Virulence variation of Israeli populations of Puccinia graminis f. sp. tritici during the period 2009 – 2019

Abstract This paper is dedicated to the memory of the APS Fellow Prof. Yehoshua Anikster (1934 -2023). A total of 336 urediniospore isolates of Pucciniagraminis f. sp. tritici (Pgt) were derived from samples collected in Israel from 2009 to 2019 and analyzed for virulence with the standard set of 20 differentials. Seventy-two virulence phenotypes were identified during the survey. Two Pgt phenotypes (TKTTF, TTTTF) were found in nine annual populations while 49 appeared in only one year. The yearly pathogen collections of 2009 – 2014 differed from the collections of 2015-2018, and the 2019 collection diverged from all others. No virulence to Sr24 and Sr31 indicators of UG99 was detected. Comparing the 2009 – 2014 and 2015 – 2018 periods, virulence frequencies declined on Sr17, 30, and 38 genes from 0.853 - 0.973 to 0.308 – 0.587, whereas the frequency on Sr36 rose (0.418 vs. 0.865). The average relative virulence complexity of the Pgt phenotypes decreased from 0.833 (2009 - 2014) and 0.786 (2015 – 2018) to 0.671 in 2019. Variability within the annual populations gradually increased over time. The Pgt collections of isolates in 2009 – 2014 and 2015 – 2018 were significantly different (p = 0.01). The effective number of different annual populations in 2009 – 2018 was 2.04 (β-variation = 0.116). Since Pgt does not over-summer in Israel, the northern source of inoculum from Turkey and Russia seems the most probable.