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Leaf rust, caused by the fungus Puccinia triticina, is the most common rust disease of wheat in wheat‐producing areas worldwide. The Israeli population of P. triticina has been consistently monitored since 1993. A total of 784 single urediniospore isolates from Triticum aestivum were analysed during 2000–15. The structure of the pathogen population has changed to a large extent since 2000. The annual populations of P. triticina were separated into two distinct groups, 2000–11 and 2012–15, while populations of 2000–5 and 2006–12 were differentiated to a lesser extent. The change in the population originating from T. aestivum during the period 2000–15 is less significant compared to changes in the 1990s described previously. Diversity within the annual populations of P. triticina was rather stable during the period studied. Three new pathotypes, characterized by virulences on Lr3ka and Lr30 genes, became dominant between 2012 and 2015, while all but one prevailing pathotypes in 2000–11 were avirulent on these two genes. Significant changes in virulence frequencies on a number of Lr genes (Lr2c, Lr3ka, Lr15, Lr21, Lr23, Lr26, Lr30) and pairwise associations of virulences (mainly with Lr2c and Lr26) were registered in 2012–15 or earlier. It is postulated that the composition and pathotype structure of the P. triticina population in Israel is determined by wind‐disseminated urediniospores from neighbouring regions, where the migration of P. triticina from the eastern part of the Mediterranean Sea and from the Horn of Africa seem to have the greatest influence. [ABSTRACT FROM AUTHOR]

Leaf rust, caused by the fungus Puccinia triticina, is the most common rust disease of wheat in wheat-producing areas worldwide. The Israeli population of wheat leaf rust has been consistently monitored since 1993. A total of 840 single urediniospore isolates from Triticum aestivum (567), T. dicoccoides (119) and T. durum (154) were analysed during 1993-2008. The structure of the pathogen population has changed to a large extent since 1993. The annual populations of P. triticina were separated into two distinct groups: 1993-1999 and 2000-2008. Differentiation among the annual pathogen populations, as well as between the overall populations of the 1990s and 2000s, could be mainly attributed to the following forces: (i) migration of leaf rust urediniospores from neighbouring regions; and (ii) selection pressure of new yellow rust-resistant wheat cultivars that have been introduced into Israel since 1997. Genetic multiplicity of wild emmer contributes to P. triticina variability in Israel. Leaf rust populations collected from common wheat, wild emmer and durum wheat differed. The population that originated from T. durum was rather stable during the years of the survey, whereas that from T. aestivum changed significantly from the 1990s to the 2000s. Diversity within the annual populations of P. triticina was highest in 1994 when many new pathotypes and associations between virulences were observed. Single-step derivatives of the new pathotypes became dominant after 2000. Significant changes in virulence frequency to a number of Lr genes (e.g. Lr2a, Lr15, Lr17, Lr21, Lr26) were also registered in 2000-2008. [ABSTRACT FROM AUTHOR]

Rust, caused by Puccinia dracunculina, is the main foliar disease of open-field tarragon ( Artemisia dracunculus) crops in Israel. As not much is known about the biology or epidemiology of this pathogen, the long-term objective of the current study was to accumulate the knowledge needed to develop an effective, environmentally friendly means of adequately managing the disease. Puccinia dracunculina is an autoecious brachy-form pathogen, but it is not known whether the life cycle is completed under field conditions in Israel. Field observations and greenhouse studies revealed that although the telial stage is produced, the pathogen overwinters in the uredinial stage. In vitro experiments were used to quantify the temperature and wetness requirements for urediniospore germination and to calculate the daily duration of conducive weather ( DDCW); DDCW was defined as the number of hours during which temperature ranged between 15 and 25°C and RH was >90%. Cumulative DDCW values ( CDDCW) were a good predictor of disease under natural conditions in two growing seasons. Disease onset occurred when CDDCW values reached a level of 10 and the relationship between log CDDCW values and season-long severity values (in logit) was highly significant, explaining 90·6% of the variation. [ABSTRACT FROM AUTHOR]

Nuclear DNA amount, determined by the flow cytometry method, in diploids, natural and synthetic allopolyploids, and natural and synthetic autopolyploids of the tribe Triticeae (Poaceae) is reviewed here and discussed. In contrast to the very small and nonsignificant variation in nuclear DNA amount that was found at the intraspecific level, the variation at the interspecific level is very large. Evidently changes in genome size are either the cause or the result of speciation. Typical autopolyploids had the expected additive DNA amount of their diploid parents, whereas natural and synthetic cytologically diploidized autopolyploids and natural and synthetic allopolyploids had significantly less DNA than the sum of their parents. Thus, genome downsizing, occurring during or immediately after the formation of these polyploids, provides the physical basis for their cytological diploidization, that is, diploid-like meiotic behavior. Possible mechanisms that are involved in genome downsizing and the biological significance of this phenomenon are discussed. [ABSTRACT FROM AUTHOR]