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United States Department of Agriculture

Agricultural Research Service

International Agriculture
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International Projects on Cucurbit Diseases

Cucurbits are important economic crops in many parts of the world.  In the last 25 years, there have been changes in cultural methods which include introduction of hybrid cultivars, transplanting, plastic mulch, drip irrigation, and increased plant density without adequate rotation.  Some of these changes have likely contributed to an increase in the number and intensity of soil-borne diseases that cause significant economic losses.

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ARS and Osu host Governor from the Philippines

Eisenhower Fellows recipient, Governor Miguel Dominquez, of Sarangani Province, the Philippines, visited the USDA/ARS South Central Agricultural Research Laboratory and Wes Watkins Agricultural and Extension Center Lane OK. The Governor met with location staff and with stakeholders. These types of interactions help to better the understanding of peoples of different cultures and to foster agriculture on an international scale.

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Weed control in biofuel feedstock crops

The South Central Agricultural Research Laboratory (SCARL) conducts research on the production of biofuel feedstock crops.  Dr. Charles Webber, an agronomist located at SCARL, is accumulating information on production systems with an emphasis on weed control in biofuel feedstock crops.  Weed control is one of the most persistent, and yield limiting, problems in agriculture.  Webber has conducted research with the biodiesel feedstock crops soybean and castor bean, and the bioethanol feedstock crops corn, sweet sorghum, kenaf and sunn hemp, the last two have applicability for production of cellulosic ethanol.  Requests for information concerning biofuel crops have been received, and responded to, from Argentina, Australia, Azerbaijan, Belize, Canada, China, Costa Rica, Ecuador, Ghana, Great Britain, Israel, Italy, Japan, Mexico, Philippines, Romania, Saudi Arabia, South Korea, and Vietnam.  As a result of these interactions consortiums have been developed and the potential for new ventures in agricultural enterprises exist. Sharing of this type of information helps in the development of sustainability of these crops.

Dr. Charles Webber, III, USDA/ARS South Central Agricultural Research Laboratory, 911 Hwy. 3W, Lane, OK email:

From Turkmenistan, finding genetic diversity to improve melons.

The National Plant Germplasm System (NPGS) website tells why germplasm collection and conservation of genetic material is important: “The world's food supply is based on intensive agriculture, which relies on genetic uniformity.  But this uniformity increases crop vulnerability to pests and stresses.”

Genetic diversity is needed to develop new varieties which can resist pests, diseases, and environmental stresses.  The NPGS aids scientists in: acquiring, preserving, evaluating, documenting, and distributing crop germplasm.

A trip to Turkmenistan was made possible with financial support of the USDA, ARS, Germplasm Resources Laboratory.  In country organization was made possible by Andrew Paul and Nafisa Yuldasheva, Public Affairs Section, Embassy of the United States of America, Ashgabat, Turkmenistan, and Charyguly Ovezov of the Turkmen Food Industry Association.  Jumagul Saypullayeva provided translation.

Turkmenistan has a tradition of melon (Cucumis melo L.) and watermelon [Citrullus lanatus (Thunb.) Matsum. & Nakai] production, but land races and old varieties are in danger of genetic erosion.  Many farmers have stopped growing older watermelon varieties in favor of imported open-pollinated or recently developed hybrids.

The need to collect seed from this region to preserve melon diversity was previously documented, so the USDA, NPGS funded an expedition in summer 2008 with the government of Turkmenistan and the collaboration of the Turkmen National Institute of Desert, Flora and Fauna (TNIDFF).  Seed were collected from 14 sites across the five regions of Turkmenistan. The party was comprised of James McCreight (USDA-ARS, U.S. Agricultural Research Station, Salinas, CA), Todd Wehner (Department of Horticultural Science, North Carolina State University, Raleigh, NC), Ejebay Kokanova (Laboratory of Invertebrate Animals, TNIDFF, Ashgabat, Turkmenistan), and Angela Davis (USDA-ARS, South Central Agricultural Research Laboratory, Lane, OK).

The team met with nationally known farmers and melon and watermelon selectionists, sharing seed and information on growing practices and pest control.  All seed lines were divided into two parts, one was retained by the TNIDFF; the other turned over to the NPGS, plant introductions stations at Ames, Iowa (melon) and Griffin, Georgia (watermelon).  Seed will become openly available when each line has been amplified.

Seeds of 74 melon accessions and 22 watermelon accessions representing old and modern varieties (land races and selections) were obtained from farmers, wholesale fruit markets, and seed dealers.

Opportunities for collaborative disease and insect control research were identified. Melons appeared to be more affected by insect pests and diseases than watermelon. Silver leaf whitefly and melon aphid are widespread, and serious threats warrant development of effective control programs.

There is potential for acquisition of additional accessions of melon and watermelon from Durdy Nepes (Sayrahs Etrap, Akhal), Omurguly Ahmedov (Sayat Etrap, Lebap), and Maral Orazbayeva (Gudabag Etrap, Dashoguz), contributors of germplasm.

Dr. Angela Davis (email:, USDA/ARS, South Central Agricultural Research Laboratory, 911 Hwy. 3W, Lane, OK

International effort to identify cucurbit powdery mildew resistance genes

Background on powdery mildew on watermelon

Since about 2000 powdery mildew has become an emerging disease affecting watermelon (Citrullus lanatus var. lanatus) in the main production areas in the United States.  This disease is of great concern to the watermelon industry since powdery mildew is difficult to control and can severely impact yield and fruit quality.  Although new to watermelon this disease affects other cucurbit crops world wide.  Breeding for powdery mildew resistance in melon (Cucumis melo) and cucumber (Cucumis sativus L.) started in the 1930’s with considerable success.

Two fungi cause powdery mildew in cucurbits: Golovinomyces cichoracearum (formerly Erysiphe cichoracearum DC) and Podosphaera xanthii (syn. Sphaerotheca fuliginea auct. p.p.).  P. xanthii is the most commercially destructive of the two and has been identified as the causal agent of watermelon powdery mildew in the United States.  Two pathogenically distinct races, race 1 and race 2, have been identified affecting watermelon.

Application of fungicides adds cost to growers, and continued research on powdery mildew control measures, and resistant cultivars, are needed to maintain sustainability of watermelon production.

New Agricultural Products for Sustainable Farming and Industry

A fellowship from the Organization for Economic Co-operation and Development was awarded to Dr. Angela Davis to support a 14 week stay at Dr. Michelle Pitrat’s laboratory at the Institut National de la Recherche Agronomique, Genetique et Amelioration des Fruits et Legumes, BP 94, 84143 Montfavet cedex, France, to begin developing tools to isolate resistance genes to powdery mildew, and to speed incorporation of resistance genes into watermelon cultivars.

Watermelon populations which segregate for powdery mildew resistance were studied to map resistance genes and to develop molecular marker assisted screening tools.  These tools can be used by breeders to rapidly screen watermelon breeding lines and their offspring for powdery mildew resistance.

The techniques performed during the fellowship included: DNA isolation and quantification, AFLP analysis to fine map the powdery mildew resistance gene to linkage group XII, single P. xanthii spore isolation, in vitro culture of powdery mildew (both P. xanthii, and G. cichoracearum), and leaf disk assays to test for powdery mildew resistance in melon.

The theories examined included how to: produce recombinant inbred lines to produce populations for mapping resistance gene statistics on disease resistance ratings, develop marker assisted selection, sequence mapped resistance gene regions, isolate specific genes in that area, and develop techniques to map resistance genes to linkage groups, CAPS, QTL, and RFLP.

If successful these experiments will yield a rapid method to screen for powdery mildew resistance in watermelon and possibly other cucurbits.  This can result in decreased fungicide use in these crops without decreases in yield due to powdery mildew.  The fellowship was the start of collaboration between Dr. Michelle Pitrat’s laboratory and the USDA/ARS South Central Agricultural Research Laboratory to further examine resistance to powdery mildew in watermelon.

Dr. Angela Davis (email:, USDA/ARS, South Central Agricultural Research Laboratory, 911 Hwy. 3W, Lane, OK

Last Modified: 6/11/2009
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