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Sunflower downy mildew is a disease of high global economic impact as well as a causal agent that is extremely difficult to eradicate. During the past decades, several approaches for the determination of Plasmopara halstedii (Ph) races have been used worldwide and are discussed in this review. Procedures of isolation, cultivation and maintenance of Ph isolates, as well as the screening of sunflower for resistance, are also critically reviewed. The predominant, globally used resistance screening protocol is a 'whole seedling immersion' inoculation. 'Soil drench' inoculation allows more precise control of the number of Ph zoosporangia applied to a single sunflower seedling. A detached leaf assay has been described, but it has been used mainly for Ph subcultivation and fungicide tests. For race determination, a differential set consisting of nine sunflower genotypes has been used since 1988, coupled with a numerical triplet code for virulence phenotyping of Ph. The increasing variability in global Ph populations has demonstrated the inadequacy of the current set of differentials, and several researchers have proposed additional public lines as new differentials. Furthermore, bulk isolates may show different results in repeated tests, as Ph may contain genetically distinct zoospores within a single zoosporangium. For precise race determination, single zoosporangia or single zoospore isolates are advisable. However, due to low success of isolation, approximately 1-2%, this method cannot be applied in routine Ph race screening. Methods surveyed in this review have a broad spectrum of applications, including taxonomic studies. [ABSTRACT FROM AUTHOR]

Sunflower downy mildew (SDM) caused by Plasmopara halstedii , is a major disease of sunflower. Eleven resistance genes have been identified, but allelic relationships among these genes are not clear. This study examined the inheritance and allelic relationships of genes conferring resistance to SDM races 1, 2 and 3 (virulence phenotypes 100, 300 and 700, respectively) and confirmed a twelfth resistance gene. Three USDA Plant Introductions, AMES 3235, PI 497250, and PI 497938, and three released lines, RHA 266, RHA 274 and DM-2 were studied. RHA 266 has only the Pl 1 gene for race 1 resistance. Digenic inheritance of resistance was found in AMES 3235, PI 497250, and RHA 274. These lines have the Pl 1 and Pl 12 genes, conferring resistance to race 1, and the Pl 2 and Pl 11 genes, conferring resistance to race 2. DM-2 and PI 497938 have Pl 12 (but not Pl 1) for resistance to race 1, the Pl 12 gene (but not the Pl 2) for resistance to race 2, and Pl 5 for resistance to race 3. These resistance genes will serve as a foundation for future gene designations and genetic diversity studies of resistance to SDM. [ABSTRACT FROM AUTHOR]

Collections of the causal agent of sunflower downy mildew (Plasmopara balstedii) (PH) from several European and North and South American countries were used to inoculate a series of sunflower inbred lines to differentiate races. Race 3 was identified from Argentina; race 4 from France, Hungary, and Bulgaria; race 6 from Canada and France; and race 7 from Argentina. This is the first report of race 3 in South America and of race 4 in Europe, and is the first identification of races 6 and 7. Reactions of USDA lines RHA-274, RHA-325, and DM-2 differentiate races 2, 6, and 7, with RHA-274 resistant to all three. Thirty-three commercial hybrids from 11 countries were tested; 70 % were resistant to race 2, only 27 % had resistance to race 6, and none were resistant to race 4. Surveys to determine the relative proportions of the various races within each country are needed to assess their potential impact. The USDA lines HA-335, HA-336, HA-337, HA-338, HA- 339, RHA-340, HA-R4, and HA-R5 are resistant to all seven mildew races and could be utilized for the production of PH resistant hybrids. For die short term, it appears that seed treatment with metalaxyl may be die most effective control. [ABSTRACT FROM AUTHOR]

A total of 82 isolates of Plasmopara halsredii, collected from all production areas of Hungary between 1976 and 1993, were assessed for their virulence pattern on a standard set of sunflower differentials under glasshouse conditions. The isolates were classified into six pathogenic races each representing a particular virulence phenotype. From 1976 until 1988 all the isolates were found to be virulent only on sunflowers possessing no known resistance genes, thus classified as race I. There was an apparent shift in the virulence of the P. halstedii population collected after 1988. Six races (1 2, 3. 4. 8 and 9) were identified among the 45 samples collected between 1989 and 1993, with races 1 and 3 predominant, at a frequency of 35% each. While the increase in race virulence is undoubtedly due to selection imposed by resistant hybrids, the origin of the new races is unknown. Whether new races have arisen from the indigenous P. halstedii population, or whether they have been imported from abroad, can only be reliably determined by DNA techniques, such as fingerprinting. [ABSTRACT FROM AUTHOR]

Resistance to the prevailing races of sunflower rust, Puccinia helianthi Schw., is lacking in the commercial hybrids (Helianthus annuus L.). The objective of this study was to identify new sources of resistance to the four North American rust races in wild Helianthus species, and to determine their mode of inheritance. Seventy-eight accessions of H. annuus L., H. argophyllus Torrey and Gray, and H. petiolaris Nutt. were evaluated in the greenhouse. Resistance to races 1, 2, 3, and 4 was observed in 25, 28, 15, and 26 % of the plants, respectively, and 10% of the plants were resistant to all four races. Seven accessions that had a high percentage of resistant plants to all the four races were selected and one resistant plant from each accession was crossed with susceptible inbred line HA89. Three to four F[SUB1] plants resistant to all four races from each cross were backcrossed with HA89. F[SUB1] plants from PI-413118 × HA89 and PI 413175 × HA89 were resistant to all four races. The PI 413023 × HA89 F[SUB1] plants were 100 % resistant to races 3 and 4 and segregated in a 3 1 resistant (R) to susceptible (S) ratio to races 1 and 2. The other four F[SUB1] combinations segregated 3R : 1S ratios to all four races. BC[SUB1] F[SUB1] progenies revealed that plants from PI 413048, PI 413037, PI 413038, and PI 413171 used in the crosses possessed two dominant genes in heterozygous condition for resistance to each of the four races, whereas plants from PI 413023 possessed two dominant genes in heterozygous condition for resistance to each of races 1 and 2, and one dominant resistance gene in homozygous condition for each of races 3 and 4. Plants from PI 413118 and PI 413175 carried a single dominant gene in homozygous condition for resistance against each of the four races. [ABSTRACT FROM AUTHOR]

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The article presents the registration of two maintainer and three restorer Sclerotinia-tolerant oilseed sunflower germplasms. The two maintainers include HA 451 and HA 452. Two maintainer and three restorer oilseed sunflower germplasms were developed and released by the Agricultural Research Service of the U.S. Department of Agriculture and the North Dakota Agriculture Experiment Station. These germplasms were selected for their tolerance to Sclerotinia head and stalk rot which is a major sunflower disease. They also provide diversity for agronomic characteristics and oil quality. These germplasms are available for use by industry and public researchers to create hybrids, parental lines, or germplasms with increased tolerance to Sclerotinia head and stalk rot.

The article presents the registration of the Three Virus Resistant Sunflower Genetic Stocks, developed and released by the U.S. Department of Agriculture-Agricultural Research Service and the North Dakota Agricultural Experiment Station.

The article reports on the registration of HA 444, HA 445 and HA 446, maintainer and RHA 447, restorer on high oleic oilseed sunflower germplasms developed by the United States Department of Agriculture-ARD, Fargo and the North Dakota Agricultural Experiment Station in North Dakota. These germplasms have a high-oleic fatty acid concentration that is intended to be used by the sunflower industry and the public researchers. HA 44 is derived from F6 to F7 maintainer line which is selected from the cross HA 434/HA 406. The pedigree breeding method used to develop HA 444, HA 455, and HA 446 are the same. While RHA 447 is derived from F7 to F8 restorer line which is selected from the cross RHA 377/ RHA 348.

The article reports on the registration of HA 442, imidazolinone herbicide-resistant maintainer and RHA 443, fertility restorer of the oilseed sunflower germplasms developed by United States Department of Agriculture-ARD, Fargo and the North Dakota Agricultural Experiment Station in North Dakota. These germplasms were developed as the resistant to the imidazoline herbicide imazamox intended to be used by the sunflower industry and the public researchers. The HA 442 is derived from F6 to F7 maintainer lines which are selected from the cross HA 425/87CAEB//HA434/HA 412 with a high oleic fatty acid concentration. While RHA 443 was derived from F6 to F7 restorer line which is selected for the cross RHA 426/RHA 419//RHA 377/AS 4379.

The article reports on the registration of RHA 439, RHA 440, restorer and HA 441, sclerotinia tolerant oilseed sunflower germplasms developed by the United State Department of Agriculture-ARS, Fargo and North Dakota Agricultural Experiment Station in North Dakota. These germplasms are used to create hybrids and parental lines with improved Sclerotinia intended for the use of the sunflower industry and public researchers. The RHA 439 was derived from F7 to F8 restorer line selected from the cross RHA 377/AS 3211. The lines of RHA 439 and RHA 440 was selected by evaluating the testcross hybrids that were artificially inoculated under the mist irrigation. While 441 was derived from F7 to F8 maintainer lines that were selected form the cross of HA 412/SD.

The article presents the registration of three maintainer oilseed sunflower germplasms. The three maintainers include HA 456, HA 457 and HA 412 HO. The germplasms were developed and released by the Agricultural Research Service of the U.S. Department of Agriculture, and the North Dakota Agricultural Experiment Station. These high-oleic germplasms are available for use by industry and public researchers to create hybrid, parental lines, or germplasms with a midoleic or high-oleic fatty acid concentration in the oil.

The article presents the registration of a sunflower germplasm resistant to rust, downy mildew, and virus, developed and released by the U.S. Department of Agriculture-Agricultural Research Service and the North Dakota Agricultural Experiment Station.