Remarkable recent changes in the genetic diversity of the avirulence gene AvrStb6 in global populations of the wheat pathogen Zymoseptoria tritici

Septoria tritici blotch (STB), caused by the fungus Zymoseptoria tritici, is one of the most economically important diseases of wheat. Recently, both factors of a gene-for-gene interaction between Z. tritici and wheat, the wheat receptor-like kinase Stb6 and the Z. tritici secreted effector protein AvrStb6, have been identified. Previous analyses revealed a high diversity of AvrStb6 haplotypes present in earlier Z. tritici isolate collections, with up to c.18% of analysed isolates possessing the avirulence isoform of AvrStb6 identical to that originally identified in the reference isolate IPO323. With Stb6 present in many commercial wheat cultivars globally, we aimed to assess potential changes in AvrStb6 genetic diversity and the incidence of haplotypes allowing evasion of Stb6-mediated resistance in more recent Z. tritici populations. Here we show, using targeted resequencing of AvrStb6, that this gene is universally present in field isolates sampled from major wheat-growing regions of the world in 2013–2017. However, in contrast to the data from previous AvrStb6 population studies, we report a complete absence of the originally described avirulence isoform of AvrStb6 amongst modern Z. tritici isolates. Moreover, a remarkably small number of haplotypes, each encoding AvrStb6 protein isoforms conditioning virulence on Stb6-containing wheat, were found to predominate among modern Z. tritici isolates. A single virulence isoform of AvrStb6 was found to be particularly abundant throughout the global population. These findings indicate that, despite the ability of Z. tritici to sexually reproduce on resistant hosts, AvrStb6 avirulence haplotypes tend to be eliminated in subsequent populations.     

The distribution of Zn65 in the cotyledons ofVicia faba and its translocation during the growth and maturation of the plant

Summary The uptake of Zn⁶⁵ by seeds ofVicia faba, soaked in a Zn⁶⁵Cl₂ solution and maintained within the experimental condition described in the text, was constant and did not depend on the amount of the radionuclide given. However, the percentage of the total absorbed Zn⁶⁵ retained by seed coats varied according to the cultural variety ofVicia faba. Most of the Zn⁶⁵ entering the seed, remained bound to the seed coat, the remainder entered the embryo and cotyledons and was concentrated around the abaxial part of this latter, lessening towards the adaxial region. The fate of the isotope was followed in all stage of plant development. Its distribution was represented as counts per minute per unit mass (dry) of plant tissue, and on a percentage basis. In general, zinc decreased in the main root acropetally then increased at the root stem transition zone, decreased again in the first internode than increased acropetally towards the apex of the stem. Anthers had the highest counts per unit mass compared to other plant organs, including the rest of the flower. Zn⁶⁵ distribution calculated on a percentage basis increased in that order: Roots, stem, leaves in one month old plants and older. These observations held also in plants grown from —Zn medium and from seeds to which radioactive zinc was introduced before and during the formation of their pods. Water-soluble Zn⁶⁵ was also investigated in different plant's organs. Some of these results are compared and discussed with those previously obtained using a histochemical method.     

New and effective entrapment of polyelectrolyte-enzyme-complexes in LentiKats

Amyloglucosidase EC 3.2.1.3 was used as model for the immobilisation of enzymes in poly(vinylalcohol) hydrogel (LentiKats) lenses. The entrapment of the enzyme in PVA-hydrogel based on a two-step procedure, firstly its coupling to polyelectrolytes increased the structure level of the enzyme, and subsequently, the resulting complex was entrapped in LentiKats. The immobilised enzyme retained 45% of its original activity and lost no activity over five repeated batch runs.     

Dual hydrolysis model of the slowly biodegradable substrate in activated sludge systems

Experimental assessment of the hydrolysis rate coefficients for both domestic sewage and a number of industrial wastewaters was performed with emphasis on two different hydrolysis mechanisms associated with the readily and slowly hydrolyzable COD fractions. The adopted dual hydrolysis model was justified on the basis of significantly different rate constants. The hydrolysis rate of particulate COD occurred at such a slow rate that would significantly interfere with endogenous decay. © Rapid Science Ltd. 1998