New Races of the Sunflower Downy Mildew Pathogen (Plasmopara halstedii) in Europe and North and South America

Abstract

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 the short term, it appears that seed treatment with metalaxyl may be the most effective control.

Changes in sunflower breeding over the last fifty years

“…In Europe, breeding programmes led to all widely grown varieties carrying the resistance genes Pl1 and Pl2 and there followed almost 20 years (until 1988) with no problem from this disease. However in the USA, problems appeared more quickly, with new races from 1980 (Gulya et al, 1991), which could be considered to be logical co-evolution. Chemical control (by metalaxyl seed treatment) was only of very temporary use, the parasite soon showed resistance (Albourie et al, 1998).…”

First Report of Plasmopara halstedii New Races 705 and 715 on sunflower from the Czech Republic - Short Communication

“…Recently, several modifications have been made in the third triplet, e.g. at the position of D8 the USDA's line HA-R5 (Gulya et al 1991) has been replaced by INRA's selection QHP-1 (Tourvieille de Labrouhe et al 2000Labrouhe et al , 2012 and newly by a further reselection named QHP-2 (Pierre Desray, INRA, pers. comm.).…”

“…The existence of P. halstedii races was confirmed in the 1970s when a new race was detected in the USA which was able to overcome sunflower resistance gene Pl 1 , which ensured resistance to the European race (Zimmer 1974). Changes in virulence of P. halstedii in 1980s led to the introduction of a new nomenclature system based on the reaction of nine sunflower differential lines bearing various Pl resistance genes and race identification by a triplet code (Sackston et al 1990;Gulya et al 1991;Gulya 1995 18 races had been reported from Europe (Virányi et al 2015) and 20 races from America (Gulya 2007). Over the past 7 years this number increased to a total of 24 races in Europe and 36 in America.…”

Identification of Downy Mildew Resistance Loci in Sunflower Germplasm

“…The first report of Pl 2 was published by Zimmer and Kinman (1972) and Fick and Zimmer (1974), who showed that both HA61 and RHA274 harboured a single dominant gene Pl 2 giving resistance to race 300. Based on the gene for gene hypothesis, Gulya et al (1991), suggested that RHA274 carried not only Pl 2 , giving resistance to race 300 but also Pl 9, giving resistance to race 310. However, they did not study genetic segregation patterns for the two genes.…”