Alternative Fungicide Spraying for the Control of Powdery Mildew Caused by Sphaerotheca fusca on Greenhouse Watermelon (Citrullus lanatus)

Euryops pectinatus is grown in Italy for landscape use in parks and gardens. In 2001, severe outbreaks of a previously unknown powdery mildew were observed in commercial farms located in Albenga (northern Italy). All green parts (leaves, stems, and petioles) became covered with a white mycelium. Infections were particularly severe on the upper leaf surface. With progress of the disease, infected leaves turned yellow and died. The presence of powdery mildew infections on leaves and stems only rarely was linked to growth reduction. Conidia were hyaline, cylindric to slightly doliform, did not show fibrosin bodies, borne in chains, and measured 24 to 41 × 12 to 20 μm. Cleistothecia were not observed. The pathogen was identified as Oidium sp. subgen. Fibroidium (1). Pathogenicity was confirmed by gently pressing diseased leaves on leaves of healthy E. pectinatus plants. Inoculated plants were maintained in a growth chamber at 20 to 24°C. After 12 to 14 days, powdery mildew symptoms developed. A similar disease of E. pectinatus was observed in 1999 in California and identified as being caused by Podosphaera (Sphaerotheca) fusca (2). It is possible that the powdery mildew observed in Italy belongs to the same species, also considering that recently the two genera, Podosphaera and Sphaerotheca, have been unified in the genus Podosphaera (1). References: (1) U. Braun and S. Takamatsu. Schlechtendalia 4:1, 2000. (2) G. S. Saenz et al. Plant Dis. 84:1048, 2000.

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First Report of Erysiphe cichoracearum Infecting Hedera canariensis var. azorica in Italy

Plant Disease ◽

10.1094/pdis.1999.83.2.198d ◽

1999 ◽

Vol 83 (2) ◽

pp. 198-198

Author(s):

C. Nali

Keyword(s):

New York ◽

Powdery Mildew ◽

Citrullus Lanatus ◽

Ornamental Plants ◽

Morphological Characteristics ◽

Hedera Helix ◽

Cucumis Sativus L ◽

First Report ◽

Erysiphe Cichoracearum ◽

English Ivy

A powdery mildew disease of variegated ivy (Hedera canariensis L. var. azorica) was observed on the Tyrrhenian coast in Tuscany (Italy) in spring 1998. Symptoms began as small, nearly circular reddish spots that later enlarged and coalesced. The hyaline mycelium produced abundant, ellipsoid conidia in long chains that ranged from 20 to 40 μm in length and from 12 to 25 μm in width. Cleistothecia were globose (100 to 120 μm diameter), dark brown (when mature) with a basal ring of mycelioid appendages, and contained several (up to 20) ovate asci, each generally containing two ascospores. Ascospores were hyaline, one-celled, ellipsoid (20 to 35 μm in length and 10 to 20 μm in width). The morphological characteristics of this fungus were those given for Erysiphe cichoracearum DC. Infection also was found on English ivy (Hedera helix L.). It is reported that this species is, occasionally, subject to powdery mildew caused by E. cichoracearum (1). Conidia from infected leaves were shaken onto leaves of melon (Cucumis melo L.), cucumber (Cucumis sativus L.), watermelon (Citrullus lanatus [Thunb.] Matsum. & Nakai), lettuce (Lactuca sativa L.), tomato (Lycopersicon esculentum Mill.), tobacco (Nicotiana tabacum L.) and variegated and English ivy. After 7 days, the disease was observed on cucumber, melon, watermelon, tobacco, and variegated ivy. Examination confirmed that test plants were infected with E. cichoracearum. This is the first report of E. cichoracearum on variegated ivy in Italy. Reference: (1) P. P. Pirone. 1970. Diseases and Pests of Ornamental Plants. The Ronald Press, New York.

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First Report of Powdery Mildew Caused by Sphaerotheca fusca on Tomatillo in California

Plant Disease ◽

10.1094/pdis.1998.82.6.711c ◽

1998 ◽

Vol 82 (6) ◽

pp. 711-711 ◽

Cited By ~ 1

Author(s):

S. T. Koike ◽

R. F. Smith

Keyword(s):

Powdery Mildew ◽

Fungal Growth ◽

Premature Senescence ◽

First Report ◽

Powdery Mildew Disease ◽

Salinas Valley ◽

Germ Tubes ◽

Husk Tomato ◽

Sphaerotheca Fusca ◽

Commercial Field

Tomatillo or husk tomato (Physalis ixocarpa Brot.) is an annual Solanaceous bush grown for its fruit, which are harvested when the fruit fill the enlarged calyx and are used primarily in Hispanic cooking. In the summer of 1997, commercial field-grown tomatillo in the Salinas Valley (Monterey County) was severely affected by a powdery mildew disease. Fungal growth was found on leaves, petioles, and calyces and resulted in twisting, desiccation, and premature senescence of the tissues. The mycelium was white to gray, ectophytic, amphigenous, and effuse. Mycelial appressoria were indistinct. Conidiophore foot cells were straight, cylindric, measured 36.1 to 61.1 µm (mean 47.0) × 11.1 to 13.9 µm (mean 11.7), and were followed by 1 to 3 shorter cells. Doliform conidia were formed in chains and measured 25.0 to 50.0 µm (mean 32.5) × 11.1 to 22.2 µm (mean 17.7). The length-to-width ratios of conidia generally were less than 2.0, and fibrosin bodies were present. Germ tubes usually were laterally inserted, lacked conspicuous appressoria, and were of the pannosa-type. Cleistothecia were not observed. Based on these characters, the fungus was identified as Sphaerotheca fusca (Fr.) Blumer, Beitr. Krypt.-Fl. Schweiz (1). Pathogenicity was confirmed by gently pressing infected leaves onto leaves of potted tomatillo. Inoculated plants were kept in a chamber at 100% humidity for 48 h, and then maintained in a greenhouse. Powdery mildew developed on inoculated plants after 12 to 14 days, while uninoculated plants did not develop disease. The experiment was conducted a second time and the results were the same. This is the first report of a powdery mildew disease of tomatillo in California. Reference: (1) U. Braun. Nova Hedwigia 89:1, 1987.

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Inheritance of Resistance to Powdery Mildew Race 2 in Citrullus lanatus var. lanatus

HortScience ◽

10.21273/hortsci.48.10.1227 ◽

2013 ◽

Vol 48 (10) ◽

pp. 1227-1230 ◽

Cited By ~ 5

Author(s):

Antonia Y. Tetteh ◽

Todd C. Wehner ◽

Angela R. Davis

Keyword(s):

Powdery Mildew ◽

Citrullus Lanatus ◽

Dominant Gene ◽

Breeding Strategy ◽

Dominance Model ◽

Narrow Sense Heritability ◽

Stem Resistance ◽

Nonallelic Interactions ◽

Race 2 ◽

Moderate Resistance

Information on the mode of inheritance of powdery mildew resistance in watermelon is important for designing a breeding strategy for the development of new cultivars. Resistance in the watermelon accession PI 270545 was investigated by generation means analysis by crossing it with susceptible PI 267677. The analyses showed involvement of two genes, a recessive resistance gene, pmr-1, and a dominant gene for moderate resistance, Pmr-2. Resistance to powdery mildew in the leaf had a large dominance effect and a heritability of 71%. The additive-dominance model was inadequate in explaining variation in leaf resistance as revealed by the joint scaling test. However, nonallelic interactions could not be detected by the nonweighted six-parameter scaling test. For stem resistance, the additive-dominance model was adequate, and inheritance was controlled mainly by additive effects. A high narrow-sense heritability of 79% suggested that selection for stem resistance in early generations would be effective.

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First Occurrence of Cucurbit Powdery Mildew Caused by Race 3-5 of Podosphaera fusca in Spain

Plant Disease ◽

10.1094/pdis-93-10-1073b ◽

2009 ◽

Vol 93 (10) ◽

pp. 1073-1073 ◽

Cited By ~ 4

Author(s):

J. A. Torés ◽

J. M. Sánchez-Pulido ◽

F. López-Ruiz ◽

A. de Vicente ◽

A. Pérez-García

Keyword(s):

Powdery Mildew ◽

Citrullus Lanatus ◽

Morphological Characteristics ◽

Fungal Growth ◽

Powdery Mildew Fungus ◽

First Occurrence ◽

New Race ◽

First Time ◽

Cucurbit Powdery Mildew ◽

Podosphaera Fusca

A new race of cucurbit powdery mildew was observed for the first time on melon (Cucumis melo) in three research greenhouses in the Axarquia area of southern Spain during the spring of 2008. Fungal growth appeared as white powdery colonies initially restricted to the upper leaf surfaces. Morphological characteristics of colonies, conidiophores, conidia, germ tubes, and appressoria indicated that the powdery mildew fungus was Podosphaera fusca (also known as P. xanthii) (3), a fungal pathogen extensively reported in the area (1). However, the fungus developed on plants of melon cv. PMR 6, which is resistant to races 1 and 2 of P. fusca, suggesting that the fungus could belong to race 3, a race of P. fusca not yet reported in Spain. Race determination was carried out by inoculating the third true leaf of a set of differential melon genotypes that were maintained in a greenhouse. Symptoms and colonization observed on cvs. Rochet, PMR 45, PMR 6, and Edisto 47 indicated that the isolates belonged to race 3-5 of P. fusca. Fungal strains of races 1, 2, and 5 of P. fusca (all present in Spain) were used as controls. Pathotype designation was determined by inoculating different cucurbit genera and species (2). In addition to melon, the isolates were pathogenic on zucchini (Cucurbita pepo) cv. Diamant F1, but failed to infect cucumber (C. sativus) cv. Marketer and watermelon (Citrullus lanatus) cv. Sugar Baby; therefore, the isolates were pathotype BC (2). Races 1, 2, 4, and 5 of P. fusca have been previously reported in the area (1). The occurrence of race 3-5 represents another challenge in the management of cucurbit powdery mildew in Spain. References: (1) D. del Pino et al. Phytoparasitica 30:459, 2002. (2) E. Křístková et al. Sci. Hortic. 99:257, 2004. (3) A. Pérez-García et al. Mol. Plant Pathol. 10:153, 2009.

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Evaluation of Watermelon and Related Species for Resistance to Race 1W Powdery Mildew

Journal of the American Society for Horticultural Science ◽

10.21273/jashs.132.6.790 ◽

2007 ◽

Vol 132 (6) ◽

pp. 790-795 ◽

Cited By ~ 24

Author(s):

Angela R. Davis ◽

Amnon Levi ◽

Antonia Tetteh ◽

Todd Wehner ◽

Vincent Russo ◽

...

Keyword(s):

Powdery Mildew ◽

Citrullus Lanatus ◽

Plant Introduction ◽

The United States ◽

Common Disease ◽

Podosphaera Xanthii ◽

Sphaerotheca Fuliginea ◽

Wild Type ◽

Intermediate Resistance ◽

Cultivated Species

Powdery mildew [Podosphaera xanthii (Castagne) Braun & Shishkoff (syn. Sphaerotheca fuliginea auct. p.p.)] is now a common disease on watermelon [Citrullus lanatus (Thunb.) Matsum. & Nakai] in the United States. In this study, the entire available U.S. Plant Introduction collection of Citrullus Schrad. ex Eckl. & Zeyh. species was evaluated for resistance to P. xanthii race 1W. The collection consists of four Citrullus species and one Praecitrullus Pangalo species [C. lanatus var. citroides (L.H. Bailey) Mansf., C. colocynthis (L.) Schrad., C. rehmii De Winter, and P. fistulosus (Stocks) Pangalo]. Wild-type accessions tended to be more resistant more often than the cultivated species, C. lanatus var. lanatus. None were immune, eight of the 1573 accessions exhibited high levels of resistance, and another 86 demonstrated intermediate resistance. Stem and leaf disease severity were weakly correlated (r 2 = 0.64, P = 0.001). The majority of accessions having resistance were collected in Zimbabwe. Resistance was found in four species.

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First Report of Powdery Mildew of Tomato Caused by an Erysiphe sp. in Spain

Plant Disease ◽

10.1094/pdis.1998.82.5.592c ◽

1998 ◽

Vol 82 (5) ◽

pp. 592-592 ◽

Cited By ~ 8

Author(s):

L. Olalla ◽

J. A. Torés

Keyword(s):

Powdery Mildew ◽

Citrullus Lanatus ◽

Morphological Characteristics ◽

Fungal Growth ◽

Cucumis Sativus L ◽

The United Kingdom ◽

Summer Squash ◽

Infected Tomato ◽

Plant Pathol ◽

Cucumis Melo L

A new powdery mildew disease of tomato (Lycopersicum esculentum Mill.) was observed for the first time in several greenhouses in Almería (Spain) in March through June 1997. Fungal growth appeared as typical, white, powdery mildew colonies that were restricted to upper leaf surfaces. Initially, individual colonies were small and nearly circular in shape but later enlarged and coalesced to cover the whole leaf surface. Conidia were produced singly on unbranched, 3-cell conidiophores, and were cylindrical to ovate, ranging in size from 27.6 to 43.5 μm (mean = 35.3, SD = 3.8) in length and from 14.1 to 23.2 μm (mean = 19.0, SD = 2.2, n = 95) in width. No fibrosin bodies were observed. Germ tubes were formed from the ends of conidia. Appressoria from mycelia were single and moderately lobed. Conidiophores measured from 56.6 to 108.8 μm (mean = 84.8, SD = 14.2) with straight foot cells 24.7 to 55.1 μm (mean = 38.6, SD = 7.5) in length, and from 7.3 to 10.2 μm (mean = 8.0, SD = 1) in width. Morphological characteristics of this powdery mildew are similar to those previously given for the Erysiphe sp. described in the United Kingdom (1) and Greece (2). Cleistothecia were not found, so species identification was not made. Conidia from infected tomato leaves were shaken onto leaves of melon (Cucumis melo L. ‘Rochet’), cucumber (Cucumis sativus L. ‘Bellpuig’), summer squash (Cucurbita pepo L. ‘Black Beauty’), watermelon (Citrullus lanatus (Thunb.) Matsum. & Nakai ‘Sugar Baby’) and tomato cvs. Roma, Daniela, and Marmande. After 7 days the disease was observed on summer squashes, melons, and all tomato cultivars, but not on watermelons or cucumbers. References: (1) J. T. Fletcher et al. Plant Pathol. 37:594, 1988. (2) D. J. Vakalounakis and A. Papadakis. Plant Pathol. 41:372, 1992.

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Screening of Fungicide Resistance of Cucumber Powdery Mildew Pathogen, Sphaerotheca fusca in Gyeonggi Province

Research in Plant Disease ◽

10.5423/rpd.2008.14.2.095 ◽

2008 ◽

Vol 14 (2) ◽

pp. 95-101 ◽

Cited By ~ 6

Author(s):

Jin-Young Kim ◽

Sun-Sung Hong ◽

Jae-Wook Lim ◽

Kyeong-Yeol Park ◽

Hong-Gi Kim

Keyword(s):

Powdery Mildew ◽

Fungicide Resistance ◽

Cucumber Powdery Mildew ◽

Gyeonggi Province ◽

Powdery Mildew Pathogen ◽

Sphaerotheca Fusca

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First Report of Podosphaera xanthii Race 1W Causing Powdery Mildew of Watermelon in California

Plant Disease ◽

10.1094/pdis-05-13-0552-pdn ◽

2014 ◽

Vol 98 (1) ◽

pp. 158-158 ◽

Cited By ~ 7

Author(s):

J. Mercier ◽

M. J. Muscara ◽

A. R. Davis

Keyword(s):

Powdery Mildew ◽

Citrullus Lanatus ◽

Field Isolate ◽

Central Valley ◽

Spore Suspension ◽

Growth Chamber ◽

Tween 20 ◽

Podosphaera Xanthii ◽

Breeding Lines ◽

Field Plots

In September and October 2012, powdery mildew was detected on watermelon (Citrullus lanatus var. lanatus) plants of various breeding lines growing in field plots in Davis, California. Plants had partially necrotic leaves, yellowing to brown in color, with white surface mycelium and faint sporulation. No teleomorph was observed. Infected leaves were collected for examination and a spore suspension of the field isolate was made in water with 0.01% Tween 20 to spray inoculate watermelon seedlings of cultivar Dixie Lee with two true leaves. Plants were incubated in a growth chamber (22 to 26°C, 12-h photoperiod) for approximately 10 days, until sporulation was apparent. Microscopic observation of conidial chains showed that they had clearly crenate edges indicative of Podosphaera xanthii (4). To confirm the identity of the pathogen, we used Podosphaera-specific primers PFITS-F (5′-CCAACTCGTGCTGAGTGT-3′) and PF5.8-R (5′-TGTTGGTTTCTTTTCCTCCG-3′) to amplify and sequence the internal transcribed spacer regions of the nuclear rDNA. The 326-bp sequence had 98% homology to the GenBank sequence (accessions JQ340082.1 and AB774158.1) for P. xanthii. Infected ‘Dixie Lee’ leaves were used to make a spore suspension (approximately 5 × 104 conidia/ml) as described above to inoculate watermelon, melon, and squash seedlings (2 to 3 plants per cultivar) in a greenhouse. It caused severe symptoms on all watermelon plants cv. Charleston 76, P8, and Sugar Baby in the form of a powdery mildew with surface mycelium and chains of conidia, with leaves becoming gradually more necrotic and eventually dying, with the appearance of a melting down. Non-inoculated plants did not develop symptoms. The isolate also infected all squash plants ‘Zucchini Elite’ and melon powdery mildew differentials Iran H and ‘Védrantais.’ On these plants, the pathogen produced a powdery mildew (white surface mycelium with sporulation) but did not cause extensive necrosis. All other melon powdery mildew differentials (‘PMR5,’ ‘PMR45,’ WMR29, MR1, PI 124112, and PI 313970) did not develop any powdery mildew. A follow-up test in a growth chamber (22 to 26°C, 12-h photoperiod) with the same set of species and cultivars gave the same results. Based on these results, we conclude that this isolate belongs to race 1W (1,2). The presence of race 1W could have implications in disease management for this crop in the Central Valley of California as most cultivars are not resistant to it and the disease has been shown to cause severe damage in other states (1,3). References: (1) A. R. Davis et al. J. Am. Soc. Hort. Sci. 132:790, 2007. (2) J. D. McCreight. Amer. Soc. Hort. Sci. 131:59, 2006. (3) A. Y. Tetteh et al. Crop Sci. 50:933, 2010. (4) T. A. Zitter. Page 28 in: Compendium of Cucurbit Diseases, The American Phytopathological Society, St. Paul, MN, 1996.

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