Relation between Phenylalanine ammonia-lyase activity and total phenolic content.

<p>Phenylalanine ammonia-lyase (PAL) activity and total phenolic content (expressed as gallic acid equivalents) were measured in extracts from potato tuber tissue treated with water (Control), a concentrated culture filtrate (CCF) from <i>Phytophthora infestans</i> or purified lipopolysaccharides (LPS) from <i>Pectobacterium atrosepticum</i>. By cultivar means of water and LPS treated samples are represented as white symbols, CCF treated samples as black symbols. Experiments were performed on 5 potato cultivars (Ackersegen, BF15, Bintje, Kerpondy, Saturna) from tuber batches produced in 2009 and used for experiments after 2 months of storage (circles) and after 10 months of storage (boxes). Lines were drawn by using coefficients of a linear model fitted to by-cultivar means for PAL activity and total phenolic content.</p

A general interaction model coupling physiological response with key life history traits of the pathogen.

<p>The model revolves around a key life history trait, pathogen growth, which drives both physiological (light shaded boxes and bold solid lines) and demographic responses (white boxes and dotted lines). The physiological part of the model derives from the PAMP-triggered response model <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0023331#pone.0023331-Jones1" target="_blank">[5]</a>. It is assumed to occur in all pathosystems; however, defense reactions can also lead to enhance necrosis, and hence to enhanced symptoms of disease – as is the case in <i>Phytophthora infestans</i> (dotted lines). Pathogen growth varies between pathosystems, according to host exploitation strategies. In all cases, enhanced pathogen growth leads to more disease; however, in biotrophic pathogens like <i>P. infestans</i>, which reproduce on living tissue, growth can lead the pathogen to escape tissue before effective defense reactions take place. This model explains why although the PAMP-triggered response model probably works in all cases, opposite relationships can be observed when plotting the intensity of defense reactions against host resistance (i.e. disease symptoms).</p

Phenylalanine ammonia-lyase activity in protein extracts from elicitor-treated parenchymatous potato tuber tissue.

<p>Activity was measured after 7.5 h of contact with either water as the control (white bars) or elicitors such as a concentrated culture filtrate (CCF) from <i>Phytophthora infestans</i> (black bars) or purified lipopolysaccharides (LPS) from <i>Pectobacterium atrosepticum</i> (grey bars). Potato cultivars (ac = Ackersegen, bf = BF15, bi = Bintje, ke = Kerpondy, sa = Saturna) used were produced in 2008 and 2009. Tubers produced in 2008 were used after 8 months of storage (batch A), tubers produced in 2009 were used after 2 months (batch B) and after 10 months (batch C) of storage. Data for batch C are means from two replicate experiments (vs. one for batches A and B); in each experiment, for each cultivar and treatment, four disks from different tubers were pooled and aliquoted to constitute four different samples. Bars represent the means ± standard error of phenylalanine ammonia-lyase activity in at least two samples per treatment and cultivar combination. Stars above bars indicate significant differences between the control and tuber tissue treated with the concentrated culture filtrate or lipopolysaccharides, respectively (Dunnett's test, p<0.05).</p

Different defense-disease relations illustrated by a ‘see-saw but see-see’ model.

<p>For <i>Pectobacterium atrosepticum</i> (A), the model describes the interaction according to the ‘see-saw principle’: increased defense is associated with decreased disease. For <i>Phytophthora infestans</i> (B), the model describes the interaction according to the ‘see-see principle’: increased defense is associated with increased disease. A plausible explanation for these differences is proposed by a general interaction model (<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0023331#pone-0023331-g008" target="_blank">Figure 8</a>).</p

Phenylalanine ammonia-lyase activity and disease severity in potato tubers pre-treated with CCF.

<p>Tuber slices of cultivar Bintje were surface-treated with 100 µl of a concentrated culture filtrate (CCF) of <i>Phytophthora infestans</i> at a concentration of 400 µg.ml⁻¹ or with water as the control. Slices were incubated during 7.5 h at 20°C and subsequently assayed for <b>Phenylalanine ammonia-lyase</b> (PAL) activity (A) or inoculated with pathogens. For <i>Pectobacterium atrosepticum</i> (B), weight of soft rot developed during 5 days at 20°C was measured. For <i>P. infestans</i> (C), disease developed during 5 days at 17°C and is expressed as reflective density. PAL activity was determined in four aliquot samples prepared form pooled tissue of 5 tuber slices and disease severity was determined in 10 tuber slices. Bars correspond to means ± standard error of data from two replicate experiments. Different letters above bars indicate significant differences between means of treatments (Tukey's test, p<0.05).</p

Phenylalanine ammonia-lyase activity in relation to disease symptoms by <i>Pectobacterium atrosepticum</i> (A) or <i>Phytophthora infestans</i> (B).

<p>PAL activity was measured in extracts from tuber tissue treated with water (Control), a concentrated culture filtrate (CCF) from <i>P. infestans</i> or purified lipopolysaccharides (LPS) from <i>P. atrosepticum</i>. Disease severity caused by <i>P. atrosepticum</i> and <i>P. infestans</i> was measured in tubers from 5 potato cultivars (Ackersegen, BF15, Bintje, Kerpondy, Saturna). Experiments were performed on 3 tuber batches produced in 2008 and 2009. Tubers produced in 2008 were used after 8 months of storage (batch A), tubers produced in 2009 were used after 2 months (batch B) and after 10 months (batch C) of storage. White boxes represent by-cultivar means of phenylalanine ammonia-lyase activity in replicate samples for Control and ‘LPS treatments, while black boxes represent by-cultivar means of phenylalanine ammonia-lyase activity in CCF treated samples. Results from two experiments on batch C were grouped before calculating means. Lines were drawn using coefficients of linear models fitted to by-cultivar means including results from pathogenicity tests of <i>P. atrosepticum</i> and <i>P. infestans</i> as co-variable, respectively.</p

Effect of chlorogenic acid on pathogen growth.

<p>Pathogen growth was determined in culture medium enriched with chlorogenic acid to 0, 200 and 350 µg.ml⁻¹ . Concentrations of <i>Pectobacterium atrosepticum</i> in liquid culture were determined after 40 h of contact (A). Radial mycelium growth of <i>Phytophthora infestans</i> from mycelia disks on solid culture medium was measured after 7 days (B). Bars represent the means ± standard error of results from two replicate experiments. Different letters above bars indicate significant differences between treatments (Tukey's test, p<0.05).</p

Phytophthora infestans genotypes

21 isolates of Phytophthora infestans were genotyped at 12 microsatellite loci: D13, PinfSSR8, PinfSSR4, PinfSSR11, PinfSSR6a, PinfSSR3, Pi4B, Pi70, Pi63, Pi04, G11 and PinfSSR2. Binary data indicate presence (1) or absence (0) of alleles