelial growth ofP. infestans in vitro. The results showed enhanced effect of mancozeb in BABA-induced plants, suggesting, therefore, that lower dosages of this fungicide may be sufficient to control late blight or downy mildew under field conditions. http://www.phytoparasitica.org posting July 15, 2003.