Population biology of Puccinia graminis : implications for the epidemiology and control of stem rust

• Barberry has made a noticeable comeback in the agricultural landscape after the repeal in 1994 of a law requiring its eradication. It has brought with it not only biological diversity, but also stem rust caused by Puccinia graminis (Pers.). Rusts have been known and feared for centuries. This thesis presents the results of studies of the population structure of P. graminis and connects this information to the epidemiology of stem rust. The studies were done by using SSR (simple sequence repeat) markers on samples from different hosts, years and areas. The results show that P. graminis genetically is a very diverse pathogen and no correlation in population structure could be detected between fields or years. However, there was a clear genetic differentiation between the forma specialis infecting oats and the forma specialis infecting rye and wheat. The aecial morphology also differed between the two, and the differentiation was reflected in a phylogenetic study. It was thus shown that P. graminis could be divided into two phylogenetically distinct species. The grass host is the driving force in the evolution of these species. In addition, Puccinia arrhenatheri was identified from barberry and its grass host. The presence of barberry, the alternate host of the pathogen, drives stem rust epidemics in oats, and removal of the barberry bushes would not only limit development of the disease but also reduce the genetic variation in the stem rust pathogen. Even if the fungus rarely goes through a sexual cycle, such as the situation in Tajikistan, the genetic variation is high in that country. The mere presence of barberry within an area enables a large genetic variability within the pathogen. Stem rust does not seem to be common on wheat in Sweden. This may be due to the lack of virulent genotypes of the pathogen, but if they were present, stem rust could become a major problem in wheat production, since all the prerequisites for epidemics are already present.

Ämnesord

LANTBRUKSVETENSKAPER  -- Lantbruksvetenskap, skogsbruk och fiske -- Jordbruksvetenskap (hsv//swe)

AGRICULTURAL SCIENCES  -- Agriculture, Forestry and Fisheries -- Agricultural Science (hsv//eng)

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