Evaluation of U.S. Plant Introductions of Watermelon for Resistance to Powdery Mildew

Two hundred sixty-six Citrullus lanatus (Thumb.) Matsum. & Nakai accessions (Plant Introductions and named cultivars) were tested against a race 2 Sphaerotheca fuliginea (Schlechtend.: Fr.) Pollacci isolate to evaluate for resistance to powdery mildew disease. Growth room-grown seedlings were artificially inoculated with conidia from watermelon host leaves at 2-day intervals from the appearance of the first true leaf until test results data were taken, when the second true leaf was fully expanded. Plants were evaluated on a 1 to 9 scale of increasing disease severity. Disease indices (DIs) were calculated as weighted averages for each entry. All genotypes with resistant plants (powdery mildew rating 1 to 3) were reevaluated in a replicated test of 3 replications of 10 plants each. Disease indices were again calculated. Twenty-two plant introductions (PIs) and one named variety displayed intermediate resistance to powdery mildew in the replicated test with DIs ranging from 5.0 to 6.0.

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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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Sources of Resistance to Race 2WF Powdery Mildew in U.S. Watermelon Plant Introductions

HortScience ◽

10.21273/hortsci.46.10.1349 ◽

2011 ◽

Vol 46 (10) ◽

pp. 1349-1352 ◽

Cited By ~ 8

Author(s):

Haiying Zhang ◽

Shaogui Guo ◽

Guoyi Gong ◽

Yi Ren ◽

Angela R. Davis ◽

...

Keyword(s):

Powdery Mildew ◽

Citrullus Lanatus ◽

Podosphaera Xanthii ◽

Sphaerotheca Fuliginea ◽

Sources Of Resistance ◽

Foliar Disease ◽

Breeding For Resistance ◽

Plant Introductions

Powdery mildew of cucurbits, incited by Podosphaera xanthii (Castagne) Braun & Shishkoff (syn. Sphaerotheca fuliginea auct. p.p.), is an economically important foliar disease. which is now common in watermelon [Citrullus lanatus (Thunb.) Mastum. & Nakai]. This disease occurs in all watermelon-growing areas and can reduce yields by up to 30%. Finding and breeding for resistance to this disease is important to reduce dependence on fungicides and to use in combination with fungicides to limit the spread of fungicide-resistant P. xanthii. This is the first English report that race 2WF of P. xanthii can infect watermelon. It is the prevalent race of watermelon powdery mildew in Beijing.

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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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A New Source of Resistance to Anthracnose (Race 2) in Watermelon

HortScience ◽

10.21273/hortsci.29.2.111 ◽

1994 ◽

Vol 29 (2) ◽

pp. 111-112 ◽

Cited By ~ 7

Author(s):

G.E. Boyhan ◽

J.D. Norton ◽

B.R. Abrahams ◽

H.H. Wen

Keyword(s):

Disease Resistance ◽

Screening Test ◽

Citrullus Lanatus ◽

The Other ◽

Plant Introductions ◽

Susceptible Control ◽

Race 2

In an anthracnose [Colletotricum obiculare (Berk. & Mont.) Arx.] screening test of 76 plant introductions (PIs), commercial Chinese watermelons [Citrullus lanatus (Thunb.) Matsum. & Nakai], and `Crimson Sweet', PI 512385 had the highest disease resistance with a mean rating of 4.5 (1= resistant, 9 = susceptible). In a second test with PI 512385, which included material with previously reported resistance (PIs 270550,326515, 271775,271779,203551, 299379, and 189225), and `Crimson Sweet' (susceptible control), PI 512385 had significantly higher resistance than `Crimson Sweet' but was not significantly more resistant than the other PIs evaluated. PI 512385 had a mean rating of 2.2 in the second test.

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UPDATE ON POWDERY MILDEW RESISTANCE SCREENING IN WATERMELON

HortScience ◽

10.21273/hortsci.40.3.872c ◽

2005 ◽

Vol 40 (3) ◽

pp. 872c-872

Author(s):

Angela R. Davis ◽

Todd C. Wehner ◽

Amnon Levi ◽

Stephen R. King

Keyword(s):

United States ◽

South Carolina ◽

Powdery Mildew ◽

Resistance Genes ◽

Citrullus Lanatus ◽

Germplasm Collection ◽

The United States ◽

The Past ◽

Race 1 ◽

Race 2

Powdery mildew has been reported on Citrullus lanatus in Africa and Europe for the past 9 years, and in the United States for the past 6 years. During this time, it has occurred in the main watermelon production areas in the U.S. and has been documented in nine states (South Carolina, Georgia, Florida, Oklahoma, Texas, Maryland, New York, Arizona, and California). This is of great concern to the watermelon industry since powdery mildew is difficult to control and can have a severe impact on yield and fruit quality due to loss of photosynthetic area and sunscald. Finding resistant C. lanatus germplasm is needed for the development of commercial varieties containing this resistance. This report summarized the status of an ongoing project to screen the entire USDA–ARS C. lanatus germplasm collection. Currently, the collection is being screened for race 1 and race 2 Podosphaera xanthii (syn. Sphaerotheca fuliginea auct. p.p.), the causal agent of powdery mildew in C. lanatus in the United States. Resistance genes appear to exist for both races and the genes conferring resistance to race 1 appear to be different than race 2 resistance genes. Allelism tests are currently in process to determine the number of resistance genes present.

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Powdery Mildew Resistant Rootstocks that Impart Tolerance to Grafted Susceptible Watermelon Scion Seedlings

Plant Disease ◽

10.1094/pdis-09-17-1384-re ◽

2018 ◽

Vol 102 (7) ◽

pp. 1290-1298 ◽

Cited By ~ 7

Author(s):

Chandrasekar S. Kousik ◽

Mihir Mandal ◽

Richard Hassell

Keyword(s):

United States ◽

Powdery Mildew ◽

Disease Severity ◽

Citrullus Lanatus ◽

The United States ◽

Bottle Gourd ◽

Economic Losses ◽

Podosphaera Xanthii ◽

Lagenaria Siceraria ◽

True Leaf

Powdery mildew (PM) is a major foliar disease causing serious economic losses of cucurbit crops grown in the United States. The pathogen Podosphaera xanthii, which causes PM, is known to infect seedlings, stems, foliage, petioles, and fruit of cucurbit crops. In recent years, grafting watermelon on resistant rootstocks for managing soilborne diseases has been gaining popularity in the U.S.A. However, grafting for managing foliar diseases has not yet received adequate attention. Three greenhouse experiments were conducted during the summer months of 2012, 2013, and 2014 to determine if PM-resistant rootstocks could impart resistance to a susceptible watermelon scion. Susceptible watermelon scion ‘Mickey Lee’ seedlings were grafted onto 25 watermelon (Citrullus lanatus, C. amarus, C. mucosospermus) and four bottle gourd (Lagenaria siceraria) rootstocks. Grafted plants were inoculated with a 2 × 104 conidia ml−1 suspension of P. xanthii conidia and disease severity was rated 14 days after inoculation. Mickey Lee grafted on six PM-resistant watermelon rootstocks had significantly (P ≤ 0.05) lower PM severity on cotyledons, 2nd true leaf, and upper leaves (rating for 3rd to 7th or 8th true leaf) compared with Mickey Lee grafted on susceptible watermelon USVL677-PMS or bottle gourd USVL848-PMS rootstocks. However, some of the resistant watermelon rootstocks did not impart significant resistance to the scion. The resistant bottle gourd rootstocks USVL482-PMR and USVL351-PMR provided significantly greater levels of resistance, compared with many of the resistant watermelon rootstocks. Grafting watermelon on resistant rootstocks may help mitigate the effects of PM on susceptible scion seedlings.

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Melon-Powdery Mildew Interactions Reveal Variation in Melon Cultigens and Podosphaera xanthii Races 1 and 2

Journal of the American Society for Horticultural Science ◽

10.21273/jashs.131.1.59 ◽

2006 ◽

Vol 131 (1) ◽

pp. 59-65 ◽

Cited By ~ 40

Author(s):

James D. McCreight

Keyword(s):

Powdery Mildew ◽

Virulence Factors ◽

Cucumis Melo ◽

Podosphaera Xanthii ◽

Sphaerotheca Fuliginea ◽

Race 1 ◽

New Races ◽

Race 2 ◽

Serious Disease ◽

Greenhouse Tests

Powdery mildew is a serious disease of melon (Cucumis melo L.) worldwide. Twenty-two melon cultigens have been used to define 22 reported races of the pathogen Podosphaera xanthii (sect. Sphaerotheca) xanthii (Castag.) U. Braun & N. Shish. Comb. nov. [syn. Sphaerotheca fuliginea (Schlecht. ex Fr.) Poll.]. Discrepancies in the reactions of eight cultigens to populations of P. xanthii races 1 and 2 in California, Japan, and Spain revealed genetic differences among them that can be used to differentiate P. xanthii race 1 and 2 populations in these countries. Implicit in these results is the existence of previously unknown virulence factors in these populations of P. xanthii races 1 and 2 that permit designation of new races of P. xanthii on melon. Synthesis of these results with previous reports resulted in the identification of 28 putative races of P. xanthii on melon that include eight variants of race 1 and six variants of race 2. Six of the cultigens exhibited resistant blisters in response to heavy infection by P. xanthii in field and greenhouse tests.

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RESISTANCE OF WATERMELON (CITRULLUS LANATUS VAR. CITROIDES) GERMPLASM FOR RESISTANCE TO ROOT-KNOT NEMATODES

HortScience ◽

10.21273/hortsci.41.3.520a ◽

2006 ◽

Vol 41 (3) ◽

pp. 520A-520

Author(s):

J. A. Thies ◽

A. Levi

Keyword(s):

Citrullus Lanatus ◽

Nematode Resistance ◽

Root Knot Nematode ◽

Sources Of Resistance ◽

Root Knot Nematodes ◽

Nematode Reproduction ◽

Plant Introductions ◽

Race 1 ◽

Race 2 ◽

Moderate Resistance

Root-knot nematodes (Meloidogyne incognita, M. arenaria, and M. javanica) cause severe damage to watermelon and resistance has not been identified in any watermelon cultivar. In greenhouse tests, we evaluated 265 U.S. plant introductions (PIs) for nematode resistance (based on root galling and nematode reproduction), and identified 22 PIs of Citrullus lanatus var. citroides as moderately resistant to M. arenaria race 1. In subsequent tests, these 22 PIs exhibited low to moderate resistance to M. incognita race 3 and M. arenaria race 2. Three watermelon (C. lanatus var. lanatus) cultivars (Charleston Gray, Crimson Sweet, and Dixie Lee), three C. colocynthis PIs, and four C. lanatus var. citroides PIs, all previously shown to be susceptible to M. arenaria race 1, were susceptible to M. incognita race 3 and M. arenaria race 2. The C. lanatus var. citroides PIs that are most resistant to both M. incognita and M. arenaria should be useful sources of resistance for developing root-knot nematode resistant watermelon cultivars.

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Identification of Resistance to Fusarium oxysporum f. sp. niveum Race 2 in Citrullus lanatus var. citroides Plant Introductions

HortScience ◽

10.21273/hortsci.47.3.334 ◽

2012 ◽

Vol 47 (3) ◽

pp. 334-338 ◽

Cited By ~ 34

Author(s):

W. Patrick Wechter ◽

Chandrasekar Kousik ◽

Melanie McMillan ◽

Amnon Levi

Keyword(s):

North America ◽

Fusarium Oxysporum ◽

Fusarium Wilt ◽

Citrullus Lanatus ◽

Plant Introductions ◽

Major Disease ◽

Seedling Inoculation ◽

The World ◽

Potential Sources ◽

Race 2

Fusarium wilt (FW) is a major disease of watermelon in North America and around the world. Control of this disease is difficult because the soilborne causal agent Fusarium oxysporum f. sp. niveum (Fon) produces chlamydospores that remain infectious in the soil for many years. Although various levels of resistance to Fon Races 0 and 1 exist in watermelon cultivars, no resistance to Race 2 or 3 has been reported. In this study, we used seed and seedling inoculation procedures to screen 110 U.S. PIs of wild watermelon (Citrullus lanatus var. citroides) for resistance to Race 2 FW. Of these 110 accessions, 15 showed significantly higher resistance to Fon Race 2 than that found in the watermelon cultivars Sugar Baby or Charleston Grey as well as in the C. lanatus var. citroides PI 296341 that was reported to contain resistance to FW. PI 271769, another C. lanatus var. citroides that was previously reported as containing resistance to FW, is among the 15 resistant accessions described here. These 15 accessions are potential sources for resistance to Race 2 FW in watermelon breeding.

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UPDATE ON POWDERY MILDEW RESISTANCE SCREENING IN WATERMELON

HortScience ◽

10.21273/hortsci.40.3.871a ◽

2005 ◽

Vol 40 (3) ◽

pp. 871a-871

Author(s):

Angela R. Davis ◽

Todd C. Wehner ◽

Amnon Levi ◽

Stephen R. King

Keyword(s):

United States ◽

South Carolina ◽

Powdery Mildew ◽

Resistance Genes ◽

Citrullus Lanatus ◽

Germplasm Collection ◽

The United States ◽

The Past ◽

Race 1 ◽

Race 2

Powdery mildew has been reported on Citrullus lanatus in Africa and Europe for the past nine years, and in the United States for the past 6 years. During this time, it has occurred in the main watermelon production areas in the U.S. and has been documented in nine states (South Carolina, Georgia, Florida, Oklahoma, Texas, Maryland, New York, Arizona, and California). This is of great concern to the watermelon industry since powdery mildew is difficult to control and can have a severe impact on yield and fruit quality due to loss of photosynthetic area and sunscald. Finding resistant C. lanatus germplasm is needed for the development of commercial varieties containing this resistance. This report summarized the status of an ongoing project to screen the entire USDA–ARS C. lanatus germplasm collection. Currently, the collection is being screened for race 1 and race 2 Podosphaera xanthii (syn. Sphaerotheca fuliginea auct. p.p.), the causal agent of powdery mildew in C. lanatus in the United States. Resistance genes appear to exist for both races and the genes conferring resistance to race 1 appear to be different than race 2 resistance genes. Allelism tests are currently in process to determine the number of resistance genes present.

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