Fig. 2: Effects of d-tagatose on a plant host–oomycete pathogen model system, Arabidopsis thaliana ecotype Col-0–Hyaloperonospora arabidopsidis isolate Noco2.

Disease severity and pathogen development after treatment of leaves with d-tagatose at 0–400 mM or 1% (w/v) (ca. 50 mM), water (Control) or other sugars. Symptoms at 0, 10, or 20 days post inoculation (dpi) (Scale bar = 1 cm) (a). Typical hyphal growth in inoculated leaves with or without 1% d-tagatose treatment (Scale bar = 2 mm) (b). Mean (±SD) hyphal growth on 111 to 138 cotyledons for each treatment at 7 days after inoculation was rated based on percentage of entire leaf area with hyphae: +++ for 75 to 100% of leaf; ++ for 25% to 74%; + for <24%; and – for no hyphae (Three independent replications were done); typical hyphal growth for each rating is shown in the same panel (c). In planta production of conidiospores (d), conidiophores (e), and oospores (f). Data presented are representative of six (d) or three (e, f) independent experiments. Typical morphology of structures examined in panels d–f (images are 200 × 200 µm) (g). Effects of deoxygenated d-tagatose at position C-6 (6dT) (50 mM) compared with those caused by d-tagatose (DT) (50 mM) on conidial production in planta. Data shown are representative of six independent experiments (h). Typical conidial germination after 48 h on germination medium in microtiter plates with or without 25 or 400 mM d-tagatose treatment of conidia, which were pregerminated for 6 h without sugars (scale bar = 50 µm) (i). Length of germ tubes after 48 h on germination medium in microtiter plates with 0–400 mM d-tagatose or d-mannitol compared with conidia pregerminated for 6 h without these sugars. Representative of 60 to 93 independent germ tubes lengths were measured (j). Mean of conidial germination (±SD) after 24 h on germination medium in microtiter plates compared with germination on medium with 50 mM of d-tagatose (DT) or 6dT. Data presented are representative of 4–6 independent experiments (n = 85–263 per group) (k). Means with different letters differed significantly at p < 0.05 in a Tukey–Kramer multiple comparison test.