Virulence structure of the Blumeria graminis (dc.) Speer f. sp. tritici (em. Marchal) population occurring in Serbia

Abstract

Powdery mildew (caused by Blumeria graminis f. sp. tritici) is the common disease of wheat in the agroecological conditions of Serbia. The ability of sexual and asexual reproduction, as well as a high genetic flow of this pathogen, make B. graminis f. sp. tritici genetically very divergent, with a significant potential for adaptability and change in the virulence of its population. So far, a large number of pathotypes of this pathogen have been identified, while a large number is constantly produced and effective resistance of wheat is short-termed. Improving wheat resistance to powdery mildew is an important task of breeding programs worldwide. The objective of this research was to determine and characterize the virulence structure of the B. graminis f. sp. tritici population that originate from the territory of Serbia, as well as the dynamics of its change over the years. During the examined period virulence of sexual stage of B. graminis f. sp. tritici population was identified for all wheat resistance genes (Pm genes) and in all investigated locations. Cluster analysis showed a high degree of genetic diversity of B. graminis f. sp. tritici isolates, depending on the year. Statistically significant differences were found between the virulence genes, as well as the linear trend of change in the virulence frequency of the genes during the investigated period. The lowest frequency of virulence in the population was found for the combination of the V-5+6 gene, while the frequency of the virulent genes V-6 and V-7 was at a consistently high level. The most significant change in the population was characteristic for the combination of the V-2+4b+6. Data were analyzed for associations among pairs of avirulence genes, and a positive avirulent relationship was established between the pairs of genes virulence to Pm17 and Pm2+6, Pm2 and Pm2 +; Pm2 + and Pm3a; Pm2 + and Pm1+2+9; Pm2+ and Pm2+4a+ 6; Pm3a and Pm8; Pm3a and Pm1+2+9; Pm3a and Pm2+6; Pm8 and Pm17; Pm17 and Pm1+2+9; Pm17 and Pm2 6 and gene pairs Pm1+2+9 and Pm2+6. Pyramiding these gene pairs can be a good strategy for extending the period of effectiveness of the resistance of a particular variety of wheat. The lowest frequency of virulence of the sexual stage of population was determined at the location of Sremska Mitrovica. The highest coefficient of genetic distances is established between isolates originating from a given location and isolates originating from other investigated locations. Between the genetic and geographical distance of B. graminis f. sp. tritici isolates a statistically significant linear relationship was not found. Virulence structure of the asexual population indicated that the complexity of the powdery mildew pathotypes grows with the crop growth. In this part of population the genes virulence to Pm3a and Pm2 + have not been found. The highest frequency of virulence had gene virulence to Mld resistance gene. Statistically significant correlations were found between the sexual and asexual population of the examined pathogen. The research was also aimed at determining the resistance of wheat genotypes to powdery mildew. High level of partial resistance was found in seven tested wheat genotypes whose parents have combination of the Pm5+6 gene, as well as a combination of the Pm5+6 and Pm2+4b+6 genes. Based on the study of the virulence structure of the powdery mildew population in this research, it is considered that the combination of the Pm5+6 gene is the carrier of the resistance of the given genotypes

Prouzrokovač pepelnice (Blumeria graminis f. sp. tritici) je stalni pratilac proizvodnje pšenice u agroekološkim uslovima Srbije. Sposobnost seksualne i aseksualne reprodukcije, kao i visok genetski protok patogena, čine da je prouzrokovač pepelnice genetski veoma divergentan, značajnog potencijala za adaptabilnost i promenu u virulentnosti populacije. Do sada je utvrđen znatan broj patotipova ovog patogena, dok se veliki broj konstantno stvara, te je efikasna otpornost pšenice kratkotrajne prirode. Rad na selekciji na otpornost pšenice prema prouzrokovaču pepelnice je važan zadatak oplemenjivačkih programa širom sveta. Cilj istraživanja je bio utvrđivanje strukture virulentnosti populacije patogena B. graminis f. sp. tritici koja potiče sa teritorije Srbije, kao i dinamike njene promene tokom godina. U polnoj populaciji prouzrokovača pepelnice identifikovana je virulentnost prema svim genima pšenice za otpornost prema prouzrokovaču pepelnice (Pm geni), tokom ispitivanih godina i u svim ispitivanim lokalitetima. Utvrđene su statistički značajne razlike u virulentnosti gena patogena prema Pm genima domaćina, kao i linearni trend promene frekvencije virulentnosti gena polne populacije B. graminis f. sp. tritici. Najnižu frekvenciju virulentnosti u populaciji tokom ispitivanog perioda ispoljila je kombinacija gena V-5+6, dok je frekvencija virulentnih gena V-6 i V-7 gena bila na konstantno visokom nivou. Najznačajnija promena u populaciji je karakteristična za kombinaciju gena V-2+4b+6. U polnoj populaciji patogena u ispitivanom periodu nijedan izolat nije ispoljio virulentnost prema kombinaciji gena Pm17, Pm2+, Pm2+6 i Pm5+6. Klaster analizom utvrđen je visok stepen genetičkog diverziteta izolata u zavisnosti od godine. Analizom veze između gena avirulentnih lokusa utvrđena je pozitivna avirulentna veza između parova gena virulentnih prema Pm17 i Pm2+6, Pm2 i Pm2+; Pm2+ i Pm3a; Pm2+ i Pm1+2+9; Pm2+ i Pm2+4a+6; Pm3a i Pm8; Pm3a i Pm1+2+9; Pm3a i Pm2+6; Pm8 i Pm17; Pm17 i Pm1+2+9; Pm17 i Pm2+6 i parova gena Pm1+2+9 i Pm2+6. Piramiding ovih parova gena može biti dobra strategija za produžetak perioda efikasnosti otpornosti određene sorte. Najniža frekvencija virulentnosti polne populacije utvrđena je u lokalitetu Sremska Mitrovica. Najveći koeficijent genetičke udaljenosti utvrđen je između izolata koji potiču sa datog lokaliteta i izolata koji potiču sa ostalih ispitivanih lokaliteta. Između genetičke i geografske udaljenosti izolata prouzrokovača pepelnice za ispitivane lokalitete nije utvrđena statistički značajna linearna veza. Analiza strukture virulentnosti bespolne populacije ukazala je da komplekstnost patotipova prouzrokovača pepelnice raste sa porastom useva. Geni patogena za virulentnost prema genima Pm3a i Pm2+ nisu utvrđeni. Najvišu frekvenciju virulentnosti imao je gen za virulentnost prema Mld genu za otpornost pšenice prema prouzrokovaču pepelnice. Statistički značajne korelacije su utvrđene između polne i bespolne populacije ispitivanog patogena. Istraživanja su imala za cilj i određivanje otpornosti genotipova pšenice koja je uslovljena promenom u populaciji prouzrokovača pepelnice. Visok nivo parcijalne otpornosti ispoljilo je sedam genotipova koji u svojoj genealogiji imaju roditelja sa kombinacijom gena Pm5+6, kao i kombinacijom gena Pm5+6 i Pm2+4b+6. Na osnovu ispitivanja strukture virulentnosti populacije prouzrokovača pepelnice smatra se da je kombinacija gena Pm5+6 nosioc otpornosti datih genotipova.