Hybridization between Pyrenophora teres Forms in Natural Populations of Russia and the Republic of Belarus

Abstract

Two forms of the pathogenic fungus Pyrenophora teres, P. teres f. teres (a net form) and P. teres f. maculata (a spot form), cause different disease signs, net or spot blotch, on barley leaves. The net form of P. teres is widespread wherever barley is cultivated, while the spot form was first identified in Krasnodar krai of Russia in 2011 and Brest oblast of Belarus in 2016. The two forms of the pathogen easily mate each other in laboratory conditions, but their hybrids either do not form or are difficult to detect in nature. The question as to whether hybrids between the net and spot forms are produced and maintained in natural populations is pressing and bears applied significance because different genes determine resistance to the different P. teres forms in barley. Hybrid forms may be virulent to resistance donors used in breeding. The objective of this work was to search Russian and Belarussian natural populations for hybrids between P. teres f. teres and P. teres f. maculata with the use of new form-specific markers, Ptt and Ptm. The study included 138 single-conidium isolates from four P. teres f. maculatа and four P. teres f. teres populations. The isolates were collected from commercial barley plantations of Leningrad oblast, Krasnodar krai (Russia), and Brest oblast (Belarus) from 2013 to 2016. A genotyping with 10 form-specific markers was performed in all isolates. Several isolates were found to combine markers of both of the P.teres forms and were conventionally identified as hybrids between the forms. Hypotheses were advanced to explain the occurrence of hybrids in natural populations. The most plausible hypothesis suggests that sexual or somatic hybridization between the two forms coexisting in barley plantations accounts for the origin of the P. teres isolates that combine markers specific to P. teres f. teres and markers specific to P. teres f. maculata in their genomes. It is also possible that a third, possibly ancestral, intermediate form was preserved during divergence in the species P. teres.