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

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.

Download Full-text

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.

Download Full-text

Poor Control of Cucurbit Powdery Mildew Associated with First Detection of Resistance to Cyflufenamid in the Causal Agent, Podosphaera xanthii, in the United States

Plant Health Progress ◽

10.1094/php-06-18-0029-br ◽

2018 ◽

Vol 19 (3) ◽

pp. 222-223 ◽

Cited By ~ 1

Author(s):

Margaret T. McGrath ◽

Zachary F. Sexton

Keyword(s):

United States ◽

Powdery Mildew ◽

High Resistance ◽

The United States ◽

Management Tool ◽

Common Disease ◽

Podosphaera Xanthii ◽

Resistance Risk ◽

Action Committee ◽

Group Knowledge

This report is about the first known occurrence of resistance to cyflufenamid, a Fungicide Resistance Action Committee (FRAC) code U6 fungicide, in Podosphaera xanthii in the United States. This fungus causes powdery mildew in cucurbit crops, the most common disease of this important crop group. Knowledge about resistance is important for guiding fungicide programs. Mobile, targeted fungicides, which have moderate or high resistance risk, are the most effective management tool for this disease. The pathogen is a documented high resistance risk organism having already developed resistance to fungicides in FRAC groups 1, 3, 7, 11, and 13.

Download Full-text

Corn and Cucurbits from Wetherill Mesa

Memoirs of the Society for American Archaeology ◽

10.1017/s0081130000004470 ◽

1965 ◽

Vol 19 ◽

pp. 136-152 ◽

Cited By ~ 5

Author(s):

Hugh C. Cutler ◽

Winton Meyer

Keyword(s):

United States ◽

Cucurbita Pepo ◽

The United States ◽

Bottle Gourd ◽

Lagenaria Siceraria ◽

Plant Parts ◽

Northern Arizona ◽

Growing Seasons ◽

Slow Development ◽

Agricultural Areas

AbstractMost corn from the Mesa Verde area belongs to a complex derived from hybridization of a small-cobbed flint-pop corn with an 8-rowed flour corn. This cross produced 12- to 14-rowed flint and flour corn (the typical Basketmaker corn) and the variable Pima-Papago corn. After Pueblo I, probably late Pueblo II, there was an increase in the number of 8-rowed cobs and a decrease in 12- to 14-rowed cobs. The corn is similar to collections from sites of comparable age excavated in northern Arizona near Navajo Mountain. The uniformity and the slow development of corn types probably reflect peripheral conditions, especially adaptation to short growing seasons and limited cultural interchange.Practically all of the squash was Cucurbita pepo, the species which spread over all agricultural areas of the United States. There were a few specimens of Cucurbita mixta and of the bottle gourd, Lagenaria siceraria. Some rinds of the two species of Cucurbita gave evidence of their use for scrapers and containers, uses to which the bottle gourd is put almost exclusively in sites to the south. The rarity of the bottle gourd and the absence of seeds and plant parts of cotton suggest that these plants were rarely, if ever, grown in the region.

Download Full-text

First Report of Resistance to Quinoxyfen in Podosphaera xanthii, Causal Agent of Cucurbit Powdery Mildew, in the United States

Plant Health Progress ◽

10.1094/php-03-17-0018-br ◽

2017 ◽

Vol 18 (2) ◽

pp. 94-94 ◽

Cited By ~ 3

Author(s):

M. T. McGrath

Keyword(s):

United States ◽

Powdery Mildew ◽

High Resistance ◽

The United States ◽

Management Tool ◽

Common Disease ◽

Podosphaera Xanthii ◽

Effective Management ◽

Group 13 ◽

Resistance Risk

This brief reports the first known occurrence of resistance to quinoxyfen, a quinoline (FRAC Group 13) fungicide, in Podosphaera xanthii in the United States. This fungus causes powdery mildew in cucurbit crops, the most common disease of this important crop group. Mobile, targeted fungicides, which have moderate or high resistance risk, are the most effective management tool for this disease. The pathogen is a documented high resistance-risk organism, having already developed resistance to fungicides in FRAC Groups 1, 3, 7, and 11.

Download Full-text

First Detection of Boscalid Resistance in Podosphaera xanthii in the United States Associated With Failure to Control Cucurbit Powdery Mildew in New York and New Jersey in 2009

Plant Health Progress ◽

10.1094/php-03-17-0014-br ◽

2017 ◽

Vol 18 (2) ◽

pp. 93-93 ◽

Cited By ~ 2

Author(s):

M. T. McGrath ◽

C. A. Wyenandt

Keyword(s):

United States ◽

New York ◽

Powdery Mildew ◽

Resistance Management ◽

The United States ◽

Management Tool ◽

Podosphaera Xanthii ◽

Resistance Risk ◽

Causal Pathogen ◽

Succinate Dehydrogenase Inhibitor

The most effective management tool for powdery mildew on cucurbit crops is mobile, targeted fungicides having a moderate or high resistance risk and the causal pathogen has proven to be a high-risk organism. Information about occurrence of resistance to a new chemical group and impact on resistance management is important for guiding fungicide programs and contributing to scientific knowledge about resistance development. This brief reports the first known occurrence of resistance to a succinate dehydrogenase inhibitor fungicide in Podosphaera xanthii in the United States.

Download Full-text

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.

Download Full-text

First Report of the Cucurbit Powdery Mildew Fungus (Podosphaera xanthii) Resistant to Strobilurin Fungicides in the United States

Plant Disease ◽

10.1094/pdis.2003.87.8.1007a ◽

2003 ◽

Vol 87 (8) ◽

pp. 1007-1007 ◽

Cited By ~ 18

Author(s):

M. T. McGrath ◽

N. Shishkoff

Keyword(s):

United States ◽

New York ◽

Powdery Mildew ◽

The United States ◽

Podosphaera Xanthii ◽

Commercial Use ◽

Strobilurin Fungicides ◽

Research Fields ◽

Cucurbit Powdery Mildew ◽

Dmi Resistance

Resistance to strobilurin fungicides was documented in isolates collected from three fungicide efficacy experiments conducted in research fields in Georgia (GA), North Carolina (NC), and New York (NY). In these fields in 2002, strobilurins (fungicide group 11, quinone outside inhibitors [QoI]) when used alone on a 7-day schedule (use pattern not labeled) did not effectively control cucurbit powdery mildew. Strobilurin efficacy declined dramatically after the second application in New York (3). Efficacy also was reduced in commercial fields in Kentucky and research fields in Arizona, California, Kentucky, Illinois, Michigan, and Virginia in 2002 where strobilurins were used predominantly or exclusively. Isolates were collected on 22 July and 8 and 17 October after the last of four, five, and five applications of strobilurin (trifloxystrobin formulated as Flint or azoxystrobin formulated as Quadris) in experiments conducted by J. D. Moore in Chula, GA, M. McGrath in Riverhead, NY, and G. J. Holmes in Clayton, NC, respectively. A leaf-disk bioassay was used to determine fungicide sensitivity (2). Strobilurin sensitivity was determined using trifloxystrobin at 0, 0.5, 5, 50, and 100 μg/ml. Four of nine NY isolates, 19 of 21 GA isolates, and 13 of 15 NC isolates were resistant to strobilurins (grew well on disks treated with trifloxystrobin at 100 μg/ml). The geometric mean of the azoxystrobin baseline was 0.258 μg/ml for Podosphaera xanthii isolates collected in 1998 and 1999 in North America (4). Poor control with strobilurins under field conditions was associated with reduced sensitivity in vitro. Strobilurin sensitivity appeared to be qualitative as reported elsewhere (1). Two sensitive and three resistant isolates responded similarly when tested in another laboratory using kresoxim-methyl and pyraclostrobin (H. Ypema, personal communication). These findings and experiences elsewhere with QoI-resistant P. xanthii indicate that cross-resistance probably extends among multiple QoI's (1). Strobilurins have been available for commercial use in the United States since 1998, when azoxystrobin received Section 18 registration in some states. Federal registration was granted in March 1999. Strobilurin resistance was detected after 2 years of commercial use elsewhere in the world (1). All isolates tested in the current study were from research fields where selection pressure for resistance could have been higher than in commercial fields where strobilurins are used with demethylation inhibitors (DMIs; fungicide group 3) and contact fungicides in alternation or tank mixtures to prevent or delay resistance development. Resistance in commercial fields will reduce the utility of strobilurins, including those not yet registered, and eliminate an important tool for managing DMI resistance. Strobilurins and DMIs are the only systemic fungicides registered for cucurbit powdery mildew in the United States. Managing DMI resistance may be challenged by multiresistant strains. Strobilurin-resistant isolates also exhibited reduced sensitivity to DMIs, tolerating triadimefon at 50 to 100 μg/ml (2). One suggestion to improve resistance management is to apply a contact fungicide with strobilurins as well as DMIs. References: (1) H. Ishii et al. Phytopathology 91:1166, 2001. (2) M. T. McGrath et al. Plant Dis. 80:697, 1996. (3) M. T. McGrath and N. Shishkoff. Fungic. Nematic. Tests. (In press). (4) G. Olaya et al. Phytopathology (Abstr.) 90 (suppl):S57, 2000.

Download Full-text

Genotyping-by-Sequencing for Analysis of the Genetic Variation of Podosphaera xanthii, Incitant of Cucurbit Powdery Mildew

Plant Disease ◽

10.1094/pdis-03-19-0513-re ◽

2020 ◽

Vol 104 (3) ◽

pp. 951-957 ◽

Cited By ~ 2

Author(s):

Y. Xiang ◽

A. N. Miller ◽

M. McGrath ◽

M. Babadoost

Keyword(s):

United States ◽

New York ◽

Powdery Mildew ◽

Cucumis Melo ◽

Cucurbita Pepo ◽

Genotyping By Sequencing ◽

The United States ◽

Podosphaera Xanthii ◽

Internal Transcribed Spacer Region ◽

Significant Difference

This research was conducted to identify species causing powdery mildew on cucurbits and to determine genetic variations among isolates of the pathogen. We collected 109 isolates from six cucurbit species hosts (Cucumis melo, Cucumis sativus, Cucurbita maxima, Cucurbita moschata, Cucurbita pepo, and Lagenaria siceraria) in California, Illinois, Indiana, Michigan, New York, Texas, Washington, and Wisconsin in the United States and in Italy. By sequencing the internal transcribed spacer region of the nuclear rDNA of these 109 isolates, Podosphaera xanthii was found as the only species causing powdery mildew on cucurbits in the United States. Genotyping-by-sequencing was applied to these 109 isolates to investigate their genetic diversity, which showed a trend of isolates clustering from New York and Italy. In addition, the virulence of 36 isolates was compared and a significant difference (P < 0.0001) was found among them. Furthermore, results of the virulence tests of 28 isolates from Illinois showed significant effects of collection years, hosts, and locations on the virulence of the isolates.

Download Full-text

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.

Download Full-text