Use of Uptake Spraying Oil to Improve Fungicidal Activity of the Triazole Fungicide Fenbuconazole on Puccinia triticina and Puccinia striiformis Rusts of Wheat

Fenbuconazole, a broad spectrum triazole fungicide with restricted uptake and consequent redistribution within wheat plants, has been perceived to possess limited curative properties when formulated as a suspension concentrate (SC). Field and greenhouse studies demonstrated that curative and to a lesser extent protectant activity of fenbuconazole on wheat leaf rust (Puccinia triticina) and stripe rust (Puccinia striiformis f.sp. tritici) was improved by the addition of the adjuvant Uptake™ Spraying Oil (Uptake is a trademark of Dow AgroSciences). The purpose of this study was to determine if the addition of adjuvant increased penetration of fenbuconazole into wheat tissue and if this was correlated with enhanced redistribution within the plant and the observed increase in activity. These data confirm that the addition of adjuvant improved penetration of fenbuconazole into wheat leaves and was responsible for the observed increase in biological activity of the fenbuconazole suspension concentrate formulation. In addition, adjuvant decreased the amount of material washed off with water a result suggesting the potential for improved rain-fastness in the field. Fenbuconazole's fungicidal activity against cereal rusts could be limited by poor penetration into plant tissue unless a suitable adjuvant is incorporated into the spray solution. Accepted for publication 31 January 2013. Published 28 May 2013.

Microscopical observations of Sphaerellopsis filum, a parasite of Puccinia recondita

<i>Sphaerellopsis filum</i> is a well-known parasite associated with many species of rust fungi. It is of frequent occurrence as parasite of cereal rusts: <i>Puccinia recondita</i>, <i>P. coronata</i>, <i>P. graminis</i>, <i>P. hordei</i> and <i>P. striiformis</i>. Uredial sori of <i>Puccinia recondita</i> f.sp. <i>tritici</i> infected with <i>Sphaerellopsis filum</i> were examined by light and scanning microscope to determine morphology of hyperparasite as well as the parasite-hyperparasite contact. The microscopical examination of infected uredinia clearly showed the intimate connection of <i>S. filum</i> with its rust host.

Nonhost Resistance of Rice to Rust Pathogens

Rice is atypical in that it is an agricultural cereal that is immune to fungal rust diseases. This report demonstrates that several cereal rust species (Puccinia graminis f. sp tritici, P. triticina, P. striiformis, and P. hordei) can infect rice and produce all the infection structures necessary for plant colonization, including specialized feeding cells (haustoria). Some rust infection sites are remarkably large and many plant cells are colonized, suggesting that nutrient uptake occurs to support this growth. Rice responds with an active, nonhost resistance (NHR) response that prevents fungal sporulation and that involves callose deposition, production of reactive oxygen species, and, occasionally, cell death. Genetic variation for the efficacy of NHR to wheat stem rust and wheat leaf rust was observed. Unlike cereal rusts, the rust pathogen (Melampsora lini) of the dicotyledenous plant flax (Linum usitatissimum) rarely successfully infects rice due to an apparent inability to recognize host-derived signals. Morphologically abnormal infection structures are produced and appressorial-like structures often don't coincide with stomata. These data suggest that basic compatibility is an important determinate of nonhost infection outcomes of rust diseases on cereals, with cereal rusts being more capable of infecting a cereal nonhost species compared with rust species that are adapted for dicot hosts.

Airborne nomadic pathogens: does virulence accumulate along the way from Paris to Beijing?

It is well established that race-specific resistance selects for the specifically matching genes effecting virulence in the pathogen. As well, the use of different R-genes in time makes virulence complexity, VC (the number of virulences per pathogen genotype), to increase. Moreover, it becomes obvious here that the wind-dispersed cereal rusts and mildews are obligate nomads and highly mobile. As a consequence of these points and as a result of modelling, VC was expected to increase in the direction of predominant winds, e.g. from west to east across Europe, and it did by approximately one or more virulences per 1000 km. Starting from the barley mildew pathogen, comprehensive evidence is also available from leaf rust on wheat covering some 5000 km from Western Europe into Siberia. The impact of our findings for population genetics across Europe and Asia is supposed to be considerable and worth further elucidating, e.g., within the 6^th EU Framework Programme.