Fungicide Sensitivity in Strawberry Powdery Mildew caused by Podosphaera aphanis in California

Plant Disease ◽  
2021 ◽  
Author(s):  
Michael George Palmer ◽  
Gerald Holmes
Keyword(s):  
Powdery Mildew ◽  
Production Systems ◽  
Disease Incidence ◽  
Fruit Production ◽  
Organic Production ◽  
Fungicide Sensitivity ◽  
First Report ◽  
Plant Nursery ◽  
Foliar Fungicide ◽  
Santa Maria

Field observations suggest that reduced fungicide sensitivity exists in field populations of Podosphaera aphanis, the causal agent of strawberry powdery mildew (SPM). SPM is one of the most common diseases in strawberry production and is controlled using foliar fungicide applications. This study characterizes the sensitivity of 19 P. aphanis isolates to the most common fungicides used against SPM in California. Isolates were collected from commercial fruit production fields in Oxnard, Ventura, Santa Maria, Salinas, and Watsonville, and from a plant nursery in Balico, California. Healthy, unfurled strawberry leaves (cv. Monterey) free of any visual disease symptoms were removed from actively growing plants and treated with one of six commercially formulated fungicides using the minimum labeled rate and inoculated with conidia of P. aphanis. Inoculated leaves were incubated at 20°C under 16/8 hours of day/night lighting and assessed for disease incidence (%) after 14 days. Pathogen growth on the treated leaflets constituted a measure of insensitivity to the fungicide. The six fungicide treatments and their average disease incidence on treated leaves for the 19 isolates are penthiopyrad (51.4%), quinoxyfen (41.5%), myclobutanil (39.8%), trifloxystrobin (19.8%), cyflufenamid (19.3%), and fluopyram + trifloxystrobin (3.5%). The average disease incidence for the trifloxystrobin treatment was raised significantly by two isolates considered to be resistant to the product (disease incidence > 66.6%). Two isolates collected from organic production systems were sensitive to all fungicides. We document compromised fungicide efficacy due to resistance to most of the fungicides currently used for control of SPM in California. This is the first report of resistance in P. aphanis to any fungicide in California and the first report of resistance in P. aphanis to penthiopyrad and quinoxyfen worldwide.

scholarly journals Effect of pruning on disease incidence of apple scab and powdery mildew in integrated and organic apple production

2005 ◽  
Vol 11 (1) ◽  
Author(s):  
I. J. Holb
Keyword(s):  
Powdery Mildew ◽  
Production System ◽  
Production Systems ◽  
Venturia Inaequalis ◽  
Disease Incidence ◽  
Apple Scab ◽  
Organic Production ◽  
Environmentally Benign ◽  
Apple Cultivars ◽  
Apple Production

In a three-year study, the effect of two winter pruning treatments (strong and weak) on apple scab (Venturia inaequalis) and powdery mildew (Podosphaera leucotricha) was evaluated on six apple cultivars (`Rewena', `Elstar', 'Liberty', 'Gala', 'Pilot' and `Jonica') in two environmentally-benign apple production systems (integrated and organic). Results on apple scab showed that compared to the integrated production system, the pathogen caused significantly more infection on the leaves of cvs. `Elstar', 'Gala' and `Jonica' in the organic production system. The effect of pruning treatments on apple scab was mainly detectable on the cultivars susceptible to the disease such as cvs. 'Gala' and `Jonica'. The weak pruning correlated with a higher level of apple scab infection than the strong pruning, especially in the organic production system. Primary mildew infection was very low in both protection systems (below 2 %), therefore, effect of pruning on primary mildew infection could not be analysed. Low secondary mildew incidence was detected in the organically treated orchard part; however, incidence of powdery mildew was significantly higher (P> 0.05) on cvs. 'Elstar', 'Pilot' and `Jonica' in the integrated orchard part compared to cvs. 'Gala', 'Rewena' and 'Liberty'. The highest incidence of mildew was on cv. 'Elstar'. Pruning had very low effect on incidence of secondary mildew infection on leaves.

scholarly journals Effect of reduced spray programmes on incidences of apple scab, powdery mildew and codling moth damage in environmentally freindly apple production systems

2009 ◽  
Vol 15 (4) ◽  
Author(s):  
I. J. Holb ◽  
M. Fazekas ◽  
F. Abonyi ◽  
P. Lakatos ◽  
S. Thurzó ◽  
...  
Keyword(s):  
Powdery Mildew ◽  
Production Systems ◽  
Apple Scab ◽  
Codling Moth ◽  
Fruit Production ◽  
Organic Production ◽  
Integrated Production ◽  
Growth Capacity ◽  
Apple Production

Still a large amount of pesticides and spary applications are used in environmentally friendly fruit production systems; therefore, the aim of our study was first to test the in vitro effeicacy of some fungicides against a key apple disease (apple scab), and secondly to evaulate the effectiveness of reduced spray programmes against apple scab, powdery mildew and coding moth in integrated and organic apple orchards. In vitro efficacy of 7 fungicides (Champion 50 WP, Kocide 2000, Nordox 75 WG, Olajos rézkén, Kumulus S, Rézkén, Rézoxiklorid) and another 6 fungicides (Score 25 EC, Efuzin 500 SC, Systane, Folicur Solo, Zato Plusz, Rovral) approved in organic and integrated production systems, respectively, were tested against apple scab. Altogether four spray programmes were performed i) standard integrated: sprays followed by forecasting systems during the season, ii) reduced integrated: sprays followed by forecasting systems but only 75% of the spray numbers used during the season-long spray programme, iii) standard oragnic: sprays applied every 7–14 days during the season and iv) reduced organic: 60% of the spray numbers used during the season-long spray programme. In vitro results showed that fungicides (with active ingredients of copper and sulphur) applied in organic production showed relatively high percent growth capacity of the apple scab fungus. Rézkén showed the highest and Kumilus S the lowest efficacy against apple scab. Fungicides applied in integrated production showed relatively low percent growth capacity of the apple scab fungus. Score 25 EC showed the highest and Rovral the lowest efficacy against apple scab. Field study showed that reduced spray programmes did not increase significantly scab incidence in the integrated field. However, scab incidence increased significanly (above 30%) in the reduced spray programme for the organic orchard.Mildew incidence was low (below 5%) in both integrated and organic spray programmes. Mildew incidence on both shoots and fruits increased significanly in the reduced spray programme for the organic orchard. Incidence of codling moth damage was affected the most by standard vs. reduced spray programmes. Though incidence remained below 10% in the integrated plots, the incidence was significantly higher in the reduced spray programme compared to the standard programme. Similar results were obtained for organic spary programmes, but the incidence was 10 times higher and the differences among the two programmes were larger.,

scholarly journals Effect of Compost Amendments on Disease Severity and Yield of Tomato in Conventional and Organic Production Systems

Plant Disease ◽  
2002 ◽  
Vol 86 (2) ◽  
pp. 156-161 ◽  
Author(s):  
P. A. Abbasi ◽  
J. Al-Dahmani ◽  
F. Sahin ◽  
H. A. J. Hoitink ◽  
S. A. Miller
Keyword(s):  
Disease Severity ◽  
Production Systems ◽  
Disease Incidence ◽  
Organic Production ◽  
Fruit Rot ◽  
High Rate ◽  
Bacterial Spot ◽  
Marketable Yield ◽  
Tomato Production ◽  
Compost Amendments

Field trials were conducted over 2 years to assess the effects of compost amendments on disease development in organic and conventional processing tomato (Lycopersicon esculentum L.) production systems. The incidence of anthracnose fruit rot was reduced in organic tomato plots amended with a high rate of composted cannery wastes compared with the incidence in nonamended control plots in 1998 when disease incidence was high. Marketable yield was increased by 33% in compost-amended organic plots. Plots amended with a high compost rate had more ripe fruit than the nonamended control. The incidence of anthracnose and of total disease on fruit was less on the cultivar OH 8245 than on Peto 696. Total fruit yield of OH 8245 but not Peto 696 in organic plots was increased by amendment with composted cannery wastes. In conventional tomato production, composted yard wastes increased disease severity on foliage both years but reduced bacterial spot incidence on fruit in 1997, when disease pressure was high. The incidence of anthracnose was not affected by composted yard wastes. Marketable and total fruit yields of Peto 696 were not increased in compost-amended conventional plots. The plant activator Actigard reduced foliar disease severity and the incidence of bacterial spot and anthracnose on fruit, while increasing yield of marketable fruit.

scholarly journals First Report of Powdery Mildew Caused by Podosphaera xanthii on Cucurbita argyrosperma in Mexico

Plant Disease ◽  
2021 ◽  
Author(s):  
José Francisco Díaz-Nájera ◽  
Sergio Ayvar-Serna ◽  
Antonio Mena-Bahena ◽  
Guadalupe Arlene Mora-Romero ◽  
Karla Yeriana Leyva-Madrigal ◽  
...  
Keyword(s):  
Powdery Mildew ◽  
Microscopic Examination ◽  
Disease Incidence ◽  
Phylogenetic Analyses ◽  
Its Region ◽  
Likelihood Method ◽  
28S Rrna ◽  
Podosphaera Xanthii ◽  
Voucher Specimen ◽  
First Report

Cucurbita argyrosperma, commonly named as winter or cushaw squash, is highly sought for its seeds, which have important uses in culinary arts. During the autumn 2021, powdery mildew-like signs and symptoms were observed on cushaw squash in several commercial fields located in Cocula, Guerrero, Mexico. Signs were initially appeared as whitish powdery patches on both sides of leaves and then covering entire leaves and causing premature senescence. The disease incidence was estimated to be 80% in about 1000 plants in two fields. The mycelium was amphigenous, persistent, white in color, and occurred in dense patches. A voucher specimen was deposited in the Herbarium of the Colegio Superior Agropecuario del Estado de Guerrero under the accession number CSAEG22. For the morphological characterization by light microscopy, fungal structures were mounted in a drop of lactic acid on a glass slide. Microscopic examination showed nipple-shaped hyphal appressoria. Conidiophores (n = 30) were straight, 100 to 190 × 10 to 12 μm and produced 2 to 6 conidia in chains. Foot-cells were cylindrical, 41 to 78 μm long, followed by 1 to 2 shorter cells. Conidia (n = 100) were ellipsoid-ovoid to barrel-shaped, 29.5 to 39.1 × 19.4 to 22.7 μm, and contained conspicuous fibrosin bodies. Germ tubes were produced from a lateral position on conidia. Chasmothecia were not observed during the growing season. The morphological characters were consistent with those of the anamorphic state of Podosphaera xanthii (Braun and Cook 2012). For further confirmation, total DNA was extracted from conidia and mycelia following the CTAB method (Doyle and Doyle 1990), and the internal transcribed spacer (ITS) region and part of the 28S gene were amplified by PCR, and sequenced. The ITS region of rDNA was amplified using the primers ITS5/ITS4 (White et al. 1990). For amplification of the 28S rRNA partial gene, a nested PCR was performed using the primer sets PM3 (Takamatsu and Kano 2001)/TW14 (Mori et al. 2000) and NL1/TW14 (Mori et al. 2000) for the first and second reactions, respectively. Phylogenetic analyses using the Maximum Likelihood method, including ITS and 28S sequences of isolates of Podosphaera spp. were performed and confirmed the results obtained in the morphological analysis. The isolate CSAEG22 grouped in a clade with isolates of Podosphaera xanthii. The ITS and 28S sequences were deposited in GenBank under accession numbers OL423329 and OL423343, respectively. Pathogenicity was confirmed by gently dusting conidia from infected leaves onto ten leaves of healthy C. argyrosperma plants. Five non-inoculated leaves served as controls. The plants were maintained in a greenhouse at 25 to 35 ºC, and relative humidity of 60 to 70%. All inoculated leaves developed similar signs to the original observation after 10 days, whereas control leaves remained symptomless. Microscopic examination of the fungus on inoculated leaves showed that it was morphologically identical to that originally observed on diseased plants, fulfilling Koch’s postulates. Podosphaera xanthii has been previously reported on C. maxima, C. moschata, and C. pepo in Mexico (Yañez-Morales et al. 2009; Farr and Rossman 2021). To our knowledge, this is the first report of P. xanthii causing powdery mildew on C. argyrosperma in Mexico. This pathogen is a serious threat to C. argyrosperma production in Mexico and disease management strategies should be developed.

scholarly journals Analyses of the pathogen and weather components of disease progress for modeling apple scab epidemics in integrated and organic production systems

2003 ◽  
Vol 9 (3-4) ◽  
Author(s):  
I. J. Holb
Keyword(s):  
Relative Humidity ◽  
Growth Rates ◽  
Production Systems ◽  
Disease Incidence ◽  
Apple Scab ◽  
Organic Production ◽  
Regression Analyses ◽  
Integrated Production ◽  
Disease Progress ◽  
Weather Parameters

The pathogen and weather components of apple scab disease progress were analysed in a three-year study, in two environmental-friendly production systems (organic and integrated) on cvs. `Idared', `Jonica' and 'Mutsu'. Linear regression analyses of transformed disease incidence and severity data and "area under the disease progress curves" (AUDPC) were used for the analysis of the pathogen component. To evaluate the role of the weather component in apple scab epidemic, first, the weekly disease increase was determined at a certain week (n). Weekly disease increase was related to rainfall, relative humidity, Mills' wetness period, temperature and interaction between temperature and relative humidity. Five different periods were used in the analyses: i) week (n-1), ii) week n(n-1), iii) week (n-2), iv) week (n-1)(n-2) and v) week n(n-1)(n-2). In the analyses of the pathogen component, the best transformation function was the logistic one. Regression analyses showed that disease growth rates were higher for disease incidence and for the organic production system than for disease severity and for the integrated production system, respectively. Disease growth rates for leaf incidence were higher than fruit incidence on all the three cultivars. AUDPC values showed great differences in both leaf and fruit incidences among cultivars and between the two production systems. The results the of analyses of the weather component showed that the best relationships between disease increase and weather parameters were found for fruit incidence and leaf incidence in week (n-2) in the organic and integrated production systems, respectively. Results also demonstrated that in week n(n-1) temperature played a more important role in the fungus development than the water parameters (relative humidity, rainfall and leaf wetness). Consequently, infection process is significantly dependent on almost all weather parameters, but during the incubation period the most important weather parameter is the temperature. Results were compared with similar studies and biological interpretations of the analyses are discussed.

scholarly journals Effect of Production System and Pruning on Temporal Development of Cercospora depazeoides and on Berry Yield in Black Elderberry Orchards

Plant Disease ◽  
2009 ◽  
Vol 93 (6) ◽  
pp. 625-631 ◽  
Author(s):  
I. J. Holb ◽  
J. M. Gáll ◽  
B. Fodor
Keyword(s):  
Leaf Spot ◽  
Production Systems ◽  
Disease Incidence ◽  
Organic Production ◽  
Integrated System ◽  
Disease Development ◽  
Temporal Development ◽  
Cercospora Leaf Spot ◽  
Organic System ◽  
Disease Progress

In a 2-year study, the temporal development of Cercospora leaf spot (Cercospora depazeoides) and berry yield were evaluated in two production systems (integrated and organic) and in two winter pruning treatments (trees pruned to four and eight scaffolds) in two black elderberry (Sambucus nigra) orchards in Hungary. Under organic production, leaf spot onset occurred 2 to 4 weeks earlier (mid- and late July) in both years and both orchards compared with the integrated program. Disease then continuously progressed until the final assessment date (late September) in both years, reaching a maximum final disease incidence of 15.9% in the integrated system and of 38.2% in the organic system. In general, disease progress after late August was greater on trees pruned to eight scaffolds than on trees pruned to four scaffolds in both production systems. Both final disease incidence and area under the disease progress curves (AUDPC) were significantly lower (P < 0.001) in the integrated treatments compared with organic ones. Across all treatments, both disease measures were significantly (P < 0.05) lower on trees pruned to four scaffolds compared with trees pruned to eight scaffolds. However, when the effect of pruning on final disease incidence and AUDPC was analyzed separately for integrated and organic systems, pruning caused uniformly significant differences in disease development only for the organic system. Berry yield was significantly higher (P < 0.05) in the integrated system compared with the organic system, but pruning showed no significant effect on yield. Overall, pruning to four scaffolds resulted in consistently lower disease development in organic production compared to integrated. Thus, winter pruning may be useful as a Cercospora leaf spot management practice in organic elderberry orchards.

Organic fruit production in British Columbia

2009 ◽  
Vol 89 (4) ◽  
pp. 677-692 ◽  
Author(s):  
G H Neilsen ◽  
D T Lowery ◽  
T A Forge ◽  
D Neilsen
Keyword(s):  
Vitis Vinifera ◽  
Malus Domestica ◽  
Production Systems ◽  
Fruit Production ◽  
Organic Production ◽  
Current Status ◽  
Vitis Vinifera L ◽  
Fruit Crops ◽  
Malus Domestica Borkh ◽  
Organic Fruit

British Columbia has climatic conditions suitable for the production of a wide range of high-value fruit crops, and has the highest rate of increase of organic production in Canada. This review assesses the current status of organic fruit production using a case study of the three most valuable fruit crops currently grown: apple (Malus × domestica Borkh.), grape (Vitis vinifera L.) and high bush blueberry (Vaccinium corybosum L.). The review emphasizes the current status of organically acceptable management of crop resources and crop protection from insects and diseases. Central to organic production are soil management strategies designed to maintain soil fertility and increase soil biological activity and biodiversity by increasing soil organic matter content. Composts and organic amendments that require vigilant testing of their variable and often lower nutrient content are substituted for the chemical fertilizers of conventional production. Increased effort to manage vegetation within and between planting rows is necessitated by an inability to use herbicides. Thus, techniques such as mulching, cultivation and cover cropping are important. Management of insects and diseases requires detailed information of the agro-ecosystem and the unique interactions between pests and specific crops. Organic approaches to minimize pest damage include altered production practices or applications of organically approved control products. Some aspects of organic production systems have received little or no research. In irrigated areas, there is little information available on water management that supports conservation and the specific needs of organic production systems. Historically, research on organic production systems has not received the financial support allocated to conventional system research. Many research needs are identified in this review both applicable to all three fruit crops studied, but also specific to the individual crop. It is argued that future consumer demand calls for an acceleration of research on organic fruit production systems. Key words: Malus × domestica Borkh., organic soil, insect and disease management, Vaccinium corybosum L., Vitis vinifera L.

scholarly journals Bokashi, Boiled Manure and Penergetic Applications Increased Agronomic Production Variables and May Enhance Powdery Mildew Severity of Organic Tomato Plants

Horticulturae ◽  
2021 ◽  
Vol 7 (2) ◽  
pp. 27
Author(s):  
Fernando Teruhiko Hata ◽  
Mauricio Ursi Ventura ◽  
Gustavo Adolfo de Freitas Fregonezi ◽  
Romário Fortunato de Lima
Keyword(s):  
Powdery Mildew ◽  
High Efficiency ◽  
Production Systems ◽  
Tomato Fruit ◽  
Fruit Size ◽  
Fruit Production ◽  
Organic Fertilizers ◽  
Soluble Solids ◽  
Total Soluble Solids ◽  
Tomato Yield

Research on organic fertilizers are of crucial importance for sustainable production systems with high efficiency of natural resource use. The objective of this study was to evaluate organic sources of fertilization (boiled manure (BM), effective microorganism (EM) Bokashi, and Penergetic) for their effects on agronomic variables (fruit size and yield, total soluble solids) and on foliar powdery mildew severity of tomato (Solanum lycopersicum L.). The crops were grown during two cropping cycles in protected cultivation. The treatments were: Control (water only); 50 g per plant of EM Bokashi compost in two applications; Penergetic at 1.5 g L−1 applied to the substrate before planting or sprayed on the plants 14 days after transplanting; and BM at 2.5%, 5.0%, 7.5%, and 10% concentrations (vol/vol) in water, via fertigation. Fruit production and quality were assessed. The effects of treatments on powdery mildew (Leveillula taurica Lév. G. Arnaud) were analyzed by using a diagrammatic scale. Bokashi, 10% BM, and Penergetic increased fruit production of the first three fruit trusses. Bokashi treatment increased tomato fruit diameter. The effects on fruit length and total soluble solids varied with each crop cycle. Powdery mildew severity increased with 10% BM, compared to the control. Both 10% BM and Penergetic presented similar fruit production to Bokashi and are good candidates as substitutes for Bokashi as organic fertilizers/amendments while maintaining tomato yield.

scholarly journals First Report of Powdery Mildew Caused by Podosphaera xanthii on Cuphea hyssopifolia (Lythraceae) in Mainland China

Plant Disease ◽  
2021 ◽  
Author(s):  
Irum Mukhtar ◽  
Ruiting Li ◽  
IBATSAM KHOKHAR ◽  
Ruanni Chen ◽  
Yunying Cheng ◽  
...  
Keyword(s):  
Powdery Mildew ◽  
Disease Incidence ◽  
Large Subunit ◽  
Mainland China ◽  
Lsu Rdna ◽  
Podosphaera Xanthii ◽  
Powdery Mildew Fungus ◽  
Potential Threat ◽  
First Report ◽  
Plant Pathol

Cuphea hyssopifolia (Mexican heather) is a popular evergreen perennial shrub used for ornamental and medicinal purposes. Due to its high ornamental value, it is often used as a ground cover in parks and gardens in China. During February and March 2019 & 2020, powdery mildew was observed on C. hyssopifolia in the districts of Minhou and Jinshan of Fuzhou, China. Disease incidence was 70% but of low severity with only a few older leaves showing yellowing and wilting. Sparse irregular patches of white superficial powdery mildew observed on both sides of mature and young leaves. The powdery mildew fungal appressoria that occurred on epigenous hyphae, were indistinct to nipple-shaped, hyaline, and smooth. Conidiophores were erect, smooth, 80 to 210 × 10 to 12 µm, and produced two to eight crenate-shaped conidia in chains. Foot-cells of conidiophores were straight, cylindric, and 30 to 65 × 10 to12 µm. Conidia were hyaline, smooth, ellipsoid-ovoid to barrel-shaped, 25 to 38 × 16 to 20 µm with distinct fibrosin bodies. Germ tubes were simple to forked and produced from the lateral position of the germinating conidia. No chasmothecia were observed on the surface of infected leaves. Based on the morphology of the imperfect state, the powdery mildew fungus was identified as Podosphaera xanthii (Castagne) U. Braun & N. Shishkoff (Braun and Cook 2012). To confirm fungal identification, total DNA was extracted (Mukhtar et al., 2018) directly from epiphytic mycelia on infected leaves collected from both districts. Internal transcribed spacer (ITS) regions and the partial large subunit (LSU) rDNA were amplified using primers ITS1/ITS4 and LSU1/LSU2 (Scholin et al. 1994, White et al. 1990), respectively. The sequences were deposited in GenBank (ITS: MW692364, MW692365; LSU: MW699924, MW699925). The ITS and LSU sequences were 99 to 100 % identical to those of P. xanthii in GenBank, (ITS: MT568609, MT472035, MT250855, and AB462800; LSU: AB936276, JX896687, AB936277, and AB936274). Koch’s postulates were completed by gently pressing diseased leaves onto leaves of five healthy potted C. hyssopifolia plants that were held in a greenhouse at 24 to 30°C without humidity control. Five non-inoculated plants served as controls. Inoculated plants developed symptoms after 6 to 10 days, whereas the controls remained symptomless. The morphology of the fungus on the inoculated leaves was identical to that observed on the originally diseased leaves. Previously, Podosphaera sp. has been reported on C. rosea in the United Kingdom (Beales & Cook 2008) and P. xanthii on C. hyssopifolia in Taiwan (Yeh et al. 2021). To our knowledge, this is the first report of powdery mildew caused by P. xanthii on C. hyssopifolia in mainland China. Our field observations suggest that the P. xanthii infections would be a potential threat to the health of C. hyssopifolia in China. References: Beales, P. A., and Cook, R. T. A. 2008. Plant Pathol. 57:778. Braun, U., Cook, R. T. A. 2012. The Taxonomic Manual of the Erysiphales (Powdery Mildews). CBS Biodiversity Series 11: CBS. Utrecht, The Netherlands. Mukhtar, I., et al. 2018. Sydowia.70:155. Scholin, C. A., et al. 1994. J. Phycol. 30:999. White, T. J., et al. 1990. Page 315 in: PCR Protocols: A Guide to Methods and Applications. Academic Press, San Diego, CA. Yeh, Y. W., et al. 2021. Trop. Plant Pathol. 46:44.

scholarly journals First Report of Canola Powdery Mildew Caused by Erysiphe polygoni in Argentina

Plant Disease ◽  
2004 ◽  
Vol 88 (10) ◽  
pp. 1163-1163 ◽  
Author(s):  
S. Gaetán ◽  
M. Madia
Keyword(s):  
Powdery Mildew ◽  
Buenos Aires ◽  
Disease Incidence ◽  
Fungal Growth ◽  
The United States ◽  
Climatic Conditions ◽  
Width Ratio ◽  
Infected Leaf ◽  
First Report ◽  
Erysiphe Polygoni

Canola (Brassica napus) is a developing oleaginous crop grown commercially in the Buenos Aires and Santa Fe provinces of Argentina. During the autumn of 2003, typical signs of powdery mildew were observed on canola plants in experimental field plots in Buenos Aires. Average disease incidence was 42% on 3- to 6-month-old canola cultivars developed in the following countries: Argentina (Eclipse, Impulse Master, Mistral, and Nolza); Australia (Oscar and Rainbow); Canada (Sentry); France (Cadillac, Camberra, and Capitol); and Sweden (Maskot, Sponsor, and Wildcat). The range of incidence on these cultivars was 35 to 93%. Other cultivars exhibited an apparent high level of resistance or escaped disease. These included: Charlton (Argentina); 46CO3, Dunkeld, Insignia, Mystic, Monty, Outback, Rivette, and Surpass 400 (Australia), and Caviar (France). Climatic conditions in Buenos Aires, especially rainfall, from March to May 2003 were apparently favorable for powdery mildew development. On susceptible cultivars, fungal growth was observed on leaves, stems, and pods that resulted in premature senescence of the tissues. The mycelium, with multilobed hausthoria, was white to gray, dense or fine, and in patches or covering the entire adaxial leaf surfaces. Appressoria were lobed and conidiophores were straight. Foot cells were cylindrical, straight, measured 35 to 42 × 7 to 10 μm, and were followed by two cells. Conidia were produced singly, cylindrical to ovoid, and measured 36 to 40 × 18 to 20 μm. The conidial length-to-width ratio was 2.0. No fibrosin bodies were observed in the conidia and conidia germinated at the ends. Cleistothecia were not observed. On the basis of mycelial, conidial, and hausthoria characteristics observed on six leaves for each affected cultivar, the fungus was identified as Erysiphe polygoni DC (1). Pathogenicity was confirmed on 5-week-old canola plants of cvs. Eclipse, Impulse, Master, Mistral, and Maskot by gently pressing (1 min) one adaxial infected leaf with abundant sporulation onto one adaxial healthy leaf. The experiment, which included five inoculated plants and three noninoculated control plants for each cultivar, was conducted in a greenhouse at 22 to 24°C and maintained at 75% relative humidity with no supplemental light. Inoculated and control plants were covered with polyethylene bags for 48 h after inoculation. Powdery mildew developed on all inoculated plants of all cultivars after 12 to14 days. The control plants did not develop disease. The experiment was repeated with similar results. E. polygoni has a worldwide distribution (2); however, the results suggest that this fungus may be a threat to the main cultivars being grown in Argentina (Eclipse, Impulse, Master, Mistral, and Nolza), since high levels of disease incidence, as much as 70%, were observed. Under propitious environments, this pathogen could cause severe yield losses in commercially grown canola in Argentina. To our knowledge, this is the first report of canola powdery mildew caused by E. polygoni in Argentina. References: (1) H. J. Boesewinkel. Rev. Mycol. Tome 41:493, 1977. (2) D. F. Farr et al. Fungi on Plants and Plant Products in the United States. The American Phytopathological Society, St.Paul, MN, 1989.

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