Oomycetes systemicity

Jacobson DJ et al. Persistent, systemic, asymptomatic infections oJAlbugo Candida, an oomycete parasite, detected in three wild crucifer species. Can J Bot 76 739-750, 1998. 

Copper, as copper sulfate, was first used to control Tilletia caries in wheat but its main use, as Bordeaux mixture, is in the control of Oomycetes in a wide spectrum of crops such as potato, tomato and vines or in combination with systemics such as cymoxanil. 

Cymoxanil. Cymoxanil (Figure 4.34) is a systemic urea with protectant and curative activity against Oomycetes, particularly Plasmo-para viticola on vine and Phytophthora infestans (potato late blight). 

Osmotrophs are organotrophic organisms that acquire nutrients from their environment one molecule at a time. Osmotrophs include most members of the bacteria and archaea domains, as well as fungi and several protistan groups. Except in association with coarse organic particles where eukaryotic fungi and oomycetes are prominent, prokaryotes dominate heterotrophic metabolism, so are the focus of the text that follows. We use the term bacteria loosely, recognizing that heterotrophic archaea may well be major consitituents of the microbial loop of many systems. 

Metalaxyl and most of its active analogues are chiral molecules. Chirality is caused by the asymmetric carbon atom in the alkyl side chain of the alanine moiety. The two optically pure enantiomers S (+) and R (-) differ widely in their biological activity both in vitro and in vivo. In all experiments, the R (-) enantiomer was more active than its antipode S (+) (22, 24, 30). The main characteristics of metalaxyl have been discussed in detail by several authors (J, 21, 28, 29, 32> 38). Of particular value is the rapid uptake of metalaxyl by the plant tissue, especially under the wet conditions that favor foliar Oomycete diseases. Acylalanines are easily translocated in the vascular system of the plant after foliar, stem or root treatment (35, 47). The predominant route of transport is the transpiration stream, thus apoplastic (12, 35). Symplastic transport occurs but is much less evident (35, 47). In potatoes treated by foliar sprays of metalaxyl concentrations (0.02-0.04 ppm), Bruin et al. (SO were able to demonstrate protection of harvested tubers from late blight. 

In conclusion, all the new systemic fungicides against Oomycetes had an immediate need for mixing partners. It can be assumed that this will also hold true for future systemic fungicides. This use concept calls for flexibility both on the part of industry, national registration authorities, and the extension services to make safe and powerful products available for plant protection. 

Professor Schwinn discussed new advances in the chemical control of plant parasitic Oomycetes and Peronosporales. Some of the most devastating foliar and root diseases are caused by these fungi, hut they are often not controlled by systemic fungicides which control... 

Here we review our research results concerning zoospore attractants, repellents, cytotoxins and inhibitors of zoospore motility together with bioassay systems to survey chemical regulators toward zoospores. The first part of this review described some new findings on the effects of host-specific plant signals on chemotaxis and differentiation of oomycete zoospores. The potential role and mode of action of nonhost secondary... 

Furalaxyl is a systemic fungicide used for preventive or curative control of diseases caused by soil-borne oomycetes, whereas the related Metalaxyl is... 

Fungi are used extensively as model developmental systems in biochemistry and genetics. An early classical study of steroid-mediated morphogenesis involved the Oomycete Ac/i/ya ambisexualis (Raper 1939, 1940). The ascomycetous yeast Saccharomyces cerevisiae is the most extensively studied eukaryote in many areas of signal transduction (Kurjan 1993 Ferguson et al. 1994 Grishin et al. 1994 Schultz et al. 1995), especially as it relates to cell division and sexual reproduction. 

Another interesting systemic phosphorus compound is fosetyl Al, a systemic fungicide. It has preventive and curative activity against many Oomycetes on many different crops. This combination of a phosphite and aluminium gives the necessary chemical and physical properties to the material to make it an effective fungicide. 

One of the newer systemic fungicides, foestyl, is the aluminium salt of ethyl phosphite and has activity against diseases caused by Oomycetes such as Phytophthora and downy mildews. It is registered for use on nonbearing citrus, ornamentals, and pineapples. 

---