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The properties and effects of two plant resistance suppressors (1,3-β-1,6-β-glucan and a pentasaccharide of xyloglucan origin) involved in the pathosystem of potato (Solanum tuberosum) and the causal agent of blight (Phytophthora infestans(Mont) de Bary) were compared. The microbial 1,3-β-1,6-β-glucan suppressed the defense response over a narrow concentration range (10−2 M), whereas the plant pentasaccharide had a broad range of effective concentrations (10−12 to 10−6 M). In the pathosystem of potato and the causal agent of late blight, the β-glucan caused a local and race-specific suppressor effect on the plant host defense response. In contrast, the pentasaccharide caused both local and systemic suppression of potato resistance and the presence of terminal fucosyl residue in the xyloglucan oligosaccharine played a decisive role in its effect. The recognition of both suppressors by potato cell membrane sites is discussed.