The first report of Plasmopara halstedii race 337 in the Russian Federation

Sunflower downy mildew caused by Plasmopara halstedii (Farl.) Berl. et de Toni is a destructive and widespread disease. More than 50 races of P. halstedii have been recorded worldwide. In 2020, in the Russian Federation (Zernogradsky district, Rostov region), a globally new race 337 was identified for the first time. The pathogen was identified on the plants of a foreign sunflower hybrid bearing the resistance gene Pl₆. According to the five-digit racial nomenclature, its virulence profile was determined as 337 53. It is the first P. halstedii race recorded in the Russian Federation that simultaneously infects all differential lines of the 3^rd triplet, i.e., HA-R4, HA-R5 and HA-335. The sunflower lines RHA-274, 803-1, PSC8, RHA-419 and RHA-340 were resistant to it. All the collected isolates of the new race were susceptible to the fungicide mefenoxam.

SUNFLOWER: DESCRIPTION OF SUNFLOWER LINES IN THE CONTEXT OF THEIR RESISTANCE TO DOWNY MILDEW (PLASMOPARA HALSTEDII (FARL.) BERL. ЕT DE TONI)

This catalogue presents the results of the three-year (2016–2018) field study of 325 sunflower lines and cultivars from the VIR collection in the context of their resistance to downy mildew (caused by Plasmopara halstedii (Farl.) Berl. еt de Toni). In addition to general description, lines unaffected by downy mildew during all three years of testing are identified, along with those that were resistant in 2016 and 2018 but showed susceptibility in 2017. The catalogue is addressed to plant pathologists, geneticists and breeders.

New and High Virulent Pathotypes of Sunflower Downy Mildew (Plasmopara halstedii) in Seven Countries in Europe

Downy mildew of sunflower, caused by Plasmopara halstedii (Farl.) Berl. et de Toni, is a relevant disease of this crop. High virulent pathotypes have been identified in several countries, while there are few data on the spread of P. halstedii pathotypes in some important sunflower-growing areas of Europe. The goal of this study was to give up-to-date information on the pathotype structure of P. halstedii in Hungary and provide some actual data on the virulence phenotype of the pathogen for six European countries. Infected leaves of different sunflower hybrids and volunteers were collected in seven countries (Hungary, Bulgaria, Serbia, Turkey, Greece, Romania, and Italy) between 2012 and 2019. A universally accepted nomenclature was used with a standardized set of sunflower differential lines for pathotype characterization of isolates. The virulence pattern of the isolates was determined by a three-digit code (coded virulence formula, CVF). A total of 109 P. halstedii isolates were characterized. As a result of our survey, 18 new P. halstedii pathotypes were identified in Europe. Two out of the eighteen pathotypes were detected from the Asian part of Turkey. The detailed distribution of pathotypes in Hungary is also discussed.

Updated Characterization of Races of Plasmopara halstedii and Entomopathogenic Fungi as Endophytes of Sunflower Plants in Axenic Culture

The management of downy mildew (Plasmopara halstedii) in sunflower, is heavily dependent on genetic resistance, whilst entomopathogenic fungi (EF) can reduce other sunflower diseases. In this work, we characterized P. halstedii from Spain and other countries collected in the past few years. Twenty-three races were identified (the most frequent in Spain being 310, 304, 705 and 715), with an increasing proportion of highly virulent races. Five isolates from countries other than Spain overcame the resistance in RHA-340. In addition, we assessed the efficacy of five EF against downy mildew and their effects on sunflower growth in axenic conditions. None of the entomopathogens reduced disease severity, nor did they have any effect on plant growth when applied together with P. halstedii. In contrast, three EF reduced some of the plant growth variables in the absence of the pathogen. Microbiological and molecular diagnostics suggest that the axenic system and the short experimental time used in this study did not favor the successful establishment of EF in the plants or their potential biocontrol effect. Our results show a shift in P. halstedii racial patterns and suggest that soil as a growth substrate and long infection times are needed for EF effectiveness against downy mildew.

Evaluation of horizontal resistance of sunflower (Helianthus annuus L.) to downy mildew (Plasmopara halstedii)

Downy mildew is one of the most important diseases of sunflower crop around the world caused by Plasmopara halstedii (Farl.) Berl.et de Toni. The aim of our study was to evaluate the horizontal resistance of elite and prospective lines to downy mildew in field conditions. Experiments were conducted at All-Russia Research Institute of Oil Crops (VNIIMK) in 2016–2020. Released and prospective sunflower lines bred at VNIIMK were studied, divided into four groups on the base of their race-specific resistance in laboratory tests. Experimental design was randomized blocks with two replications. Evaluation was made by recording all the recognizable symptoms of downy mildew from emergence till flowering. The results obtained allowed us to identify the lines with the highest race non-specific resistance to downy mildew: VK 678 (5.3%), VK 653 (7.3%), VA 760 (3.3%), VA 93 (2.0%) and VK 732 (6.3%). The final aim is the development of sunflower hybrids with the most durable resistance to downy mildew, combining one parental line with the major gene (Pl15) most effective for the specific location and the second parental line with a high level of horizontal resistance to downy mildew.

Mycoses as causes of biotic stress in sunflower production

Osjetljivost suncokreta na biotski stres uvelike određuje vrijednosti agronomskih svojstava. Uzročnici biotskog stresa mogu biti različiti, a u svijetu pa tako i u Hrvatskoj se po svome utjecaju izdvajaju bolesti. Uslijed pojave različitih biljnih bolesti, u pojedinim godinama prinosi zrna i ulja suncokreta mogu biti reducirani i preko 50%. Najčešći uzročnici bolesti suncokreta su gljive, a prema stupnju štete koje prave ističu se Sclerotinia sclerotiorum, Diaporthe/Phomopsis helianthi i Plasmopara halstedii te u nešto manjoj mjeri Alternaria helianthi, Phoma macdonaldii, Puccinia helianthi, Verticillium spp., Botrytis cinerea, Macrophomina phaseolina i Erysiphe cichoracearum. Kreiranje otpornih/tolerantnih linija iz divljih formi suncokreta, a zatim transfer poželjnih gena u komercijalne linije i hibride je najčešći oblik povećanja otpornosti/tolerantnosti linija i hibrida suncokreta na biotski stres. U ovom postupku značajnu ulogu ima primjena molekularnih markera. Pored toga važan je stalni monitoring, ali i pravovremena primjena agrotehničkih, kemijskih i bioloških mjera.

New data on pathotype distribution and mefenoxam tolerance of Plasmopara halstedii in Hungary

Sunflower downy mildew (Plasmopara halstedii) is one of the major diseases that can be controlled by using resistant cultivars and seed dressings; however, several isolates have developed tolerance to some fungicides and the resistance has also been overcome by new pathotypes. We aimed to examine the pathotype distribution in Hungary and to test the pathotypes' mefenoxam sensitivity. The isolates, which provided the basis of the research were collected from different regions of Hungary between 2014 and 2017 and, later, their pathotypes were identified. According to our results, pathotype 704 was one of the most widespread in Hungary, but pathotype 730, pathotype 724 and pathotype 700 were also detected. Seven out of ten isolates caused relatively high disease rates on the mefenoxam-treated and inoculated sunflower plants with P. halstedii. The pathogen has a high genetic variability which enhances the possibility to develop fungicide resistance. Furthermore, this variability can easily contribute to the breakdown of the resistant genes of the resistant hybrids. Both features can reduce the effectiveness of management; therefore, the continuous monitoring of this oomycete is very important.